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An environmental and economic sustainability assessment method for the retrofitting of residential buildings
Energy and Buildings 74 (2014) 132–140
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An environmental and economic sustainability assessment method for the retrofitting of residential buildings Ikbal Cetiner ∗ , Ecem Edis Istanbul Technical University, Faculty of Architecture, Taskisla, Taksim, Istanbul, 34437, Turkey
a r t i c l e
i n f o
Article history: Received 17 February 2013 Received in revised form 4 January 2014 Accepted 9 January 2014 Keywords: Environmental–economic sustainability assessment Residential building Retrofit
a b s t r a c t Due to the effects of a building’s whole life cycle processes on the environment and economy, there is an increasing interest in sustainability assessment of new and existing buildings. In Turkey, there is a large building stock constructed before legislative measures on energy efficiency were implemented. This article defines an environmental and economic sustainability assessment method to evaluate the effectiveness of existing residential building retrofits for reducing their space heating energy consumptions and the resulting emissions. The proposed method is based on the life cycle assessment method, and evaluates the environmental and economic sustainability performance of building envelope retrofits; i.e., adding thermal insulation and replacing windows. The intent of this method is to support the decision making process of building owners, users or architects in selecting the most beneficial retrofit alternatives in Turkey. In its current state, the database based on this methodology covers detached buildings located in Istanbul, with a natural gas-fired central heating system. Crown Copyright © 2014 Published by Elsevier B.V. All rights reserved.
1. Introduction The construction industry in general and buildings in particular are key drivers of natural resource consumption and emissions to the environment, apart from their effects on the economy and society. Considering these effects that occur throughout a buildings’ whole life cycle, including but not limited to production of construction materials, demolition of building and waste disposal, various assessment methods and tools are being developed to account for the different aspects of sustainability. In Turkey, the issue of sustainability has only recently started to become a concern, and has generally focused on the efficient use of energy. The Turkish standard on thermal insulation of newly constructed buildings, TS 825 [1] became mandatory in 2000. The Energy Efficiency Act (No. 5627) and the associated Regulation on Energy Performance of Buildings (No. 27075) were issued in 2007 and 2008, respectively. They cover both existing buildings and new construction, and are intended primarily for labelling, although performance criteria are defined in the regulation as well. The use phase space conditioning energy consumption and the associated emissions are two of the major aspects of buildings on achieving environmental and economic sustainability. There is a large existing building stock in Turkey constructed before the adoption of the aforementioned legislations, and thus have no thermal
∗ Corresponding author. Tel.: +90 212 2931300; fax: +90 212 2514895. E-mail addresses: [email protected], [email protected] (I. Cetiner), [email protected] (E. Edis).
insulation. In municipal areas of Turkey, buildings that primarily consist of dwelling units constitute the largest portion (almost 75%) of all buildings [2], and accounted for approximately 32% of total energy consumption between the years 1999 and 2008 [3]. Therefore, a research project was undertaken to develop an assessment method for evaluating the efficiency of retrofits applied to existing residential buildings in terms of environmental and economic sustainability, mainly for reduction in energy consumption and the resulting reductions in emissions [4], considering general strategies/policies of building sustainability assessment schemes on new constructions and existing buildings. In new constructions, there is an opportunity to consider sustainability with a wider perspective. In addition to the impacts directly related to the building, issues at larger scales such as land use or public transportation alternatives are also evaluated. In existing buildings, on the other hand, the focus is mainly on the reduction of consumptions and emissions directly related to the operation of buildings. As space conditioning energy constitutes one of the largest consumptions of a building during its operation period, the scope of method was limited with space conditioning. Additionally, a database was built based on this methodology. In this context, Istanbul was determined as the pilot city since most of the buildings constructed in the municipal areas of Turkey are in this city (approximately 11%), and Izmir and Ankara follow it with the figures of 7% and 5%, respectively. Additionally, approximately 89% of the buildings in Istanbul primarily consist of dwelling units [2]. In order to determine building types in terms of issues such as plan scheme and window to wall ratio, detached residential buildings in Istanbul were randomly selected while the data on selected buildings were gathered through field
0378-7788/$ – see front matter. Crown Copyright © 2014 Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.enbuild.2014.01.020
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surveys. For some selected buildings, space heating energy consumptions were then calculated by an energy simulation program, and compared with actual consumption to determine a correction factor. Finally, energy consumption and sustainability levels of buildings types were calculated to construct the database. This database includes data for detached residential buildings in Istanbul with a natural gas-fired central heating system. In this paper, this assessment method is explained, its use is exemplified and its benefits and limitations are discussed. 2. Approaches used in the assessment of environmental and economic sustainability of building retrofits Various building sustainability assessment methods and tools are being developed as sustainability issues become a worldwide concern. In general, characteristics of each method and the tools differ considerably one from another. Happio and Viitaniemi [5] analysed seventeen widely-known building environmental assessment (BEA) tools by considering different aspects such as their users or life cycle phases covered. Within these tools, only five of them were listed for building retrofit assessment, whereas three of them were classified as ‘whole building assessment frameworks’ and the remaining as ‘whole building design or decision-support tools’. Ding [6] made a critical analysis of twenty BEA methods used in different countries, and proposed a conceptual sustainability index model. He also commented on the lack of BEA methods for early design stages, the omission of financial aspects in some BEA methods, and the lack of a consensus on scoring and weighting. Ng, Chen and Wong [7] analysed carbon emission determination approaches of six widely known BEA tools, and explained a study they performed on an office building. They concluded that rather than whole life cycle stages, only operation stage carbon emissions were mainly evaluated by these tools, and it was usually made in a qualitative manner. They also mentioned that since baseline, benchmarking and auditing methods differed in terms of selected tools, carbon reduction level of a building varied depending on the tool used in the assessment. In the sustainability literature, there are various studies that analyse or compare widely-known BEA methods and tools, in addition to the aforementioned ones. However, sustainability studies not only focus on method and tool generation for ‘whole building’ assessment, but also there are studies focusing on different subsystems of a building or on more specific issues of sustainability such as energy use reduction. Dall’O, Galante and Pasetti [8], for instance, studied the energy saving potential of retrofitting residential building stock in five municipalities of Milan (Italy). They selected retrofit alternatives only for the building envelope, which were replacement of windows, additional fac¸ade insulation, additional roof insulation and new sealing to reduce ventilation losses. In the calculation of potential energy saving of each retrofit alternative, a retrofitting factor ‘i’ that was assumed to be determined by local authorities was used. They also calculated economic payback time of each retrofit alternative for different tax deduction scenarios. In their study, material production energy was not included in the energy calculations, and energy and economic savings were considered separately. Cellura et al. [9] also studied environmental benefits of building retrofits in the context of Italy, and proposed an assessment model. The retrofit actions they studied were wall insulation, window replacement, installation of solar thermal collectors for providing hot water and installation of condensing boilers, which were determined by considering the government-defined actions with a tax deduction. In the study, they assumed that consumers might spend additional income obtained by energy saving for other
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consumer goods. Therefore, they included the environmental effects of consumer behaviour into their assessment model. Juan, Gao and Wang [10] developed a computer based decisionsupport system for the sustainable renovation of office buildings, and determined six main sustainability criteria based on the analysis of widely-known assessment schemes. They also determined building characteristics affecting these criteria, and designed a questionnaire for the condition assessment of a building which used pre-determined assessment scores and predefined renovation alternatives. By the hybrid use of two algorithms; genetic and A* search algorithms, the optimal renovation scenario with lower cost and higher quality was determined for the building under consideration. For validating the model, they made some energy calculations as well, to understand the reduction provided by the suggested renovations. However, energy calculations were normally not included in their decision-support system. Asadi et al. [11] proposed a multi-objective optimization model for building retrofits in terms of environmental and economic performances. The retrofit strategies they studied were external wall insulation, roof insulation, window replacement and installation of solar collectors, and they assumed the use of different materials/technologies for each retrofitting strategy. Energy savings obtained by retrofitting were assumed to be calculated according to a simple model adapted from the Portuguese code. In the optimization process, they utilized the Tchebycheff approach and in the calculations, they allowed the use of mutually varying weights for energy and cost reduction. They reported that optimum retrofit strategies changed with the change in assigned weights. Wang et al. [12] reviewed multi-criteria/objective decision making (MCDM) methods used in sustainable energy field, namely in the selection of energy supply systems. MCDM is also an issue related to the evaluation of retrofit alternatives. They classified MCDM methods into three categories: elementary methods, unique synthesizing criteria and outranking. ELECTRE and PROMETHEE were some examples given for outranking category. Analytical hierarchy process and fuzzy weighted sum were some examples of unique synthesizing criteria, and weighted sum and weighted product methods were the examples of elementary methods. It was noted that the weighted sum method is the most commonly used approach in sustainable energy systems. Poveda and Lipsett [13] reviewed credit weighting approaches of some sustainability assessment and rating systems. They noted that in LEED, BREEAM, GBTool, and Green Star, scores obtained in different categories are weighted and summed up to achieve the overall score. In determining the weights of categories, use of the analytical hierarchy process and considering inputs from stakeholders and the scientific community are some of the methods used. Murray, Rocher and O’Sullivan [14] studied the retrofitting of an educational building by both numerical simulation and field measurement. They compared the effectiveness of static and dynamic simulations in determining energy consumption. They showed that both dynamic and static simulations deviated from the measured consumptions (approximately 9–15%), and simulation results were found to be generally higher than the actual consumption. Güc¸yeter and Günaydin [15] analysed an existing office building by numerical simulation and indoor condition monitoring in order to develop an optimized envelope retrofitting strategy. The space heating/cooling energy saving efficiency of each strategy was evaluated by comparing with the base case without any retrofitting. They reported considering the simulation calibration model studies that heating period simulation results were higher than the actual consumption, and it was the opposite for the cooling period. Investment payback time of each retrofitting strategy was also calculated by using the net present value approach considering the energy savings. In selection of optimized strategies, they considered ‘larger
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decrease in energy consumption’, ‘shorter payback time’ and ‘better indoor environment’ as criteria. There is also a Europe-based effort to structure the variety of energy-related features of existing buildings, which is called TABULA (Typology Approach for Building Stock Energy Assessment) Project [16]. It is supported by Intelligent Energy Europe, and focuses mainly on residential buildings. Energy performance of a building is correlated with its features, called parameters, and thus, it was assumed that if these features were known for a given building, it would be possible to estimate its energy performance quickly. The parameters determined were ‘building’s region or climatic zone’, ‘construction year class’, and ‘building size’. Building size was represented by four sub-classes: single-family, terraced, multi-family houses and apartment blocks. In addition, typical building envelope assemblies and heat supply system types were also determined for each class. Heating energy, non-renewable primary energy, total primary energy, CO2 emissions, and heating costs were calculated for each type considering its existing state and two different refurbishment scenarios. Apart from the aforementioned studies, there are numerous others on renovating buildings considering different aspects, and Ma, Cooper, Daly and Ledo [17] provided a thorough review of these and the methods used.
