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Energy and Buildings 74 (2014) 132–140

Contents lists available at ScienceDirect

Energy and Buildings

j ourna l ho me pa g e: www.elsev ier .com/ locate /enbui ld

n environmental and economic sustainability assessment methodor the retrofitting of residential buildings

kbal Cetiner ∗, Ecem Edisstanbul Technical University, Faculty of Architecture, Taskisla, Taksim, Istanbul, 34437, Turkey

r t i c l e i n f o

rticle history:eceived 17 February 2013eceived in revised form 4 January 2014ccepted 9 January 2014

eywords:

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 isan increasing interest in sustainability assessment of new and existing buildings. In Turkey, there is alarge building stock constructed before legislative measures on energy efficiency were implemented.This article defines an environmental and economic sustainability assessment method to evaluate theeffectiveness of existing residential building retrofits for reducing their space heating energy consump-

nvironmental–economic sustainabilityssessmentesidential buildingetrofit

tions and the resulting emissions. The proposed method is based on the life cycle assessment method, andevaluates 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 decisionmaking process of building owners, users or architects in selecting the most beneficial retrofit alternativesin Turkey. In its current state, the database based on this methodology covers detached buildings located

l gas-

in Istanbul, with a natura

. Introduction

The construction industry in general and buildings in particu-ar are key drivers of natural resource consumption and emissionso the environment, apart from their effects on the economy andociety. Considering these effects that occur throughout a build-ngs’ whole life cycle, including but not limited to production ofonstruction materials, demolition of building and waste disposal,arious assessment methods and tools are being developed toccount for the different aspects of sustainability.

In Turkey, the issue of sustainability has only recently startedo become a concern, and has generally focused on the efficientse of energy. The Turkish standard on thermal insulation of newlyonstructed buildings, TS 825 [1] became mandatory in 2000. Thenergy Efficiency Act (No. 5627) and the associated Regulation onnergy Performance of Buildings (No. 27075) were issued in 2007nd 2008, respectively. They cover both existing buildings and newonstruction, and are intended primarily for labelling, althougherformance criteria are defined in the regulation as well.

The use phase space conditioning energy consumption and thessociated emissions are two of the major aspects of buildings on

chieving environmental and economic sustainability. There is aarge existing building stock in Turkey constructed before the adop-ion of the aforementioned legislations, and thus have no thermal

∗ Corresponding author. Tel.: +90 212 2931300; fax: +90 212 2514895.E-mail addresses: cetinerikb@itu.edu.tr, ikbalcetiner@yahoo.com (I. Cetiner),

cem@itu.edu.tr (E. Edis).

378-7788/$ – see front matter. Crown Copyright © 2014 Published by Elsevier B.V. All rittp://dx.doi.org/10.1016/j.enbuild.2014.01.020

fired central heating system.Crown Copyright © 2014 Published by Elsevier B.V. All rights reserved.

insulation. In municipal areas of Turkey, buildings that primarilyconsist of dwelling units constitute the largest portion (almost 75%)of all buildings [2], and accounted for approximately 32% of totalenergy consumption between the years 1999 and 2008 [3]. There-fore, a research project was undertaken to develop an assessmentmethod for evaluating the efficiency of retrofits applied to exist-ing residential buildings in terms of environmental and economicsustainability, mainly for reduction in energy consumption and theresulting reductions in emissions [4], considering general strate-gies/policies of building sustainability assessment schemes on newconstructions and existing buildings. In new constructions, there isan opportunity to consider sustainability with a wider perspective.In addition to the impacts directly related to the building, issues atlarger scales such as land use or public transportation alternativesare also evaluated. In existing buildings, on the other hand, thefocus is mainly on the reduction of consumptions and emissionsdirectly related to the operation of buildings. As space condition-ing energy constitutes one of the largest consumptions of a buildingduring its operation period, the scope of method was limited withspace conditioning. Additionally, a database was built based onthis methodology. In this context, Istanbul was determined as thepilot city since most of the buildings constructed in the municipalareas of Turkey are in this city (approximately 11%), and Izmir andAnkara follow it with the figures of 7% and 5%, respectively. Addi-tionally, approximately 89% of the buildings in Istanbul primarily

consist of dwelling units [2]. In order to determine building typesin terms of issues such as plan scheme and window to wall ratio,detached residential buildings in Istanbul were randomly selectedwhile the data on selected buildings were gathered through field

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I. Cetiner, E. Edis / Energy a

urveys. For some selected buildings, space heating energy con-umptions were then calculated by an energy simulation program,nd compared with actual consumption to determine a correc-ion factor. Finally, energy consumption and sustainability levelsf buildings types were calculated to construct the database. Thisatabase includes data for detached residential buildings in Istan-ul with a natural gas-fired central heating system. In this paper,his assessment method is explained, its use is exemplified and itsenefits and limitations are discussed.

