DETERMINING OPTIMAL COMBINATION OF PASSIVE SOLAR DESIGN PARAMETERS IN NOVI SAD

8/9/2019 DETERMINING OPTIMAL COMBINATION OF PASSIVE SOLAR DESIGN PARAMETERS IN NOVI SAD

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III МЕЂУНАРОДНИ СИМПОЗИЈУМ СТУДЕНАТА

ДОКТОРСКИХ СТУДИЈА ИЗ ОБЛАСТИ ГРАЂЕВИНАРСТВА, АРХИТЕКТУРЕ И ЗАШТИТЕ

ЖИВОТНЕ СРЕДИНЕ

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Sanja Stevanović1

Marija Pavličić2

Aleksandra Marinković3

ОДРЕЂИВАЊЕ ОПТИМАЛНЕ КОМБИНАЦИЈЕ ПАРАМЕТАРА

ПАСИВНОГ СОЛАРНОГ ДИЗАЈНА У НОВОМ САДУ

Резиме: Са порастом свести о потреби за што мањим ослањањем на фосилна горива и што већим коришћењем обновљивих извора енергије за грејање зграда , технике пасивног соларног дизајна у пројектовању поново добијају на значају. Пасивни соларни дизајн укључује одговарајућу оријентацију објекта , позицију и површину прозора , правилно коришћење енергетски ефикасних прозора , сенчења и термалне масе , како би се сунчева енергија што боље искористила за

догревање током зиме , а да се притом сачува термални комфор станара током лета. Циљ овог рада је да открије оптималну комбинацију ових параметара на примеру типичне породичне куће

у Новом Саду , процењујући утрошену енергију за грејање и хлађење за различите комбинације параметара помоћу симулација у програму RETScreen. Резултати овог истраживања се могу користити као препоруке у градњи нових кућа , и у одређеној мери код обнављања постојећих кућа.

Кључне речи: Пасивни соларни дизајн , оријентација објекта , површина и ефикасност прозора ,

сенчење прозора

DETERMINING OPTIMAL COMBINATION OF PASSIVE SOLAR

DESIGN PARAMETERS IN NOVI SAD

Abstract: With growing awareness for the need to lesser a reliance on fossil fuels and to increase the useof renewable energy for heating buildings, passive solar design techniques again gain in importance in

building design. Passive solar design involves the appropriate object orientation, the proper sizing,

positioning and energy efficiency of windows, summer shading of windows and thermal mass in order to

better use available solar energy to reduce heating needs in winter, while maintaining the thermal

comfort of occupants during summer. The aim of this study is to identify the optimal combination of these

parameters on the case study of a one-family home in Novi Sad, by estimating the heating and cooling

energy needs for different parameter combinations with simulations in RETScreen software. The resultsof this study can be used as recommendations in the construction of new houses, and to some extent, in

the renewal of existing homes.

Key words: Passive solar design, Building orientation,Windows sizing and efficiency, Window summer

shading

1 Research Associate, Faculty of Sciences and Mathematics, University of Niš, Višegradska 33, 18000 Niš, Serbia, e-mail:

[email protected] Teaching Assistant, Faculty of Technical Sciences, University of Priština, Kneza Miloša 7, 38220 Kosovska Mitrovica,

Serbia, e-mail: [email protected] Teaching Assistant, School of Higher Technical Professional Education, Aleksandra Medvedeva 20, 18000 Niš, Serbia, e-

mail: [email protected]


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1. INTRODUCTION

Passive solar design involves the proper orientation of buildings and proper location and surface area

for windows, as well as the correct use of energy efficient windows, shading, thermal mass and envelopeinsulation to reduce both heating and cooling energy demand. The primary elements in passive solar

heating systems are windows. Glass has the beneficial property of transmitting solar radiation allowing

energy from the sun to enter the building and warm the interior spaces. Glass is, however, opaque tothermal (long-wave) radiation, thus heat is not as easily transmitted back outdoors. This „greenhouse

effect“ is particularly useful for supplying heating energy in the winter. Clearly, the larger the windows,

the more sunlight will enter the building. However, windows are not as thermally insulating as thebuilding walls. A passive solar design should optimize window surface area, orientation and thermal

properties to increase the energy input from the sun and minimise heat losses to the outside, while

ensuring occupant comfort.