3. An environmental and economic sustainability assessment method for retrofitting building elements and its generation The following method is generated for evaluating the environmental and economic impacts of different retrofit alternatives that will be performed on a particular residential building in order to determine efficient alternatives. Retrofits include only applications to existing building elements for reducing the space conditioning energy consumption, and exclude the structural and service systems. The proposed method, in brief, determines the environmental, economic and overall performance of predetermined retrofit alternatives, considering the characteristics and remaining life of a particular building. It allows the user to define the relative importance of environmental and economic performance for determining the overall performance. In its current state, the database developed based on this methodology covers detached buildings located in Istanbul with a natural gas-fired central heating system. However, it can be used as a base for evaluating buildings in Istanbul with a natural gas-fired individual heating system in each apartment. The environmental and economical impacts of space cooling during the summer are not included because air conditioning is not a common practice in residential buildings in Istanbul. In the following subsections, the components and assessment model of the proposed method, and methods used in generating the database are explained. The order of the subsections is designed in relation to the order of processes required to evaluate a building by using the proposed method, and the details of each process are given in the associated subsections.
3.1. Building types and their determination The use of the proposed method is based on selecting the most comparable building type predefined in the database by considering the characteristics of a particular building that will be evaluated. In a building’s life cycle, space conditioning energy consumption is one of the major constituents causing environmental and economic impacts. Characteristics of a building affecting energy consumption and thus affecting its environmental and economic
Table 1 The characteristics affecting the total space conditioning consumptions of a building during its remaining life. Scale
Building’s environment
Building
Building element
Characteristics
Exterior climate Locations and dimensions of surrounding buildings Surface characteristics of surrounding items
Orientation Total number of stories Plan scheme and its dimensions Age and remaining life
Window to wall ratio (WWR) Assemblies and materials of building envelope
Note: During the generation of building types, for the characteristics given in italics, the mostly preferred option determined during the field surveys was used.
sustainability were determined, and classified into three groups as given in Table 1. In order to define building types considering the characteristics given in Table 1, sixty detached residential buildings with natural gas-fired central heating systems in six different neighbourhoods of Istanbul were randomly selected and analysed. In practical application of the central limit theorem, it is generally accepted that sample size equal or greater than thirty is sufficient to have a normal distribution, although there are also some opponents to this minimum value [18]. Finding thirty buildings that had specified characteristics was not possible in each neighbourhood. Therefore, considering the maximum number of buildings present in some neighbourhoods, random selection of 10 buildings from each neighbourhood was preferred. The data on these buildings were gathered through field surveys at building sites and project analyses on documents present in the archives of associated municipalities. Considering the commonly preferred options for each characteristic given in Table 1, building types were generated. For some of the characteristics, which are given with italics in Table 1, only the mostly preferred option was used for keeping the calculation workload at a reasonable level. The sequence of steps in selecting the most comparable building type is identified in Fig. 1, and options available for all characteristics are in grey boxes. In the figure, boxes with dashed lines represent the options that can be added into the database with further study. Additional steps will take place for their inclusion, after the development of the current database. When a characteristic of a particular building is not exactly the same as the predefined building types’, either the most comparable option or two comparable options will be selected. This process is detailed in Section 4. 3.2. Predefined retrofit alternatives and their generation In the proposed method, predefined retrofit alternatives are used in selecting the efficient retrofit alternatives that will be applied to a particular building. Heat gain and loss through the envelope of a building occurring in association with the materials used in the element assemblies are the main determinants of space conditioning energy consumptions. In Istanbul, in most of the residential buildings constructed before 2000, the year the Turkish Standard ‘TS 825-Thermal insulation in buildings’ was enforced as a mandatory standard, the external envelopes were thermally uninsulated, and single layer glass panes were usually used for the windows as observed during the field surveys. Therefore, insulating the building envelope, which includes external walls and projected floors, roof floors and floors above unheated basements, and replacing the window systems were selected as the main strategy in retrofitting the residential buildings. Since residential buildings in Turkey generally have projected floors above the ground floor, it is a common practice to insulate these floors together with external
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Fig. 1. Processes and options available in selecting the most comparable building type considering the characteristics of a particular building selected to be evaluated.
walls. Therefore, retrofits of these two elements were combined as one retrofitting alternative. Widely preferred thermal insulation materials and window systems were determined by market search for defining the retrofit alternatives. Retrofit alternatives generated within this context, considering the values defined in the associated Turkish Standard TS 825 [1] and gathered through market search, are given in Table 2. Following the selection of the most comparable building type for a particular building, environmental and economic performances of each retrofit alternative are
shown in the assessment tool (i.e. the Ms Excel sheet containing the database). 3.3. Assessment model of the method In determining the efficient retrofit alternatives, as aforementioned, the overall performance that is calculated by considering environmental and economic performances of the retrofits is used for the evaluation.
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Table 2 Predefined retrofit alternatives used in the method. Retrofit alternative
Options available for retrofit–materials
Replacing window system Insulating external wall and projected floor Insulating roof floor Insulating floor above unheated basement Insulating all elements
Wooden frame+IGU XPS (t: 5 cm) GW (t: 6 cm) XPS (t: 4 cm) XPSa
PVC frame+IGU EPS (t: 5 cm) – EPS (t: 4 cm) EPSa
– RW (t: 5 cm) – RW (t: 4 cm) RWa
a In the retrofit alternative ‘insulating all elements’, glass wool is used at roof and PVC frame with insulating glass unit (IGU) is used at windows. The thicknesses (t) of the insulation materials used at other building elements are the same as the ones given in preceding rows.
3.3.1. Determination of the environmental sustainability performance The environmental performance is determined by comparing ‘total environmental impact of a building type without any retrofit’ with ‘total environmental impact of the same building when any of the retrofits are applied’ by using Eq. (1) NRi,j = (NIi − NIj ) ×
100 NIi
(1)
where NR is the environmental performance, NI is the environmental impact (eco-points), and the indices i and j are the building type and the retrofit alternative planned to be used respectively. The units and scales of environmental and economic impacts are different from each other. In order to compare and combine these impact results, the gain or loss ratio of each of them is found, and these ratio values are regarded as performance points gained on a ±(0–100) scale. Finding the simple difference between the impacts of a building type with and without retrofit is not preferred because of the differences in units and scales. In the results, a negative value indicates that there is a loss in the environmental performance rather than a gain. Determination of environmental impacts is based upon the life cycle assessment (LCA) method and the following items are considered while determining the environmental impacts: (i) Total space heating energy required during the remaining life of a building type (with or without any retrofit) and the resulting emissions and wastes; (ii) Maintenance of the external envelope required during the remaining life of a building and the resulting consumptions, emissions and wastes due to material production, transportation and construction processes; (iii) Retrofit process and the consumptions, emissions and wastes resulting from the material production, transportation and construction processes. The total life of a building is accepted to be 50 years, taking the ‘normal’ life span defined by EOTA for building products as a reference [19]. Space heating energy consumptions of buildings were calculated by a building energy simulation program, EnergyPlus 4.0, and the calculated results were then multiplied with a correction factor in order to achieve more realistic consumption results. For this purpose, actual energy consumptions of some selected buildings were gathered from the natural gas supply company [20], and the average energy consumption of the last five years was compared with the energy simulation results of these buildings. The correction factor of 1.45 was then determined considering the comparison. In the energy consumption calculations, interior air temperature was set to a certain temperature. However, in Turkey, use of thermostatic radiator valves regulating the interior air temperature was not common. Therefore, the great distinction among the actual and calculated consumptions, which caused a correction factor of 1.45, was found meaningful. In the energy simulations made for determining the correction factor and energy consumptions of predefined building
types, each apartment was modelled as an individual thermal zone. Internal heat load effects with schedules (occupancy, lights and equipments), internal mass effects (stairwell walls) and infiltration/natural ventilation effects were considered as well. Considering the average household size of 3.85 in Istanbul [21], four people were assumed to be living in each apartment in order to determine occupancy loads. The activity levels of these people were specified as 131.8 W/person, and the clothing type was assumed to be 1 clo 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 set to provide a 23 ◦ C internal air temperature between 7.00 and 24.00 h while 18 ◦ C between 24.00 and 7.00 h. LCA considers the entire life cycle of a product, from raw material extraction and acquisition, through energy and material production and manufacturing, to use and end of life treatment and final disposal. In an LCA study, there are four stages, which are goal and scope definition, inventory analysis (LCI), impact assessment (LCIA) and interpretation [22]. The LCIA phase of the LCA approach includes selection of impact categories, category indicators and characterization models, assignment of LCI results to the selected impact categories (classification) and calculation of category indicator results (characterization) Following these, optionally the magnitude of the category indicator results relative to reference information may be calculated (normalization), and indicator results may be converted using numerical factors based on value-choices (weighting). Normalization and weighting processes should be performed for achieving a single score [23]. However, specific normalization and weighting factors for Turkey are not present, and thus the Impact 2002+ model, which is an impact assessment model including the aforementioned factors [24], was used to determine the total environmental impacts as a single score. The single score is a dimensionless figure, and it is called as the eco-indicator point (eco-point). Environmental impacts associated with space heating, maintenance and retrofit processes were calculated by using an LCA based environmental assessment program, SimaPro 7.1 [25]. The Ecoinvent v2.0 database of the program, which is one of the most extensive LCI database, was used in the inventory analysis associated with the aforementioned processes [26]. 3.3.2. Determination of the economic sustainability performance Similar to the determination of environmental performance, economic performance is determined by comparing ‘total economic impact of a building type without any retrofit’ with ‘total economic impact of the same building when any of the retrofits is applied’ by using Eq. (2) CRi,j = (CIi − CIj ) ×
100 CIi
(2)
where CR is the economic performance, CI is the economic impact (TRY), and the indices i and j are the building type and retrofit alternative planned to be used respectively. A negative value of CRi,j indicates that there is a loss in economic performance rather than a gain when the retrofit alternative is applied.
