Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track -...

243
POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN THE CENTRAL EUROPE AREA: Analysis of two case studies located in Czech Republic and Italy Supervisors: prof. Giuliana Iannaccone Co-Supervisors: prof. Jan Růžička of the České Vysoké Učení Technické Author Paolo Lo Conte 852448 Academic Year 2016-2017

Transcript of Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track -...

Page 1: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

POLITECNICO DI MILANO

Building and Architectural Engineering

Track - Building Engineering

STRATEGIES FOR ENERGY RETROFITTING OF EXISTING

SCHOOL BUILDING IN THE CENTRAL EUROPE AREA:

Analysis of two case studies located in Czech Republic and Italy Supervisors:

prof. Giuliana Iannaccone

Co-Supervisors:

prof. Jan Růžička of the České Vysoké Učení Technické

Author

Paolo Lo Conte

852448

Academic Year 2016-2017

Page 2: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

Page 3: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

TABLE OF CONTENTS

1 Regulation Framework .................................................................................................................... 1

1.1 Energy Savings Policy in the European Union ......................................................................... 1

1.1.1 The role of the public building ............................................................................................ 2

1.1.2 Potential savings from school buildings .......................................................................... 6

1.2 Analysis of two case studies: Italy and Czech Republic ........................................................... 8

1.2.1 Italian Regulation............................................................................................................. 8

1.2.2 Regional Legislation ....................................................................................................... 10

1.2.3 Czech Regulation ........................................................................................................... 13

2 Description: Case study “Lecco” .................................................................................................... 17

2.1 Geographical and historical overlook .................................................................................... 17

2.2 Architectural construction..................................................................................................... 20

2.3 Energy data collection ........................................................................................................... 21

2.3.1 Envelope Characteristics ............................................................................................... 22

2.3.2 Internal Conditions ........................................................................................................ 30

2.3.3 Technological Plant ....................................................................................................... 32

2.3.4 Energy classification ...................................................................................................... 38

3 Description: Case study “Buštěhrad” ............................................................................................ 41

3.1 Geographical and historical overlook .................................................................................... 41

3.2 Architectural construction..................................................................................................... 43

3.3 Energy data collection ........................................................................................................... 45

3.3.1 Envelope Characteristics ............................................................................................... 45

3.3.2 Internal Conditions ........................................................................................................ 50

3.3.3 Technological Plant ....................................................................................................... 51

3.3.4 Energy Classification ...................................................................................................... 55

4 Climatic analysis ............................................................................................................................ 57

4.1 Geographical framework ....................................................................................................... 57

4.2 Outdoor dry-bulb temperature ............................................................................................. 58

4.3 External relative humidity ..................................................................................................... 59

4.4 Horizontal radiation .............................................................................................................. 60

4.5 Wind exposure ...................................................................................................................... 61

4.6 Rainfall precipitation analysis ................................................................................................ 62

4.7 Snow precipitation ................................................................................................................ 63

Page 4: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

4.8 Seismic activity ...................................................................................................................... 63

4.8.1 Lecco .............................................................................................................................. 63

4.8.2 Buštěhrad ...................................................................................................................... 64

5 Energy Diagnosis: Case study “Lecco” ........................................................................................... 67

5.1 Energy Performance of the Building ..................................................................................... 67

5.1.1 Energy Consumption ..................................................................................................... 67

5.1.2 Economic and Environmental Impact ........................................................................... 68

5.1.3 Heating Consumption .................................................................................................... 70

5.1.4 Heat Gains ..................................................................................................................... 71

5.1.5 Heat Losses .................................................................................................................... 72

5.1.6 Solar Energy Analysis ..................................................................................................... 74

5.2 Internal Comfort .................................................................................................................... 76

5.2.1 Thermal Comfort ........................................................................................................... 78

5.2.2 Adaptive Thermal Comfort Model ................................................................................ 80

5.2.3 Indoor air quality ........................................................................................................... 83

5.2.4 Daylight Analysis ............................................................................................................ 85

6 Energy Diagnosis: Case study “Buštěhrad” ................................................................................... 89

6.1 Energy Performance of the Building ..................................................................................... 89

6.1.1 Energy Consumption ..................................................................................................... 89

6.1.2 Economic and Environmental Impact ........................................................................... 90

6.1.3 Heating Consumptions .................................................................................................. 92

6.1.4 Heat gains ...................................................................................................................... 93

6.1.5 Heat Losses .................................................................................................................... 94

6.1.6 Solar energy analysis ..................................................................................................... 96

6.2 Internal Comfort .................................................................................................................... 98

6.2.1 Thermal Comfort ........................................................................................................... 98

6.2.2 Adaptive thermal comfort criteria ................................................................................ 99

6.2.3 Indoor air quality ......................................................................................................... 100

6.2.4 Daylight Analysis .......................................................................................................... 101

7 Envelope Optimization ................................................................................................................ 105

7.1 Design philosophy ............................................................................................................... 105

7.1.1 Technical Analysis ........................................................................................................ 107

Page 5: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

7.1.2 Economic Analysis ....................................................................................................... 108

7.1.3 Environmental analysis ................................................................................................ 109

7.2 Case study “Lecco” .............................................................................................................. 110

7.2.1 External thermal insulating coating ............................................................................ 110

7.2.2 Internal thermal insulation .......................................................................................... 114

7.2.3 Attic Insulation ............................................................................................................ 120

7.2.4 Roof insulation ............................................................................................................ 123

7.2.5 Basement Insulation .................................................................................................... 127

7.2.6 Ground-contact element insulation ............................................................................ 129

7.2.7 Glazing optimization .................................................................................................... 132

7.2.8 Envelope retrofit: Proposed intervention ................................................................... 141

7.3 Case study “Bustehrad” ....................................................................................................... 145

7.3.1 External thermal insulation coating ............................................................................ 145

7.3.2 Internal thermal insulation .......................................................................................... 148

7.3.3 Attic Insulation ............................................................................................................ 153

7.3.4 Roof insulation ............................................................................................................ 155

7.3.5 Basement insulation .................................................................................................... 158

7.3.6 Ground-contact element insulation ............................................................................ 158

7.3.7 Glazing optimization .................................................................................................... 160

7.3.8 Envelope retrofit: Proposed intervention ................................................................... 165

8 Plant Optimization ....................................................................................................................... 169

8.1 Photovoltaic system ............................................................................................................ 169

8.1.1 Parametric solar radiation analysis ............................................................................. 169

8.2 Stand-Alone plant refurbishment ....................................................................................... 172

8.2.1 Case study “Lecco” ...................................................................................................... 173

8.2.2 Case study “Bustehrad” ............................................................................................... 175

8.3 Heat pump technology ........................................................................................................ 178

8.3.1 Design choice ............................................................................................................... 179

8.3.2 Case study “Lecco” ...................................................................................................... 180

8.3.3 Case study “Bustehrad” ............................................................................................... 182

Conclusions

Bibliography

Appendices

Page 6: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

Page 7: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

INDEX OF FIGURES

Figure 1-1: Share of non-residential buildings in UE [5] ....................................................................... 2

Figure 1-2: Annual thermal energy consumption per country of CE .................................................... 3

Figure 1-3: Benchmarks for energy consumption in secondary schools ............................................... 3

Figure 1-4: Average energy use school profile [6] ................................................................................. 4

Figure 1-5: Flowchart of Energy Consumption ..................................................................................... 5

Figure 1-6: Distribution of schools in the Italian and age [5] ................................................................. 6

Figure 1-7: Consumption reduction potential by 2020 from complete renovation of schools starting [6]

................................................................................................................................................................. 7

Figure 2-1: Territorial overview of the case study building ................................................................. 17

Figure 2-2: School “Giosuè Carducci”, 1909 ....................................................................................... 18

Figure 2-3: School “Giosuè Carducci”, 2016 ........................................................................................ 18

Figure 2-4: Capture of the 3D representation of the case study area (21 September 12:00). ............... 19

Figure 2-5: Ground floor plan of the case study building ..................................................................... 20

Figure 2-6: Stone masonry wall ............................................................................................................ 23

Figure 2-7: Hollow clay planks slab ..................................................................................................... 24

Figure 2-8: Brick vault slab .................................................................................................................. 25

Figure 2-9: Basement crawl-space slab. ............................................................................................... 25

Figure 2-10: Wood beam structure roof ............................................................................................... 25

Figure 2-11: Single glazed wooden window ........................................................................................ 26

Figure 2-12: Double layer brick wall .................................................................................................... 27

Figure 2-13: Brick internal partition ..................................................................................................... 27

Figure 2-14: Concrete bearing wall ...................................................................................................... 28

Figure 2-15: Hollow core concrete slab ................................................................................................ 28

Figure 2-16: Single glazed metal window ............................................................................................ 29

Figure 2-17: School building boiler ...................................................................................................... 33

Figure 2-18: Lateral and front view of the gas air heater installed onto the gym's external wall ......... 34

Figure 2-19: Table C.1 - GHG global warming potentials, EN ISO 14064. ........................................ 35

Figure 2-20: Existing cast-iron radiators. ............................................................................................. 36

Figure 2-21: Existing air heater. ........................................................................................................... 36

Figure 2-22: On the left the supposed scheme of the distribution system: Prospectus 22 of the EN ISO

11300-2. On the right the installed circulation pumps. ......................................................................... 37

Figure 2-23: Reference Building definition. ......................................................................................... 38

Figure 2-24: Energy Performance Certification "APE". ....................................................................... 39

Page 8: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

Figure 3-1: Central Bohemia region, CZ .............................................................................................. 41

Figure 3-2: Territorial overview of the case study building .................................................................. 41

Figure 3-3: Oty Pavla school in the 1900-1920 on the left, and Oty Pavla school nowadays on the right.

............................................................................................................................................................... 42

Figure 3-4: Capture of the 3D representation of the case study area (21 May 12:00). ......................... 42

Figure 3-5: Internal facades of the building (on the left), roof structure (on the right). ....................... 43

Figure 3-6: Wood beam slab structure .................................................................................................. 47

Figure 3-7: Wood beam ceiling ............................................................................................................ 48

Figure 3-8: Slab made of vault in steel beams ...................................................................................... 48

Figure 3-9: Stone ground slab ............................................................................................................... 49

Figure 3-10: Wood beam structure roof ............................................................................................... 49

Figure 3-11: Boiler system used as heating system .............................................................................. 52

Figure 3-12: DHW boiler...................................................................................................................... 52

Figure 3-13: Cast iron radiator ............................................................................................................. 54

Figure 3-14: Distribution scheme ......................................................................................................... 54

Figure 3-15: Energy classes [kWh/m2y] for different building types.................................................... 55

Figure 4-1: Primary Energy consumption ............................................................................................. 68

Figure 4-2: Trendline of the economic-environmental impact of the school building per year ........... 69

Figure 4-3: Economic and Environmental Impact -%- of different energy-class building. ................. 69

Figure 4-4: Annual PE consumption for Heating Demand ................................................................... 70

Figure 4-5: Monthly PE consumption for Heating Demand [kWh/(m2y)] ........................................... 70

Figure 4-6: Heat Gains in terms of kWh/(m2y) and %. ........................................................................ 71

Figure 4-7: Contribution in terms of % of the elements of the old part (left) and the recent part (right)

of the building to the global Heat Losses of the case study. ................................................................. 72

Figure 4-8: Daily average incident solar radiation [Wh/m2] calculated on the 4 different orientation.74

Figure 4-9: Solar analysis radiation on SW, NW, NE, SE oriented wall (from left to right) ............... 75

Figure 4-10: Diversification of the classrooms by window’s orientation ............................................. 77

Figure 4-11: Discomfort hours % of the classrooms, dived by glazing’s orientation, during the cooling

season. ................................................................................................................................................... 79

Figure 4-12: Adaptive Thermal Comfort check of the classrooms divided by orientation, according to

TM52 ..................................................................................................................................................... 83

Figure 4-13: Distribution in percentage of the CO2 level present in the classroom, divided by orientation.

............................................................................................................................................................... 84

Figure 4-14: UDI -%- of the classrooms, divided by orientation. ........................................................ 86

Figure 5-1: Primary Energy Consumption............................................................................................ 89

Page 9: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

Figure 5-2: Trendline of the economic-environmental impact of the school building per year. .......... 91

Figure 5-3: Economic and Environmental Impact -%- of different energy-class building. ................. 91

Figure 5-4: Annual PE consumption for Heating Demand. .................................................................. 92

Figure 5-5: Monthly PE consumption for Heating Demand [kWh/(m2y)] ........................................... 93

Figure 5-6: Heat Gains in terms of kWh/(m2y) and %. ........................................................................ 93

Figure 5-7: Contribution in terms of % of the elements of the building to the global Heat Losses of the

case study. ............................................................................................................................................. 94

Figure 5-8: Daily average incident solar radiation [Wh/m2] calculated on the 4 different orientation.96

Figure 5-9: Solar analysis radiation on S, E, N, W oriented wall (from left to right) .......................... 97

Figure 5-10: Discomfort hours % of the classrooms, dived by glazing’s orientation, during the cooling

season. ................................................................................................................................................... 99

Figure 5-11: Distribution in percentage of the CO2 level present in the classroom, divided by orientation.

............................................................................................................................................................. 100

Figure 5-12: UDI -%- of the classrooms, divided by orientation. ...................................................... 103

Figure 6-1:Displacement and attenuation of a thermal wave ............................................................. 108

Figure 6-2: NW facade of the old part of the school building ............................................................ 110

Figure 6-3: Representation of the payback time -x axis- and of the economic benefit -y axis- of each of

the case scenarios chosen for the external thermal insulation, Lecco ................................................. 113

Figure 6-4: Representation of the return year -x axis- and of the emission benefit -y axis- of each of the

case scenarios chosen for the external thermal insulation, Lecco ....................................................... 114

Figure 6-5: NW facade of the old part of the school building ............................................................ 115

Figure 6-6: Calcium silicate insulation panels .................................................................................... 115

Figure 6-7: Representation of the return year -x axis- and of the emission benefit -y axis- of each of the

case scenarios chosen for the internal thermal insulation.................................................................... 119

Figure 6-8: Attic in the old part of the building .................................................................................. 120

Figure 6-9: Roll insulation of the attic ................................................................................................ 121

Figure 6-10: Rigid panel attic insulation............................................................................................. 121

Figure 6-11: Representation of the return year -x axis- and of the economic benefit -y axis- of each of

the case scenarios chosen for the attic insulation ................................................................................ 123

Figure 6-12: Google earth capture of the roof of the two parts of the case study school building ..... 123

Figure 6-13: Representation of the return year -x axis- and of the economic benefit -y axis- of each of

the case scenarios chosen for the roof insulation ................................................................................ 127

Figure 6-14: Basement of the old part of the building ........................................................................ 127

Figure 6-15: Vault aluminum structure ............................................................................................... 128

Figure 6-16: Aerogel horizontal insulation ......................................................................................... 129

Page 10: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

Figure 6-17: Representation of the return year -x axis- and of the economic benefit -y axis- of the work

representing the insulation of the gym ................................................................................................ 132

Figure 6-18: Chosen PVC glazing ...................................................................................................... 133

Figure 6-19: VMC's heat recovery scheme ......................................................................................... 135

Figure 6-20: Adaptive Thermal Comfort criteria check of the classrooms divided by orientation,

considering the installation of a CMV system. The verification has been done according to TM52.. 138

Figure 6-21: Distribution in percentage of the CO2 level present in the classroom, divided by orientation

and considering the installation of a CMV system, Lecco .................................................................. 139

Figure 6-22: Representation of the payback year -x axis- and of the economic benefit -y axis- of the

work representing the refurbishment of the glazing area of Lecco’s school ....................................... 140

Figure 6-23: Different case scenarios analyzed for the energy retrofit of Lecco’s school building ... 142

Figure 6-24: Analysis of the heating energy demand reduction % – x axis- and the cost of the investment

[k€] - y axis- of the different case scenarios considered for the for the energy retrofit of Lecco’s school

building................................................................................................................................................ 144

Figure 6-25:SE facade of the old part of the school building ............................................................. 145

Figure 6-26: Representation of the payback time -x axis- and of the economic benefit -y axis- of each

of the case scenarios chosen for the external thermal insulation, Buštěhrad ...................................... 148

Figure 6-27: Representation of the return year -x axis- and of the emission benefit -y axis- of each of

the case scenarios chosen for the internal thermal insulation, Buštěhrad ........................................... 152

Figure 6-28: Roof structure of Bustehrad’s school ............................................................................. 153

Figure 6-29: Representation of the return year -x axis- and of the economic benefit -y axis- of each of

the case scenarios chosen for the attic insulation in Buštěhrad ........................................................... 155

Figure 6-30: Bustherad's roof structure ............................................................................................... 155

Figure 6-31: Representation of the return year -x axis- and of the economic benefit -y axis- of each of

the case scenarios chosen for the roof insulation in Buštěhrad ........................................................... 158

Figure 6-32: Representation of the return year -x axis- and of the economic benefit -y axis- of each of

the case scenarios chosen for the ground floor insulation in Buštěhrad .............................................. 160

Figure 6-33: Discomfort hours % of the classrooms, dived by glazing’s orientation, during the cooling

season. ................................................................................................................................................. 163

Figure 6-34: Distribution in percentage of the CO2 level present in the classroom, divided by orientation

and considering the installation of a CMV system, Buštěhrad............................................................ 164

Figure 6-35: Representation of the payback year -x axis- and of the economic benefit -y axis- of the

work representing the refurbishment of the glazing area of Bustehrad’s school ................................ 165

Figure 6-36: Different case scenarios analyzed for the energy retrofit of Lecco’s school building ... 166

Figure 6-37: Analysis of the heating energy demand reduction % – x axis- and the cost of the investment

Page 11: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

[k€] - y axis- of the different case scenarios considered for the for the energy retrofit of Bustehrad’s

school building .................................................................................................................................... 168

Figure 7-1: Solar radiation analysis on the PV panels placed in the starting position on the roof of

Lecco’s school ..................................................................................................................................... 170

Figure 7-2: Solar radiation analysis on the PV panels placed in the starting position of Bustehrad’s

school .................................................................................................................................................. 171

Figure 7-3: Representation of the payback time -x axis- and of the economic benefit -y axis- of each of

the case scenarios chosen for the plant refurbishment, Lecco ............................................................. 175

Figure 7-4: Representation of the payback time -x axis- and of the economic benefit -y axis- of each of

the case scenarios chosen for the plant refurbishment, Bustehrad ...................................................... 177

Page 12: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

Page 13: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

INDEX OF TABLES

Table 1.1: Representation of the numerical data representing the building ......................................... 21

Table 1.2: Parameters recreating users’ activity ................................................................................... 30

Table 1.3: Lighting and machinery profile ............................................................................................ 30

Table 1.4:Infiltration rate values[ach] ................................................................................................... 31

Table 1.5: Natural ventilation [l/(sm2)] for internal school spaces ....................................................... 31

Table 1.6: Mechanical exhaust ventilation ............................................................................................ 32

Table 1.7: Activation periods of the technological plants ..................................................................... 32

Table 1.8: Efficiency value for a class C boiler .................................................................................... 33

Table 1.9: Energy classes of the energy certification ............................................................................ 39

Table 2.1: Parameters representing the building ................................................................................... 44

Table 2.2: Parameters recreating users’ activity .................................................................................... 50

Table 2.3: Light system and machinery profile ..................................................................................... 50

Table 2.4: Infiltration rate ..................................................................................................................... 51

Table 2.5: Ventilation rate for each heated space inside the building ................................................... 51

Table 2.6: Activation profile of the technological plant ........................................................................ 52

Table 3.1: Natural philosophy’s parameters to maintain comfort conditions and improve learning

performances. ........................................................................................................................................ 76

Table 3.2: DLF and Illuminance values for each class. ........................................................................ 86

Table 4.1: DLF and Illuminance values for each class ....................................................................... 102

Table 5.1: Thermal transmittance U limitations in Italy and in CZ, defined by national regulations . 106

Table 5.2: Correction factor btr,U from EN ISO 12831:2006 ............................................................... 106

Table 5.3: Glazing’s thermal transmittance limitations in Italy and in CZ, defined by national regulations

[21] [40] ............................................................................................................................................... 107

Table 5.4: Thermal coating scenario considered for the retrofit intervention located in Lecco.......... 111

Table 5.5: Environmental and economic analysis of the different scenarios ...................................... 111

Table 5.6: Dynamic properties of the different case scenarios Table 5.7: Limit values set by standard

[21] ...................................................................................................................................................... 112

Table 5.8: Heating reductions obtained with the external thermal coating ......................................... 113

Table 5.9: Internal thermal insulation scenario considered for the retrofit, Lecco ............................. 115

Table 5.10: Dynamic properties of the case scenario Table 5.11: Limit values set by standard [21]

............................................................................................................................................................. 117

Table 5.12: Cost of thermal bridge intervention ................................................................................. 117

Table 5.13: Heating reductions obtained with the internal thermal coating, Lecco ............................ 118

Page 14: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

Table 5.14: Cost of thermal bridge intervention ................................................................................. 118

Table 5.15: Cost of the different case scenarios intervention .............................................................. 118

Table 5.16: Different combination case scenarios .............................................................................. 119

Table 5.17: Case scenarios of attic retrofit in the old part of the building .......................................... 121

Table 5.18:Case scenarios of attic retrofit in the recent part of the building....................................... 121

Table 5.19: Heating reductions obtained with the attic thermal insulation ......................................... 122

Table 5.20: Case scenarios of the roof insulation intervention in Lecco ............................................ 125

Table 5.21: Dynamic properties of the different case scenarios Table 5.22: Limit values set by

standard [21] ........................................................................................................................................ 125

Table 5.23: Performances of the old part roof .................................................................................... 126

Table 5.24: Heating reductions obtained with the attic thermal insulation in Lecco .......................... 126

Table 5.25: Component solutions for each of the presented energy retrofit interventions ................. 130

Table 5.26: Heating reductions obtained with the thermal insulation of the gym .............................. 131

Table 5.27: Glazing’s component thermal properties. Thermal transmittance of the proposed windows

............................................................................................................................................................. 133

Table 5.28: Case scenarios considered for the retrofit of the glazing areas of the case study building in

Lecco ................................................................................................................................................... 136

Table 5.29: Heating reductions with the complete refurbishment of the glazing area and CMV combined,

Lecco ................................................................................................................................................... 139

Table 5.30: Thermal coating scenario considered for the retrofit of the case study located in Buštěhrad

............................................................................................................................................................. 146

Table 5.31: Dynamic properties of the scenarios Table 5.32: Limit values set by standard [21] 146

Table 5.33: Heating reductions obtained with the external thermal coating applied onto the case study

Buštěhrad ............................................................................................................................................. 147

Table 5.34: Internal thermal insulation scenario considered for the retrofit, Buštěhrad ..................... 149

Table 5.35: Dynamic properties of the scenario, Bustehrad Table 5.36: Limit values set by standard

[21] ...................................................................................................................................................... 150

Table 5.37: Cost of the intervention, CZ ............................................................................................. 151

Table 5.38: Heating reductions obtained with the internal thermal coating, Buštěhrad ..................... 151

Table 5.39: Case scenario combination, Buštěhrad ............................................................................. 152

Table 5.40: Case scenarios of attic retrofit for the school building of Bustehrad ............................... 153

Table 5.41: Heating reductions obtained with the attic thermal insulation applied onto the case study

Buštěhrad ............................................................................................................................................. 154

Table 5.42: Case scenarios of the roof insulation intervention in Bustehrad ...................................... 156

Table 5.43: Dynamic properties of the scenario, Bustehrad Table 5.44: Limit values set by standard

Page 15: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

[21] ...................................................................................................................................................... 156

Table 5.45: Performances of the old part roof .................................................................................... 157

Table 5.46: Heating reductions obtained with the attic thermal insulation in Bustehrad .................... 157

Table 5.47: Case scenarios for the ground floor insulation in Bustehrad ........................................... 159

Table 5.48: Heating reductions obtained with the ground floor thermal insulation in Bustehrad ...... 159

Table 5.49: Glazing’s component thermal properties. Thermal transmittance of the proposed windows

............................................................................................................................................................. 161

Table 5.50: Case scenarios considered for the retrofit of the glazing areas of the case study building in

Bustherad ............................................................................................................................................. 162

Table 5.51: Heating reductions with the complete refurbishment of the glazing area and CMV combined,

Buštěhrad ............................................................................................................................................. 164

Table 6.1: PV panels dimension, Lecco .............................................................................................. 171

Table 6.2: Solar radiation optimization of the PV panels positioning, Lecco ..................................... 171

Table 6.3: PV panels dimension, Buštěhrad ........................................................................................ 172

Table 6.4: Solar radiation optimization of the PV panels positioning, Buštěhrad .............................. 172

Table 6.5: Plant 1 costs, Lecco ............................................................................................................ 173

Table 6.6: Reduction of the electric and thermal energy consumption of the school building of Lecco

............................................................................................................................................................. 174

Table 6.7: Plant 1 costs, Bustehrad ..................................................................................................... 176

Table 6.8: Reduction of the electric and thermal energy consumption of the school in Bustehrad .... 176

Page 16: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

Page 17: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

INDEX OF APPENDICES

Appendix I - Validation of the energy models

Appendix II – Thermal analysis of the window

Appendix III – Economic index of the case scenarios

Appendix IV – Dimensioning verification of radiators served by an air/water heat pump

INDEX OF THE GRAPHIC TABLES

Elementary school G.Carducci, Lecco – Plans

Elementary school G.Carducci, Lecco – Elevations

Elementary school Bustehrad – Plans

Elementary school Bustehrad – Elevations

Page 18: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

Page 19: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

ABSTRACT

Nel valutare il dispendio energetico dell’Europa non è possibile trascurare il contributo relativo al

comparto delle costruzioni, ed in special modo le istituzioni pubbliche. I dati dimostrano che è proprio

questo settore, in particolar modo il patrimonio edilizio esistente, a poter garantire il più grande

potenziale di risparmio di energia. Per promuovere corrette misure di efficientamento energetico è

necessario avvalersi di metodi di calcolo e strumenti che permettano di prevedere, con buona

attendibilità, il reale consumo energetico degli edifici esistenti, cosicché, di conseguenza, sia possibile

stabilire scenari di riqualificazione appropriati, sia da un punto di vista tecnologico che economico, e

determinare con esattezza i risparmi conseguibili a seguito degli interventi stessi.

Il presente lavoro di tesi si sviluppa proprio all’interno di questo contesto, ovvero, definisce il consumo

energetico di due edifici scolastici situati in due città diverse della regione dell’Europa Centrale, quali

Lecco (IT) e Bustehrad (CZ), e si pone quindi l’obiettivo di valutare le opportunità di risparmio

energetico e soprattutto la possibilità di stabilire interventi di efficientamento energetico applicabili, con

risultati positivi ed omogenei tra loro, ad una vasta gamma di edifici scolastici presenti nel patrimonio

centro europeo. Il lavoro si struttura principalmente in tre fasi.

La prima fase ha l’obiettivo di definire e raccogliere i dati riguardanti le caratteristiche degli edifici in

analisi, considerandone in particolare, i requisisti relativi l’ambito urbanistico, architettonico,

impiantistico e gestionale. Simultaneamente avviene l’inserimento dei dati raccolti all’interno di un

software di simulazione energetica in regime dinamico (IES VE), allo scopo di definire e validare un

modello energetico rappresentativo delle condizioni reali degli edifici presi in esame. Nella seconda fase

si è proceduto con la scelta delle soluzioni di miglioramento delle prestazioni dell’involucro e degli

impianti dei due edifici presi in esame, per raggiungere l’obiettivo previsto dall’attuale normativa

europea riguardo gli edifici riqualificati. La terza fase, sviluppata in simultanea con la seconda,

rappresenta lo studio dell’ impatto energetico ed economico che le stesse soluzioni di miglioramento

delle prestazione prima citate, hanno sui due edifici presi come casi studio.

PAROLE CHIAVE

Simulazione energetica in regime dinamico, ottimizzazione energetica, riqualificazione energetica,

risparmio energetico, analisi energetica, analisi del comfort termico interno, impatto economico e

ambientale, costo dell’investimento, tempo di ammortamento, edifici scolastici nell’Europa centrale

Page 20: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

Page 21: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

ABSTRACT

In assessing Europe’s energy consumptions, it is not possible to neglect the contribution related to the

construction sector, and especially public institutions. The data show that it is precisely this sector, in

particular the existing building stock, that can guarantee the greatest potential for energy savings. In

order to promote correct energy efficiency measures, it is necessary to use calculation methods and tools

that make it possible to predict, with good reliability, the real energy consumption of existing buildings,

so that it is therefore possible to establish appropriate redevelopment scenarios, both from a point

technological and economic view, and determine exactly the savings achievable as a result of the

interventions themselves.

This thesis work develops within this context, as it defines the energy consumption of two school

buildings located in two different cities of the Central European region, such as Lecco (IT) and

Buštěhrad (CZ), and it therefore sets the goal of evaluating energy saving opportunities and in particular

the possibility of establishing energy efficiency measures that can be applied, with positive and

homogeneous results, to a wide range of school buildings present in the central European heritage. The

work is structured mainly in three phases.

The first phase aims to define and collect data concerning the characteristics of the analyzed buildings,

considering in particular the requisites concerning the urban, architectural, plant and management areas.

Simultaneously, the data collected is inserted in a dynamic energy simulation software (IES VE) in order

to define and validate an energy model that is representative of the real conditions of the buildings

examined. In the second phase, it has been analyzed the choice of solutions, to improve the performances

of the envelope and the systems of the two buildings, in order to achieve the requirements set by the

current European legislation, regarding retrofitted buildings. The third phase, developed simultaneously

with the second, represents the study of the energy and economic impact that the same performance

improvement solutions mentioned above, have on the two case study school buildings.

KEYWORDS

Dynamic energy simulation, energy optimization, energy retrofit, energy saving, energy analysis, indoor

thermal comfort analysis, economic and environmental impact, investment cost, payback time, school

building in Central Europe

Page 22: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

Page 23: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

INTRODUCTION

Educational buildings account for 17% of the total European floor space of non-residential building

stock. With an average specific energy consumption estimated at 280kWh/m2, it is at least 40% higher

than the equivalent value for the residential sector. Central Europe Regions vary greatly in their policy

frameworks and have a wide disparity in their current performance and targets, but as a general trend,

most are at risk of missing their targets for energy consumptions. The share of renewables in gross final

consumption of energy (20%) is one of the headline indicators of the Europe 2020 strategy. The

frontrunners in Central Europe were Austria and Slovenia with a share of 32.6% and 21.5% in 2013.

Croatia, Italy, Germany and Czech Republic rank in the middle with a share between 18% and 12.4%

and Hungary is at the back of the pack at 9.1%. Although some strategic and action plans were made,

the main obstacle for speeding up the process is the lack of public funding and low awareness about

possibilities. The project, through the organization of existing knowledge in an integrated methodology,

wants to develop an effective communication strategy addressing the necessary development of skills

for public owners of educational buildings in the Central Europe area in order to support their decision-

making processes and increase their potential to access to financial support.

This thesis work addresses the necessary implementation of an integrated strategy promoting a large-

scale energy retrofitting of the public educational building stock in the CE area. The innovativeness of

the approach is based on the statement that public educational buildings need specific measures that are

not covered by the existing regulatory frameworks, tools or methodologies. This work develops tailored

planning for these buildings so to address the long-term objective of deep retrofitting promoting a

technologically logical step-by-step approach that can be managed with affordable budgets and

profitable investments and without interrupting the operation of the school during the year. The goals

are increasing energy efficiency and implementing renewables in existing public infrastructure through

the development and the demonstration of integrated strategies for the effective and sustainable energy

retrofitting of public educational buildings. This work supports the overall program goal of reducing

carbon emission in the cities of Central Europe, creating an enabling framework to promote large scale

energy retrofit of existing public educational buildings.

Page 24: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

Page 25: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

1

CHAPTER 1

1 Regulation Framework

It will be analyzed the European regulations framework seen as European Union and as single Member

State. Starting from the standard at European level to the implementation done by each of the Member

State considered for the analysis, which are Italy and Czech Republic.

1.1 Energy Savings Policy in the European Union

In Europe, over the last few years, energy issues have been the focus of many directives and action

plans, with the aim of raising awareness among the governments of the State Members.

Buildings are a strategic focus of European policies aiming to achieve a sustainable and competitive

low-carbon economy by 2020. The European Commission encourages Member States (MS) to decrease

energy consumption in buildings and convert national building stocks from energy consumers to energy

producers through retrofit measures and renewable energy sources (RES).

EU Directives require that public authorities should adopt exemplary actions to achieve this target.

The main policy that governments are trying to implement is the Energy Climate Package 20-20-20 [1],

a set of measures planned by the European Union (EU) for the period following the end of the Kyoto

Protocol [2]. The package, part of an Action Plan approved in 2007, came into force in June 2009 and

will be valid from January 2013 to 2020. The EU, over this period, has committed itself to reaching

three goals: reduction of 20% of the emission of CO2 compared to 1990; 20% of the energy, on the basis

of consumption, coming from renewables; saving 20% of primary energy consumption to 2020

compared to a reference scenario.

The EU’s “2020 Europe Strategy” [1] for employment and smart and sustainable growth includes among

its main objectives the energy efficiency, which is always emphasized in the European political program

as a means of addressing the threefold challenge of the economic crisis, energy dependence and climate

change.

NEEAPs (National Energy Efficiency Action Plans) have the task of showing estimates of state

consumption, measures already implemented and energy efficiency forecasts and improvements that

individual countries expect to achieve. The NEEAPs submitted by the State Members during the

reporting period under Directive 2006/32/EC on Energy Services Directive (ESD) have suggested that

the efforts implemented so far are not in line with the target set for 20 % of energy efficiency by 2020.

To address this problem, it was established in the November 2012 the Directive 2012/27UE “Energy

Efficiency Directive” [3] (EED), which explains to MS how to work to achieve the 20% efficiency

Page 26: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

2

target set by the Climate-Energy Package . In addition, this directive requires each MS to set its own

national consumption reduction target, which will be monitored by the European Commission with the

prerogative of intervention where necessary with binding measures and adjustments for the countries at

risk.

The EED adopted by the European Parliament has become the central instrument for the UE’s energy

policies. It intensifies MS’ efforts to manage energy more efficiently at all stages of the energy chain,

from transformation to distribution for the final consumption. The key measures in the Directive are:

- Renovation of some public buildings, and public procurement of energy-efficient materials

(Articles 4 and 5).

- Energy efficiency obligation schemes, which require utility companies to help their customers

save energy (an annual final energy reduction of 1.5 per cent has been set as a goal) (Article 6).

- Energy audits to be compulsory for large companies. These will be carried out every three years

(Article 7).

- More information to be provided for metering and billing (Article 8).

For many MS, the 2014 Action Plan, under the EED, was the third, following the 2007 and 2011 ESD

requirements. To ensure continuity between the different action plans, they were written based on

information on efficiency measures contained in previous NEEAPs. The deadline for submitting the

NEEAPs was 30 April 2014 and will then be submitted every three years.

1.1.1 The role of the public building

The EU database classifies buildings in residential and non-residential buildings, and based on the type

of the building it shows data about the stock of the selected type and also energy data linked to the

building characteristics.

Non-residential buildings represent around the

10 % of the European building stock, there are

over 15 million of buildings located in the

European territory classified as Non-residential

building [4]. The European territory is wide and

various, therefore there are different scenarios

regarding energy consumption in the, above

mentioned, buildings classification. In

particular, there more than 800,000 buildings

entirely or partly used as schools. With regard to their location 40 % of school building are concentrated

Figure 1-1: Share of non-residential buildings in UE [4]

Page 27: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

3

in the Central part of Europe, such as Germany, Italy, Austria, Czech Republic, Hungary, Croatia, and

more than 20 % are located in the Northern part of Europe [4]. Furthermore, about 29% of schools are

located in very small municipalities (up to 5000 inhabitants), and roughly the same percentage are in

medium sized municipalities.

Educational building are classified as

non-residential buildings, the average

annual values of thermal energy show

the comparison between the

consumption for non-residential

buildings and educational between

different states of the Central Europe.

From the graph it’s clear that for most

of the countries the average for the non-

residential buildings is really close to

the one of the educational, this is reasonable since, as said, the education buildings represents around

7% of non-residential buildings throughout the European territory [4]. The stats regarding the

educational buildings show that the consumption per country are close one to each other, this means that

even if the European territory is very diversified, the starting point for school’s energy optimization is

similar in every country. This sets some benchmarks in order to understand the average condition of a

school in Europe and, as said before, in order to be able to set the starting point of the retrofit strategy.

Another important benchmark is highlighted by the table here represented, it’s possible to see an

approximation of expense for each child, based on the data collected by the Energy Consumption Guide.

Good practice benchmarks represents the energy performance of the top 25% of schools, while Typical

benchmarks are the average energy performance of all schools [4].

The table shows the price for each student school, it was done in order to have a simple and fats way to

calculate how much a school with a fixed number of students will consume by fossil fuel and electricity

and have an easy way to understand the energy cost of old buildings such as schools in this case.

The majority of existing school buildings present inefficient systems and technologies. They often use

Good

practiceTypical

Good

practiceTypical

Good

practiceTypical

Good

practiceTypical

136 174 11.07 15.26 24 30 15.53 19.56

Secondary schools

Fossil Fuel

€/pupils

Electricity

kWh/m2 €/pupilskWh/m2

0 50 100 150 200 250 300

Austria

Croatia

Czechia

Germany

Hungary

Italy

Slovakia

Slovenia

kWh/m2

Non-residential

Educational

Figure 1-2: Annual thermal energy consumption per country of CE

Figure 1-3: Benchmarks for energy consumption in secondary schools

Page 28: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

4

traditional heating systems, in particular radiators for heat distribution and gas/oil-fired boilers for

generation . Space heating is still the main end-use with more than 40% of heating needs met using

natural gas in 2012 [5].

The major cause of high energy consumption is

represented by the Space heating of the classrooms. Most

schools present outdated thermal energy plant, with old

boilers with a low efficiency(sometimes lower than 50

%), really far behind from the values achievable with the

new technology used in the NZEB buildings (i.e.

condensing boilers). The lack of maintenance and proper

know-how is another key aspect on why the energy

consumption are so high for schools, they may lead to

high involuntary leakage of the plants and even lower

values of efficiency due to the possible unknown

presence of damages and dirt throughout the thermal

plant and the distribution system. The overall efficiency of the plant is given also by the specific

efficiency of the emission system present in the school, in particular in the classrooms. The most

common emission terminals are the cast iron radiators, the major feature of this system is its high thermal

inertia, this term means the ability to retain heat for a long time even after the heat source has gone out,

a characteristic that is typical of cast iron due to the physical structure of this alloy, but also its great

disadvantage when igniting. To heat the cast iron heaters it is necessary water at a temperature of 65-80

°C , which is very high (certainly not an energy-saving temperature!) and the time to warm an

environment is much slower, in addition the thermal yield is lower, this means that for the same heat

transfer, cast iron heaters will be larger than other types [5].

The disadvantages due to inefficient plant are combined with the high thermal losses due to the opaque

and transparent envelope, they create a sort of cause and effect relationship since the presence of a

permeable envelope increases the losses of the envelope therefore increasing the energy needed from

the plant in order to guarantee comfort, this obviously overstresses the plant, which in case the plant is

already inefficient will only mean more involuntary losses from the system and higher consumption

due to the higher energy demand of the thermal plant, basically that’s what it’s possible to see from the

figure below. The starting point are the two major influencer the “Envelope” and the “Plant”, depending

on the performances of the two it’s possible to understand whether they have a positive or a negative

impact on the energy consumption of the building, depending on the properties of the envelope we can

define the losses and calculate the energy demand, needed to guarantee internal comfort, in the same

way the efficiency is defined by the plant. The energy consumption of the building is represented as

Figure 1-4: Average energy use school profile [5]

Page 29: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

5

“Energy need x Efficiency”, this is because in this case it’s relevant the individual and combine effect

of the characteristic of the envelope and the plant. The flowchart intention is to highlight the combined

effect of low performance envelope and plant, in this case the envelope will increase the energy needed

to guarantee the project fixed temperatures, this means that not only the consumption will be high

because of the low efficiency of the plant but it will be even higher since the inefficient plant will have

to generate more energy in order to compensate the losses of the envelope.

he high consumption and the inefficiency of the building’s component is obviously due to the age of

construction of those buildings. School all over Europe have been classified as “old” or “long-standing”

this is showed by the various European surveys in which it’s possible to identify the average construction

year.

The diagram shows the share of School buildings

located in the European territory based on the

construction period. It’s easy to understand that

the period in which more school can be located is

the one between 1961 and 1980, been WWII over

at the end of 1945, it’s reasonable to see that the

period 1946-1960 represents an introduction to

the massive reconstruction and improvement of

the ’60. Less than 25% of the school present in

the territory was built before the European Union was found, therefore before any European energy plan

Figure 1-5: Flowchart of Energy Consumption

Page 30: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

6

was even in the minds of the State Members, in this particular case, relevant importance is taken by

National energy legislations that were passed before any of the EEP. An important example of national

legislation is the Italian Parliament’s ordinary law n 373/76 [6] which contains the standards for the

containment of energy consumption for thermal uses in buildings.

The 75% of Italian schools dates before

energy laws and the distribution in the

territory from north to south does not

change. The 33% of the school buildings

dates before law n° 373/76 and about the

50% has been realized after the law

nonetheless, the energy quality did not

improve dramatically [7] .

The 25% of the school building dates after

‘80s and thus towards the “Law 10” [8] , in

which it was finally showed a complex National Energy Plan, with the addition of studies on the

renewable energies.

Moreover, the progressive ageing of the schools means a crucial need of improvement and performance

to accomplish current standards and EU Directives. The school building stock counts over 62,000

schools of which about 45,000 public, largely overtake the public housing sector with about 1 million

TEP of energy consumption per year of which 70% of heating and 30% of electricity. The potential of

reduction, with effects on energy, environment and social aspects is impressive. A first step towards

energy efficiency can be implemented by promoting energy behavioral awareness with low cost actions

and a 20% of estimated effectiveness.

1.1.2 Potential savings from school buildings

Energy saving that can be derived from improvements to existing school buildings are potentially large

because of their typical high energy consumption linked to inefficient systems and poor thermal

insulation thickness. With the aim of improving energy efficiency in public buildings (e.g., offices,

schools, health facilities, infrastructures), energy services companies “ESCOs” are being more common

nationally.

A study has been carried out on the potential savings deriving from energy retrofit in schools in

compliance with the EED [9] . Potential savings refer to the saving achievable if, in the period 2014–

2020, energy efficiency actions would be put into practice with a cost-optimal approach to achieve

saving of 60% in the public sector and 40% in the private sector. To assess these potential savings, the

Figure 1-6: Distribution of schools in the Italian and age [4]

Page 31: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

7

Italian school building stock has been analyzed. The floor area of public and private schools that can be

renovated each year has been estimated at 6 million m2 (about 3800 buildings). This total includes about

1 million m2 private schools and 5 million m2 public schools.

For this stock, the study considers actions differentiated by climatic zone and applicability. Among them

there are: thermal insulation of roof and heat-dispersing external walls, thermal insulation of floors or

floors/ceilings bordering on unheated spaces, replacement of existing windows with high-energy

performance windows, upgrading heating/cooling control systems, replacement of heat generators, use

of high-efficiency heat recovery systems, installation of automation systems or a building energy

management system (BEMS), replacement of lighting and external solar screens.

Specifically, the total energy savings achievable from schools by 2020 are estimated as follows: 617

GWh/y for private schools and 5821 GWh/y for public schools. The difference in energy saving

percentages between public and private sectors stems from the fact that public buildings are mainly

constructed prior to 1980 and their starting energy performance is poorer. The estimated investments

for these retrofit projects amount to around 6.54 billion €/y, and should yield potential energy savings

of 6.438 GWh/y by 2020. At European level, the added value deriving from specialized construction

activities that include renovation work and energy retrofits has been estimated as 283 billion € in 2011,

66% of this value is linked to the EU building sector. In particular, specialized construction activities

supported 7.84 million jobs in the EU building sector, and 1.55 million in Italy. In more detail, activities

linked to building envelope (e.g., roofing, walls and floor covering, glazing) have been quantified at 166

billion in the same year [10] .

Energy saving measures focusing on

envelope and thermal plants can

decrease strongly the consumption

with additional costs however about

40% of the school buildings are in

need of maintenance and the retrofit

measures could be included inside this

cost item. The cost percentage of

energy retrofit measures in school

buildings show that the control and upgrading of lighting and thermal systems have low costs in

Figure 1-7: Consumption reduction potential by 2020 from complete renovation of schools starting [5]

Page 32: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

8

comparison with envelope solutions such as insulation of the vertical and horizontal opaque portions or

thermal enhancement of transparent surfaces. The cost of measures focusing on the envelope can affect

by 10% to 46% the refurbishment interventions [11]. Furthermore, the age of the school building stock,

defines the typologies of envelope and the associated thermal plant. In fact the 70% of the national

school buildings is realized with reinforced concrete frame structure with brick infill walls and it is

equipped with a gas boiler heating system [11]. In any case, for buildings realized after the 1976 a thin

insulation layer in the opaque envelope can be expected. The average heating energy consumption for

public schools is about 180 kWh/m2year whereas the requirement for new construction is about 30-40

kWh/m2year. Thus, it is not appropriate supplement with an additional cooling need this amount of

energy inasmuch cooling systems diffusion had a dramatic growth in the last 15 year in the housing

sector. The requirement of comfort is however pushing and the capacity of the envelope to reduce and

manage the heat gains with dynamic thermal properties has been introduced in the national regulations

since 2009 [12].

1.2 Analysis of two case studies: Italy and Czech Republic

Every European nation implements the regulations issued by the European Union, at national level, in a

different way one from another. In this paragraph it will be analyzed how the two nations analyzed

through this work, have implanted their regulations.

1.2.1 Italian Regulation

At national level, since the so called Law 10 [8] , Issued in 1991, the emphasis is on energy saving and

rational use of energy and the diffusion of renewable sources. In addition to assigning specific tasks to

local and regional authorities, this law seeks to reduce energy consumption in public and private

buildings with the obligation of energy certification.

The Ministerial Decree of 26 June 2015 [13] concerns the application in the Italian territory of the

European Directive 2010/31/EU. It is an indispensable tool for the promotion of nearly zero energy

buildings. The purpose is to define how the energy performance calculation of buildings, the use of

renewable sources, the requirements and the minimum requirements for energy performance are applied.

The criteria apply to both public and private buildings, new buildings or existing ones undergoing

restructuring. The 26th of June 2015, the Ministry for Economic Development (MISE) announced the

publication of three key decrees for adapting to European building energy efficiency standards and the

deadlines to be met for restructurings.

The first decree [13] is aimed at defining the new ways of calculating the energy performance and the

new minimum efficiency requirements for new buildings and those undergoing renovation.

Page 33: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

9

A second decree [13] adapts the draft technical design diagrams to the new regulatory framework,

depending on the different types of works: new constructions, major renovations, energy re-

qualifications.

With the third decree [13], the standards for the certification of energy performance of buildings (APEs)

were updated. The new APE model will be valid throughout the country and, along with a new

commercial announcement scheme and the National Energy Certificate Database (SIAPE), will provide

citizens, administrations and operators with more information on the efficiency of the ‘ Building and

plants, allowing for easier comparison of the energy quality of different real estate units and orienting

the market towards buildings with better energy quality.

From 1 January 2021, new buildings and those undergoing significant renovations will have to be

implemented in such a way as to minimize energy consumption and to cover them to a minimum with

the use of renewable sources. For public buildings, this deadline is anticipated until January 1, 2019, the

three measures, will enter into force on 1 October 2015 and will thus allow Italy to be fully in line with

European directives .

Let’s start by analyzing the first of the three decrees (all dated 26 June), which deals with the

methodologies for calculating energy performance and the definition of building requirements and

minimum requirements. It defines the modalities for the application of the methodology for calculating

the energy performance of buildings, including the use of renewable sources, and the minimum energy

performance requirements and requirements for buildings and real estate units. The Decree applies

(Article 6) [13] to the Regions and Autonomous Provinces that have not yet taken measures to transpose

Directive 2010/31 / EU [14]. The decree contributes to the definition and updating:

- the methodologies for calculating the energy performance of buildings in accordance with the

general principles of art. 3 of MD 26/6/2015;

- minimum requirements for buildings and installations;

- building energy classification systems, including the definition of the common information

system, also in collaboration with the Department of Public Function of the Presidency of the

Council of Ministers;

- the monitoring, analysis, evaluation and adaptation of the national and regional energy

legislation referred to in Articles 10 and 13 of the Legislative Decree.

The second decree stipulates that its provisions are directly applicable in the regions and autonomous

provinces that have not yet adopted their own energy performance attestation instruments in accordance

with Directive 2010/31 / EU. If they had adopted their own instruments, they should take measures to

encourage, within two years of the entry into force of the Decree, the adaptation of its regional

instruments to the Guidelines. The decree seeks to promote the homogeneous and coordinated

Page 34: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

10

application of the certification of the energy performance of buildings and real estates by defining:

- the National Guidelines for the Certification of Energy Performance of Buildings;

- instruments for linking, conciliation and cooperation between the State and regions;

- the establishment of a common information system throughout the national territory for the

management of a national catastrophe of energy performance certificates and thermal

installations.

The Guidelines are contained in Annex 1 to MD 26/6/2015 [13] and include:

- calculation methods, even simplified for small-scale buildings and low-quality energy

performances, with a view to reducing the cost to the citizen;

- the APE format, referred to in Appendix B of the Guidelines, including all energy efficiency

data of the building and the use of renewable sources in it, in order to enable citizens to

evaluate and compare buildings different;

- the sales or lease announcement scheme referred to in Appendix C of the Guidelines, which

uniformizes the information on the energy quality of buildings supplied to citizens;

- the definition of the common information system throughout the national territory.