Our goal here is to study the influence of different passive design options on the heating and coolingenergy load of a small, two-storey house located in Novi Sad. Having in mind that the most influential

factor on the heating and cooling energy load are the thermal properties of building envelope, we have

chosen to work with two different envelope types – the one that represents the current building practice in

Serbia, so-called „demit-facade“, and another one which is close to passive house standard and offersmuch better insulation properties. Our main hypothesis is that the better insulated house will enable the

use of larger window surface area, hence allow more natural daylight within the house, without increasingits energy needs. We are also interested in determining whether the continental climate of Novi Sad

allows for the use of significantly larger windows in the most optimal energy configuration. For theevaluation of the annual heating and cooling energy load, we use RETScreen software [1].

Similar studies have been considered earlier in the literature. The impact of different kinds of glazing

systems (two double and two triple glazings), window size (from 16% to 41% of window to floor arearatio), orientation of the main windowed facade and internal gains on winter and summer energy need and

peak loads of a well insulated residential building in four different European cities – Paris, Milan, Niceand Rome – has been evaluated in [2]. The best orientation of the building, windows size, thermal

insulation thickness from energetic, economic and environmental point of view for typical residentialbuilding located in Mediterranean region have been discussed in [3]. The insulation thickness of the walls

and roof, the window type, the thickness of an internal thermal mass wall, and the night ventilation airchange rate were optimised for a simple model of a detached house in Sydney in [4].

2. RETSCREEN SOFTWAREThe RETScreen Energy Efficiency Model can be used to evaluate the energy production (or savings),

life-cycle costs and greenhouse gas emissions reduction and financial performance associated with

passive solar designs and/or energy efficiency measures. The model is intended for low-rise residential

applications, and it applies in any location where there is a significant heating load. Basically, the model

can be used to determine how the more efficient windows and better insulated building envelope affectbuilding energy use. The calculation of solar gains to a building, and the amount of heat lost byconduction is relatively complex, dependent upon the solar radiation and outdoor temperature, as well as

the thermal properties of the windows and building envelope. The most accurate analysis is to computethese heat transfer on an hourly basis based on detailed characteristics of the building. However, hourly

data is rarely available for performing a detailed analysis. Simplifying assumptions of RETScreen includecalculating heat loss and gain based on monthly average solar radiation levels and outdoor temperature, asopposed to hour-by-hour data. The utilisation of the solar heat gains in reducing heating demand is based

on a method developed by Barakat and Sander [5], with window thermal properties adjustments based onthe size of the window using an approach of Baker and Henry [6]. While some margin of error isintroduced by simplifying the models, comparison with more complex software models shows that the

RETScreen model performs accurately enough to be an acceptable pre-feasibility tool.

The RETScreen model was tested against HOT2-XP [7], a version of HOT2000 detailed hourly

energy analysis software, to assess the accuracy of the calculated energy flow by simulated the same,

typical Canadian house with two different glazing types. RETScreen underestimated the benefit of thewindow upgrade by 18%, a difference acceptable at the pre-feasibility stage. The second evaluation was

to see how RETScreen ranked the energy performance of windows, compared to that predicted by the


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Energy Rating (ER) method [8], which is a Canadian standard that was developed based on hourly energy

simulations. RETScreen has closely matched the ER systems in terms of ranking window performance.

3. CASE STUDY PARAMETERS

The possible parameter values selected for the case study are listed in the following subsections. Their

choice reflect the options that are either available in Serbia or widely accepted in building practices.

3.1. Location and climate data

Location of the house is in Novi Sad, with latitude 45° 15’ north and longitude 19° 51’ east. Climate

data is available in RETScreen, where air temperature, relative humidity, daily solar radiation onhorizontal surface, wind speed, heating degree-days and cooling degree-days are based on ground

measurements, while the atmospheric pressure and earth temperature are based on NASA globalsatellite/analysis data.