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Determination of economic impacts is based upon the life cycle cost analysis method, and the following items are considered during the calculations: (i) Cost of space heating energy consumption during the remaining life of a building type (with or without any retrofits); (ii) Cost of maintenance processes covering material, transportation and construction costs that are required during the remaining life of a building type; (iii) Cost of retrofits covering material, transportation and construction costs. The amount of space heating energy consumption used for calculating the associated costs were based upon the results obtained from EnergyPlus simulations as explained in Section 2.3.3. The unit costs required for the calculations were obtained from IGDAS [20], TEDAS [27], ISKI [28] and Petrol Ofisi [29] for natural gas, electricity, water and gasoline costs respectively, and from constructor firms for maintenance and retrofits. The net present value approach was used for determining the present values of the costs that would occur in the remaining life of a building. The associated discount rate was defined using the constant-dollar analysis approach suggested by the U.S. Department of Energy [30]. The discount rate of 6.71% was determined by finding the difference between the consumer inflation rates of 2010 [31] and the preceding five years’ average rate of treasury bonds from the Under-Secretariat of the Treasury, Republic of Turkey [32]. 3.3.3. Determination of the overall sustainability performance The overall performance of any retrofit is determined by using Eq. (3)
SPi,j =
NRi,j × mn + CRi,j × mC 100
(3)
where SP is the sustainability performance (−), NR is the environmental performance (−), CR is the economic performance (−), m is the importance ratio (%). The indices i and j are the building type and the retrofit alternative planned to be used respectively, and n and c indicate the environmental and economic performances respectively. The sum of mc and mn is 100. The method used to find the overall performance bases on weighted-sum method used in multi-objective decision making. It is preferred because a simple evaluation with only two criteria (i.e. environmental and economic performances) was intended. Following the determination of the most comparable building type and observation of the individual environmental and economic performances of retrofits, the importance ratio of environmental performance relative to economic performance is defined by the user for determining the overall performance of each retrofit alternative. However, whenever the most comparable building type considerably varies from the actual building for some of the characteristics, it is beneficial to select the second (or the third, if necessary) comparable building type, and evaluate its performance results for understanding the effect of change in the characteristic on the points achieved. The retrofit alternative that has the highest overall performance represents the most efficient alternative depending on the importance ratios defined by the user, and the one that has the lowest overall performance represents the least efficient alternative. Theoretically, the highest overall performance is 100, which is only possible when the environmental and economic impacts of a retrofitted building type are both zero. However, among all building types investigated, the highest overall point achieved is 50.78, when the importance ratios of environmental and economic performances were selected to be equal to each other.
Fig. 2. South and west facades, and schematic floor plan and section of the example building.
4. Example application A residential building located in Uskudar Municipality of Istanbul was chosen for presenting the application of the proposed method. It is one of a number of buildings in a housing development zone, and all the surrounding buildings have a similar number of stories. A photograph showing the south and west facades along with a schematic floor plan and section of the building are given in Fig. 2. The first step in evaluating the efficiency of retrofits on the environmental and economic sustainability of a building is to select the most comparable building type considering its characteristics. For this purpose, information on the characteristics of the aforementioned building was gathered (Table 3). To select the most comparable building type from the database, the filtering tool of the program was used. In Fig. 3, a screenshot showing the filtering process is given. The plan type, orientation, number of stories, external wall material and its thickness, roof form, window frame and glazing type, and stairwell location of the most comparable building type selected for evaluating the efficiency of the retrofits are exactly the same as the actual building under evaluation. Only building age, area of one storey, WWR and distance to the surrounding buildings are different. The area of one storey is smaller, and the WWR is bigger than those of the actual building. It is 230 m2 and 20% at the selected building type for the floor area and WWR, respectively, while it is 309.58 m2 and 16.29%, respectively, at the actual building. The age of the selected building type is one year less than the actual building (21 years old). The actual building is at a distance of 12 m from the surrounding buildings in front, and 7 m in rear. However, these distances are 20 m and 4 m, respectively, for the selected building type. Following the selection of the most comparable building type, the environmental and economic performance results, which are given in Table 4, were observed in the database separately for each predefined retrofit alternative. Calculated environmental and economic impact values, which are not present in the database, are also added to Table 4. These results clearly indicate that the sustainability performance decreases as the environmental and economic impacts increase. According to the environmental performance results, retrofitting of all elements has the highest performance (approximately 49–51 points), mainly due to the reduced space heating energy consumption. When all elements are retrofitted by using XPS for instance, the total consumption during its remaining life reduces from 6,186 MWh to 2,865 MWh. Thermally insulating the external wall and projected floor, and thermally insulating the roof floor yield 33–35 points and 11.16 points, respectively. Thermally insulating the floor above the unheated basement has the lowest performance with only a gain of 2 points, which is considerably minor when compared to that of other retrofit alternatives. For the retrofit alternatives that allow the use of different thermal
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Table 3 Characteristics of the building used in the example application. Building characteristics
Existing state
City/municipality Distance to the surrounding buildings (m) Plan type Orientation of the facades with long sides Building age Number of stories (excluding basement) Exterior wall material and its thickness (cm) Thermal insulation condition of the exterior wall, roof and ground floor Roof form WWR–average of different orientations (%) Window frame material, glazing and glass type
Istanbul/Uskudar Front and back: ∼12 rear: ∼7 Rectangular 14.50 × 21.35 = 309.58 m2 E–W 21 5 Brick–13.5 Uninsulated Hipped roof 16.29 Most of them are PVC framed double glazed with float glass, and few of them are timber framed single glazed with float glass. In the centre, unheated and uninsulated
Stairwell location and its thermal properties
Fig. 3. A screenshot showing the filtering process for WWR.
insulation materials, the highest gains are achieved when XPS is used, followed by EPS and RW, respectively. According to the economic performance results, apart from insulating the floor above the unheated basement and insulating
the all elements with RW, all other retrofit alternatives have an economic performance ranging between 8 and 18 points, which is considerably lower than the environmental performance. Thermally insulating the floor above the unheated basement with RW
Table 4 Environmental and economic sustainability performances of predefined retrofit alternatives. Retrofit alternative
Retrofit material(s)
NI (eco-points)
CI (TRY)
NR (points)
CR (points)
Insulating exterior wall and projected floor
XPS EPS RW GW XPS EPS RW XPS EPS RW
239.07 243.86 246.41 328.57 360.63 362.17 362.54 179.97 185.64 188.52
170320.24 171934.41 192332.43 19017.56 209466.30 209601.22 213687.78 188061.34 189608.37 219229.73
35.36 34.06 33.37 11.16 2.49 2.07 1.97 51.34 49.81 49.03
18.42 17.65 7.88 8.99 −0.33 −0.39 −2.35 9.93 9.19 −5.00
Insulating roof floor Insulating floor above unheated basement
Insulating all elements
While determining the performance points, PVC double glazing already present at the building is accepted to complete its life span and then be replaced.
