Building heat demand_and_moisture

ESTIMATION OF HEAT DEMAND IN BUILDINGS

HERENA TORIOPPRE, SS 10/11

OLDENBURG

05.05.2011 SS 10/11 2

CONTENTS• INTRODUCTION

– ENERGY SITUATION IN BUILDING SECTOR

• PHYSICAL PRINCIPLES– HEAT TRANSFER– MOISTURE TRANSFER

• ENERGY BALANCES– STEADY STATE BEHAVIOR– DYNAMIC BEHAVIOR - THERMAL INERTIA

• CALCULATION METHODS– MONTHLY METHOD– SIMPLIFIED METHOD

05.05.2011 SS 10/11 3

• ENERGY CONSUMPTION IN GERMANY

Energy consumption by sectors (Germany)

Households, 45%Transport, 28%

Industry, 27%

Source: VDEW-Materialien: Endenergieverbrauch in Deutschland, 2002

Space heating,

81%

Domestic hot water demand,

13%

Lighting, 5%

ENERGY SITUATIONINTRODUCTION PHYS. PPLES. ENERGY BALANCES CALC. METHODS

05.05.2011 SS 10/11 4

Others 8%Electricity 4%

Distric heating 7%

Carbon 2%

Gasoil 36%

Natural gas 43%

• FUELS USED IN GERMANY TO SUPPLY THE SPACE HEATINGDEMAND

Renewables are here!

Source: VDEW-Materialien: Endenergieverbrauch in Deutschland, 2002


05.05.2011 SS 10/11 5

IN GERMANY EnEV - “Energie-einsparverordnung”:– Limits the maximal energy demand for buildings according

to their constructive details– Establishes a calculation method for the energy demand of

a building -> basis for comparison– Defines different building “categories” according to their

energy consumption


05.05.2011 SS 10/11 6

ENERGY SITUATION

INTRODUCTION PHYS. PPLES. ENERGY BALANCES CALC. METHODS

05.05.2011 SS 10/11 7

Heat demand:• Typical building: 80 – 300 kWh/m2a

• “Low Energy house” : 40 – 79 kWh/m2a

• “Three-liters house”: 16 – 39 kWh/m2a

• “Passive house”: max. 15 kWh/m2a

• “Zero-Energy house”: 0 kWh/m2a


05.05.2011 SS 10/11 8


– Approved July08 -> Jan 09

– Application to new buildings

RENEWABLE ENERGY HEAT STANDARD “EEWärmegesetz”:

• Biogas 30%• Solar: 15%, 0.03-0.04m2coll/m2living area • Others (biofuels, wood, geothermal or environmental heat) 50%

05.05.2011 SS 10/11 9

ENERGY BALANCE IN A TYPICAL BUILDING

Transmission losses

Ventilation losses

Solar heat gains

Internal gains

Heat supplied by heating system

0%

20%

40%

60%

80%

100%

Cold bridges %Ventilation losses %Transmission losses %

Biggest energy saving potential!!!

GENERAL BALANCESINTRODUCTION PHYS. PPLES. ENERGY BALANCES CALC. METHODS

05.05.2011 SS 10/11 10

• BUILDING ENVELOPE: Heat losses can amount up to 75% of total heat losses

Roof 19%External walls

20%

Floor to crawl space 9%

Windows 52%

Percentage of heat losses through different constructive parts of the envelope

BASIC USED SOLUTION: Reduction of the major heat losses using better materials in the building envelope

Moving to energy efficient buildings…


GENERAL BALANCES

05.05.2011 SS 10/11 11

• CONDUCTION

Tin

Tout

λmaterial [W/mK]

dmaterial [m]

[m2K/W]

∑= layerwall RRlayerl

layerlayer

dR

λ=

∑==

layer

layerwall

wall dRU

λ

11

[m2K/W]

[W/m2K]

)(, outinwallwallwallT TTAUQ −⋅⋅=

T


HEAT TRANSFER

05.05.2011 SS 10/11 12

∑ ++==

elayer

layer

i

wallwall

hd

hR

U11

11

λ

[W/m2K]

Superficial heat transmission coefficient: [0 -100 W/m2K]

• Floor to unheated basement

• Roof in summer conditions• Roof under winter conditions!