3.2. House design

The house is intended for four-person family. The outer dimensions of the house are: 10m x 6m in thebasis, two stories with a total 6m height. The house designs, with three different window surface areas,

are represented in Figures 1, 2 and 3.

Figure 1. House design with 12m2 of south oriented windows.



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We have considered two options for a building envelope: one that represents a current building

practice in Serbia and another one that represents a well-insulated house that to some extent approaches

passive building standard, obtained more-or-less by simply adding an extra layer of insulation to astandard wall. This additional layer of insulation consists of expanded polystyrene (EPS) on walls, which

is a popular insulation material and produced by several factories in Serbia, as well as extruded

polystyrene (XPS) on the ground floor and the flat roof.

The structure of the ground floor, outer walls and roofing for both the standard and well-insulatedbuilding envelope are shown in Table 1.

Table 1. The structure of floors, walls and roofs in standard and well-insulated building envelopes.

Building component Standard envelope Thickness Well-insulated envelope Thickness

Ground floor Ceramic tiles

Cement screed

Vapor barrier

Expanded polystyrene (EPS)

Protective concrete

Waterproofing

Concrete

Gravel

1.5 cm

5 cm

5 cm

4 cm

0.5 cm

12 cm

10 cm

Ceramic tiles

Cement screed

Waterproofing

Concrete

Extruded polystyrene (XPS)

Gravel

1.5 cm

5 cm

10 cm

20 cm

10 cm

Flooring U-value 0.509 W/m /°C 0.171 W/m /°C

Walls Cement plaster


Brick – multiple cores

Cement stucco

0.5 cm

5 cm

19 cm

2 cm

Cement plaster



Cement stucco

0.5 cm

20 cm

19 cm

2 cm

Walls U-value 0.489 W/m2 /°C 0.166 W/m

2 /°C

Roofing Gravel


Concrete


Cement stucco

10 cm

5 cm

4 cm

16 cm

1.5 cm

Gravel


Concrete


Cement stucco

10 cm

20 cm

4 cm

16 cm

1.5 cm

Roofing U-value 0.488 W/m2 /°C 0.167 W/m

2 /°C


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In RETScreen simulation runs, the temperature space heating set point was 20°C, while the

temperature space cooling set point was 26°C. In agreement with local customs in Novi Sad, a house is

heated with natural gas, with seasonal efficiency of 75%, while air conditioners are used for cooling, with

seasonal coefficient of performance 3.25.

Air change rate was selected to be 0.5 ach for both the standard and well-insulated building, so that the

ventilation leaks and natural infiltriration do not interfere with the influence of studied buildingparameteres on the heating and cooling energy loads.

3.3. Building orientation

Building orientation is an important parameter for the heating and cooling energy load of buildings.Naturally, the south side of the building is the one receiving solar energy in the Northern hemisphere and

mostly influencing the performance of a passive solar design. However, our goal was also to test the

sensitivity and the influence of the deviation of the building’s south side from true south to the energyneeds. In that respect, we have tested three different house orientations: towards true south

(azimuth = 0°), towards the south-east (azimuth = -30°) and towards the south-west (azimuth = +30°).

3.4. Window types

One of the most important design parameters in passive solar design is the proper choice of windows –

frame and glazing type, sizes and shading options. For this study, three different glazing types were

considered: double clear glazing, triple clear glazing and triple, low-emissivity glazing. Double glazing isa current building standard in Serbia, while triple glazing is rarely found among residential buildings. Theframing for all three glazing types is taken to be aluminum with thermal break, so that only glazing type

influences the energy loads. The U-values and the solar heat gain coefficients of these three window typesare given in Table 2.

Table 2. The parameters of studied window types.

Window type U-value (W/m2 /°C) Solar heat gain coefficient

Double glazing, clear 3.42 0.66

Triple glazing, clear 2.60 0.59

Triple glazing, low-e 2.44 0.40

3.5. South-facing windows sizes

Since the size of south windows is more important than the size of windows on other three sides, we

have opted to fix the size of windows on the north side of the house to 0.72m2 (this is the total size of

north-oriented windows on both stories) and those on the east and the west side of the building to 2.80m2

each. The smallest size of north-oriented windows reduces the heat loss through windows, while a

relatively small size of west side windows is used because the building is typically warmer at the end ofthe day and likely needs less solar energy for heating in the afternoon.

