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Assessing the effect of facade variations on post-construction period environmental sustainability of residential buildings
Sustainable Cities and Society 6 (2013) 68–76
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Assessing the effect of facade variations on post-construction period environmental sustainability of residential buildings I. Cetiner ∗ , E. Edis Istanbul Technical University, Faculty of Architecture, Taskisla, Taksim, 34437 Istanbul, Turkey
a r t i c l e
i n f o
Article history: Received 30 May 2012 Received in revised form 5 September 2012 Accepted 18 September 2012 Keywords: Residential building Environmental impact Energy consumption
a b s t r a c t An important amount of the environmental impacts based on building energy consumption in postconstruction period is resulting from facade. Hence investigating these impacts and developing some measures are necessary to create a sustainable built environment. This issue is examined in a research project, which is being conducted to develop a sustainable building assessment method and sustainable renovation techniques for existing residential stock in Istanbul. To determine representative building types, field surveys were conducted, and the projects provided from the associated municipalities were analyzed. This study intends to investigate the effect of facade variations on post-construction period environmental sustainability of some determined building types. According to the results, the increase in the WWR slightly decreases the heating energy consumption, and consecutively the environmental impacts in the thermally not-insulated buildings, while it increases the heating energy consumption, and consecutively the environmental impacts in the thermally insulated buildings. Using thermal insulation, in both types of buildings, in all WWR’s and orientations, is considerably effective for reducing both energy consumption and environmental impacts. Global warming potential (GWP) constitutes most of the environmental impacts resulting from building’s heating energy consumption. Human toxicity, acidification, eutrophication and photochemical oxidation potentials are in negligible amounts when compared to GWP. © 2012 Elsevier B.V. All rights reserved.
1. Introduction All processes and activities carried out during the whole life cycle of a building result in energy consumption and consequently environmental impacts threatening human health, such as increase of environmental pollution, decrease of renewable resources, and change of climatic conditions. In order to assess and reduce these impacts resulting from buildings, a number of environmental assessment methods, for instance for new and existing buildings have been developing in some countries since 1990s. Building Research Establishment Environmental Assessment Method (BREEAM), The Leadership in Energy and Environmental Design (LEED), Hong Kong Building Environmental Assessment Method (HK-BEAM), and Building for Environmental and Economic Sustainability (BEES) are the most widely known building environmental assessment tools. In Turkey, there is not any developed method yet, neither for evaluating the new buildings nor the existing buildings. However, only in Istanbul, there is a large existing building stock, approximately 870,000 buildings,
∗ Corresponding author. Tel.: +90 212 2931300; fax: +90 212 2514895. E-mail addresses: [email protected], [email protected] (I. Cetiner). 2210-6707/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.scs.2012.09.005
that needs to be assessed in terms of environmental impacts. Almost 89% of this stock is residential buildings (SIS, 2000), which extensively contribute to energy consumption in post-construction period. This number reveals the importance of improving the residential stock in terms of buildings’ overall environmental impact. Reducing the environmental impacts in post-construction period can be provided by improving building systems/subsystems. Facade, for instance, is a subsystem which is responsible for a considerable amount of building environmental impacts based on energy consumption. Hence investigating the impacts resulting from the properties of facade and developing some measures are essential to create a sustainable built environment. Building aspect ratio, window to wall ratio (WWR), window type, glass/glazing type, composition of the exterior envelope and thermal insulation material/thickness are some building parameters which influence heating/cooling energy usage because of heat loss/gain through facade and consequently building environmental impacts, as also mentioned by Jones, Lannin, and Williams (2001) in their study explaining the data requirements and modeling of buildings’ energy use at urban scale. Studies on investigating the effects of changing those building parameters on the consequent environmental impacts usually focus on the opaque components of exterior envelope and investigate the effect of adding thermal
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Table 1 Results of the plan scheme and feature analyses of the selected buildings. Number of apartments on a storey (number of buildings)
Number of buildings according to plan form, location of stairwell, and number of stories
Square-like plan (width/length: 0.7–1) 10 buildings sa :8 hx :5
2 apartments (20)
sb :2 hy :5
Rectangular plan (width/length: <0.7) 9 buildings sb :2 hy :7
sa :5 hx : 1
3 buildings sa :3
3 apartments (8)
hx :5
1 buildings sc :1 hx :1
sc :2 hz :1
2 buildings sa :2
hx :1 4 apartments (20)
Complex plan
11 buildings sa :11 hy :5
hy :2
hx :1
hc :1
sa :2 hx :3
3 buildings sb :1
sa :1 hy :1
sd :1 hz :1
hy :2
4 buildings sb :2 hy :1
5 buildings sb :1 hy :5
sa :1
6 apartments (1)
1 building sa :1 hx :1
No building
No building
8 apartments (1)
No building
1 building sa :1 hy :1
No building
sc :3
Abbreviations and indices: s: number of stairwells; a: located at the center; b: one side exposed to outside; c: two sides exposed to outside; d: three sides exposed to outside; h: number of buildings; x: low-rise (1–5 stories); y: middle-rise (6–10 stories); z: high-rise (more than 10 stories). Note: The application projects of 10 selected buildings were not available in the archives of the associated municipalities.
insulation to minimize energy consumption. Sunikka (2005) presented a case study for the renewal of five-storey dwelling located in Rotterdam, the Netherlands. According to the results of this study, in the case of using additional thermal insulation together with new windows, the total gas consumption was reduced by 44% and a 40,327 kg CO2 reduction was achieved. Erlandsson, Levin, and Myhre (1997) presented a case study conducted to compare the saved emissions achieved from reduced heating and the pollutant effects resulting from the manufacturing and transportation of materials when additional wall insulation was used in a threestorey model building. They reported that, for the investigated type of thermal insulation (i.e. mineral wool) application, the pollutant effect was remarkably small when compared to savings. Cetiner and Edis (2009) investigated the effect of building’s heating energy consumption on the environmental impacts for different thermal insulation cases of an actual residential building located in Istanbul. They found that the highest rate of improvement in reduction of heating energy consumption was achieved in the case of renewing the exterior walls (about 32.77%). In addition, the figures of global warming, acidification and eutrophication potentials occurring due to XPS manufacturing were either too small or zero, although savings in energy and environmental impacts achieved due to reduction in heating energy consumption as the result of using thermal insulation were considerably high. Balaras et al. (2007) in their study on evaluating the Hellenic building stock in
terms of energy consumption, emissions and potential energy savings, indicated that apart from other measures, thermal insulation of external walls and roof, sealing of joints and using double glazing for the refurbishment of existing buildings helped to reduce CO2 emissions at varying levels both at single dwellings and apartment buildings. Radhi (2010), in his study on selecting wall cladding system for different wall assemblies considering the resultant CO2 emissions, mentioned that use of thermal insulation at the wall assembly reduced the energy consumption and consequent emissions especially due to reduction in cooling demand. Research studies directly investigating the effect of changing other building properties, apart from exterior wall assembly, on the resulting environmental impacts are comparatively less in number. To evaluate building’s environmental impacts, Su and Zhang (2010) analyzed office buildings with different window types and WWRs considering the building parameters. They reported that the life cycle energy consumption and environmental emissions of external envelope decreased linearly as the WWR increased. In general, the main objectives of the research studies are different, and building properties such as WWR are usually considered as effecting variables. Tzempelikos and Athienitis (2007), in their numerical simulation study of an hypothetical office space, to investigate the effect of shading design on cooling and lighting demand of building, also investigated the effect of WWR on heating and cooling loads. They reported that both heating and cooling
Table 2 ‘Orientation – WWR’ matrix for the SQ2 and SQ4 type buildings. Orientation (number of buildings)
WWR 5–10%
11–15%
16–20%
21–25%
26–30%
31–35%
36–40%
N (11) S (11)
2 1
3 2
2 1
1 3
1 1
1 2
1 1
E (11) W (11) NE (10)
0 0 1
0 1 4
5 4 1
3 3 2
2 1 2
0 2 0
1 0 0
NW (10) SE (10) SW (10)
1 0 0
3 1 0
1 6 4
3 2 6
1 0 0
1 0 0
0 1 0
Total number of facades for each WWR
5
14
24
23
8
6
4
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Table 3 Data on selected cases for sustainability evaluation. Main case code
SQ4
SQ2
Description Plan dimensions – width × length (m) Distances from surrounding buildings – front, sides, back (m) Number of stories Investigated window to wall ratios Window frame – glazing type Stairwell location, type and size – width × length (m)
Square plan with 4 apartments 20 × 20 20, 4, 4
Square plan with 2 apartments 14.5 × 14.5 20, 4, 4
1 unheated basement + 5 residential stories 10%, 20%, 30% PVC frame – 6/12/6 mm air filled insulated glass unit At center, straight flight, 2.50 × 6.40
1 unheated basement + 5 residential stories 10%, 20%, 30% PVC frame – 6/12/6 mm air filled insulated glass unit At center, dog-leg 2.70 × 4.30
to a specific thermal insulation thickness. In addition, the resulting pollutant emissions for different fuel types increased as the WWR increased both for walls with and without thermal insulation. When considered together with the findings of the aforementioned research studies, investigating the effects of facade properties on environmental impacts will significantly contribute to reduce the emissions and energy resource consumption of the existing residential stock in Turkey. This study, hence, aims to investigate the effect of facade variations on post-construction period environmental sustainability for the residential buildings in Istanbul, considering building parameters such as WWR, building dimension, orientation, and conditions like using additional external thermal insulation.