. Approaches used in the assessment of environmentalnd economic sustainability of building retrofits

Various building sustainability assessment methods and toolsre being developed as sustainability issues become a worldwideoncern. In general, characteristics of each method and the toolsiffer considerably one from another.

Happio and Viitaniemi [5] analysed seventeen widely-knownuilding environmental assessment (BEA) tools by considering dif-erent aspects such as their users or life cycle phases covered.

ithin these tools, only five of them were listed for building retrofitssessment, whereas three of them were classified as ‘whole build-ng assessment frameworks’ and the remaining as ‘whole buildingesign or decision-support tools’.

Ding [6] made a critical analysis of twenty BEA methods usedn different countries, and proposed a conceptual sustainabilityndex model. He also commented on the lack of BEA methods forarly design stages, the omission of financial aspects in some BEAethods, and the lack of a consensus on scoring and weighting.Ng, Chen and Wong [7] analysed carbon emission determination

pproaches of six widely known BEA tools, and explained a studyhey performed on an office building. They concluded that ratherhan whole life cycle stages, only operation stage carbon emissionsere mainly evaluated by these tools, and it was usually made

n a qualitative manner. They also mentioned that since baseline,enchmarking and auditing methods differed in terms of selectedools, carbon reduction level of a building varied depending on theool used in the assessment.

In the sustainability literature, there are various studies thatnalyse or compare widely-known BEA methods and tools, in addi-ion to the aforementioned ones. However, sustainability studiesot only focus on method and tool generation for ‘whole building’ssessment, but also there are studies focusing on different sub-ystems of a building or on more specific issues of sustainabilityuch as energy use reduction.

Dall’O, Galante and Pasetti [8], for instance, studied the energyaving potential of retrofitting residential building stock in fiveunicipalities of Milan (Italy). They selected retrofit alternatives

nly for the building envelope, which were replacement of win-ows, additional fac ade insulation, additional roof insulation andew sealing to reduce ventilation losses. In the calculation ofotential energy saving of each retrofit alternative, a retrofittingactor ‘i’ that was assumed to be determined by local authoritiesas used. They also calculated economic payback time of each

etrofit alternative for different tax deduction scenarios. In theirtudy, material production energy was not included in the energyalculations, and energy and economic savings were consideredeparately.

Cellura et al. [9] also studied environmental benefits of buildingetrofits in the context of Italy, and proposed an assessment model.he retrofit actions they studied were wall insulation, windoweplacement, installation of solar thermal collectors for providing

ot water and installation of condensing boilers, which wereetermined by considering the government-defined actions with

tax deduction. In the study, they assumed that consumers mightpend additional income obtained by energy saving for other

ildings 74 (2014) 132–140 133

consumer goods. Therefore, they included the environmentaleffects of consumer behaviour into their assessment model.

Juan, Gao and Wang [10] developed a computer based decision-support system for the sustainable renovation of office buildings,and determined six main sustainability criteria based on the analy-sis of widely-known assessment schemes. They also determinedbuilding characteristics affecting these criteria, and designed aquestionnaire for the condition assessment of a building whichused pre-determined assessment scores and predefined renova-tion alternatives. By the hybrid use of two algorithms; geneticand A* search algorithms, the optimal renovation scenario withlower cost and higher quality was determined for the buildingunder consideration. For validating the model, they made someenergy calculations as well, to understand the reduction providedby the suggested renovations. However, energy calculations werenormally not included in their decision-support system.

Asadi et al. [11] proposed a multi-objective optimization modelfor building retrofits in terms of environmental and economic per-formances. The retrofit strategies they studied were external wallinsulation, roof insulation, window replacement and installationof solar collectors, and they assumed the use of different mate-rials/technologies for each retrofitting strategy. Energy savingsobtained by retrofitting were assumed to be calculated accordingto a simple model adapted from the Portuguese code. In the opti-mization process, they utilized the Tchebycheff approach and inthe calculations, they allowed the use of mutually varying weightsfor energy and cost reduction. They reported that optimum retrofitstrategies changed with the change in assigned weights.

Wang et al. [12] reviewed multi-criteria/objective decision mak-ing (MCDM) methods used in sustainable energy field, namely inthe selection of energy supply systems. MCDM is also an issuerelated to the evaluation of retrofit alternatives. They classifiedMCDM methods into three categories: elementary methods, uniquesynthesizing criteria and outranking. ELECTRE and PROMETHEEwere some examples given for outranking category. Analyticalhierarchy process and fuzzy weighted sum were some examplesof unique synthesizing criteria, and weighted sum and weightedproduct methods were the examples of elementary methods. It wasnoted that the weighted sum method is the most commonly usedapproach in sustainable energy systems.