T

TRANSMISSION LOSSES: Conduction + convection


HEAT TRANSFER

05.05.2011 SS 10/11 13

Geometric thermal bridgeMaterial caused thermal bridge

Source: Maas

• DEFINITION: Places on the envelope where, during the heating period, higher heat flows and lower inner surface temperatures occur.

• CAUSES:


HEAT TRANSFERTHERMAL BRIDGES

05.05.2011 SS 10/11 14

Ψ = Coefficient of losses throughthermal bridge, [W/mK]

f = (superficial) Temperature factor , [-]

Θsi= surface temperature inside wall

Θe = exterior temperature

Θi = indoor temperature

f=0 -> exterior temperature

f=1 -> indoor air temperature

Source: Maas


HEAT TRANSFERTHERMAL BRIDGES• CHARACTERISATION:

05.05.2011 SS 10/11 15

Source: Maas



05.05.2011 SS 10/11 16

Source: Maas



05.05.2011 SS 10/11 17

VENTILATION (CONVECTION) LOSSES


HEAT TRANSFER

05.05.2011 SS 10/11 18

VENTILATION LOSSES• Definition: Energy losses due to the exchange of an air flow

between the building and the surroundings• Characterization: measured in h-1 = represents the portion of

the total (heated) building volume exchanged in one hour• Causes:

– Air leakages in the building envelope: constructive problem / solution

– Health and Safety reasons: necessary to allow pollutants leave the living space

According to building typology (residential, office buildings, hospitals…) minimum air exchange rates have to be assured


HEAT TRANSFER

05.05.2011 SS 10/11 19

VENTILATION LOSSES

Source: Recknagel

Tight envelope (n50<3h-1)

Untight envelope (n50> 5h-1)

Regulable Ventilation units

Window open up without cross ventilation

Window open up with cross ventilation

Window open without cross ventilation

Window open with cross ventilation

Air exchange


HEAT TRANSFER

05.05.2011 SS 10/11 20

VENTILATION LOSSES

TYPICAL VALUES for a non efficient old building: 1,5 – 2 h-1 or even higher (through air leakages in envelope)

According to EnEV (Energieeinsparverordnung) in Germany:

Mech.vent.: 0,4Air leakages: 0,2

Air leakages: 0,6Air leakages: 0,7Values allowed in EnEV, h-1

Efficient building with mechanical ventilation system

Efficient (proven tight) building without mechanical ventilation system

Non efficient building


HEAT TRANSFER

05.05.2011 SS 10/11 21

• Transport mechanisms:– DIFFUSION– CONVECTION

(ventilation)– (SORPTION)