160000
70000
140000
60000
120000
50000
100000
40000
80000 30000
60000
20000
40000
10000
20000 0
Window heat gain/loss (kWh)
Thermally Not-Insulated Buildings Heating energy consumption (kWh)
load increased as WWR increased for south, north and west orientations, and they selected 30% WWR for their further research on the effect of shading design considering the requirements associated with thermal and visual interior conditions. Wang, Zmeureanu, and Rivard (2005), in their study on developing an optimization model for multi-objective green building design also considered the impact of changing WWR. For the case study, where numerical energy simulations of an office building were used, they presented that WWR of 20%, among values between 20% and 80%, was found optimal for all solution alternatives generated considering the variables such as wall type, insulation thickness or orientation. Yun, McEvoy, and Steemers (2007), in their numerical simulation study of an hypothetical office space for evaluating the energy performance of ventilated photovoltaic (PV) facade, considered the effect of changing WWR on both heating and cooling load, and effectiveness of PV facade as well. They reported that, for a south facing facade, heating energy consumption decreased slightly as the WWR increased since solar heat gain was higher than heat loss due to convection and radiation from the window. Only in the case of using single glazing rather than using a more advanced solution (i.e. low-e glazing), heating demand slightly increased as the WWR increased. Radhi (2009), in the study where he discussed the effectiveness of building envelope codes of Bahrain in the reduction of electricity consumption and CO2 emissions, investigated the effect of WWR on cooling and lighting loads of commercial and office buildings by numerical simulation. He reported that cooling demand increased as the WWR increased, but for the lighting load it was found to be the opposite. Ozkan and Onan (2011), in their study focusing on the optimization of thermal insulation thickness for different climatic regions of Turkey according to different WWRs that was based on using generalized equations to find savings per unit wall area, presented that annual heating energy consumption increased as the glazing area, i.e. WWR, increased, but not with a linear manner up
0 0.1
0.2
0.3
0.1
SQ2
0.2
0.3
SQ4 Heating energy consumption Window heat gain
25
4000
20 15
3000
10 5
2000
0
1000
-5
0
-10
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Months Direct average solar radiation Minimum dry bulb temperature Maximum dry bulb temperature Fig. 1. Annual average climatic data.
160000
70000
140000
60000
120000
50000
100000
40000
80000 30000
60000
20000
40000
10000
20000 0
Window hat gain/loss (kWh)
5000
Dry bulb temperature (0C)
Direct solar radiation (Wh/m2)
30
Heating energy consumption (kWh)
Thermally Insulated Buildings 35
6000
0 0.1
0.2
SQ2
0.3
0.1
0.2
0.3
SQ4 Heating energy consumption Window heat gain
Fig. 2. Total heating energy consumption, window heat gain and loss results of SQ2 and SQ4 type buildings for different WWRs.
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Table 4 The selected functional building elements for sustainability evaluation. Functional building elements
Without thermal insulation
With thermal insulation
Exterior wall system – above grade
Exterior to interior E.R. 3 cm Brick 19 cm I.R. 2 cm
Exterior to interior E.R. 3 cm Brick 19 cm Polystyrene 5 cm I.R. 2 cm
Exterior wall system – below grade
Exterior to interior E.R. 3 cm R.C. 20 cm I.R. 2 cm
Exterior to interior E.R. 3 cm Water insulation R.C. 20 cm Polystyrene 3 cm I.R. 2 cm
Roof system –between attic and top storey
Top to bottom R.C. 10 cm I.R. 2 cm
Top to bottom Polystyrene 5 cm R.C. 10 cm I.R. 2 cm
Floor system – slab on grade
Top to bottom Tile 2 cm Screed 3 cm Water insulation Concrete 10 cm Blockage 15 cm Earth
Top to bottom Tile 2 cm Screed 3 cm Polystyrene 3 cm Water insulation Concrete 10 cm Blockage 15 cm Earth
Floor system – between heated and unheated spaces
Top to bottom Wood parquet 2 cm Screed 3 cm R.C. 10 cm I.R. 2 cm
Top to bottom Wood parquet 2 cm Screed 3 cm Polystyrene 7 cm R.C. 10 cm I.R. 2 cm
Internal Wall – between heated and unheated spaces (stairwells)
Interior to interior I.R. 2 cm Brick 9 cm I.R. 2 cm
Interior to interior I.R. 2 cm Brick 9 cm Polystyrene 3 cm I.R. 2 cm
Abbreviations: E.R.: exterior rendering; I.R.: interior rendering; R.C.: reinforced concrete.
2.1. Field survey and application project analysis – determination of building types and facade variations
thermally not-insulated buildings, 10 from each residential region, were randomly selected during the field surveys and initial information about these buildings were provided from the concierges of these buildings. Subsequently, application projects of these buildings were provided from the associated municipalities, and projects were analyzed to determine the mostly used building types in respect to the number of apartments on a storey, plan form and location of the stairwell, and facade variations considering different WWRs according to orientation and exterior wall assemblies. Results of these analyses and the decisions made in line with these results can be summarized as follows:
In Istanbul, 5% of the residential buildings have central heating system (SIS, 2000). In order to determine the building types in terms of plan scheme, and facade variations in terms of WWR and exterior wall assembly, six different residential regions in Istanbul, where buildings with central heating system are mostly located, were determined and field surveys were conducted to select example buildings. These regions are Bakirkoy and Florya on the European side of Istanbul, and Rahmanlar, Maltepe, Acibadem and Kos¸uyolu on the Anatolian side of Istanbul. A total of 60 centrally heated and
• Plan form: Square-like plan with four apartments (SQ4) and square-like plan with two apartments (SQ2) were the types that were mostly used, as seen in Table 1 and the type ‘rectangular plan with two apartments’ follows them. Among these types, squarelike plans were selected for conducting further investigations, in order to make comparative sustainability analyses. • Number of storey: The SQ4 and SQ2 type buildings were usually low-rise (1–5 storey) and middle-rise (6–10 storey) buildings (see Table 1). In this study, investigation of low-rise buildings
2. Methodology The study covers multi-storey detached apartment buildings located in Istanbul that have central heating system and which do not have any thermal insulation at the exterior walls. In this respect, field surveys, application project analyses, energy simulations and sustainability assessments, which are explained in the following sections, were conducted.