Poveda and Lipsett [13] reviewed credit weighting approachesof some sustainability assessment and rating systems. They notedthat in LEED, BREEAM, GBTool, and Green Star, scores obtained indifferent categories are weighted and summed up to achieve theoverall score. In determining the weights of categories, use of theanalytical hierarchy process and considering inputs from stake-holders and the scientific community are some of the methodsused.

Murray, Rocher and O’Sullivan [14] studied the retrofitting of aneducational building by both numerical simulation and field mea-surement. They compared the effectiveness of static and dynamicsimulations in determining energy consumption. They showed thatboth dynamic and static simulations deviated from the measuredconsumptions (approximately 9–15%), and simulation results werefound to be generally higher than the actual consumption.

Güc yeter and Günaydin [15] analysed an existing office build-ing by numerical simulation and indoor condition monitoring inorder to develop an optimized envelope retrofitting strategy. Thespace heating/cooling energy saving efficiency of each strategy wasevaluated by comparing with the base case without any retrofitting.They reported considering the simulation calibration model studiesthat heating period simulation results were higher than the actual

consumption, and it was the opposite for the cooling period. Invest-ment payback time of each retrofitting strategy was also calculatedby using the net present value approach considering the energysavings. In selection of optimized strategies, they considered ‘larger

1 nd Buildings 74 (2014) 132–140

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Table 1The characteristics affecting the total space conditioning consumptions of a buildingduring its remaining life.

Scale Building’senvironment

Building Buildingelement

Characteristics Exterior climateLocations anddimensions ofsurroundingbuildingsSurfacecharacteristics ofsurrounding items

OrientationTotal number ofstoriesPlan schemeand itsdimensionsAge andremaining life

Window towall ratio(WWR)Assemblies andmaterials ofbuildingenvelope

34 I. Cetiner, E. Edis / Energy a

ecrease in energy consumption’, ‘shorter payback time’ and ‘betterndoor environment’ as criteria.

There is also a Europe-based effort to structure the variety ofnergy-related features of existing buildings, which is called TAB-LA (Typology Approach for Building Stock Energy Assessment)roject [16]. It is supported by Intelligent Energy Europe, andocuses mainly on residential buildings. Energy performance of

building is correlated with its features, called parameters, andhus, it was assumed that if these features were known for a givenuilding, it would be possible to estimate its energy performanceuickly. The parameters determined were ‘building’s region or cli-atic zone’, ‘construction year class’, and ‘building size’. Building

ize was represented by four sub-classes: single-family, terraced,ulti-family houses and apartment blocks. In addition, typical

uilding envelope assemblies and heat supply system types werelso determined for each class. Heating energy, non-renewable pri-ary energy, total primary energy, CO2 emissions, and heating

osts were calculated for each type considering its existing statend two different refurbishment scenarios.

Apart from the aforementioned studies, there are numerous oth-rs on renovating buildings considering different aspects, and Ma,ooper, Daly and Ledo [17] provided a thorough review of thesend the methods used.

. An environmental and economic sustainabilityssessment method for retrofitting building elements andts generation

The following method is generated for evaluating the environ-ental and economic impacts of different retrofit alternatives thatill be performed on a particular residential building in order toetermine efficient alternatives. Retrofits include only applicationso existing building elements for reducing the space condition-ng energy consumption, and exclude the structural and serviceystems.

The proposed method, in brief, determines the environmen-al, economic and overall performance of predetermined retrofitlternatives, considering the characteristics and remaining life of aarticular building. It allows the user to define the relative impor-ance of environmental and economic performance for determininghe overall performance. In its current state, the database devel-ped based on this methodology covers detached buildings locatedn Istanbul with a natural gas-fired central heating system. How-ver, it can be used as a base for evaluating buildings in Istanbulith a natural gas-fired individual heating system in each apart-ent. The environmental and economical impacts of space cooling

uring the summer are not included because air conditioning is not common practice in residential buildings in Istanbul.

In the following subsections, the components and assessmentodel of the proposed method, and methods used in generating

he database are explained. The order of the subsections is designedn relation to the order of processes required to evaluate a buildingy using the proposed method, and the details of each process areiven in the associated subsections.

.1. Building types and their determination

The use of the proposed method is based on selecting the mostomparable building type predefined in the database by consider-ng the characteristics of a particular building that will be evaluated.

In a building’s life cycle, space conditioning energy consump-ion is one of the major constituents causing environmental andconomic impacts. Characteristics of a building affecting energyonsumption and thus affecting its environmental and economic

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 asgiven in Table 1.