1 - 2 liters/day person

2 people house: ca. 2liters/day person

4 people house: ca. 4liters/day person

Source: Maas


MOISTURE TRANSFER

05.05.2011 SS 10/11 22

Source: Maas


MOISTURE TRANSFER

Air temperature

Max

imal

wat

erco

nten

tin

air

9.4g

10°C

7.9g

05.05.2011 SS 10/11 23


CARRIER (MOLIERE) DIAGRAM

05.05.2011 SS 10/11 24


CARRIER (MOLIERE) DIAGRAM1.- 100%RH, 20°C,14.5g/kg

2.- 100%RH, 10°C,7.5g/kg

3.- 70%RH, 20°C, 7g/kg

4.- 85%RH,17°C, 7g/kg

Air density ≈ 1.2kg/m3

Dew point temperature

05.05.2011 SS 10/11 25

Source: Maas

Air temperature

Rel. humidity

Dew

poin

t tem

pera

ture


MOISTURE TRANSFER

Air temperature

Rel. humidity

Dew

poin

t tem

pera

ture

05.05.2011 SS 10/11 26


MOISTURE TRANSFERSUPERFICIAL TEMPERATURETHERMAL BRIDGES

External wall - corner

Indoor air temp. 20°C

70%RH

SurfacetemperaturesMax. relative humidity

Outdoor air temp. -15°C

05.05.2011 SS 10/11 27


MOISTURE TRANSFERMOLD GROWTH

05.05.2011 SS 10/11 28

Source: Maas


MOISTURE TRANSFER

Relative humidity, %

Pro

babi

lity

of g

row

th

Surf. temperature, °C

Pro

babi

lity

of g

row

th

HUMIDITY TEMPERATURE

MOLD GROWTH

05.05.2011 SS 10/11 29

Source: Maas


MOISTURE TRANSFERWATER CONDENSATION

MOLD GROWTH

Rel. Humidity

05.05.2011 SS 10/11 30

Source: Maas


MOISTURE TRANSFEREXAMPLEMold growth is more restrictive condition Rel.

Humidity

05.05.2011 SS 10/11 31

Source: Maas

Description DescriptionDescription Unit Unit

Temperature

Heat conductivity

Thermal resistance

Heat flow

Heat transm. Coeff.

Partial vapor pressure

Material transm. Coeff.

Vapor diffusivity

Resistance to vapor diffusion

Vapor diffussion flow


MOISTURE TRANSFERDIFFUSION

05.05.2011 SS 10/11 32

Air

Insulation

Concrete

Metal

Bitumen

Source: Maas

material

air

material

material

air

air

material

aird

d

ZZ

δδ

δ

δμ ===

[-]dmaterial=dair


MOISTURE TRANSFERDIFFUSION

05.05.2011 SS 10/11 33

Source: Maas


MOISTURE TRANSFER

40 (50/400)Wood

Tight(100000000)

Alu-foil

5-1030-100

InsulationKorkPU foams

70-150Concrete

μMaterial

DIFFUSION - EXAMPLE

1086

472281

g

g = 0.421 g/m2h

[m h Pa / kg]

05.05.2011 SS 10/11 34

Source: Maas


MOISTURE TRANSFERCONVECTION - EXAMPLE

05.05.2011 SS 10/11 35

Source: Maas

Ps = 1170 Pa

R = 462 J/kgK

Ps = 139 Pa


MOISTURE TRANSFERCONVECTION - EXAMPLE

Vh,buil=50m3 ; n=0.8 h-1

Vvent=40m3/h (=Vh,buil*n)

Ti=20°C, RH=50%

Te=-10°C, RH=80%

-10°C 1.15

1.15 263.15304.3

and

and

05.05.2011 SS 10/11 36

Source: Maas


MOISTURE TRANSFERCOMPARISONCONVECTION - DIFFUSION

g

Aint,walls=22.5 m2

n = 0.8 h-1

Outside: 80% RH, -10°C

Inside: 50% RH, 20°C

g = 0.421 g/m2h

9.47 g/h304.3 g/h

05.05.2011 SS 10/11 37

Source: Maas

Humidity production

Req

uire

dai

r exc

hang

eRel. humidity


MOISTURE TRANSFERCONVECTION:Air exchange

05.05.2011 SS 10/11 38

Qv

In order to keep

the room temperature

at a constant acceptable value

Energy Supplied = Heat Losses - Energy Gains

STEADY STATE

Transmission losses

Ventilation losses

Solar heat gains

Internal gains


“Passive gains”“Active gains”

QT


ENERGY BALANCES

05.05.2011 SS 10/11 39

TRANSMISSION LOSSES

– INCLUDING THERMAL BRIDGES

– TOTAL TRANSMISSION LOSSES

)(,,, outinienvienvenvT TTAUQ −⋅⋅Σ=

)()( ,,, outinenvtbienvienvbuilT TTAUAUQ −⋅⋅Δ+⋅Σ=

envelopetbienvienvbuildingT AUAUH ⋅Δ+⋅Σ= ,,, [W/K]