1.2.2 Regional Legislation

The National MD 26/6/2015 has been transposed in July 17, 2015 and has updated the regional discipline

that defines the minimum energy efficiency requirements of buildings, whether in the case of new

construction or renovation, and how to calculate the energy needs of buildings, by issuing a decree to

the editorial office of a single text, aimed at containing the new implementing provisions. This single

text ,technically described as a Consolidated Law ,was approved by Decree no. 6480 of 30.7.2015 and

was incorporated by Decree no. 224 of January 18, 2016. The need to provide further operational

clarification and to adjust the procedure for the calculation of energy efficiency on buildings also in

relation to some indications highlighted by the Ministry of Economic Development, has led to the

approval, by Decree No.176/2016 , of a new Consolidated Law which therefore replaces the decrees

previously approved.

For these reasons, it was decided to approve this update in order to implement energy saving, rational

use of energy and renewable energy sources in buildings in accordance with the fundamental principles

set out in European Directive 2010/31 / EU 19 May 2010 and Legislative Decree 19 August 2005, no.

192 , as well as the implementing provisions approved by DGR of 17/7/2015.

The provisions contained in Decree No.176 of 12 January 2017 [15] concerning issues related to the

energy-saving of buildings affect different themes: from wrap-around to those relating to technical

installations, sanitary water, lighting, ventilation and of winter and summer air conditioning. In addition,

within the Decree n.176 of 12 January 2017 [15], a section on the energy performance certificate is

Page 35: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

11

devoted, which should, from 1 January 2016, be present in all buildings at the end of the works and

before Declaration of agility. The Energy Performance Certificate (APE) is the synthetic document

produced by the owner of the building attesting to the value resulting from the calculation of the energy

performance of the building to which it refers. In addition to the APE, Decree No.176 of January 12,

2017 extends the directives in terms of inspections and inspections related to the energy efficiency of

buildings and the energy classification of buildings.

Depending on the requirements we could distinguish three main application areas:

- New construction;

- Major renovations;

- First level;

- Second level;

- Energy retrofit.

The definition of Major renovations is explained through a simple layout presented in the figure below.

Basically first level renovation stands for an intervention which involves more than 50 % of the envelope

and the simultaneous refurbishment of the heating/cooling plant. While the second level renovation

stands for intervention which involves more than 25 % of the envelope and it could also affect the

heating/cooling plant.

Finally, the decree identifies the category of “energy retrofit” for all non-attributable interventions to

previous cases and which have, however, an impact on the energy performance of the building. Basically

they stand for interventions that either involve less than 25 % of the envelope or the installation of a

new heating/cooling plant, consisting on either the simple replacement of the generations systems or the

complete refurbishment of the thermal plant. The figure below shows summarily what is the definition

of an “energy retrofit” intervention.

Figure 1-8: Major renovations definition, by the Ministerial Decree of the 26th of June 2015

Page 36: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

12

Through this work the interventions analyzed will involve only second level renovations and energy

retrofit interventions. As matter of fact it will be studied how the retrofit of the envelope of the buildings

and the refurbishment of the thermal plant will impact the energy consumptions and the operations costs

of the case studies. The emissions and the distribution system will be left as they are now, therefore no

first level renovation intervention will be analyzed.

So here are listed the verification requested from the decree: verification of energy needs, of the average

coefficient of thermal exchange, of the transparent technical closures and of the efficiency of the plants.

These verifications are made basically comparing the values of the renovated building with the one of a

reference building , which has the same exact characteristics of the building with fixed energy

parameters.

1.2.2.1 Italian national energy certification

At national level, the measure of the energy performance of a building (Epi) indicates how much energy

a building consumes during a year per square meter of treated floor area (TFA). The Epi of an existing

building built before national Law 10/91 is generally between 200 and 300 kWh/m2y with fuel

consumption between 10 and 30 L oil/m2y. The Epi of a building designed and built according to current

legislation is between 15 and 130 kWh/m2y with fuel consumptions between 1.5 and 13 L oil/m2y. The

“APE” [16](Attestato Prestazione Energetica) has a maximum time limit of ten years from its release

and is updated to any renovation or upgrading intervention relating to building elements or technical

installations such as to modify the energy class of the building or the real estate unit. This validity is

subject to compliance with the requirements for energy efficiency control operations of the technical

installations of the building, in particular for thermal installations, including any adjustments required

by the regulations set out in the decree of the President of the Republic of 16 April 2013 , N. 74. In the

Figure 1-9: Energy retrofit interventions definition, by the Ministerial Decree of the 26th of June 2015

Page 37: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

13

event of non-compliance with these provisions, the APE shall expire on 31 December of the year

following the date on which the first expiry date for the above-mentioned energy efficiency control

operations is foreseen.

Each APE must be drawn up by an authorized person according to Presidential Decree No. 75 of 16

April 2013 [17] and presents, for the building or real estate unit:

- overall energy performance, both in terms of

total primary energy and non-renewable primary

energy, through their respective indices;

- the energy class determined by the global

energy performance index expressed in non-

renewable primary energy;

- the energy quality of the building to contain

energy consumption for heating and cooling,

through the thermal performance indices useful

for winter and summer air conditioning in the

building;

- reference values, such as the minimum energy

efficiency requirements in force under the law;

- carbon dioxide emissions;

- the energy exported;

- recommendations for improving energy

efficiency with proposals for more meaningful

and cost-effective interventions, distinguishing

between major restructuring measures and

energy redevelopment.

In addition, the APE should report information related to improving energy performance, such as

financial incentives and the opportunity to perform energy diagnosis.

The 26/6/2015 Decree [19] also specifies that the authorized subject will have at least one inspection at

the building or real estate unit subject to attestation, in order to find and verify the data necessary for its

predisposition.

1.2.3 Czech Regulation

The Climate Protection Policy of the Czech Republic [19] along with the Strategy on Adaptation to

Climate Change [20] in the Czech Republic represent specific policies regarding climate change. The

Figure 1-10: Italian Energy Performance Certification

Page 38: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

14

Climate Protection Policy was adopted by the Czech government in March 2017 and replaced former

National Program to reduce the Climate Change impacts in the Czech Republic. The Policy defines main

objectives in the climate protection at the national level to ensure the fulfilment of the greenhouse gas

emission reduction objectives in order to reach international commitments of the Czech Republic.

Furthermore it contributes towards gradual long-term transition to sustainable low emission economy.

The Policy further sets primary and indicative emission reduction targets, which should be reached in a

cost efficient manner. Measures are proposed in the following key areas: energy, final energy

consumption, industry, transport, agriculture and forestry, waste, science, research development and

voluntary tools.

The plan seeks to improve energy efficiency and cut greenhouse gas (GHG) emissions by developing

renewable energy and expanding nuclear power capacity. The plan aims to:

- cut energy consumption per unit of GDP by 3-5% per year;

- increase the share of renewable energy to 16% by 2030;

- increase the share of transport fuel from alternative sources such as gas or biofuels to 20% by

2020.

However, it found the Czech Republic energy intensity and GHG emissions per capita were

comparatively high, and that transport sector emissions continued to increase. The National Climate

Change Plan is thus being reviewed to emphasize measures targeting the industry and transport sectors,

which contribute the most to GHG emissions, as well as to take into account the evolution of domestic,

European and global political negotiations on climate change since 2004.

The Policy covers a period from 2017 to 2030 and provides outlook until 2050. The first evaluation is

planned in 2021 and on the basis of such evaluation the Policy will be updated by 2023. In October 2015

the Czech government adopted the Strategy on Adaptation to Climate Change [19] in the Czech

Republic. This document represents a national adaptation strategy and includes assessment of the

climate change impacts and proposals for specific adaptation measures, legislative and partial economic

analysis, etc.

The Czech Republic’s national indicative targets have been set in line with the document “Update of the

Czech Republic’s State Energy Policy” [21] . This is a key strategic document which aims to ensure a

reliable, safe, and environmentally friendly energy supply for the needs of the population and economy

of the Czech Republic, at competitive and affordable prices under standard conditions. Further to the

passing of Directive 2012/27/EU of the European Parliament and of the Council on energy efficiency,

the Czech Republic has launched a process to transpose it into national legislation.

The most important act regarding energy saving in building construction is represented by the “New

Green Savings 2014+” [22] [19] , the Ministry of the Environment’s program administered by the State

Environmental Fund of the Czech Republic represents the green investment scheme of Czech Republic

Page 39: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

15

and is focusing on energy savings and renewable energy sources in family houses. The Program’s

objective is to improve the environment by reducing greenhouse gas emissions through the improved

energy efficiency of buildings, the support of residential development with very low energy performance

and the efficient use of energy sources, as well as saving energy in final consumption and stimulating

the economy of the Czech Republic with other social benefits, which are for example, increasing the

quality of citizens living, improving the appearance of cities and municipalities, starting long-term

progressive. Promotes energy saving reconstructions of houses and apartment buildings, replacement of

unsuitable heating sources and usage of renewable energy.

1.2.3.1 Czech national energy certification

On 19 September 2012, the Czech parliament overruled a presidential veto and passed the “Amendment”

[23] which imposes additional obligations on builders of new buildings, as well as on owners of certain

buildings already in use, including the obligation to have an energy performance certificate “EPC”

issued.

The Amendment imposes a new obligation on the owners of completed residential and administrative

buildings already in use. As of 1 January 2015, the owners of such buildings are obliged to ensure the

EPC. The Amendment sets later terms for fulfilment of the above-stated obligations in relation to the

surface area of a building. At the latest by 1 January 2019, all completed residential and administrative

buildings are required to have the EPC.

Furthermore, the building owner must ensure the EPC

prior to any purchase or lease of a whole building or any

purchase of building’s compact parts (residential or non-

residential premises) as of 1 January 2013. After 1

January 2016, even the lease of residential or non-

residential premises shall be subject to the obligation

and the landlord will have to submit the EPC to the

future tenant at the latest by the signing day of the lease

agreement.

With regard to the purchase and lease of the building or

its compact parts, the owner is obliged to ensure the

EPC, submit the EPC to all potential buyers before the

conclusion of the contract and hand over the EPC to the

buyer at the latest by the conclusion of the contract. If

publishing any information or marketing materials with

respect to the purchase or lease of the building or its Figure 1-11: Czech Energy Performance

certification

Page 40: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

16

compact parts, the owner of the building is obliged to include the data from the EPC.

The EPC shall indicate the building’s energy performance on a scale of A to G, making the information

on expected energy consumption in the building accessible to potential buyers or tenants. It expires

within ten years at the most or as soon as the building undergoes major reconstruction.

The EPCs are to be elaborated and issued exclusively by energy experts authorized and listed by the

Ministry of Industry and Trade. The list of experts will be available on the website of the Ministry. Due

to increased demand of the EPCs at the beginning of next year, a significant increase in price for

elaboration and issuance of the EPC can be expected.

Page 41: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

17

CHAPTER 2

2 Description: Case study “Lecco”

Within this chapter it will be proposed and analyzed a case study, identified among the many taken into

consideration, chosen on the basis of the data and information actually available to perform this in the

most complete way this work, following the analysis method described and deepened in the previous

paragraphs.

2.1 Geographical and historical overlook

The first case study taken in consideration is a school building located in Lombardy, exactly in the city

of Lecco. The city of Lecco is located on the side of the homonymous lake, oriental branch of the Como

lake, and on the shore of the Adda river, its urban agglomeration has more than 114,000 inhabitants and

includes several neighboring municipalities.

Figure 2-1: Territorial overview of the case study building

At the ground level the entire building is surrounded by a moderate amount of green surface, represented

by the courtyard of the school, the access to the school is possible through a one-way street that goes

beside the main entrance of the school, located on the old part of the school building. Unfortunately the

figure representing the territorial overview of the building is old, therefore it’s not possible to see the

newly constructed residential building present on the right of the school, this will be highlighted later

one in the analysis of the case study.

Page 42: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

18

The school building is located in an urban area of the city of Lecco, the context in which the proposed

building is inserted is characterized by the presence of settlements for the most part residential and

moderate size, with the main square occupied by a church. The morphology of the area has changed

during the years, finally the street area has been decrease in order to have a bigger sidewalk to protect

the students from the moving cars, and to facilitate the traffic created in the entrance hours from the

student’s parents.

The case study building is an elementary school called “Giosuè Carducci”, as the famous poet,

composed of two part, each of the part has its own structure and was built in a different age, together on

plan they form a L shape around the stairwell, which represents the focus of the whole building.

The elementary school building was initially built

in the 1901, than it went under some

reconstruction until in the 1961 the building was

expanded, a new a body was added to the original

structure, giving to the overall plan a L shape. The

recent part of the building can be identified in

between the 1961-1980 years. Due to the different

building age construction the two parts present

different element structure and different input for

the energy model dynamic simulation, as it will be shown in the following paragraph. The whole

building accounts for a total of 13 classroom distributed so that 4 of them are in the recent part of the

building, while the other are in the old part. As explained the recent part has a significant lower amount

of classes respect to the old one, this is because the recent part was built especially to integrate a school

gym, therefore the major amount of surface area is dedicated to this function.

Figure 2-3: School “Giosuè Carducci”, 2016

Figure 2-2: School “Giosuè Carducci”, 1909

Page 43: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

19

This is how the whole building looks nowadays, comparing the pictures from the different years it’s

possible to see that the old building hasn’t changed that much. What is visible in this real-life pictures

is than translated into a 3D modelling of the whole case study area, this was done in order to have a

more complete analysis, with more credible results which reflect reality more. In the modeling of the

surroundings the data about the buildings were taken upon a visual inspection confirmed by detailed

researches through the technology available.

Figure 2-4: Capture of the 3D representation of the case study area (21 September 12:00).

From the picture above is also possible to see the shadows on the building and on the surroundings in

order to try to have some ideas about the shading action of the surroundings on the case study building,

highlighted in blue. As seen, the school building is surrounded by moderate height buildings alternated

by a green area around the internal façade.

The urban context in which the building is inserted is characterized by the presence of medium-sized

and small dimensions building that do not rise for more than four floors, except for the new residential

building built in front of the school’s courtyard. The average height and the low density of the

surrounding building make sure that the buildings surrounding the project’s site do not generate shadings

that are particularly incident on the body of factory of the residence, so as to ensure a correct daylight

factor and, above all, do not hinder the possible solar gains in the coldest seasons. To determine the level

of shadowing on the building within one calendar year, an analysis was performed related to the shadows

that are generated during the equinoxes and the solstices, presented in the annexes.

N

Page 44: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

20

2.2 Architectural construction

To reconstruct the planimetry, the company that administers the building was contacted, through which

it was possible to access the cadastral documentation of the building.

For a better accuracy in the analysis procedure, it was subsequently performed a survey of maximum on

the exterior of the building in order to verify that the dimensions reported on the cadastral plants

correspond exactly to those real.

The whole building, as seen from the pictures, has various element’s structures, the stone structure of

and the tiles inclined roof of the old part is not present in the recent part, where the hollow brick masonry

is used as load-bearing structure and the roof is made of a metal sheet. The differences are visible on the

whole structure, the old part has 3 floor above the ground, opposed to the only 2 of the recent, while the

underground is present in both parts, the function is different as for the recent part is designated for the

gym while the old part is simply used as storage. The plan lets understand the separation of the two

different parts of the building, it also gives an overlook on the inside and surrounding of the school

building’s area.

Figure 2-5: Ground floor plan of the case study building

RECENT PART

OLD PART

Page 45: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

21

The structural element are different for the two parts of the building, as mentioned before, this means

that they will be studied as two separate entities in the following dispersions analysis. The peculiarity

of the building is that the façade that is exposed on the North-West direction, which is the one on the

street side, has an architectural value, since as seen in the previous pictures it has been constructed more

than 100 years ago, and it still shows the aesthetic characteristic of that particular time. This means that

when proposing the improvement cases there will always be a special attention on this feature, therefore

there won’t be any improvement work that can damage the image of this architectural value.

The floors of the building follow the imprinting of the ground floor, with the difference that on the upper

floors all the space is used for the classroom, therefore the two parts wont’ be separate bodies as it’s

visible here, but they will be connected in order to create a bigger educative space. In order to have a

more detailed view of the building’s distribution and technology reference is made to the annexes, where

it’s possible to see all the plans and the complete overview of the building.

The table here presented gives a

numerical tool in order to

understand the distribution and the

composition of the case study

building. Once more is obvious

that the impact of the old part of

the building is higher than the

recent, therefore in a retrofitting

view the most critical importance

has to be given to the technologies

of the old part. Another important aspect is the one related to the glazing area of the construction, which

represents more or less 20% of the external wall area, in both cases, indicating the need for accurate

analysis regarding the optimization of the windows, and the related thermal bridges. Finally the data

about the Surface-Volume ratio shows that most of the spaces have high ceilings, increasing the volume

of the building, especially increasing the volume of space that has to be heated in order to guarantee

thermal comfort for the users thus increasing the energy needs.

2.3 Energy data collection

The purpose of this first phase is to collect as more information as possible about the building,

considering those concerning the urban, architectural and plant design aspects. The site survey is the

first approach with reality with which one is confronting and plays a very important role within this type

of analysis.

Element Unit Building

Old part Recent Part Whole

Floor # 3+1 2+1 3+1

Floor area [m2] 906.7 467.79 1374.49

Heated Space [m2] 671.46 437.1 1108.56

External Wall area [m2] 754.42 544.5 1298.92

Glazing area [m2] 133.36 112.75 246.11

Average Height [m] 3.5 3.5 3.5

Volume [m3] 3082.7 2163.6 5246.3

S/V [m2/m3] 0.29 0.22 0.26

Table 2.1: Representation of the numerical data representing the building

Page 46: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

22

2.3.1 Envelope Characteristics

After defining the dimensions of the envelope, the defining analysis has moved on to the definition of

the materials that make up the transparent structure and the vertical and horizontal opaque ones. To

collect this information is

It was essential to have an interview with the headmaster of the school, which became available in

providing the necessary documentation for the retrieval of information concerning materials used in

construction. In fact, in this case it would not have been sufficient to know specifically the thicknesses

and thermal characteristics of the materials that make up the masonry, the floors, the roof and the doors

and windows. Unfortunately the old age of the building, added to the lack of documentation of the public

building defined a big uncertainty on the materials and on the element structures of the building,

therefore it has been taken another step into a research study of the building typology and characteristic

of the European territory, divided by age of construction. In order to do this it has been used the famous

research founded by the IEE [24] called Project Tabula [25], which includes the “Building Typology

Brochures” for each of the partner country in their respective language, through which it was possible

to study the construction characteristics of a numerous example of case studies set with boundary

conditions similar to the specific case study building of this thesis work. Basically the research is a

database in which one can find any construction related information regarding a specific building

typology depending on the location and on the age of construction. Therefore having knowledge about

the case study building’s age, location and typology, and comparing the data of the research with the

personal knowledge and the information received by the school institution the final data about the

construction elements of the building and their characteristic were extrapolated.

Once this phase was completed, it was possible to calculate through the EN ISO 6946 [26] the value of

thermal transmittance of the structural packages and the glazing, which is the thermal flow exchanged

between exterior and interior through a material or a transparent body. This data, obtained by crossing

the related information the orientation and adjacency of each structure with the thermal characteristics

of each layer of material of which it is composed, it has been useful to know the thermal dispersions and

the level of insulation of the building. Regarding the glazed surfaces made up of window, in addition to

the size and exposure it has to be also considered the material of the frame and the type of glass: single,

double, with or without double glazing.

2.3.1.1 Old Part Building

In order to make the distinction more clear the two bodies of the building have been separated in this

paragraph, so that it will be easier to show different characteristics of the structure element of the case

study building. This first section will be focused on the elements of the old part building.

Page 47: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

23

Construction elements characteristics of the old part of the case study building:

- External Wall: E.W. 1/E.W. 2

This structure is composed of stone masonry stacked vertically. The use of this type material as load-

bearing structure assures an high value of thermal mass for the building. The mass of a building enables

it to store heat, providing “inertia” against temperature fluctuations, the thermal mass will absorb

thermal energy when the surroundings are higher in temperature than the mass, and give thermal energy

back when the surroundings are cooler. This type of masonry is used for the load-bearing structure at

each floor of the old body of the school, with the difference that the upper floor have a lower thickness

of stone “E.W. 2” respect to the ground floor “E.W. 1”. This behavior is typical of the building

constructed with stone masonry.

E.W. 1 0.53 U [W/m2K] 2.26

Component Thickness Conductivity Resistance

[-] [m] [W/mK] [m2K/W]

Internal lime cement plaster 0.015 0.88 0.017

Stone masonry 0.5 2.1 0.24

External lime cement plaster 0.015 0.88 0.017

E.W. 2 0.6 U [W/m2K] 2.10

Component Thickness Conductivity Resistance

[-] [m] [W/mK] [m2K/W]

Internal lime cement plaster 0.015 0.88 0.017

Stone masonry 0.57 2.1 0.271

External lime cement plaster 0.015 0.88 0.017

- Underground Wall: U.W. 1

The walls of the underground floor are ground-contact walls therefore in order to calculate the effect of

the ground instead of the external air in the calculation, the surface resistance have been changed

according to the EN ISO 13370 [27]. The structure is the same as in the other floor with a different

thickness of the masonry layer.

U.W.1 0.75 U [W/m2K] 0.95

Component Thickness Conductivity Resistance

[-] [m] [W/mK] [m2K/W]

Internal lime cement plaster 0.015 0.88 0.017

Brick 0.75 2.1 0.357

Figure 2-6: Stone masonry wall

Page 48: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

24

- Internal Wall: I.W. 1

The internal wall modelling does not affect the thermal properties of the building, since they’re not part

of the envelope, but in order to have a clear diversification of the different spaces inside the building

they have been modelled, and their structure is the same as the external wall. The same structure is used

as wall in contact to unheated internal spaces.

I.W. 1 0.53 U [W/m2K] 1.88

Component Thickness Conductivity Resistance

[-] [m] [W/mK] [m2K/W]

Internal lime cement plaster 0.015 0.88 0.017

Stone masonry 0.5 2.1 0.238

Internal lime cement plaster 0.015 0.88 0.017

- Internal Slab: I.S. 1

The slab used as horizontal partition to delimitate two different heated space is made of hollow clay

planks set into a composite layer made of steel beams and concrete. This kind of structure is used for

every slab used to separate internal heated spaces, but also for the slab used to separate the last heated

floor of the building from the attic space present under the roof structure, which is unheated.

- Underground Slab: U.S. 1

The underground slab stands for the slab which defines the separation from the ground floor, which is

an heated space, from the underground floor, which is unheated in this case. The structure of this slab is

composed of a brick vault set into a composite layer, as seen before, made of steel beams and cocrete.

I.S. 1 0.285 U [W/m2K] 1.60

Component Thickness Conductivity Resistance

[-] [m] [W/mK] [m2K/W]

Clay Tiles 0.02 0.72 0.028

Composite: Cast Concrete + Steel 0.2 1.304 0.153

Hollow Flat Block 0.05 0.3 0.167

Internal Lime Plaster 0.015 0.88 0.017

Figure 2-7: Hollow clay planks slab

Page 49: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

25

Figure 2-10: Wood beam structure roof

U.S. 1 0.25 U [W/m2K] 1.36

Component Thickness Conductivity Resistance

[-] [m] [W/mK] [m2K/W]

Burnt Brick 0.15 0.71 0.21

Filling clay layer 0.1 1.3 0.08

Levelling layer 0.06 1.4 0.043

Clay Tiles 0.02 0.72 0.028

- Ground Slab: G.S. 1

The ground slab is the slab present on the underground floor, and which is directly in contact with the

ground. This type of structure is a bit different from the previous ones since here the load bearing layer

is made of reinforced concrete set on a crawl space, used to separate the floor of the slab from the ground.

The use of a crawling space is also used to fight against the humidity produced by the ground, even

though this practice is complicated. In order to calculate the ground-contact coefficient it has been used

the calculation proposed by the UNI 13370 [27], as seen before. Concerning the crawl space, the layer

is considered as a ventilated area, and the standard says that the ventilated layer have no influence in the

thermal resistance calculation.

- Roof : R. 1

The roof structure is typical for the Italian territory, it’s composed by a double structure made of crossed

wooden beam and a small wooden structure used to lay the roof tiles. In this case the roof is put on an

unheated space, therefore it’s thermal efficiency is not significantly relevant for the thermal properties

of the building due to the presence of another slab between heated and unheated spaces.

R. 1 0.26 U [W/m2K] 5.77

Component Thickness Conductivity Resistance

[-] [m] [W/mK] [m2K/W]

Clay tiles 0.02 0.6 0.033

Wood layer 0.06 0.16 -

Wood beam 0.18 - -

G.S. 1 0.65 U [W/m2K] 0.95

Component Thickness Conductivity Resistance

[-] [m] [W/mK] [m2K/W]

Concrete layer 0.05 1.15 0.043

Air Layer 0.3 - -

Reinforced Concrete 0.3 2.3 0.13

Figure 2-9: Basement crawl-space slab.

Figure 2-8: Brick vault slab

Page 50: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

26

- Glazed surface: W. 1

The windows present in the old part of the building are all the same. The typical window is made of a

single glazed window put into a wooden frame. The frame pattern is visible from the picture taken in

the visual survey done in the first steps of the analysis. The shading system present in the old part of the

building is represented by internal curtains manually adjustable. In order to simulate the manual

adjustment of the curtains, in the simulation model it has been a set an value of 300 W/m2 for the incident

radiation to turn on or off the curtains.

Net U-value 4.7 [W/m2K]

Net R-value 0.1738 [m2K/W]

Glazed Surface

Component Thickness Conductivity Resistance Transmittance g-value

[-] [mm] [W/mK] [m2K/W] [W/m2K] [-]

Clear float 6 1.06 0.0038 5.75 0.87

Frame

Type Transmittance Percentage

[-] [W/m2K] %

Hardwood 2.50 33

Figure 2-11: Single glazed wooden window

Page 51: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

27

Figure 2-13: Brick internal partition

2.3.1.2 Recent Part Building

In this part of the paragraph it will be presented the characteristics of the envelope of the recent body of

the building, which was built approximately in the 1960 and was added to the original structure of the

school building. Construction elements characteristics of the recent part of the case study building:

- External Wall: E.W. 3

The external wall of the recent body of the building is made of bricks, in this case it’s possible to see

one of the most used techniques used in Italy to build the load bearing perimeter of a building, this is

still used nowadays for new constructions, obviously with some technical adjustment. The construction

is called “cassa vuota” it literally means that the two layer of bricks with inside a non-ventilated layer

of air, make an empty box. In this case, instead of the recent part, the thermal mass is not really high

therefore the thermal inertia of this part of the building is not significant factor, but the overall thermal

properties are better thanks to the quality of the material and the exploit of the air layer.

E.W. 3 0.4 U [m2K/W] 1.15

Component Thickness Conductivity Resistance

[-] [m] [W/mK] [m2K/W]

Internal lime cement plaster 0.01 0.88 0.01

Burnt Brick 0.15 0.6 0.25

Air 0.08 - 0.18

Burnt Brick 0.15 0.6 0.25

External lime cement plaster 0.01 0.88 0.01

- Internal Wall: I.W. 2

Also in this case the internal walling was modelled mainly to separate the internal environment so that

the thermal input of the various spaces could be diversified and therefore more detailed. This type of

structure is also used to separate the unheated spaces present in the inner part of the building, from the

heated spaces.

I.W. 2 0.22 U [m2K/W] 1.62

Component Thickness Conductivity Resistance

[-] [m] [W/mK] [m2K/W]

Internal lime cement plaster 0.01 0.88 0.011

Burnt Brick 0.2 0.6 0.333

Internal lime cement plaster 0.01 0.88 0.011

Figure 2-12: Double layer brick wall

Page 52: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

28

Figure 2-15: Hollow core concrete slab

- Underground Wall: U.W. 2

In this case the structure of the underground wall is different from the one of the upper floors. The

structure is made of a concrete layer, used to bear the load coming from the surrounding ground. Also

in this case the calculation were made according to UNI 13370 [27].

U.W. 2 0.4 U [m2K/W] 0.70

Component Thickness Conductivity Resistance

[-] [m] [W/mK] [m2K/W]

Internal lime cement plaster 0.01 0.88 0.011

Concrete Layer 0.4 1.6 0.250

- Internal Slab: I.S. 2

The structure used for the slabs is the traditional one used all over italy, also nowadays. It is composed

of a conrete layer lighten by hollow blocks made of brick, from this the name “hollow core concrete

slab”. As seen in the picture in between the hollow block there are reinforced beams shaped as triangles

which represent the stiff part of the slab structure and on top of the little beams and hollow bricks is laid

down another layer of concrete.

This type of structure is used for every slab present in the building, except made for the roof and the

gorund-conctact floor which present some obvious adjustment.

I.S. 2 0.275 U [m2K/W] 1.73

Component Thickness Conductivity Resistance

[-] [m] [W/mK] [m2K/W]

Clay Tiles 0.02 0.72 0.0278

Reinforced Concrete Block 0.18 0.8 0.23

Concrete layer 0.06 1.28 0.047

Internal Lime Plaster 0.015 0.88 0.0170

- Ground slab: G.S. 2

The ground slab is the slab present on the underground floor, and which is directly in contact with the

ground. This structure is assumed really similar to the one present in the old body of the structure

therefore mentions are made to the Figure 2-9.

Figure 2-14: Concrete bearing wall

Page 53: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

29

Figure 2-16: Single glazed metal window

Ground Slab 0.67 U [m2K/W] 0.72

Component Thickness Conductivity Resistance

[-] [m] [W/mK] [m2K/W]

Linoleum Floor 0.01 0.18 0.056

Concrete layer 0.06 1.15 0.052

Air Layer 0.3 - -

Reinforced Concrete 0.3 2.3 0.13

- Roof: R. 2

The structure of the roof is the same seen in the Figure 2-15 with the simple replacement of the cover of

the slab, in fact the top layer made of ceramic tile is now replaced by an uninsulate corrugated metal

sheet put on top of the structure in order to protect it from the external environment. The roof structure

is slightly inclined, is not the usual structure seen in the old part of the building.

Roof 0.24 U [m2K/W] 2.01

Component Thickness Conductivity Resistance

[-] [m] [W/mK] [m2K/W]

Metal Cladding 0.02 40 0.001

Reinforced Concrete Block 0.24 0.8 0.30

Concrete layer 0.06 1.28 0.047

Lime Plaster 0.01 0.88 0.011

- Glazed surface: W. 2

As for the old part of the building, also in the recent one the windows have approximately the same

structure all over the perimeter. The windows are made of a single pane of clear glass put into a metal

frame without any thermal brake. The shading system is the same as presented before, it is composed

of a manually adjustable curtain, which in the simulation model is translated into a curtain activated on

the exceeding of 300 W/m2 of incident solar radiation.

Net U-value 5.75 [W/m2K]

Net R-value 0.17 [m2K/W]

Glazed Surface

Component Thickness Conductivity Resistance Transmittance g-value

[-] [mm] [W/mK] [m2K/W] [W/m2K] [-]

Clear float 6 1.06 0.0038 5.75 0.87

Frame

Type Transmittance Percentage

[-] [W/m2K] %

Metal 5.88 33

Page 54: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

30

2.3.2 Internal Conditions

In order to model a more accurate behavior of the heated spaces of the building, during both the cold

and the warm period, it has been decided to create a “typical” profile, able to simulate the parameters

related to the indices and the factors that most influence the internal conditions of the heated and

unheated spaces of the case study building.

Occupancy

The first parameter to set was the one related to the occupancy of the spaces, so it has been defined an

occupancy period and rate of the heated spaces. The analysis has been simulated considering the case

of a typical school day , considering the occupancy only for the classrooms. This means that the internal

gains due to the sensible and latent heat coming from the people are considered only for the classrooms

and not for the other heated spaces. The parameters presented were taken from the guide lines expressed

by the MIUR, in this case the occupancy of the school is intended similar to the one of an office, which

means that it was supposed that the students use the classrooms from Monday to Friday, from 8 to 17.

This is done in order to promote an intense occupancy rate according to a more efficient use of the

spaces, an example can be the exploit of the classrooms in the afternoons for some extra-curricular

activities. The period of occupancy is the same as the one imposed by the school regulation, it is applied

from the 1st of September to the 30th of June. The sensible and latent heat represent the heat gains

produced from the users activity, which contribute to the reduction of energy needs during the winter

period.

Table 2.2: Parameters recreating users’ activity

2.3.2.1 Lighting system and machinery

In addition to these gains it has been considered, for every used space of the case study building the

internal gains produced by the lighting system and the heat coming from the use of typical machinery

used in the school environment according to the EN ISO 12464 [28] and the CIBSE guide A [29].

The simulation of the lighting system was

applied to each of the spaces of the case study,

considered heated and used. In order to

recreate the manual adjustment from the user,

depending on the natural light available linked

to the outside conditions, it was created an accurate activation profile applied to the lighting system. The

Occupancy Density Sensible heat Latent heat

Annual Weekdays [pers/m2] [W/pers] [W/pers]

1st September- 30th June 8:00-17:00 0.5 90 60

Component Occupancy Heat gains

- weekdays [W/m2]

Lighting System 8:00-17:00 7

Machinery 8:00-17:00 5

Table 2.3: Lighting and machinery profile

Page 55: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

31

activation depends on 4 different profile, one for each season, in which the value of the lighting system

goes from 1 to 0 (1 means on and 0 means off), and depends on the hour of the day. This means that the

value expressing the influence of the lighting system to the internal gains of the heated spaces, is

different for each hour of the day and each season of the year. These activation profile were modelled

following the guidelines provided by the UK building regulations [30], which contains some useful info

through which is possible to recreate real-life internal conditions.

The simulation of the machinery used in the heated spaces was more simple, in this case it was simulated

the heat coming from the use of typical school machineries, as computers or projectors and etc. The

values related to the heat produced that is than considered in the energy simulation as internal gains, are

taken from the EN ISO 12464 [28].

2.3.2.2 Infiltration and Natural Ventilation

The same level of detail and accuracy was used also to simulate the parameters that have a negative

impact on the energy balance of the case study, such as the infiltration and ventilation losses, which are

related to the interaction of the building with the outside air. The infiltration represents the air that from

the outside goes through the imperfection of the building to the inner spaces, increasing the internal

temperature of the conditioned spaces. The infiltration rate is calculated based on the air leakage of the

envelope of the building, both the opaque and the

transparent. It is usually calculated through the use of the

blower door test, which sets the infiltration rate of a building

based on the difference of pressure from the inside to the outside, with a fixed applied pressure of 50

Pa. In this case it was not possible to use this type of test so it was necessary to find some empirical

values, that could be applied to the building of the case study. The CIBSE guide A [29] gives empirical

values for air infiltration rate due to air infiltration for rooms in buildings on normally-exposed sites in

winter, classifying buildings for store height and level of air tightness. Considering that the building is

made of 3 stories above ground and considering the building as “leaky” (which represents an existing

building that does not comply with current regulations), due to the age of the building, the standard

provides an empirical value for the blower door test, after that through a conversion value ( obtained

when dividing the 50 Pa air change rate by the calculated average annual infiltration rate) it is obtained

the requested value for air infiltration rate during the winter period.

Concerning the heat losses

coming from the opening of the

windows, it has been modelled a

profile which provides the standard’s value of natural ventilation rate. The values for the ventilation

rates have been taken from the CIBSE guide A [29], in this case to each heated spaces is assigned a

Infiltration Old part Recent Part

[ach] 0.25 0.22

Table 2.4:Infiltration rate values[ach]

Ventilation Kitchen Toilet Gym Classroom Hall/Corridor

[l/(s*m2)] 0.9 1.2 1.5 0.6 0.3

Table 2.5: Natural ventilation [l/(sm2)] for internal school spaces

Page 56: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

32

value of natural ventilation considered the minimum in order to maintain indoor air quality, so basically

it’s the air change rate of the heated spaces. The profile created for the natural ventilation of the spaces

is linked to the occupancy schedules, therefore the natural ventilation will be considered when the users

will need to change the air of the enclosure, which is from 08:00 to 17:00, as seen in Table 2.2.

In the case study building there are also some heated spaces

that don’t have any kind of openings in their specific envelope

area, but have to respect the regulations regarding the change

of the air present in the room. In these cases it has been

hypothesized, and then verified through the visual survey, the presence of extract fans, used only for the

recirculation of air as expressed in the standards [29]. The mechanical exhaust fan are powered by

electricity, so in this case they either represent an heat loss in terms of ventilation, and consume energy

to be activated. They were applied to the blind toilet present on the ground floor of the old part of the

building, and the changing room, located underground, in the recent part of the building.

2.3.3 Technological Plant

Other than the data relating to the materials used for the envelope’s structure, the school principal has

made himself available to provide information about the technical plants that supply energy to the entire

building. This information were than verified through the visual survey done in the technical rooms of

the building, in which the plants are installed. The school building is equipped with a central system

used for the thermal heating of the specified heated spaces, and the preparation of the DHW (domestic

hot water) for the building. Combined with the central system there are two small separated system used

for the DHW of the kitchen/washing room, in the old part of the building, and the locker rooms in the

recent part.

The period of activity of the central heating

system is the same as presented by the

guidelines of the MIUR [18], the DHW

preparation instead, is continuous

throughout the entire annual school period. During the day, as seen in the table the heating system is

continuously on while the DHW preparation is strictly linked to the occupancy of the room, as matter

of fact the DHW is required directly from the users while the settings of the heating system are imposed

by the institution. This is due to the fact that most of the heating system present in the school system are

old, therefore in most of the cases the consumption given by the on-off procedure is so high that keeping

the heating system always on may reduce the consumption, in addition the type of system present in this

buildings are quite big and complex therefore it may be a problem to find an adequate technician

Exhaust Changing room Toilet

[l/s] 100 75

[W/(l/s)] 0.6 0.4

Table 2.6: Mechanical exhaust ventilation

Heating DHW

15th October – 15th April 1st September – 30th June

On continuously 8:00 -18:00 weekdays

Table 2.7: Activation periods of the technological plants

Page 57: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

33

available to do the on-off procedure when needed.

2.3.3.1 Generation System

The production of thermal energy is attributed to the wall-mounted

gas boiler “Carbofuel” produced by the Italian company Riello. The

boiler was installed in the 1998, inside a ventilated technical room

located in the underground level of the old part of the building, and

has a thermal power of 322 kW and an effective thermal power of

290 kW. The old age of the system and of the building made the

search for more detailed information difficult, therefore in order to

model the system in the best way, some of the parameters were

calculated through the use national and European standards.

The efficiency of the boiler was calculated through the use of the UNI

11300-2 [31] with the method of the pre-calculated generation

efficiency for hot water generators. The formula used to calculate the efficiency is:

𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 = 𝐵𝑎𝑠𝑒 𝑣𝑎𝑙𝑢𝑒 + 𝐹1 + 𝐹2 + 𝐹3 + 𝐹4

The base value and the values F1,F2,F3 and F4 depends on the type of boiler considered. In this case

the heating system is composed of a class C sealed chamber boiler, the typical boiler with sealed

chamber and forced draft, are models in which the combustion takes place inside closed sections that

receive the combustion air from outside and which, thanks to an electric fan, push the exhaust fumes

outside in a forced way making them pass through special pipes. The values for a class C boiler are:

The different values of F1, F2, F3, F4 are given by

standard based on the different characteristics of the

installed boiler. The value of F1 is the ratio between

the thermal power installed and the required design

power, therefore it was necessary to calculate the thermal power required to heat the case study building,

this value was calculated thorough the EN ISO 442 [32]. The heating need depends on the climate zone

in which the city of the building is located. Italy has been divided into six climatic zones by the decree

of the President of the Republic of 26 August 1993, n. 412. The coefficients for calculating this

requirement range from 27 to 42 W/m3, corrective coefficients are also foreseen for cases in which

standard conditions are not respected, considering, for example, the level of insulation of the

environment. The city of Lecco is located in the climatic zone E, with a coefficient equal to 37 W/m3,

therefore the design energy need for heating will be the product of this coefficient times the volume of

the heated space. So after calculating the required design power, it will be possible to calculate the ratio

between that value and the actual thermal power in order to calculate the value of F1. The value F2 is

Base

Value

F1 F2 F4

1 2 4

93 0 -2 -5 -4 -1

Table 2.8: Efficiency value for a class C boiler

Figure 2-17: School building boiler

Page 58: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

34

considered whenever the system is installed outside, while the value F3 when the chimney is higher than

10 m. So the result will be:

𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 = 93 − 4 − 1 = 88

The calculation has given as final value that the boiler installed in the building of the case study has an

efficiency equal to 88%, therefore this value will be used for the simulation calculations.

Concerning the heated space of the gym, the conditioning is attributed to the installation of a gas air

heater combined with an own burner directly applied onto the vertical external wall, with a max. nominal

thermal power equal to 85 kW. Following the procedure listed before the air heater has an efficiency:

𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 = 93 − 2 − 1 = 90

Figure 2-18: Lateral and front view of the gas air heater installed onto the gym's external wall

Page 59: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

35

2.3.3.2 Fuel

The systems used for the heating of the selected spaces and for the production of DHW are fueled by

natural gas, methane to be precise. The cost of the methane gas in Italy is equal to 0.7 €/m3, considering

an ideal consumption equal to 9.6 kWh/m3 and dividing this value by the efficiency we have a real

consumption of 8.64 kWh/m3, that sets for the consumption of methane gas a cost of 0.081 €/m3.

2.3.3.3 Emission Gasses

The procedure to calculate the emissions linked to the case study building has been extracted from the

EN ISO 14064-1 [33]. In this case the emission, are in particular the Greenhouse Gasses “GHG”

emissions, caused by the combustion of the methane gas happening in the chamber of the boilers to

generate thermal power used for the heating system and the DHW preparation, and the use of electricity

for the systems present in the building.

The GHG emissions are typically expressed through the means of the equivalent carbon dioxide “CO2e”,

which is a measure for describing how much global warming a given type and amount of greenhouse

gas may cause, using the functionally equivalent amount or concentration of carbon dioxide (CO2) as

the reference. The formula used to calculate the CO2e is:

𝐶𝑂2𝑒 = ∑𝑖(𝐺𝑊𝑃𝑖 ∗ 𝐸𝑖)

Figure 2-19: Table C.1 - GHG global warming potentials, EN ISO 14064.

Page 60: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

36

- the CO2e is the equivalent CO2 emissions expressed in ton/year;

- GWPi is the Global Warming Potential of each of the GHG considered. The GWP is a relative measure

of how much heat a greenhouse gas traps in the atmosphere, it compares the amount of heat trapped by

a certain mass of the gas in question to the amount of heat trapped by a similar mass of carbon dioxide;

- Ei is the GHG emissions.

The study carried out, consistent with the IPCC principles [34], contemplates CO2 emissions as the most

significant greenhouse gas in terms of quantity and therefore the other greenhouse gases contained in

the table below are neglected. For this reason it can be said that the estimated CO2 emissions in the

study correspond totally to the CO2e emissions indicated by the UNI ISO 14064 standard [33].

The conversion factors used for the combustion of the methane gas is equal to 0.203 kg CO2/kWh, while

the factor for the electricity is equal to 0.519 kg CO2/kWh, values were extracted from the Carbon Trust.

2.3.3.4 Emission System

The emission system for both of the parts of the school

building, is represented by the use of cast iron radiators, put in

each of the spaces considered heated in the case study. The cast-

iron radiators have an high thermal inertia, this means that this

type of radiators will need more time to reach the set point

temperature , thus increasing the energy needs and gas

emissions due to the fact that the boiler has to be activated for

a longer period, increasing the time in which the combustion of natural gas produces thermal energy.

The only exception is the emission system present in the gym,

as matter of fact in this space 3 air heaters, installed on the upper

part of the vertical wall, account for the entire emission of heat

needed. The air heater is a more effective heating emission

system for gyms , rather than traditional radiators, this is due to

the fact that an air heater can be installed at a great height, thus

is possible to heat a bigger volume space, such as the one of a

gym.

2.3.3.5 Control system

The emission system of the heating plant is controlled manually and only through an on/off valve located

on the bottom part of the radiators, and the same type if control is applied to the air heater installed in

the gym. An on/off control system is obviously a symptom on an inefficient system design, since this

Figure 2-20: Existing cast-iron radiators.

Figure 2-21: Existing air heater.

Page 61: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

37

control implies the absence of the ability to adjust the temperature depending on the different conditions

of the inside and/or the outside., thus defining an increase in the energy use.

2.3.3.6 Distribution System

The data about the distribution system, have been hypothesized according to the visual survey done in

the technical room located in the underground floor of the old part of the building and the standards

regarding the system efficiency [31] . The distribution system is considered as a zone heating system

with horizontal distribution, powered by vertical mullions (usually running in the stair case) as described

in the Prospectus 22 of the EN ISO 11300-2 [31]. The zone heating system is located in the underground

floor with a slip-rings distribution, and a level of insulation insufficient or inexistent (for example pre-

insulated pipe with reduced thickness or bare tube inserted in corrugate pipe).

This suppositions brought a calculated value of 93% for the efficiency of the distribution system of the

case study building, this sets the value of the overall seasonal heating efficiency of the system “ScoP”

equal to 83.7 %.

2.3.3.7 DHW Production

In this case the calculation procedure has been carried out in two different ways, one for the DHW

required for the correct functioning of the toilets present in the building, and another one based on the

presence of two separated boilers installed in the locker room, located in the recent part of the building,

and in the washing room, located in the old part.

The procedure used to calculate the required DHW for a school has been taken from the EN ISO 11300-

2 [31] with the simple formula, applied for each class:

𝑉𝑤 = 𝑎 ∗ 𝑁𝑢 = 0.17 [𝑙

ℎ]

- a is the specific daily requirement in liters / (day × Nu) obtainable from Table 31, and for school is

Figure 2-22: On the left the supposed scheme of the distribution system: Prospectus 22 of the EN ISO 11300-2.

On the right the installed circulation pumps.

Page 62: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

38

equal to 0.2;

- Nu is a variable parameter depending on the type of building that can be obtained from Table 31, and

for school is equal to the number of students.

This volume of DHW is produced by the central system, described in the § 2.3.3.1, therefore in the

simulation the values related to the efficiency of the DHW preparation will be the same as the one

presented for the central system, considering that the DHW will increase the energy consumption of the

system.

The central system is combined with two standalone methane gas water heater installed in the locker

room and in the washing room, used to produce the DHW needed for the two spaces. The water heater

boiler located in the locker room has a capacity of 150 L and produces a thermal power of 7.2 kWh,

while the one located in the washing room has a capacity of 100 L and thermal power of 4.4 kWh. Both

the water heater can be classified as open chamber boiler, also known as a type B appliance, it is a boiler

or water heater designed to be connected to an evacuating duct for the combustion’s products to the

outside of the installation room, the combustion air is taken directly from the installation environment

that must be permanently aerated. A water heater classified as type B and considered without the

guidance flame, a flame which is always on and allows instantaneous production of hot water to start,

can be considered with an efficiency equal to 77 % according to the EN ISO 11300-2 [31].

2.3.4 Energy classification

The energy certification is based on the comparison of the energy consumption of the real life building

with the ones of the reference building. The reference building has the same geometry as the real

building (shape, volume, floor area, surfaces of construction elements and components), orientation,

territorial location, intended use and boundary conditions, and having predetermined thermal

characteristics and energy parameters defined by standard.

The settings of the reference building are given by the Ministerial Decree of the 26th of June 2015 [18],

in the section of the minimum requirements present in the “Annex A- minimum requirements”.

Reference System: Generation and utilization efficiency set by standard

Reference Envelope: Transmittance set by standard

REAL BUILDING REFERENCE BUILDING

Figure 2-23: Reference Building definition.

Page 63: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

39

The definition of the energy classes depends on the reference building, in particular on the non-

renewable primary energy “EPgl,nren,rif”. After calculating the energy classes, the definition of the energy

class of the real life building is found thanks to the use of the table here presented, comparing the EPgl,nren

which is the non-renewable primary energy of the real building, with the maximum EPgl,nren,rif of each of

the energy classes.

Class A4 ≤ 0,40 EPgl,nren,rif

0,40 EPgl,nren,rif < Class A3 ≤ 0,60 EPgl,nren,rif

0,60 EPgl,nren,rif < Class A2 ≤ 0,80 EPgl,nren,rif

0,80 EPgl,nren,rif < Class A1 ≤ 1,00 EPgl,nren,rif

1,00 EPgl,nren,rif < Class B ≤ 1,20 EPgl,nren,rif

1,20 EPgl,nren,rif < Class C ≤ 1,50 EPgl,nren,rif

1,50 EPgl,nren,rif < Class D ≤ 2,00 EPgl,nren,rif

2,00 EPgl,nren,rif < Class E ≤ 2,60 EPgl,nren,rif

2,60 EPgl,nren,rif < Class F ≤ 3,50 EPgl,nren,rif

Class G > 3,50 EPgl,nren,rif

Table 2.9: Energy classes of the energy certification Figure 2-24: Energy Performance Certification "APE".

Page 64: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

40

Page 65: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

41

CHAPTER 3

3 Description: Case study “Buštěhrad”

Within this chapter it will be proposed and analyzed a case study, identified among the many taken into

consideration, chosen on the basis of the data and information actually available to perform this in the

most complete way this work, following the analysis method described and deepened in the previous

paragraphs.

3.1 Geographical and historical overlook

The second case study taken in consideration is a school building

located in Czech Republic, exactly in the city of Buštěhrad.

Buštěhrad (formerly Buštěves or Buckov) is a small, rapidly

developing town in central Bohemia, located 5 km east of Kladno

and 19 km northwest of the center of Prague, at an average

altitude of 322 m. It is based on a remarkable geological base in

the area inhabited for thousands of years, part of its rich history

are extraordinary personalities and events of Czech and European history. City to which also belongs

the east situated settlement Bouchalka , has an area of 7.61 square kilometers and a population of

approximately 3300 of the population.