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Table 5 The properties of the selected building materials. Materials
Properties
Exterior rendering Interior rendering Brick Polystyrene Tile Reinforced concrete Screed Wood parquet Glassa Air gap PVC frame a b
•
•
•
•
Conductivity (W/m K)
Density (kg/m3 )
Specific heat (J/kg K)
Thermal absorptance
Solar absorptance
1.4 0.87 0.45 0.033 0.1 2.1 1.4 0.12 0.9 0.024 1.8b
2000 1800 1000 28 1000 2400 2000 540 – – –
840 840 880 1500 880 1000 840 1210 – 1006.1 –
0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 – – –
0.3 0.3 0.5 0.2 0.5 0.65 0.65 0.7 – – 0.2
Solar transmittance (normal incidence) of glass is 0.77. Value given for PVC frame is the conductance value (W/m2 K).
was aimed and 5-storey buildings were selected for sustainability assessment. These buildings were at the borderline with middlerise buildings as well. Therefore, they can also be used for initial predictions. Preferred WWRs: The WWR-orientation interrelation matrix for the facades of SQ4 and SQ2 type buildings is given in Table 2. The mostly preferred WWRs were 16–20% and 21–25% with similar number of buildings for each, and the next two WWRs following those were 11–15% and 26–30% respectively. Considering these figures, WWRs of 10%, 20% and 30% were selected for sustainability assessments. Area of the storey: Average storey areas of SQ4 and SQ2 type buildings were 405 and 209 square meters (m2 ) respectively. Considering the fact that there was no specific pattern in terms of preferred WWRs according to the orientation (see Table 2), investigation of true squares as the plan schemes were decided for evaluating the effects related with changing orientations. Hence, side dimensions of squares for SQ4 and SQ2 cases were determined as 20 m and 14.5 m respectively. Distances from surrounding buildings: The interrelations of selected buildings with their surrounding buildings were investigated during the analysis as well. The distances between buildings were in line with the Istanbul Municipality regulations, and considering the projections at the upper floors, the distances were selected as 4 m from the back and sides and 20 m from the front, assuming that there is a road of 12 m width between two buildings (see Table 3). Stairwell location and type: All of the stairwells of SQ4 type buildings were at the center and they were usually straight-flight type of stairs. The stairwells of SQ2 type buildings were mostly at the center, and they were usually dog-leg type of stairs. Therefore, stairwells of the investigated cases were determined in line with these facts and the selected dimensions for the stairwells for each building type are given in Table 3.
• Functional building elements: The facade assembly mostly used in the investigated application projects was brick with rendering on both sides. Hence, a brick wall of 19 cm width was selected for sustainability assessments. The assembly and materials of other functional building elements were generated as well as given in Table 4, considering the usually preferred materials. 2.2. Determination of total heating energy consumption and assessment of environmental impacts In Istanbul, residential buildings usually do not have individual or central cooling system. In the selected buildings, none of them have central cooling system and most of the apartments do not have individual cooling system as well. Therefore, in the research study, only heating energy consumption was considered for sustainability evaluations. Energy consumed for heating within a one-year period (heating from the beginning of October to the end of April, i.e. 7 months) and heat loss through exterior walls according to orientation in the selected cases for different WWRs were determined by an energy simulation program, EnergyPlus, which has been developed to model heating, cooling, ventilating, lighting and other energy flows and consumptions in buildings (DOE, 2006). The computations were executed considering the information on the buildings, element assemblies and material properties given in Tables 3–5, and the annual monthly climatic data of Istanbul, which has a temperate-humid climate, given in Fig. 1. Most of the existing buildings in Istanbul, as aforementioned, do not have any thermal insulation at the exterior envelope and therefore calculations were executed on building models without thermal insulation. However, in order to see the effect of using additional thermal insulation, simulations were done on building models with thermal insulation at the exterior envelope as well. In the energy simulations, each storey was modeled as an individual thermal zone. Internal heat load effects with schedules
Table 6 The equivalency factors for the emissions according to the kind of environmental impact (EPA, 1998). Emissions
NOx CO CO2 CH4 SO2 Lead PM1 a PM2 b a b
Equivalency factors for environmental impacts GWP (kg CO2 equiv.)
AP (kg SO2 equiv.)
EP (kg PO4 equiv.)
POP (kg ethylene equiv.)
HP (kg 1,4-dichlorobenzene equiv.)
– – 1.0 25 – – – –
0.5 – – – 1.2 – – –
0.13 – – – – – – –
– 0.027 – 0.06 0.048 – – –
1.2 – – – 0.096 466.517 0.82 0.82
Condensable particulate matters. Filterable particulate matters.
180000 160000 140000 120000 100000 80000 60000 40000 20000 0
73
Thermally Not-insulated Buildings 180
SQ2-0
SQ4-0 SQ2-1 0 : Thermally insulated buildings 1: Thermally not-insulated buildings WWR
0.1
0.2
SQ4-1
Opaque surface inside face 2 conduction heat loss (W/m )
Opaque Surface Inside Face Conduction Loss (W)
I. Cetiner, E. Edis / Sustainable Cities and Society 6 (2013) 68–76
160 140 120 100 80 60 40
20 0 10%
0.3
20%
30%
10%
Orientation
700
20%
30%
SQ4 S
W
N
E
600
Thermally Insulated Buildings
500 400
300 200 100
0 SQ2-0
SQ4-0 SQ2-1 0 : Thermally insulated buildings 1: Thermally not-insulated buildings WWR
0.1
0.2
SQ4-1
0.3
Fig. 3. Total opaque surface inside face conduction heat loss (a) through the whole exterior wall area and (b) per unit exterior wall area.
Opaque surface inside face 2 conduction heat loss (W/m )
Opaque Surface Inside Face Conduction Loss (W/m2)
SQ2
50 45 40 35 30 25 20 15 10 5 0 10%
20%
Orientation
(occupancy, lights and equipments), internal mass effects (stairwell walls) and infiltration/natural ventilation effects were considered as well. Three people were assumed to be living in each apartment, for the determination of occupancy loads. The activity levels of these people were specified as 131.8 W/person, and the clothing type was assumed to be 1clo in the heating season. Internal air velocity was assumed as 0.137 m/s while the infiltration rate was specified as 0.01 m3 /s and the natural ventilation rate was 0.02 m3 /s. The heating system was admitted to provide 23 ◦ C internal air temperature between 7.00 and 24.00 h while 18 ◦ C between 24.00 and 7.00 h. In all of the selected buildings, natural gas is used in the heating system. Emissions resulted from natural gas combustion were provided from Environmental Protection Agency AP-42 report (EPA, 1998). Emissions of natural gas combustion considered in this study are nitrogen oxides (NOx ), carbonmonoxide (CO), carbondioxide (CO2 ), methane (CH4 ), sulphurdioxide (SO2 ), lead and particulate matters (PM). The environmental impacts resulting from these emissions are global warming, acidification, eutrophication, photochemical oxidation and human toxicity. Each emission can contribute to different impacts. NOx emissions, for instance, have an effect on human health, acidification, and global warming while SO2 emissions cause acidification, photochemical oxidation and human toxicity. Contributions to each environmental impact are determined by equivalency factors which indicate how much a substance contributes to a problem compared to a reference substance (UNEP, 1996). In the study, global warming potential (GWP – measured relative to the effect of 1 kg CO2 ), acidification potential (AP – measured relative to the effect of 1 kg SO2 ), eutrophication potential (EP – measured relative to the effect of 1 kg PO4 ), photochemical oxidation potential (POP – measured relative to the effect of 1 kg ethylene) and human toxicity potential (HP, measured relative to the effect of 1.4 kg dichlorobenzene) caused by the emissions
30%
10%
SQ2
20%
30%
SQ4 S
W
N
E
Fig. 4. Opaque surface inside face conduction heat loss per 1 m2 of exterior wall area according to orientations for different WWRs.
of heating energy consumption of seven months within a oneyear use period for different WWRs were determined by using the equivalency factors provided from CML-IA database of the Leiden University-Institute of Environmental Sciences (CML, 2008). Table 6 shows the emissions according to the kind of environmental impact and their equivalency factors. 3. Results and discussion Results of both energy simulations and environmental impact calculations according to different WWR’s are presented and discussed for the determined cases in the following sections. 3.1. Energy simulation results Total heating energy consumption and window heat gain/loss results of SQ2 and SQ4 type buildings with and without thermal insulation, according to different WWRs, determined by the energy simulation program are given in Fig. 2. In the thermally not-insulated SQ2 and SQ4 type buildings, the increase in the WWR slightly decreases the total heating energy consumption. However, in the thermally insulated SQ2 and SQ4 type buildings, the increase in the WWR increases the total heating energy consumption. Heat gain and loss through the windows, and opaque surface inside face conduction loss are the determinants of heating energy consumption. Heat gain amounts through the windows are similar both in the thermally insulated and not insulated buildings, as given in Fig. 2. However, heat loss amounts are higher in the thermally insulated buildings, since diffuse irradiation of internal surfaces, which
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Fig. 5. Total heating energy consumption per 1 m2 of heated floor area of SQ2 and SQ4 type buildings for different WWRs. Fig. 6. Global warming potentials of SQ2 and SQ4 type buildings for different WWRs.