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Table 5 Overall sustainability performances when different importance ratios are used. Retrofit alternative
Retrofit material(s)
Overall sustainability performances for different environmental/economic importance ratios (%)
XPS EPS RW GW XPS EPS RW XPS EPS RW
Insulating exterior wall and projected floor
Insulating roof floor Insulating floor above unheated basement
Insulating all elements
results in a small economic loss up to 2 points, and thermally insulating the all building with RW causes a bigger loss of 5 points. The second step in evaluating the efficiency of predefined retrofit alternatives is by determination of the importance ratio of environmental sustainability performance relative to economic sustainability performance. In the database, in default, the importance ratios of environmental and economic performances are defined equally as 50%. As mentioned before, it is possible for the user to select different importance ratios. Overall performances of each retrofit alternative when different importance ratios are used for environmental and economic performances are given in Table 5. When importance ratios of environmental and economic sustainability performances are selected to be equal to each other, all retrofit alternatives increase the overall sustainability of the building to some extent, except for thermally insulating the floor above the unheated basement with RW. In general, insulating all elements provide the highest gain, followed by insulating external wall and projected floor, and insulating roof floor, respectively. Thermally insulating the floor above the unheated basement with XPS or EPS has a minor effect on increasing the overall sustainability of the building. As given in Table 4, thermally insulating all elements with RW causes a loss of 5 points in the economic performance while there is a considerable gain of 49.03 points in the environmental performance. Therefore, a positive value can be achieved for overall sustainability performance, which indicates a gain. It is the same for insulating the floor above the unheated basement with XPS and EPS. The effect of changing importance ratios can be observed in the case of insulating the floor above the unheated basement with RW, where the loss in economic performance is higher than the gain in environmental performance. When the importance ratio of economic performance is decreased to 30%, a positive value indicating a gain can be achieved for overall performance (Table 5). Situations observed at insulating all elements and the floor above unheated basement with RW show that, apart from evaluating the overall performance, it is important to evaluate
30/70
50/50
70/30
23.50 22.57 15.53 9.64 0.52 0.35 −1.05 22.35 21.37 11.21
26.89 25.86 20.63 10.07 1.08 0.84 −0.19 30.63 29.50 22.01
30.28 29.14 25.73 10.51 1.65 1.33 0.68 38.91 37.62 32.82
environmental and economic performances separately if a gain is requested for each performance. In addition, depending on the users’ priorities (i.e. environmental vs. economic gain) a gain or loss in the overall performance can be observed for the same retrofit alternative. The last step is the selection of an efficient retrofit alternative and depends on the objective/priorities of the user: • If the importance ratios of environmental and economic sustainability performances are equal to each other, the most efficient retrofit alternative will be insulating all elements with XPS, and it is the same when the importance ratio of environmental performance is considerably higher; • If the importance ratio of economic sustainability performance is considerably higher than that of environmental performance, then the most efficient retrofit alternative will be insulating external wall and projected floors with XPS. In addition, as the method is based upon evaluating the overall sustainability performance of predefined building types, some characteristics of the most comparable building may vary considerably. Therefore, as aforementioned, it will be beneficial to analyse the results of a second comparable building type before deciding on the efficient retrofit alternative. In the example application chosen, the floor area of the case building is considerably different from those of other building types. Therefore the results of the second comparable building, which has a floor area of 420 m2 (Table 6), are considered during the last phase, and it is observed that the most efficient retrofit alternatives for different priorities do not change when the floor area increases. In addition, comparative evaluation of the sustainability performance results given in Tables 4–6 shows that the sustainability performance of each retrofit alternative decreases as the floor area increases. Therefore it is safe to assume that the actual sustainability performance of the case study building would be somewhere between these points.
Table 6 Sustainability performance results of the second comparable building type. Retrofit alternative
Retrofit material(s)
NR
CR
SPa (70/30)
SPa (50/50)
SPa (30/70)
Insulating exterior wall and projected floor
XPS EPS RW GW XPS EPS RW XPS EPS RW
29.59 28.50 27.83 10.26 1.56 1.50 1.29 46.27 44.71 43.79
12.74 12.16 2.02 7.91 −2.07 −2.01 −5.07 3.49 2.74 −12.33
24.54 23.60 20.09 9.56 0.47 0.44 −0.62 33.44 32.12 26.95
21.17 20.33 14.93 9.09 −0.25 −0.26 −1.89 24.88 23.73 15.73
17.80 17.06 9.76 8.62 −0.98 −0.96 −3.16 16.32 15.33 4.51
Insulating roof floor Insulating floor above unheated basement
Insulating all elements
a
Numbers within the parenthesis indicate the importance ratios of environmental and economic performances respectively.
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Other distinctions between the actual building and selected building type were WWR and distance to surrounding buildings. It is important to note that during a real application, the effects of varying WWR should also be studied. However, in the current state of the database, it is not possible to evaluate the effect of varying distances to surrounding buildings, which will be considered in future research. 5. Concluding remarks This paper introduces a method developed for evaluating the retrofits applied to the building elements of existing detached residential buildings with a natural gas-fired central heating system to increase their environmental and economic sustainability by reducing space conditioning energy consumption during their remaining life. It excludes structural and services systems’ retrofits. In environmental terms, it is based on the LCA approach. Therefore, it considers not only space conditioning energy consumption and resulting emissions, but also the resulting effects of material production and construction processes for retrofitting and maintenance processes. In economic terms, similarly, costs associated with construction and maintenance operations are considered, as well as the cost of space conditioning. The overall sustainability performance calculated by considering both environmental and economic performances together is used to determine the efficient retrofit alternatives depending on the priorities of the user. With these features, the method differs from other methods considering only use period energy consumptions or treating environmental and economic effects separately. The evaluation procedure of the method is based on selecting the most comparable building type for a particular building under consideration, and evaluating the effectiveness of predefined retrofit alternatives. This approach allows for estimating the gain or loss in the performance without making detailed energy and environmental impact simulations for a specific building, which would be costly especially in the case of privately owned apartment buildings. In its current state, the database of the method covers detached residential buildings located in Istanbul, with a natural gas-fired central heating system. Building types were defined by field and archive surveys. Energy consumption and environmental impacts of each building type were determined by computer simulations. In the calculations, space cooling energy was not included since currently it is not a common practice in Istanbul. This method is designed to be used by building owners, users or architects in order to decide which retrofit alternative(s) is more suitable for their buildings in the usage period, considering the overall sustainability results pertaining to the predefined alternatives. However, some definitions and explanations should be given as a manual for them to select the most comparable building type and to determine sustainability importance ratios. The database can be evolved by considering different cities, building characteristics, and life cycle inventory data that will be generated for Turkey. Acknowledgement This paper presents the method generated in the research project numbered 108K418 supported by The Scientific and Technical Research Council of Turkey (TUBITAK). References [1] TSE, TS 825-Thermal Insulation Requirements for Buildings, Turkish Standards Institute (TSE), Ankara, 2009 (in Turkish). [2] SIS, Building Census 2000, State Institute of Statistics (SIS)–Prime Ministry of Republic of Turkey, Ankara, 2000. [3] ETKB, The Report of Greenhouse Gas Reduction Work Group, Ministry of Energy and Natural Resources (ETKB), Ankara, 2006 (in Turkish).