Figure 3-2: Territorial overview of the case study building

Figure 3-1: Central Bohemia region, CZ

Page 66: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

42

The case study school building is located in a residential area, as seen from the picture the school is

located on the main road, Tyrsova street, of the small village called Buštěhrad. The area in which the

school is inserted is mainly residential, even though the school building itself represents the limit of the

small village, thus meaning that the school is pretty isolated in the rural context of the Czech lands. The

surrounding area is mainly constituted of small residential buildings that go up to a max of 4 floor height,

with the typical Czech construction technology, luckily the buildings are well spaced therefore there is

no problem involving the overlapping or the excessive shading of one building to an another.

The building taken as case study is the elementary school “Oty Pavla” of Buštěhrad built in the 1891,

which was then placed side by side with another school building erected in the late ’60, in the Figure

3-2Figure 3-3: Oty Pavla school in the 1900-1920 on the left, and Oty Pavla school nowadays on the

right. Is visible as the cross-shaped building present next to the case study building. The Figure 3-3

shows how although a lot of years have passed from the construction of this school, the outer frame of

the building has been kept the same as it was in the 1900. This gives a major importance on the style of

the facades of the building, as matter of fact the façade oriented toward the street (the on the right in the

Figure 3-3) is protected by the Czech Republic culture, as it represents a symbol of their national

architecture technology and style.

Figure 3-4: Capture of the 3D representation of the case study area (21 May 12:00).

Figure 3-3: Oty Pavla school in the 1900-1920 on the left, and Oty Pavla school nowadays on the right.

N

Page 67: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

43

As said before, and as visible through the Figure 3-4, all the surrounding buildings have a moderate

height respect to the case study building (highlighted in blue), in addition it’s clear that the building is

surrounded by a lot of vegetation, as matter of fact its perimeter is defined by trees of 2/3 stories height.

3.2 Architectural construction

To reconstruct the planimetry, the company that administers the building was contacted, through which

it was possible to access the cadastral documentation of the building. For a better accuracy in the analysis

procedure, it was subsequently performed a survey of maximum on the exterior of the building in order

to verify that the dimensions reported on the cadastral plants correspond exactly to those real.

The building dates back to 1891 and has approximately a square floor plan, it has four above-ground

floors and one story underground and is used as a school building for the first grade of elementary

school. In the underground floor there is a boiler room and storage areas for discarded furniture (school

benches, chairs, etc.). In 1st floor – 3rd floor there are school premises (classrooms, etc.) and the 4th floor

is just an empty under-roof storage story. The vertical support system of the building is a brick wall

made of solid bricks, the thickness of the perimeter walls is 750 mm on the ground floor and 600 mm in

the 1st and 2nd floor while the horizontal supporting structures are wooden beams, mirrored vaults in the

halls, and brick vaults above the underground floor. The staircase of the school building is a U-shaped

two-aisle, the stairs leading to the roof story are spiral reinforced concrete.

During the years the building has going through some renovations, fortunately it was possible to receive

some general info about this small and big operationals:

- In the 1991 the roof was reconstructed, now it present itself as an hipped roof made of brazed

tiles;

- In the 1999/2000 the facades of the buildings were fixed;

- In the 2005 thermostatic valves have been installed on the radiators of the building.

From the picture above it’s possible to understand and see the listed reconstruction interventions done

Figure 3-5: Internal facades of the building (on the left), roof structure (on the right).

Page 68: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

44

on the building throughout the years.

The table here presented gives an empirical tool in order

to understand the distribution and the composition of the

case study building. An important aspect is the one related

to the glazing area of the construction, which represents

more than 20% of the external wall area indicating the

need for accurate analysis regarding the optimization of

the windows, and the related thermal bridges. Finally the

data about the Surface-Volume ratio shows that most of

the spaces have high ceilings, increasing the volume of the

building, especially increasing the volume of space that has to be heated in order to guarantee thermal

comfort for the users thus increasing the energy needs.

As said before the plan has a semi rectangular shape, with the core representing by the rectangular

shaped staircases located onto the North-West façade of the building. The staircases located inside of

the heated space of the building is next to another staircase, but this one is unheated and is used only to

get to the roof of the structure, therefore represents a buffer zone between the internal stair cases and the

outside environment. The configuration of the internal spaces at the ground floor can be taken as a

reference since all the floor follow the same internal distribution. This school building presents only

Element Unit Building

Floor # 3+1

Floor area [m2] 1558.72

Heated Space [m2] 1025.43

External Wall area [m2] 802.65

Glazing area [m2] 169.5

Average Height [m] 3.85

Volume [m3] 3756.43

S/V [m2/m3] 0.3

Table 3.1: Parameters representing the building

Page 69: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

45

classes and offices, as matter of fact unlike the case study located in Lecco (§ 2.2) there’s no kitchen

and gym inside the perimeter of the building. In order to solve the absence of the gym inside the building,

the students of the case study school can exploit the outdoor spaces and the gym of the adjacent school

building, while for the absence of the kitchen, the meals are directly given to the students in their

classroom with the use of service food trucks coming directly inside the perimeters of the building.

3.3 Energy data collection

The purpose of this first phase is to collect as more information as possible about the building,

considering those concerning the urban, architectural and plant design aspects. The site survey is the

first approach with reality with which one is confronting and plays a very important role within this type

of analysis.

3.3.1 Envelope Characteristics

After defining the dimensions of the envelope, the defining analysis has moved on to the definition of

the materials that make up the transparent structure and the vertical and horizontal opaque ones. To

collect this information is

It was essential to have an interview with the headmaster of the school, which became available in

providing the necessary documentation for the retrieval of information concerning materials used in

construction. In fact, in this case it would not have been sufficient to know specifically the thicknesses

and thermal characteristics of the materials that make up the masonry, the floors, the roof and the doors

and windows. Unfortunately the old age of the building, added to the lack of documentation of the public

building defined a big uncertainty on the materials and on the element structures of the building,

therefore it has been taken another step into a research study of the building typology and characteristic

of the European territory, divided by age of construction. In order to do this it has been used the famous

research founded by the IEE [1] called Project Tabula [2], which includes the “Building Typology

Brochures” for each of the partner country in their respective language, through which it was possible

to study the construction characteristics of a numerous example of case studies set with boundary

conditions similar to the specific case study building of this thesis work. Basically the research is a

database in which one can find any construction related information regarding a specific building

typology depending on the location and on the age of construction. Therefore having knowledge about

the case study building’s age, location and typology, and comparing the data of the research with the

personal knowledge and the information received by the school institution the final data about the

construction elements of the building and their characteristic were extrapolated.

Once this phase was completed, it was possible to calculate through the EN ISO 6946 [26] the value of

Page 70: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

46

thermal transmittance of the structural packages and the glazing, which is the thermal flow exchanged

between exterior and interior through a material or a transparent body. This data, obtained by crossing

the related information the orientation and adjacency of each structure with the thermal characteristics

of each layer of material of which it is composed, it has been useful to know the thermal dispersions and

the level of insulation of the building. Regarding the glazed surfaces made up of window, in addition to

the size and exposure it has to be also considered the material of the frame and the type of glass: single,

double, with or without double glazing.

Construction elements characteristics of the old part of the case study building:

- External Wall: E.W. 1/E.W. 2

This structure is composed of burned brick stacked vertically. The use of this type material as load-

bearing structure assures an high value of thermal mass for the building. The mass of a building enables

it to store heat, providing “inertia” against temperature fluctuations, the thermal mass will absorb

thermal energy when the surroundings are higher in temperature than the mass, and give thermal energy

back when the surroundings are cooler. This type of material is used for the load-bearing structure at

each floor of the old body of the school, with the difference that the upper floor have a lower thickness

of stone “E.W. 2” respect to the ground floor “E.W. 1”. This behavior is typical of the building

constructed with bricks.

E.W. 1 0.77 U W/m2K] 0.92

Component Thickness Conductivity Resistance

[-] [m] [W/mK] [m2K/W]

Internal lime cement plaster 0.01 0.88 0.011

Burnt Brick 0.75 0.84 0.89

External lime cement plaster 0.01 0.88 0.011

E.W. 2 0.62 U [W/m2K] 1.10

Component Thickness Conductivity Resistance

[-] [m] [W/mK] [m2K/W]

Internal lime cement plaster 0.01 0.88 0.011

Burnt Brick 0.6 0.84 0.714

External lime cement plaster 0.01 0.88 0.011

- Underground Wall: U.W. 1

The walls of the underground floor are ground-contact walls therefore in order to calculate the effect of

the ground instead of the external air in the calculation, the surface resistance have been changed

according to the EN ISO 13370 [27]. The structure is the same as in the other floor with a different

Page 71: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

47

thickness of the burnt brick layer.

U.W.1 0.75 U W/m2K] 0.94

Component Thickness Conductivity Resistance

[-] [m] [W/mK] [m2K/W]

Burnt Brick 0.75 0.84 0.893

- Internal Wall: I.W. 1

The internal wall modelling does not affect the thermal properties of the building, since they’re not part

of the envelope, but in order to have a clear diversification of the different spaces inside the building

they have been modelled, and their structure is the same as the external wall. The same structure is used

as wall in contact to unheated internal spaces.

I.W. 1 0.62 U W/m2K] 1.00

Component Thickness Conductivity Resistance

[-] [m] [W/mK] [m2K/W]

Internal lime cement plaster 0.01 0.88 0.011

Burnt Brick 0.6 0.84 0.714

Internal lime cement plaster 0.01 0.88 0.011

- Internal Slab: I.S. 1

The internal slab of the building, used to separate one floor from another, is composed of a mixed

structure composed of an embarkment layer used to lay the flooring on top of the load bearing layer

consisting of wood beams.

I.S. 1 0.5 U W/m2K] 0.97

Component Thickness Conductivity Resistance

[-] [m] [W/mK] [m2K/W]

Internal lime cement plaster 0.02 0.88 0.023

Wood layer 0.015 0.15 0.100

Wood beam 180x240 0.24 0.12 2.000

Wood Decking 0.025 0.15 0.167

Embarkment layer 0.15 1 0.150

Wood subfloor 0.026 0.15 0.173

Wood layer 0.024 0.15 0.160

- Roof Slab: R.S. 1

The structure used for the slab that separates the under-roof layer from the last upper heated space is the

same as the one used for the internal slab. In this case study building, as in Lecco seen in the § 2.3.1,

Figure 3-6: Wood beam slab structure

Page 72: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

48

the story created just under roof structure and on top of the last heated floor is an under-roof layer used

for storage purposes.

- Underground Slab: U.S. 1

The underground slab stands for the slab which defines the separation from the ground floor, which is

an heated space, from the underground floor, which is unheated in this case. The structure of this slab is

composed of a brick vault set into a composite layer, as seen before, made of steel beams and concrete.

This structure, as seen from the § 2.3.1, is similar to the one seen in the case study building located in

Lecco, this is really important for the purpose of this work because it’s clear that even though the

constructions are located in two different countries they have some similar technologies, due to the

similar construction history of the specific part of central Europe.

U.S. 1 0.25 U [W/m2K] 1.03

Component Thickness Conductivity Resistance

[-] [m] [W/mK] [m2K/W]

Burnt Brick 0.4 0.88 0.455

Embarkment layer 0.3 1 0.300

Wood subfloor 0.026 0.15 0.173

- Ground Slab: G.S. 1

The structure used for the ground slab is really poor, it consists only of a flooring put onto a screed

concrete use a separation layer from the inner space and the ground. This is done because usually the

underground level of the building in Czech Republic are used as storage systems, therefore are usually

unheated.

R.S. 1 0.5 U [W/m2K] 1.23

Component Thickness Conductivity Resistance

[-] [m] [W/mK] [m2K/W]

Internal lime cement plaster 0.02 0.88 0.023

Wood layer 0.015 0.15 0.100

Wood beam 180x240 0.24 0.12 2.000

Wood Decking 0.025 0.15 0.167

Embarkment layer 0.15 1 0.150

Wood subfloor 0.026 0.15 0.173

Wood layer 0.024 0.15 0.160

Figure 3-8: Slab made of vault in steel beams

Figure 3-7: Wood beam ceiling

Page 73: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

49

- Roof : R. 1

The roof structure it’s composed by a double structure made of crossed wooden beam and a small

wooden structure used to lay the roof tiles. In this case the roof is put on an unheated space, therefore

it’s thermal efficiency is not significantly relevant for the thermal properties of the building due to the

presence of another slab between heated and unheated spaces. Once again here it’s possible to see the

similarities between the construction technologies of the two different countries, § 2.3.1.

- Glazed surface: W. 1

The windows present in the old part of the building are all the same. The typical window is made of a

single glazed window put into a wooden frame. The frame pattern is visible from the picture taken in

the visual survey done in the first steps of the analysis. The shading system present in the old part of the

building is represented by internal curtains manually adjustable. In order to simulate the manual

adjustment of the curtains, in the simulation model it has been a set an value of 300 W/m2 for the incident

radiation to turn on or off the curtains.

Net U-value 4.9 [W/m2K]

Net R-value 0.1757 [m2K/W]

Glazed Surface

Component Thickness Conductivity Resistance Transmittance g-value

[-] [mm] [W/mK] [m2K/W] [W/m2K] [-]

Clear float 6 1.06 0.0038 5.75 0.87

G.S. 1 0.30 U [W/m2K] 3.25

Component Thickness Conductivity Resistance

[-] [m] [W/mK] [m2K/W]

Floor Screed 0.1 1.15 0.087

Stone layer 0.2 1.8 0.11

R. 1 0.26 U [W/m2K] 1.82

Component Thickness Conductivity Resistance

[-] [m] [W/mK] [m2K/W]

Clay tiles 0.02 0.6 0.033

Wood layer 0.06 0.16 0.375

Wood beam 0.18 - -

Frame

Type Transmittance Percentage

[-] [W/m2K] %

Hardwood 2.50 25

Figure 3-9: Stone ground slab

Figure 3-10: Wood beam structure roof

Page 74: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

50

3.3.2 Internal Conditions

In order to model a more accurate behavior of the heated spaces of the building, during both the cold

and the warm period, it has been decided to create a “typical” profile, able to simulate the parameters

related to the indices and the factors that most influence the internal conditions of the heated and

unheated spaces of the case study building. The profile used for this case study is similar to the one

presented for the case study located in Lecco in the § 2.3.2, therefore in this case there will be a faster

presentation of the data.

Occupancy

The first parameter to set was the one related to the occupancy of the spaces, so it has been defined an

occupancy period and rate of the heated spaces. The analysis has been simulated considering the case

of a typical school day , considering the occupancy only for the classrooms. This means that the internal

gains due to the sensible and latent heat coming from the people are considered only for the classrooms

and not for the other heated spaces. The parameters presented were taken from the guidelines imposed

by the Czech Republic government, which means that it was supposed that the students use the

classrooms from Monday to Friday, from 8 to 17 (as seen in the case study in Lecco). This is done in

order to promote an intense occupancy rate according to a more efficient use of the spaces, an example

can be the exploit of the classrooms in the afternoons for some extra-curricular activities. The period of

occupancy is the same as the one imposed by the school regulation, it is applied from the 1st of September

to the 30th of June. The sensible and latent heat represent the heat gains produced from the users activity,

which contribute to the reduction of energy needs during the winter period.

3.3.2.1 Lighting system and machinery

In addition to these gains it has been considered, for every used space of the case study building the

internal gains produced by the lighting system and

the heat coming from the use of typical machinery.

All the parameters used to simulate the gains in

the school environment are given according to the

EN ISO 12464 [28] and the CIBSE guide A [29].

The simulation of the lighting system was applied to each of the spaces of the case study, considered

heated and used. In order to recreate the manual adjustment from the user, depending on the natural light

Occupancy Density Sensible heat Latent heat

Annual Weekdays [pers/m2] [W/pers] [W/pers]

1st September- 30th June 8:00-17:00 0.5 90 60

Table 3.2: Parameters recreating users’ activity

Component Occupancy Heat gains

- weekdays [W/m2]

Lighting System 8:00-17:00 7

Machinery 8:00-17:00 5

Table 3.3: Light system and machinery profile

Page 75: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

51

available linked to the outside conditions, it was created an accurate activation profile applied to the

lighting system. The activation depends on 4 different profile, one for each season, in which the value

of the lighting system goes from 1 to 0 (1 means on and 0 means off), and depends on the hour of the

day. This means that the value expressing the influence of the lighting system to the internal gains of

the heated spaces, is different for each hour of the day and each season of the year.

3.3.2.2 Infiltration and Natural Ventilation

The same level of detail and accuracy was used also to simulate the parameters that have a negative

impact on the energy balance of the case study, such as the infiltration and ventilation losses, which are

related to the interaction of the building with the outside air. The infiltration represents the air that from

the outside goes through the imperfection of the building to the inner spaces, increasing the internal

temperature of the conditioned spaces. The CIBSE guide A [29] gives

empirical values for air infiltration rate due to air infiltration for rooms in

buildings on normally-exposed sites in winter, classifying buildings for store

height and level of air tightness. Considering that the building is made of 3 stories above ground and

considering the building as “leaky” (which represents an existing building that does not comply with

current regulations), due to the age of the building, the standard provides an empirical value for the

blower door test, after that through a conversion value ( obtained when dividing the 50 Pa air change

rate by the calculated average annual infiltration rate) it is obtained the requested value for air infiltration

rate during the winter period.

The values for the ventilation

rates have been taken from the

CIBSE guide A [29], in this case

to each heated spaces is assigned a value of natural ventilation considered the minimum in order to

maintain indoor air quality, so basically it’s the air change rate of the heated spaces. The profile created

for the natural ventilation of the spaces is linked to the occupancy schedules, therefore the natural

ventilation will be considered when the users will need to change the air of the enclosure, which is from

08:00 to 17:00.

3.3.3 Technological Plant

Other than the data relating to the materials used for the envelope’s structure, the school principal has

made himself available to provide information about the technical plants that supply energy to the entire

building. This information were than verified through the visual survey done in the technical rooms of

the building, in which the plants are installed. The school building is equipped with a central system

Infiltration Building

[ach] 0.25

Table 3.4: Infiltration rate

Ventilation Kitchen Toilet Gym Classroom Hall/Corridor

[l/(s*m2)] 0.9 1.2 1.5 0.6 0.3

Table 3.5: Ventilation rate for each heated space inside the building

Page 76: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

52

used for the thermal heating of the specified heated spaces, combined with small separated water boiler

used for the DHW preparation, needed for the school building.

The period of activity of the central heating system is the same as presented by the guidelines of the

government, the DHW preparation instead, is continuous throughout the entire annual school period.

During the day, as seen in the table the heating system is continuously on while the DHW preparation

is strictly linked to the occupancy of the room, as matter of fact the DHW is required directly from the

users while the settings of the heating system are imposed by the institution. This is due to the fact that

most of the heating system present in the school system are old, therefore in most of the cases the

consumption given by the on-off procedure is so

high that keeping the heating system always on

may reduce the consumption, in addition the

type of system present in this buildings are quite

big and complex therefore it may be a problem to find an adequate technician available to do the on-off

procedure when needed.

3.3.3.1 Generation System

The building is heated by three low-pressure hot-water boilers powered by natural gas and has a total

calorific power equal to 150 kW. The system was installed in the 1995 in an adequate technical room

located in the underground story of the building. In this case it was possible to receive all the information

and data related to the machinery used for the heating system of the building. The system can be

classified as a class C boiler and has a forced draft closed with a pressure vessel with an efficiencies

equal to 90%, and the circulation of water is ensured by the use of various pumps located in the technical

room. The heating water temperature is thermally regulated depending on the outside temperature, but

this control is not completely automatic and must be operated by the janitor.

The DHW preparations is left to the small water boiler present at each floor placed in the consumption

Heating DHW

1st October – 30th April 1st September – 30th June

On continuously 8:00 -18:00 weekdays

Table 3.6: Activation profile of the technological plant

Figure 3-11: Boiler system used as heating system Figure 3-12: DHW boiler

Page 77: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

53

space. The system is constituted by electrical boilers with a max capacity of 125l. The warm water

produced is used to wash people, clean rooms and eat food. The DHW heating water temperature is

thermally regulated depending on the outside temperature, but this control is not completely automatic

and must be operated by the janitor. The existing system is tight so there are no significant losses, the

water quality is good and there is no need to modify it.

3.3.3.2 Fuel

The systems used for the heating of the selected spaces are fueled by natural gas, methane to be precise.

The cost of the methane gas in Czech Republic is equal to 0.5 €/m3 (taken from the CNG Europe [35]),

considering an ideal consumption equal to 10.5 kWh/m3 and dividing this value by the efficiency we

have a real consumption of 9.45 kWh/m3, that sets for the consumption of methane gas a cost of 0.053

€/m3.

3.3.3.3 Emissions Gasses

As said in the § 2.3.3.3 of the case study located in Lecco, the emission gasses taking in consideration

are the Greenhouse Gasses “GHG” emissions, caused by the combustion of the methane gas happening

in the chamber of the boilers to generate thermal power used for the heating system and the DHW

preparation, and the use of electricity for the systems present in the building.

The GHG emissions are typically expressed through the means of the equivalent carbon dioxide “CO2e”,

which is a measure for describing how much global warming a given type and amount of greenhouse

gas may cause, using the functionally equivalent amount or concentration of carbon dioxide (CO2) as

the reference. The formula used to calculate the CO2e is:

𝐶𝑂2𝑒 = ∑𝑖(𝐺𝑊𝑃𝑖 ∗ 𝐸𝑖)

- the CO2e is the equivalent CO2 emissions expressed in ton/year;

- GWPi is the Global Warming Potential of each of the GHG considered. The GWP is a relative measure

of how much heat a greenhouse gas traps in the atmosphere, it compares the amount of heat trapped by

a certain mass of the gas in question to the amount of heat trapped by a similar mass of carbon dioxide;

- Ei is the GHG emissions.

The conversion factors used for the combustion of the methane gas is equal to 0.203 kg CO2/kWh, while

the factor for the electricity is equal to 0.519 kg CO2/kWh, these values were extracted from the Carbon

Trust standards.

Page 78: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

54

3.3.3.4 Emission system

The emission system is represented by the use of cast iron

radiators, put in each of the spaces considered heated in the

case study. The cast-iron radiators have an high thermal

inertia, this means that this type of radiators will need more

time to reach the set point temperature , thus increasing the

energy needs and gas emissions due to the fact that the boiler

has to be activated for a longer period, increasing the time in

which the combustion of natural gas produces thermal energy.

3.3.3.5 Control system

The radiators located in the toilet and in the hall of the case study building are equipped with thermostatic

valve with a thermostatic head. With the use of the valves it’s possible to adapt the internal temperature

of the heated spaces depending on the outside temperature, thus reducing the energy waste given by the

over-use of thermal energy used for heating.

3.3.3.6 Distribution system

The data about the distribution system, have been hypothesized

according to the visual survey done in the technical room located in the

underground floor of the old part of the building and the standards

regarding the system efficiency [31] . The distribution system is

considered as a zone heating system with horizontal distribution,

powered by vertical mullions (usually running in the stair case) as

described in the Prospectus 22 of the EN ISO 11300-2 [31]. The

distribution system is considered as a zone heating system with horizontal distribution, powered by

vertical mullions running in the interior side of exterior walls.

The pipes present a medium layer of insulation, done with various materials (cotton muslin, cups) not

fixed stably by a protective layer. This suppositions brought a calculated value of 92% for the efficiency

of the distribution system of the case study building, this sets the value of the overall seasonal heating

efficiency of the system “ScoP” equal to 82.8 %.

3.3.3.7 DHW Production

The procedure used to calculate the required DHW for a school has been taken from the EN ISO 11300-

Figure 3-13: Cast iron radiator

Figure 3-14: Distribution scheme

Page 79: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

55

2 [9] with the simple formula, applied for each class:

𝑉𝑤 = 𝑎 ∗ 𝑁𝑢 = 0.17 [𝑙

ℎ]

- a is the specific daily requirement in liters / (day × Nu) obtainable from Table 31, and for school is

equal to 0.2;

- Nu is a variable parameter depending on the type of building that can be obtained from Table 31, and

for school is equal to the number of students.

The DHW preparation is done by the independent water heater boiler presented in the § 3.3.3.1. The

water heater can be classified as open chamber boiler, also known as a type B appliance, it is a boiler or

water heater designed to be connected to an evacuating duct for the combustion’s products to the outside

of the installation room, the combustion air is taken directly from the installation environment that must

be permanently aerated. A water heater classified as type B and considered without the guidance flame,

a flame which is always on and allows instantaneous production of hot water to start, can be considered

with an efficiency equal to 77 % according to the EN ISO 11300-2 [31].

3.3.4 Energy Classification

In the Czech Republic, the same methodology is used for all regions and all building types. The

recommended calculation procedure is based on published CEN standards and applicable Czech

Technical Standards. The energy performance is expressed by the total annual energy consumption,

including heating, cooling, DHW preparation, mechanical ventilation, lighting and auxiliary energy

needed for standardized building..

The energy labels classifies buildings on an efficiency scale ranging from A (high energy efficiency) to

G (poor efficiency). Class C is a minimum EP requirement level for new buildings and for existing

building going under major renovation.

The aim of the EP certificate is to inform residents and building owners/users, and encourage them to

take energy saving measures, the methodology is described in the EPC implementing regulation [36].

Figure 3-15: Energy classes [kWh/m2y] for different building types

Page 80: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

56

Page 81: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

57

CHAPTER 4

4 Climatic analysis

In order to be able to fully understand the following energy analysis, and in order to creat a climatic

background it has been decided to analyze the climatic factors of both of the location of the case studies,

and to compare them in order to understand what are the similarities and the difference and how they

could affect the energy analysis.

All the data presented, and thus used to create a climatic background for the thesis work, were taken

from the national agency database. For the Italian data the source used is the ARPA database [37], while

for the Czech ones it has been used the database of Agency for the Protection of Nature and Landscape

Conservation of the Czech Republic [38].

Since the climatic data of Bustehrad were not available, the study has been diverted onto the climatic

conditions of Prague, which will be assumed as the same as Bustehrad.

4.1 Geographical framework

As already explained, the proposed study will involve two cities

located in the Central Europe area, as they are Italy and Czech

Republic. More precisely the city that will be analyzed will be

Lecco and Bustehrad .

Lecco is a city of northern Italy, 50 km north of Milan, the capital

of the province of Lecco. It lies at the end of the south-eastern

branch of Lake Como. The Bergamo Alps rise to the north and

east, cut through by the Valsassina of which Lecco marks the

southern end. The lake narrows to form the river Adda, which

crosses the entire city.

Buštěhrad is a small town in Central Bohemian Region of the

Czech Republic, located 20 km northwest of Prague.

In order to have an idea of the framework of the analysis it has

been decided to present the average temperature of the main city included in the Central Europe Area.

In this case it will be possible to see the reliability of the assumptions made in the introduction and the

possible deviation of the results depending on the city. The Figure 4-2, represents the yearly average

temperature of the main cities of the Central Europe Area, through which it is possible to see the

differences between them. The data used for the analysis were collected from the EPA Network [39].

Figure 4-1: Central Europe framework

Page 82: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

58

The graph states that the assumption made were reliable, thus the temperature of the regions included in

the CE are close to each other, so the weather will have a similar impact on the energy dispersions of

the buildings located in this area.

4.2 Outdoor dry-bulb temperature

The climatic analysis starts with the study of the outside temperature of the two case study taken in

consideration: Lecco and Buštěhrad. The study will include the comparison of the results.

-3

-1

1

3

5

7

9

11

13

15

17

19

21

January March May July September November

[°C] Milan Praha Berlin Wien Budapest Zagreb Warsaw Bratislava Lubiana

-15

-10

-5

0

5

10

15

20

25

30

35[°C] Lecco Prague

January February March April May June July August September October November December

December Figure 4-2: Central Europe main cities’ yearly average temperature

January February March April May June July August September October November December

December Figure 4-3: Hourly outdoor dry-bulb temperature of the two case studies

Page 83: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

59

The outdoor temperature recorded in Lecco is higher respect to the one of Buštěhrad almost

homogenously throughout the year. This was highly predictable since Bustehrad is located in Czech

Republic, therefore is situated in a northern location respect to Lecco, which is part of Italy so is still, in

a small scale, affected by the Mediterranean climate.

In order to have a more clear view of the climate of the two case studies, it has been decide to create a

temperature profile for each of the cities, in order to analyze minimum, maximum and average yearly

temperature.

Analyzing the temperature profile is clear that the two locations have similar behavior. The curves

defining the average temperature show that the differences between the hotter climate of Lecco and the

colder climate of Buštěhrad is pretty homogeneous throughout the years, and it seems to be

approximately equal to ¾ °C. The maximum temperatures recorded as similar, even though they are

reached in different periods of the years, on the other hand the minimum are a bit different, since the

lowest Czech temperature recorder is equal to -5 °C while the Italian one is -1 °C.

The major difference is the presence of colder peaks during the winter in Buštěhrad, while in Lecco the

winter’s temperature is more homogeneous as it stays near to 0/1 °C.

4.3 External relative humidity

The second criteria to define the external climatic conditions is the external relative humidity perceived

in the location.

The graph presented in the Figure 4-5, shows once more the compatibility of the results obtained for the

two case studies. Although the value of external relative humidity fluctuates throughout the year, the

two different case studies present a similar behavior.

-6

-2

2

6

10

14

18

22

26

30

34[°C] Lecco Prague Minimum Maximum Average

January February March April May June July August September October November December

December Figure 4-4: Monthly temperature profile of the two case studies

Page 84: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

60

The climate of Lecco is characterized by low relative humidity during the winter, this could be due to

the presence of the lake, which crosses the city, which lowers the humidity in the cold seasons. On the

other hand the mid-seasons in Prague seem to be the ones with the highest percentage of relative

humidity, this data is crucial for the thermal comfort analysis presented later on in the work.

4.4 Horizontal radiation

The next step is the analysis of the global radiation, which stands for the intensity (irradiance) of

solar radiation falling on the horizontal plane.

30

40

50

60

70

80

90

100% Lecco Prague

0

50

100

150

200

250

300

350[W/m2] Lecco Prague

January February March April May June July August September October November December

December Figure 4-5: Daily average external relative humidity of the two case study location

January February March April May June July August September October November December

December

Page 85: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

61

Once more the results are similar for the two case studies. It has to be highlighted that the max. radiation

recorded is equal to 350 W/m2 which is not a bad results, creating a starting idea of exploiting the

available radiation.

4.5 Wind exposure

The analysis deals with the intensity and the direction of the recorded data of the wind of the two

locations, in order to understand the impact on the external climate.

In order to have a clear idea of the effect of the wind on the environment it has been decided to present

the Beaufort scale used to classify the effect of the wind speed [40]. The scale relates the effects of the

wind with the ones of the sea, and then classifies the resulting consequences.

Level Speed

Wind Consequence

[m/s] Environment Sea

0 0-0.2 Calm Smoke ascends vertically State zero

1 0.3-1.5 Wind blows The wind drifts the smoke State one

2 1.6-3.3 Light breeze The leaves move State two

3 3.4-5.4 Breeze Leaves and branches constantly shaken State two

4 5.5-7.9 Intense breeze The wind raises dust and dry leaves State three

5 8-10.7 Tense breeze Shrubs with leaves are swirling State four

6 10.8-13.8 Fresh wind Big branches are shaken State five

7 13.9-17.1 Strong wind Whole trees shaken, difficulty walking State six

8 17.2-20.7 Moderate storm Broken branches, impossible walking Sate seven

Table 4.1: Beaufrot scale of wind intensity

The graph presented in the Figure 4-7 shows the average per year of the record values of wind speed

for the two cities taken in exam.

3.33.84.34.85.35.86.36.87.37.88.38.89.39.8

10.310.8

[m/s] Wind Level 3 Wind Level 4 Wind Level 5 Lecco Prague

Figure 4-6: Hourly global radiation of the two case study location

Figure 4-7: Yearly average wind speed values of the two case study location

January February March April May June July August September October November December

December

Page 86: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

62

Most of the time of the year records a value of wind speed which is classified as Wind level 3 and 4,

therefore no evident impact is made by the wind onto the climatic external conditions of the two case

studies.

4.6 Rainfall precipitation analysis

The effect of rainfall in some cases can be major, therefore in order not to have any possible

complications it has been decided to go on with the rainfall analysis.

It has been decided to represents the distribution of the amount of rainfall precipitations fallen during

an entire year, month by month. The results show higher quantity of precipitation recorded for Buštěhrad

respect to Lecco, even though the quantity seen don’t represent a problem in this case.

0

2

4

6

8

10

12

14

16

18n° days <2mm 2-5mm 5-10mm 10-20mm 20-50mm Prague

<2mm 2-5mm 5-10mm 10-20mm 20-50mm Milan

Figure 4-8: Yearly amount of rainfall precipitation of the two case study location

Page 87: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

63

4.7 Snow precipitation

The effect of the amount of snow fallen during a year in some cases can be major, therefore in order not

to have any possible complications it has been decided to go on with the rainfall analysis.

In order to do this it has been decided to analyze the amount of snow fallen recorded from the 2012 to

the 2016, thanks to the database mentioned earlier.

The graph presents either the number of days in which it has been recorded snow precipiation and the

amount of snow fallen. Basically it shows that there is a higher number of days of snow in Prague respect

to Lecco, due to the higher latitude and the numerous mountains present.

4.8 Seismic activity

The last step consists on evaluating the seismic activities recorded in the two areas, in order to have a

complete view on the geographical framework of the case studies.

4.8.1 Lecco

The seismic classification of the national territory has introduced specific technical regulations for the

construction of buildings, bridges and other works in geographic areas characterized by the same seismic

risk. Here there is the seismic zone for the territory of Lecco [41].The criteria for updating the Seismic

Hazard Map [42] has divided the whole national territory into four seismic zones based on the value of

the horizontal maximum acceleration (ag) on rigid or flat ground, which has a probability of 10% being

2012

2013

2014

2015

2016

2017

2012

2013

2014

2015

2016

2017

0

5

10

15

20

25

30

0 5 10 15 20 25 30 35 40 45 50 55 60 65

n° days

[mm]

Prague Lecco

Figure 4-9: Amount of snow precipitation for the year 2012-2016 of the two case study location

Page 88: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

64

exceeded in 50 years. Peak ground acceleration (PGA) is equal to the maximum ground acceleration

that occurred during earthquake shaking at a location.

PGA is equal to the amplitude of the largest

absolute acceleration recorded on an

accelerogram at a site during a particular

earthquake. Unlike the Richter and moment

magnitude scales, it is not a measure of the

total energy (magnitude, or size) of an

earthquake, but rather of how hard the earth

shakes at a given geographic point. The peak

horizontal acceleration (ag max) is the most

commonly used type of ground acceleration

in engineering applications. It is often used

within earthquake engineering (including

seismic building codes) and it is commonly plotted on seismic hazard maps. In an earthquake, damage

to buildings and infrastructure is related more closely to ground motion, of which PGA is a measure,

rather than the magnitude of the earthquake itself. For moderate earthquakes, PGA is a reasonably good

determinant of damage; in severe earthquakes, damage is more often correlated with peak ground

velocity.

Seismic Zone

Description Horizontal Maximum

Acceleration (ag)

1 Indicates the most dangerous area where severe earthquakes can occur. Ag > 0.25 g

2 Area where severe earthquakes can occur. 0.15 < ag ≤ 0.25 g

3 Area that may be subject to severe earthquakes but rare. 0.05 < ag ≤ 0.15 g

4 It is the least dangerous area, where earthquakes are rare and it is up to

the Regions to prescribe the obligation of anti-seismic design. Ag ≤ 0.015 g

4.8.2 Buštěhrad

A seismic zonation map was included in the building code standards (ČSN 73 0036). Recently a new

map was completed on the basis of earthquake catalogues for Central European countries delimiting

seism genic areas and maximum possible earthquake intensities, as well as information on suppression

of macro seismic intensities. In this map, values of seismic loading are expressed in terms of the macro

seismic intensities (MSK scale) with 10% probability of exceedance in 50 years. Related values

employed for seismic zone delineation for the National Application Document of EUROCODE 8 (CR-

CSN P ENV 1998-1- 1) are expressed in terms of the effective peak acceleration as shown below.

Table 4.2: Lombardy seismic hazard map

Page 89: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

65

The seismic map of the Czech Republic shows that the zone in which Prague, and its surroundings, are

located is a Seismic Zone 1, with a peak ground acceleration equal to 0.015g, this means that these zones

are not considered seismically active. The classification made is also based on the seismic history of the

related zone, therefore in the area of Prague, among the last decades no earthquakes with high intensity

have been spotted.

Page 90: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

66

Page 91: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

67

CHAPTER 5

5 Energy Diagnosis: Case study “Lecco”

The chapter will be focused on the presentation of the energy analysis done on the selected building,

following the boundary conditions and the input listed before, chapter 2. The results will be presented

through the means of tables and graphs, in order to represent the significant data chosen to describe the

energy scenario of the building, in the most efficient and self-explanatory way. There will be a major

distinction between the output data coming from the energy simulation describing the energy

consumption of the building, and the one describing the internal condition of the building environment.

The outputs coming from the energy simulation have been divide so that the results can be presented as

“Energy Performance” and “Internal Comfort Condition” of the analyzed building case.

5.1 Energy Performance of the Building

The energy performance of the building represents the output data related to the energy contribution of

the building. This means that are here represented all the data that useful to outline the energy and

environmental framing of the building, analyzed in such detail to easily highlight the major problems.

This has been done, taking in consideration the fact that the work of an energy retrofit starts from the

energy performance of the state of the art and from the critical analysis of the results obtained through

the energy simulation.

5.1.1 Energy Consumption

The energy consumption of the building, calculated through the use of the dynamic energy simulation

software, is here represented as “PE” which stands for Primary Energy, calculated through the

conversion factors presented in the input chapter, , in the § 2.3.3.

Primary Energy Consumptions: 315.27 MWh

Primary Energy Consumptions per area: 307.87 kWh/m2

Energy Classification: Class F

The figure represented below shows how the consumptions of the building is divided into the sub-

elements taken in consideration in the energy modelling design. The consumption due to the heating

system is equal to almost 80% of the total PE, this highlights the importance and the relevance of

decreasing the heating consumption of the school building through the step-by-step approach presented

in this energy retrofit work.

Page 92: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

68

The results given by the simulation are in line with the typical consumption of a school building, as seen

in the previous chapter. The PE consumptions related to the DHW are relatively low, as seen in the

previous chapter, the hot water consumptions in a school building are typically low due to the non-

constant demand related to the hours in which the school is occupied, indeed the presence of a school

gym and of a school canteen raises the concerns toward the decrease of this specific consumption. As

already highlighted before, this results represent the base guidelines to understand towards which

direction the retrofit has to go in order to maximize the requalification and minimize the waste of money

and time. For this reason in the further analysis the DHW, the Equipment and the Light consumptions

will be considered negligible as the attention will be focused on the reduction of the PE consumptions

of the heating system.

5.1.2 Economic and Environmental Impact

In order to define the environmental impact of the emission produced by the school building , we will

consider the amount of Carbon Dioxide equivalent (CO2e) emissions, considering the hypothesis and

the standard values expressed in the previous chapter about the input boundary conditions. With the

introduction of the CO2e it’s possible to describe with one unit of measure the global impact of the

building, considering the Green House Gas (GHG) emissions of it, linked to the use of electricity and

thermal energy presented in the previous paragraph. Concerning the economic impact, it has been

considered the amount of euros spent every year in order to fulfill the building’s energy needs, both

thermal and electric.

GHG emissions: 50.89 ton CO2e/y

Energy bill: 24592.6 €/y

The graph presented below was made in order to give a complete overview of the impact caused by the

energy-inefficient school building, taken in consideration.

020406080

100120140160180200220240260280300320[kWh/m2y]

76%

15%

4%5%

Heating

DHW

Equipment

Light

Figure 5-1: Primary Energy consumption

Page 93: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

69

The school building taken in consideration can work as an example, in order to give an idea on what

happens with an old and neglected building. Choosing the year of interest, through the trendline, it’s

easy to locate the wanted output values of GHG emissions [ton CO2e] and the thousands of euros [k€]

needed to run the energy systems of the school building. The impact of the building was calculated

taking in consideration the energy bill and the GHG emissions caused by the combustion of methane,

due to the boilers serving the heating and DHW demand, and the use of electricity, due to the boilers’

electric consumptions and the ones related to the equipment and lighting demand ( as represented in the

previous paragraph).

Figure 5-2: Trendline of the economic-environmental impact of the school building per year

In order to have a more global view on the GHG emissions and on the energy bill of buildings, the Case

Study building has been compared with a Class A1 building, which actually represents the reference

case seen in the previous chapter, and a Class A4

building, which is the highest energy class

possible. The emissions and the bill related to the

fictitious building in energy class A1 and A4,

have been calculated considering the maximum

value of energy consumption for each energy

class calculated in the previous chapter

according to the national energy classification.

The graph here represented highlights the

differences presented between the case study and

energy-efficient building, in terms of euros and CO2e. This graph highlights the importance of

retrofitting the case study since we could experience some major decrease in the energy bills which

means less money spent for the operational of the building, and considering the fact that our case study

is a school, less money spent for the building will mean less money wasted for every citizen.

0 300 600 900 1200 1500 1800 2100 2400 2700

04008001200160020002400280032003600400044004800520056006000

0

10

20

30

40

50

60

70

80

90

100

110[ton CO2e][yrs]

[k€]

Trendline per year

Guide Lines

Intersection Point

68.88%88.62%

45.42%

80.05%

05

101520253035404550556065

Case Study Class A1 Class A4

Energy Bill [k€]

GHG emissions [Ton CO2e]

% - Reduction from Case Study

Figure 5-3: Economic and Environmental Impact -%- of

different energy-class building.

Page 94: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

70

5.1.3 Heating Consumption

As said in the previous paragraph the major cause of energy consumption in the case study building is

represented by the combustion of natural gas into thermal energy provided to the boiler of the heating

system.

The graph expresses the primary energy

consumed each year in order to produce

enough thermal energy so that the heating

system can balance the building’s losses

and keep the temperature of the heated

spaces at the set point, no matter the

boundary conditions. Going further in

detail, through a critical analysis of the

results coming from this graph, it’s

obvious that the high energy

consumptions are due to excessive dispersions in means of Transmission imposed by a leaky and

inefficient envelope. This means that the attention will be focused primarily on the envelope of the

school building, both opaque and transparent component, so that the consumption can be reduced and

the retrofit can go on, thank to continuous analysis. The graph basically says that the energy retrofit of

the case study has to begin with the optimization of the envelope. Given the fact that the building is

located in the North of Italy and that for this case the months of July and August (in which usually

schools are closed) have not been taken into account, the value of the Solar gains seem reasonable. Also

the values presented in the graph related to the Ventilation losses and the Internal gains are in agreement

with the input data of the model, and with the fact that being the case study a school it’s normal to have

similar values for internal gains and natural ventilation, since the high activity of the students in the

classrooms is balanced by the continuous opening of the windows.

53.68

21.1573.57

232.73233.61

0

40

80

120

160

200

240

280

320

Contributions Dispersions

[KWh/(m2y)]

Energy Use

Transmission

Ventilation

Solar

Internal

Figure 5-4: Annual PE consumption for Heating Demand

05

1015202530354045505560

January February March April May June September October November December

Internal Gains

Solar Gains

Ventilation Losses

Transmission Losses

Energy Use

Figure 5-5: Monthly PE consumption for Heating Demand [kWh/(m2y)]

Page 95: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

71

To understand the behavior of the variables that contribute to the calculation of the consumption of

primary energy related to the heating demand, it has been presented a graph representing the monthly

condition values of the specified variables. First thing it is possible to double check that every input in

the model was insert in the right way since the results presented are in line with the hypothesis expressed

in the previous chapter. As matter of fact the value of energy use is zero for the months on May to

September and is almost the half of the average month for April and October in which the hating system

is active only for 15 days, and not the whole month as for the others. Of course the highest consumption

is experienced in the coldest month which is January, this is due to the really high transmission losses

(the temperature in January goes below 0°C) and the low solar gains, imposed by the low number of

hours of sun exposure. This is due to the angle of the sun during the winter, which also influences the

shading that the other buildings provide onto the case study, reducing the solar radiation coming into

the building through the glazing area.

5.1.4 Heat Gains

The heat gains of the case study building are a consequence of the input data, presented in the previous

chapter. In order to understand the behavior of the building in terms of positive impacts to the energy

balance, the heat gains calculated through the energy simulation of the study case have been studied and

broken down into the principal sources of gains.

The graph presented highlights the statement made before, the gains coming from the solar radiation

passing through the glazing part of the building, is similar to the ones coming from the internal sensible

and latent heat generated by the Equipment, Light and People present in the heated space. The values

related to the solar gains are relatively high for the climate of the city in which the building is located,

this is due to the high area of glazing part of the building, the fact that the glazing are located in all the

surfaces orientation and the high value of total solar factor “gtot” of the old windows present in the

building, an high gtot means that more solar radiation is transmitted to the inner spaces while less

21.15; 28%

41.83; 56%

4.65; 6%

7.20; 10%

53.68; 72%

Solar

Internal

People

Equipment

Light

Figure 5-6: Heat Gains in terms of kWh/(m2y) and %.

Page 96: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

72

percentage in reflected and blocked.

The value expressing the sensible and latent heat produced by the people inside the heated space

accounts for almost half of the heat gains of the building, this is in line with the hypothesis presented in

the input chapter, the high activity of students and the elevated number of people inside the space are

the major contributors.

5.1.5 Heat Losses

The analysis goes further in detail, focusing the attention on the variables that contribute to the

dispersion of heat from the case study building. For the analysis presented before, the variables in

discussion, are the Ventilation and the Transmission Losses, which in the energy analysis of the building

are balanced by the sum of Internal Gains, the Solar Gains and the Energy received from the heating

system.

The graph, as the caption says, represents the values in terms of % of the contribution of each element

of both part the of the building, the old and the recent one, to the global Heat Losses of the case study,

this means that looking at the graph it’s possible to understand the negative impact of each element,

taken in account in the energy balance of the case study building. For this analysis the two building’s

part have been considered separated, this is due to the fact that the they have different structures of

envelope’s elements, both opaque and transparent (as seen in the descriptive chapter). For this reason

they present also different output related to the infiltration losses, due to the different air leakages of the

W.O; 19.9

W.U; 0.2W.G; 0.5

F.U; 4.5

F.G; 0.6

F.R; 6.2R; 6.8

W; 9.9

T; 0.4

V; 10.2

I; 5.3 OLD PART

W.O-Walls vs Outside W.U-Walls vs Unheated W.G-Walls vs Ground F.U-Floor vs Unheated

F.G-Floor vs Ground F.R-Floor vs Roof R-Roof W-Windows

T-Thermal bridge V-Ventilation I-Infiltration

W.O; 7.0

W.U; 1.1

W.G; 0.9

F.U; 0.6F.G; 0.6

R; 6.5W; 10.2

T; 0.1

V; 5.6

I; 2.9RECENT PART

Figure 5-7: Contribution in terms of % of the elements of the old part (left) and the recent part (right) of the

building to the global Heat Losses of the case study.

Page 97: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

73

two parts, linked to the age and structure of the building elements and different input data concerning

the infiltration and the ventilation of the building’s spaces.

The results highlights the similar behavior of the two distinct parts of the building, since in both graphs

the biggest contribution are represented by the elements in contact with the outside, and the losses due

to the infiltration rate. The external walls, “W.O.- Walls vs Outside”, are the elements which have a

bigger negative impact on the building’s performance, followed by the glazing part of the building, “W-

Windows”, as a matter of fact if we sum the % contribution of these two variable of the building we

have that more than 30% of the heat losses of the building comes from the outer envelope of the old

part, and almost 20% comes from the one of the recent part, combined they sum up to 50% of the global

heat losses of the case study. Taking in consideration this facts and data, the first idea that comes to

mind is that the requalification of the external wall and the glazing part of the entire building will be one

of the most challenging part of the energy retrofit, and on the other hand it will be one of the most

significant energy-reduction work.

The high infiltration losses are due to the infiltration rate, presented in the input chapter, linked to the

air leakage of the energy-inefficient envelope of both parts of the building, in this case the absence of

the thermal insulation and the presence of and old bearing structure both in stones and bricks, for each

part of the building, plays the biggest part in conjunction with the presence of old low-transmittance

windows through the entire case study building. Another aspects that contributes to the high value of

infiltration losses, is the fact that instead of natural ventilation, this is not controllable but it’s actually a

phenomenon to which the building is subjected to, therefore it is always present, no matter the occupancy

of the space, and it always affects the heating demand, while the natural ventilation is controlled by the

users present in the heated spaces, which will open the windows, letting natural ventilation, according

the internal and external conditions of the specific space. The infiltration losses and the losses by the

outer envelope are strictly connected, this is because the infiltration is based on the difference of pressure

between the inside and the outside of the heated space, and the pressure inside of the space is linked to

the permeability of the outer skin of the building and the ability of it to keep the designated pressure.

The definition of air permeability is “Infiltration air flowrate per unit surface area of the envelope, at the

reference pressure difference” therefore it’s easy to understand that it depends on the air tightness of the

building, determined by the envelope’s thermal performances. This basically means that with the

improvement of the envelope we will have a double benefit, since there will be an obvious reduction of

heat losses attributed to the envelope’s element and also a reduction coming from the infiltration losses,

due to the increase of air permeability through the addition of thermal insulation to the outer skin of the

case study building.