is taken into account in the heat gain and loss calculations by the software, is greater due to higher internal surface temperatures of exterior walls. In addition, the amount of increase in the heat loss through the windows by the increase of WWR is slightly greater in the thermally insulated buildings. Moreover, as given in Fig. 3a, the amount of decrease in the opaque surface conduction heat loss by the increase of WWR is greater in the thermally not insulated buildings. Therefore, due to combined effect of those differences, in the thermally insulated buildings, increase of the WWR increases the heating energy consumption, but in the thermally not insulated buildings, the heating energy consumption slightly decreases as the WWR increases. In addition, using thermal insulation lowers total heating energy consumption in considerable amounts in both SQ2 and SQ4 type of buildings. The reduction is about 63%, 57% and 51% for both type of buildings with WWRs of 10%, 20% and 30% respectively. Opaque surface conduction heat loss through the whole exterior wall area and per unit wall area (both excluding windows), and losses according to orientations per unit exterior wall area for different WWRs are given in Figs. 3 and 4 respectively. Heat loss through the whole exterior wall area decreases both in thermally insulated and not insulated buildings, as the WWR increases. This is the same for thermally insulated buildings in the case of heat loss per unit wall area. However, in the thermally not insulated buildings, heat loss per unit exterior wall area increases as the WWR increases, since the rate of decrease of heat loss is smaller than the rate of decrease of exterior wall area. When heat losses according to orientations are analyzed, as given in Fig. 4, both for thermally insulated and not insulated buildings, most of the conduction heat
losses occur on the facade surfaces oriented to north. The conduction heat losses on west, east and south orientations respectively follow it. However, in the thermally insulated buildings, the amount of change according to orientations is smaller than that of the thermally not insulated buildings. In addition, using thermal insulation, for both types of buildings with all WWR’s, results in about 70% decrease in the opaque surface conduction heat losses of the facades in all orientations. Fig. 5 presents the total heating energy consumption results per 1 m2 heated floor area according to different WWRs for both thermally insulated and not-insulated buildings. In SQ4 type building, where heated floor area is bigger, the energy consumption per m2 is lower when compared to SQ2 type having less heated floor area. This is due to the fact that, in SQ4 type, exterior wall area (including window area) per 1 m2 of heated floor area is smaller than that of SQ2 type (i.e. ∼0.48 m2 and ∼0.66 m2 respectively). In addition, as aforementioned, the increase in the WWR decreases the total heating energy consumption in the thermally not-insulated buildings, although it increases the total heating energy consumption in the thermally insulated buildings. 10 points increase in the WWR affects the energy consumption %1 in the thermally not insulated types, although it affects 14% in the thermally insulated buildings. 3.2. Environmental impact results The environmental impacts of a one-year period heating energy consumption for different WWRs are given in Figs. 6 and 7 for both thermally not-insulated and insulated buildings. Among the emissions occurring due to natural gas combustion, CO2 emissions
I. Cetiner, E. Edis / Sustainable Cities and Society 6 (2013) 68–76
such as WWR, building dimension, orientation, and conditions like using additional external thermal insulation. In accordance with the results, concerning mid-rise square-like planned buildings that have 210 and 400 m2 of floor areas at a single storey, the following remarks can be concluded:
Environmental Impacts (kg)
25 20 15
10 5
SQ4
SQ2
10%-1 20%-1 30%-1
10%-0 20%-0 30%-0
SQ2
10%-1 20%-1 30%-1
10%-0 20%-0 30%-0
0
SQ4
0: Thermally not-insulated building 1: Thermally insulated building Human toxicity
Acidification
3 2 2 1 1
SQ4
SQ2
10%-1 20%-1 30%-1
10%-1 20%-1 30%-1
SQ2
10%-0 20%-0 30%-0
0 10%-0 20%-0 30%-0
Environmental Impacts (kg)
75
SQ4
0: Thermally not-insulated building 1: Thermally insulated building Eutrophication
Photochemical oxidation
Fig. 7. Environmental impacts of SQ2 and SQ4 type buildings for different WWRs.
constitute most of the emissions to air, which causes global warming. The increase in WWR decreases GWP for the buildings without insulation because of the reduction in the total heating energy consumption while it causes an increase in GWP in the cases with thermal insulation (see Fig. 6). The highest decrease in GWP, as a result of using thermal insulation, is achieved in the case of the WWR of 10%. HP caused by NOx , SO2 , lead and particulate matters is the biggest environmental impact after GWP. AP due to NOx and SO2 emissions, EP due to NOx emissions and photochemical oxidation due to CO, CH4 and SO2 emissions follow them respectively, but these impacts are in negligible amounts when compared with global warming potential. The increase in WWR, as in the case of GWP, decreases these impacts in the thermally not-insulated buildings whereas it causes an increase in these impacts in the thermally insulated buildings (see Fig. 7). HP, for instance, decreases about 10, 9, and 81.4 kg dichlorobenzene equiv. , in thermally insulated SQ2 type building, for the WWRs of 10%, 20%, and 30%, respectively. 4. Concluding remarks This study that aims to investigate the effect of facade variations on post-construction period environmental sustainability of the residential buildings in Istanbul considers building parameters
• Increase in WWR slightly decreases total heating energy consumption and consecutively environmental impacts in the thermally not-insulated buildings, while it increases total heating energy consumption and the resulting environmental impacts in the thermally insulated buildings. • In the thermally not-insulated buildings, the effect of the increase in WWR on total heating energy consumption is in negligible amounts, but it should be considered in thermally insulated buildings. • As heated floor area increases, total heating energy consumption per 1 m2 decreases because exterior wall area per 1 m2 of heated floor area reduces for both thermally not-insulated and insulated buildings. • Using thermal insulation, in both types of buildings with all WWR’s and orientations, is considerably effective for reducing both heating energy consumption and environmental impacts. • GWP constitutes most of the environmental impacts resulting from building’s heating energy consumption. HP, AP, EP and POP follow it respectively, but these are in negligible amounts when compared to GWP. Increase in WWR decreases these impacts in the thermally not-insulated buildings whereas it causes an increase in these impacts in the thermally insulated buildings. These results, in the context of the project, will be utilized to generate standard representations of residential buildings in accordance with the existing buildings’ parameters and built environment, and to evaluate the contribution of these parameters (e.g. WWR, building dimension, orientation, and conditions like using additional external thermal insulation) on the sustainability of buildings. Acknowledgment The presented study was a part of the research project numbered 108K418 and supported by The Scientific and Technical Research Council of Turkey (TUBITAK). References Balaras, C. A., Gaglia, A. G., Georgopoulou, E., Mirasgedis, S., Sarafidis, Y., & Lalas, D. P. (2007). European residential buildings and empirical assessment of the Hellenic building stock, energy consumption, emissions and potential energy savings. Building and Environment, 42(3), 1298–1314. Cetiner, I., & Edis, E. (2009). Assessing the effect of building elements on postconstruction period environmental sustainability of residential buildings for renovation decisions. In 3rd CIB international conference on smart and sustainable built environments Delft, the Netherlands. CML. (2008). CML-IA version 3.4. The Netherlands: Leiden University, Institute of Environmental Sciences. DOE. (2006). EnergyPlus manual: Documentation V.1.4 – Input–output references. USA: US Dept. of Energy. EPA. (1998). AP 42 compilation of air pollutant emission factors. Natural gas combustion NC: U.S. Environmental Protection Agency. Erlandsson, M., Levin, P., & Myhre, L. (1997). Energy and environmental consequences of an additional wall insulation of a dwelling. Building and Environment, 32(2), 129–136. Jones, P. J., Lannin, S., & Williams, J. (2001). Modelling building energy use at urban scale. In Seventh international IBPSA conference Rio de Janeiro, Brazil. Ozkan, D. B., & Onan, C. (2011). Optimization of insulation thickness for different glazing areas in buildings for various climatic regions in Turkey. Applied Energy, 88(4), 1331–1342. Radhi, H. (2009). Can envelope codes reduce electricity and CO2 emissions in different types of buildings in the hot climate of Bahrain? Energy, 34(2), 205–215. Radhi, H. (2010). On the optimal selection of wall cladding system to reduce direct and indirect CO2 emissions. Energy, 35(3), 1412–1424.
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SIS. (2000). Building census 2000. Ankara: State Institute of Statistics – Prime Ministry of Republic of Turkey. Sunikka, M. (2005). CO2 reduction in the renovation of postwar housing areas: A feasibility study. In The proceedings of the 4th triennial international conference on rethinking and revitalizing construction safety, health, environment and quality South Africa, (pp. 496–507). Su, X., & Zhang, X. (2010). Environmental performance optimization of window-wall ratio for different window type in hot summer and cold winter zone in China based on life cycle assessment. Energy and Buildings, 42(2), 198–202.