[W]

[W]


THERMAL LOSSESenv,i = walls, floor, roof,

windows

(separately for each of them)

05.05.2011 SS 10/11 40

nVH builhV ⋅⋅= 34.0,

)( outinVV TTHQ −⋅=

VENTILATION LOSSES

76.0, ⋅= bruttobuilh VV

Heat capacity of air [Wh/m3K]

[W/K]

HEATED volume of the building [m3]

According to the German regulation EnEV, can be simplified:

n = air exchange rate [h-1]


THERMAL LOSSES

05.05.2011 SS 10/11 41

TOTAL LOSSES (TRANSMISSION+VENTILATION)

– Transmission Losses

– Ventilation Losses

– Total Losses

)()()( ,,, outinToutinenvtbienvienvbuilT TTHTTAUAUQ −⋅=−⋅⋅Δ+⋅Σ=


)()( outinVTlosses TTHHQ −⋅+=


THERMAL LOSSES

[W]

[W]

[W]

05.05.2011 SS 10/11 42

WINDOWS– Upane = 3 – 0.6 [W/m2K]

-> great influence on heat demand

– SHGC, g = 0.5 – 0.8 [-]-> great influence on

cooling demand

– ε = 0.84– εlow = 0.2 !!!


THERMAL LOSSES + GAINS

05.05.2011 SS 10/11 43

Qv

Energy Supplied = Heat Losses - Energy Gains +- Energy Stored

ENERGY BALANCE - DYNAMIC BEHAVIOR

Transmission losses

Ventilation losses

Solar heat gains

Internal gains


QT


ENERGY - DYNAMIC

05.05.2011 SS 10/11 44

0

500

1000

1500

2000

2500

3000

Woo

d

Gla

ss

Min

eral

insu

latio

n

Foam

gla

ss

San

d

Bric

k

Alu

min

ium

Con

cret

e

Wat

er

rho

[kg/

m3]

0

1000

2000

3000

4000

5000

Woo

d

Gla

ss

Min

eral

insu

latio

n

Foam

gla

ss

Sand

Bric

k

Alum

iniu

m

Con

cret

e

Wat

er

c [J

/kgK

]

Specific heat capacity

density

Source: Wikipedia

iiiisto dAcC ⋅⋅⋅= ρ


ENERGY - DYNAMICTHERMAL MASS

05.05.2011 SS 10/11 45

0

1

2

3

4

5

Woo

d

Gla

ss

Min

eral

insu

latio

n

Foam

gla

ss

San

d

Bric

k

Alu

min

ium

Con

cret

e

Wat

er

lam

bda

[W/m

K]

Source: Wikipedia

THERMAL MASS

0

500

1000

1500

2000

2500

3000

Woo

d

Gla

ss

Min

eral

insu

latio

n

Foam

gla

ss

San

d

Bric

k

Alu

min

ium

Con

cret

e

Wat

er

rho

[kg/

m3]

0

1000

2000

3000

4000

5000

Woo

d

Gla

ss

Min

eral

insu

latio

n

Foam

gla

ss

Sand

Bric

k

Alum

iniu

m

Con

cret

e

Wat

er

c [J

/kgK

]


THERMAL MASS237

05.05.2011 SS 10/11 46

Tem

pera

ture

Thickness

Concrete Insulation

Source: Maas

Tem

pera

ture




05.05.2011 SS 10/11 47

Sola

r rad

iatio

nO

utdo

orTe

mpe

ratu

re

Source: Maas

U-Value[W/m2K]

Mass[kg/m2]

Out

door

Tem

pera

ture

Ene

rgy

flow

Time of day




Sola

r ra

diat

ion

6cm

40cm

43.5cm

26cm

05.05.2011 SS 10/11 48

TOTAL LOSSES (TRANSMISSION+VENTILATION)

– Transmission Losses

– Ventilation Losses

– Total Losses

)()()( ,,, outinToutinenvtbienvienvbuilT TTHTTAUAUQ −⋅=−⋅⋅Δ+⋅Σ=


)()( outinVTlosses TTHHQ −⋅+=

Tin is the indoor desired temperature: regarded as a CONSTANT value,typically set between 19 and 21°C for the heating period.