Page 98: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

74

5.1.6 Solar Energy Analysis

The solar analysis helps understand the interaction of the building, in this case the building’s envelope,

and the solar radiation coming from the sun, basically this analysis will show the pro and the cons of

letting inside the inner spaces the sun’s radiation. For the purpose of this analysis the solar radiation has

two opposite effect on the building’s performances, a positive one related to the heating solar gains and

a negative one related to the overheating of the spaces.

For the calculation of the heating energy demand the contribution coming from the solar radiation is

accounted as solar gains, therefore in this case the impact of the radiation coming through the envelope

and into the heated space is positive, a way to reduce the energy demand is actually to increase the solar

gains throughout the heating period. On the other hand, the solar radiation coming through the envelope

in the cooling period will increase the internal temperature of the heated spaces giving rise to a possible

phenomenon of overheating, in which the spaces’ temperature may tend to unbearable internal

conditions for the users.

This analysis will provide a global view on the construction design philosophy used, at the time, that

took part in the decision of the building’s orientation.

In this case considering that in the school building there are 4 different glazing’s orientation, it has been

represented the average solar radiation incident on the wall according to the different orientation. The

results presented in the graph are interesting, the first peculiarity is the behavior of the South-West

oriented wall, which actually shows higher values of solar radiation in winter rather than in the mid and

hot season, this is due to the obstacles present around the case study building, as a matter of fact the

South-West part of the building is the only one which is not shaded by a tall building, therefore there

0

50

100

150

200

250

300

350

South-West North-West

North-East South-East

January February March April May June September October November December

December Figure 5-8: Daily average incident solar radiation [Wh/m2] calculated on the 4 different orientation.

Heating Season Cooling Season Heating Season

Page 99: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

75

will be a bigger amount of solar radiation hitting the surface.

In order to fully understand whether the solar radiation are a benefit or a malus for the case study, it has

been highlighted the two different period, the heating period in which more the radiation the better and

the cooling period in which high solar radiation usually means discomfort. Considering the cooling

season the orientation with the highest values of solar radiation are the South-West and South-East,

which means that the space which will have walls oriented like this will have chance to encounter

overheating, on the other hand this two orientation have the highest values also for the heating period,

as seen before.

The screenshots of the solar analysis run through the dynamic simulation software, attached above, helps

understand the results and commented presented earlier about the output coming from the analysis

related to the incident solar radiation hitting the different vertical component of the case study building.

The comments related to the incident solar radiation graph, are confirmed by these screenshots in which

is possible to see the annual solar radiation [kWh/m2] hitting the envelope of the building. The elements

oriented towards the South West direction (first on the left) are the ones with the biggest values, while

the ones oriented towards North East present the lowest values.

In this case is also visible the shading action of the surrounding buildings towards the case study

building, and the effect that they have on the incident solar radiation. The four different screen shots

refer to the 21 of March, day of the Spring Equinox, at midday.

Figure 5-9: Solar analysis radiation on SW, NW, NE, SE oriented wall (from left to right)

Page 100: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

76

5.2 Internal Comfort

The factors that determine the quality of the internal space related to the improvement of students’

apprenticeship are related to measurable values. The parameters that define the internal comfort

conditions, related to the design criterion of naturalness, are also identified in the current legislation,

however, specific values derived from the researches conducted to determine the optimal conditions for

improving the learning performance show how some non-normative values are optimal for the well-

being, comfort, and cognitive response of school building tendencies. The following is a summary table

summarizing the standard values, the values included in national legislation (D.M. 18/12/1975), and the

recommended values for the classroom, associated with performance enhancements of learning

compared to sector studies. Usually in the existing school facilities, the cooling system is not present

and the indoor air temperature in the hot and mild seasons is not controlled. The standard value of the

temperature therefore refers to the heating period. The following table highlights the detailed parameters

that will be examined later in the discussion.

PARAMETERS UNIT STANDARD

TEST

VALUES

EFFECTS ON

LEARNING REF.

AIR

Temperature °C 20±2 20-25 +2-4% for every -1°C

ISO

77

30

Ventilation l/sp 3 8 +75 from 5 to 15*

CO2 emission ppm - < 1000 +1-2.5%**

LIG

HT

Illuminance lux 300 Better quality UN

I 10

840

EN

ISO

12

464

-1

Daylighting (FDL) % 3 Shadings control

Useful daylight

Illuminance (UDI) lux <2000 [300-2000]

SO

UN

D

Partitions’ Resistance db 40 Noise from the inside D.M

. 13

/09

/19

97

UN

I 11

367

Windows’ Resistance db 25 Noise from the outside

Walls’ Resistance db 35

Reverberation Time

(TR) s 1.2

Check the noise

frequency of the room

Table 5.1: Natural philosophy’s parameters to maintain comfort conditions and improve learning performances.

Also note that:

* the minimum ventilation value is equal to 3 l/sp and 8 l/sp is a standard value; in the national standard

the value varies from 2.5 to 5 vol/h according to the level of instruction of the school; highlighting the

improve of the learning performance, the scientific literature sets value from 5 to 15 l/sp;

** a values lower than 1000 ppm is associated to an healthier environment and it has been observed a

reduction of 1 to 2.5% of absences due to illness;

The most influent parameter on the learning performances is the light ( from 19 to 48% more than the

Page 101: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

77

others), this means that the quality and quantity of the natural light that the classroom receives is

significant for the abilities of the students. Therefore, the orientation of the glazing, the ratio glazing/area

of the floor and big openings not oriented towards direct sunlight are the drivers to an inefficient

configuration of the classroom. The different configurations for the various methods of learning that are

carried out in a classroom require different positions of the students in respect to the windows or walls.

The realization of a large glazing, which is a result of the standard limitation for which the ratio between

the surface of the windows and the ones of the floor as to be equal to 1/5-1/7, creates a link between the

inner space and the nature, this is an important principle for the natural philosophy design. In this case

though, the light as an even bigger variable impact related to the position of the users.

In order to evaluate in detail the internal conditions of the classroom, dynamic simulations have been

done on the case study building.

This paragraph of the chapter will be focused on the heated spaces classified as classrooms, therefore to

make the presentation of the results clearer and easier, the classroom have been codified, as seen in the

picture below.

The diversification of the classrooms has been done taking in consideration the different floors and the

different orientation of the glazing present in each classroom. The classrooms of the recent part of the

building are located only on one floor, the first one, while the classes of the old part are located on each

floor from the ground to the third, but the morphology of the classes doesn’t change from one floor to

another, therefore it was useless to show each floor’s plan in this case, but it has been used only the

typical floor. The table helps understand the morphology and the main characteristics of the classrooms,

also in this case the floor have not been considered, but the diversification was made only on the different

opening’s orientation.

Code Openings Floor Ratio

Class [m2] orientation [m2] %

C.X.1 11.66 SE-SW 51 22.86

C.X.2 4.9 SE 35 14.00

C.X.3 10.76 NW-SW 43.68 24.63

C.X.4 6.31 NE 31.27 20.18

C.X.5 6.31 NE 31.27 20.18

C.X.6 9.31 NE 47.17 19.74

C.X.7 12.96 SW 33.92 38.21

C.X.8 6 NW 27.06 22.17

C - Classroom

X - Floor

Figure 5-10: Diversification of the classrooms by window’s orientation

Page 102: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

78

5.2.1 Thermal Comfort

Thermal comfort is the condition of mind that expresses satisfaction with the thermal environment and

is assessed by subjective evaluation (ANSI/ASHRAE Standard 55) [43]. Maintaining this standard of

thermal comfort for occupants of buildings or other enclosures is one of the important goals of HVAC

(heating, ventilation, and air conditioning) design engineers. Thermal neutrality is maintained when the

heat generated by human metabolism is allowed to dissipate, thus maintaining thermal equilibrium with

the surroundings. The main factors that influence thermal comfort are those that determine heat gain and

loss, namely metabolic rate, clothing insulation, air temperature, mean radiant temperature, air speed

and relative humidity. Psychological parameters, such as individual expectations, also affect thermal

comfort. The Predicted Mean Vote (PMV) model stands among the most recognized thermal comfort

models. It was developed using principles of heat balance and experimental data collected in a controlled

climate chamber under steady state conditions. The adaptive model, on the other hand, was developed

based on hundreds of field studies with the idea that occupants dynamically interact with their

environment. Occupants control their thermal environment by means of clothing, operable windows,

fans, personal heaters, and sun shades. The PMV model can be applied to air-conditioned buildings,

while the adaptive model can be generally applied only to buildings where no mechanical systems have

been installed. There is no consensus about which comfort model should be applied for buildings that

are partially air-conditioned spatially or temporally. Thermal comfort calculations according to

ANSI/ASHRAE Standard 55 [43] can be freely performed with the CBE Thermal Comfort Tool for

ASHRAE 55. Similar to ASHRAE Standard 55 there are other comfort standards like EN 15251 [44]

and the ISO 7730 standard [45].

With regard to thermal comfort, the final figure to be assessed is the degree of well-being perceived by

occupants in the space considered. The useful tool for this purpose is constructed by theoretical

principles and measurement methods for predicting the perceived thermal sensation of people. The

78 eometr-hygrometric environment is described through appropriate physical quantities with

standardized methodologies [46]. The size considered for the comfort temperature is the operating

temperature:

𝑇𝑂𝑃 = ℎ𝑟 ∗ 𝑇𝑚𝑟 + ℎ𝑐 ∗ 𝑇𝑎

ℎ𝑐𝑟

Where:

hr is the radiative exchange coefficient;

Tmr is the mean radiant temperature;

Ta is the air temperature;

hc is the convective exchange coefficient;

Page 103: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

79

hcr is the adduction coefficient.

According to the EN ISO ISO 7730 [45] and the ASHRAE 55 [43] show as comfort condition:

Top = 20-24°C, UR= 30-70 % in the heating period;

Top = 23-26°C, UR= 30-70 % in the cooling period.

The hours of discomfort are the ones in which the temperature of the heated space, during the cooling

period, is higher than the comfort limit set at 26 °C, as presented before.

Compared to the studies related to the definition of the parameters for improving the I performance, the

set-point temperature in the winter period should be maintained within a range of 20 to 22 ° C. However,

in mid and summer seasons, indoor air temperature can’t be controlled but experimental evidence in the

field of temperature-related learning has shown that a temperature of 22-24 °C improves performance,

even though temperatures ranging from 25 to 32 °C are permitted in the British guidelines and at the

national level no recommended values are stated.

In order to understand the internal thermal conditions of the heated space classified as classrooms inside

the case study building, it has been calculated -in percentage %- the discomfort hours through the energy

simulation software used presented before.

The graph shows, as seen in the caption, the total percentage of discomfort hours during the cooling

season, which means that it has been calculated the ratio in percentage between the total hours of a

normal school day – 8 a.m. to 18:00 p.m. – and the hours, in this range, in which the temperature is

higher than the defined cooling comfort temperature, set at 26 °C. In this calculation it has been

considered only the school days – Monday to Friday – in which the heating system is off, not taking in

consideration the summer period in which the school is not used – from 16th April to 30th June and from

1st to 30th September – in order to have more accurate and realistic outputs.

The classrooms have been divided by exposition, from the small plan previously presented in Figure

5-10 it’s easy to understand the differentiation of the classrooms, by floor (first number of the code for

0

2

4

6

8

10

12

14

16

18

20

22

24

C.0.1 C.1.1 C.2.1 C.0.2 C.1.2 C.2.2 C.1.3 C.2.3 C.2.8 C.1.4 C.1.5 C.1.6 C.1.7

SE-SW SE NW-SW NW NE SW

Figure 5-11: Discomfort hours % of the classrooms, dived by glazing’s orientation, during the cooling

season.

Old Part Recent Part

Page 104: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

80

the classrooms – C.X) and by glazing’s orientation (second number – C.X.X.). The differentiation by

orientation has been done in order to see the effect of the sun exposure on the classroom, in the cooling

period the building is free floating (no conditioning system is on) and the temperature of the inner spaces

depends mainly on the sun radiation hitting and passing through the glazing part of the envelope, the

amount of radiation depends on the incident angle on the surfaces, linked to the height and the orientation

of the specific surface.

The Figure 5-11 gives a global view on the thermal condition on the different classrooms, in more than

half of them the internal temperature is over the set point for a period equal or greater than 10% of the

time that a student is present in the space, this means that the school is subjected to overheating during

the cooling season, this will be an important input for the energy retrofit design philosophy. It’s obvious

that the thermal comfort performances of the part of the school built in the ’60, the recent part, has better

results than the old one, due to a more global study done at the time of construction on the optimal

orientation of the classrooms, and due to the different structure of the vertical element of the envelope

of the two different part, as a matter of fact the transmittance of the envelope of the recent part is lower

than the one of the old part, therefore in the hot season there will be less heat transfer between the

building and the surroundings , stopping the heat from coming into the inner spaces.

It’s interesting to compare the results output from the Figure 5-11 and the ones from the incident solar

radiation, presented in the previous paragraph §5.1.6. It’s clear that the high value of solar incident solar

radiation hitting the SW and SE oriented wall, in the cooling period, is a major contributor to the

overheating of the classrooms C.X.2 and C.X.3 (at each floor). A curios output is the one related to the

NW oriented classroom, in this case we have result values similar to the ones of the worst case (SE-

SW), this is explained by the small dimension of the heated space, as a matter of fact this is the smallest

heated spaces classified as class room, as seen in Figure 5-10. Due to the small dimension of the space,

the sensible and latent gains coming from the user’s body, become more relevant and the incident solar

radiation is not the major influencer for this particular case.

5.2.2 Adaptive Thermal Comfort Model

Over the past four decades, the PMV model has been adopted by a number of researchers worldwide to

assess indoor thermal environment [47]. In general, PMV model works well in built environment with

HVAC systems. For naturally ventilated (or free-running) buildings, however, the indoor temperature

considered most comfortable increases significantly in warmer climates, and decreases in colder climate

regions [48]. This is not surprising given the fact that ‘‘Fanger was quite clear that his PMV model was

intended for application by the heating, ventilation and air-conditioning (HVAC) industry in the creation

of artificial climates in controlled spaces’’ [47].

Page 105: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

81

The heat-balanced PMV model does allow the option of changing the level of activity (hence the

corresponding metabolic rate) and clothing. The experimental works (upon which the PMV model is

based), however, was conducted in climate chambers. Such arrangement did not give any indication of

how the occupants would change these two parameters in an attempt to adapt to the surrounding

environment. In practice, more often than not, assumptions have to be made about the on-going activity

and clothing. This tends to limit the application of the PMV model to a more static thermal environment

usually associated with airconditioned spaces [49]. In general, people are not passive recipients of their

immediate environment, but constantly interacting with and adapting to it. The return towards comfort

is pleasurable. Therefore, if there is any discomfort due to changes in the thermal environment, people

would tend to act to restore their thermal comfort. Broadly speaking, there are three different categories

of adaptation – physiological, behavioral and psychological [50] . Physiological adaptation (in terms of

acclimatization) is not likely to play a major role in affecting occupants’ thermal comfort for the

moderate range of thermal conditions prevailing in the built environment. Psychological adaption refers

to the effects of cognitive, social and cultural variables, and describes how and to what the extent habits

and expectations might change people’s perceptions of the thermal environment. Behavioral adaptation

is by far e most dominant factor in offering people the opportunity to adjust the body’s heat balance to

maintain thermal comfort, such as changing the activity and clothing levels & opening/closing windows

and switching on fans. A consequence of adaptive principle is that occupants try and hopefully become

adjusted to their immediate thermal environment.

It has been shown from field studies that PMV model works pretty well in air-conditioned premises, but

not in naturally ventilated buildings. PMV tends to over-predict the subjective warmth in the built

environment, especially in warmer climates. Humphreys [51] argued that thermal comfort standard like

the ISO 7730 based on PMV model was not entirely suitable for general applications, therefore the

ASHRAE Standard 55 [43] was revised to include an adaptive model for naturally ventilated buildings.

5.2.2.1 Adaptive Thermal Comfort Criteria

In order to calculate the adaptive thermal comfort applied to the case study building it has been decided

to follow the instructions and limitations imposed by the CIBSE Guide A [29], in particular the TM52

[52]. The following three criteria, taken together, are used to assess the risk of overheating of buildings

in the UK and Europe. A room or building that fails any two of the three criteria is classed as overheating.

- Criterion 1 Hours of Exceedance (He): sets a limit for the number of hours that the operative

temperature can exceed the threshold comfort temperature (upper limit of the range of comfort

temperature) by one degree or more during the occupied hours of a typical non-heating season

(1st May to the 30th September). The number of hours (He) during which ΔT is greater than or

Page 106: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

82

equal to one degree (K) during the period May to September inclusive shall not be more than

3% of occupied hours. Provides useful information about the building’s thermal characteristics

and potential risk of overheating over the range of weather conditions to which it will be

subjected.

- Criterion 2 – Daily Weighted Exceedance (We): deals with the severity of overheating, which

can be as important as its frequency, the level of which is a function of both temperature rise

and its duration. This criterion sets a daily limit for acceptability. To allow for the severity of

overheating the weighted Exceedance (We) shall be less than or equal to 6 in any one day. This

criterion covers the severity of overheating, which is arguably more important than its

frequency, and sets a daily limit of acceptability.

- Criterion 3 – Upper Limit Temperature (Tup): sets an absolute maximum daily temperature for

a room, beyond which the level of overheating is unacceptable. It is used to set an absolute

maximum value for the indoor operative temperature the value of ∆T shall not exceed 4°C. The

threshold or upper limit temperature is fairly self-explanatory and sets a limit beyond which

normal adaptive actions will be insufficient to restore personal comfort and the vast majority of

occupants will complain of being ‘too hot’. This criterion covers the extremes of hot weather

conditions and future climate scenarios.

The result of the technical memorandum is that a room that fails any two of the three criteria is classed

as overheated and thus fails the TM52 check. This check has been adopted in this case study, in order

to define the thermal comfort of the classrooms, respecting the hypothesis made in the § 5.2.1, of the

school building. For each classroom in addition to the Operative temperature, already seen in the

previous paragraph, it has been calculated the Daily running mean temperature, which represents the

exponentially weighted running mean of the daily mean outdoor air temperature and the Maximum

adaptive temperature, depending on the running mean temperature and the building category, according

to the guidelines of TM52 [52].

0

2

4

6

8

10

12

14

C.0.1 C.1.1 C.2.1 C.0.2 C.1.2 C.2.2 C.1.3 C.2.3 C.2.8 C.1.4 C.1.5 C.1.6 C.1.7

SE-SW SE NW-SW NW NE SW

Criteria 1 Criteria 2Criteria 3 Limit-Criteria 1Limit-Criteria 2 Limit-Criteria 3

Failed Class

Page 107: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

83

Figure 5-12: Adaptive Thermal Comfort check of the classrooms divided by orientation, according to TM52

The Figure 5-112 represents the TM52 check applied to the classrooms of the school building, taking in

consideration the different orientations, as seen in§ 5.2.1. The graph represents the output values of the

classrooms related to each of the criteria presented, therefore for every space is presented the % of

exceedance hours for the Criterion 1, the max. daily degree hours in °C for the Criterion 2 and the

maximum ΔT in °C for the Criterion 3; in addition there’s also represented the limit, as a dashed line,

for each of the criteria. In this way it’s easy to understand which and how many classrooms pass the

criteria and are classified as overheated.

Most of the classes don’t pass the criterion 2, and on the other hand easily pass the criterion 3, this means

that even if the class can be considered overheated, the overheating will create an uncomfortable

environment, otherwise the effect of the overheating would be unacceptable for the users of the specific

space. The classes C.1.2 and the C.2.2 are marked in red to highlight the fact that they are classified as

overheated, since both don’t pass the criteria 1 and 2. Keeping in mind the results coming from the

Figure 5-11 it was obvious that the classrooms that would have been classified as overheated were going

to be to ones, with walls oriented towards South-East. The energy retrofit will take into this results and

will increase the internal comfort conditions of the overheated spaces.

5.2.3 Indoor air quality

According to some researches made in 2015 from the Gruppo Studio Nazionale Inquinamento Indoor

(GdS) of ISS, it has been pointed out that the amount of CO2 in the atmospheric air corresponds to 719

mg/m3 (400 ppmv). Usually the concentration of CO2 in the indoor air is higher than the outdoor, and

depends on the presence and number of occupants in the space, which of course require continuously

oxygen to breath and their activities. It is necessary to try to keep the level of CO2 inside a defined range

provided by regulations, in order to avoid unpleasant consequences on the health of people inside the

room, an environmental welfare inside the space must always be guaranteed. For environmental welfare

it is intended the particular psychological condition in which the individual reaches a well-being

condition, in terms of microclimate (hygrometric comfort), air quality (respiratory system), noise

(acoustic comfort) etc.

The Indoor Air Quality (IAQ) represents an important aspect for what concern the public health. The

consequences of an unhealthy work environment could lead to a serious health problem to the people

inside the space, as called Sick-Building Syndrome (SBS) which consists in a collection of symptoms,

such as headache, eyes, nausea, concentration issues, fatigue and particularly sensitivity to the odors.

To ensure a correct development of the lecture and to not occur in unpleasant effects, the amount of

carbon dioxide level inside the closed space should be always verified.

The standard provides some threshold that doesn’t have to be overtaken to avoid dangerous level of

Page 108: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

84

CO2 inside the space. Of course the main parameter that influenced the level of carbon dioxide is the

ventilation rate, of which the natural regulation provides some standard values according to different

typologies of educational buildings. The level of carbon dioxide in a closed space are reported below in

compliance with the regulation ISO 7730 [45]:

- normal outdoor level of CO2: 350 – 450 ppm;

- acceptable outdoor level: lower than 600 ppm;

- odor problems: 600 – 1000;

- ASHRAE standards: 1000 ppm;

- light drowsiness: 1000 – 2500 ppm;

- light health issues: 3000 – 5000 ppm;

- health problems: > 5000 ppm.

All values above 1000 ppm must be avoided to not encounter health problems. In general, ventilation

rates should keep CO2 concentrations below 1000 ppm to create indoor air quality conditions acceptable

to people inside the space.

Figure 5-13: Distribution in percentage of the CO2 level present in the classroom, divided by orientation.

Fortunately none of the classroom taken in exam present hourly values for CO2 concentration higher

than 2500 ppm, this means that in no circumstances the users of the heated space will have some

noticeable effect on the health. For all the classes studied, the hours during which the concentration falls

in the 1000<CO2<2500 ppm range represent the highest percentage, this means the student during the

school days will usually feel some discomfort due to the concentrations values, but they will never feel

anything more dangerous than discomfort. This output is really important for the internal condition of

an heated space, especially if the heated space is a classroom, since in this case the users need the

maximum comfort possible in order to increase their learning performances, therefore during the

presentation of the optimization cases it will be encountered the possibility to reduce, or at least don’t

increase, the CO2 concentrations inside the classrooms.

0102030405060708090

100

C.0.1 C.1.1 C.2.1 C.0.2 C.1.2 C.2.2 C.1.3 C.2.3 C.2.8 C.1.4 C.1.5 C.1.6 C.1.7

SE-SW SE NW-SW NW NE SW

% <600 ppm 600<CO2<1000 ppm 1000<CO2<2500 ppm

Page 109: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

85

5.2.4 Daylight Analysis

Natural daylight is one of the most important aspect of the design of buildings, a special attention is

given to the evaluation of the daylight in the public building and in this case, the aim of this section is

to focus the attention on the natural lightning in educational buildings. A good natural daylight promotes

better didactical outcomes of students, better learning and teaching performances and improvements of

the physiological and psychological well-being and comfort of people inside the space. A good design

of daylight is also an advantage for energy saving, limiting the amount of hours in which the electric

lightning is switched on.

Several parameters rule the natural daylight, the standards focused the attention on the aero illuminance

ratio that has to be followed in order to get a uniform and well distributed illuminance inside the room,

which of course, changes according to the different destination of use of the space; for secondary class

the ratio between the transparent and the opaque envelope considered stand in the range of 1/5-1/7

(transparent part should be 1/5-1/7 of the total floor area m2 ).

Shades area or area with an excessive amount of light should be avoided to not experiencing unpleasant

effects as eye fatigue, verifiable both for poor quality of light, and excessive amount of lux that cause

unpleasant glare. For the daylight analyses an important aspect is also the choice of the transparent

envelope used, in particular for what concerns the visible transmittance (τvis) that characterized the

windows. Firstly, a general study of the illuminance on the work place has been evaluated, in order to

see if the values of illuminance where in compliance with the one suggested by the reference standards

[28]. The parameters analyzed are:

- Hourly Daylight Illuminance, expressed in lux

- Useful Daylight Illuminance (UDI), which is defined as the amount of time (expressed as a

percentage) in which, at a certain point, the internal amount of illuminance fall in the range

between 100 and 2000 lux.

- The average daylight factor (DLF), defined as the ratio between the mean lightning inside the

space and the outdoor lightning due to the sky, expressed in %.

The comfort level is necessary to permit people to have an efficient working execution, and that the

activities designated for that particular space are not compromised due to an excessive or low amount

of lux. The daylight factor is a parameter introduced in order to evaluate the natural lightning inside a

closed space, and aim to guarantee an optimal daylight illuminance inside the space. On the inside of a

closed room, the illuminance distributed along the geometry is characterized by three parameters: the

amount of light coming from the outside (sky), the contribution of the light due to reflections of the light

rays hitting the external surfaces and the reflection due to the multiple reflections of the light in the inner

Page 110: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

86

space. In the evaluation of the illuminance conditions, the analysis is made considering the most

improper case which consists of absence of direct solar radiation, called overcast sky. Imposed the cast

sky as the optimal condition for the calculation and the working plane at an height of 0.85 m from the

ground, the ratio between the internal and external illuminance should be constant and it is independent

on days and hours of the year: the mean daylight factor represents a value, expressed as a percentage,

defined as the ratio between the illuminance calculated at a certain point on the inside and the

illuminance measured on the outside on a horizontal surfaces without obstacles.

In order to not limiting the calculation, the DLF is taken as a mean of more points inside the room aiming

to evaluate the global illumination inside the space. The values of the daylight factor could vary

according to the destination of use, as reported in the table below. Some threshold value are defined in

the standards The value of the daylight factor and

of the illuminance, as explained before in § 5.2, for

educational building is defined by the EN ISO

12464-1 [28]. As seen in the table, all the spaces

classified as classrooms present in the case study

building pass both of the verification imposed by

the standard, either for the minimum for the average

value of Daylight Illuminance and the minimum for

the average value of the DLF.

Daylight Illuminance (UDI) has been calculated,

which consists in the percentage of time in which

the sensor point on the grid registers a value of

illuminance in the range between 100 and 2000 lux,

which are the minimum and maximum threshold of daylight illuminance allowable in the space. Then,

as a further analysis the Over lit Percentage has been evaluated, which consist in the harm illuminance,

hence the percentage of time in which the sensor over-takes the value of 2000 lux.

Figure 5-14: UDI -%- of the classrooms, divided by orientation.

0102030405060708090

100

C.0.1 C.1.1 C.2.1 C.0.2 C.1.2 C.2.2 C.1.3 C.2.3 C.2.8 C.1.4 C.1.5 C.1.6 C.1.7

SE-SW SE NW-SW NW NE SW

% <100 lux 100-500 lux 500-2000 lux >2000 lux

% > 3 % [lux] > 300 lux

C.0.1 6.4 V 787 V

C.1.1 6.4 V 787 V

C.2.1 6.4 V 787 V

C.0.2 3 V 354 V

C.1.2 3 V 354 V

C.2.2 3 V 354 V

C.1.3 5.5 V 670 V

C.2.3 5.5 V 670 V

NW C.2.8 5.6 V 687 V

C.1.4 4.7 V 569 V

C.1.5 4.6 V 567 V

C.1.6 5 V 616 V

SW C.1.7 9.7 V 1182 V

NW-SW

NE

SE-SW

DLFOrientation Class

Illuminance

SE

Table 5.2: DLF and Illuminance values for each class.

Page 111: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

87

The graph represents the percentage, during the school days (as delimited in the previous chapter), of

time in which the value of the illuminance calculated inside each of the classroom falls inside the 4

ranges taken in consideration: less than 100lux, defines an inefficient lighting comfort; included between

100 and 500 lux, which represents the range in which the daylighting can be considered acceptable;

included between 500-2000 lux, which is the best range for illuminance inside a classroom; and over

2000 lux, representing the Over lit percentage. The results presented are in accordance with the ones

coming from the DLF analysis presented in the Table 5.2, the classes in which the daylighting can be a

seen as a problem are the ones oriented on the South East direction (C.X.2), their illuminance’s values

fall more often in the insufficient daylight range than the other classes, while the ones oriented towards

the South West direction present the best values of illuminance.

Page 112: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

88

Page 113: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

89

CHAPTER 6

6 Energy Diagnosis: Case study “Buštěhrad”

As seen in the chapter 5, the chapter will be focused on the presentation of the energy analysis done on

the selected building, following the boundary conditions and the input listed before, in the chapter 3.

There will be a major distinction between the output data coming from the energy simulation describing

the energy consumption of the building, and the one describing the internal condition of the building

environment. The outputs coming from the energy simulation have been divide so that the results can

be presented as “Energy Performance” and “Internal Comfort Condition” of the analyzed building case.

6.1 Energy Performance of the Building

The energy performance of the building represents the output data related to the energy contribution of

the building. This means that are here represented all the data that useful to outline the energy and

environmental framing of the building, analyzed in such detail to easily highlight the major problems.

6.1.1 Energy Consumption

The energy consumption of the building, calculated through the use of the dynamic energy simulation

software, is here represented as “PE” which stands for Primary Energy, calculated through the

conversion factors presented in the input chapter, in the § 2.3.3.

Primary Energy Consumptions: 257.38 MWh

Primary Energy Consumptions per area: 251.22 kWh/m2

Energy Classification: Class G

020406080

100120140160180200220240260

[kWh/m2y]

84%

8%

7%4%

Heating

DHW

Equipment

Light

Figure 6-1: Primary Energy Consumption

Page 114: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

90

The two case studies have similar energy consumption, this was highly predictible since the two

buildings were supposed to be similar in order to present a complete and efficent work. Even though

they have similar consumptions, they have really different energy classification, this is due to the two

different energy scales used in each country.

The Figure 6-1 shows how the consumptions of the building is divided into the sub-elements taken in

consideration in the energy modelling design. The consumption due to the heating system is equal to

more than 80% of the total PE, this highlights the importance and the relevance of decreasing the heating

consumption of the school building through the step-by-step approach presented in this energy retrofit

work. The results given by the simulation are in line with the typical consumption of a school building

as seen in the previous chapter, as matter of fact the percentages are really similar to the ones of the case

study building located in Lecco, as seen in §5.1.1, with the main difference represented by the

consumption due to the DHW preparation. The school building located in Lecco presents an independent

gym, with linked locker rooms, and a kitchen, with a linked washing room, this sparks the DHW demand

of the school, thus increasing the consumption, while the students of the school in Buštěhrad use the gm

of an adjacent school building and they eat pre-cooked meals delivered directly to the school.

As already highlighted before, this results represent the base guidelines to understand towards which

direction the retrofit has to go in order to maximize the requalification and minimize the waste of money

and time. For this reason in the further analysis the DHW, the Equipment and the Light consumptions

will be considered negligible as the attention will be focused on the reduction of the PE consumptions

of the heating system.

6.1.2 Economic and Environmental Impact

In order to define the environmental impact of the emission produced by the school building , it will be

considered the amount of Carbon Dioxide equivalent (CO2e) emissions, considering the hypothesis and

the standard values expressed in the previous chapter about the input boundary conditions. With the

introduction of the CO2e it’s possible to describe with one unit of measure the global impact of the

building, considering the Green House Gas (GHG) emissions of it, linked to the use of electricity and

thermal energy presented in the previous paragraph. Concerning the economic impact, it has been

considered the amount of euros spent every year in order to fulfill the building’s energy needs, both

thermal and electric.

GHG emissions: 53.75 ton CO2e/y

Energy bill: 14022.3 €/y

If we compare the results for the two cases, looking at the § 5.1.2, it’s possible to see that the values of

GHG emissions are really similar, which was predictable considering the similar values of combustion

Page 115: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

91

of CO2 used, while the cost of the energy bull is much lower in Czech republic due to the low specific

cost of electricity in the country.

The graph presented below was made in order to give a complete overview of the impact caused by the

energy-inefficient school building, taken in consideration. The school building taken in consideration

can work as an example, in order to give an idea on what happens with an old and neglected building.

Choosing the year of interest, through the trendline, it’s easy to locate the wanted output values of GHG

emissions [ton CO2e] and the thousands of euros [k€] needed to run the energy systems of the school

building. The impact of the building was calculated taking in consideration the energy bill and the GHG

emissions caused by the combustion of methane, due to the boilers serving the heating and DHW

demand, and the use of electricity, due to the boilers’ electric consumptions and the ones related to the

equipment and lighting demand ( as represented in the previous paragraph).

In order to have a more global view on the GHG emissions and on the energy bill of buildings, the Case

Study building has been compared with a Class C building, which actually represents the acceptable

energy class for buildings nowadays for the standards,

and a Class A building, which is the highest energy

class possible. The emissions and the bill related to the

fictitious building in energy class A1 and A4, have

been calculated considering the maximum value of

energy consumption for each energy class calculated in

the previous chapter according to the national energy

classification. The graph here represented highlights

the differences presented between the case study and

energy-efficient building, in terms of euros and CO2e.

This graph highlights the importance of retrofitting the

case study since we could experience some major decrease in the energy bills which means less money

0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400

04008001200160020002400280032003600400044004800520056006000

0

10

20

30

40

50

60

70

80

90

100

110[tonCO2 eq.][yrs]

[K€]

Trendline per year

Guide Lines

Intersection Point

Figure 6-2: Trendline of the economic-environmental impact of the school building per year.

47.59%

81.05%

33.75%

76.05%

0

5

10

15

20

25

30

35

40

45

50

55

Case Study Class C Class A

Energy Bill [k€]

GHG emissions [Ton CO2e]

% - Reduction from Case Study

Figure 6-3: Economic and Environmental Impact -

%- of different energy-class building.

Page 116: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

92

spent for the operational of the building, and considering the fact that our case study is a school and

therefore is a public building, less money spent for the building will mean less money wasted for every

citizen.

6.1.3 Heating Consumptions

As said in the previous paragraph the major cause of energy consumption in the case study building is

represented by the combustion of natural gas into thermal energy provided to the boiler of the heating

system.

The graph expresses the primary energy

consumed each year in order to produce

enough thermal energy so that the heating

system can balance the building’s losses and

keep the temperature of the heated spaces at

the set point. Going further in detail, through

a critical analysis of the results coming from

this graph, it’s obvious that the high energy

consumptions are due to excessive

dispersions in means of Transmission

imposed by a leaky and inefficient envelope. The graph basically says that the energy retrofit of the case

study has to begin with the optimization of the envelope. Given the fact that the building is located in

the North Europe and that for this case the months of July and August (in which usually schools are

closed) have not been taken into account, the value of the Solar gains seem reasonable. Also the values

presented in the graph related to the Ventilation losses and the Internal gains are in agreement with the

input data of the model, and with the fact that being the case study a school it’s normal to have similar

values for internal gains and natural ventilation, since the high activity of the students in the classrooms

is balanced by the continuous opening of the windows.

Recalling the § 5.1.3, it’s possible to see that the value of energy heating demand is similar in the two

case studies, with the only difference involving the solar gains, which in this case are equal to half of

the amount present in the case study located in Lecco, as matter of fact Buštěhrad is located in the north

part of Europe therefore the glazing areas receives a smaller amount of solar radiation, combined with

the orientation of the building. Even though the gain are smaller in this case, the energy needed is less,

due to the smaller value of thermal transmissions through the envelope of the building.

To understand the behavior of the variables that contribute to the calculation of the consumption of

primary energy related to the heating demand, it has been presented a graph representing the monthly

47.90

20.50

54.51

211.84199.54

0

40

80

120

160

200

240

280

320

Contributions Dispersions

[KWh/m2y]

Energy Use

Transmission

Ventilation

Solar

Internal

Figure 6-4: Annual PE consumption for Heating Demand.

Page 117: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

93

condition values of the specified variables.

First thing it is possible to double check that every input in the model was insert in the right way since

the results presented are in line with the hypothesis expressed in the previous chapter. As matter of fact

the value of energy use is zero for the months on May to September and is almost the half of the average

month for April and October in which the hating system is active only for 15 days, and not the whole

month as for the others.

Of course the highest consumption is experienced in the coldest month which is January, this is due to

the really high transmission losses (the temperature in January goes below 0°C) and the low solar gains,

imposed by the low number of hours of sun exposure. This is due to the angle of the sun during the

winter, which also influences the shading that the other buildings provide onto the case study, reducing

the solar radiation coming into the building through the glazing area.

6.1.4 Heat gains

The heat gains of the case study building are a consequence of the input data, presented in the previous

chapter.

0

4

8

12

16

20

24

28

32

36

40

44

January February March April May June September October November December

Internal Gains Solar Gains Ventilation Losses

Transmission Losses Heating Demand

Figure 6-5: Monthly PE consumption for Heating Demand [kWh/(m2y)]

Figure 6-6: Heat Gains in terms of kWh/(m2y) and %.

20.50; 30%

37.22; 55%

6.40; 9%4.28; 6%

47.89984181; 70%

Solar

Internal

People

Equipment

Light

Page 118: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

94

In order to understand the behavior of the building in terms of positive impacts to the energy balance,

the heat gains calculated through the energy simulation of the study case have been studied and broken

down into the principal sources of gains.

The graph presented highlights the statement made before, the gains coming from the solar radiation

passing through the glazing part of the building, is similar to the ones coming from the internal sensible

and latent heat generated by the Equipment, Light and People present in the heated space. The values

related to the solar gains are relatively high for the climate of the city in which the building is located,

this is due to the high area of glazing part of the building, the fact that the glazing are located in all the

surfaces orientation and the high value of total solar factor “gtot” of the old windows present in the

building, an high gtot means that more solar radiation is transmitted to the inner spaces while less

percentage in reflected and blocked.

The value expressing the sensible and latent heat produced by the people inside the heated space

accounts for almost half of the heat gains of the building, this is in line with the hypothesis presented in

the input chapter, the high activity of students and the elevated number of people inside the space are

the major contributors.

6.1.5 Heat Losses

The analysis goes further in detail, focusing the attention on the variables that contribute to the

dispersion of heat from the case study building. For the analysis, the variables in discussion, are the

Ventilation and the Transmission Losses, which in the energy analysis of the building are balanced by

the sum of Internal Gains, the Solar Gains and the Energy received from the heating system

W.O; 25.6

W.U; 0.6W.G; 1.0

F.U; 2.6

F.G; 2.1

F.R; 8.6

R; 5.9W; 23.8

R.F; 3.9

T; 0.9

V; 17

I; 9 W.O-Walls vs Outside

W.U-Walls vs Unheated

W.G-Walls vs Ground

F.U-Floor vs Unheated

F.G-Floor vs Ground

F.R-Floor vs Roof

R-Roof

W-Windows

R.F-Roof Windows

T-Thermal bridge

V-Ventilation

I-Infiltration

Figure 6-7: Contribution in terms of % of the elements of the building to the global Heat Losses of the case study.

Page 119: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

95

The graph, as the caption says, represents the values in terms of % of the contribution of each element

to the global Heat Losses of the case study, this means that looking at the graph it’s possible to

understand the negative impact of each element taken into account in the energy balance of the case

study building.

The results highlights the similar behavior of the two case studies building ( recalling the §5.1.5), since

in both graphs the biggest contribution is represented by the elements in contact with the outside, and

the losses due to the infiltration rate. The external walls, “W.O.- Walls vs Outside”, are the elements

which have a bigger negative impact on the building’s performance, followed by the glazing part of the

building, “W-Windows”, as a matter of fact if we sum the % contribution of these two variable of the

building we have that more than 40% of the heat losses of the building comes from the outer envelope.

Taking in consideration this facts and data, the first idea that comes to mind is that the requalification

of the external wall and the glazing part of the entire building will be one of the most challenging part

of the energy retrofit, and on the other hand it will be one of the most significant energy-reduction work.

The high infiltration losses are due to the infiltration rate, presented in the input chapter, linked to the

air leakage of the energy-inefficient envelope of both parts of the building, in this case the absence of

the thermal insulation and the presence of and old bearing structure both in bricks, for each part of the

building, plays the biggest part in conjunction with the presence of old low-transmittance windows

through the entire case study building. Another aspects that contributes to the high value of infiltration

losses, is the fact that instead of natural ventilation, this is not controllable but it’s actually a phenomenon

to which the building is subjected to, therefore it is always present, no matter the occupancy of the space,

and it always affects the heating demand, while the natural ventilation is controlled by the users present

in the heated spaces, which will open the windows, letting natural ventilation, according the internal and

external conditions of the specific space. The infiltration losses and the losses by the outer envelope are

strictly connected, this is because the infiltration is based on the difference of pressure between the

inside and the outside of the heated space, and the pressure inside of the space is linked to the

permeability of the outer skin of the building and the ability of it to keep the designated pressure. The

definition of air permeability is “Infiltration air flowrate per unit surface area of the envelope, at the

reference pressure difference” therefore it’s easy to understand that it depends on the air tightness of the

building, determined by the envelope’s thermal performances. This basically means that with the

improvement of the envelope we will have a double benefit, since there will be an obvious reduction of

heat losses attributed to the envelope’s element and also a reduction coming from the infiltration losses,

due to the increase of air permeability through the addition of thermal insulation to the outer skin of the

case study building.

Page 120: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

96

6.1.6 Solar energy analysis

The solar analysis helps understand the interaction of the building, in this case the building’s envelope,

and the solar radiation coming from the sun, basically this analysis will show the pro and the cons of

letting inside the inner spaces the sun’s radiation. For the purpose of this analysis the solar radiation has

two opposite effect on the building’s performances, a positive one related to the heating solar gains and

a negative one related to the overheating of the spaces.

For the calculation of the heating energy demand the contribution coming from the solar radiation is

accounted as solar gains, therefore in this case the impact of the radiation coming through the envelope

and into the heated space is positive, a way to reduce the energy demand is actually to increase the solar

gains throughout the heating period. On the other hand, the solar radiation coming through the envelope

in the cooling period will increase the internal temperature of the heated spaces giving rise to a possible

phenomenon of overheating, in which the spaces’ temperature may tend to unbearable internal

conditions for the users.

In this case considering that in the school building there are 4 different glazing’s orientation, it has been

represented the average solar radiation incident on the wall according to the different orientation. The

results presented in the graph are interesting, the first peculiarity is the behavior of the South oriented

wall, which actually shows higher values of solar radiation in winter rather than in the mid and hot

season, this is due to angle of rotation of the sun, which in the summer is so high in the sky that irradiates

directly only the roof of the building. As a matter of fact the amount of solar radiation hitting the surfaces

is equal for all the directions in the cooling season.

0

50

100

150

200

250

300

350

[W/m2] South East West North

January February March April May June September October November December

Heating Season Cooling Season Heating Season

Figure 6-8: Daily average incident solar radiation [Wh/m2] calculated on the 4 different orientation.

Page 121: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

97

In order to fully understand whether the solar radiation are a benefit or a malus for the case study, it has

been highlighted the two different period, the heating period in which more the radiation the better and

the cooling period in which high solar radiation usually means discomfort. Considering the cooling

season the orientation with the highest values of solar radiation are the South-West and South-East,

which means that the space which will have walls oriented like this will have chance to encounter

overheating, on the other hand this two orientation have the highest values also for the heating period,

as seen before.

The screenshots of the solar analysis run through the dynamic simulation software, attached above, helps

understand the results and commented presented earlier about the output coming from the analysis

related to the incident solar radiation hitting the different vertical component of the case study building.

The comments related to the incident solar radiation graph, are confirmed by these screenshots in which

is possible to see the annual solar radiation [kWh/m2] hitting the envelope of the building. The elements

oriented towards the South direction (first on the left) are the ones with the biggest values, while the

ones oriented towards North present the lowest values.

In this case is also visible the shading action of the surrounding buildings towards the case study

building, and the effect that they have on the incident solar radiation. The four different screen shots

refer to the 21 of March, day of the Spring Equinox, at midday.

Figure 6-9: Solar analysis radiation on S, E, N, W oriented wall (from left to right)

Page 122: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

98

6.2 Internal Comfort

The factors that determine the quality of the internal space related to the improvement of students’

apprenticeship are related to measurable values.

6.2.1 Thermal Comfort

Thermal comfort is the condition of mind that expresses satisfaction with the thermal environment and

is assessed by subjective evaluation (ANSI/ASHRAE Standard 55) [43]. With regard to thermal

comfort, the final figure to be assessed is the degree of well-being perceived by occupants in the space

considered. The useful tool for this purpose is constructed by theoretical principles and measurement

methods for predicting the perceived thermal sensation of people. The 98 eometr-hygrometric

environment is described through appropriate physical quantities with standardized methodologies [46].

The size considered for the comfort temperature is the operating temperature:

𝑇𝑂𝑃 = ℎ𝑟 ∗ 𝑇𝑚𝑟 + ℎ𝑐 ∗ 𝑇𝑎

ℎ𝑐𝑟

Where:

hr is the radiative exchange coefficient;

Tmr is the mean radiant temperature;

Ta is the air temperature;

hc is the convective exchange coefficient;

hcr is the adduction coefficient.

According to the EN ISO ISO 7730 [45] and the ASHRAE 55 [43] show as comfort condition:

Top = 20-24°C, UR= 30-70 % in the heating period;

Top = 23-26°C, UR= 30-70 % in the cooling period.

The hours of discomfort are the ones in which the temperature of the heated space, during the cooling

period, is higher than the comfort limit set at 26 °C, as presented before.

Compared to the studies related to the definition of the parameters for improving the I performance, the

set-point temperature in the winter period should be maintained within a range of 20 to 22 ° C. However,

in mid and summer seasons, indoor air temperature can’t be controlled but experimental evidence in the

field of temperature-related learning has shown that a temperature of 22-24 °C improves performance,

even though temperatures ranging from 25 to 32 °C are permitted in the British guidelines and at the

national level no recommended values are stated.

In order to understand the internal thermal conditions of the heated space classified as classrooms inside

the case study building, it has been calculated -in percentage %- the discomfort hours through the energy

Page 123: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

99

simulation software used presented before.

The graph shows, as seen in the caption,

the total percentage of discomfort hours

during the cooling season, which means

that it has been calculated the ratio in

percentage between the total hours of a

normal school day – 8 a.m. to 18:00 p.m.

– and the hours, in this range, in which

the temperature is higher than the

defined cooling comfort temperature, set

at 26 °C. In this calculation it has been

considered only the school days – Monday to Friday – in which the heating system is off, not taking in

consideration the summer period in which the school is not used – from 1st May to 30th June – in order

to have more accurate and realistic outputs.

The classrooms have been divided by exposition, from the small plan previously presented it’s easy to

understand the differentiation of the classrooms, by floor (first number of the code for the classrooms –

C.X) and by orientation (second number – C.X.X.). The differentiation by orientation has been done in

order to see the effect of the sun exposure on the classroom, in the cooling period the building is free

floating (no conditioning system is on) and the temperature of the inner spaces depends mainly on the

sun radiation hitting and passing through the glazing part of the envelope, the amount of radiation

depends on the incident angle on the surfaces, linked to the height and the orientation of the specific

surface.

The Figure 6-10 gives a global view on the thermal condition on the different classrooms, all of them

present low percentage of discomfort hours. This is in line with the predictions, since the climate of

Buštěhrad is rigid, and the simple opening of the windows (simulate through the use of the dynamic

analysis software) counterbalance the mild climate of the months of May and June. The results presented

in this case study are much better than the one presented for the case study in Lecco (§5.2.1), as said

before this is due to the differences climatic conditions of the two buildings.

6.2.2 Adaptive thermal comfort criteria

In order to have a more global and complex view on the thermal comfort of the inner spaces of the

building, it can be used the adaptive thermal comfort model as showed in §5.2.2.

In order to calculate the adaptive thermal comfort applied to the case study building it’s needed to follow

the instructions and limitations imposed by the CIBSE Guide A [29], in particular the TM52 [52]. In

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

C.0.1 C.1.1 C.2.1 C.0.2 C.1.2 C.2.2 C.0.3 C.1.3 C.2.3 C.1.4 C.2.4

South-West South-East North-East North-West

Figure 6-10: Discomfort hours % of the classrooms, dived by

glazing’s orientation, during the cooling season.

Page 124: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

100

this case though, the really low amount of hours of discomfort hours, and the mild temperature recorded

inside the classrooms in the cooling room, made useless the study of the adaptive thermal comfort of

the inner spaces of the case study in Buštěhrad.

6.2.3 Indoor air quality

The Indoor Air Quality (IAQ) represents an important aspect for what concern the public health. The

consequences of an unhealthy work environment could lead to a serious health problem to the people

inside the space, as called Sick-Building Syndrome (SBS) which consists in a collection of symptoms,

such as headache, eyes, nausea, concentration issues, fatigue and particularly sensitivity to the odors.

To ensure a correct development of the lecture and to not occur in unpleasant effects, the amount of

carbon dioxide level inside the closed space should be always verified.

The standard provides some threshold that doesn’t have to be overtaken to avoid dangerous level of

CO2 inside the space. Of course the main parameter that influenced the level of carbon dioxide is the

ventilation rate, of which the natural regulation provides some standard values according to different

typologies of educational buildings. The level of carbon dioxide in a closed space are reported below in

compliance with the regulation ISO 7730 [15]:

- normal outdoor level of CO2: 350 – 450 ppm;

- acceptable outdoor level: lower than 600 ppm;

- odor problems: 600 – 1000;

- ASHRAE standards: 1000 ppm;

- light drowsiness: 1000 – 2500 ppm;

- light health issues: 3000 – 5000 ppm;

- health problems: > 5000 ppm.