[4] I. Cetiner, E. Edis, Assessing the use period environmental and economic sustainability at building element scale of the existing residential stock in Istanbul and developing the improvement alternatives, Research Report (108K418), The Scientific and Technological Research Council of Turkey (TUBITAK), Ankara, 2011 (in Turkish). [5] A. Happio, P. Viitaniemi, A critical review of building environmental assessment tools, Environmental Impact Assessment Review 28 (2008) 469–482. [6] G.K.C. Ding, Sustainable construction–the role of environmental assessment tools, Journal of Environmental Management 86 (2008) 451–464. [7] S.T. Ng, Y. Chen, J.M.W. Wong, Variability of building environmental assessment tools on evaluating carbon emissions, Environmental Impact Assessment Review 38 (2013) 131–141. [8] G. Dall’O., A. Galante, G. Pasetti, A methodology for evaluating the potential energy savings of retrofitting residential building stocks, Sustainable Cities and Society 4 (2012) 12–21. [9] M. Cellura, A. Di Gangi, S. Longo, A. Orioli, An Italian input–output model for the assessment of energy and environmental benefits arising from retrofit actions of buildings, Energy and Buildings 62 (2013) 97–106. [10] Y. Juan, P. Gao, J. Wang, A hybrid decision support system for sustainable office building renovation and energy performance improvement, Energy and Buildings 42 (2010) 290–297. [11] E. Asadi, M.G. da Silva, C. Antunes, L. Dias, Multi-objective optimization for building retrofit strategies: a model and an application, Energy and Buildings 44 (2012) 81–87. [12] J. Wang, Y. Jing, C. Zhang, J. Zhao, Review on multi-criteria decision analysis aid in sustainable energy decision-making, Renewable and Sustainable Energy Reviews 13 (2009) 2263–2278. [13] C. A. Poveda, M.G. Lipsett, A Review of Sustainability Assessment and Sustainability/Environmental Rating Systems and Credit Weighting Tools, Journal of Sustainable Development, Vol. 4, No. 6, 36-55. [14] S.N. Murray, B. Rocher, D.T.J. O’Sullivan, Static simulation: a sufficient modelling technique for retrofit analysis, Energy and Buildings 47 (2012) 113–121. [15] B. Güc¸yeter, H.M. Günaydın, Optimization of an envelope retrofit strategy for an existing office building, Energy and Buildings 55 (2012) 647–659. [16] TABULA Project team, Typology approach for building stock energy assessment, in: Main Results of the TABULA Project – The Final Report, Institut Wohnen und Umwelt GmbH, Darmstadt, 2012. [17] Z. Ma, P. Cooper, D. Daly, L. Ledo, Existing building retrofits: methodology and state-of-the-art, Energy and Buildings 55 (2012) 889–902. [18] H. Chang, K. Huang, C. Wu, Determination of sample size in using central limit theorem for Weibull distribution, Information and Management Sciences 17 (3) (2006) 31–46. [19] EOTA, Assumption of Working Life of Construction Products in Guidelines for European Technical Approvals and Harmonized Standards–Guidance Document 002, European Organisation for Technical Approvals, Brussels, 1999. [20] IGDAS, Natural Gas Supply Company of Istanbul, IGDAS, 2010, personal communication. [21] TSI, Turkey’s Statistical Yearbook 2008, Turkish Statistical Institute, Ankara, 2009. [22] ISO, ISO 14040 – Environmental Management–Life Cycle Assessment– Principles and Framework, first ed., International Organization for Standardization, Switzerland, 2006. [23] ISO, ISO 14040 – Environmental Management–Life Cycle Assessment– Requirements and Guidelines, First ed., International Organization for Standardization, Switzerland, 2006. [24] O. Jolliet, M. Margni, S. Humbert, J. Payet, G. Rebitzer, R. Rosenbaum, IMPACT 2002+: a new life cycle impact assessment methodology, International Journal of Life Cycle Assessment 8 (2003) 324–330. [25] PRé, About SimaPro, Product Ecology Consultants, 2013, http://www.presustainability.com/simapro-lca-software, last accessed: 15.07.13. [26] R. Frischknecht, JungbluthF N., AlthausF H.J., T. Heck, G. Doka, S. Hellweg, R. Hischier, T. Nemecek, G. Rebitzer, M. Spielmann, G. Wernet, Overview and methodology, Ecoinvent Report No.1, Swiss Centre for Life Cycle Inventories, Dübendorf, 2007. [27] TEDAS, Unit price of electricity in 2010, in: Turkish Electricity Distribution Joint-Stock Company, TEDAS¸, 2013, http://www.tedas.gov.tr/ tarifeler xls/2010 trf/2010yilitarife.xls, last accessed: 07.01.13. [28] ISKI, Unit price of tap water in 2010, in: Istanbul Water and Sewage Office, ISKI, 2013, http://www.iski.gov.tr/Web/UserFiles/File/suBirimFiyatlari/ 2010 Su Birim Fiyatlari.swf, last accessed: 07.01.13. [29] Petrol Ofisi, Unit Price of Gasoline in June 2010, Petrol Ofisi, 2013, http://gm.poas.com.tr/POASFIYAT/Fiyatlar.aspx?u=guest, last accessed: 07.01.13. [30] A.S. Rushing, B.C. 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Energy and Buildings journal homepage: www.elsevier.com/locate/enbuild
An environmental and economic sustainability assessment method for the retrofitting of residential buildings Ikbal Cetiner ∗ , Ecem Edis Istanbul Technical University, Faculty of Architecture, Taskisla, Taksim, Istanbul, 34437, Turkey
a r t i c l e
i n f o
Article history: Received 17 February 2013 Received in revised form 4 January 2014 Accepted 9 January 2014 Keywords: Environmental–economic sustainability assessment Residential building Retrofit
a b s t r a c t Due to the effects of a building’s whole life cycle processes on the environment and economy, there is an increasing interest in sustainability assessment of new and existing buildings. In Turkey, there is a large building stock constructed before legislative measures on energy efficiency were implemented. This article defines an environmental and economic sustainability assessment method to evaluate the effectiveness of existing residential building retrofits for reducing their space heating energy consumptions and the resulting emissions. The proposed method is based on the life cycle assessment method, and evaluates the environmental and economic sustainability performance of building envelope retrofits; i.e., adding thermal insulation and replacing windows. The intent of this method is to support the decision making process of building owners, users or architects in selecting the most beneficial retrofit alternatives in Turkey. In its current state, the database based on this methodology covers detached buildings located in Istanbul, with a natural gas-fired central heating system. Crown Copyright © 2014 Published by Elsevier B.V. All rights reserved.
1. Introduction The construction industry in general and buildings in particular are key drivers of natural resource consumption and emissions to the environment, apart from their effects on the economy and society. Considering these effects that occur throughout a buildings’ whole life cycle, including but not limited to production of construction materials, demolition of building and waste disposal, various assessment methods and tools are being developed to account for the different aspects of sustainability. In Turkey, the issue of sustainability has only recently started to become a concern, and has generally focused on the efficient use of energy. The Turkish standard on thermal insulation of newly constructed buildings, TS 825 [1] became mandatory in 2000. The Energy Efficiency Act (No. 5627) and the associated Regulation on Energy Performance of Buildings (No. 27075) were issued in 2007 and 2008, respectively. They cover both existing buildings and new construction, and are intended primarily for labelling, although performance criteria are defined in the regulation as well. The use phase space conditioning energy consumption and the associated emissions are two of the major aspects of buildings on achieving environmental and economic sustainability. There is a large existing building stock in Turkey constructed before the adoption of the aforementioned legislations, and thus have no thermal
∗ Corresponding author. Tel.: +90 212 2931300; fax: +90 212 2514895. E-mail addresses: [email protected], [email protected] (I. Cetiner), [email protected] (E. Edis).
insulation. In municipal areas of Turkey, buildings that primarily consist of dwelling units constitute the largest portion (almost 75%) of all buildings [2], and accounted for approximately 32% of total energy consumption between the years 1999 and 2008 [3]. Therefore, a research project was undertaken to develop an assessment method for evaluating the efficiency of retrofits applied to existing residential buildings in terms of environmental and economic sustainability, mainly for reduction in energy consumption and the resulting reductions in emissions [4], considering general strategies/policies of building sustainability assessment schemes on new constructions and existing buildings. In new constructions, there is an opportunity to consider sustainability with a wider perspective. In addition to the impacts directly related to the building, issues at larger scales such as land use or public transportation alternatives are also evaluated. In existing buildings, on the other hand, the focus is mainly on the reduction of consumptions and emissions directly related to the operation of buildings. As space conditioning energy constitutes one of the largest consumptions of a building during its operation period, the scope of method was limited with space conditioning. Additionally, a database was built based on this methodology. In this context, Istanbul was determined as the pilot city since most of the buildings constructed in the municipal areas of Turkey are in this city (approximately 11%), and Izmir and Ankara follow it with the figures of 7% and 5%, respectively. Additionally, approximately 89% of the buildings in Istanbul primarily consist of dwelling units [2]. In order to determine building types in terms of issues such as plan scheme and window to wall ratio, detached residential buildings in Istanbul were randomly selected while the data on selected buildings were gathered through field
0378-7788/$ – see front matter. Crown Copyright © 2014 Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.enbuild.2014.01.020
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surveys. For some selected buildings, space heating energy consumptions were then calculated by an energy simulation program, and compared with actual consumption to determine a correction factor. Finally, energy consumption and sustainability levels of buildings types were calculated to construct the database. This database includes data for detached residential buildings in Istanbul with a natural gas-fired central heating system. In this paper, this assessment method is explained, its use is exemplified and its benefits and limitations are discussed. 2. Approaches used in the assessment of environmental and economic sustainability of building retrofits Various building sustainability assessment methods and tools are being developed as sustainability issues become a worldwide concern. In general, characteristics of each method and the tools differ considerably one from another. Happio and Viitaniemi [5] analysed seventeen widely-known building environmental assessment (BEA) tools by considering different aspects such as their users or life cycle phases covered. Within these tools, only five of them were listed for building retrofit assessment, whereas three of them were classified as ‘whole building assessment frameworks’ and the remaining as ‘whole building design or decision-support tools’. Ding [6] made a critical analysis of twenty BEA methods used in different countries, and proposed a conceptual sustainability index model. He also commented on the lack of BEA methods for early design stages, the omission of financial aspects in some BEA methods, and the lack of a consensus on scoring and weighting. Ng, Chen and Wong [7] analysed carbon emission determination approaches of six widely known BEA tools, and explained a study they performed on an office building. They concluded that rather than whole life cycle stages, only operation stage carbon emissions were mainly evaluated by these tools, and it was usually made in a qualitative manner. They also mentioned that since baseline, benchmarking and auditing methods differed in terms of selected tools, carbon reduction level of a building varied depending on the tool used in the assessment. In the sustainability literature, there are various studies that analyse or compare widely-known BEA methods and tools, in addition to the aforementioned ones. However, sustainability studies not only focus on method and tool generation for ‘whole building’ assessment, but also there are studies focusing on different subsystems of a building or on more specific issues of sustainability such as energy use reduction. Dall’O, Galante and Pasetti [8], for instance, studied the energy saving potential of retrofitting residential building stock in five municipalities of Milan (Italy). They selected retrofit alternatives only for the building envelope, which were replacement of windows, additional fac¸ade insulation, additional roof insulation and new sealing to reduce ventilation losses. In the calculation of potential energy saving of each retrofit alternative, a retrofitting factor ‘i’ that was assumed to be determined by local authorities was used. They also calculated economic payback time of each retrofit alternative for different tax deduction scenarios. In their study, material production energy was not included in the energy calculations, and energy and economic savings were considered separately. Cellura et al. [9] also studied environmental benefits of building retrofits in the context of Italy, and proposed an assessment model. The retrofit actions they studied were wall insulation, window replacement, installation of solar thermal collectors for providing hot water and installation of condensing boilers, which were determined by considering the government-defined actions with a tax deduction. In the study, they assumed that consumers might spend additional income obtained by energy saving for other