Tzempelikos, A., & Athienitis, A. K. (2007). The impact of shading design and control on building cooling and lighting demand. Solar Energy, 81(3), 369–382. UNEP. (1996). Life cycle assessment: What it is and how to do it. Nairobi, Kenya: United Nations Environment Programme Industry and Environment. Wang, W., Zmeureanu, R., & Rivard, H. (2005). Applying multi-objective genetic algorithms on green building design optimization. Energy and Buildings, 40(11), 1512–1525. Yun, G. Y., McEvoy, M., & Steemers, K. (2007). Design and overall performance of a ventilated photovoltaic Fac¸ade. Solar Energy, 81(3), 383–394.
Contents lists available at SciVerse ScienceDirect
Sustainable Cities and Society journal homepage: www.elsevier.com/locate/scs
Assessing the effect of facade variations on post-construction period environmental sustainability of residential buildings I. Cetiner ∗ , E. Edis Istanbul Technical University, Faculty of Architecture, Taskisla, Taksim, 34437 Istanbul, Turkey
a r t i c l e
i n f o
Article history: Received 30 May 2012 Received in revised form 5 September 2012 Accepted 18 September 2012 Keywords: Residential building Environmental impact Energy consumption
a b s t r a c t An important amount of the environmental impacts based on building energy consumption in postconstruction period is resulting from facade. Hence investigating these impacts and developing some measures are necessary to create a sustainable built environment. This issue is examined in a research project, which is being conducted to develop a sustainable building assessment method and sustainable renovation techniques for existing residential stock in Istanbul. To determine representative building types, field surveys were conducted, and the projects provided from the associated municipalities were analyzed. This study intends to investigate the effect of facade variations on post-construction period environmental sustainability of some determined building types. According to the results, the increase in the WWR slightly decreases the heating energy consumption, and consecutively the environmental impacts in the thermally not-insulated buildings, while it increases the heating energy consumption, and consecutively the environmental impacts in the thermally insulated buildings. Using thermal insulation, in both types of buildings, in all WWR’s and orientations, is considerably effective for reducing both energy consumption and environmental impacts. Global warming potential (GWP) constitutes most of the environmental impacts resulting from building’s heating energy consumption. Human toxicity, acidification, eutrophication and photochemical oxidation potentials are in negligible amounts when compared to GWP. © 2012 Elsevier B.V. All rights reserved.
1. Introduction All processes and activities carried out during the whole life cycle of a building result in energy consumption and consequently environmental impacts threatening human health, such as increase of environmental pollution, decrease of renewable resources, and change of climatic conditions. In order to assess and reduce these impacts resulting from buildings, a number of environmental assessment methods, for instance for new and existing buildings have been developing in some countries since 1990s. Building Research Establishment Environmental Assessment Method (BREEAM), The Leadership in Energy and Environmental Design (LEED), Hong Kong Building Environmental Assessment Method (HK-BEAM), and Building for Environmental and Economic Sustainability (BEES) are the most widely known building environmental assessment tools. In Turkey, there is not any developed method yet, neither for evaluating the new buildings nor the existing buildings. However, only in Istanbul, there is a large existing building stock, approximately 870,000 buildings,
∗ Corresponding author. Tel.: +90 212 2931300; fax: +90 212 2514895. E-mail addresses: [email protected], [email protected] (I. Cetiner). 2210-6707/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.scs.2012.09.005
that needs to be assessed in terms of environmental impacts. Almost 89% of this stock is residential buildings (SIS, 2000), which extensively contribute to energy consumption in post-construction period. This number reveals the importance of improving the residential stock in terms of buildings’ overall environmental impact. Reducing the environmental impacts in post-construction period can be provided by improving building systems/subsystems. Facade, for instance, is a subsystem which is responsible for a considerable amount of building environmental impacts based on energy consumption. Hence investigating the impacts resulting from the properties of facade and developing some measures are essential to create a sustainable built environment. Building aspect ratio, window to wall ratio (WWR), window type, glass/glazing type, composition of the exterior envelope and thermal insulation material/thickness are some building parameters which influence heating/cooling energy usage because of heat loss/gain through facade and consequently building environmental impacts, as also mentioned by Jones, Lannin, and Williams (2001) in their study explaining the data requirements and modeling of buildings’ energy use at urban scale. Studies on investigating the effects of changing those building parameters on the consequent environmental impacts usually focus on the opaque components of exterior envelope and investigate the effect of adding thermal
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Table 1 Results of the plan scheme and feature analyses of the selected buildings. Number of apartments on a storey (number of buildings)
Number of buildings according to plan form, location of stairwell, and number of stories
Square-like plan (width/length: 0.7–1) 10 buildings sa :8 hx :5
2 apartments (20)
sb :2 hy :5
Rectangular plan (width/length: <0.7) 9 buildings sb :2 hy :7
sa :5 hx : 1
3 buildings sa :3
3 apartments (8)
hx :5
1 buildings sc :1 hx :1
sc :2 hz :1
2 buildings sa :2
hx :1 4 apartments (20)
Complex plan
11 buildings sa :11 hy :5
hy :2
hx :1
hc :1
sa :2 hx :3
3 buildings sb :1
sa :1 hy :1
sd :1 hz :1
hy :2
4 buildings sb :2 hy :1
5 buildings sb :1 hy :5
sa :1
6 apartments (1)
1 building sa :1 hx :1
No building
No building
8 apartments (1)
No building
1 building sa :1 hy :1
No building
sc :3
Abbreviations and indices: s: number of stairwells; a: located at the center; b: one side exposed to outside; c: two sides exposed to outside; d: three sides exposed to outside; h: number of buildings; x: low-rise (1–5 stories); y: middle-rise (6–10 stories); z: high-rise (more than 10 stories). Note: The application projects of 10 selected buildings were not available in the archives of the associated municipalities.
insulation to minimize energy consumption. Sunikka (2005) presented a case study for the renewal of five-storey dwelling located in Rotterdam, the Netherlands. According to the results of this study, in the case of using additional thermal insulation together with new windows, the total gas consumption was reduced by 44% and a 40,327 kg CO2 reduction was achieved. Erlandsson, Levin, and Myhre (1997) presented a case study conducted to compare the saved emissions achieved from reduced heating and the pollutant effects resulting from the manufacturing and transportation of materials when additional wall insulation was used in a threestorey model building. They reported that, for the investigated type of thermal insulation (i.e. mineral wool) application, the pollutant effect was remarkably small when compared to savings. Cetiner and Edis (2009) investigated the effect of building’s heating energy consumption on the environmental impacts for different thermal insulation cases of an actual residential building located in Istanbul. They found that the highest rate of improvement in reduction of heating energy consumption was achieved in the case of renewing the exterior walls (about 32.77%). In addition, the figures of global warming, acidification and eutrophication potentials occurring due to XPS manufacturing were either too small or zero, although savings in energy and environmental impacts achieved due to reduction in heating energy consumption as the result of using thermal insulation were considerably high. Balaras et al. (2007) in their study on evaluating the Hellenic building stock in
terms of energy consumption, emissions and potential energy savings, indicated that apart from other measures, thermal insulation of external walls and roof, sealing of joints and using double glazing for the refurbishment of existing buildings helped to reduce CO2 emissions at varying levels both at single dwellings and apartment buildings. Radhi (2010), in his study on selecting wall cladding system for different wall assemblies considering the resultant CO2 emissions, mentioned that use of thermal insulation at the wall assembly reduced the energy consumption and consequent emissions especially due to reduction in cooling demand. Research studies directly investigating the effect of changing other building properties, apart from exterior wall assembly, on the resulting environmental impacts are comparatively less in number. To evaluate building’s environmental impacts, Su and Zhang (2010) analyzed office buildings with different window types and WWRs considering the building parameters. They reported that the life cycle energy consumption and environmental emissions of external envelope decreased linearly as the WWR increased. In general, the main objectives of the research studies are different, and building properties such as WWR are usually considered as effecting variables. Tzempelikos and Athienitis (2007), in their numerical simulation study of an hypothetical office space, to investigate the effect of shading design on cooling and lighting demand of building, also investigated the effect of WWR on heating and cooling loads. They reported that both heating and cooling
Table 2 ‘Orientation – WWR’ matrix for the SQ2 and SQ4 type buildings. Orientation (number of buildings)
WWR 5–10%
11–15%
16–20%
21–25%
26–30%
31–35%
36–40%
N (11) S (11)
2 1
3 2
2 1
1 3
1 1
1 2
1 1
E (11) W (11) NE (10)
0 0 1
0 1 4
5 4 1
3 3 2
2 1 2
0 2 0
1 0 0
NW (10) SE (10) SW (10)
1 0 0
3 1 0
1 6 4
3 2 6
1 0 0
1 0 0
0 1 0
Total number of facades for each WWR
5
14
24
23
8
6
4
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Table 3 Data on selected cases for sustainability evaluation. Main case code
SQ4
SQ2
Description Plan dimensions – width × length (m) Distances from surrounding buildings – front, sides, back (m) Number of stories Investigated window to wall ratios Window frame – glazing type Stairwell location, type and size – width × length (m)
Square plan with 4 apartments 20 × 20 20, 4, 4
Square plan with 2 apartments 14.5 × 14.5 20, 4, 4
1 unheated basement + 5 residential stories 10%, 20%, 30% PVC frame – 6/12/6 mm air filled insulated glass unit At center, straight flight, 2.50 × 6.40
1 unheated basement + 5 residential stories 10%, 20%, 30% PVC frame – 6/12/6 mm air filled insulated glass unit At center, dog-leg 2.70 × 4.30
to a specific thermal insulation thickness. In addition, the resulting pollutant emissions for different fuel types increased as the WWR increased both for walls with and without thermal insulation. When considered together with the findings of the aforementioned research studies, investigating the effects of facade properties on environmental impacts will significantly contribute to reduce the emissions and energy resource consumption of the existing residential stock in Turkey. This study, hence, aims to investigate the effect of facade variations on post-construction period environmental sustainability for the residential buildings in Istanbul, considering building parameters such as WWR, building dimension, orientation, and conditions like using additional external thermal insulation.