All values above 1000 ppm must be avoided to not encounter health problems. In general, ventilation

rates should keep CO2 concentrations below 1000 ppm for acceptable indoor air quality conditions.

0

20

40

60

80

100

C.0.1 C.1.1 C.2.1 C.0.2 C.1.2 C.2.2 C.0.3 C.1.3 C.2.3 C.1.4 C.2.4

South-West South-East North-East North-West

% <600 ppm 600<CO2<1000 ppm 1000<CO2<2500 ppm

Figure 6-11: Distribution in percentage of the CO2 level present in the classroom, divided by orientation.

Page 125: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

101

Fortunately none of the classroom taken in exam present hourly values for CO2 concentration higher

than 2500 ppm, this means that in no circumstances the users of the heated space will have some

noticeable effect on the health. For all the classes studied, the hours during which the concentration is

less than 600 ppm represent the highest percentage, this means the student during the school days will

usually feel some discomfort due to the concentrations values, but they will never feel anything more

dangerous than discomfort. This output is really important for the internal condition of an heated space,

especially if the heated space is a classroom, since in this case the users need the maximum comfort

possible in order to increase their learning performances, therefore during the presentation of the

optimization cases it will be encountered the possibility to reduce, or at least don’t increase, the CO2

concentrations inside the classrooms.

6.2.4 Daylight Analysis

Natural daylight is one of the most important aspect of the design of buildings, a special attention is

given to the evaluation of the daylight in the public building and in this case, the aim of this section is

to focus the attention on the natural lightning in educational buildings. A good natural daylight promotes

better didactical outcomes of students, better learning and teaching performances and improvements of

the physiological and psychological well-being and comfort of people inside the space. A good design

of daylight is also an advantage for energy saving, limiting the amount of hours in which the electric

lightning is switched on.

Firstly, a general study of the illuminance on the work place has been evaluated, in order to see if the

values of illuminance where in compliance with the one suggested by the reference standards [28]. The

parameters analyzed are:

- Hourly Daylight Illuminance, expressed in lux

- Useful Daylight Illuminance (UDI), which is defined as the amount of time (expressed as a

percentage) in which, at a certain point, the internal amount of illuminance fall in the range

between 100 and 2000 lux.

- The average daylight factor (DLF), defined as the ratio between the mean lightning inside the

space and the outdoor lightning due to the sky, expressed in %.

The comfort level is necessary to permit people to have an efficient working execution, and that the

activities designated for that particular space are not compromised due to an excessive or low amount

of lux. The daylight factor is a parameter introduced in order to evaluate the natural lightning inside a

closed space, and aim to guarantee an optimal daylight illuminance inside the space. On the inside of a

closed room, the illuminance distributed along the geometry is characterized by three parameters: the

Page 126: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

102

amount of light coming from the outside (sky), the contribution of the light due to reflections of the light

rays hitting the external surfaces and the reflection due to the multiple reflections of the light in the inner

space. In the evaluation of the illuminance conditions, the analysis is made considering the most

improper case which consists of absence of direct solar radiation, called overcast sky. Imposed the cast

sky as the optimal condition for the calculation and the working plane at an height of 0.85 m from the

ground, the ratio between the internal and external illuminance should be constant and it is independent

on days and hours of the year: the mean daylight factor represents a value, expressed as a percentage,

defined as the ratio between the illuminance calculated at a certain point on the inside and the

illuminance measured on the outside on a horizontal surfaces without obstacles.

In order to not limiting the calculation, the DLF is

taken as a mean of more points inside the room

aiming to evaluate the global illumination inside

the space. The values of the daylight factor could

vary according to the destination of use, as

reported in the table below. Some threshold value

are defined in the standards The value of the

daylight factor and of the illuminance, as

explained before in § 5.2, for educational building

is defined by the EN ISO 12464-1 [28]. As seen

in the table, all the spaces classified as classrooms

present in the case study building pass both of the

verification imposed by the standard, either for the

minimum for the average value of Daylight Illuminance and the minimum for the average value of the

DLF. Daylight Illuminance (UDI) has been calculated, which consists in the percentage of time in which

the sensor point on the grid registers a value of illuminance in the range between 100 and 2000 lux,

which are the minimum and maximum threshold of daylight illuminance allowable in the space. Then,

as a further analysis the Over lit Percentage has been evaluated, which consist in the harm illuminance,

hence the percentage of time in which the sensor over-takes the value of 2000 lux.

The graph represents the percentage, during the school days (as delimited in the previous chapter), of

time in which the value of the illuminance calculated inside each of the classroom falls inside the 4

ranges taken in consideration: less than 100lux, defines an inefficient lighting comfort; in between 100

and 500 lux, which represents the range in which the daylighting can be considered acceptable; in

between 500-2000 lux, which is the best range for illuminance inside a classroom; and over 2000 lux,

representing the Over lit percentage.

Orientation Class DLF Illuminance

% > 3 % [lux] > 300 lux

South-West

C.0.1 3.4 V 415 V

C.1.1 3.4 V 415 V

C.2.1 3.4 V 415 V

South-East

C.0.2 3.3 V 400 V

C.1.2 3.3 V 400 V

C.2.2 3.3 V 400 V

North-East

C.0.3 3.3 V 400 V

C.1.3 3.3 V 400 V

C.2.3 3.3 V 400 V

North-West C.1.4 3.4 V 412 V

C.2.4 3.4 V 412 V

Table 6.1: DLF and Illuminance values for each class

Page 127: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

103

The results presented are in accordance with the ones coming from the DLF analysis presented in the

Error! Reference source not found., the classes have similar behaviors, for all of them the range with t

he highest percentage is represented by the on in which the illuminance falls in between 100 and 500

lux, which as said previously guarantees lighting comfort.

Confronting the two case studies, with the help of the Figure 5-14, it’s clear that the classes of the case

study located in Buštěhrad have a similar behavior, regardless the orientation and the floor, while in

Lecco there are big differences. Nevertheless the classrooms of both the case studies present acceptable

values for DLF and UDI, therefore this won’t be an issue during the retrofit work presented in this

master thesis.

0102030405060708090

100

C.0.1 C.1.1 C.2.1 C.0.2 C.1.2 C.2.2 C.0.3 C.1.3 C.2.3 C.1.4 C.2.4

South-West South-East North-East North-West

% <100 lux 100-500 lux 500-2000 lux >2000 lux

Figure 6-12: UDI -%- of the classrooms, divided by orientation.

Page 128: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

104

Page 129: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

105

CHAPTER 7

7 Envelope Optimization

The optimization of the envelope will not be based on a step by step approach but it will be focused on

single interventions, this means that listed all the possible intervention that can be possibly done on the

envelope, they will be taken separately and each one of them will be analyzed in various aspects such

as: technical, energetical, environmental and economical.

7.1 Design philosophy

For the technical point of view, taking in consideration the output data of the diagnosis previously done

on the buildings, there will be presented for each intervention different case scenarios, in order to fulfill

all the possible needs of the building. This different scenarios will also have different environmental

impact on the building, so that it can be analyzed the differences between normal practice materials and

natural material through the retrofit of the building. In order to study the environmental impact of each

scenario it has been considered for each material composing the building solution introduced in the

specific intervention, the amount of Embodied Energy “EE” and the Embodied Carbon “EC”. Basically

it will be done a life cycle inventory analysis, collecting data about the embodied and operational energy

of the different scenarios, according to the ICE [53] database.

The EE is defined as the total primary energy consumed from direct and indirect processes associated

with a product or service and within the boundaries of cradle-to-gate. This includes all activities from

material extraction (quarrying, mining), manufacturing, transportation and right through to fabrication

processes until the product is ready to leave the final factory gate.

The EC is the sum of fuel related carbon emissions (i.e. embodied energy which is combusted but not

the feedstock energy which is retained with the material) and process related carbon emissions (i.e. non

fuel related emissions which may arise, for example, from chemical reactions). This can be measured

from cradle-to-cradle, cradle-to-grave, or from cradle to grave. The ICE data is cradle-to-gate.

The energetical aspect will be tackled presenting the energy savings given by the single intervention,

and in a similar way the economical one will be estimated through the payback period of the investment.

Therefore the choice of the case scenario will be done trying to find the more interesting solutions

according to the output of the diagnosis previously developed on the case study building.

The interventions considered during this thesis work are done in a deep retrofit perspective, therefore

the standard used as reference is the EPBD 2 [14], which is than acknowledged by the Italian Ministry

with the Ministerial Decree of the 26th June 2015, and in the Czech Republic with the ČSN 73 0540

Page 130: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

106

[54]. The standard gives a limitation on the thermal transmittance of the elements on which the deep

retrofit will be focused on, those limitations will be seen later on in the analysis of the specific

operations. Since the limit values for the two European countries are a little bit different, in order to

have a more global view and make the comparison of the two cases studies easier, it has been decided

to take as final limitation value the thermal transmittance defined as “Recommended” by the Czech

regulation ČSN 73 0540 [54].

Structure Element Required U Italy

[W/(m2K)]

Required U CZ

[W/(m2K)]

Recommended U

[W/(m2K)]

External Wall 0.28 0.30 0.25

Roof 0.24 0.24 0.20

Attic 0.24* 0.30 0.20

Basement ceiling 0.3625* 0.40 0.32

Slab on ground 0.29** 0.45 0.25

Ground-contact walls 0.28** 0.45 0.25

* In the case of structures delimiting the heated space towards unheated rooms, the transmittance limit

values must be respected by the transmittance of the structure divided by the correction factor of the

heat exchange between heated and unheated environment, as indicated in the UNI TS 11300-1 [55]

standard in tabular form. This applies for both the attic located in the under-roof space, and the basement

located in the underground level. Therefore the correcting value that has to be used is:

Adjacent space Correction factor btr,U

Underground floor

- With external openings 0.8

Attic floor

- High ventilation rate of the attic (e.g. roofs covered with tiles or other

discontinuous roofing materials) without felt or wall covering

1.0

** In the case of structures facing the ground, the transmittance limit values must be respected by the

equivalent transmittance of the structure taking into account the effect of the ground calculated

according to UNI EN ISO 13370 [27].

As it can be seen in the Table 7.3 the limit U values for glazing area, considering a deep retrofit

intervention, are set in both case studies to 1.40 W/(m2K). This is in disagreement with the comparison

of the two regulations done in the previous paragraphs, in which the Italian limitations for each of the

intervention presented were highlighted as more strict.

Table 7.1: Thermal transmittance U limitations in Italy and in CZ, defined by national regulations

Table 7.2: Correction factor btr,U from EN ISO 12831:2006

Page 131: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

107

Structure Element Required U Italy

[W/(m2K)]

Required U CZ

[W/(m2K)]

Recommended U

[W/(m2K)]

Glazed Surfaces 1.40 1.40 1.20

As previously done, the set limitation that will be used will be the one equal to the U value recommended

in the Czech regulation [54] U equal to 1.20 W/(m2K), which is more strict respect to the required one.

This will guarantee high energy performance to the building’s envelope and also and improvement in

the indoor thermal comfort, decreasing the infiltration and increasing the homogeneity of the internal

temperatures.

Another standards’ limitation is the one setting the solar transmission factor “ggl+sh“ for glazing

components so that: ggl+sh ≤ 0.35.

7.1.1 Technical Analysis

As matter of fact thanks to the analysis of the internal condition, in the § 3.2.1, it has been highlighted

a problem of overheating inside a small number of classrooms therefore in the design process this has

been taken into account. Considering that the case study does not involve the presence of a mechanical

cooling mechanism, the addition of thermal insulation on the outside wall, for the cooling period, won’t

directly imply an increase of comfort inside of the heated spaces, but it will decrease the transpiration

of the external wall structure. In order to quantify the effect of the different thermal insulation applied

to the wall in terms of cooling comfort, it has been considered the thermal inertia of the specific material

used as thermal insulation.

The thermal inertia is the capacity of a building component:

- To attenuate the fluctuations of the internal ambient temperature due to internal and external

heat loads varying in during the day(solar radiation, equipment, artificial light and people);

- Accumulate the heat and release it after a certain number of hours over time.

The summer period, undervalued in the European energy certification of buildings, involves high

consumption for cooling and discomfort conditions in our temperate climates, and must therefore be

taken into account. Being characterized by variable thermal loads around the day and more clearly than

in winter, the summer season calls into question the thermal inertia of the building envelope. The thermal

inertia can be described through two dynamic thermal property:

- Periodic thermal transmittance 𝑌𝑖𝑒 = 𝑈 ∗ 𝑓𝑑 [W/(m2K)];

- Internal thermal capacity Cip [kJ/(m2K)].

Table 7.3: Glazing’s thermal transmittance limitations in Italy and in CZ, defined by national regulations [21] [54]

Page 132: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

108

The Yie is the product between : the attenuation

factor fd, which represents the ratio between

the amplitude of the exiting thermal flow and

the entering one into a structure element; and

the stationary thermal transmittance U.

The periodic thermal transmittance represents

both the degree of damping of the thermal

wave coming from the outside and the phase

displacement φ of the same wave, which

represents the time which the peak of the

maximum external temperature takes to go completely through a structure element of the specific

building.

The Cip periodic internal thermal capacity, calculated as Yie, according to UNI EN ISO 13786 [42]

represents the capacity of a building component to accumulate the thermal loads coming from inside.

The higher the value of the Cip (mass placed inside), the greater the heat accumulation. The accumulation

of internal thermal loads by a wall makes it possible to keep surface temperatures at acceptable levels,

i.e. with fluctuations and limited values throughout the day, in favor the environmental comfort

conditions for summer.

7.1.2 Economic Analysis

In order to have an economic view of the proposed interventions it has been decided to analyze the

payback time of the investment, based on the intervention’s cost and the energy cost savings obtained

through the years, in order to make this case more global as possible some hypothesis and simplifications

had to be done. The cost of the intervention was calculated in a simple straightforward way, considering

the cost of the materials and of the installation summed with a fixed percentage of increase due to

expenses directly related to the works done for the preparation and use of the construction site (i.e.

scaffoldings, preparation of the land, etc.). This cost is than summed up to the cost of the operational

energy bore every year by the school system considering the new interventions done on the envelope.

This sum is than subtracted to the operational energy cost bore by the school system without the new

intervention, defining the economic benefit of the investment.

𝐵€ = (𝐶0 + ∑ 𝐶𝑟

𝑛

𝑖=0

) − ∑ 𝐶𝑛𝑟

𝑛

𝑖=1

The variables presented are:

- B€ the economic benefit of the investment;

att

enu

ati

on

n

phase displacement

thermal wave

Figure 7-1:Displacement and attenuation of a thermal wave

Page 133: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

109

- C0 the initial cost of the investment made;

- Cr the operational energy cost of the retrofitted building for each year;

- Cnr the operational energy cost of the non-retrofitted building for each year;

- I the year considered.

In this way it’s pretty clear that when the economic benefit B€ is equal to 0, the “i” of the formula, which

stands for the year considered in the calculation, represents the “payback year”, that can be defined as

the year in which there is no difference between pre and after retrofit in terms of costs.

𝐵€ = (𝐶0 + ∑ 𝐶𝑟

𝑛

𝑖=0

) − ∑ 𝐶𝑛𝑟

𝑛

𝑖=1

= 0

In the calculations, all the cost related to the maintenance have been neglected. Since in this case the

will is to highlight the difference between the cost before and after the works, it has been decided to

assume that the costs related to the maintenance don’t change from the pre and after retrofitted works.

In addition in order to make the case study useful for any country and any application field, in the costs

and the savings no cost deduction coming from the government have been considered, and on top of this

the cost of the investment has been considered without any kind of rate of interest, assuming that the

cost will be bore entirely in the first year.

In order to have comparable results, it has been decided to present the results exclusively in euros, so it

has been adopted a standard rate change from Czech crowns to Euros equal to: 25 CZK = 1 €.

7.1.3 Environmental analysis

Concerning the environmental part, it has been decided to discover and understand the impact of the

retrofitting intervention on the GHG emissions of the buildings. In order to do this, it’s necessary to

introduce the Be, which represents the benefit in terms of GHG emissions of the intervention.

𝐵𝑒 = (𝐸𝐶𝑚 + ∑ 𝐸𝑟

𝑛

𝑖=0

) − ∑ 𝐸𝑛𝑟

𝑛

𝑖=1

The environmental benefit Be is defined by:

- ECm the embodied carbon, from cradle to gate, of the material used for the intervention;

- Er the GHG emission, in terms of CO2e, of the retrofitted building for each year;

- Enr the GHG emission, in terms of CO2e, of the non-retrofitted building for each year;

- I the year considered.

𝐵𝑒 = (𝐸𝐶𝑚 + ∑ 𝐸𝑟

𝑛

𝑖=0

) − ∑ 𝐸𝑛𝑟

𝑛

𝑖=1

= 0

In this way it’s pretty clear that when the emission benefit Be is equal to 0, the “i” of the formula, which

Page 134: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

110

stands for the year considered in the calculation, represents the “return year”, that can be defined as the

year in which there is no difference between pre and after retrofit in terms of GHG emissions.

As done for the economic part, also in this case some assumptions had to be made in order to simplify

the calculations and to clarify the goal of the work. The goal of this analysis was to understand the

differences between the different case scenarios in terms of GHG emissions. For this reason as emission

produced by the retrofitting intervention it has been considered only the EC of the material used, without

considering the emission cause by the transportation and the installation, so that the comparison could

be focused only on the different materials used in the different cases.

7.2 Case study “Lecco”

According to the needs and the criticalities highlighted through the energy analysis previously presented

in chapter 5 in this section it will be presented the different case scenarios chosen for each retrofit

intervention proposed and considered feasible/energetically beneficial, for the case study school

building located in Lecco.

7.2.1 External thermal insulating coating

The coating of the outer envelope of the

building with thermal insulation, is one of

the most common procedure done in order

to decrease the amount of energy

consumption of the specific building. This

technique allows the building also to

receive a complete makeover of the facades

considering that the thermal coating

includes a new external finish, this can contribute to spark up the aesthetic value of obsolete buildings.

Therefore since the building will radically change its look the external coating of the facades is

considered an invasive procedure. For this reason this technique can’t be applied to all of the facades of

the historical part of the building built at the beginnings of the 20th century. The façade of the old part

of the building oriented towards North-West, which is the only one that is exposed on the street, has

aesthetic architectural value therefore its appearance can’t be modified meaning that no thermal

insulation can be applied. For this type of façade it will be presented later on in the script an internal

insulation solution.

Figure 7-2: NW facade of the old part of the school building

Page 135: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

111

7.2.1.1 Design choice

Analyzing the output data of the energy diagnosis presented in the §5, it has been decided to present

three different scenario of intervention for this specific procedure. The three different scenario will

change in terms of thermal insulation material and external finish, for the remainder it will be all the

same, as matter of fact in all the scenario the element structure will have the same thermal transmittance

set at 0.25 [W/(m2K)], as defined in Table 7.1.

Scenario Insulation λ d s Finishing

Material [W/mK] [kg/m3] [cm] Material

EXT. 1 EPS with graphite 0.031 35 11 Acrylic

EXT. 2 Rockwool 0.034 115 12 Breathable

EXT. 3 Wood Fiber 0.04 145 14 Breathable

As said in the previous paragraph the three scenarios will have different environmental and economic

impact, this is visible through the Table 7.5 here presented.

Through the table it’s easy to understand the differences between the three presented scenarios, as the

first solution with EPS represents the most common one therefore has the lowest price and highest

environmental impact, while on the opposite the third solution with Wood fiber has an higher cost and

a low environmental impact.

Scenario

Recent part Old part

EE EC Cost EE EC Cost

[MJ/m2] [KgCO2/m2] €/m2 [MJ/m2] [KgCO2/m2] €/m2

EXT. 1 372.12 14.97 44.37 409.33 16.47 44.38

EXT. 2 241.49 11.13 83.44 263.44 12.14 85.38

EXT. 3 216.78 8.29 99.99 233.45 8.93 102.25

The values of EE and EC are taken by the ICE [53], therefore they only refer to cradle-to-gate, this

means that this analysis is purely theoretical and it based on a simple collection of data related to the EE

and EC of the single material composing the building component solution presented, without taking in

consideration the data related to the installation and the processes techniques.

As matter of fact thanks to the analysis of the internal condition, in the § 5.2.1, it has been highlighted

a problem of overheating inside a small number of classrooms therefore in the design process this has

been taken into account. Considering that the case study does not involve the presence of a mechanical

cooling mechanism, the addition of thermal insulation on the outside wall, for the cooling period, won’t

directly imply an increase of comfort inside of the heated spaces, but it will decrease the transpiration

of the external wall structure. In order to quantify the effect of the different thermal insulation applied

Table 7.4: Thermal coating scenario considered for the retrofit intervention located in Lecco

Table 7.5: Environmental and economic analysis of the different scenarios

Page 136: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

112

to the wall in terms of cooling comfort, it has been considered the thermal inertia of the specific material

used as thermal insulation.

7.2.1.2 Thermal inertia of the case scenario

For this intervention, considering that it is based on the application of material insulation on the outside

of the envelope, the thermal inertia of the different scenarios will be compared based only on the

different values of Periodic thermal transmittance Yie defined by the different material used for each

scenario. Here are presented the values defining the dynamic properties of the different case scenarios

previously defined in the table below.

It’s easy to understand the big overcome of adding thermal insulation to the external face of the walls,

since all of the scenarios present better thermal values compared to the base case, no matter the kind of

material used as thermal insulation. The lower is the value expressing the attenuation fd and the lower is

the amplitude of the thermal flow entering the building component, and at the same time the lower is

the value of the periodic thermal resistance Yie and the higher are the value of the phase displacement φ

and the damping. In addition to that, it’s possible to see the differences and the similarities of the two

construction techniques used in the two different part of the building, as already presented this is due

to different age of construction.

It’s easy to see that the construction element used in the old part made of stone has better dynamic

properties’ value, due to the higher thermal mass respect to the one used in the recent part of the building

made of a double layer of bricks with an air cavity in between. The Table 7.65 is given by the National

Guide Lines [18], and it highlights that the retrofitted building components in all of the case scenarios,

and in all of the part of the building analyzed can be classified as “excellent” from a summer thermal

performance point of view. In addition to this it has to be said that the National Guide Lines [18] sets

also, the limit for the value of the periodic thermal transmittance Yie equal to a maximum of 0.10

[W/(m2K)], therefore all the scenarios are below the limit.

Case

Recent part Old part

fd φ Yie fd φ Yie

- [h] [W/m2K] - [h] [W/m2K]

Base 0.216 11.43 0.246 0.147 11.78 0.341

1 0.04 15.59 0.010 0.034 15.14 0.008

2 0.036 17.22 0.008 0.031 17 0.008

3 0.025 20.58 0.006 0.02 20.67 0.005

φ fd Performance

φ > 12 fd < 0.15 excellent

10 < φ < 12 0.15 < fd < 0.30 good

8 < φ < 10 0.30 < fd < 0.40 average

6 < φ < 8 0.40 < fd < 0.60 sufficient

φ < 6 fd < 0.60 mediocre

Table 7.6: Dynamic properties of the different case scenarios Table 7.7: Limit values set by standard [18]

Page 137: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

113

7.2.1.3 Heating consumption savings

In this paragraph it will be analyzed the perks of doing the specific intervention explained in the previous

paragraph. In this case the intervention is the application of an external thermal coating onto the facades

of the case study building exception made for the protected façade (as presented in § 7.2.1) and the

perks are represented by the energy and economic savings and the GHG emission reductions.

Scenario

Heating

Primary Energy Energy cost GHG emissions Reduction

[kWh/m2y] [€] [tonCO2] [%]

Base 233.61 17974.10 45.04 -

Ext. Insulation 163.06 12581.87 31.53 30%

From the table it’s easy to understand the profits, speaking about heating consumptions, coming from

the application of the thermal insulation as previously explained. The reduction obtained through the

application of the thermal insulation is equal to 30% of the initial value, this refers to all of the values

presented in the table, so for the: primary energy, energy cost and the GHG emissions.

7.2.1.4 Economic and environmental impact

The cost of the intervention was calculated in a simple straightforward way, considering the cost of the

materials and of the installation taken from the “Prezziario Lombardia”, which is the pricelist for civil

works in the Lombardy region, summed with a 20% of increase due to expenses directly related to works

needed to be done in order to make the application of the thermal insulation possible (i.e. scaffoldings,

preparation of the land, etc.).

Table 7.8: Heating reductions obtained with the external thermal coating

-60

-40

-20

0

20

40

60

80

100

120

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

[k€]

yrs

EXT 1 EXT 2

EXT 3 Payback time

Figure 7-3: Representation of the payback time -x axis- and of the economic benefit -y axis- of each of the case

scenarios chosen for the external thermal insulation, Lecco

Page 138: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

114

The graph of the Figure 7-3 describes the payback time through a simple x-y diagram, on the y-axis it’s

represented the B€ economic benefit, while on the x-axis it’s represented the years corresponding to the

specific economic benefit. Through the description previously made, it’s easy to understand that the

year in which the value of B€ equal to 0, therefore there’s no benefit and neither a malus, corresponds to

the payback year, which represents the year in which the cost of the investment has been recouped.

The most convenient scenario is represented by the use of EPS with graphite, which as seen before

represents one of the cheapest material used for the thermal coating insulation interventions, to which

corresponds a payback time equal to 6 years. On the other hand the use of Wood fiber insulation material

will lead to the doubling of the payback years since in this case it will be equal to more than 12 years.

Concerning the environmental part, it has been decided to discover and understand the impact of the

retrofitting intervention on the GHG emissions of the buildings.

From the graph is easy to understand that the choice of the material has a small impact on the GHG

emission of a building, therefore choosing as insulation a synthetic material like EPS over a Rockwool

doesn’t mean necessarily that the choice would have a bigger impact on the environment. As said the

graph here presented was done just to have a comparison method between the environmental impact of

the materials used for the retrofitting work, so since the emission due to other important construction

site activities( i.e. transportation and application) have not been considered, the Figure 7-4 can’t give

the real output of how many years the retrofit will take in order to equalize the emission of the building

before the specific work.

7.2.2 Internal thermal insulation

In this paragraph it will be presented a retrofit operation that can be done in order to insulate a protected

façade from the inside of the specific building. As highlighted before in the §7.2.1, the peculiarity of

-10-505

10152025303540455055

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

[tonCO2]

yrs

EXT 1 EXT 2 EXT 3

Figure 7-4: Representation of the return year -x axis- and of the emission benefit -y axis- of each of the case

scenarios chosen for the external thermal insulation, Lecco

Page 139: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

115

this case study building is the presence of

an architecturally protected façade whose

appearances can’t be modified, and so for

this reason the thermal coating in the

previous intervention, could be applied on

the entire envelope exception made for the

protected façade of the old part of the

building which overlooks the main street.

Basically the intervention can be seen as an application of thermal insulation panels directly onto the

protected façade walls from the inside of the building, therefore no aesthetic restrictions have been

violated.

7.2.2.1 Design choice

As done for the external thermal insulation coating intervention, also in this case it has been considered

3 different intervention scenarios, done with 3 different thermal insulation materials. This is done

because one of the goal of the work here presented is to show the possible energy retrofit intervention

applicable to the specific building, studying the different scenario through various technical aspects.

The three different scenario taken in consideration, as said before, will have an equal thermal

transmittance set at 0.25 [W/(m2K)], they are presented through the Table 7.9.

Scenario Insulation λ d s Finishing Cost

Material [W/mK] [kg/m3] [cm] Material €/m2

INT. 1 Polyester Fiber 0.034 50 12 Plasterboard 37.87

INT. 2 Rockwool 0.035 70 12 Plasterboard 45.73

INT. 3 Calcium Silicate 0.039 115 14 Internal Paint 52.00

For the case scenario “INT. 1” the intervention is based

on the application of calcium silicate insulation panels,

through the use of adhesive and levelling layer, onto the

façade from the inner space. The choice of this

insulation material is given by the fact that the

installation will be done from the inside and the space

insulated is a classroom, therefore it will be very

important to contrast the high production of water vapor

coming from the students and guarantee a moderate IAQ. Calcium silicate based panels ensure a

comfortable indoor climate thanks to the active regulation of air humidity and at the same time warmer

Table 7.9: Internal thermal insulation scenario considered for the retrofit, Lecco

Figure 7-5: NW facade of the old part of the school building

Figure 7-6: Calcium silicate insulation panels

Page 140: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

116

interior surfaces. Their pH value of 10 acts as an anti-mold, therefore an excellent material for the

restoration of humid spaces. The calcium silicate-based panels are glued with adhesives that guarantee

the capillary connection between the wall and the panel. Of course, the final wall paint must also be of

similar quality because it is really a wrong painting that ruins the intervention and the high quality of

the material just laid.

The application method is different for the case scenario “INT. 2” and “INT. 3”, where the insulation

has been applied through a dry wall system. The insulation of the walls takes place with the installation

of a metal framework made of C-profile mullions and transoms which will guide the application of the

thermal insulation panels, covered by a dry plasterboard wall. The choice of rockwool for the case

“INT.2” is given by the will to give the possibility to exploit the Mass-spring-Mass effect of the dry

system presented, in order to consider a thermal-acoustic insulation scenario. In the “INT.3” it is

presented a low-cost solution defined by the use of an eco-friendly insulation material obtained by the

reuse of PET plastic, in form of polyester fiber insulation panels. This material is completely non-toxic

and it present itself as free from any allergic substance or harmful to health, resistant to molds, moisture,

rodents and insects, free from any substance and chemical treatment and free from resins and glues in

general.

7.2.2.2 Thermal inertia of the case scenario

As presented in the § 7.2.1.2, the envelope will be evaluated also for its summer performances through

the comparison of the thermal inertia of the wall for the solution proposed for each case scenario. In this

case since the intervention involves the application of material insulation from the inside of the spaces,

the thermal inertia of each scenario will be compared through both of the dynamic properties presented

before:

- Periodic thermal transmittance 𝑌𝑖𝑒 = 𝑈 ∗ 𝑓𝑑 [W/(m2K)];

- Internal thermal capacity Cip [kJ/(m2K)].

The Cip periodic internal thermal capacity, calculated as Yie, according to UNI EN ISO 13786 [56]

represents the capacity of a building component to accumulate the thermal loads coming from inside.

The higher the value of the Cip (mass placed inside), the greater the heat accumulation. The accumulation

of internal thermal loads by a wall makes it possible to keep surface temperatures at acceptable levels,

i.e. with fluctuations and limited values throughout the day, in favor the environmental comfort

conditions for summer.

It’s easy to see that the construction element used in the third case scenario has better dynamic

properties’ value, due to the higher thermal mass of the calcium silicate base panel insulation respect to

the dry wall system used in the second and in the third case scenario.

Page 141: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

117

Phase displacement Attenuation Performance

φ > 12 fd < 0.15 excellent

10 < φ < 12 0.15 < fd < 0.30 good

8 < φ < 10 0.30 < fd < 0.40 average

6 < φ < 8 0.40 < fd < 0.60 sufficient

φ < 6 fd < 0.60 mediocre

The Table 7.109 is given by the National Guide Lines [18], and it highlights that the retrofitted building

components in all of the case scenarios, and in all of the part of the building analyzed can be classified

as “excellent” from a summer thermal performance point of view. In addition to this it has to be said

that the National Guide Lines [18] sets also, the limit for the value of the periodic thermal transmittance

Yie equal to a maximum of 0.10 [W/(m2K)], therefore all the scenarios are below the limit.

7.2.2.3 Criticalities of the intervention

The application of thermal insulation material from the inside perimeter of a building, is a retrofit

intervention which brings to light a lot of risks and significant detail that have to be taken care of.

For this case study the application on the perimeter walls of thermal insulation from the inside space

gives birth to a number of critical thermal bridges, caused by the fact that two different modus operandi,

i.e. internal and external thermal coating of the envelope, have been considered coexisting for the retrofit

of the building.

In the Annexes all the possible thermal bridges occurring in this case of intervention have been studied,

and for each of them it has been presented a “simple” solution capable of limiting the value of the linear

thermal transmittance Ψ so that the construction elements solutions presented in the work comply with

the thermal transmittance -U- limitations imposed in the § 7.1.

The interventions made to reduce the impact of the thermal

bridges occurring, are the punctual application of internal

pre-finished insulation panels applied onto internal walls,

and the application on each floor of the old part of the

building of a suspended ceiling with the addition of a rigid panel insulation material. The pre-finished

insulation is made of pre-coupled boards of PF (polyester fiber) and plaster board with an integrated

vapor barrier, while the suspended ceilings is made of a rigid rockwool panel with a plasterboard

finishing. In order to have a more comprehensive view of the economic investment needed for the global

intervention, all of the processing techniques listed before, i.e. the thermal bridge solution interventions,

have been taking into account in the global cost of investment.

7.2.2.4 Heating consumption savings

Scenario fd φ Yie Cip

- [h] [W/m2K] [kJ/m2K]

Base case 0.147 11.78 0.341 79.9

INT. 1 0.064 14.7 0.014 18

INT. 2 0.063 14.92 0.015 18.3

INT. 3 0.049 17.14 0.012 29.2

Table 7.10: Dynamic properties of the case scenario Table 7.11: Limit values set by standard [18]

Thermal bridge Intervention

Cost

€/m2 €

Suspended insulated ceiling 29.38 19727.49

Insulated dry wall 25.37 4262.16

Table 7.12: Cost of thermal bridge intervention

Page 142: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

118

In this paragraph it will be analyzed the perks of doing the specific intervention explained in the previous

paragraph. In this case the intervention is the application of an internal thermal coating onto the protected

façade (as presented in § 7.2.2) and the perks are represented by the energy and economic savings and

the GHG emission reductions.

Scenario

Heating

Primary Energy Energy cost GHG emissions Reduction

[kWh/m2y] [€] [tonCO2] [%]

Base 233.61 17974.10 45.04 -

Int. Insulation 139.64 10774.78 27.00 40%

From the Table 7.13 is easy to understand the profits, speaking about heating consumptions, coming

from the application of the thermal insulation as previously explained. The reduction obtained through

the application of the thermal insulation is equal to 40% of the initial value, this refers to all of the values

presented in the table, so for the: primary energy, energy cost and the GHG emissions. This results

brings to light the importance and how easy it is to reduce the impact of a building through simple and

aimed interventions, such the coating of the envelope of the case study building.

7.2.2.5 Economic impact

The difference between the cost of the different case scenarios is small, as seen in the Table 7.15,

therefore the different use of the insulation material presented won’t affect the total cost of the

investment.

From the Table 7.15 and Table 7.14 is easy to understand that the cost, in euro, bore only for the

intervention needed to withstand the thermal bridges has a similar amount respect to the cost bore for

the insulation of the external wall for each case scenario. Actually in this case the cost of the works

related to the thermal bridges account for almost 45% of the total investment needed to withstand the

studied intervention, for this reason the amount needed to bear the total investment of the intervention

doesn’t change depending on the insulation material chosen for each case scenario.

For the case study presented the retrofit intervention here showed of the application of thermal insulation

onto the perimeter wall from the inner spaces is not a standalone intervention but it has to be combined

with the application of the external thermal coating insulation presented in the § 7.2.1.

Table 7.13: Heating reductions obtained with the internal thermal coating, Lecco

Scenario Insulation Cost

Material €/m2 €

INT. 1 Polyester Fiber 37.87 29803.30

INT. 2 Rockwool 45.73 31010.74

INT. 3 Calcium Silicate 52.00 31972.69

Thermal bridge Intervention

Cost

€/m2 €

Suspended insulated ceiling

29.38 19727.49

Insulated dry wall 25.37 4262.16

Table 7.14: Cost of thermal bridge intervention Table 7.15: Cost of the different case scenarios intervention

Page 143: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

119

For this reason it has been decided to create 3 different

case scenario presenting the combination of the two

intervention presented until now. The first scenario

represents the cheapest and most used combination of

the materials used for the insulation from the outside and

the inside, while the third one represents the most expensive and performing combination.

In order to have an economic view of the proposed interventions it has been decided to analyze the

payback time of the investment, based on the intervention’s cost and the energy cost savings obtained

through the years, in order to make this case more global as possible some hypothesis and simplifications

had to be done. The cost of the intervention was calculated in a simple straightforward way, considering

the cost of the materials and of the installation taken from the “Prezziario Lombardia”, which is the

pricelist for civil works in the Lombardy region, summed with a fixed percentage of increase due to

expenses directly related to the works done for the preparation and use of the construction site (i.e.

scaffoldings, preparation of the land, etc.).

The graph of the Figure 7-7 represents the different economic benefit coming from each of the case

scenarios presented in the Table 7.16.

The case scenario 1, which represents the cheapest one, has a payback time equal to almost 9 year, this

means that before 10 years from the end of the construction the cost of the investment will be equalized

and the money saved thanks to the reduction of the energy needs will go directly into the cashflow of

the case study building. On the other hand the case 3, which represents the most expensive one, has a

payback time equal to 14 years, therefore even the most expensive case scenario has a decent payback

time, highlighting the great benefits descending from the retrofit intervention regarding the vertical

-100

-80

-60

-40

-20

0

20

40

60

80

100

120

140

160

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

[k€]

yrs

INT 1 INT 2

INT 3 Payback time

Table 7.16: Different combination case scenarios

Scenario

Insulation

Material

EXT. INT.

EXT+INT 1 EPS with graphite Polyester Fiber

EXT+INT 2 Rockwool Rockwool

EXT+INT 3 Wood fiber Calcium Silicate

Figure 7-7: Representation of the return year -x axis- and of the emission benefit -y axis- of each of the case

scenarios chosen for the internal thermal insulation

Page 144: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

120

opaque envelope of the case study building.

7.2.3 Attic Insulation

The old part of the case study school building presents

an unheated space between the roof and the last heated

slab, which is easily accessible. In this paragraph it will

be proposed the insulation of the last heated slab of the

old part of the building through the use of insulation

materials in form of rolls and panels put on the floor of

the attic, so that the insulation performs its benefits only

for the heated space, avoiding heating unused spaces

such as the attic itself. On the other hand, as seen in the general description of the building in the chapter

2, the recent part of the building constructed in the late ’60 doesn’t have this type of space, but the last

heated slab corresponds to the roof. In this case it has been proposed a non-invasive intervention

consisting in the application of thermal insulation onto the last heated slab from the inside space of the

building. This means that in both part of the building it is proposed the thermal insulation of the last

heated slab without intervening on the roof structure.

7.2.3.1 Design choice

The positive aspect of the building that has to be exploit in this case, is the presence in the old part of an

unheated space between the roof and the last heated slab, defined as attic, and the fact that it is easily

accessible, even though unfortunately this space is not present in the recent part of the building. The

attic can be used in two different ways, as a buffer zone which means that it will be considered as an

unusable space and on the other hand it can be used as storage or functional room. For this reason it has

been decided to present two different feasible intervention for the thermal insulation of the attic, one

will concern only the thermal insulation of the last heated slab while the other one will include the

refurbishment of the flooring of the attic, so that this space can be qualified as usable. On the other hand

both of the interventions will be combined with the thermal insulation of the last heated slab of the recent

part of the building from the inside of the building, through the use of a suspended ceiling.

The choice of mineral wools is given by the fact that the insulation is going to be applied in inside spaces

therefore in this case the use of man-made vitreous fiber guarantees the use of a non-toxic and bio

soluble material which will not harm the users. The application of the insulation will be done on the last

floor therefore it will be useful to exploit the thermal and acoustical insulation of the mineral wools.

Scenario Insulation λ d s Flooring Cost

Figure 7-8: Attic in the old part of the building

Page 145: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

121

In a technical point of view,

considering the old part of the

building, the first intervention can be

properly described as the thermal

insulation of the last heated slab

through the simple and only application on the slab extrados of a roll of rockwool insulation, so that the

attic space and its accessibility can be exploited at the lowest price and labor. In the second option it is

proposed the refurbishment of the attic space, through the use of a glass wool rigid insulation topped

with a dry system flooring, so that the surface can be walkable and the space classified usable.

The intervention proposed for the

slab of the recent part of the

building consists on the insulation

of the last heated slab of the

structure through the application

of a mineral material thermal insulation protected from a plasterboard suspended ceiling applied directly

on the slab intrados.

The choice of rockwool rolls is driven by the fact that it’s the most used intervention whenever there is

a not walkable attic which is accessible and allows an easy manual laying, even though in some cases

wood fiber can also be useful (especially for insulation against summer heat). It is sufficient to lay on

the floor the insulation that may be protected by means of a vapor barrier placed between the insulation

and the floor itself.

For the refurbishment of the attic floor the intervention consists on the application of a separation layer

between the smoothed surface and the rigid glass wool insulation, laid through the use of a wooden

support system, on top of which is needed to lay a walkable layer which will also work as load

distribution. The flooring is made through the use of a dry system composed of a gypsum fiber double

levelling layer topped by a gypsum flooring.

Material [W/mK] [kg/cm3] [cm] Material €/m2

ATT. 1 Rockwool

roll 0.038 26 0.17 - 14.57

ATT. 2 Glasswool

panel 0.033 125 0.14

Dry system

70.24

Table 7.17: Case scenarios of attic retrofit in the old part of the building

Scenario Insulation λ d s Finishing Cost

Material [W/mK] [kg/cm3] [cm] Material €/m2

ATT. 1 Rockwool

panel 0.034 60 0.15 Plasterboard 62.7

ATT. 2 Glasswool

panel 0.032 75 0.14 Plasterboard 77.7

Table 7.18:Case scenarios of attic retrofit in the recent part of the building

Figure 7-9: Roll insulation of the attic

Dry flooring

Insulation

Support system

Figure 7-10: Rigid panel attic insulation

Page 146: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

122

7.2.3.2 Heating consumption savings

In this paragraph it will be analyzed the perks of doing the specific intervention explained in the previous

paragraph. In this case the intervention is the application of an internal thermal insulation onto the slab

extrados, for the old part of the building, and on the slab intrados for the recent one (as presented in §

7.2.3) and the perks are represented by the energy and economic savings and the GHG emission

reductions.

Scenario

Heating

Primary Energy Energy cost GHG emissions Reduction

[kWh/m2y] [€] [tonCO2] [%]

Base 233.61 17974.10 45.04 -

Attic Insulation 202.79 15647.17 39.21 13%

From the Table 7.19 is easy to understand the profits, speaking about heating consumptions, coming

from the application of the thermal insulation as previously explained. The reduction obtained through

the application of the thermal insulation is equal to 13% of the initial value, this refers to all of the values

presented in the table, so for the: primary energy, energy cost and the GHG emissions. The percentage

of energy savings is in line with the thermal losses analysis presented previously in § 5.1.5, and is quite

reasonable considering that this intervention will concern a quite small surface area.

7.2.3.3 Economic Impact

The cost of the intervention was calculated in a simple straightforward way, considering the cost of the

materials and of the installation taken from the “Prezziario Lombardia”, which is the pricelist for civil

works in the Lombardy region, summed with a fixed percentage of increase due to expenses directly

related to works needed to be done in order to make the application of the thermal insulation possible

(i.e. scaffoldings, preparation of the land, etc.).

The graph presented in the Figure 7-11 represents the economic analysis of the two case scenarios

presented in the § 7.2.3.1. As explained before it has been considered a cost percentage increase due to

construction site works, therefore for this analysis it has been considered a 10% increase of the cost for

the case scenario of rockwool and 20% for the second one of the glass wool taking in consideration the

fact that the second intervention involves an higher labor rate. The results highlights the economic

benefit of the first case scenario, in which the insulation is made with rockwool material in both part of

the building, as matter of fact the payback time is in this case equal to 7 years while for the second

scenario it doubles up to almost 14 years. This means that the scenario has to be chosen considering the

importance of the refurbishment over the cost of the intervention.

Table 7.19: Heating reductions obtained with the attic thermal insulation

Page 147: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

123

7.2.4 Roof insulation

In this section it will be analyzed the possible case scenarios concerning the refurbishment of the roofing

structure of the two part of the cases study building. As it can be seen from the Figure 7-12 and the

Figure 7-8 the two roofs of the parts of the building are completely different

-40

-30

-20

-10

0

10

20

30

40

50

60

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

[k€]

yrs

ATTIC 1 ATTIC 2

Payback time

Figure 7-11: Representation of the return year -x axis- and of the economic benefit -y axis- of each of the case

scenarios chosen for the attic insulation

Figure 7-12: Google earth capture of the roof of the two parts of the case study school building

Page 148: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

124

As matter of fact as already highlighted in § 7.2.3 the old part of the building presents an attic space

placed on top of the last heated slab which is covered by a clay tiles hip roof supported by a wood beam

structure, on the other hand the recent part of the building has a typical concrete slab structure roof with

on top a corrugated metal sheet. Therefore it will be presented different case scenarios for this

intervention applicable on each part of the building roof.

This intervention is usually applied whenever the roof is directly in contact with the heated space, i.e.

in the recent part of the building, or/and when there’s the will to transform an attic into an habitable

space, i.e. the attic space in the old part of the building. This means that the intervention for the old part

of the building has to be combined with the insulation of the attic slab presented in the § 7.2.3.1, in order

to insulate all the exposed elements.

7.2.4.1 Design choice

The first design choice has been the decision of neglecting the possibility of refurbish the roofs

transforming them into green roofs or in ventilated ones.

The option of the green roof has been neglected due to the high costs of the intervention and the fact

that it will represent a peculiar work therefore it’s applicability in a large scale would be missing, not

considering also the fact that it will completely transform the exterior of the existing building.

In ventilated roofs the natural cavity, which clearly separates the covering layer from the underlying

insulating layer, facilitates the activation of “ascensional convective motions”, which subtract most of

the heat that would otherwise be transmitted to the underlying layers, and allows moisture to escape

without compromising the thermal insulation power of the underlying layers and the air space itself. In

order to activate this mechanism, the outside air must enter the gap in the gutter and must exit the ridge

through a vent element. In this way in winter the ventilation leaves the insulating material dry, avoiding

condensation, in summer the fresh air, which penetrates from the eaves line, heats up in the air space

and becomes lighter and comes out from the ridge, subtracting heat from the structure. Ventilated roofs,

compliant with the UNI 9460 and UNI 8627 standards, can produce a lowering of the temperature after

the hours of summer insolation and improve the thermal comfort of the attic, especially in cases where

it has been chosen to renovate it to transform it into an attic.

Generally ventilated roofs are applied to make the attic rooms habitable, so considering that the old part

of the building presents an uninsulated attic space, it will be impossible to convert it to habitable,

therefore this choice has been discarded. Concerning the recent part of the building, as said before the

ventilated roof must have a minimum flow section in order to activate the convective motions (UNI

9460) given by the thickness of the air cavity and the inclination and length of the roof, so considering

that the roof has a slope of approximately 5% an high air cavity thickness would be needed, defining

this solution unfeasible.

Page 149: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

125

For this reason it has been decided to propose a requalification of the existing roof of both of the parts

of the building, consisting on the application of a thermal insulation layer, included all the protection

materials, underneath the existing roof cover. This means that it will be temporarily removed the roofing

covering structure and then re-placed on top of a new supporting structure laid on a new insulation layer

consisting of a different thermal insulation material for each case scenario.

As it can be seen from the Table 7.20 the different case scenarios change only on the type of thermal

insulation material used under the roof structure. As insulation materials it has been decided to present

the same ones used throughout the previous proposed interventions.

7.2.4.2 Thermal inertia of the case scenario

For this intervention, considering that it is based on the application of material insulation on the outside

of the envelope, the thermal inertia of the different scenarios will be compared based only on the

different values of Periodic thermal transmittance Yie defined by the different material used for each

scenario. Here are presented the values defining the dynamic properties of the different case scenarios

previously defined in the Table 5.2.

Scenario

Old part Recent part

fd φ Yie fd φ Yie

- [h] [W/m2K] - [h] [W/m2K]

ROOF 1 0.915 2.87 0.181 0.073 13.5 0.015

ROOF 2 0.515 8.18 0.1 0.048 17.18 0.01

ROOF 3 0.24 12.18 0.049 0.028 20.14 0.006

The lower is the value expressing the attenuation fd and the lower is the amplitude of the thermal flow

entering the building component, and at the same time the lower is the value of the periodic thermal

resistance Yie and the higher are the value of the phase displacement φ and the damping. In addition to

this it has to be said that the National Guide Lines [18] sets also, the limit for the value of the periodic

thermal transmittance Yie equal to a maximum of 0.10 [W/(m2K)], therefore all the scenarios are below

the limit.

It’s easy to understand that the results related to the old part of the building are not satisfactory. This is

Intervention Old part Recent Part

Scenario Insulation λ d s Cost s Cost

Material [W/mK] [kg/cm3] [cm] €/m2 [cm] €/m2

ROOF 1 EPS 0.031 40 14 74.27 13 69.53

ROOF 2 Rockwool 0.036 140 16 89.98 15 89.36

ROOF 3 Wood fiber 0.038/0.042 145/205 17 96.78 17 106.78

φ fd Performance

φ > 12 fd < 0.15 excellent

10 < φ < 12 0.15 < fd < 0.30 good

8 < φ < 10 0.30 < fd < 0.40 average

6 < φ < 8 0.40 < fd < 0.60 sufficient

φ < 6 fd < 0.60 mediocre

Table 7.21: Dynamic properties of the different case scenarios Table 7.22: Limit values set by standard [18]

Table 7.20: Case scenarios of the roof insulation intervention in Lecco

Page 150: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

126

due to the fact that roof structure is supported by punctual wooden beams that

are not considered in the thermal analysis of the structure, therefore the only

layer opposed to the thermal dispersions is represented from the new inserted

thermal insulation layer. In this case it’s more clear the difference given by

the choice of different thermal insulation, as matter of fact only the

application of a wood fiber insulation layer would guarantee good thermal inertia properties and

therefore would represent the optimal technical solution.