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consumer goods. Therefore, they included the environmental effects of consumer behaviour into their assessment model. Juan, Gao and Wang [10] developed a computer based decisionsupport system for the sustainable renovation of office buildings, and determined six main sustainability criteria based on the analysis of widely-known assessment schemes. They also determined building characteristics affecting these criteria, and designed a questionnaire for the condition assessment of a building which used pre-determined assessment scores and predefined renovation alternatives. By the hybrid use of two algorithms; genetic and A* search algorithms, the optimal renovation scenario with lower cost and higher quality was determined for the building under consideration. For validating the model, they made some energy calculations as well, to understand the reduction provided by the suggested renovations. However, energy calculations were normally not included in their decision-support system. Asadi et al. [11] proposed a multi-objective optimization model for building retrofits in terms of environmental and economic performances. The retrofit strategies they studied were external wall insulation, roof insulation, window replacement and installation of solar collectors, and they assumed the use of different materials/technologies for each retrofitting strategy. Energy savings obtained by retrofitting were assumed to be calculated according to a simple model adapted from the Portuguese code. In the optimization process, they utilized the Tchebycheff approach and in the calculations, they allowed the use of mutually varying weights for energy and cost reduction. They reported that optimum retrofit strategies changed with the change in assigned weights. Wang et al. [12] reviewed multi-criteria/objective decision making (MCDM) methods used in sustainable energy field, namely in the selection of energy supply systems. MCDM is also an issue related to the evaluation of retrofit alternatives. They classified MCDM methods into three categories: elementary methods, unique synthesizing criteria and outranking. ELECTRE and PROMETHEE were some examples given for outranking category. Analytical hierarchy process and fuzzy weighted sum were some examples of unique synthesizing criteria, and weighted sum and weighted product methods were the examples of elementary methods. It was noted that the weighted sum method is the most commonly used approach in sustainable energy systems. Poveda and Lipsett [13] reviewed credit weighting approaches of some sustainability assessment and rating systems. They noted that in LEED, BREEAM, GBTool, and Green Star, scores obtained in different categories are weighted and summed up to achieve the overall score. In determining the weights of categories, use of the analytical hierarchy process and considering inputs from stakeholders and the scientific community are some of the methods used. Murray, Rocher and O’Sullivan [14] studied the retrofitting of an educational building by both numerical simulation and field measurement. They compared the effectiveness of static and dynamic simulations in determining energy consumption. They showed that both dynamic and static simulations deviated from the measured consumptions (approximately 9–15%), and simulation results were found to be generally higher than the actual consumption. Güc¸yeter and Günaydin [15] analysed an existing office building by numerical simulation and indoor condition monitoring in order to develop an optimized envelope retrofitting strategy. The space heating/cooling energy saving efficiency of each strategy was evaluated by comparing with the base case without any retrofitting. They reported considering the simulation calibration model studies that heating period simulation results were higher than the actual consumption, and it was the opposite for the cooling period. Investment payback time of each retrofitting strategy was also calculated by using the net present value approach considering the energy savings. In selection of optimized strategies, they considered ‘larger
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decrease in energy consumption’, ‘shorter payback time’ and ‘better indoor environment’ as criteria. There is also a Europe-based effort to structure the variety of energy-related features of existing buildings, which is called TABULA (Typology Approach for Building Stock Energy Assessment) Project [16]. It is supported by Intelligent Energy Europe, and focuses mainly on residential buildings. Energy performance of a building is correlated with its features, called parameters, and thus, it was assumed that if these features were known for a given building, it would be possible to estimate its energy performance quickly. The parameters determined were ‘building’s region or climatic zone’, ‘construction year class’, and ‘building size’. Building size was represented by four sub-classes: single-family, terraced, multi-family houses and apartment blocks. In addition, typical building envelope assemblies and heat supply system types were also determined for each class. Heating energy, non-renewable primary energy, total primary energy, CO2 emissions, and heating costs were calculated for each type considering its existing state and two different refurbishment scenarios. Apart from the aforementioned studies, there are numerous others on renovating buildings considering different aspects, and Ma, Cooper, Daly and Ledo [17] provided a thorough review of these and the methods used.
3. An environmental and economic sustainability assessment method for retrofitting building elements and its generation The following method is generated for evaluating the environmental and economic impacts of different retrofit alternatives that will be performed on a particular residential building in order to determine efficient alternatives. Retrofits include only applications to existing building elements for reducing the space conditioning energy consumption, and exclude the structural and service systems. The proposed method, in brief, determines the environmental, economic and overall performance of predetermined retrofit alternatives, considering the characteristics and remaining life of a particular building. It allows the user to define the relative importance of environmental and economic performance for determining the overall performance. In its current state, the database developed based on this methodology covers detached buildings located in Istanbul with a natural gas-fired central heating system. However, it can be used as a base for evaluating buildings in Istanbul with a natural gas-fired individual heating system in each apartment. The environmental and economical impacts of space cooling during the summer are not included because air conditioning is not a common practice in residential buildings in Istanbul. In the following subsections, the components and assessment model of the proposed method, and methods used in generating the database are explained. The order of the subsections is designed in relation to the order of processes required to evaluate a building by using the proposed method, and the details of each process are given in the associated subsections.
3.1. Building types and their determination The use of the proposed method is based on selecting the most comparable building type predefined in the database by considering the characteristics of a particular building that will be evaluated. In a building’s life cycle, space conditioning energy consumption is one of the major constituents causing environmental and economic impacts. Characteristics of a building affecting energy consumption and thus affecting its environmental and economic
Table 1 The characteristics affecting the total space conditioning consumptions of a building during its remaining life. Scale
Building’s environment
Building
Building element
Characteristics
Exterior climate Locations and dimensions of surrounding buildings Surface characteristics of surrounding items
Orientation Total number of stories Plan scheme and its dimensions Age and remaining life
Window to wall ratio (WWR) Assemblies and materials of building envelope
Note: During the generation of building types, for the characteristics given in italics, the mostly preferred option determined during the field surveys was used.
sustainability were determined, and classified into three groups as given in Table 1. In order to define building types considering the characteristics given in Table 1, sixty detached residential buildings with natural gas-fired central heating systems in six different neighbourhoods of Istanbul were randomly selected and analysed. In practical application of the central limit theorem, it is generally accepted that sample size equal or greater than thirty is sufficient to have a normal distribution, although there are also some opponents to this minimum value [18]. Finding thirty buildings that had specified characteristics was not possible in each neighbourhood. Therefore, considering the maximum number of buildings present in some neighbourhoods, random selection of 10 buildings from each neighbourhood was preferred. The data on these buildings were gathered through field surveys at building sites and project analyses on documents present in the archives of associated municipalities. Considering the commonly preferred options for each characteristic given in Table 1, building types were generated. For some of the characteristics, which are given with italics in Table 1, only the mostly preferred option was used for keeping the calculation workload at a reasonable level. The sequence of steps in selecting the most comparable building type is identified in Fig. 1, and options available for all characteristics are in grey boxes. In the figure, boxes with dashed lines represent the options that can be added into the database with further study. Additional steps will take place for their inclusion, after the development of the current database. When a characteristic of a particular building is not exactly the same as the predefined building types’, either the most comparable option or two comparable options will be selected. This process is detailed in Section 4. 3.2. Predefined retrofit alternatives and their generation In the proposed method, predefined retrofit alternatives are used in selecting the efficient retrofit alternatives that will be applied to a particular building. Heat gain and loss through the envelope of a building occurring in association with the materials used in the element assemblies are the main determinants of space conditioning energy consumptions. In Istanbul, in most of the residential buildings constructed before 2000, the year the Turkish Standard ‘TS 825-Thermal insulation in buildings’ was enforced as a mandatory standard, the external envelopes were thermally uninsulated, and single layer glass panes were usually used for the windows as observed during the field surveys. Therefore, insulating the building envelope, which includes external walls and projected floors, roof floors and floors above unheated basements, and replacing the window systems were selected as the main strategy in retrofitting the residential buildings. Since residential buildings in Turkey generally have projected floors above the ground floor, it is a common practice to insulate these floors together with external
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Fig. 1. Processes and options available in selecting the most comparable building type considering the characteristics of a particular building selected to be evaluated.
walls. Therefore, retrofits of these two elements were combined as one retrofitting alternative. Widely preferred thermal insulation materials and window systems were determined by market search for defining the retrofit alternatives. Retrofit alternatives generated within this context, considering the values defined in the associated Turkish Standard TS 825 [1] and gathered through market search, are given in Table 2. Following the selection of the most comparable building type for a particular building, environmental and economic performances of each retrofit alternative are
shown in the assessment tool (i.e. the Ms Excel sheet containing the database). 3.3. Assessment model of the method In determining the efficient retrofit alternatives, as aforementioned, the overall performance that is calculated by considering environmental and economic performances of the retrofits is used for the evaluation.
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Table 2 Predefined retrofit alternatives used in the method. Retrofit alternative
Options available for retrofit–materials
Replacing window system Insulating external wall and projected floor Insulating roof floor Insulating floor above unheated basement Insulating all elements
Wooden frame+IGU XPS (t: 5 cm) GW (t: 6 cm) XPS (t: 4 cm) XPSa
PVC frame+IGU EPS (t: 5 cm) – EPS (t: 4 cm) EPSa
– RW (t: 5 cm) – RW (t: 4 cm) RWa
a In the retrofit alternative ‘insulating all elements’, glass wool is used at roof and PVC frame with insulating glass unit (IGU) is used at windows. The thicknesses (t) of the insulation materials used at other building elements are the same as the ones given in preceding rows.