This is also in line with our goal to determine the largest possible size of south-facing windows that

still provides a substantial decrease in the heating and cooling energy needs. We have tested three

different choices for the total size of south-facing windows: 12m2, 21m

2 and 30m

2. The smallest choice of

12m2, together with the windows sizes at remaining facades, satisfies the regulatory minimum of 1/7 oftotal floor area needed to ensure proper daylighting, while the other two choices are supposed to provide

more natural daylight within the house.

3.6. Summer shading of south-facing windows

Due to the large size of south-facing windows in all scenarios, we have also considered the option ofadequately shading south windows to reduce the amount of unwanted solar heat gain during the summer

months, which would increase the cooling energy load or make a building uncomfortably warm in

summer. Since the shading is provided by terrace roof above the windows, the shading coefficient was


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chosen to be 41%, in order to account for the morning and late afternoon sun which cannot be shaded.

Thus, this represents the average shading factor during summer months. There were no shading during

winter months (the shading coefficient is 0%) in order to study the influence of solar heat gain in space

heating.

Windows on other sides (east, west and north) were not shaded, as the eastern and western sun are

typically low and shading from low sunrays would also block the views from the house. Moreover, thewindow sizes at the east and west building side are low compared to the south windows, thus their

influence on heating and cooling load is considered to be much lower than the influence of south

windows.

4. SIMULATION RESULTS

A total of 108 parameter value combinations were simulated with RETScreen. To resume materialfrom previous subsections, the following parameter choices were iterated:

• Two values for building envelope insulation: standard and well-insulated;

• Three glazing types: double clear, triple clear and triple low-emissivity glazing;

• Three south windows sizes: 12m2, 21m

2 and 30m

2;

• Three building orientations: south (azimuth = 0°), south-east (azimuth = -30°) and south-west

(azimuth = +30°);

• Shading of south windows during summer monts: present or not present.

The first important observation is that the impact of the building orientation on the total heating andcooling energy needs is not too high – the energy needs of south-east or south-west oriented house are at

most 2.18% larger than energy needs of south oriented house, ceteris paribus. This is an important findingfor the architects, as it provides enough freedom to orient the building in accordance to neighboring

buildings or structures, without too much sacrifice on the energy needs.

Table 3. The cooling and heating energy needs for standard envelope and well-insulated envelope

Glazingtype

South-facing

windows

size

Summershading

Standardenvelope,

cooling energy

(electricity,MWh)

Standardenvelope,

heating energy

(natural gas,m

3)

Well-insulatedenvelope,

cooling energy

(electricity,MWh)

Well-insulatedenvelope,

heating energy

(natural gas,m

3)

Double,clear

12 m2 no 2.675 1,179.5 2.414 730.7yes 2.163 1,179.5 1.902 730.7

21 m2 no 3.686 1,209.6 3.432 826.8

yes 2.789 1,209.6 2.536 826.8

30 m2 no 4.696 1,283.6 4.451 940.2

yes 3.416 1,283.6 3.170 940.2

Triple,

clear

12 m2 no 2.432 1,131.5 2.171 673.6

yes 1.974 1,131.5 1.713 673.6

21 m2 no 3.323 1,125.3 3.070 741.2

yes 2.522 1,125.3 2.269 741.2

30 m

2

no 4.214 1,172.1 3.968 826.4yes 3.069 1,172.1 2.824 826.4

Triple,low-e

12 m2 no 1.875 1,237.2 1.614 701.3

yes 1.565 1,237.2 1.304 701.3

21 m2 no 2.491 1,180.9 2.238 740.3

yes 1.948 1,180.9 1.695 740.3

30 m2 no 3.108 1,187.7 2.862 803.5

yes 2.332 1,187.7 2.087 803.5


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Other design parameters have far greater impact on the heating and cooling energy needs compared to

the building orientation. From that reason, we have shown in Table 3 the cooling energy needs (in MWh)

and heating energy needs (in m3 of natural gas) estimated by RETScreen for south orientation only. These

estimates offer the following insights:

• Summer shading of south-facing windows appears to be the single most important parameter

influencing the cooling energy needs – the presence of shading reduces the cooling energy

needs between 16.5% and 28.8%. This reduction is somewhat greater for well-insulated

building envelope.