7.2.4.3 Heating consumption savings

In this paragraph it will be analyzed the perks of doing the specific intervention explained in the previous

paragraph. In this case the intervention is the application of an internal thermal insulation onto the slab

extrados, for the old part of the building, and on the slab intrados for the recent one (presented in § 7.2.4)

and the perks are represented by the energy and economic savings and the GHG emission reductions.

Scenario

Heating

Primary Energy Energy cost GHG emissions Reduction

[kWh/m2y] [€] [tonCO2] [%]

Base 233.61 17974.10 45.04 -

Roof Insulation 205.41 15849.68 39.71 12%

From the Table 7.24 is easy to understand the profits, speaking about heating consumptions, coming

from the application of the thermal insulation as previously explained. The reduction obtained through

the application of the thermal insulation is equal to 12% of the initial value, this refers to all of the values

presented in the table, so for the: primary energy, energy cost and the GHG emissions. The percentage

of energy savings is in line with the thermal losses analysis presented previously in § 5.1.5, and is quite

reasonable considering that this intervention will concern a quite small surface area.

Comparing the results here presented with the one given for the attic insulation in § 7.2.3.2 it’s possible

to see that the two interventions basically give the same savings output but they need a much different

amount of money to be done, the choice of choosing one over another has to be done carefully analyzing

all the pros and cons of each of them.

7.2.4.4 Economic Impact

The cost of the intervention was calculated in a simple straightforward way, considering the cost of the

materials and of the installation taken from the “Prezziario Lombardia”, which is the pricelist for civil

works in the Lombardy region, summed with a 20/25 % percentage of increase due to expenses directly

related to works needed to be done in order to make the application of the thermal insulation possible

Old Part Performance

ROOF 1 mediocre

ROOF 2 average

ROOF 3 good

Table 7.23: Performances

of the old part roof

Table 7.24: Heating reductions obtained with the attic thermal insulation in Lecco

Page 151: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

127

(i.e. scaffoldings, preparation of the land, etc.).

The graph in the Figure 7-13 describes what has already been said before, that this is an high cost

intervention, therefore before pursuing this type of works it has to be considered all the other low cost

scenario previously presented in the attic insulation intervention, § 7.2.3. As matter of fact the solution

ROOF 1 which represent the cheapest case scenario has a payback time equal to 15 years, this remarks

the high costs of this type intervention.

7.2.5 Basement Insulation

In this section of the work presented it will be analyzed the insulation, from the inner spaces, of the

unheated space underneath the heated space of the case study building.

As already seen in § 2.2/3.2 the recent part of

the building does not have any unheated space

under the classrooms, as matter of fact beneath

them is located the gym which takes up the

ground and the underground floor, while on the

other hand the old part of the building presents

an unheated basement located underground

directly underneath the entrance and the

classrooms of the ground floor level. The ceiling

of the basement located in the old part of the building is visible from the Figure 7-14. It’s easy to

understand that the option of applying thermal insulation onto the basement’s ceiling from the inside

it’s not an everyday procedure but it takes an high amount of effort.

Figure 7-13: Representation of the return year -x axis- and of the economic benefit -y axis- of each of the case

scenarios chosen for the roof insulation

Figure 7-14: Basement of the old part of the building

-80

-60

-40

-20

0

20

40

60

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

[k€]

yrs

ROOF 1 ROOF 2

ROOF 3 Payback time

Page 152: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

128

7.2.5.1 Criticalities of the intervention

As previously said, this intervention involves only the old part of the building, where the critical analysis

is focused on the ceiling of the basement, which is made of a brick vault.

It’s clear that the application of thermal insulation material from

the basement itself onto the curved ceiling it’s an unfeasible

intervention, a solution could be the one of crafting a tailored

aluminum sub-structure which will help the positioning of the

curved flexible thermal insulation material, as it can be seen in

Figure 7-15. This solution would end up to be way too expensive

and complex than all of the other retrofit intervention proposed,

as matter of fact through the thermal losses chart presented in the

§ 5.1.5 it’s possible to see that the heat dispersed through the basement ceiling accounts for the 4% of

the total dispersion losses of the building through the envelope, therefore this intervention has been

neglected.

So considering that the insulation can’t be applied from the unheated space, the only remaining solution

would be the one of applying the thermal insulation onto to the floor of the ground level, so that the heat

would stay in the heated zones without dispersions towards the unheated underground. But also this

scenario is complex, due to the fact that the structure of the ground floor slab is made of a brick barrel-

vault constructed in the beginning of the 1900 (as all the old part of the building), therefore it will be

difficult to interact with it.

An option could be the one of removing the existing floor and the concrete levelling screed underneath

it in order to replace it with a thermal concrete levelling layer with on top a thermal insulation layer and

a new flooring system. This option will interfere with the structure of the vault slab, therefore a structural

analysis has to be done before going further in the study of the proposed solution, this means that it will

be necessary to strengthen the existing slab with a composite slab. Clearly this is an unfeasible

intervention for the purposes of this thesis work therefore it won’t be taken in consideration.

The last chance would be the one of applying thermal insulation directly onto the existing floor,

enhancing its thermal properties without increasing the load borne from the slab. This could be done

with the application of innovative thermal insulation material with an high thermal conductivity such as

Aerogel, so that the limit thermal transmittance imposed by the standard can be achieved with a low

thickness insulation layer.Here is presented how the new slab of the ground floor level will look, after

the retrofit proposed with the aerogel insulation. Unfortunately the problem in this case is represented

from the high costs of the material, as matter of fact the aerogel solution presented would cost

approximately 250 €/m2 just for the materials, without taking in consideration the costs related to the

Figure 7-15: Vault aluminum structure

Page 153: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

129

application, and the resulting additional costs due to the all the craft work needed for the joints

connecting the new floor with the existing vertical walls

Insulated Ground floor slab 0.37 U [W/m2K] 0.32

Component Thickness Conductivity Resistance

[-] [m] [W/mK] [m2K/W]

Slab 0.23 0.71 0.324

Levelling layer 0.06 1.4 0.043

Existing floor 0.02 0.72 0.028

Aerogel panel insulation 0.035 0.015 2.333

Vapor barrier 0.003 0.17 0.018

Floating Floor 0.02 0.6 0.033

It’s unreasonable to think that a school may look to an high cost solution like this, considering also the

small impact it would have on the energy savings (§ 5.1.5), therefore also this scenario has been

neglected.

The goal of this thesis work is to present feasible and low-key retrofit intervention applicable to a large

scale of buildings, with similarities to the case studies presented, therefore as briefly explained with

some examples it has been decided not to present any case scenarios for this type of intervention,

considering it unrelated to the topic of this work.

7.2.6 Ground-contact element insulation

The last intervention analyzed is the one taking in consideration the thermal insulation of the structure

elements that are in contact with the ground. The old part of the case study building presents an unheated

underground level used as storage, therefore it will be useless to think to insulate the walls and the floors

of this space considering that insulating an unheated space won’t guarantee any evident thermal benefit

for the upper heated spaces. On the other hand the recent part of the building presents a gym which takes

up two floor of the building, the ground floor and also the underground floor. This means that the

insulation of the walls and of the floor in contact with the ground would directly affect the energy needed

to heat the space and thus decreasing the consumption of gas.

The underground level of the recent part of the case study building is a gym, and as already seen in §

2.3.3.1 the heating system is independent and completely detached from the central heating system of

the building. Therefore it has been proposed to insulate all the partitions of the gym of the school in

order to create a box, in which the system can be turned on only for a couple of hours and then the heat

would be kept into the heated box without interaction with the boundary conditions.

Figure 7-16: Aerogel horizontal insulation

Page 154: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

130

7.2.6.1 Design choice

The intervention will lean towards the complete thermal insulation of the heated space classified as a

gym, so it won’t be affected from the surrounding anymore. This means that the insulation work will be

separated in:

- thermal insulation of the ground-contact slab;

- thermal insulation of the ground-contact walls;

- thermal insulation of the ceiling adjacent to an heated space.

From the heat losses diagram presented in § 5.1.5 it can be seen that the heat dispersions attributed to

the inefficient thermal properties of the structure elements of the gym, is relatively low and it can be

accounted to more or less 3 % of the total dispersions of the envelope of the entire building. For this

reason this type of intervention is actually recommended whenever there’s an independent space, as this

one, and there’s the will to upgrade it making it self-sustained.

The fact that this intervention most reasonably won’t have a big impact on the energy consumptions of

the building, has led the design choice of the intervention previously listed. As matter of fact the choice

has been directed towards low cost solutions present on the building market right now, without taking

in consideration multiple case scenario as done before.

Component Insulation λ d s Finishing Cost

Material [W/mK] [kg/cm3] [cm] Material €/m2

Ground-contact slab XPS insulation 0.032 35 4 Linoleum flooring 25.24

Ground-contact wall Polyester fiber 0.034 50 6 Dry wall system 31.35

Heated ceiling EPS 0.031 33 4 Suspended ceiling 23.34

For the thermal insulation of the floor facing the ground, it has been proposed to cover the actual flooring

with a rigid panel of XPS insulation, in order to guarantee excellent thermal properties combined with

mechanical resistance, on top of which it will be laid a concrete screed as support to the new flooring

system. In this way it will be created a barrier between the floor of the heated space and the underlying

ground, guaranteeing the appropriate amount of mechanical resistance needed in high impact

environment such as the gym.

For the wall in contact with the ground it has been proposed a simple solution, already analyzed before,

consisting on the application of thermal insulation panels made of polyester fiber directly onto the

vertical walls, protected by a dry wall system. It is obtained from the recycling of PET plastics, free

from any substance allergic or harmful to health, unaffected by mold, moisture, rodents and insects, free

of any substance and chemical treatment and free of resins and glues in general. The use of this material

is really important in this case considering the possible humidity coming from the adjacent ground, and

the fact that the users of this space will be children.

Table 7.25: Component solutions for each of the presented energy retrofit interventions

Page 155: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

131

Concerning the insulation from the above heated space represented by classrooms it has been decided

to adopt the economic choice of a plasterboard suspended ceiling with the application of rigid panels of

EPS insulation, in order to guarantee high thermal insulation at a low cost. In this case it could have

been considered also the use of a mineral wool insulation suspended ceiling in order to separate the two

environment also in terms of acoustics, since the noise coming form the gym could bother the students

located on the above classrooms, but the high cost of this particular solution combined to the low energy

impact of the entire intervention has classified this type of intervention unrealistic for the case study

represented.

7.2.6.2 Heating consumption savings

In this paragraph it will be analyzed the pros of doing the specific intervention explained in the previous

paragraph. In this case the intervention is the application of thermal insulation onto the perimeter

partitions of the gym located in the recent part of the building (presented in §7.2.6), and the perks are

represented by the energy and economic savings and the GHG emission reductions.

Scenario

Heating

Primary Energy Energy cost GHG emissions Reduction

[kWh/m2y] [€] [tonCO2] [%]

Base 233.61 17974.10 45.04 -

Gym Insulation 223.66 17592.37 43.24 4%

From the Table 7.26 is easy to understand the profits, speaking about heating consumptions, coming

from the application of the thermal insulation as previously explained. The reduction obtained through

the application of the thermal insulation is equal to 4% of the initial value, this refers to all of the values

presented in the table, so for the: primary energy, energy cost and the GHG emissions. As previously

said, this is in accordance with the heat losses analysis presented in § 5.1.5, therefore the low energy

impact was already expected.

7.2.6.3 Economic impact

The cost of the intervention was calculated in a simple straightforward way, considering the cost of the

materials and of the installation taken from the “Prezziario Lombardia”, which is the pricelist for civil

works in the Lombardy region, summed with a fixed percentage of increase, equal to 10 %, due to

expenses directly related to works needed to be done in order to make the application of the thermal

insulation possible (i.e. scaffoldings, preparation of the land, etc.).

Table 7.26: Heating reductions obtained with the thermal insulation of the gym

Page 156: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

132

The Figure 7-17 shows the payback time considered for the investment needed in order to complete the

retrofit work presented, of complete insulation of the gym located in the recent part of the building. The

return year for this investment is quite high, as it sums up to almost 30 years. This is due to the fact the

energy consumption reduction given by this work is relatively low, while the cost is actually high,

considering that it involves an high amount of surface. For this considerations this intervention can be

considered as an high risk investment, and the choice must be dictated by motivations that overcome the

economic disadvantages here presented.

7.2.7 Glazing optimization

Through the heat losses graph presented in§ 5.1.5, it’s easy to understand the impact that the glazing

surfaces of both of the parts of the building have on the global heat losses of the building coming from

the thermal inefficiency of the envelope. The losses coming from the windows of the old part of the

building account for almost 10% of the envelope’s losses and at the same time the ones of the recent

part account for another 10% of the losses, therefore the two sum up 20% of the losses, without

considering the infiltration losses strictly connected to the presence of leaky windows.

For this reason it has been decided to consider the complete refurbishment of the glazing areas of the

building, which includes the removal of the existing windows and the application of new insulating

windows.

-30

-20

-10

0

10

20

30

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

[k€]

yrs

Gym insulation Payback time

Figure 7-17: Representation of the return year -x axis- and of the economic benefit -y axis- of the work

representing the insulation of the gym

Page 157: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

133

7.2.7.1 Design choice

The design choice process in this particular case was really straight forward, as matter of fact a the end

of a first phase of data collection it has been decided to refurbish

the old windows of both of the building, replacing them with new

double glazing windows with a frame made of PVC.

This choice has been made considering the low prices of this

solution and the high thermal efficiency that can be achieved even

with market standard solution. In addition to that the PVC frame

comes in a great variety of color and texture, therefore it will be

really simple to recreate the image of the existing wood for the old

part of the building, thus not altering the aesthetic value of the

facades, and the aluminum for the recent part.

Technically the solution proposed consists of a double glazing

window, composed of 33.1/ 16 AR/ 33.1 LE. This means that is

made of a first security laminated float of 6 mm, with a 16 mm of

cavity filled with argon, and a final thermal and low emissivity float of 6 mm. Here it has been presented

the summary table that sums up all the thermal characteristic of the new glazing element:

Glazed Surface

Component Thickness

[-] [mm]

Low E float 6

Argon 16

Clear float 6

The thermal transmittance of the glazing proposed has been calculated through the UNI EN ISO 10077-

2 [43], as it can be seen in the annexes, with the additional help of the Pilkington spectrum online

software.

The choice of the low emissivity glass is given by the fact that with the use of this glasses, it is possible

to reflect inward part of the heat emitted as thermal radiation from the bodies contained in the inhabited

areas, considerably reducing the heat loss. The heat is reflected by the plate treated analogously to what

happens with a mirror that reflects purely luminous radiation.

The reduction of the radiative component of the double glazing is obtained by modifying the

spectrophotonic characteristics of the glasses, by means of the molecular deposition of particularly

selective oxides and metals capable of reflecting the purely thermal radiation. The low emissivity glass

is nothing more than an insulating glass, consisting of two or more plates spaced by one or more spacer

Frame Net U-value Net R-value

Type Transmittance Percentage [W/m2K] [m2K/W]

[-] [W/m2K] % 1.18 0.90

PVC 1.29 33

Figure 7-18: Chosen PVC glazing

Table 7.27: Glazing’s component thermal properties. Thermal transmittance of the proposed windows

Page 158: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

134

profiles. An insulating glass differs from a simple glass, because it is endowed with a particular

treatment, thanks to which it is possible to contain the dispersions.

Concerning the design of the window the proposed intervention is only the one just presented, but in

this work it has been decided to distinguish another energy retrofit work consisting on the refurbishment

of the od glazing area, as previously explained, and the installation of a mechanical ventilation system.

This is done in order to differentiate a stand-alone work on the windows, which will take in consideration

the only refurbishment of the glazing, from an integrated energy retrofit work in which the optimization

of the envelope is combined with technological solution assigned to the improvement of the internal

condition of the spaces.

The attention to indoor air quality in schools is even shown by the development of many guidelines and

regulations concerning the appropriate ventilation rates to be used for these kind of spaces. A common

experience, is that a big difference can be observed between required and real ventilation rates in these

so sensitive buildings. Many studies in the field have shown that ventilation in classrooms is too poor.

One reason is that often schools do not have mechanical ventilation system; furthermore, when

mechanical systems are installed, often their bad control leads to very expensive operation, so managers

are discouraged to use them, because big ventilation rates means big energy expense and noise, mainly),

taking care of safety and energy saving and having special attention to provide easy maintenance.

The design choices considered now “required” for an efficient home for winter heating and summer air

conditioning include controlled mechanical ventilation with heat recovery to guarantee the correct air

exchange without “ever” opening windows (and therefore saving on heating).

In this case study it will be analyzed a controlled mechanical ventilation with double flow heat recovery:

the stale air extracted from the humid rooms and the air taken from the outside, previously filtered, are

conveyed into a heat recovery unit that ensures the preheating of the renewal air avoiding the

contamination of the two flows. The most common type is the double flow controlled mechanical

ventilation which is characterized by having a double ventilation system, formed by separate distribution

channels:

- A duct controls and regulates air intake;

- the other is dedicated to extract air;

- the air flows in the two ducts are managed by separate electric fans.

The advantages of controlled mechanical ventilation systems with double-flow heat recovery are many

compared to the single-flow version. The main one is the ability to treat, filter, heat or cool outdoor air,

guaranteeing constant exchange and recovery of heat from exhausted air. The heat recovery allows you

to take advantage of all the advantages of ventilation, ensuring the low energy consumption of the

building. In case of restoration this solution would reduce consumption and increase the energy

classification of the building.

Page 159: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

135

Cross-flow heat recovery units are static recovery

systems, i.e. they have no moving elements. They

are characterized by the coupling of usually metal

plates, even if there are recoveries with paper

plates, suitably treated to stiffen them and make

them self-extinguishing. In the case of cross-flow

recovery with metal plates, it is possible to find on

the market units with plates in natural aluminum,

aluminum coated with special epoxy paints in case

of use in corrosive environments, but also with

stainless steel plates used in all those situations where maximum internal hygiene of the machine is

required or where the air passing through it has particularly high temperatures (200 ° C). Finally, in

some cases, to reduce costs or in the case of aggressive environments, plastics or even glass can be used.

The spacing between the plates is variable depending on the type of use. The heat transfer inside a cross-

flow recovery takes place through the heat transfer by convection, on both sides of the plate, and by

conduction through the thickness of the plate itself. Since the convective coefficients are much smaller

than the thermal conductivity of the plates, it follows that the efficiency of the heat exchange is not

substantially influenced by the thickness and the material with which the heat exchanger is made.

Usually the plate heat recovery units are equipped with a bypass damper which excludes part or all of

the outside air from the recovery treatment. This method of reducing the flow rate, is also used in case

of frost risk in winter, or much more simply to take advantage of free-cooling or direct-cooling, ie in all

those situations where the outside air has temperature conditions such as to be able to use it directly to

heat or cool the rooms, without requiring any further treatment. They are systems that allow yields of

40-70%, with the possibility of reaching even 80% in the case of use of heat recovery units with

countercurrent air flows, as it will be used in the case study.

Usually this efficiency is calculated as the ratio between the real and the theoretical difference between

the inlet and outlet temperatures (supposing that the flows have equal masses):

𝜂 =△𝑇𝑟𝑒𝑎𝑙

△𝑇𝑡ℎ=

𝑇𝑖𝑛𝑙𝑒𝑡−𝑇𝑒𝑥𝑡

𝑇𝑖𝑛𝑡−𝑇𝑒𝑥𝑡

To understand the importance of the heat recovery, here it has been brought a practical example:

- Externa air: -5 °C;

- Internal air: 20 °C;

- Inlet air: to determine.

∆Tth = 20 – (-5) = 25 °C; ∆Treal = η*(∆Tth) = η* 25 → Tinlet = η* 25 + Text.

So if it is considered an heat recovery with a η = 80%, than:

Figure 7-19: VMC's heat recovery scheme

Page 160: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

136

Tinlet = η* 25 + Text = 0.8* 25 + (-5) = 15°C.

With this simple example it’s easy to understand the impact of the presence of an heat recovery system,

which will help the existing generation system bear the heating load of the case study building.

For the reasons above explained, it has been decide to present two separate chances of glazing

optimization: one representing the refurbishment of the existing windows, and the other one including

also the installation of a controlled mechanical ventilation system “CMV”.

Scenario Windows Frame U Ventilation Cost

# glazing Material [W/(m2K)] Type €/m2 €

WIN 1 Double – low e PVC 1.18 Natural 340.00 83677.40

WIN 2 Double – low e PVC 1.18 CMV 465.00 133677.40

The costs presented are higher respect to the ones analyzed until now with the other retrofit solutions

studied. For the costs of the windows it has been considered included all the extra cost related to the

removal and disposal of the existing windows and the following installation of the new glazing,

including the labor needed for the possible brickwork job.

7.2.7.2 Technical Analysis

The technical analysis done on the glazing solution presented is deepened in the annexes regarding the

thermal analysis of the windows proposed.

Concerning the mechanical ventilation, the proposed solution has been considered only after some

technical considerations. First of all in order to have the idea of the machine that had to be installed

some hypothesis had to done. The will was to install a CMV system that could “replace” the opening of

the windows, therefore decreasing the losses for ventilation rationalizing the external flow, and decrease

the internal temperature and the CO2 concentration in the cooling season. Therefore it has been decide

to propose a CMV system with heat recovery and free-cooling switch included.

The free cooling technology is based on the fact that when the outside air reaches a lower temperature

than the internal one, before putting it into the environment, it interrupts the heat recovery function so

as to keep the thermal condition unchanged. The air introduced into the rooms is naturally fresh, for a

natural air conditioning and at no cost. It is particularly useful in mid-seasons or at night in summer

when the outside temperature is more comfortable. Taking advantage of the difference in temperature

between inside and outside, the free cooling technology optimizes the comfort of the rooms without the

use of air conditioning. The system autonomously depending on the external temperature brakes or starts

the activity of the heat exchanger, ensuring a constant well-being and an effective reduction in

consumption.

In order to have a better understanding of the economic impact of the installation of the machine, it has

Table 7.28: Case scenarios considered for the retrofit of the glazing areas of the case study building in Lecco

Page 161: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

137

been proceeded with the overall dimensioning of the mechanical ventilation, using the ISO 10339 [44].

As said the dimensioning is not accurate, but is done only to estimate the amount of inlet air needed.

Considering (from [44]):

- the “school” crowding index: ns = 0.50 pers/m2 ;

- the “school” external air flow: Qop = 7*10-3 m3/s per person;

- design air flow: Qd = 4800 m3/h;

- project air flow: Qpr = 5000 m3/h.

Basically the calculation has told that the CMV system that has to be installed has to have a capacity

equal to or greater than 5000 m3/h, meaning that the system will be expensive and also complex to

install.

After the considerations it has been decided to adopt this kind of technological solution onto the case

study building in order to admire and comment the possible effects on the energy and comfort parameters

of the heated spaces.

First of all the CMV should decrease the operative temperature of the internal spaces during the cooling

period, especially thanks to the free cooling system which is really effective in the mid seasons and for

night cooling, so that there’s an increase in the thermal comfort perceived by the users. In order to do

this it will be presented the TM52 calculation of adaptive thermal comfort criteria, presented in the §

5.2.2.1. Before presenting the results it will be reminded shortly what are the criteria and how they

interact with the thermal comfort of the spaces:

- Criterion 1 Hours of Exceedance (He): sets a limit for the number of hours that the operative

temperature can exceed the threshold comfort temperature (upper limit of the range of comfort

temperature) by one degree or more during the occupied hours of a typical non-heating season

(1st May to the 30th September).

- Criterion 2 – Daily Weighted Exceedance (We): deals with the severity of overheating, which

can be as important as its frequency, the level of which is a function of both temperature rise

and its duration. This criterion sets a daily limit for acceptability. To allow for the severity of

overheating the weighted Exceedance (We) shall be less than or equal to 6 in any one day.

Criterion 3 – Upper Limit Temperature (Tup): sets an absolute maximum daily temperature for

a room, beyond which the level of overheating is unacceptable. It is used to set an absolute

maximum value for the indoor operative temperature the value of ∆T shall not exceed 4°C. This

criterion covers the extremes of hot weather conditions and future climate scenarios.

The result of the technical memorandum is that a room that fails any two of the three criteria is classed

as overheated and thus fails the TM52 check.

Page 162: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

138

The graph from the Figure 7-20 can be easily compared to the one from the Figure 5-12, in which it has

been presented the same data, with and without the installation of a CMV system. It’s pretty clear how

profitable is the use of a mechanical ventilation, since from the graph it’s highlighted the fact tat in the

base case two of the classrooms didn’t pass the criteria verification, while with the CMW installation

all the spaces considered can be classified as in agreement with the current thermal comfort regulations.

The same comparison: Base case vs. Installation of CMV, can be done also considering the CO2

concentration inside the classrooms of the case study building.

It will be analyzed the calculation, presented in the § 6.2.3, and it will be compared with the calculation

applied to the case study including the installation of the CMV. Juts for a reminder it will be presented

the CO2 threshold for a classroom presented by the standard [45].

The standard provides some threshold that doesn’t have to be overtaken to avoid dangerous level of

CO2 inside the space. Of course the main parameter that influenced the level of carbon dioxide is the

ventilation rate, of which the natural regulation provides some standard values according to different

typologies of educational buildings. The level of carbon dioxide in a closed space are reported below in

compliance with the regulation ISO 7730 [15]:

- normal outdoor level of CO2: 350 – 450 ppm;

- acceptable outdoor level: lower than 600 ppm;

- odor problems: 600 – 1000;

- ASHRAE standards: 1000 ppm;

- light drowsiness: 1000 – 2500 ppm;

- light health issues: 3000 – 5000 ppm;

- health problems: > 5000 ppm.

The graph presented in the Figure 7-21 can be easily compare with the one presented in the Figure 5-13,

in order to have a first clear understanding of the impact of the CMV.

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

C.0.1 C.1.1 C.2.1 C.0.2 C.1.2 C.2.2 C.1.3 C.2.3 C.2.8 C.1.4 C.1.5 C.1.6 C.1.7

SE-SW SE NW-SW NW NE SW

Criteria 1 Criteria 2

Criteria 3 Limit-Criteria 1

Limit-Criteria 2 Limit-Criteria 3

Figure 7-20: Adaptive Thermal Comfort criteria check of the classrooms divided by orientation, considering the

installation of a CMV system. The verification has been done according to TM52

Page 163: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

139

Basically what can be seen is that the installation of a CMV system, as the one presented, leads to a

drastic reduction of CO2 concentration, bringing them to regulation’s limit. As it can be seen from the

graph, the percentage corresponding to the time in which the CO2 is less than 1000 ppm, accounts for

almost 80 % of the occupied hours, meaning that for the amount of time the concentration inside the

classrooms are lower than the limitation imposed by the ASHRAE. Nevertheless it’s possible to see that

in 20% of the hours in which the classes are occupied the concentration gets as high as 1200 ppm,

exceeding the limitations imposed by the ASHRAE but still guaranteeing an adequate indoor quality.

7.2.7.3 Heating consumption savings

In this paragraph it will be analyzed the pros of doing the specific intervention explained in the previous

paragraph. In this case the intervention is the complete refurbishment of the glazing area, and the

possible installation of a CMV system (presented in §7.2.7.1), and the perks are represented by the

energy and economic savings and the GHG emission reductions.

Scenario

Heating

Primary Energy Energy cost GHG emissions Reduction

[kWh/m2y] [€] [tonCO2] [%]

Base 232.94 17974.10 45.04 -

Glazing 171.06 13455.27 33.07 27%

Glazing + CMV 158.40 12222.39 30.62 32%

The Table 7.29 is clear on the energy results of the proposed intervention. The savings obtained on the

energy consumptions due to the thermal conditioning of the heated spaces of the case study building

through the replacement of the existing windows with updated insulating glazing accounts for 27% of

the total heating energy needs. These results are in agreement on what presented earlier in the § 5.1.5,

considering that it was supposed that the glazing area accounted for 20% of the thermal losses coming

0

20

40

60

80

100

C.0.1 C.1.1 C.2.1 C.0.2 C.1.2 C.2.2 C.1.3 C.2.3 C.2.8 C.1.4 C.1.5 C.1.6 C.1.7

SE-SW SE NW-SW NW NE SW

% <600 ppm 600<CO2<1000 ppm 1000<CO2<1200 ppm

Table 7.29: Heating reductions with the complete refurbishment of the glazing area and CMV combined, Lecco

Figure 7-21: Distribution in percentage of the CO2 level present in the classroom, divided by orientation and

considering the installation of a CMV system, Lecco

Page 164: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

140

from the envelope inefficiency.

The energy reduction gave by the installation of the CMV system is given by the fact that these

procedure will automatize the inlet of fresh air into the heated spaces. These means that ideally there

won’t be the necessity to open the windows anymore, considering that the inlet of extracted air from the

CMV will bear the needed air recirculation. So the energy savings will be attributed to the fact that the

won’t be any natural ventilation losses, and the losses due to the inlet of external air will be mechanically

controlled, therefore optimizing the process.

7.2.7.4 Economic Impact

The cost of the intervention was calculated in a simple straightforward way, considering the cost of the

materials and of the installation taken from the “Prezziario Lombardia”, which is the pricelist for civil

works in the Lombardy region, which include all the additional expenses directly related to works

needed to be done in order to make the application possible.

The graph presented in the Figure 7-22 represents the payback time of the investment involved for the

refurbishment of the glazing area and the optional installation of a CMV system. The first thing that

jumps to the attention is the fact that the two lines representing the economical behaviors of the two

separate investment have different slopes, this is because the two cases have different impact on the

energy savings of the building, as presented in § 7.2.7.3.

The costs of the inventions presented before, made clear that the refurbishment will be translated into a

big impact investment in this case. The payback year of the investment for the case of the only

refurbishment of the windows is equal to more than 18 years, this means that the cash flow of the case

-140

-120

-100

-80

-60

-40

-20

0

20

40

60

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

[k€]

yrs

WIN 2 WIN 1 Payback time

Figure 7-22: Representation of the payback year -x axis- and of the economic benefit -y axis- of the work

representing the refurbishment of the glazing area of Lecco’s school

Page 165: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

141

study school building will be negative from the year of the construction until 18 years after.

For the costs of the CMV system, it has been considered the purchase of all the components of the

system, included all the ramifications, and the labor due to the installation. In the price it has been

included, by the manufacturer, the costs for the ordinary maintenance. Nevertheless the graph highlights

the high payback time of the investment involving the CMV installation. This can be lowered thanks to

an integrated approach, which means that it can be proposed a new system involving the combination

of the conditioning system with an integrated ventilation system, as it will be presented later on the in

the work related to the plant system.

7.2.8 Envelope retrofit: Proposed intervention

In order to have a complete view on what has been analyzed until this point, it has been decided to sum

up all the proposed intervention and create some combinations. This means that the retrofit works

proposed are going to be combined together in order to analyze different scale of retrofit. The analysis

goes from to the stand alone cases previously proposed to integrated approach retrofit, in which all the

dispersive components of the envelope have been insulated.

In order to compare all the combination and thus to understand the profit coming from each of the retrofit

scenarios, first it has to be done a summary representation of the multiple cases taken in consideration

for this analysis.

As said, basically what has been done was combine together all the possible retrofit works, previously

explored, in order to get to the maximum energy demand reduction possible through envelope

optimization only. All the scenarios combined are exactly the ones analyzed in the previous paragraphs.

Through this analysis it will be possible to see what are the differences between a retrofit work done

with an integrated approach, and one done with distinct interventions not related to each other.

One of the benefit of designing a retrofit through an integrated approach, is that the impact of the thermal

bridges occurring with the application of thermal insulation can be reduced, as matter of fact intervening

on more elements of the envelope lets the designer have more possibility to develop efficient

connections between them. This will have an evident positive influence on the energy efficiency of the

intervention as well as on the investment needed to fund the works.

The table presented in the figure presented below, shows all the mentioned scenarios that have been

studied, and that are than considered feasible for an energy retrofit intervention applicable to the case

study school building located in Lecco.

Page 166: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

142

Gym Insulation Glazing Mechanical ventilaiton

EPS rigid Rockwool rigid Wood fiber rigid Polyester fiber Rockwool Calcium Silicate Rockwool roll Glass wool HD EPS HD Rockwool HD Wood fiber HD Synthetic material Low-e CMV Heat recovery

Case 1.1

Case 1.2

Case 1.3

Case 2.1

Case 2.2

Case 2.3

Case 3.1

Case 3.2

Case 4.1

Case 4.2

Case 4.3

Case 5.1

Case 6.1

Case 7.1

Case 8.1

Case 8.2

Case 8.3

Case 9.1

Case 9.2

Case 9.3

Case 10.1

Case 10.2

Case 10.3

Case 11.1

Case 11.2

Case 11.3

Case 12.1

Case 12.2

Case 12.3

Case 13.1

Case 13.2

Case 13.3

Case 14.1

Case 14.2

Case 14.3

Case 15.1

Case 15.2

Case 15.3

Case 16.1

Case 16.2

Case 16.3

Case 17.1

Case 17.2

Case 17.3

Case 18.1

Case 18.2

Case 18.3

Case 19.1

Case 19.2

Case 19.3

Case 20.1

Case 20.2

Case 20.3

Case 21.1

Case 21.2

Case 21.3

Case 22.1

Case 22.2

Case 22.3

Case 23.1

Case 23.2

Case 23.3

Case 24.1

Case 24.2

Case 24.3

Case 25.1

Case 25.2

Case 25.3

Case 26.1

Case 26.2

Case 26.3

Case 27.1

Case 27.2

Case 27.3

Wall external Insulation Wall internal insulation Attic insulation Roof insulationSCENARIO

Figure 7-23: Different case scenarios analyzed for the energy retrofit of Lecco’s school building

Page 167: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

143

After defining all the case scenarios, the next and final step would be the analysis of them in terms of

reduction of the energy needed to heat the inner space, and the cost of the investment bore by the owner,

in this case the municipality, for the retrofit work.

The graph represented in the Figure 7-24 basically sums all the study done on the envelope of the school

building located in Lecco. It has been decided to represent 27 different retrofit interventions, sub-divided

into 3 case scenarios for each of the interventions, as seen in Figure 7-23.

The energy reduction changes only between the different retrofit interventions, while it stays the same

no matter the case scenario analyzed for each specific intervention. In this way it was possible to

construct a line for each retrofit intervention analyzed, so that this line could represent the range in which

the economic investment, bore for the different case scenarios of the specific intervention, would lay

into. The construction of the Intervention’s line was made joining the three points representing the three

different related case scenarios. So the construction points represent each of the 3 case scenario studied

for the specific intervention, as matter of fact for each line the lowest point represents the most economic

solution analyzed, while the top one represents the most expensive one.

Analyzing the results coming from the graph presented in the Figure 7-24, the first thing that can be

seen is that the exploit of an aimed integrated approach used for an envelope energy retrofit could lead

to a reduction equal to almost 85% of the energy needed for the existing heating system for the space

conditioning of the school building. As said this value has to be considered without any modification of

the technological plants existing nowadays, this remarks even more the great impact achievable with an

aimed retrofit intervention.

The maximum energy reduction is achieved thanks to the intervention classified as “Case 21”, in which

the retrofit is aimed towards the insulation of the external perimeter wall (from the outside and the

inside), the attic extrados, the ground-contact elements of the gym combined with the refurbishment of

the glazing area and the installation of a Controlled Mechanical Ventilation with Heat recovery. The

minimum amount needed to fund the work is equal to 250 thousands of euro.

This means that if we analyze this case, the cost needed to reduce the heating energy needs of 1 kWh,

equal to: CER = 1.54 €/kWh. This cost/reduction analysis [€/kWh] is deepened, for all the other

intervention proposed, in the annexes presented at the end of this research work.

From the graph it is also possible to spot the most cost-effective intervention . This means that the ratio

between the cost of the investment and the energy reduction will be the lowest analyzed. This

intervention is the “Case 1” for which the ratio “cost/energy reduction” is equal to: CER = 0.26 €/kWh.

As matter of fact the use of the economic scenario for this intervention, will lead to a 27 % energy

reduction, with an expense equal to almost 25 thousands of euro. In the “Case 22” the retrofit

intervention is aimed towards the insulation of the external perimeter wall, with the application of

thermal insulation the outside without intervening on the protected façade an all the other dispersive

Page 168: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

144

envelope components.

It’s clear that the in this case the cheapest intervention is not the most convenient one, as matter of fact

the cheapest solution studied is the “Case 3”, which represents the insulation of the attic and which has

a cost/energy reduction ratio equal to: C€ = 0.60 €/kWh; which is lower respect to other cases.

This does not mean that the intervention proposed in the “Case 3” is not feasible and should be avoided,

but it’s just to point out which will be the direction to take, in case of a deep retrofit work. Then of

course in case of necessity or in case of particular boundary conditions one could decide to choose one

solution over another, no matter the cost-effectiveness comparison.

1

2

3

4

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

0

25

50

75

100

125

150

175

200

225

250

275

300

325

350

375

400

425

10% 15% 20% 25% 30% 35% 40% 45% 50% 55% 60% 65% 70% 75% 80% 85%

[k€] Investment cost

Energy reduction

Case 1 Case 2 Case 3 Case 4 Case 5 Case 6 Case 7

Case 8 Case 9 Case 10 Case 11 Case 12 Case 13 Case 14

Case 15 Case 16 Case 17 Case 18 Case 19 Case 20 Case 21

Case 22 Case 23 Case 24 Case 25 Case 26 Case 27

Figure 7-24: Analysis of the heating energy demand reduction % – x axis- and the cost of the investment [k€] - y

axis- of the different case scenarios considered for the for the energy retrofit of Lecco’s school building

Page 169: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

145

7.3 Case study “Bustehrad”

According to the needs and the criticalities highlighted through the energy analysis previously presented

in chapter 6 in this section it will be presented the different case scenarios chosen for each retrofit

intervention proposed and considered feasible/energetically beneficial, for the case study school

building located in Bustehrad.

The case study analyzed locate in Buštěhrad has the same exact peculiarities as he one locate in Lecco,

as it will be seen throughout the chapter.

7.3.1 External thermal insulation coating

The coating of the outer envelope of the

building with thermal insulation, is one

of the most common procedure done in

order to decrease the amount of energy

consumption of the specific building.

This technique allows the building also

to receive a complete makeover of the

facades considering that the thermal

coating includes a new external finish,

this can contribute to spark up the

aesthetic value of obsolete buildings.

As done for the case study locate in Lecco, § 7.2.1, since the building will radically change its look the

external coating of the facades is considered an invasive procedure. For this reason this technique can’t

be applied to all of the facades of the historical part of the building built at the beginnings of the 20th

century. The façade of the old part of the building oriented towards South-East, which is the only one

that is exposed on the street, has aesthetic architectural value therefore its appearance can’t be modified

meaning that no thermal insulation can be applied. For this type of façade it will be presented later on

in the script an internal insulation solution.

7.3.1.1 Design choice

Analyzing the output data of the energy diagnosis presented in the §5, it has been decided to present

three different scenario of intervention for this specific procedure. The three different scenario will

change in terms of thermal insulation material and external finish, for the remainder it will be all the

same, as matter of fact in all the scenario the element structure will have the same thermal transmittance

Figure 7-25:SE facade of the old part of the school building

Page 170: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

146

set at 0.25 [W/(m2K)], as defined in Table 7.1

Scenario Insulation λ d s Finishing Cost

Material [W/mK] [kg/m3] [cm] Material €/m2

EXT. 1 EPS with graphite 0.031 35 10 Acrylic 44.78

EXT. 2 Rockwool 0.034 115 11 Breathable 59.32

EXT. 3 Wood Fiber 0.04 145 13 Breathable 69.14

The results presented are in line of what seen before, for the case located in Lecco (§ 7.2.1), as the most

economic solution is represented by the first option, in which the insulation material chosen is the EPS

with graphite.

The attention is caught by the differences between the prices presented in the cost analysis of the two

case study presented. The prices shown for the case study located in Buštěhrad has overall lower prices

respect to the one of Lecco. With a detail analysis is possible to notice that actually the cost of the

solution 1 (the one with the EPS with graphite) has pretty much the same cost, in the two different

countries, and this is due to the fact that it’s safe to say that it is the most used material for thermal

external coating for Czech Republic and Italy. Concerning the costs of the two natural materials, the

costs in CZ are much lower to the ones applied in Italy, this can be linked to the fact that the use of

natural materials is more diffused in countries like Czech Republic, in which the production of these

materials doesn’t rely 100% on big international companies as in Italy, therefore making the market

more competitive. In this way the differences between the different material, for the school of Buštěhrad

is really low, making the choice of the material based more on the technical analysis rather than the

economic one.

7.3.1.2 Thermal Inertia of the case scenarios

For this intervention, considering that it is based on the application of material insulation on the outside

of the envelope, the thermal inertia of the different scenarios will be compared based only on the

different values of Periodic thermal transmittance Yie defined by the different material used for each

scenario. Here are presented the values defining the dynamic properties of the different case scenarios

previously defined.

Phase displacement Attenuation Performance

φ > 10 fd < 0.15 excellent

10 < φ < 12 0.15 < fd < 0.30 good

8 < φ < 10 0.30 < fd < 0.40 average

6 < φ < 8 0.40 < fd < 0.60 sufficient

φ < 6 fd < 0.60 mediocre

Table 7.30: Thermal coating scenario considered for the retrofit of the case study located in Buštěhrad

Scenario fd φ Yie

- [h] [W/m2K]

Base case 0.102 14.450 0.24

EXT. 1 0.024 17.217 0.009

EXT. 2 0.019 18.209 0.005

EXT. 3 0.012 21.6 0.003

Table 7.31: Dynamic properties of the scenarios Table 7.32: Limit values set by standard [18]

Page 171: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

147

The thermal inertia calculated for the base case ( i.e. outside walls without any kind of insulation), is

higher compared to the one of Lecco, this is due to fact that the perimeter walls in Czech Republic during

the 1900 were completely made of burnt bricks piled together in order to reach a thickness equal to more

than 60 cm, meaning that the structure was highly capable of absorbing and keeping the heat. As for the

cost of the solutions, the differences between the different values expressing the thermal inertia of the

different solutions is not high, as for the school in Italy, this evens a little bit all the solution on the

technical point of view.

Even though the differences are not that high, the best solution is represented by the application of wood

fiber insulation (EXT. 3), for which the thermal inertia of the wall reaches values so that the phase

displacement is equal to more than 20 hours, meaning that the time lag between reaching the maximum

external temperature in the inner spaces is more than 20 hours.

7.3.1.3 Heating consumption savings

In this paragraph it will be analyzed the perks of doing the specific intervention explained in the previous

paragraph. In this case the intervention is the application of an external thermal coating onto the facades

of the case study building exception made for the protected façade and the perks are represented by the

energy and economic savings and the GHG emission reductions.

Scenario

Heating

Primary Energy

Energy cost

GHG emissions Reduction

[kWh/m2y] [€] [tonCO2] [%]

Base 199.05 10303.04 42161.00 -

Ext. Insulation 136.72 7076.70 28958.52 31%

Is easy to understand the profits, speaking about heating consumptions, coming from the application of

the thermal insulation as previously explained. The reduction obtained through the application of the

thermal insulation is equal to 31% of the initial value, this refers to all of the values presented in the

table, so for the: primary energy, energy cost and the GHG emissions.

The results are in agreement of what seen for the case study located in the city of Lecco, § 7.2.1.3. This

represented the first comparable results obtained till now. From these results it’s obvious that the impact

of the interventions are quite similar.

7.3.1.4 Economic Impact

The cost of the intervention was calculated in a simple straightforward way, considering the cost of the

materials and of the installation of the specified work interventions. The analysis has been based on the

Table 7.33: Heating reductions obtained with the external thermal coating applied onto the case study Buštěhrad

Page 172: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

148

experience gained analyzing multiple case studies located in Czech Republic, and considered relevant

for the work intervention presented. Using this Czech case studies as guide lines, it has been possible to

create a small database recreating the costs for all the interventions, also through the help of Czech

Republic native colleague that collaborated with the thesis analysis. It was also possible to understand

the labor costs of the interventions which were than summed as a fixed percentage of increase, together

with the expenses directly related to works needed to be done in order to make the application of the

thermal insulation possible (i.e. scaffoldings, preparation of the land, etc.).

The three case scenarios represented have different behavior respect to the ones seen for the case study

located in Lecco, § 7.2.1.4. Taken in exam the most economic case, pointed out as the EXT.1, even

though the cost of the material is the same as the one seen in Italy, the lower energy reduction given by

the energy efficient intervention combined with the lower cost of gas in Czech Republic (thus decreasing

the positive impact given by the reduction of energy needs on the energy bill) leads to an longer payback

time respect to Lecco.

Another peculiarity is again, that the three case scenarios in this case (especially the EXT.2 and the

EXT.3) have smaller differences between each other, making the choice even more difficult. In the case

of Lecco the most expensive solution had a payback time double respect to the most economic one,

while for Bustehrad the differences are less obvious.

7.3.2 Internal thermal insulation

In this paragraph it will be presented a retrofit operation that can be done in order to insulate a protected

façade from the inside of the specific building. As highlighted before in the , the peculiarity of this case

study building is the presence of an architecturally protected façade whose appearances can’t be

modified, just as it was analyzed for the case study located in Lecco, § 7.2.2.

-60

-40

-20

0

20

40

60

80

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

[k€]

yrs

EXT 1 EXT 2

EXT 3 Payback time

Figure 7-26: Representation of the payback time -x axis- and of the economic benefit -y axis- of each of the

case scenarios chosen for the external thermal insulation, Buštěhrad

Page 173: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

149

7.3.2.1 Design choice

As done for the external thermal insulation coating intervention, also in this case it has been considered

3 different intervention scenarios, done with 3 different thermal insulation materials. This is done

because one of the goal of the work here presented is to show the possible energy retrofit intervention

applicable to the specific building, studying the different scenario through various technical aspects.

The three different scenario taken in consideration, as said before, will have an equal thermal

transmittance set at 0.25 [W/(m2K)], they are presented through the Table 5.7.

Scenario Insulation λ d s Finishing Cost

Material [W/mK] [kg/m3] [cm] Material €/m2

INT. 1 Calcium Silicate 0.039 115 12 Internal Paint 53.27

INT. 2 Rockwool rigid panels 0.035 70 11 Plasterboard 40.86

INT. 3 Polyester Fiber 0.034 50 10 Plasterboard 33.83

Comparing the costs presented for the two case studies, it’s clear that as before also in this case the costs

of the interventions calculated in Czech Republic are lower than the one in Italy. One peculiarity is

represented by the cost of the Calcium silicate solution (INT.1) which has approximately the same price

in both countries. This is mainly due to the fact that the solution is rarely used in Czech Republic, as

matter of fact considering that its main features are the summer performances, it’s understandable that

a cold country like Czechia doesn’t really look for this kind of solution.

For the case scenario “INT. 1” the intervention is based on the application of calcium silicate insulation

panels, through the use of adhesive and levelling layer, onto the façade from the inner space. The choice

of this insulation material is given by the fact that the installation will be done from the inside and the

space insulated is a classroom, therefore it will be very important to contrast the high production of

water vapor coming from the students and guarantee a moderate IAQ.

The application method is different for the case scenario “INT. 2” and “INT. 3”, where the insulation

has been applied through a dry wall system. The insulation of the walls takes place with the installation

of a metal framework made of C-profile mullions and transoms which will guide the application of the

thermal insulation panels, covered by a dry plasterboard wall. The choice of rockwool for the case

“INT.2” is given by the will to give the possibility to exploit the Mass-spring-Mass effect of the dry

system presented, in order to consider a thermal-acoustic insulation scenario. In the “INT.3” it is

presented a low-cost solution defined by the use of an eco-friendly insulation material obtained by the

reuse of PET plastic, in form of polyester fiber insulation panels.

Table 7.34: Internal thermal insulation scenario considered for the retrofit, Buštěhrad

Page 174: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

150

7.3.2.2 Thermal inertia of the case scenario

As presented in the § 7.2.1.2, the envelope will be evaluated also for its summer performances through

the comparison of the thermal inertia of the wall for the solution proposed for each case scenario. In this

case since the intervention involves the application of material insulation from the inside of the spaces,

the thermal inertia of each scenario will be compared through both of the dynamic properties presented

before:

- Periodic thermal transmittance 𝑌𝑖𝑒 = 𝑈 ∗ 𝑓𝑑 [W/(m2K)];

- Internal thermal capacity Cip [kJ/(m2K)].

The Cip periodic internal thermal capacity, calculated as Yie, according to UNI EN ISO 13786 [56]

represents the capacity of a building component to accumulate the thermal loads coming from inside.

The higher the value of the Cip (mass placed inside), the greater the heat accumulation. The accumulation

of internal thermal loads by a wall makes it possible to keep surface temperatures at acceptable levels,

i.e. with fluctuations and limited values throughout the day, in favor the environmental comfort

conditions for summer.

It’s easy to see that the construction element used in the third case scenario has better dynamic

properties’ value, due to the higher thermal mass of the calcium silicate base panel insulation respect to

the dry wall system used in the second and in the third case scenario.

Phase displacement Attenuation Performance

φ > 10 fd < 0.15 excellent

10 < φ < 12 0.15 < fd < 0.30 good

8 < φ < 10 0.30 < fd < 0.40 average

6 < φ < 8 0.40 < fd < 0.60 sufficient

φ < 6 fd < 0.60 mediocre

As expected the results show higher values of internal thermal capacity for the Calcium Silicate solution

(INT.1) due to the higher mass of the insulation material. The results here presented are comparable to

the ones of Lecco, even though in this case the internal thermal capacity values of each scenario is lower,

meaning that there structure will be less able to store the heat coming from the inside, due to the fact

that there’s more mass on the outside of the structure.

7.3.2.3 Criticalities of the intervention

As seen in the § 7.2.2.3, this type of intervention is complex, and it involves certain operation

criticalities, that are going to be briefly shown again.