For which time-step do we apply this

equation?

Depends on the data we have for the

outdoor temperature…


[W]

[W]

[W]

05.05.2011 SS 10/11 49

TOTAL LOSSES

• Tout represents MONTHLY mean values• tM represents the number of days of the month considered

24)()( ⋅⋅−⋅+Σ= MoutinVTmonthstTTHHQ

losses

MONTHLY METHODINTRODUCTION PHYS. PPLES. ENERGY BALANCES CALC. METHODS

[Wh/a]

05.05.2011 SS 10/11 50

• gi represents the energy transmissivity of the window glass; typically is around 0.6

• FF represents the % of glass against frame in the window area; typically is around 0.7

• Fs represents the % of shadowing over the glass• Gwindow represents the incident solar radiation onto the

window, in Wh/m2

windowsFiwindowsmonthswindowsSolar GFFgAQ ⋅⋅⋅⋅Σ=,

SOLAR HEAT GAINS


[Wh/a]

05.05.2011 SS 10/11 51

WINDOWS, 52% of total losses:1. Avoid heat losses -> Better insulation materials:

- Uw= 3 - 0.6 W/m2K

2. Increase solar heat gains -> Orientation- Highest solar irradiation on the south façade,

high potential for solar heat gains -> maximize glazed surface facing south

- North façade receives very few solar irradiation, low potential for solar gains and high heat losses through windows -> minimize glazed surfaces

Single or two pane window

Three pane window filled with Ar/Kr

Yearly variation of solar path in the sky

Does not require much more planning effort. Typ. In efficient houses

Requires integral planning of the building integrated into its environmentTyp. Approach passive houses


THERMAL LOSSES + GAINS

05.05.2011 SS 10/11 52

• Internal heat gains depend on the use pattern of the building: office, hospital, residential…

• For residential buildings: constant hourly value of 5 W/m2, per m2

useful area in the building

MtAQ Nmonthsgains ⋅⋅⋅Σ= 245int_

INTERNAL HEAT GAINS


[Wh/a]

05.05.2011 SS 10/11 53

– Simplification:

– Actually, not all energy gains can be “used”:

• η depends on the heat storage capacity of the building structureand its materials, which is a function of ρ [kg/m3], c [Wh/kgK], d [m], A [m2] of the material:

gainswindowsSolarlossesh QQQQ int_, −−=

)( int_, gainswindowsSolarlossesh QQQQ +−= η

iiiisto dAcC ⋅⋅⋅= ρ

ENERGY DEMAND


[Wh/a]

[Wh/a]

[W/K]

05.05.2011 SS 10/11 54

– Types of building constructions according to its heat capacity

• LIGHT– Csto/A < 50 Wh/m2K

• HEAVY– Csto/A > 130 Wh/m2K

– η = 0.9 for light buildings– η = 0.95 for heavy buildings

)( int_, gainswindowsSolarlossesh QQQQ +−= η

ENERGY DEMAND


[Wh/a]

[-]

[-]

05.05.2011 SS 10/11 55

– BUILDING WITH ZONES AT DIFFERENT TEMPERATURES:

• German Norm: gives correction factors, Fx, that have to be applied to obtain the HT corrected of the building