3.3.1. Determination of the environmental sustainability performance The environmental performance is determined by comparing ‘total environmental impact of a building type without any retrofit’ with ‘total environmental impact of the same building when any of the retrofits are applied’ by using Eq. (1) NRi,j = (NIi − NIj ) ×
100 NIi
(1)
where NR is the environmental performance, NI is the environmental impact (eco-points), and the indices i and j are the building type and the retrofit alternative planned to be used respectively. The units and scales of environmental and economic impacts are different from each other. In order to compare and combine these impact results, the gain or loss ratio of each of them is found, and these ratio values are regarded as performance points gained on a ±(0–100) scale. Finding the simple difference between the impacts of a building type with and without retrofit is not preferred because of the differences in units and scales. In the results, a negative value indicates that there is a loss in the environmental performance rather than a gain. Determination of environmental impacts is based upon the life cycle assessment (LCA) method and the following items are considered while determining the environmental impacts: (i) Total space heating energy required during the remaining life of a building type (with or without any retrofit) and the resulting emissions and wastes; (ii) Maintenance of the external envelope required during the remaining life of a building and the resulting consumptions, emissions and wastes due to material production, transportation and construction processes; (iii) Retrofit process and the consumptions, emissions and wastes resulting from the material production, transportation and construction processes. The total life of a building is accepted to be 50 years, taking the ‘normal’ life span defined by EOTA for building products as a reference [19]. Space heating energy consumptions of buildings were calculated by a building energy simulation program, EnergyPlus 4.0, and the calculated results were then multiplied with a correction factor in order to achieve more realistic consumption results. For this purpose, actual energy consumptions of some selected buildings were gathered from the natural gas supply company [20], and the average energy consumption of the last five years was compared with the energy simulation results of these buildings. The correction factor of 1.45 was then determined considering the comparison. In the energy consumption calculations, interior air temperature was set to a certain temperature. However, in Turkey, use of thermostatic radiator valves regulating the interior air temperature was not common. Therefore, the great distinction among the actual and calculated consumptions, which caused a correction factor of 1.45, was found meaningful. In the energy simulations made for determining the correction factor and energy consumptions of predefined building
types, each apartment was modelled as an individual thermal zone. Internal heat load effects with schedules (occupancy, lights and equipments), internal mass effects (stairwell walls) and infiltration/natural ventilation effects were considered as well. Considering the average household size of 3.85 in Istanbul [21], four people were assumed to be living in each apartment in order to determine occupancy loads. The activity levels of these people were specified as 131.8 W/person, and the clothing type was assumed to be 1 clo 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 set to provide a 23 ◦ C internal air temperature between 7.00 and 24.00 h while 18 ◦ C between 24.00 and 7.00 h. LCA considers the entire life cycle of a product, from raw material extraction and acquisition, through energy and material production and manufacturing, to use and end of life treatment and final disposal. In an LCA study, there are four stages, which are goal and scope definition, inventory analysis (LCI), impact assessment (LCIA) and interpretation [22]. The LCIA phase of the LCA approach includes selection of impact categories, category indicators and characterization models, assignment of LCI results to the selected impact categories (classification) and calculation of category indicator results (characterization) Following these, optionally the magnitude of the category indicator results relative to reference information may be calculated (normalization), and indicator results may be converted using numerical factors based on value-choices (weighting). Normalization and weighting processes should be performed for achieving a single score [23]. However, specific normalization and weighting factors for Turkey are not present, and thus the Impact 2002+ model, which is an impact assessment model including the aforementioned factors [24], was used to determine the total environmental impacts as a single score. The single score is a dimensionless figure, and it is called as the eco-indicator point (eco-point). Environmental impacts associated with space heating, maintenance and retrofit processes were calculated by using an LCA based environmental assessment program, SimaPro 7.1 [25]. The Ecoinvent v2.0 database of the program, which is one of the most extensive LCI database, was used in the inventory analysis associated with the aforementioned processes [26]. 3.3.2. Determination of the economic sustainability performance Similar to the determination of environmental performance, economic performance is determined by comparing ‘total economic impact of a building type without any retrofit’ with ‘total economic impact of the same building when any of the retrofits is applied’ by using Eq. (2) CRi,j = (CIi − CIj ) ×
100 CIi
(2)
where CR is the economic performance, CI is the economic impact (TRY), and the indices i and j are the building type and retrofit alternative planned to be used respectively. A negative value of CRi,j indicates that there is a loss in economic performance rather than a gain when the retrofit alternative is applied.
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Determination of economic impacts is based upon the life cycle cost analysis method, and the following items are considered during the calculations: (i) Cost of space heating energy consumption during the remaining life of a building type (with or without any retrofits); (ii) Cost of maintenance processes covering material, transportation and construction costs that are required during the remaining life of a building type; (iii) Cost of retrofits covering material, transportation and construction costs. The amount of space heating energy consumption used for calculating the associated costs were based upon the results obtained from EnergyPlus simulations as explained in Section 2.3.3. The unit costs required for the calculations were obtained from IGDAS [20], TEDAS [27], ISKI [28] and Petrol Ofisi [29] for natural gas, electricity, water and gasoline costs respectively, and from constructor firms for maintenance and retrofits. The net present value approach was used for determining the present values of the costs that would occur in the remaining life of a building. The associated discount rate was defined using the constant-dollar analysis approach suggested by the U.S. Department of Energy [30]. The discount rate of 6.71% was determined by finding the difference between the consumer inflation rates of 2010 [31] and the preceding five years’ average rate of treasury bonds from the Under-Secretariat of the Treasury, Republic of Turkey [32]. 3.3.3. Determination of the overall sustainability performance The overall performance of any retrofit is determined by using Eq. (3)
SPi,j =
NRi,j × mn + CRi,j × mC 100
(3)
where SP is the sustainability performance (−), NR is the environmental performance (−), CR is the economic performance (−), m is the importance ratio (%). The indices i and j are the building type and the retrofit alternative planned to be used respectively, and n and c indicate the environmental and economic performances respectively. The sum of mc and mn is 100. The method used to find the overall performance bases on weighted-sum method used in multi-objective decision making. It is preferred because a simple evaluation with only two criteria (i.e. environmental and economic performances) was intended. Following the determination of the most comparable building type and observation of the individual environmental and economic performances of retrofits, the importance ratio of environmental performance relative to economic performance is defined by the user for determining the overall performance of each retrofit alternative. However, whenever the most comparable building type considerably varies from the actual building for some of the characteristics, it is beneficial to select the second (or the third, if necessary) comparable building type, and evaluate its performance results for understanding the effect of change in the characteristic on the points achieved. The retrofit alternative that has the highest overall performance represents the most efficient alternative depending on the importance ratios defined by the user, and the one that has the lowest overall performance represents the least efficient alternative. Theoretically, the highest overall performance is 100, which is only possible when the environmental and economic impacts of a retrofitted building type are both zero. However, among all building types investigated, the highest overall point achieved is 50.78, when the importance ratios of environmental and economic performances were selected to be equal to each other.
Fig. 2. South and west facades, and schematic floor plan and section of the example building.
4. Example application A residential building located in Uskudar Municipality of Istanbul was chosen for presenting the application of the proposed method. It is one of a number of buildings in a housing development zone, and all the surrounding buildings have a similar number of stories. A photograph showing the south and west facades along with a schematic floor plan and section of the building are given in Fig. 2. The first step in evaluating the efficiency of retrofits on the environmental and economic sustainability of a building is to select the most comparable building type considering its characteristics. For this purpose, information on the characteristics of the aforementioned building was gathered (Table 3). To select the most comparable building type from the database, the filtering tool of the program was used. In Fig. 3, a screenshot showing the filtering process is given. The plan type, orientation, number of stories, external wall material and its thickness, roof form, window frame and glazing type, and stairwell location of the most comparable building type selected for evaluating the efficiency of the retrofits are exactly the same as the actual building under evaluation. Only building age, area of one storey, WWR and distance to the surrounding buildings are different. The area of one storey is smaller, and the WWR is bigger than those of the actual building. It is 230 m2 and 20% at the selected building type for the floor area and WWR, respectively, while it is 309.58 m2 and 16.29%, respectively, at the actual building. The age of the selected building type is one year less than the actual building (21 years old). The actual building is at a distance of 12 m from the surrounding buildings in front, and 7 m in rear. However, these distances are 20 m and 4 m, respectively, for the selected building type. Following the selection of the most comparable building type, the environmental and economic performance results, which are given in Table 4, were observed in the database separately for each predefined retrofit alternative. Calculated environmental and economic impact values, which are not present in the database, are also added to Table 4. These results clearly indicate that the sustainability performance decreases as the environmental and economic impacts increase. According to the environmental performance results, retrofitting of all elements has the highest performance (approximately 49–51 points), mainly due to the reduced space heating energy consumption. When all elements are retrofitted by using XPS for instance, the total consumption during its remaining life reduces from 6,186 MWh to 2,865 MWh. Thermally insulating the external wall and projected floor, and thermally insulating the roof floor yield 33–35 points and 11.16 points, respectively. Thermally insulating the floor above the unheated basement has the lowest performance with only a gain of 2 points, which is considerably minor when compared to that of other retrofit alternatives. For the retrofit alternatives that allow the use of different thermal
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Table 3 Characteristics of the building used in the example application. Building characteristics
Existing state
City/municipality Distance to the surrounding buildings (m) Plan type Orientation of the facades with long sides Building age Number of stories (excluding basement) Exterior wall material and its thickness (cm) Thermal insulation condition of the exterior wall, roof and ground floor Roof form WWR–average of different orientations (%) Window frame material, glazing and glass type
Istanbul/Uskudar Front and back: ∼12 rear: ∼7 Rectangular 14.50 × 21.35 = 309.58 m2 E–W 21 5 Brick–13.5 Uninsulated Hipped roof 16.29 Most of them are PVC framed double glazed with float glass, and few of them are timber framed single glazed with float glass. In the centre, unheated and uninsulated
Stairwell location and its thermal properties
Fig. 3. A screenshot showing the filtering process for WWR.