For this case study the application on the perimeter walls of thermal insulation from the inside space

Scenario fd φ Yie Cip

- [h] [W/m2K] [kJ/m2K]

INT. 1 0.241 18.230 0.010 21.45

INT. 2 0.018 19.870 0.006 15.15

INT. 3 0.013 20.34 0.004 13.00

Table 7.35: Dynamic properties of the scenario, Bustehrad Table 7.36: Limit values set by standard [18]

Page 175: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

151

gives birth to a number of critical thermal bridges, caused by the fact that two different modus operandi,

i.e. internal and external thermal coating of the envelope, have been considered coexisting for the retrofit

of the building.

In the Annexes all the possible thermal bridges occurring in this case of intervention have been studied,

and for each of them it has been presented a “simple” solution capable of limiting the value of the linear

thermal transmittance Ψ so that the construction elements solutions presented in the work comply with

the thermal transmittance -U- limitations imposed in the § 7.1.

The interventions made to reduce the impact of the thermal

bridges occurring, are the punctual application of internal

pre-finished insulation panels applied onto internal walls, and

the application on each floor of the old part of the building of

a suspended ceiling with the addition of a rigid panel

insulation material. The pre-finished insulation is made of pre-coupled boards of PF (polyester fiber)

and plaster board with an integrated vapor barrier, while the suspended ceilings is made of a rigid

rockwool panel with a plasterboard finishing. In order to have a more comprehensive view of the

economic investment needed for the global intervention, all of the processing techniques listed before,

i.e. the thermal bridge solution interventions, have been taking into account in the global cost of

investment.

7.3.2.4 Heating consumption savings

In this paragraph it will be analyzed the perks of doing the specific intervention explained in the previous

paragraph. In this case the intervention is the application of an internal thermal coating onto the protected

façade and the perks are represented by the energy and economic savings and the GHG emission

reductions.

Scenario

Heating

Primary Energy Energy cost GHG emissions Reduction

[kWh/m2y] [€] [tonCO2] [%]

Base 199.05 10303.04 42161.00 -

Int. Insulation 124.09 6423.07 26283.80 38%

Once again, the actual energy reduction obtained with the thermal insulation of the vertical components

of the structure for the case study in Buštěhrad is lower respect to the one in Lecco. This could be due

to simple considerations, as the thermal losses diagram presented in § 6.1.5 highlights the impact of the

glazing are onto the energy leakage of the building, also in agreement with the Glazing/opaque ratio

stated for the building.

Overall an energy reduction higher than 30% of the initial case is reached, meaning that the even with a

Intervention Cost

€/m2 €

suspended ceiling 19.84 17856.00

insulated dry wall 17.45 3141.00

Table 7.37: Cost of the intervention, CZ

Table 7.38: Heating reductions obtained with the internal thermal coating, Buštěhrad

Page 176: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

152

partial retrofit (considering only the opaque wall) an evident difference can be made.

7.3.2.5 Economic Impact

For the case study presented the retrofit intervention here showed of the application of thermal insulation

onto the perimeter wall from the inner spaces is not a standalone intervention but it has to be combined

with the application of the external thermal coating insulation presented in the § 7.3.1.

For this reason it has been decided to create 3

different case scenario presenting the combination of

the two intervention presented until now. The first

scenario represents the cheapest and most used

combination of the materials used for the insulation

from the outside and the inside, while the third one

represents the most expensive and performing combination.

In order to have an economic view of the proposed interventions it has been decided to analyze the

payback time of the investment, based on the intervention’s cost and the energy cost savings obtained

through the years, in order to make this case more global as possible some hypothesis and simplifications

had to be done.

The cost of the intervention was calculated in a simple straightforward way, considering the cost of the

materials and of the installation of the specified work interventions. The analysis has been based on the

experience gained analyzing multiple case studies located in Czech Republic, and considered relevant

for the work intervention presented. It was also possible to understand the labor costs of the interventions

which were than summed as a fixed percentage of increase, together with the expenses directly related

to the site work area.

The payback time for the investment involving the thermal insulation of the vertical wall either from the

-80

-60

-40

-20

0

20

40

60

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

[k€]

yrs

INT 1 INT 2

INT 3 Payback time

Scenario

Insulation

Material

EXT. INT.

1 EPS with graphite Polyester Fiber

2 Rockwool Rockwool rigid panels

3 Wood fiber Calcium Silicate

Table 7.39: Case scenario combination, Buštěhrad

Figure 7-27: Representation of the return year -x axis- and of the emission benefit -y axis- of each of the case

scenarios chosen for the internal thermal insulation, Buštěhrad

Page 177: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

153

inside and the outside of the case study building located in Buštěhrad, is clearly a point of disagreement

between the two case studies located in two different parts of Central Europe.

It’s clear that the impact of the retrofit of the vertical opaque envelope is much higher in the case study

located in Lecco, respect to the one of Buštěhrad. As matter of fact the cheapest solution studied for the

Italian case presents a payback time which is half of the one of the Czech’s. This can be read as a signal

for which an integrated approach, considering all the construction elements.

The drastic difference is given by the fact that the two case study reach different energy reduction with

the analyzed intervention, plus the two thermal losses diagram combined with the lower cost of gas in

Czechia highlight the difficulty in lowering the costs of the energy bill in Buštěhrad.

7.3.3 Attic Insulation

As seen through the paper, the same intervention proposed for the case study located in Lecco, will be

applied onto the case study of Buštěhrad in order to compare the differences and the similarities.

The case study presents an unheated space

between the roof and the last heated slab, easily

accessible. In this paragraph it will be proposed

the insulation of the last heated slab of the old

part of the building through the use of insulation

materials in form of rolls and panels put on the

floor of the attic, so that the insulation performs

its benefits only for the heated space, avoiding

heating unused spaces such as the attic itself.

7.3.3.1 Design choice

The positive aspect of the building that has to be exploit in this case, is the presence in the old part of an

unheated space between the roof and the last heated slab, defined as attic, and the fact that it is easily

accessible, even though unfortunately this space is not present in the recent part of the building. The

attic can be used in two different ways, as a buffer zone which means that it will be considered as an

unusable space and on the other hand it can be used as storage or functional room.

Scenario Insulation λ d s Flooring Cost

Material [W/mK] [kg/m3] [cm] Material €/m2

1 Rockwool roll insulation 0.038 26 15 - 11.31

2 Glasswool rigid panel 0.033 125 13 Dry system 53.03

Table 7.40: Case scenarios of attic retrofit for the school building of Bustehrad

Figure 7-28: Roof structure of Bustehrad’s school

Page 178: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

154

For this reason it has been decided to present two different feasible intervention for the thermal

insulation of the attic, one will concern only the thermal insulation of the last heated slab while the other

one will include the refurbishment of the flooring of the attic, so that this space can be qualified as

usable.

Once more it’s clear the difference between the two interventions, which are similar to the one presented

for Lecco. This highlights the cost effectiveness of applying roll insulation instead of a rigid one

combined with a new floor system. Although it has to be said that the attic placed in the school building

is spacious and it has also roof light windows which can be a significant factor in the case of a complete

refurbishment of the space. From the surveys and the analysis done, without considering the two

different economic benefit given by the scenarios, the most suitable solution would be the one of

restoring the attic in order to make it useful, maybe also deciding to heat it.

7.3.3.2 Heating consumption saving

In this paragraph it will be analyzed the perks of doing the specific intervention explained in the previous

paragraph. In this case the intervention is the application of an internal thermal insulation onto the slab

extrados, for the old part of the building, and on the slab intrados for the recent one (as presented in §

5.2.3) and the perks are represented by the energy and economic savings and the GHG emission

reductions.

Scenario

Heating

Primary Energy

Energy cost

GHG emissions

Reduction

[kWh/m2y] [€] [tonCO2] [%]

Base 199.05 10303.04 42161.00 -

Attic Insulation 167.97 8694.31 35577.91 16%

The energy effectiveness of the intervention it’s pretty clear, and it’s also in line with the heat losses

diagram presented in § 6.1.5. As it was assumed since the energy savings coming from the opaque wall

in this case were lower than the Italian case, the insulation applied to the roof would have a bigger

impact for the school of Buštěhrad as shown by the Table 7.41.

7.3.3.3 Economic impact

The cost of the intervention was calculated in a simple straightforward way, considering the cost of the

materials and of the installation of the specified work interventions. The analysis has been based on the

experience gained analyzing multiple case studies located in Czech Republic, and considered relevant

for the work intervention presented. It was also possible to understand the labor costs of the interventions

Table 7.41: Heating reductions obtained with the attic thermal insulation applied onto the case study Buštěhrad

Page 179: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

155

which were than summed as a fixed percentage of increase, together with the expenses directly related

to the site work area.

The solution ATTIC 1, representing the choice of thermal insulating the attic extrados with the

application of roll insulation, has outstanding results. The payback time for this scenario is less than 5

years, meaning that the doing this work will automatically show a profit for the school, in terms of real

money, after less than 5 years from the construction year. This exploit was not a real surprise, since from

the cost analysis previously done, the huge benefit were already evident.

7.3.4 Roof insulation

In this section it will be analyzed the possible case scenarios

concerning the refurbishment of the roofing structure of the case

study building. The building presents an attic space placed on

top of the last heated slab which is covered by a clay tiles hip

roof supported by a wood beam structure.

This intervention is usually applied whenever the roof is directly

in contact with the heated space, i.e. in the recent part of the

building, or/and when there’s the will to transform an attic into

an habitable space, i.e. the attic space in the old part of the building.

7.3.4.1 Design choice

It has been decided to propose a requalification of the existing roof of both of the parts of the building,

consisting on the application of a thermal insulation layer, included all the protection materials,

underneath the existing roof cover. This means that it will be temporarily removed the roofing covering

structure and then re-placed on top of a new supporting structure laid on a new insulation layer consisting

-40

-20

0

20

40

60

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

[k€]

yrs

ATTIC 1 ATTIC 2 Payback time

Figure 7-29: Representation of the return year -x axis- and of the economic benefit -y axis- of each of the case

scenarios chosen for the attic insulation in Buštěhrad

Figure 7-30: Bustherad's roof structure

Page 180: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

156

of a different thermal insulation material for each case scenario.

Scenario Insulation λ d s Cost

Material [W/mK] [kg/m3] [cm] €/m2

ROOF. 1 EPS with graphite 0.031 40 15 43.39

ROOF. 2 Rockwool 0.036 140 17 53.21

ROOF. 3 Wood Fiber 0.038/0.042 145/205 19 78.75

These case shows even more the differences on the construction market of the costs applied in Italy and

the one applied in Czech Republic. The cost for the intervention involving the use of EPS with graphite

is actually really cheap, compared to the costs found in the Italian database, therefore it could represent

an interesting solution, economically speaking.

7.3.4.2 Thermal inertia of the case scenario

For this intervention, considering that it is based on the application of material insulation on the outside

of the envelope, the thermal inertia of the different scenarios will be compared based only on the

different values of Periodic thermal transmittance Yie defined by the different material used for each

scenario. Here are presented the values defining the dynamic properties of the different case scenarios

previously defined.

The structure of the roof of the case study building located in Buštěhrad is really similar to the one of

Lecco’s school, as seen in § 3.3.1, therefore the results may not vary a lot.

Phase displacement Attenuation Performance

φ > 10 fd < 0.15 excellent

10 < φ < 12 0.15 < fd < 0.30 good

8 < φ < 10 0.30 < fd < 0.40 average

6 < φ < 8 0.40 < fd < 0.60 sufficient

φ < 6 fd < 0.60 mediocre

The lower is the value expressing the attenuation fd and the lower is the amplitude of the thermal flow

entering the building component, and at the same time the lower is the value of the periodic thermal

resistance Yie and the higher are the value of the phase displacement φ and the damping. In addition to

this it has to be said that the National Guide Lines [18] sets also, the limit for the value of the periodic

thermal transmittance Yie equal to a maximum of 0.10 [W/(m2K)], therefore all the scenarios are below

the limit.

It’s easy to understand that the results related to the old part of the building are not satisfactory. This is

Scenario fd φ Yie

- [h] [W/m2K]

ROOF 1 0.915 2.87 0.181

ROOF 2 0.515 8.18 0.1

ROOF 3 0.24 12.18 0.049

Table 7.43: Dynamic properties of the scenario, Bustehrad Table 7.44: Limit values set by standard [18]

Table 7.42: Case scenarios of the roof insulation intervention in Bustehrad

Page 181: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

157

due to the fact that roof structure is supported by punctual wooden beams that

are not considered in the thermal analysis of the structure, therefore the only

layer opposed to the thermal dispersions is represented from the new inserted

thermal insulation layer. In this case it’s more clear the difference given by

the choice of different thermal insulation, as matter of fact only the

application of a wood fiber insulation layer would guarantee good thermal inertia properties and

therefore would represent the optimal technical solution.

7.3.4.3 Heating consumption savings

In this paragraph it will be analyzed the perks of doing the specific intervention explained in the previous

paragraph. In this case the intervention is the application of an internal thermal insulation onto the slab

extrados, for the old part of the building, and on the slab intrados for the recent one and the perks are

represented by the energy and economic savings and the GHG emission reductions.

Scenario

Heating

Primary Energy

Energy cost

GHG emissions

Reduction

[kWh/m2y] [€] [tonCO2] [%]

Base 199.05 10303.04 42161.00 -

Roof Insulation 174.44 9028.80 36946.68 12%

The energy savings are much lower than the case of the attic insulation, highlighting once more the

effectiveness of the case presented in the § 7.3.3, respect to the one presented in this paragraph. In

addition the results here presented are in agreement on what seen for the case study located in Lecco, as

also in that case the roof insulation had lower energy benefit respect to the attic insulation.

7.3.4.4 Economic Impact

The cost of the intervention was calculated in a simple straightforward way, considering the cost of the

materials and of the installation of the specified work interventions. The analysis has been based on the

experience gained analyzing multiple case studies located in Czech Republic, and considered relevant

for the work intervention presented. Using this Czech case studies as guide lines, it has been possible to

create a small database recreating the costs for all the interventions, also through the help of Czech

Republic native colleague that collaborated with the thesis analysis. It was also possible to understand

the labor costs of the interventions which were than summed as a fixed percentage of increase, together

with the expenses directly related to works needed to be done in order to make the application of the

thermal insulation possible (i.e. scaffoldings, preparation of the land, etc.).

Old Part Performance

ROOF 1 mediocre

ROOF 2 average

ROOF 3 good

Table 7.45: Performances

of the old part roof

Table 7.46: Heating reductions obtained with the attic thermal insulation in Bustehrad

Page 182: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

158

The graph describes what has already been said before, that this is an high cost intervention, therefore

before pursuing this type of works it has to be considered all the other low cost scenario previously

presented in the attic insulation intervention. As matter of fact the solution ROOF 1 which represent the

cheapest case scenario has a payback time equal to 12 years, this remarks the high costs of this type

intervention.

7.3.5 Basement insulation

The basement structure of the school building located in Buštěhrad is also a composed of a vault slab,

as in Lecco, therefore as seen in the Italian case study, § 7.2.5) the intervention consisting on the

insulation of the slab delimiting the ground floor heated spaces from the underground level, is no feasible

for this specific research work.

7.3.6 Ground-contact element insulation

The detailed description made in § 3.3.1, shows that the ground floor of the school building taken as

case study, is in direct contact with the ground through a stone made slab. As seen from the plans

attached to the paper, the underground floor of the building covers only part of the ground floor area,

leaving the majority of it exposed to the ground. In order to limit the heat transfer between the floor and

the inners spaces, it has been suggested to insulate the extrados of the ground floor slab.

Concerning the ground-contact element of the underground floor, they have not been considered for the

calculation, since they are delimiting an unhated space.

7.3.6.1 Design choice

For the design choice of the insulation of the floor of the ground level of the school building it has been

-40

-30

-20

-10

0

10

20

30

40

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

[k€]

yrs

ROOF 1 ROOF 2

ROOF 3 Payback time

Figure 7-31: Representation of the return year -x axis- and of the economic benefit -y axis- of each of the case

scenarios chosen for the roof insulation in Buštěhrad

Page 183: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

159

used a similar approach respect to the one presented for the case study of Lecco, § 7.2.6. Considering

that the impact of this work would be not so high, consulting the heat losses diagram presented in the

energy analysis of the building, it has been decided to present the most economical solution found on

the market.

The choice made was the removal of the existing floor and the supposed levelling layer, and a

consequent application of rigid thermal insulation with a dry floor system. As matter of fact it has been

supposed that the existing structure has made of a 4 cm screed used as levelling layer and on top a 2 cm

tile flooring, therefore the removal of these two layers will be equal to a 6 cm empty spot. This spot will

be than filled with XPS rigid insulation pre-coupled with a strengthening leveling layer which will be

the support of the new dry floor systems. Basically the existing layers will be replaced by a rigid thermal

insulation with supporting layer of 4.5 cm with a dry floor system of 1.5 cm, equalizing the thickness of

material removed.

Scenario Insulation λ d s Finishing Cost

Material [W/mK] [kg/cm3] [cm] Material €/m2

GROUND 1 XPS insulation 0.032 35 4.5 Dry flooring 34.25

The cost presented takes in consideration also the removal of the existing layer that represents the

existing flooring system.

7.3.6.2 Heating consumption savings

In this paragraph it will be analyzed the perks of doing the specific intervention explained in the previous

paragraph. In this case the intervention is the application of an internal thermal insulation onto the slab

extrados, for the old part of the building, and on the slab intrados for the recent one and the perks are

represented by the energy and economic savings and the GHG emission reductions.

Scenario

Heating

Primary Energy Energy cost GHG emissions Reduction

[kWh/m2y] [€] [tonCO2] [%]

Base 199.05 10303.04 42161.00 -

Ground Insulation 191.90 9941.95 40683.36 3.5%

The energy reduction given by this intervention is low impact, as matter of fact if affects only 3.5 % of

the heating energy use of the building, therefore the intervention can’t be qualified as energy effective.

7.3.6.3 Economic Impact

The cost of the intervention was calculated in a simple straightforward way, considering the cost of the

materials and of the installation of the specified work interventions. The analysis has been based on the

Table 7.48: Heating reductions obtained with the ground floor thermal insulation in Bustehrad

Table 7.47: Case scenarios for the ground floor insulation in Bustehrad

Page 184: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

160

experience gained analyzing multiple case studies located in Czech Republic, and considered relevant

for the work intervention presented. Using this Czech case studies as guide lines, it has been possible to

create a small database recreating the costs for all the interventions, also through the help of Czech

Republic native colleague that collaborated with the thesis analysis.

The intervention work proposed is a low energy impact retrofit, therefore the slope defining the

economic benefit derived from it each year is really low, it almost tends to a flat line. This meaning that

it won’t be possible to see any major changes during the years after this intervention. As said before this

type of work can be considered in case of an integrated approach retrofit involving all the dissipative

components, otherwise it is almost useless.

7.3.7 Glazing optimization

Through the heat losses graph presented in § 6.1.5, it’s easy to understand the impact that the glazing

surfaces of the building have on the global heat losses of the building coming from the thermal

inefficiency of the envelope, as matter of fact it accounts for more than 20 % of the total thermal losses.

For this reason it has been decided to consider the complete refurbishment of the glazing areas of the

building, which includes the removal of the existing windows and the application of new insulating

windows.

7.3.7.1 Design choice

The technology used is the same used for the case study in Lecco, § 7.2.7.1.

Technically the solution proposed consists of a double glazing window, composed of 33.1/ 16 AR/ 33.1

LE. This means that is made of a first security laminated float of 6 mm, with a 16 mm of cavity filled

with argon, and a final thermal and low emissivity float of 6 mm. Here it has been presented the summary

-20

-10

0

10

20

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

[k€]

yrs

GROUND 1 Payback time

Figure 7-32: Representation of the return year -x axis- and of the economic benefit -y axis- of each of the case

scenarios chosen for the ground floor insulation in Buštěhrad

Page 185: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

161

table that sums up all the thermal characteristic of the new glazing element:

Glazed Surface

Component Thickness

[-] [mm]

Low E float 6

Argon 16

Clear float 6

The thermal transmittance of the glazing proposed has been calculated through the UNI EN ISO 10077-

2 [57], as it can be seen in the annexes, with the additional help of the Pilkington spectrum online

software.

The choice of the low emissivity glass is given by the fact that with the use of this glasses, it is possible

to reflect inward part of the heat emitted as thermal radiation from the bodies contained in the inhabited

areas, considerably reducing the heat loss. The heat is reflected by the plate treated analogously to what

happens with a mirror that reflects purely luminous radiation.

Concerning the design of the window the proposed intervention is only the one just presented, but in

this work it has been decided to distinguish another energy retrofit work consisting on the refurbishment

of the od glazing area, as previously explained, and the installation of a mechanical ventilation system.

This is done in order to differentiate a stand-alone work on the windows, which will take in consideration

the only refurbishment of the glazing, from an integrated energy retrofit work in which the optimization

of the envelope is combined with technological solution assigned to the improvement of the internal

condition of the spaces.

In this case study it will be analyzed a controlled mechanical ventilation with double flow heat recovery:

the stale air extracted from the humid rooms and the air taken from the outside, previously filtered, are

conveyed into a heat recovery unit that ensures the preheating of the renewal air avoiding the

contamination of the two flows. The most common type is the double flow controlled mechanical

ventilation which is characterized by having a double ventilation system, formed by separate distribution

channels:

- A duct controls and regulates air intake;

- the other is dedicated to extract air;

- the air flows in the two ducts are managed by separate electric fans.

For the reasons above explained, it has been decide to present two separate chances of glazing

optimization: one representing the refurbishment of the existing windows, and the other one including

also the installation of a controlled mechanical ventilation system “CMV”.

Frame Net U-value Net R-value

Type Transmittance Percentage [W/m2K] [m2K/W]

[-] [W/m2K] % 1.18 0.90

PVC 1.29 33

Table 7.49: Glazing’s component thermal properties. Thermal transmittance of the proposed windows

Page 186: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

162

Scenario Windows Frame U Ventilation Cost

# glazing Material [W/(m2K)] Type €/m2 €

WIN 1 Double – low e PVC 1.18 Natural 290.00 43500.00

WIN 2 Double – low e PVC 1.18 CMV 415.00 93500.00

The costs presented are higher respect to the ones analyzed until now with the other retrofit solutions

studied. For the costs of the windows it has been considered included all the extra cost related to the

removal and disposal of the existing windows and the following installation of the new glazing,

including the labor needed for the possible brickwork job.

Once again the costs found in Czech Republic are lower respect to the one presented in the Italian case,

as highlighted by the Table 7.50.

7.3.7.2 Technical Analysis

The technical analysis done on the glazing solution presented is deepened in the annexes regarding the

thermal analysis of the windows proposed.

Concerning the mechanical ventilation, the proposed solution has been considered only after some

technical considerations. First of all in order to have the idea of the machine that had to be installed

some hypothesis had to done. The will was to install a CMV system that could “replace” the opening of

the windows, therefore decreasing the losses for ventilation rationalizing the external flow, and decrease

the internal temperature and the CO2 concentration in the cooling season. Therefore it has been decide

to propose a CMV system with heat recovery and free-cooling switch included.

In order to have a better understanding of the economic impact of the installation of the machine, it has

been proceeded with the overall dimensioning of the mechanical ventilation, using the ISO 10339 [58].

As said the dimensioning is not accurate, but is done only to estimate the amount of inlet air needed.

Considering (from [58]):

- the “school” crowding index: ns = 0.50 pers/m2 ;

- the “school” external air flow: Qop = 7*10-3 m3/s per person;

- design air flow: Qd = 5950 m3/h;

- project air flow: Qpr = 6000 m3/h.

Basically the calculation has told that the CMV system that has to be installed has to have a capacity

equal to or greater than 6000 m3/h, meaning that the system will be expensive and also complex to

install.

After the considerations it has been decided to adopt this kind of technological solution onto the case

study building in order to admire and comment the possible effects on the energy and comfort parameters

Table 7.50: Case scenarios considered for the retrofit of the glazing areas of the case study building in Bustherad

Page 187: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

163

of the heated spaces.

First of all the CMV should decrease the operative temperature of the internal spaces during the cooling

period, especially thanks to the free cooling system which is really effective in the mid seasons and for

night cooling, so that there’s an increase in the thermal comfort perceived by the users. In order to do

this it has been calculate once again the percentage of hours in which a typical user will feel thermal

discomfort, defined as the percentage of hours in which the Operative temperature is higher than 26°C.

The graph easily highlights the drastic reduction of the hours of discomfort measured inside the classes

of the school building located in Bustehrad. It has to be said that even before the intervention of the

CMV the values of discomfort were not alarming, considering the results presented in § 6.2.1, linked to

the cool temperatures present in Czech Republic.

The same comparison: Base case vs. Installation of CMV, can be done also considering the CO2

concentration inside the classrooms of the case study building.

It will be analyzed the calculation, presented in the § 6.2.3, and it will be compared with the calculation

applied to the case study including the installation of the CMV. Juts for a reminder it will be presented

the CO2 threshold for a classroom presented by the standard [45].

The standard provides some threshold that doesn’t have to be overtaken to avoid dangerous level of

CO2 inside the space. Of course the main parameter that influenced the level of carbon dioxide is the

ventilation rate, of which the natural regulation provides some standard values according to different

typologies of educational buildings. The level of carbon dioxide in a closed space are reported below in

compliance with the regulation ISO 7730 [15]:

- normal outdoor level of CO2: 350 – 450 ppm;

- acceptable outdoor level: lower than 600 ppm;

- odor problems: 600 – 1000;

- ASHRAE standards: 1000 ppm;

- light drowsiness: 1000 – 2500 ppm;

- light health issues: 3000 – 5000 ppm;

0.00

0.50

1.00

1.50

2.00

2.50

3.00

C.0.1 C.1.1 C.2.1 C.0.2 C.1.2 C.2.2 C.0.3 C.1.3 C.2.3 C.1.4 C.2.4

South-West South-East North-East North-West

Figure 7-33: Discomfort hours % of the classrooms, dived by glazing’s orientation, during the cooling season.

Page 188: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

164

- health problems: > 5000 ppm.

The graph presented in the Figure 7-21 can be easily compare with the one presented in the Figure 5-13,

in order to have a first clear understanding of the impact of the CMV.

As expected the installation of the CMV will reduce the concentration of the CO2 inside the classrooms,

so that the distribution will be homogeneous and that it won’t be reached the threshold of the ASHRAE

equal to 1000 ppm. Comparing the two case studies in this case the ventilation is more effective, since

the final concentration values are homogeneously lower, even though it has to be said the existing case

locate in Buštěhrad was already better than the Italian, IAQ talking.

7.3.7.3 Heating consumption savings

In this paragraph it will be analyzed the pros of doing the specific intervention explained in the previous

paragraph. In this case the intervention is the complete refurbishment of the glazing area, and the

possible installation of a CMV system, and the perks are represented by the energy and economic

savings and the GHG emission reductions.

Scenario

Heating

Primary Energy

Energy cost

GHG emissions

Reduction

[kWh/m2y] [€] [tonCO2] [%]

Base 199.05 10303.04 42161.00 -

Glazing 136.86 7083.60 28986.73 31%

Glazing + CMV 128.94 6673.69 27309.36 35%

The glazing refurbishment is highlighted as an energy effective retrofit work, this was foreseeable thanks

to the previous analysis done on the existing building, in addition to that the bigger glazing area respect

to the Italian case study determines an higher reduction for the Czech school.

0

10

20

30

40

50

60

70

80

90

100

C.0.1 C.1.1 C.2.1 C.0.2 C.1.2 C.2.2 C.0.3 C.1.3 C.2.3 C.1.4 C.2.4

South-West South-East North-East North-West

% <600 ppm 600<CO2<1000 ppm 1000<CO2<2500 ppm

Table 7.51: Heating reductions with the complete refurbishment of the glazing area and CMV combined, Buštěhrad

Figure 7-34: Distribution in percentage of the CO2 level present in the classroom, divided by orientation and

considering the installation of a CMV system, Buštěhrad

Page 189: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

165

7.3.7.4 Economic Impact

The cost of the intervention was calculated in a simple straightforward way, considering the cost of the

materials and of the installation of the specified work interventions. The analysis has been based on the

experience gained analyzing multiple case studies located in Czech Republic, and considered relevant

for the work intervention presented. Using this Czech case studies as guide lines, it has been possible to

create a small database recreating the costs for all the interventions, also through the help of Czech

Republic native colleague that collaborated with the thesis analysis.

The assumptions made until this point are confirmed by the economic analysis of the case scenarios

presented. The refurbishment of the glazing area (WIN 1) represents a beneficial intervention, as the

moderate payback time, equal to less than 15 years, is contrasted by the large amount of energy that can

be reduced with the intervention, keeping in mind the environmental impact of the energy retrofit.

The combined intervention (WIN 2) is less convenient, since in this case it has an higher payback time,

but in a bigger view it represents the intervention with the best impact on the existing building,

considering the increase of IAQ inside the classrooms.

7.3.8 Envelope retrofit: Proposed intervention

In order to have a complete view on what has been analyzed until this point, it has been decided to sum

up all the proposed intervention and create some combinations. This means that the retrofit works

proposed are going to be combined together in order to analyze different scale of retrofit. The analysis

goes from to the stand alone cases previously proposed to integrated approach retrofit, in which all the

dispersive components of the envelope have been insulated. In order to compare all the combination and

thus to understand the profit coming from each of the retrofit scenarios, first it has to be done a summary

representation of the multiple cases taken in consideration for this analysis.

-100

-80

-60

-40

-20

0

20

40

60

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

[k€]

yrs

WIN 1 WIN 2 Payback time

Figure 7-35: Representation of the payback year -x axis- and of the economic benefit -y axis- of the work

representing the refurbishment of the glazing area of Bustehrad’s school

Page 190: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

166

Ground Insulation Glazing Mechanical ventilaiton

EPS rigid Rockwool rigid Wood fiber rigid Polyester fiber Rockwool Calcium Silicate Rockwool roll Glass wool HD EPS HD Rockwool HD Wood fiber HD Synthetic material Low-e CMV Heat recovery

Case 1.1

Case 1.2

Case 1.3

Case 2.1

Case 2.2

Case 2.3

Case 3.1

Case 3.2

Case 4.1

Case 4.2

Case 4.3

Case 5.1

Case 6.1

Case 7.1

Case 8.1

Case 8.2

Case 8.3

Case 9.1

Case 9.2

Case 9.3

Case 10.1

Case 10.2

Case 10.3

Case 11.1

Case 11.2

Case 11.3

Case 12.1

Case 12.2

Case 12.3

Case 13.1

Case 13.2

Case 13.3

Case 14.1

Case 14.2

Case 14.3

Case 15.1

Case 15.2

Case 15.3

Case 16.1

Case 16.2

Case 16.3

Case 17.1

Case 17.2

Case 17.3

Case 18.1

Case 18.2

Case 18.3

Case 19.1

Case 19.2

Case 19.3

Case 20.1

Case 20.2

Case 20.3

Case 21.1

Case 21.2

Case 21.3

Case 22.1

Case 22.2

Case 22.3

Case 23.1

Case 23.2

Case 23.3

Case 24.1

Case 24.2

Case 24.3

Case 25.1

Case 25.2

Case 25.3

Case 26.1

Case 26.2

Case 26.3

Case 27.1

Case 27.2

Case 27.3

Wall external Insulation Wall internal insulation Attic insulation Roof insulationSCENARIO

Figure 7-36: Different case scenarios analyzed for the energy retrofit of Lecco’s school building

Page 191: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

167

As said, basically what has been done was combine together all the possible retrofit works, previously

explored, in order to get to the maximum energy demand reduction possible through envelope

optimization only. All the scenarios combined are exactly the ones analyzed in the previous paragraphs.

Through this analysis it will be possible to see what are the differences between a retrofit work done

with an integrated approach, and one done with distinct interventions not related to each other.

One of the benefit of designing a retrofit through an integrated approach, is that the impact of the thermal

bridges occurring with the application of thermal insulation can be reduced, as matter of fact intervening

on more elements of the envelope lets the designer have more possibility to develop efficient

connections between them. This will have an evident positive influence on the energy efficiency of the

intervention as well as on the investment needed to fund the works.

After defining all the case scenarios, the next and final step would be the analysis of them in terms of

reduction of the energy needed to heat the inner space, and the cost of the investment bore by the owner,

in this case the municipality, for the retrofit work.

The graph represented in the Figure 7-24 basically sums all the study done on the envelope of the school

building located in Lecco. It has been decided to represent 27 different retrofit interventions, sub-divided

into 3 case scenarios for each of the interventions, as seen in Figure 7-23.

The energy reduction changes only between the different retrofit interventions, while it stays the same

no matter the case scenario analyzed for each specific intervention. In this way it was possible to

construct a line for each retrofit intervention analyzed, so that this line could represent the range in which

the economic investment, bore for the different case scenarios of the specific intervention, would lay

into. The construction of the Intervention’s line was made joining the three points representing the three

different related case scenarios. So the construction points represent each of the 3 case scenario studied

for the specific intervention, as matter of fact for each line the lowest point represents the most economic

solution analyzed, while the top one represents the most expensive one.

Analyzing the results coming from the graph presented in the Figure 7-24, the first thing that can be

seen is that the exploit of an aimed integrated approach used for an envelope energy retrofit could lead

to a reduction equal to 85% of the energy needed for the existing heating system for the space

conditioning of the school building. As said this value has to be considered without any modification of

the technological plants existing nowadays, this remarks even more the great impact achievable with an

aimed retrofit intervention.

The maximum energy reduction is achieved thanks to the intervention classified as “Case 21”, in which

the retrofit is aimed towards the insulation of the external perimeter wall (from the outside and the

inside), the attic extrados, the ground-contact elements of the ground floor combined with the

refurbishment of the glazing area and the installation of a Controlled Mechanical Ventilation with Heat

recovery. The minimum amount needed to fund the work is equal to 250 thousands of euro. This means

Page 192: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

168

that if we analyze this case, the cost needed to reduce the heating energy needs of 1 kWh, will be equal

to: CER = 1.48 €/kWh.

This graph is useful for a comparison done considering the two figure representing the cost-energy ratio

of the interventions studied for the two different case studies (Figure 7-24). As matter of fact the two

cases representing the most energy effective scenario are exactly the same, they present more or less the

same percentage of energy reduction and investment costs, thus the cost of energy saving “CER” is quite

similar too. This means that the strategies applied for the case study located in Lecco are also applicable

to the Czech one, actually they will have a similar impact on the building, either economically and

energetically.

1

2

34

5

6

78

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

0

25

50

75

100

125

150

175

200

225

250

275

300

325

350

375

400

10% 15% 20% 25% 30% 35% 40% 45% 50% 55% 60% 65% 70% 75% 80% 85%

[k€] Investment cost

Energy reduction

Case 1 Case 2 Case 3 Case 4 Case 5 Case 6 Case 7

Case 8 Case 9 Case 10 Case 11 Case 12 Case 13 Case 14

Case 15 Case 16 Case 17 Case 18 Case 19 Case 20 Case 21

Figure 7-37: Analysis of the heating energy demand reduction % – x axis- and the cost of the investment [k€] - y

axis- of the different case scenarios considered for the for the energy retrofit of Bustehrad’s school building

Page 193: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

169

CHAPTER 8

8 Plant Optimization

The energy retrofit of the case study building, will not be focused only onto on the envelope of the

structure, but will be aimed also on the upgrade and optimization of the existing technological plants.

The optimization will be set on the presentation of multiple technologies applicable to the existing

conditions. The optimization will be base on the implementation of Photovoltaic panels, and the

refurbishment of the heating and DHW generation systems, in favor of new and up to date technologies.

The chapter will be split in two parts. One part will analyze an optimization solution of the existing

plants without interfering with the energy efficiency of the envelope of the building. The other part will

study different solutions involving the combination of gas-free technologies and the envelope insulation.

8.1 Photovoltaic system

The plant optimization will begin with the improvement of the existing system, with the application of

Photovoltaic panels on the roof structure of the two case study buildings.

For the Photovoltaic system, it has been decided to install an adequate amount of photovoltaic panels

with the following characteristics:

- Each module has an height of approximately 1 m and a length of 1.5 m;

- The material used for the panel is made of monocrystalline silicon, with an efficiency of 0.2;

- The peak power of each module is equal to 300 Wp;

- Efficiency of the system equal to 0.85.

So that the installation of this system could cover as much as possible the electricity needs of the specific

case study building. In order to exploit all the possible energy production given by the PV modules, it

has been decided to do a simple parametric study, for the optimization of the inclination angle and the

distance between the panels.

With the results obtained through the optimization analysis it will be possible to dimension the number

of PV panels that can be installed onto the structure, and the percentage of electricity needs covered.

8.1.1 Parametric solar radiation analysis

The parametric analysis is performed in order to optimize the positioning of the photovoltaic module

onto the roof structures of the specific case, so that the panels can receive the maximum amount of solar

Page 194: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

170

radiation available.

For this study it has been used a modelling software “Rhino” with a parametric analysis plug-in

“Grasshopper”. After the modelling of the context and the geometry of the building, it has been decided

what was going to be optimized by the software and what was going to be chosen by the designer.

In order to do this, it has to be designated the constraints and the parameters that are going to be

parametrized.

After this settings have been made, the solar radiation analysis can be performed onto the panels put in

the starting position ( equal to the suggested position), thus the optimization can be started.

8.1.1.1 Case study “Lecco”

Fort the “G. Carducci” school building of Lecco, the starting point has been locating and choosing the

pitch on which the PV panels will be installed. It has been decided to use the roof of the recent part of

the building, more precisely the pitch facing the South-West direction with an angle of 10 °.

Constraints:

- Position: South facing roof pitch;

- Height and length of each of the strings;

- Max tilt angle of the module: ⟂ to the pitch;

- Min tilt angle of the module: // to the pitch;

- Max distance between the modules: 100 cm;

- Min distance between the module: 0 cm.

Parameters:

- Tilt angle of the modules;

- Distance between the modules.

Figure 8-1: Solar radiation analysis on the PV panels placed in the starting position on the roof of Lecco’s school

Page 195: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

171

The starting position for Lecco, is equal to PV panels

with a tilt angle of 35°, as it is the recommended

inclination for the area, and relative distance between

each other equal to 50 cm. Here is also represented how

the PV panels have been grouped on the roof of the

building. It has been decide to create 4 strings made of a fixed number of PV panels.

The results of the optimization are presented through the table below, through which it is obvious that

the modification of the tilt angle and the distance of the module has a positive impact on the incident

radiation. The position that will be taken into account for the dimensioning is the optimized one, which

takes in consideration the shadings of the context.

Starting position Optimized position

Distance Tilt Radiation Distance Tilt Radiation

[cm] [°] [kWh/m2] [cm] [°] [kWh/m2]

String 1 50 35 1022.44 100 24 1047.75

String 2 50 35 967.21 100 21 997.2

String 3 50 35 971.95 100 20 993.5

String 4 50 35 936.9 100 22 954.27

The final step consists on evaluating the efficiency of the system and evaluate the production of the PV

panels. Considering the efficiency of the single module and of the system, and the number of PV panels

used, the energy production will be equal to 10202.28 kWh/y.

8.1.1.2 Case study Buštěhrad

Fort the school building of Buštěhrad, it has been decided to use the pitch of the roof facing the South-

East direction with 30 ° angle.

H b Area Panels

[m] [m] [mq] #

String 1 1 9.5 9.5 6

String 2 1 9.5 9.5 6

String 3 1 18 18 12

String 4 1 16.5 16.5 11

Table 8.1: PV panels dimension, Lecco

Table 8.2: Solar radiation optimization of the PV panels positioning, Lecco

Figure 8-2: Solar radiation analysis on the PV panels placed in the starting position of Bustehrad’s school

Page 196: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

172

The starting position for Bustherad, is equal

to PV panels with a tilt angle of 30°, as it is

the recommended inclination for the area,

and relative distance between each other

equal to 50 cm. Here is also represented how

the PV panels have been grouped on the roof

of the building. It has been decide to create 5 strings made of a fixed number of PV panels.

The results of the optimization are presented through the table below, through which it is obvious that

the modification of the tilt angle and the distance of the module has a positive impact on the incident

radiation. The position that will be taken into account for the dimensioning is the optimized one, which

takes in consideration the shadings of the context.

Starting position Optimized position

Distance Tilt Radiation Distance Tilt Radiation [cm] [°] [kWh/m2] [cm] [°] [kWh/m2]

String 1 50 30 1012.4 120 30 1044.37 String 2 50 30 1012.4 120 30 1044.37 String 3 50 30 1012.4 120 30 1044.37 String 4 50 30 1012.4 120 30 1044.37 String 5 50 30 1012.4 120 30 1044.37

In this case it’s obvious that the absence of vertical shadings onto the panels, clears the view thus the

optimization was not necessary for the tilt angle.

The final step consists on evaluating the efficiency of the system and evaluate the production of the PV

panels. Considering the efficiency of the single module and of the system, and the number of PV panels

used, the energy production will be equal to 9628.64 kWh/y.

8.2 Stand-Alone plant refurbishment

The first option that will be considered is the plant optimization of the existing building through a

complete refurbishment of the generation systems. This operation will be combined with the application

of Photovoltaic panels placed on top of the roof structure.

This intervention will not be combined with any energy retrofitting of the envelope, meaning that it will

only be focused onto the technological part of the building. The will was to analyze and understand the

impact of the efficiency of the technological plat onto the high energy demand of the building.

Since the envelope will not be modified, its energy performances wont’ be changed, thus we will be still

talking about a low energy efficiency building. So it has been decided to propose the refurbishment of

the plants, removing all the existing heating and DHW generations systems, and the installation of a

h b Area Panel

[m] [m] [mq] #

String 1 1 14.73 14.73 10

String 2 1 11.84 11.84 8

String 3 1 8.95 8.95 6

String 4 1 6.5 6.5 4

String 5 1 4.45 4.45 3

Table 8.3: PV panels dimension, Buštěhrad

Table 8.4: Solar radiation optimization of the PV panels positioning, Buštěhrad

Page 197: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

173

new condensation boiler which will cover the heating and DHW demand, combined with the application

of Photovoltaic panels, that will cover part of the electrical bill, as presented in § 8.1.

8.2.1 Case study “Lecco”

The refurbishment of the technological plant of the school located in Lecco, as previously said, will

consist on removing the existing generation systems, presented in the § 2.3.3, and the installation of a

new condensation boiler, with the combination of PV technology.

8.2.1.1 Design choice

In order to understand the impact of the boiler, it has been proceeded in an overall and fast dimensioning

of the new generation system. Considering the energy analysis done on the existing building, § 5.1.1,

and the analysis done onto the efficiency of the existing plant, it has been decided that a condensation

boiler with the power equal to 200 kW, will be sufficient to cover the heat and DHW demand of the

building in the existing conditions.

It has to be considered also the contribution of the PV panels, as in this case the production will be equal

to 10202.28 kWh/y. Comparing the energy demand, needed for the lighting and equipment system, as

well as the electricity needed to run the generations system, the energy produced by the PV panels is

equal to 85 % of the total electricity needs of the school case building.

The cost of the intervention was calculated in a simple straightforward way, considering the cost of the

materials and of the installation taken from the “Prezziario Lombardia”, which is the pricelist for civil

works in the Lombardy region.

The costs for the refurbishment of the technological plant has been

reported through a simple table. The costs of the Condensation

boiler, include: the removal of the old generation system, and the

installation of a control unit, for the modulation and the regulation

of the new heating and DHW system. With the installation of a new

generation system, it has been decided to implement the existing radiators with the installation of

Thermoelectric radiators valve “TRV”, so that the control of the emission system could be somehow

optimized. The costs of the PV system includes: the cost for the panels, the application, the sub-structure

onto which the panels will be installed, the put in action, and the control units of the system. Basically

the costs presented are intended as the final costs to have a new fully functioning generation and PV

system.

The major changes will be imposed by the new regulation system, installed onto the radiators and onto

the condensation boiler, so that the functioning of these can be now controlled either manually and

Implementation Cost

Condensation Boiler 18677

TRV valves 6160

PV system 24000

Table 8.5: Plant 1 costs, Lecco

Page 198: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

174

automatically, considering the occupation time and the outside temperature, thus reducing the energy

loss during the unoccupied hours. The new boiler will work only when students are present in the

classroom so basically from 06:00 to 18:00 ( considering that in the morning the radiators have to be

heated up a little earlier respect to the start of the lessons), and will also be turned off automatically

during the holiday or weekends, or whenever the outside temperature is higher than the one perceived

on the inside of the classrooms.

8.2.1.2 Consumption reduction

In this paragraph it will be analyzed the perks of doing the specific intervention explained in the previous

paragraph. In this case the intervention is the complete refurbishment of the generations systems of the

building with the addition of a PV system, the perks are represented by the energy and economic savings

and the GHG emission reductions.

Basically it will be compared the consumption of the building in the existing condition “Base case” and

the consumption that will be obtained if a refurbishment would be done “Plant 1”.

As it can been seen from the table, this intervention will lead to a total of 42 % of reduction of the

consumption, thus of the yearly expenses and the GHG emissions.

8.2.1.3 Economic Impact

The economic impact of the intervention is represented through an x-y axis graph, representing the

payback time of the investment and the economic benefit achievable through the energy reduction given

by the intervention.

The results show a satisfying value of payback time of the intervention, equal to 8 years. This means

that through the stand-alone intervention of refurbishment of the technological plant, it will be possible

to reduce the consumption of the school of more than 40 % and to see a positive cash flow incoming in

approximately 8 years. This highlights the impact of a well-designed and updated system, even though

the building itself in inefficient.

Primary Energy GHG emissions Operational Cost Reduction

Base Plant 1 Base Plant 1 Base Plant 1 Plant 1

[kWh/m2y] [kWh/m2y] [tonCO2] [tonCO2] [€] [€] %

Heating 232.94 136.37 45.04 26.36 15946.66 11272.97 41%

DHW 46.07 35.20 8.91 6.81 3593.17 2907.45 24%

Equipment 11.31 1.98 2.74 0.48 578.08 316.75 83%

Light 15.15 2.65 3.67 0.64 773.98 424.10 83%

Total 305.47 176.20 60.36 34.29 20891.89 14921.28 42%

Table 8.6: Reduction of the electric and thermal energy consumption of the school building of Lecco

Page 199: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

175

Through the considerations previously done it’s understandable how big is the impact of a proper

technological plant on the emissions and consumptions of a building. The first question that comes to

mid looking at these results is: “What happens than if I combine an envelope retrofit intervention with

a refurbishment of the plant? These field of application will be explored later on in the thesis work.

8.2.2 Case study “Bustehrad”

The refurbishment of the technological plant of the school located in Bustehrad, as previously said, will

consist on removing the existing generation systems, presented in the § 3.3.3, and the installation of a

new condensation boiler, with the combination of PV technology.

8.2.2.1 Design choice

In order to understand the impact of the boiler, it has been proceeded in an overall and fast dimensioning

of the new generation system. Considering the energy analysis done on the existing building, § 6.1.1,

and the analysis done onto the efficiency of the existing plant, it has been decided that a condensation

boiler with the power equal to 120 kW, will be sufficient to cover the heat and DHW demand of the

building in the existing conditions.

It has to be considered also the contribution of the PV panels, as in this case the production will be equal

to 9463.52 kWh/y. Comparing the energy demand, needed for the lighting and equipment system, as

well as the electricity needed to run the generations system, the energy produced by the PV panels is

equal to 55 % of the total electricity needs of the school case building.

In this case it can be seen that the energy produced by the PV system is pretty much the same in the two

case study, while of course the percentage of needs covered is difference due to the higher starting

electric consumption of the case study located in Lecco.

-60-40-20

020406080

100120140160

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

[k€]

yrs

Plant 1 Payback time

Figure 8-3: Representation of the payback time -x axis- and of the economic benefit -y axis- of each of the

case scenarios chosen for the plant refurbishment, Lecco

Page 200: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

176

The costs for the refurbishment of the technological plant has been

reported through a simple table. The costs of the Condensation

boiler, include: the removal of the old generation system, and the

installation of a control unit, for the modulation and the regulation

of the new heating and DHW system. With the installation of a new

generation system, it has been decided to implement the existing radiators with the installation of

Thermoelectric radiators valve “TRV”, so that the control of the emission system could be somehow

optimized. The costs of the PV system includes: the cost for the panels, the application, the sub-structure

onto which the panels will be installed, the put in action, and the control units of the system. Basically

the costs presented are intended as the final costs to have a new fully functioning generation and PV

system. As it was expected also in this case the costs for the equipment and the installation is cheaper

in Czech Republic respect to Italy, considered the lower market value of the case study.

The major changes will be imposed by the new regulation system, installed onto the radiators and onto

the condensation boiler, so that the functioning of these can be now controlled either manually and

automatically, considering the occupation time and the outside temperature, thus reducing the energy

loss during the unoccupied hours. The new boiler will work only when students are present in the

classroom so basically from 06:00 to 18:00 ( considering that in the morning the radiators have to be

heated up a little earlier respect to the start of the lessons), and will also be turned off automatically

during the holiday or weekends, or whenever the outside temperature is higher than the one perceived

on the inside of the classrooms.

8.2.2.2 Consumption reduction

In this paragraph it will be analyzed the perks of doing the complete refurbishment of the generations

systems of the building with the addition of a PV system, they will be represented by the energy and

economic savings and the GHG emission reductions.

Basically it will be compared the consumption of the building in the existing condition “Base case” and

the consumption that will be obtained if a refurbishment would be done “Plant 1”.