160000
70000
140000
60000
120000
50000
100000
40000
80000 30000
60000
20000
40000
10000
20000 0
Window heat gain/loss (kWh)
Thermally Not-Insulated Buildings Heating energy consumption (kWh)
load increased as WWR increased for south, north and west orientations, and they selected 30% WWR for their further research on the effect of shading design considering the requirements associated with thermal and visual interior conditions. Wang, Zmeureanu, and Rivard (2005), in their study on developing an optimization model for multi-objective green building design also considered the impact of changing WWR. For the case study, where numerical energy simulations of an office building were used, they presented that WWR of 20%, among values between 20% and 80%, was found optimal for all solution alternatives generated considering the variables such as wall type, insulation thickness or orientation. Yun, McEvoy, and Steemers (2007), in their numerical simulation study of an hypothetical office space for evaluating the energy performance of ventilated photovoltaic (PV) facade, considered the effect of changing WWR on both heating and cooling load, and effectiveness of PV facade as well. They reported that, for a south facing facade, heating energy consumption decreased slightly as the WWR increased since solar heat gain was higher than heat loss due to convection and radiation from the window. Only in the case of using single glazing rather than using a more advanced solution (i.e. low-e glazing), heating demand slightly increased as the WWR increased. Radhi (2009), in the study where he discussed the effectiveness of building envelope codes of Bahrain in the reduction of electricity consumption and CO2 emissions, investigated the effect of WWR on cooling and lighting loads of commercial and office buildings by numerical simulation. He reported that cooling demand increased as the WWR increased, but for the lighting load it was found to be the opposite. Ozkan and Onan (2011), in their study focusing on the optimization of thermal insulation thickness for different climatic regions of Turkey according to different WWRs that was based on using generalized equations to find savings per unit wall area, presented that annual heating energy consumption increased as the glazing area, i.e. WWR, increased, but not with a linear manner up
0 0.1
0.2
0.3
0.1
SQ2
0.2
0.3
SQ4 Heating energy consumption Window heat gain
25
4000
20 15
3000
10 5
2000
0
1000
-5
0
-10
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Months Direct average solar radiation Minimum dry bulb temperature Maximum dry bulb temperature Fig. 1. Annual average climatic data.
160000
70000
140000
60000
120000
50000
100000
40000
80000 30000
60000
20000
40000
10000
20000 0
Window hat gain/loss (kWh)
5000
Dry bulb temperature (0C)
Direct solar radiation (Wh/m2)
30
Heating energy consumption (kWh)
Thermally Insulated Buildings 35
6000
0 0.1
0.2
SQ2
0.3
0.1
0.2
0.3
SQ4 Heating energy consumption Window heat gain
Fig. 2. Total heating energy consumption, window heat gain and loss results of SQ2 and SQ4 type buildings for different WWRs.
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Table 4 The selected functional building elements for sustainability evaluation. Functional building elements
Without thermal insulation
With thermal insulation
Exterior wall system – above grade
Exterior to interior E.R. 3 cm Brick 19 cm I.R. 2 cm
Exterior to interior E.R. 3 cm Brick 19 cm Polystyrene 5 cm I.R. 2 cm
Exterior wall system – below grade
Exterior to interior E.R. 3 cm R.C. 20 cm I.R. 2 cm
Exterior to interior E.R. 3 cm Water insulation R.C. 20 cm Polystyrene 3 cm I.R. 2 cm
Roof system –between attic and top storey
Top to bottom R.C. 10 cm I.R. 2 cm
Top to bottom Polystyrene 5 cm R.C. 10 cm I.R. 2 cm
Floor system – slab on grade
Top to bottom Tile 2 cm Screed 3 cm Water insulation Concrete 10 cm Blockage 15 cm Earth
Top to bottom Tile 2 cm Screed 3 cm Polystyrene 3 cm Water insulation Concrete 10 cm Blockage 15 cm Earth
Floor system – between heated and unheated spaces
Top to bottom Wood parquet 2 cm Screed 3 cm R.C. 10 cm I.R. 2 cm
Top to bottom Wood parquet 2 cm Screed 3 cm Polystyrene 7 cm R.C. 10 cm I.R. 2 cm
Internal Wall – between heated and unheated spaces (stairwells)
Interior to interior I.R. 2 cm Brick 9 cm I.R. 2 cm
Interior to interior I.R. 2 cm Brick 9 cm Polystyrene 3 cm I.R. 2 cm
Abbreviations: E.R.: exterior rendering; I.R.: interior rendering; R.C.: reinforced concrete.
2.1. Field survey and application project analysis – determination of building types and facade variations
thermally not-insulated buildings, 10 from each residential region, were randomly selected during the field surveys and initial information about these buildings were provided from the concierges of these buildings. Subsequently, application projects of these buildings were provided from the associated municipalities, and projects were analyzed to determine the mostly used building types in respect to the number of apartments on a storey, plan form and location of the stairwell, and facade variations considering different WWRs according to orientation and exterior wall assemblies. Results of these analyses and the decisions made in line with these results can be summarized as follows:
In Istanbul, 5% of the residential buildings have central heating system (SIS, 2000). In order to determine the building types in terms of plan scheme, and facade variations in terms of WWR and exterior wall assembly, six different residential regions in Istanbul, where buildings with central heating system are mostly located, were determined and field surveys were conducted to select example buildings. These regions are Bakirkoy and Florya on the European side of Istanbul, and Rahmanlar, Maltepe, Acibadem and Kos¸uyolu on the Anatolian side of Istanbul. A total of 60 centrally heated and
• Plan form: Square-like plan with four apartments (SQ4) and square-like plan with two apartments (SQ2) were the types that were mostly used, as seen in Table 1 and the type ‘rectangular plan with two apartments’ follows them. Among these types, squarelike plans were selected for conducting further investigations, in order to make comparative sustainability analyses. • Number of storey: The SQ4 and SQ2 type buildings were usually low-rise (1–5 storey) and middle-rise (6–10 storey) buildings (see Table 1). In this study, investigation of low-rise buildings
2. Methodology The study covers multi-storey detached apartment buildings located in Istanbul that have central heating system and which do not have any thermal insulation at the exterior walls. In this respect, field surveys, application project analyses, energy simulations and sustainability assessments, which are explained in the following sections, were conducted.