0.6- Floor to ground- Walls and floor to unheated crawl

space

0.5Walls and roofs to unheated rooms

1Outside wall, window, roof, floor

Fx [-]Building part

envelopetbwallwallT AUAUH ⋅Δ+⋅Σ=

envelopetbxwallwallT AUFAUH ⋅Δ+⋅⋅Σ=

ENERGY DEMAND


05.05.2011 SS 10/11 56

• Tout represents mean DAILY values• Sets up a “heating limit” (15°C), above which no space heating is

required. For this conditions (Tin-Tout)=0• Below the “heating limit”, (Tin-Tout) is calculated and added up to

give a value of the “degrees-day”

∑ −=z

outint TTG1

15/20 )(

TOTAL HEATING DEMANDDEGREE-DAYS

DEGREE-DAYS METHODINTRODUCTION PHYS. PPLES. ENERGY BALANCES CALC. METHODS

[Kd/a]

[°Cd/a]

05.05.2011 SS 10/11 57

TOTAL HEATING DEMAND

)( int, ernalwindowssolarlossesh QQQQ −−= η

tVTdayslosses GHHQ ⋅+Σ= )( MoutinVTmonthstTTHHQ

losses⋅−⋅+Σ= )()(

windowsFiwindowsmonthswindowsSolar GFFgAQ ⋅⋅⋅⋅Σ=,

)( int ernalsolarhlosses QQQQ −−= η

windowsFiwindowsnorientatiowindowsSolar GFFgAQ ⋅⋅⋅⋅Σ=,

Ngains AQ ⋅= 22int_MtAQ Nmonthsgains ⋅⋅⋅Σ= 245int_

DEGREE-DAYS METHODINTRODUCTION PHYS. PPLES. ENERGY BALANCES CALC. METHODS

[Wh/a]

[Wh/a]

[kWh/a]

[Wh/a]

05.05.2011 SS 10/11 58

– The equations for steady state conditions are not valid here!!!-> Energy stored in the building structure plays a role

– FREEware available (Hourly simulations):DOE2, eQUEST, ePLUS (http://www.doe2.com/ )

Much more accurate results

×Require the description of the HVAC system as INPUT×Time demanding to learn how to work with them: weather

data for Stüdl Hütte, etc… may not be in database

DYNAMIC TOOLSINTRODUCTION PHYS. PPLES. ENERGY BALANCES CALC. METHODS

05.05.2011 SS 10/11 59

• STATIC (simplified) METHODS & SOFTWARE: – Based on the steady-state simple equation -> quite simple

calculations

Depends only on (rough) CLIMATIC data and the BUILDING ENVELOPE -> Does not require the description of the HVAC system as INPUT

×Much more rough results

– Examples: “DEGREE-DAY Method” and Monthly simplified method in EnEV http://www.uni-

kassel.de/fb6/bpy/de/index.html

STATIONARY METHODSINTRODUCTION PHYS. PPLES. ENERGY BALANCES CALC. METHODS

05.05.2011 SS 10/11 60

THANK YOU FOR YOUR ATTENTION!!!THANKS FOR YOUR

ATTENTION!!!!!!

05.05.2011 SS 10/11 61

EXAMPLE• AN = 147m2 ; Vbrutto = 580 m3

• Awalls = 209.34 m2; Afloor = 88.2 m2; Aroof = 88.2 m2

• Awindows: S 15 m2; E/W 10m2; N 5.5 m2

• Uwalls = 0.45 W/m2K (walls); Ufloor-roof = 0.3 W/m2K (floor and roof); Uwindows = 1.4 W/m2K (windows)

• Utb = 0.1 W/m2K• n =0.6 h-1

• Windows: Ff= 0.7; Fs=0.9;g=0.58; • Heavy building

T 19°C

Orientation Solar radiation

[j] [kWh/m²]Nord 136

Süd 349

Ost 220

West 220

• G19/10 = 2750 °Cd/a (Hamburg)

10m

7.35m

3.0m

3.0m

Building heat demand_and_moisture

Technology

Transcript of Building heat demand_and_moisture