• With the shading present, compared with the standard envelope ceteris paribus, the well-

insulated envelope reduces the cooling energy needs by 7.1-13.2% for double clear and triple

clear glazing, and by 10.5-16.6% for triple, low-emissivity glazing.

• The well-insulated envelope substantially decreases the heating energy needs compared with

the standard envelope: this reduction is between 26.8-38.0% for double clear glazing, between

29.5-40.5% for triple clear glazing and between 32.3-43.3% for triple, low-emissivity glazing.

• For well-insulated envelope, the difference in the heating energy needs between triple clear

glazing and triple, low-emissivity glazing is almost negligible – up to 4.1%; however, thedifference in the cooling energy needs is clearly in favor of triple, low-emissivity glazing

which reduces the cooling energy by a whopping 23.9-27.8%! These ratios have similarvalues for the standard envelope as well.

•

The increase in the south-facing windows surface area ceteris paribus leads to significantincreases in both the cooling and the heating energy needs in all considered scenarios (exceptfor the standard envelope with triple clear glazing when taking 21m

2 surface area instead of

12m2; however, the difference in this particular case is negligibly small).

5. CONCLUSIONS

The difference in the heating and the cooling energy needs is negligible for deviations in buildingorientation up to 30° from the south, which is an important finding, as it gives the architect the freedom to

comply with urban requirements when positioning the building.

Summer shading turns out to be the single economically most important parameter, as its effect on

reducing the cooling energy needs (by 310-1280kWh annually) far exceeds its costs.

The simulations further reveal that the climate of Novi Sad does not allow the south-facing windows

to be much larger than the minimum regulatory area necessary to ensure proper daylighting of the house.

Having in mind that the triple, low-emissivity glazing outperforms the triple clear glazing in the

cooling energy needs, while both request similar heating energy needs, our final recommendation whendesigning new houses is to combine the well-insulated envelope with the triple, low-emissivity glazing in

the continental climate of Novi Sad. The south-facing windows necessarily have to be shaded from thesummer sun, while their optimum size in this case study turns out to be 12m

2.

6. REFERENCES

[1] RETScreen software online manual, passive solar heating project analysis. RETScreenInternational Clean Energy Decision Support Centre, Ottawa, Canada, 2005, pp. 361-383. –

Available at www.retscreen.net.

[2]

A. Gasparella, G. Pernigotto, F. Cappelletti, P. Romagnoni, P. Baggio, Analysis and modelling ofwindow and glazing systems energy performance for a well insulated residential building, Energy

and Buildings 43 (2011), 1030-1037.

[3]

S. Jaber, S. Ajib, Optimum, technical and energy efficiency design of residential building in

Mediterranean region, Energy and Buildings 43 (2011), 1829-1834.

[4] S.M. Bambrook, A.B. Sproul, D. Jacob, Design optimisation for a low energy home in Sydney,Energy and Buildings 43 (2011), 1702-1711.

[5] S.A. Barakat, D.M. Sander, Utilisation of Solar Gain Through Windows for Heating Houses, BR

Note No. 184, Division of Building Research, National Research Council, Ottawa, Canada, 1982.


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[6]

J.A. Baker, R. Henry, Determination of Size-Specific U-factors and Solar Heat Gain Coefficients from Rated Values at Established Sizes – A Simplified Approach, ASHRAE Transactions 103,

Part I, 1997.

[7] HOT-XP and HOT2000, Natural Resources Canada, CANMET Energy Technology Centre,

Ottawa, Canada. – Available at www.buildingsgroup.rncan.gc.ca/software/hot2000_e.html .

[8] Energy Performance Evaluation of Windows and Other Fenestration Systems, StandardCAN/CSA A440.2, Canadian Standards Association, Toronto, Canada, 1998.

DETERMINING OPTIMAL COMBINATION OF PASSIVE SOLAR DESIGN PARAMETERS IN NOVI SAD

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