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Table 5 The properties of the selected building materials. Materials
Properties
Exterior rendering Interior rendering Brick Polystyrene Tile Reinforced concrete Screed Wood parquet Glassa Air gap PVC frame a b
•
•
•
•
Conductivity (W/m K)
Density (kg/m3 )
Specific heat (J/kg K)
Thermal absorptance
Solar absorptance
1.4 0.87 0.45 0.033 0.1 2.1 1.4 0.12 0.9 0.024 1.8b
2000 1800 1000 28 1000 2400 2000 540 – – –
840 840 880 1500 880 1000 840 1210 – 1006.1 –
0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 – – –
0.3 0.3 0.5 0.2 0.5 0.65 0.65 0.7 – – 0.2
Solar transmittance (normal incidence) of glass is 0.77. Value given for PVC frame is the conductance value (W/m2 K).
was aimed and 5-storey buildings were selected for sustainability assessment. These buildings were at the borderline with middlerise buildings as well. Therefore, they can also be used for initial predictions. Preferred WWRs: The WWR-orientation interrelation matrix for the facades of SQ4 and SQ2 type buildings is given in Table 2. The mostly preferred WWRs were 16–20% and 21–25% with similar number of buildings for each, and the next two WWRs following those were 11–15% and 26–30% respectively. Considering these figures, WWRs of 10%, 20% and 30% were selected for sustainability assessments. Area of the storey: Average storey areas of SQ4 and SQ2 type buildings were 405 and 209 square meters (m2 ) respectively. Considering the fact that there was no specific pattern in terms of preferred WWRs according to the orientation (see Table 2), investigation of true squares as the plan schemes were decided for evaluating the effects related with changing orientations. Hence, side dimensions of squares for SQ4 and SQ2 cases were determined as 20 m and 14.5 m respectively. Distances from surrounding buildings: The interrelations of selected buildings with their surrounding buildings were investigated during the analysis as well. The distances between buildings were in line with the Istanbul Municipality regulations, and considering the projections at the upper floors, the distances were selected as 4 m from the back and sides and 20 m from the front, assuming that there is a road of 12 m width between two buildings (see Table 3). Stairwell location and type: All of the stairwells of SQ4 type buildings were at the center and they were usually straight-flight type of stairs. The stairwells of SQ2 type buildings were mostly at the center, and they were usually dog-leg type of stairs. Therefore, stairwells of the investigated cases were determined in line with these facts and the selected dimensions for the stairwells for each building type are given in Table 3.
• Functional building elements: The facade assembly mostly used in the investigated application projects was brick with rendering on both sides. Hence, a brick wall of 19 cm width was selected for sustainability assessments. The assembly and materials of other functional building elements were generated as well as given in Table 4, considering the usually preferred materials. 2.2. Determination of total heating energy consumption and assessment of environmental impacts In Istanbul, residential buildings usually do not have individual or central cooling system. In the selected buildings, none of them have central cooling system and most of the apartments do not have individual cooling system as well. Therefore, in the research study, only heating energy consumption was considered for sustainability evaluations. Energy consumed for heating within a one-year period (heating from the beginning of October to the end of April, i.e. 7 months) and heat loss through exterior walls according to orientation in the selected cases for different WWRs were determined by an energy simulation program, EnergyPlus, which has been developed to model heating, cooling, ventilating, lighting and other energy flows and consumptions in buildings (DOE, 2006). The computations were executed considering the information on the buildings, element assemblies and material properties given in Tables 3–5, and the annual monthly climatic data of Istanbul, which has a temperate-humid climate, given in Fig. 1. Most of the existing buildings in Istanbul, as aforementioned, do not have any thermal insulation at the exterior envelope and therefore calculations were executed on building models without thermal insulation. However, in order to see the effect of using additional thermal insulation, simulations were done on building models with thermal insulation at the exterior envelope as well. In the energy simulations, each storey was modeled as an individual thermal zone. Internal heat load effects with schedules
Table 6 The equivalency factors for the emissions according to the kind of environmental impact (EPA, 1998). Emissions
NOx CO CO2 CH4 SO2 Lead PM1 a PM2 b a b
Equivalency factors for environmental impacts GWP (kg CO2 equiv.)
AP (kg SO2 equiv.)
EP (kg PO4 equiv.)
POP (kg ethylene equiv.)
HP (kg 1,4-dichlorobenzene equiv.)
– – 1.0 25 – – – –
0.5 – – – 1.2 – – –
0.13 – – – – – – –
– 0.027 – 0.06 0.048 – – –
1.2 – – – 0.096 466.517 0.82 0.82
Condensable particulate matters. Filterable particulate matters.
180000 160000 140000 120000 100000 80000 60000 40000 20000 0
73
Thermally Not-insulated Buildings 180
SQ2-0
SQ4-0 SQ2-1 0 : Thermally insulated buildings 1: Thermally not-insulated buildings WWR
0.1
0.2
SQ4-1
Opaque surface inside face 2 conduction heat loss (W/m )
Opaque Surface Inside Face Conduction Loss (W)
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160 140 120 100 80 60 40
20 0 10%
0.3
20%
30%
10%
Orientation
700
20%
30%
SQ4 S
W
N
E
600
Thermally Insulated Buildings
500 400
300 200 100
0 SQ2-0
SQ4-0 SQ2-1 0 : Thermally insulated buildings 1: Thermally not-insulated buildings WWR
0.1
0.2
SQ4-1
0.3
Fig. 3. Total opaque surface inside face conduction heat loss (a) through the whole exterior wall area and (b) per unit exterior wall area.
Opaque surface inside face 2 conduction heat loss (W/m )
Opaque Surface Inside Face Conduction Loss (W/m2)
SQ2
50 45 40 35 30 25 20 15 10 5 0 10%
20%
Orientation
(occupancy, lights and equipments), internal mass effects (stairwell walls) and infiltration/natural ventilation effects were considered as well. Three people were assumed to be living in each apartment, for the determination of occupancy loads. The activity levels of these people were specified as 131.8 W/person, and the clothing type was assumed to be 1clo in the heating season. Internal air velocity was assumed as 0.137 m/s while the infiltration rate was specified as 0.01 m3 /s and the natural ventilation rate was 0.02 m3 /s. The heating system was admitted to provide 23 ◦ C internal air temperature between 7.00 and 24.00 h while 18 ◦ C between 24.00 and 7.00 h. In all of the selected buildings, natural gas is used in the heating system. Emissions resulted from natural gas combustion were provided from Environmental Protection Agency AP-42 report (EPA, 1998). Emissions of natural gas combustion considered in this study are nitrogen oxides (NOx ), carbonmonoxide (CO), carbondioxide (CO2 ), methane (CH4 ), sulphurdioxide (SO2 ), lead and particulate matters (PM). The environmental impacts resulting from these emissions are global warming, acidification, eutrophication, photochemical oxidation and human toxicity. Each emission can contribute to different impacts. NOx emissions, for instance, have an effect on human health, acidification, and global warming while SO2 emissions cause acidification, photochemical oxidation and human toxicity. Contributions to each environmental impact are determined by equivalency factors which indicate how much a substance contributes to a problem compared to a reference substance (UNEP, 1996). In the study, global warming potential (GWP – measured relative to the effect of 1 kg CO2 ), acidification potential (AP – measured relative to the effect of 1 kg SO2 ), eutrophication potential (EP – measured relative to the effect of 1 kg PO4 ), photochemical oxidation potential (POP – measured relative to the effect of 1 kg ethylene) and human toxicity potential (HP, measured relative to the effect of 1.4 kg dichlorobenzene) caused by the emissions
30%
10%
SQ2
20%
30%
SQ4 S
W
N
E
Fig. 4. Opaque surface inside face conduction heat loss per 1 m2 of exterior wall area according to orientations for different WWRs.
of heating energy consumption of seven months within a oneyear use period for different WWRs were determined by using the equivalency factors provided from CML-IA database of the Leiden University-Institute of Environmental Sciences (CML, 2008). Table 6 shows the emissions according to the kind of environmental impact and their equivalency factors. 3. Results and discussion Results of both energy simulations and environmental impact calculations according to different WWR’s are presented and discussed for the determined cases in the following sections. 3.1. Energy simulation results Total heating energy consumption and window heat gain/loss results of SQ2 and SQ4 type buildings with and without thermal insulation, according to different WWRs, determined by the energy simulation program are given in Fig. 2. In the thermally not-insulated SQ2 and SQ4 type buildings, the increase in the WWR slightly decreases the total heating energy consumption. However, in the thermally insulated SQ2 and SQ4 type buildings, the increase in the WWR increases the total heating energy consumption. Heat gain and loss through the windows, and opaque surface inside face conduction loss are the determinants of heating energy consumption. Heat gain amounts through the windows are similar both in the thermally insulated and not insulated buildings, as given in Fig. 2. However, heat loss amounts are higher in the thermally insulated buildings, since diffuse irradiation of internal surfaces, which
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Fig. 5. Total heating energy consumption per 1 m2 of heated floor area of SQ2 and SQ4 type buildings for different WWRs. Fig. 6. Global warming potentials of SQ2 and SQ4 type buildings for different WWRs.