insulation materials, the highest gains are achieved when XPS is used, followed by EPS and RW, respectively. According to the economic performance results, apart from insulating the floor above the unheated basement and insulating
the all elements with RW, all other retrofit alternatives have an economic performance ranging between 8 and 18 points, which is considerably lower than the environmental performance. Thermally insulating the floor above the unheated basement with RW
Table 4 Environmental and economic sustainability performances of predefined retrofit alternatives. Retrofit alternative
Retrofit material(s)
NI (eco-points)
CI (TRY)
NR (points)
CR (points)
Insulating exterior wall and projected floor
XPS EPS RW GW XPS EPS RW XPS EPS RW
239.07 243.86 246.41 328.57 360.63 362.17 362.54 179.97 185.64 188.52
170320.24 171934.41 192332.43 19017.56 209466.30 209601.22 213687.78 188061.34 189608.37 219229.73
35.36 34.06 33.37 11.16 2.49 2.07 1.97 51.34 49.81 49.03
18.42 17.65 7.88 8.99 −0.33 −0.39 −2.35 9.93 9.19 −5.00
Insulating roof floor Insulating floor above unheated basement
Insulating all elements
While determining the performance points, PVC double glazing already present at the building is accepted to complete its life span and then be replaced.
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Table 5 Overall sustainability performances when different importance ratios are used. Retrofit alternative
Retrofit material(s)
Overall sustainability performances for different environmental/economic importance ratios (%)
XPS EPS RW GW XPS EPS RW XPS EPS RW
Insulating exterior wall and projected floor
Insulating roof floor Insulating floor above unheated basement
Insulating all elements
results in a small economic loss up to 2 points, and thermally insulating the all building with RW causes a bigger loss of 5 points. The second step in evaluating the efficiency of predefined retrofit alternatives is by determination of the importance ratio of environmental sustainability performance relative to economic sustainability performance. In the database, in default, the importance ratios of environmental and economic performances are defined equally as 50%. As mentioned before, it is possible for the user to select different importance ratios. Overall performances of each retrofit alternative when different importance ratios are used for environmental and economic performances are given in Table 5. When importance ratios of environmental and economic sustainability performances are selected to be equal to each other, all retrofit alternatives increase the overall sustainability of the building to some extent, except for thermally insulating the floor above the unheated basement with RW. In general, insulating all elements provide the highest gain, followed by insulating external wall and projected floor, and insulating roof floor, respectively. Thermally insulating the floor above the unheated basement with XPS or EPS has a minor effect on increasing the overall sustainability of the building. As given in Table 4, thermally insulating all elements with RW causes a loss of 5 points in the economic performance while there is a considerable gain of 49.03 points in the environmental performance. Therefore, a positive value can be achieved for overall sustainability performance, which indicates a gain. It is the same for insulating the floor above the unheated basement with XPS and EPS. The effect of changing importance ratios can be observed in the case of insulating the floor above the unheated basement with RW, where the loss in economic performance is higher than the gain in environmental performance. When the importance ratio of economic performance is decreased to 30%, a positive value indicating a gain can be achieved for overall performance (Table 5). Situations observed at insulating all elements and the floor above unheated basement with RW show that, apart from evaluating the overall performance, it is important to evaluate
30/70
50/50
70/30
23.50 22.57 15.53 9.64 0.52 0.35 −1.05 22.35 21.37 11.21
26.89 25.86 20.63 10.07 1.08 0.84 −0.19 30.63 29.50 22.01
30.28 29.14 25.73 10.51 1.65 1.33 0.68 38.91 37.62 32.82
environmental and economic performances separately if a gain is requested for each performance. In addition, depending on the users’ priorities (i.e. environmental vs. economic gain) a gain or loss in the overall performance can be observed for the same retrofit alternative. The last step is the selection of an efficient retrofit alternative and depends on the objective/priorities of the user: • If the importance ratios of environmental and economic sustainability performances are equal to each other, the most efficient retrofit alternative will be insulating all elements with XPS, and it is the same when the importance ratio of environmental performance is considerably higher; • If the importance ratio of economic sustainability performance is considerably higher than that of environmental performance, then the most efficient retrofit alternative will be insulating external wall and projected floors with XPS. In addition, as the method is based upon evaluating the overall sustainability performance of predefined building types, some characteristics of the most comparable building may vary considerably. Therefore, as aforementioned, it will be beneficial to analyse the results of a second comparable building type before deciding on the efficient retrofit alternative. In the example application chosen, the floor area of the case building is considerably different from those of other building types. Therefore the results of the second comparable building, which has a floor area of 420 m2 (Table 6), are considered during the last phase, and it is observed that the most efficient retrofit alternatives for different priorities do not change when the floor area increases. In addition, comparative evaluation of the sustainability performance results given in Tables 4–6 shows that the sustainability performance of each retrofit alternative decreases as the floor area increases. Therefore it is safe to assume that the actual sustainability performance of the case study building would be somewhere between these points.
Table 6 Sustainability performance results of the second comparable building type. Retrofit alternative
Retrofit material(s)
NR
CR
SPa (70/30)
SPa (50/50)
SPa (30/70)
Insulating exterior wall and projected floor
XPS EPS RW GW XPS EPS RW XPS EPS RW
29.59 28.50 27.83 10.26 1.56 1.50 1.29 46.27 44.71 43.79
12.74 12.16 2.02 7.91 −2.07 −2.01 −5.07 3.49 2.74 −12.33
24.54 23.60 20.09 9.56 0.47 0.44 −0.62 33.44 32.12 26.95
21.17 20.33 14.93 9.09 −0.25 −0.26 −1.89 24.88 23.73 15.73
17.80 17.06 9.76 8.62 −0.98 −0.96 −3.16 16.32 15.33 4.51
Insulating roof floor Insulating floor above unheated basement
Insulating all elements
a
Numbers within the parenthesis indicate the importance ratios of environmental and economic performances respectively.
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Other distinctions between the actual building and selected building type were WWR and distance to surrounding buildings. It is important to note that during a real application, the effects of varying WWR should also be studied. However, in the current state of the database, it is not possible to evaluate the effect of varying distances to surrounding buildings, which will be considered in future research. 5. Concluding remarks This paper introduces a method developed for evaluating the retrofits applied to the building elements of existing detached residential buildings with a natural gas-fired central heating system to increase their environmental and economic sustainability by reducing space conditioning energy consumption during their remaining life. It excludes structural and services systems’ retrofits. In environmental terms, it is based on the LCA approach. Therefore, it considers not only space conditioning energy consumption and resulting emissions, but also the resulting effects of material production and construction processes for retrofitting and maintenance processes. In economic terms, similarly, costs associated with construction and maintenance operations are considered, as well as the cost of space conditioning. The overall sustainability performance calculated by considering both environmental and economic performances together is used to determine the efficient retrofit alternatives depending on the priorities of the user. With these features, the method differs from other methods considering only use period energy consumptions or treating environmental and economic effects separately. The evaluation procedure of the method is based on selecting the most comparable building type for a particular building under consideration, and evaluating the effectiveness of predefined retrofit alternatives. This approach allows for estimating the gain or loss in the performance without making detailed energy and environmental impact simulations for a specific building, which would be costly especially in the case of privately owned apartment buildings. In its current state, the database of the method covers detached residential buildings located in Istanbul, with a natural gas-fired central heating system. Building types were defined by field and archive surveys. Energy consumption and environmental impacts of each building type were determined by computer simulations. In the calculations, space cooling energy was not included since currently it is not a common practice in Istanbul. This method is designed to be used by building owners, users or architects in order to decide which retrofit alternative(s) is more suitable for their buildings in the usage period, considering the overall sustainability results pertaining to the predefined alternatives. However, some definitions and explanations should be given as a manual for them to select the most comparable building type and to determine sustainability importance ratios. The database can be evolved by considering different cities, building characteristics, and life cycle inventory data that will be generated for Turkey. Acknowledgement This paper presents the method generated in the research project numbered 108K418 supported by The Scientific and Technical Research Council of Turkey (TUBITAK). References [1] TSE, TS 825-Thermal Insulation Requirements for Buildings, Turkish Standards Institute (TSE), Ankara, 2009 (in Turkish). [2] SIS, Building Census 2000, State Institute of Statistics (SIS)–Prime Ministry of Republic of Turkey, Ankara, 2000. [3] ETKB, The Report of Greenhouse Gas Reduction Work Group, Ministry of Energy and Natural Resources (ETKB), Ankara, 2006 (in Turkish).
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