Primary Energy GHG emissions Operational Cost Reduction

Base Plant 1 Base Plant 1 Base Plant 1 Plant 1

[kWh/m2y] [kWh/m2y] [tonCO2] [tonCO2] [€] [€] %

Heating 199.05 110.35 44.06 24.43 10303.04 5711.68 45%

DHW 19.50 18.69 4.32 4.14 2127.57 2038.95 4%

Equipment 15.72 7.07 4.07 1.83 1418.43 638.29 55%

Light 9.08 4.09 3.67 1.65 819.79 368.91 55%

Total 237.78 140.20 56.12 32.05 14668.84 8757.83 41%

Implementation Cost

Condensation Boiler 15688

TRV valves 4620

PV system 16337

Table 8.7: Plant 1 costs, Bustehrad

Table 8.8: Reduction of the electric and thermal energy consumption of the school in Bustehrad

Page 201: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

177

As it can been seen from the table, this intervention will lead to a total of 41 % of reduction of the

consumption, thus of the yearly expenses and the GHG emissions.

Comparing the results of the Czech case study with the Italian one, it’s incredible to see how close the

total reduction of the two are. This is a clear sign of how similar the two case studies are, and therefore

how similar will be the results coming from the energy retrofit of the specific building. The fact that the

reduction are similar is due to the fact that the existing technological plants are pretty similar, exception

made for the gym’s system in Lecco, as matter of fact they are both equipped with 20 years old gas

boiler.

8.2.2.3 Economic Impact

The economic impact of the intervention is represented through an x-y axis graph, representing the

payback time of the investment and the economic benefit achievable through the energy reduction given

by the intervention.

The results show a satisfying value of payback time of the intervention, equal to 6 years. This means

that through the stand-alone intervention of refurbishment of the technological plant, it will be possible

to reduce the consumption of the school of more than 40 % and to see a positive cash flow incoming in

approximately 6 years. This highlights the impact of a well-designed and updated system, even though

the building itself in inefficient.

Comparing the results of the two case studies, the payback time of the two investment are really close

to each other, one again the Czech case study presents a lower payback time due to lower investment

cost. Overall the results can be qualified as satisfying, as the two payback time of the case studies are

low and they are close to each other,

-60-40-20

020406080

100120140160

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

[k€]

yrs

Plant 1 Payback time

Figure 8-4: Representation of the payback time -x axis- and of the economic benefit -y axis- of each of the

case scenarios chosen for the plant refurbishment, Bustehrad

Page 202: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

178

8.3 Heat pump technology

The results coming up from the envelope optimization of both of the case studies( § 7.3.8,7.2.8) show

in the same way the presence of a whole between the most energy performing cases an the rest. As

matter of fact through the graphs in the Figure 7-24 and Figure 7-36 it’s possible to see a gap between

the cases with an energy reduction lower than 70 % and the ones with an higher percentage. It has been

decided to take those energy performing cases, and implement them with the refurbishment of the

technological plant with the installation of a PV system to cover the energy need of the building (§ 8.1)

and a gas-free technology as the Air/water heat pump to cover the heating and DHW needs.

It has been decided to neglect all the cases without the installation of VMC, since the insulation of the

envelope will require a mechanical system to guarantee an appropriate indoor quality, which otherwise

can’t be reached.

A heat pump generator is a system composed of several elements capable of transferring thermal energy

from a body at a lower temperature to a higher temperature one, using electrical energy. The advantage

in using this type of system derives from the ability to supply more thermal energy (in heating mode)

than the electric one used by the generator as it absorbs heat from the external environment.

The principal characteristic, which is also what makes a heat pump system a very efficient and high

efficiency system, is the source used to withdraw or transfer heat. Heat pumps can be of different types:

- Air / air

- Air / water

- Water / air

- Water / water

- Earth / water

Heat pumps that use air as the source are the most widespread, the most economical, but also those with

a lower efficiency. Using air, it must never be too cold: the ideal temperature to provide heating in winter

is constant at 0 ° C. In rigid climates or with frequent changes in temperature, the pump requires auxiliary

devices such as a defrosting system that uses energy, reducing the COP (Coefficient Of Performance).

The COP of a heat pump is a dimensionless coefficient that indicates the level of performance of the

system. COP is the result of the ratio between energy supplied and energy consumed: the higher the

COP, the higher the efficiency. For example, if a machine has a COP = 4, it means that for each kWh of

electricity consumed, 4 kWh of thermal energy are returned. In cooling mode, the heat pump reverses

the cycle, but the principle remains the same. In this case the performance indicator is defined as EER

(Energy Efficient Ratio).

The most performing heat pumps, thanks to a constant source sampling temperature, are those of the

Page 203: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

179

Earth/water and Water/water type. The soil, starting from 6-8 meters of depth, maintains a constant

temperature in the space of a year which is approximately around 10-15 ° C. At the same time the ground

water maintains a constant temperature around 10-12 °C during the year.

8.3.1 Design choice

As previously said the most efficient heat pumps are the geothermal ones, which exploit the mild and

constant temperature of the ground or of the ground water. But at the same time they are the most

complex ones to install, thus the most expensive.

The use of a earth/water heat pump involves a geothermic plant, with the essential needs to install a

geothermal probe in the ground at a depth of 100 m or more. In order to do this it must be possible to

access the subsoil and have no restrictions on drilling. Not all types of subsoil are suitable, it’s necessary

a type of subsoil with a sufficiently high thermal conductivity, i.e. a good ability to transport heat.

For pumps that use water as a source, it is first necessary to identify an aquifer and make sure that it is

possible to collect water from it. The difficulty consists in fact, in addition to identifying the aquifer, in

the need to obtain an authorization from the territorial municipality. This is due to the fact that if there

were breakages in the probes, the thermal liquid would risk to leak and pollute water and subsoil.

As matter of fact the water/water heat pump systems can be open loop, directly exploiting the ground

water, or in a closed loop, with an intermediate heat transfer fluid as in the classic geothermal

applications

So in addition to what said previously in the case of an open loop circuit, in which the water is pumped

into the machine and then given back to the aquifer, several controls on the temperature and the quality

of the return water have to be performed in order not to alter the water present in the aquifer. Open loop

applications require the presence of one or more boreholes for water collection and its return. Finally

the municipality usually taxes the use of the aquifer applying a cost for the extraction of the water, which

has to be added in the operational costs of the plant.

For all these reasons the application of geothermal plant has been discarded in favor of a simpler

technology as the air/water heat pump. Moreover the decision has been made considering that the air

heat pumps have the advantage that they exploit a source always available, they don’t need any

expensive boreholes or heat exchangers and no authorization for the use at all. Plus has seen in the

climatic analysis done in the chapter 4, the climate of the two locations during the winter season will

not be a problem for the installation of the heat pump. As matter of fact it is not too rigid as the average

monthly temperature is around 0 and -2 °C and is not too humid too, thus not reducing the efficiency of

the pump due to the defrosting of the machine.

Page 204: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

180

8.3.2 Case study “Lecco”

In order to understand the impact of the boiler, it has been proceeded in an overall and fast dimensioning

of the new generation system. Considering the energy analysis done on the possible optimization of the

building, § 7.2.8, and the analysis done onto the efficiency of the existing plant, it has been decided that

a condensation boiler with the power equal to 80 kW, will be sufficient to cover the heat and DHW

demand of the building in the existing conditions, with a COP equal to 3.5 as defined by standards [19].

It has to be considered also the contribution of the PV panels, as in this case the production will be equal

to 10202.28 kWh/y. This is equal to the 85 % of the energy demand, needed for the lighting and

equipment system of the school case building.

The cost of the intervention was calculated in a simple

straightforward way, considering the cost of the heat pump and of

the installation. This costs have been decided based on a cross

analysis of the multiple offers received by specific companies, for

the specific heat pump.

The combined cases analyzed for this analysis focused in the application of Heat pump onto enrgy

performing envelopes are the followings.

Basically what has been done was to select the most performing case scenario analyzed in the Envelope

retrofit (considering only the ones with VMC) and apply to the building an air/water heat pump, in order

to see what could be the most energy reduction achievable with the retrofit of the case study building.

8.3.2.1 Building’s energy reduction

Different from the cases analyzed till now, the installation of a PV system combined with an heat pump

will involve the consumption of the entire building. This will mean that this intervention will affect all

Gym Insulation Glazing Mechanical ventilaiton

EPS rigid Rockwool rigid Wood fiber rigid Polyester fiber Rockwool Calcium Silicate Rockwool roll Glass wool HD EPS HD Rockwool HD Wood fiber HD Synthetic material Low-e CMV Heat recovery PV system Heat pump

Case 28.1

Case 28.2

Case 28.3

Case 29.1

Case 29.2

Case 29.3

Case 30.1

Case 30.2

Case 30.3

Case 31.1

Case 31.2

Case 31.3

Case 32.1

Case 32.2

Case 32.3

Technological PlantSCENARIO

Wall external Insulation Wall internal insulation Attic insulation Roof insulation

Implementation Cost

Air/Water Heat pump 40000

TRV valves 6160

PV system 24000

Table 8.9: Heat Pump costs, Lecco

Figure 8-5: Different case scenarios, involving an Heat pump, for the energy retrofit of Lecco’s school building

Page 205: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

181

the components of the building, it will be possible to see PE reduction in terms of heating, DHW, lighting

and equipment. Furthermore there won’t be any gas technology present after the retrofit, since the heat

pump will run only on electricity.

PE [kWh/(m2y)] Annual Total Reduction

Heating DHW Equipment Lights PV panels* Total € Ton CO2 %

Base 232.94 46.07 11.31 15.15 - 305.47 - - -

Case 28 21.50 19.41 15.15 11.31 22.14 45.24 17798.09 51.42 85.2%

Case 29 11.62 19.41 15.15 11.31 22.14 35.36 18473.87 53.37 88.4%

Case 30 10.55 19.41 15.15 11.31 22.14 34.29 18547.05 53.59 88.8%

Case 31 16.69 19.41 15.15 11.31 22.14 40.43 18127.07 52.37 86.8%

Case 32 11.39 19.41 15.15 11.31 22.14 35.12 18489.74 53.42 88.5%

* refers to the energy production of the PV panels per year divided by the net surface of the building.

The Table 8.10 shows some outstanding results regarding the installation of an air/water Heat pump

combined with PV system onto the school building case study, considering also the retrofitted envelope.

The range of the achievable total PE energy consumption of the retrofitted building goes from 34 to 45

kWh/(m2y) with a reduction from 85 to almost 89 %. This means that choosing one of the scenario here

presented it’s possible the reduce the energy reduction of the building so that the retrofitted building

could be certified as an A4 energy class building ( § 2.3.4) , which is the lowest class possible.

8.3.2.2 Economic Impact

The graph represented in the Figure 8-6 basically sums all the study done on the envelope of the school

building located in Lecco. It has been decided to represent 5 different retrofit interventions, sub-divided

into 3 case scenarios for each of the interventions, as seen in Figure 8-5.

The energy reduction changes only between the different retrofit interventions, while it stays the same

no matter the case scenario analyzed for each specific intervention. In this way it was possible to

construct a line for each retrofit intervention analyzed, so that this line could represent the range in which

the economic investment, bore for the different case scenarios of the specific intervention, would lay

into. The construction of the Intervention’s line was made joining the three points representing the three

different related case scenarios. So the construction points represent each of the 3 case scenario studied

for the specific intervention, as matter of fact for each line the lowest point represents the most economic

solution analyzed, while the top one represents the most expensive one.

The graph shows what has already been said previously, the application of the heat pump combined with

the PV system could lead to a minimum PE total energy reduction of 85 % to which it corresponds a

minimum investment cost of 240 thousands of euro, which translates to a CER equal to 0.92 €/kWh and

a payback time of 12 years. Meaning that the cheapest integrated intervention will guarantee an elevated

Table 8.10: Heating reductions with the installation of a Heat pump onto an efficient envelope, Lecco

Page 206: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

182

reduction of energy, with a moderate expense as it is 240 thousands of euro.

The graph shows that the application of the heat pump combined with the PV system could lead to a

maximum PE total energy reduction of 89 % to which it corresponds a minimum investment cost of 320

thousands of euro, which translates to a CER equal to 1.24 €/kWh and a payback time of 16 years.

Comparing the two extreme results the “case 28” and the “Case 32”, the most cost-effective seems to

be the Case 28, even though it will reach a lower energy reduction. This particular intervention will

involve of course the installation of a air/water Heat pump combined with a PV system, onto an envelope

with insulated external walls (either from the inside and outside), performing low-e double gazing and

CMV.

8.3.3 Case study “Bustehrad”

In order to understand the impact of the boiler, it has been proceeded in an overall and fast dimensioning

of the new generation system. Considering the energy analysis done on the possible optimization of the

building, § 7.3.8, and the analysis done onto the efficiency of the existing plant, it has been decided that

a condensation boiler with the power equal to 50 kW, will be sufficient to cover the heat and DHW

demand of the building in the existing conditions, with a COP equal to 3.5 as defined by standards [19].

It has to be considered also the contribution of the PV panels, as in this case the production will be equal

to 9463.52 kWh/y. This is equal to the 55 % of the energy demand, needed for the lighting and equipment

system of the school case building.

28

31

32

29

30

200

225

250

275

300

325

350

375

400

425

450

82.5% 83.0% 83.5% 84.0% 84.5% 85.0% 85.5% 86.0% 86.5% 87.0% 87.5% 88.0% 88.5% 89.0% 89.5% 90.0%

[k€] Investment cost

Energy reduction

Case 28 Case 29 Case 30 Case 31 Case 32

Figure 8-6: Analysis of the heating energy demand reduction % – x axis- and the cost of the investment [k€] - y

axis- of the different case scenarios considered for the for the Heat pump installation in Lecco’s school building

Page 207: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

183

The cost of the intervention was calculated in a simple

straightforward way, considering the cost of the heat pump and of

the installation. This costs have been decided based on a cross

analysis of the multiple offers received by specific companies, for

the specific heat pump.

It’s clear that, as seen throughout the entire thesis work, the costs for the Czech case are lower due to

lower starting energy consumption, and the lower costs for materials and labor.

The combined cases analyzed for this analysis focused in the application of Heat pump onto energy

performing envelopes are the followings.

Basically what has been done was to select the most performing case scenario analyzed in the Envelope

retrofit (considering only the ones with VMC) and apply to the building an air/water heat pump, in order

to see what could be the most energy reduction achievable with the retrofit of the case study building.

8.3.3.1 Building’s energy reduction

Different from the cases analyzed till now, the installation of a PV system combined with an heat pump

will involve the consumption of the entire building. This will mean that this intervention will affect all

the components of the building, it will be possible to see PE reduction in terms of heating, DHW, lighting

and equipment. Furthermore there won’t be any gas technology present after the retrofit, since the heat

pump will run only on electricity.

PE [kWh/(m2y)] Annual Total Reduction

Heating DHW Equipment Lights PV panels* Total € Ton CO2 %

Base 199.05 19.50 15.72 9.08 - 243.36 - - -

Case 28 28.60 2.04 9.09 15.73 20.03 35.42 12132.33 44.74 82.7%

Case 29 17.24 2.04 9.09 15.73 20.03 24.06 12898.38 47.56 87.9%

Case 30 16.74 2.04 9.09 15.73 20.03 23.56 12932.38 47.69 88.2%

Case 31 22.09 2.04 9.09 15.73 20.03 28.91 12571.63 46.36 85.7%

Case 32 21.70 2.04 9.51 16.15 20.03 29.36 12624.27 46.55 86.1%

Gym Insulation Glazing Mechanical ventilaiton

EPS rigid Rockwool rigid Wood fiber rigid Polyester fiber Rockwool Calcium Silicate Rockwool roll Glass wool HD EPS HD Rockwool HD Wood fiber HD Synthetic material Low-e CMV Heat recovery PV system Heat pump

Case 28.1

Case 28.2

Case 28.3

Case 29.1

Case 29.2

Case 29.3

Case 30.1

Case 30.2

Case 30.3

Case 31.1

Case 31.2

Case 31.3

Case 32.1

Case 32.2

Case 32.3

Technological PlantSCENARIO

Wall external Insulation Wall internal insulation Attic insulation Roof insulation

Implementation Cost

Air/Water Heat pump 25000

TRV valves 4620

PV system 16337

Table 8.11: Heat Pump costs,

Bustehrad

Table 8.12: Heating reductions with the installation of a Heat pump onto an efficient envelope, Bustehrad

Figure 8-7: Different case scenarios, involving an Heat pump, for the energy retrofit of Bustehrad school building

Page 208: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

184

* refers to the energy production of the PV panels per year divided by the net surface of the building.

The Table 8.12 shows some outstanding results regarding the installation of an air/water Heat pump

combined with PV system onto the school building case study, considering also the retrofitted envelope.

The range of the achievable total PE energy consumption of the retrofitted building goes from 34 to 45

kWh/(m2y) with a reduction from 82 to 88 %. This means that choosing one of the scenario here

presented it’s possible the reduce the energy reduction of the building so that the retrofitted building

could be certified as an A4 energy class building ( §3.3.4) , which is the lowest class possible.

The results coming from the Table 8.12 and the Table 8.10 are once again really similar, meaning that

the impact of the installation of an heat pump will be pretty much the same. Furthermore this intervention

will guarantee in both cases the achievement of the energy class A4, even though the total energy

consumption reached in the Czech case study is lower respect to the Italian one, due to the different

energy starting point of the two cases.

8.3.3.2 Economic impact

The graph represented in the Figure 8-8 basically sums all the study done on the envelope of the school

building located in Lecco. It has been decided to represent 5 different retrofit interventions, sub-divided

into 3 case scenarios for each of the interventions, as seen in .

The energy reduction changes only between the different retrofit interventions, while it stays the same

no matter the case scenario analyzed for each specific intervention. In this way it was possible to

construct a line for each retrofit intervention analyzed, so that this line could represent the range in which

the economic investment, bore for the different case scenarios of the specific intervention, would lay

into. The construction of the Intervention’s line was made joining the three points representing the three

different related case scenarios. So the construction points represent each of the 3 case scenario studied

for the specific intervention, as matter of fact for each line the lowest point represents the most economic

solution analyzed, while the top one represents the most expensive one.

The graph shows what has already been said previously, the application of the heat pump combined with

the PV system could lead to a minimum PE total energy reduction of 82.5 % to which it corresponds a

minimum investment cost of 180 thousands of euro, which translates to a CER equal to 0.88 €/kWh and

a payback time of 10 years. Meaning that the cheapest integrated intervention will guarantee an elevated

reduction of energy, with a moderate expense of less than 200 thousands of euro.

The graph shows that the application of the heat pump combined with the PV system could lead to a

maximum PE total energy reduction of 88 % to which it corresponds a minimum investment cost of 230

thousands of euro, which translates to a CER equal to 1.10 €/kWh and a payback time of 13 years.

Comparing the two extreme results the “case 28” and the “Case 32”, the most cost-effective seems to

Page 209: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

185

be the Case 28, even though it will reach a lower energy reduction. This particular intervention will

involve of course the installation of a air/water Heat pump combined with a PV system, onto an envelope

with insulated external walls (either from the inside and outside), performing low-e double gazing and

CMV.

Comparing the Figure 8-7 and the Figure 8-5 it is possible to have a final and global view on the possible

effects of the specific integrated strategies onto different buildings located in different part of Central

Europe. Once more the results in terms of percentage, in this case percentage of total PE reduction, are

very similar for the two case study, they almost coincide. On the other hand it is possible to see that the

low cost of labor materials, makes the intervention in Czech Republic more feasible, as the “Case 28”

has a payback time of only 10 years, which is not really different from the 12 years seen for the Italian,

but still guarantees to the investor a low risk intervention, which will profit his bank account and at the

same time definitely decrease the energy emissions, contributing in the GHG emission reduction plans

present throughout all Europe.

28

3132

29

30

160

180

200

220

240

260

280

300

320

340

360

82.5% 83.0% 83.5% 84.0% 84.5% 85.0% 85.5% 86.0% 86.5% 87.0% 87.5% 88.0% 88.5% 89.0% 89.5% 90.0%

[k€] Investment cost

Energy reduction

Case 28 Case 29 Case 30 Case 31 Case 32

Figure 8-8: Analysis of the heating energy demand reduction % – x axis- and the cost of the investment [k€] - y

axis- of the different case scenarios considered for the for the Heat pump installation in Bustehrad school building

Page 210: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

186

Page 211: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

187

Conclusions

This thesis work addresses the necessary implementation of an integrated strategy promoting a large-

scale energy retrofitting of the public educational building stock in the Central Europe area. It develops

tailored planning for these buildings so to address the long-term objective of deep retrofitting promoting

a technologically logical step-by-step approach that can be managed with affordable budgets. This work

supports the overall program goal of reducing carbon emission in the cities of Central Europe, creating

an enabling framework to promote large scale energy retrofit of existing public educational buildings.

This has been done analyzing in terms of energy and costs two different case studies school buildings

located in two different part of the CE area, Italy and Czech Republic.

The data analyzed, starting from the preliminary weather analysis of the two different location, has

shown positive feedback throughout the entire work. As matter of fact the innovativeness of this work

is to focus the analysis onto school building localized in the CE, thus with the assumption that the

geographical boundaries of this area could actually correspond to climatic boundaries, so that the

climatic conditions are homogeneous.

The energy analysis done onto the existing case study school buildings has confirmed the second

assumption, for which even though the building structures and building techniques used throughout

Europe are different, schools of the CE area with similar construction age have comparable energy

consumption. Meaning that it is possible to asses and identify a common starting point for the energy

retrofit process of multiple eductional buildings located in the CE area.

The results coming from the energy analysis have been used as guidelines for the energy retrofit process.

The first part of the retrofit process involved the re-cladding of the school buildings through an energy

optimization of the envelope, thus insulating the building’s elements in contact with the outside

environment. This highlights two important aspects which have to be taken into account as fundamentals

for the retrofit process. Intervening on the most vulnerable elements (in terms of energy performances)

of the two buildings, has pointed out which are the most beneficial interventions.

As matter of fact, thanks to an accurate energy analysis of the existing case, it was possible to propose

aimed energy retrofit intervention which were applied in the same way onto the different school

buildings and that had, most importantly, similar impact onto the energy and economic consumptions

of the case studies. Basically this means that it was possible to spot the most energy-efficient

intervention for the two case studies, and that above all, they matched and had similar impact on the

existing buildings.

The work than steps into a detail analysis on the perks of using an integrated approach for the energy

retrofit interventions. It has been possible to analyze different scenarios involving different level of

detail, going from a simple refurbishment of the roof structure to a combined insulation of multiple

Page 212: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

188

dispersive elements. The results show that the exploit of an integrated approach pays off not only on the

energy and emission reduction level, but also on an economic one, pointing out the fact that aimed

combined intervention, with high investment costs, can also represent the most economically beneficial.

Moreover this work is able to mark guide lines which lead to an energy retrofit capable of reducing the

consumptions of the school buildings to a maximum of almost 90% of the initial value, with non-

invasive low budget interventions , transforming the real estate into a low energy building, certifiable in

the A4 energy class. These guidelines are based on the results extracted from the analysis done onto the

two case study, which means that they can be successfully applied to educational buildings with similar

properties located in the Central Europe area, fulfilling the goal of this thesis work.

A small and last consideration has to be done on the simple economic impact analysis done onto the

most energy-efficient intervention proposed. The investment costs considered throughout this thesis

work were calculated, without the addition of any financial benefit coming from the municipality, State

or European Union, in order to have a more plain and comparable cost. But analyzing the payback time

given by the analysis done, it’s clear that the retrofit process has to be supported by these authorities,

with some financial help, so that the combination of these benefits with aimed integrated approach

interventions re-defining the energy retrofit from possible to feasible.

Page 213: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

Bibliography

[1] European commission database, "2020 Climate & Energy package," [Online]. Available:

https://ec.europa.eu/clima/policies/strategies/2020_en.

[2] "Kyoto Protocol," in COP3 Conference of the UNFCCC, Kyoto, 1997.

[3] "Attachment 3:European Directive," in Energy Efficiency Directive EED 2012/27/UE.

[4] Europena commission datatabase, "EU building stock observatory," [Online]. Available:

https://ec.europa.eu/energy/en/eu-buildings-database.

[5] Luísa Dias Pereira, Daniela Raimondo,Stefano Paolo Corgnati, "Energy consumption in schools

– A review paper".

[6] "Italian Official Gazette n° 148," Italian republic, 07/06/1976.

[7] ENEA, "Guide to the energy efficiency of the school building," 2017.

[8] Italian Republic, "Norme per l'attuazione del Piano energetico nazionale in materia di uso

razionale dell'energia, di risparmio," Law no. 10, 9 January 1991.

[9] Italina National Energy Strategies, "Italian Energy Efficiency Action Plan," EEAP 2014, 2014.

[10] "Energy Rennovation," JRC Science and Policy Report, 2015.

[11] Arch. Roberto De marchi, "Ri-costruire a quasi km 0," 22 November 2013.

[12] Italia Republic, "DPR 59/09," Nuovo quadro di disposizioni obbligatorie (requisiti sull’efficienza

energetica degli edifici) che sostituiscono le indicazioni “transitorie” dell’Allegato I del

DLgs311/06., no. Decreto del Presidente della Repubblica n. 59, 2 April 2009.

[13] Ministro dello sviluppo economico di concerto con i Ministri dell’ambiente e della tutela del

territorio e del mare, delle infrastrutture e dei trasporti e per la semplificazione e la pubblica

amministrazione, "Linee guida nazionali per la certificazione energetica degli edifici," Decreto

interministeriale del 26 giugno , 2015.

[14] European Energy commision, Energy Performance Buildings Directive 2 - EPBD 2, Directive

2010/31/EU.

[15] Ministero dello Sviluppo economico, Aggiornamento delle disposizioni in merito alla disciplina

per l'efficenza energetica degli edifici e al relativo attestato di prestazione energetica, DECRETO

N. 176 DEL 12 GENNAIO 2017, 12/01/2017.

[16] Gazzetta Ufficiale della Repubblica Italiana, Disposizioni urgenti per il recepimento della

Page 214: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

Direttiva 2010/31/UE del Parlamento europeo e del Consiglio del 19 maggio 2010, sulla

prestazione energetica nell'edilizia, DECRETO-LEGGE n. 63, 4 giugno 2013.

[17] Regolamento recante disciplina dei criteri di accreditamento per assicurare la qualificazione e

l'indipendenza degli esperti e degli organismi a cui affidare la certificazione energetica degli

edifici, DECRETO DEL PRESIDENTE DELLA REPUBBLICA n. 75, 16 aprile 2013.

[18] Decreto del Ministero dello sviluppo economico 26 giugno 2015, Linee guida nazionali per la

certificazione energetica.

[19] "International Energy Agency "IEA"," [Online]. Available:

https://www.iea.org/policiesandmeasures/energyefficiency/.

[20] Tabula research facility, "National Scientific Report "Czech Republic"," in Typology Approach

for Building Stock Energy Assessment, 2015.

[21] European Union Law, Government Resolution No 362, EUR-LEX, 18 May 2015.

[22] European Union Law, Directive No. 1/2014, EUR-Lex.

[23] International Energy Agency of Czech Republic, "Act No. 406/2000 Coll," in Energy

Management Act, 01/01/2013.

[24] Executive Agencies for SMEs, Intelligent Energy Europe Programme (IEE), European

Commission, 2007-2013.

[25] European Commission, "Typology Approach for Building Stock Energy Assessment," in

Intelligent Energy Europe, 2009-2012.

[26] EN ISO 6946, "Calculation methods," in Building components and building elements. Thermal

resistance and thermal transmittance, European Committee, 2017.

[27] EN ISO 13370, "Calculation methods," in Thermal performance of the building. Heat trasnfer via

ground, European Committee, 2007.

[28] EN ISO 12464 - 1, "Indoor work places," in Light and lighting. Lighting of work places, European

Committee, 2011.

[29] CIBSE Guide A: Environmental Desing, CIBSE, 2015.

[30] "National Calculation Methodology," in UK Building Regulations Part L2, 2006.

[31] EN ISO 13000-2, "Evaluation of primary energy need and of system efficiencies for space heating,

domestic hot water production, ventilation and lighting for non- buildings," in Energy

performance of buildings- Part 2, European Committee, 2014.

[32] UNI EN 442, "Technical specifications and requirements," in Radiators and convectors-Part 1,

Italian Committee.

Page 215: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

[33] EN ISO 14064-1, "Specification with guidance at the organization level for quantification and

reporting of greenhouse gas emissions and removals," in Greenhouse gases- Part 1, European

Committee, 2006.

[34] Intergovernamental Panel on Climate Change "IPCC" , Guidelines for National Greenhouse Gas

Inventories, 2016.

[35] CNG Europe, "Map of Natural Gas Vehicle (NVG) Compressed natural gas (CNG) filling stations

in Europe," [Online]. Available: http://cngeurope.com/.

[36] IEA Czech Republic, "Regulation No. 148," in Energy Management Act, 2007.

[37] Agenzia Regionale per la Protezione dell'Ambiente, " ARPA Lombardia," [Online]. Available:

http://www.arpalombardia.it/Pages/Ricerca-Dati-ed-Indicatori.aspx.

[38] Ceske Republicky, "Republicky, Agenture ochrany prírody a krajiny Ceske," [Online]. Available:

http://www.ochranaprirody.cz/.

[39] "EPA", European Network of the Heads of Environment Protection Agencies,

"http://epanet.pbe.eea.europa.eu/european_epas," [Online].

[40] ARPA Lombardy, "Beaufort Scale for wind intensity".

[41] Regioncal Council of Lombardy, Decree no 2129, 2014.

[42] "PCM Ordinance n 3519," in Seismic Hazard, 28 April 2006.

[43] ASHRAE Standard 55, Thermal Environmental Condition for Human Occupancy, 2013.

[44] EN ISO 15251, Indoor environmental input parameters for design and assessment of energy

performance of buildings addressing indoor air quality, thermal environment, lighting and

acoustics, European Committee, 2007.

[45] EN ISO 7730, Predicting the perceived thermal sensation of a human being within confined

moderate environments, 1997.

[46] UNI EN ISO 7726, Measurement of physical quantities that affect the thermal sensations, 1995.

[47] J. van Hoof , Forty years of Fanger’s model of thermal comfort: comfort for all Indoor Air, 2008.

[48] RJ de Dear, GS Brager, "Thermal comfort in naturally ventilated buildings: revisions to ASHRAE

Standard 55," in Energy building, vol. Energy Build , 2015.

[49] R. de Dear, "Indoor Air," in Thermal comfort in practice, 2014.

[50] Roaf S, Nicol F, Humphreys M, Tuohy P, Boerstra A, "Twentieth century standards for thermal

comfort: promoting high energy buildings," Architectural Science review, 2011.

[51] MA Humphreys, "Thermal comfort temperatures world-wide – the current position.," in

Renewable Energy, 1996.

Page 216: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

[52] CIBSE, "The limits of thermal comfort: Avoiding Overheating in European Buildings," in

Technical Memorandum 52, Oct 2013.

[53] Sustainable Energy Research Team (SERT), Inventory of Carbon and Energy(ICE), University of

Bath UK.

[54] ČSN 73 0540, Thermal protection of buildings, Czech Committee.

[55] EN ISO 11300-1, "Determination of the building's thermal energy requirements for summer and

winter air conditioning".Energy performances of buildings- Part 1.

[56] EN ISO 13786, "Calculation methods," in Thermal performance of building components -

Dynamic thermal characteristics , 2008.

[57] EN ISO 10077-2, "Calculation of thermal transmittance- Numerical method for frames," in

Thermal performance of windows, doors and closures - Part 2, 2012.

[58] UNI 10339, Aeraulic system for internal comfort, Italian Committee, 1995.

[59] The Chartered Institution of Building Services Engineers, Degree-days: Theory and Application,

2006.

[60] Italian Republic, Decreto del Presidente della Repubblica n. 412, 31 ottobre 2009.

[61] European Environment Agency, "Heating degree days," [Online]. Available:

https://www.eea.europa.eu/data-and-maps/indicators/heating-degree-days-1/assessment.

Page 217: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

Appendices

Appendix I – Validation of the energy models

In order to see if the energy model made, is reliable, a verification has to be performed. The verification

in basically based on comparing the consumptions coming from the energy model with the real ones

coming from the energy bill.

In this case the parameter that will be compared is the amount in mc/year of natural gas used by the

heating system to fulfill the heating needs throughout the entire thermal season. To do this it’s necessary

to standardize the results coming from the software and the ones coming from the bill, these is due to

the fact that the two have to be equal in order to be comparable. This will be translated into a Degree-

days standardization.

As matter of fact the first calculation will involve the Degree days. Degree-days are essentially the

summation of temperature differences over time, and hence they capture both extremity and duration of

outdoor temperatures. The temperature difference is between a reference temperature and the outdoor

air temperature. The reference temperature is known as the base temperature which, for buildings, is a

balance point temperature, i.e. the outdoor temperature at which the heating (or cooling) systems do not

need to run in order to maintain comfort conditions. [59]

Degree-days may be calculated using different approaches and therefore different input data [59]. For

the purposes of the validation the degree-days will be calculated as the following:

𝐷𝐷 = ∑(𝑇𝑜 − 𝑇𝑠𝑒𝑡 𝑝𝑜𝑖𝑛𝑡

𝑛

𝑖=1

)

Where:

- To is the daily average outside temperature;

- Tset point is the set point temperature equal to 20 °C;

- i is equal to number of days included in a thermal season.

This will represent the actual degree days per year, which are the ones considered for the energy bill.

Unfortunately the software is not able to do this calculation for each year, changing the weather

conditions depending on the year analyzed. Therefore it has been calculated only the DD corresponding

on the outside temperature of a specific year, present in the software database.

Finally in order to standardize these two different DDs it will be presented the standard’s DD [60] [61]

(depending on the climatic zone of the city), which as the one of the software is only one, not depending

on the year.

The comparison will be done through the consultation of the energy bills referring to the thermal season

Page 218: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

of the 2015-2016 and of the 2016-2017, made available from the schools’ authorities.

The second and final step, involves the comparison of the two standardize quantities, for the two

different case studies.

Finally in order to verify the reliability of the two models it’s necessary to calculate the Deviation of the

results coming from the energy model. The deviation represents how different the results coming from

the energy model are compared the ones coming from the energy bill.

As it can be seen both of the energy models can be considered reliable, as the deviation is less than ± 10

%. As matter of fact the consumption of natural gas, expressed in [m3/year], coming from the energy

model is only 2.2 percent lower respect to the real consumptions, obtained through the energy bill,

meaning that during the modelling of the case study it has been done a slight under consideration. The

deviation for the Czech case study is equal to – 3.6%, meaning that the results coming from the energy

model are slightly lower than the real ones.

Bustehrad Degree days

Standard 3431

2015-2016 3198

2016-2017 3545

Software 3644

Standardize Consumptions

Source year m3/year

Software - 22135

Energy bill

2015-16 23227

2016-17 22651

Average 22939

Deviation -3.6%

Standardize Consumptions

Source year m3/year

Software - 23013

Energy bill

2015-16 23518

2016-17 23518

Average 23518

Deviation -2.2%

Lecco Degree days

Standard 2383

2015-2016 2166

2016-2017 2186

Software 2750

- Lecco - Bustehrad

Page 219: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

Appendix II – Thermal analysis of the window

For the thermal analysis of the elements, it has been used the thermal transmittance analysis of the

frame of the window, the study of the thermal bridge between the frame and the glass, the verification

of presence of condensation in the main joints, using the software Therm.

The thermal transmittance of the window (Uw) was found using the calculation method presented in the

standard UNI EN ISO 1077-2 [43], in which the elements are divided in frame , glass, and glass’ spacer.

Uw = AgUg + AfU𝑓 + Lgψ

g

Atot

- Uw is the thermal transmittance of the window

- Ug is the thermal transmittance of the glass

- Lg is the length of the glass

- Ag is the area of the glass

- Af is the area of the frame

- 𝜓 is the linear thermal transmittance due to the thermal bridge of the window

For the thermal calculations that will be explored further in detailed, it has been considered the boundary

conditions as shown in the figure below.

Boundary Conditions Temperature[°C] U Transmittance [W/m2k]

External -5 25

Internal vertical 20 7.7

Internal incremented 20 5

Internal horizontal 20 10

The presence of the boundary condition “Internal incremented” is done in order to consider better the

surfaces affected by a small value of thermal exchange due to convection and irradiation( it was used

Glass Length Lg Glass Area Ag Frame Area Af

[m2] [m2] [m2]

0.95 1.83 0.57

Page 220: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

wherever there were sudden change of direction).

The choice of the glass was accurately done thanks to the spectrum online software given by Pilkington:

Following the UNI EN ISO 10077-2 [43] the calculation of the transmittance of the frame (Uf) was done

replacing the glass with an insulation panel, with conductivity of λ= 0.035 W/m2K.

Page 221: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

The section of the proposed glazing is:

The results from the software are:

Frame + Insulation Panel Frame Edge

U [W/m2K] 1.14 0.6971

b [m] 0.085 0.190

Following the standard, it was later considered the real case( in which the window is composed by a

frame and a glass) , using the same boundary condition as before.

For what concerns the conductivity of the gap between the two glazings, filled with argon, it was

calculated with an hand calculation starting from the value of the Ug.

Ug = 1 W/m2K sv = 0.006 m seq = 0.016 m

λv= 0.8 W/mK Rsi= 0.13 m2K/W Rse= 0.04 m2K/W

1

𝑈𝑔 = 𝑅𝑔

𝑅𝑔 = 𝑠𝑣

𝜆𝑣 +

𝑠𝑣

𝝀𝑣 +

𝑠𝑒𝑞

𝜆𝑒𝑞 + 𝑅𝑠𝑖 + 𝑅𝑠𝑒

Material Characteristics

Component

Thermal

conductivity

[W/mK]

Insulation 0.035

PVC 0.19

Gaskets (EPDM) 0.25

Spacer (PVC) 0.19

Polyammide 6.6 0.3

Page 222: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

𝑠𝑒𝑞

𝝀𝑒𝑞 = 𝑅𝑔 −

𝑠𝑣

𝝀𝑣 +

𝑠𝑣

𝝀𝑣 + 𝑅𝑠𝑖 + 𝑅𝑠𝑒 = 0.815 m2K/W

𝝀𝑒𝑞 = 0.02 W/mK

Therefore the following calculation will be done with the value of 0,02 W/mK for the gap in between

the two glazing.

The section of the proposed glazing is:

The results from the software are:

Frame + Insulation Panel Frame Edge

U [W/m2K] 1.18 1.135

b [m] 0.085 0.190

At this point we were able to calculate the thermal bridge that occurs due to the 10 eometrical

irregolarities and the material choosen. This evaluation has been done using the subtraction of the fluxes.

We can calculate the thermal conductivity of the joint:

Vertical Section:

Horizontal Section

- Lѱ,2D = thermal conductivity [W/mK]

- Uf,g = thermal conductivity of the frame in the case of frame+ glass [W/m2K]

- bf = I of the frame [m]

- Ue = thermal conductivity of the glass in the case of frame+glass [W/m2K]

- be = length of the glass [m]

We proceed in the calculatin of the thermal linear trasmittance ψ:

Material Characteristics

Component

Thermal

conductivity

[W/mK]

Argon 0.02

Glass 1

PVC 0.19

Gaskets (EPDM) 0.25

Spacer (PVC) 0.19

Polyammide 6.6 0.3

Silica gel 0.13

Lѱ,2D = Uf,gbf + Uebe = 0.461

W/mK Lѱ,2D = Uf,gbf + Uebe = 0.469

W/mK

Page 223: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

Vertical Section

Horizontal Section

- - Uf,p= thermal conductivity of the fram in the case fram+ insulation panel [W/m2K]

- - Ug = thermal conductivity of the glass [W/m2K]

- - bg = length of the glass [m]

Now that there are all the needed values the work can go on and calculate the global thermal

transmittance of the window and check if it is acceptable.

𝑈𝑤 = 𝐴𝑔𝑈𝑔 + 𝐴𝑓𝑈𝑓 + 𝐿𝑔𝜓𝑔

𝐴𝑡𝑜𝑡= 1. 16 𝑊/𝑚2𝐾

The value obtained is lower than the limit presented in the § 7.2.7, equal to 1.3 W/m2K.

The second step that has to be done in order to satisfy the limitation imposed by the standards is the

verification of the solar transmission factor “ggl+sh“ for glazing components so that: ggl+sh ≤ 0.35. In order

to do the verification it has been followed the EN ISO 11300-1 [41].

First of all it has to be considered that the reduction factor, imposed by standard. The reduction factor

goes from 0 to 1, changing depending on the type of shading applied onto the analyzed windows. The

reduction factor is strictly related to the transmission factor for the glass “ggl” calculated through the

use of the Pilkington spectrum software. Finally it has to be accounted also for the exposition factor

“Fw” which considers the variation of the transmittance of total solar energy as a function of the angle

of incidence of solar radiation.

- ggl+sh/ggl = 0.5;

- ggl = 0.58 (Pilkington spectrtum);

- Fw = 0.916 ( considering the worst orientation, which for double glazing is represented by

East/West in May).

Considering that :

𝑔𝑔𝑙+𝑠ℎ =0.5∗ 𝑔𝑔𝑙

𝐹𝑤 = 0.316 ≤ 0.35

Therefore the verification is satisfied.

Ѱ= Lѱ,2D -Uf,pbf - Ugbg = 0.0396 W/mK

Ѱ= Lѱ,2D -Uf,pbf - Ugbg = 0.0461 W/mK

Page 224: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

Appendix III – Economic index of the scenarios

The economic index CER (Cost of Energy Saving, expressed in €/kWh) provides interesting results

regarding the economic feasibility of an intervention. This index clearly defines the economic

disbursement sustained by the user for each unit of energy saved as a result of the redevelopment

intervention.

In the present study, a value of the simplified CER will be used, defined as the ratio between the sum of

the costs of the initial investment and the expected energy savings at the end of the useful life of the

realized energy measure. The CER is expressed as follows:

𝐶𝐸𝑅 =∑ 𝐶𝑛

𝑖=0

∑ 𝐸𝑟𝑖𝑠𝑝,𝑖𝑛𝑖=1

Where:

- C = costs incurred for the intervention in the i-th year;

- Erisp,I = energy saved in the i-th year following the intervention.

In this formula only the costs I related to the initial intervention I0 are considered (therefore, the energy

costs before and after intervention are not included). The annual maintenance and operation costs were

excluded as no changes in the cost between the intervention and post-intervention were considered for

these items. Likewise, there are no financial burdens because the investment paid is considered entirely

within the first year, therefore no type of payment is deferred.

Page 225: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

Representation of the CER value [€/kWh] for each of the envelope optimization scenarios, Lecco:

Page 226: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

Representation of the CER value [€/kWh] for each of the Heat pump optimization scenarios, Lecco:

Page 227: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

Representation of the CER value [€/kWh] for each of the envelope optimization scenario, Buštěhrad:

Page 228: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

Representation of the CER value [€/kWh] for each of the Heat pump optimization scenarios, Lecco:

Page 229: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

Appendix IV – Dimensioning verification of radiators

The use of an Heat pump in a retrofit intervention, is subjected to a further verification, which is the

compatibility of this technology, which works with lower temperature respect to a gas boiler, with the

presence of cast iron radiators.

In order to do this it has been done a verification on the actual dimensions of the radiators. This means

that, considering the actual quality and properties of the existing radiators it has been calculated the right

amount of elements per radiators needed, to fulfill the thermal needs of all the heated spaces of the two

case study buildings, considering the installation of an air/water Heat pump. The man particular of heat

pumps is that they work with an average ∆T = 30 K, while gas boiler work with a ∆T = 50 K which is

the best fit for high thermal inertia cast iron radiators.

First of all it has been calculated the new Thermal Power of the existing radiatios, considering the ∆T =

30 K of the heat pump.

Radiators properties Value Formula

Thermal power with Δt = 50 K

100 W Average of radiator's thermal power

found in different data sheets

ΔT, real 30 K T,average - T,internal ambient

n 1.3 From data sheets

Thermal power with Δt = 30 K

51.48 W

After that it went on a visual survey of each of the rooms of the heated spaces of the case study buildings,

in order to collect the information about the number of elements each radiator has, and the amount of

radiators found in each classroom. Both of the school buildings presented radiators composed of 16

elements, in addition to that, only the case study located in Lecco presented some classrooms with

radiators composed of 40 elements.

Below it will be summed all the calculations done in order to perform the verification in both of the case

studies analyzed throughout the thesis work.

Page 230: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

Case study: Elementary School G. Carducci , Lecco

Thermal need Verification

kWh/year W kWh/year Need < Power

Kitchen 1381.31 4 0 3294.40 14469.01 verified

Class-C01 1036.26 4 0 3294.40 14469.01 verified

Toilet 1 299.36 1 0 823.60 3617.25 verified

Class-C02 694.40 2 0 1647.20 7234.51 verified

Hall 1150.53 4 0 3294.40 14469.01 verified

Washign room 833.52 3 0 2470.80 10851.76 verified

Class-C12 596.84 5 0 4118.00 18086.27 verified

Toilet 2 506.70 1 0 823.60 3617.25 verified

Class-C13 915.45 4 0 3294.40 14469.01 verified

Class-C11 986.63 2 0 1647.20 7234.51 verified

Toilet 3 632.72 1 0 823.60 3617.25 verified

Class-C14 827.61 0 2 4118.00 18086.27 verified

Class-C15 831.71 0 3 6177.00 27129.40 verified

Class-C16 1219.46 0 2 4118.00 18086.27 verified

Class-C22 1076.67 4 0 3294.40 14469.01 verified

Toilet 2 690.77 1 0 823.60 3617.25 verified

Class-C23 1133.93 3 0 2470.80 10851.76 verified

Hall 2 1569.81 4 0 3294.40 14469.01 verified

Class-C28 1070.55 5 0 4118.00 18086.27 verified

Class-C21 1253.43 3 0 2470.80 10851.76 verified

Hall 2 2355.92 4 0 3294.40 14469.01 verified

Hall 2 1172.73 4 0 3294.40 14469.01 verified

Hall 3 977.03 4 0 3294.40 14469.01 verified

Class-C17 665.90 0 3 6177.00 27129.40 verified

Changing room 1413.51 2 0 1647.20 7234.51 verified

Space# radiators

16 el.

# radiators

40 el.

Thermal power

Page 231: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Thesis Report | Paolo Lo Conte

Case study: Elementary School of Bustehrad

Thermal need Verification

kWh/year W kWh/year Need < Power

Class Room 1.05 1280.95 4 3088.50 13564.70 verified

Class Room 1.03 1249.01 4 3088.50 13564.70 verified

Class Room 1.02 1302.32 4 3088.50 13564.70 verified

Cloak Room 1.06 832.68 2 1544.25 6782.35 verified

Cloak Room 1.07 762.94 2 1544.25 6782.35 verified

Changing room 1.08 400.06 2 1544.25 6782.35 verified

Entrance,Hall,Stairs 1.04;1.01;1.10 1492.69 3 2316.38 10173.53 verified

Class Room 2.05 1295.66 4 3088.50 13564.70 verified

Class Room 2.03 1289.81 4 3088.50 13564.70 verified

Class Room 2.02 1274.68 4 3088.50 13564.70 verified

Class room 2.06 1208.79 4 3088.50 13564.70 verified

Hall,Stairs 2.01;2.08 941.10 3 2316.38 10173.53 verified

Common room 2.04 484.69 1 772.13 3391.18 verified

Class Room 3.06 2067.61 4 3088.50 13564.70 verified

Class Room 3.03 2059.30 4 3088.50 13564.70 verified

Class Room 3.02 1977.08 4 3088.50 13564.70 verified

Class room 3.07 1901.88 4 3088.50 13564.70 verified

Hall,Stairs 3.01;3.10 1719.26 3 2316.38 10173.53 verified

Common room 3.05 240.24 1 772.13 3391.18 verified

Girls Bathroom 1.09 714.14 1 772.13 3391.18 verified

Boys bathroom 1.11 203.80 1 772.13 3391.18 verified

Girls Bathroom 2.07 905.56 1 772.13 3391.18 verified

Boys bathroom 2.09 176.87 1 772.13 3391.18 verified

Girls Bathroom 3.08 1029.81 1 772.13 3391.18 verified

Boys bathroom 3.09 467.57 1 772.13 3391.18 verified

n.

radiators

Thermal powerSpace

Page 232: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Elementary school G.Carducci, Lecco

First Level

Graphic Table | Paolo Lo Conte

Scale 1:200

Page 233: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Elementary school G.Carducci, Lecco

Second Level

Graphic Table | Paolo Lo Conte

Scale 1:200

Page 234: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Elementary school G.Carducci, Lecco

Underground Level

Graphic Table | Paolo Lo Conte

Scale 1:200

Page 235: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Elementary school G.Carducci, Lecco

Ground Level

Graphic Table | Paolo Lo Conte

Scale 1:200

Page 236: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Elementary school G.Carducci, Lecco

Underground Level

Graphic Table | Paolo Lo Conte

Scale 1:200

Page 237: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Elementary school G.Carducci, Lecco

Elevation BB

Graphic Table | Paolo Lo Conte

Scale 1:200

Page 238: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Elementary school Bustehrad

First Level

Graphic Table | Paolo Lo Conte

Scale 1:200

Page 239: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Elementary school Bustehrad

Second Level

Graphic Table | Paolo Lo Conte

Scale 1:200

Page 240: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Elementary school Bustehrad

Roof Structure

Graphic Table | Paolo Lo Conte

Scale 1:200

Page 241: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Elementary school Bustehrad

Underground Level

Graphic Table | Paolo Lo Conte

Scale 1:200

Page 242: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Elementary school Bustehrad

Ground Level

Graphic Table | Paolo Lo Conte

Scale 1:200

Page 243: Politecnico di Milano · POLITECNICO DI MILANO Building and Architectural Engineering Track - Building Engineering STRATEGIES FOR ENERGY RETROFITTING OF EXISTING SCHOOL BUILDING IN

Elementary school Bustehrad

Elevation AA

Graphic Table | Paolo Lo Conte

Scale 1:200