is taken into account in the heat gain and loss calculations by the software, is greater due to higher internal surface temperatures of exterior walls. In addition, the amount of increase in the heat loss through the windows by the increase of WWR is slightly greater in the thermally insulated buildings. Moreover, as given in Fig. 3a, the amount of decrease in the opaque surface conduction heat loss by the increase of WWR is greater in the thermally not insulated buildings. Therefore, due to combined effect of those differences, in the thermally insulated buildings, increase of the WWR increases the heating energy consumption, but in the thermally not insulated buildings, the heating energy consumption slightly decreases as the WWR increases. In addition, using thermal insulation lowers total heating energy consumption in considerable amounts in both SQ2 and SQ4 type of buildings. The reduction is about 63%, 57% and 51% for both type of buildings with WWRs of 10%, 20% and 30% respectively. Opaque surface conduction heat loss through the whole exterior wall area and per unit wall area (both excluding windows), and losses according to orientations per unit exterior wall area for different WWRs are given in Figs. 3 and 4 respectively. Heat loss through the whole exterior wall area decreases both in thermally insulated and not insulated buildings, as the WWR increases. This is the same for thermally insulated buildings in the case of heat loss per unit wall area. However, in the thermally not insulated buildings, heat loss per unit exterior wall area increases as the WWR increases, since the rate of decrease of heat loss is smaller than the rate of decrease of exterior wall area. When heat losses according to orientations are analyzed, as given in Fig. 4, both for thermally insulated and not insulated buildings, most of the conduction heat
losses occur on the facade surfaces oriented to north. The conduction heat losses on west, east and south orientations respectively follow it. However, in the thermally insulated buildings, the amount of change according to orientations is smaller than that of the thermally not insulated buildings. In addition, using thermal insulation, for both types of buildings with all WWR’s, results in about 70% decrease in the opaque surface conduction heat losses of the facades in all orientations. Fig. 5 presents the total heating energy consumption results per 1 m2 heated floor area according to different WWRs for both thermally insulated and not-insulated buildings. In SQ4 type building, where heated floor area is bigger, the energy consumption per m2 is lower when compared to SQ2 type having less heated floor area. This is due to the fact that, in SQ4 type, exterior wall area (including window area) per 1 m2 of heated floor area is smaller than that of SQ2 type (i.e. ∼0.48 m2 and ∼0.66 m2 respectively). In addition, as aforementioned, the increase in the WWR decreases the total heating energy consumption in the thermally not-insulated buildings, although it increases the total heating energy consumption in the thermally insulated buildings. 10 points increase in the WWR affects the energy consumption %1 in the thermally not insulated types, although it affects 14% in the thermally insulated buildings. 3.2. Environmental impact results The environmental impacts of a one-year period heating energy consumption for different WWRs are given in Figs. 6 and 7 for both thermally not-insulated and insulated buildings. Among the emissions occurring due to natural gas combustion, CO2 emissions
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such as WWR, building dimension, orientation, and conditions like using additional external thermal insulation. In accordance with the results, concerning mid-rise square-like planned buildings that have 210 and 400 m2 of floor areas at a single storey, the following remarks can be concluded:
Environmental Impacts (kg)
25 20 15
10 5
SQ4
SQ2
10%-1 20%-1 30%-1
10%-0 20%-0 30%-0
SQ2
10%-1 20%-1 30%-1
10%-0 20%-0 30%-0
0
SQ4
0: Thermally not-insulated building 1: Thermally insulated building Human toxicity
Acidification
3 2 2 1 1
SQ4
SQ2
10%-1 20%-1 30%-1
10%-1 20%-1 30%-1
SQ2
10%-0 20%-0 30%-0
0 10%-0 20%-0 30%-0
Environmental Impacts (kg)
75
SQ4
0: Thermally not-insulated building 1: Thermally insulated building Eutrophication
Photochemical oxidation
Fig. 7. Environmental impacts of SQ2 and SQ4 type buildings for different WWRs.
constitute most of the emissions to air, which causes global warming. The increase in WWR decreases GWP for the buildings without insulation because of the reduction in the total heating energy consumption while it causes an increase in GWP in the cases with thermal insulation (see Fig. 6). The highest decrease in GWP, as a result of using thermal insulation, is achieved in the case of the WWR of 10%. HP caused by NOx , SO2 , lead and particulate matters is the biggest environmental impact after GWP. AP due to NOx and SO2 emissions, EP due to NOx emissions and photochemical oxidation due to CO, CH4 and SO2 emissions follow them respectively, but these impacts are in negligible amounts when compared with global warming potential. The increase in WWR, as in the case of GWP, decreases these impacts in the thermally not-insulated buildings whereas it causes an increase in these impacts in the thermally insulated buildings (see Fig. 7). HP, for instance, decreases about 10, 9, and 81.4 kg dichlorobenzene equiv. , in thermally insulated SQ2 type building, for the WWRs of 10%, 20%, and 30%, respectively. 4. Concluding remarks This study that aims to investigate the effect of facade variations on post-construction period environmental sustainability of the residential buildings in Istanbul considers building parameters
• Increase in WWR slightly decreases total heating energy consumption and consecutively environmental impacts in the thermally not-insulated buildings, while it increases total heating energy consumption and the resulting environmental impacts in the thermally insulated buildings. • In the thermally not-insulated buildings, the effect of the increase in WWR on total heating energy consumption is in negligible amounts, but it should be considered in thermally insulated buildings. • As heated floor area increases, total heating energy consumption per 1 m2 decreases because exterior wall area per 1 m2 of heated floor area reduces for both thermally not-insulated and insulated buildings. • Using thermal insulation, in both types of buildings with all WWR’s and orientations, is considerably effective for reducing both heating energy consumption and environmental impacts. • GWP constitutes most of the environmental impacts resulting from building’s heating energy consumption. HP, AP, EP and POP follow it respectively, but these are in negligible amounts when compared to GWP. Increase in WWR decreases these impacts in the thermally not-insulated buildings whereas it causes an increase in these impacts in the thermally insulated buildings. These results, in the context of the project, will be utilized to generate standard representations of residential buildings in accordance with the existing buildings’ parameters and built environment, and to evaluate the contribution of these parameters (e.g. WWR, building dimension, orientation, and conditions like using additional external thermal insulation) on the sustainability of buildings. Acknowledgment The presented study was a part of the research project numbered 108K418 and supported by The Scientific and Technical Research Council of Turkey (TUBITAK). References Balaras, C. A., Gaglia, A. G., Georgopoulou, E., Mirasgedis, S., Sarafidis, Y., & Lalas, D. P. (2007). European residential buildings and empirical assessment of the Hellenic building stock, energy consumption, emissions and potential energy savings. Building and Environment, 42(3), 1298–1314. Cetiner, I., & Edis, E. (2009). Assessing the effect of building elements on postconstruction period environmental sustainability of residential buildings for renovation decisions. In 3rd CIB international conference on smart and sustainable built environments Delft, the Netherlands. CML. (2008). CML-IA version 3.4. The Netherlands: Leiden University, Institute of Environmental Sciences. DOE. (2006). EnergyPlus manual: Documentation V.1.4 – Input–output references. USA: US Dept. of Energy. EPA. (1998). AP 42 compilation of air pollutant emission factors. Natural gas combustion NC: U.S. Environmental Protection Agency. Erlandsson, M., Levin, P., & Myhre, L. (1997). Energy and environmental consequences of an additional wall insulation of a dwelling. Building and Environment, 32(2), 129–136. Jones, P. J., Lannin, S., & Williams, J. (2001). Modelling building energy use at urban scale. In Seventh international IBPSA conference Rio de Janeiro, Brazil. Ozkan, D. B., & Onan, C. (2011). Optimization of insulation thickness for different glazing areas in buildings for various climatic regions in Turkey. Applied Energy, 88(4), 1331–1342. Radhi, H. (2009). Can envelope codes reduce electricity and CO2 emissions in different types of buildings in the hot climate of Bahrain? Energy, 34(2), 205–215. Radhi, H. (2010). On the optimal selection of wall cladding system to reduce direct and indirect CO2 emissions. Energy, 35(3), 1412–1424.
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