In order to define building types considering the character-istics given in Table 1, sixty detached residential buildings withnatural gas-fired central heating systems in six different neigh-bourhoods of Istanbul were randomly selected and analysed. Inpractical application of the central limit theorem, it is generallyaccepted that sample size equal or greater than thirty is sufficientto have a normal distribution, although there are also some oppo-nents to this minimum value [18]. Finding thirty buildings thathad specified characteristics was not possible in each neighbour-hood. Therefore, considering the maximum number of buildingspresent in some neighbourhoods, random selection of 10 build-ings from each neighbourhood was preferred. The data on thesebuildings were gathered through field surveys at building sites andproject analyses on documents present in the archives of associ-ated municipalities. Considering the commonly preferred optionsfor each characteristic given in Table 1, building types were gener-ated. For some of the characteristics, which are given with italics inTable 1, only the mostly preferred option was used for keeping thecalculation workload at a reasonable level. The sequence of steps inselecting the most comparable building type is identified in Fig. 1,and options available for all characteristics are in grey boxes. In thefigure, boxes with dashed lines represent the options that can beadded into the database with further study. Additional steps willtake place for their inclusion, after the development of the cur-rent database. When a characteristic of a particular building is notexactly the same as the predefined building types’, either the mostcomparable option or two comparable options will be selected. Thisprocess is detailed in Section 4.

3.2. Predefined retrofit alternatives and their generation

In the proposed method, predefined retrofit alternatives areused in selecting the efficient retrofit alternatives that will beapplied to a particular building. Heat gain and loss through theenvelope of a building occurring in association with the materi-als used in the element assemblies are the main determinants ofspace conditioning energy consumptions. In Istanbul, in most of theresidential buildings constructed before 2000, the year the Turk-ish Standard ‘TS 825-Thermal insulation in buildings’ was enforcedas a mandatory standard, the external envelopes were thermallyuninsulated, and single layer glass panes were usually used for thewindows as observed during the field surveys. Therefore, insulatingthe building envelope, which includes external walls and projectedfloors, roof floors and floors above unheated basements, and replac-

ing the window systems were selected as the main strategy inretrofitting the residential buildings. Since residential buildings inTurkey generally have projected floors above the ground floor, it isa common practice to insulate these floors together with external

I. Cetiner, E. Edis / Energy and Buildings 74 (2014) 132–140 135

g type

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Fig. 1. Processes and options available in selecting the most comparable buildin

alls. Therefore, retrofits of these two elements were combineds one retrofitting alternative. Widely preferred thermal insula-ion materials and window systems were determined by marketearch for defining the retrofit alternatives. Retrofit alternativesenerated within this context, considering the values defined in

he associated Turkish Standard TS 825 [1] and gathered through

arket search, are given in Table 2. Following the selection of theost comparable building type for a particular building, environ-ental and economic performances of each retrofit alternative are

considering the characteristics of a particular building selected to be evaluated.

shown in the assessment tool (i.e. the Ms Excel sheet containingthe database).

3.3. Assessment model of the method

In determining the efficient retrofit alternatives, as aforemen-tioned, the overall performance that is calculated by consideringenvironmental and economic performances of the retrofits is usedfor the evaluation.

136 I. Cetiner, E. Edis / Energy and Buildings 74 (2014) 132–140

Table 2Predefined retrofit alternatives used in the method.

Retrofit alternative Options available for retrofit–materials

Replacing window system Wooden frame+IGU PVC frame+IGU –Insulating external wall and projected floor XPS (t: 5 cm) EPS (t: 5 cm) RW (t: 5 cm)Insulating roof floor GW (t: 6 cm) – –Insulating floor above unheated basement XPS (t: 4 cm) EPS (t: 4 cm) RW (t: 4 cm)Insulating all elements XPSa EPSa RWa

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.3.1. Determination of the environmental sustainabilityerformance

The environmental performance is determined by comparingtotal environmental impact of a building type without any retrofit’

ith ‘total environmental impact of the same building when any ofhe retrofits are applied’ by using Eq. (1)

Ri,j = (NIi − NIj) × 100NIi

(1)

here NR is the environmental performance, NI is the environmen-al impact (eco-points), and the indices i and j are the building typend the retrofit alternative planned to be used respectively. Thenits and scales of environmental and economic impacts are differ-nt from each other. In order to compare and combine these impactesults, the gain or loss ratio of each of them is found, and these ratioalues are regarded as performance points gained on a ±(0–100)cale. Finding the simple difference between the impacts of a build-ng type with and without retrofit is not preferred because of theifferences in units and scales. In the results, a negative value indi-ates that there is a loss in the environmental performance ratherhan a gain.

Determination of environmental impacts is based upon the lifeycle assessment (LCA) method and the following items are con-idered while determining the environmental impacts:

(i) Total space heating energy required during the remaining lifeof a building type (with or without any retrofit) and the result-ing emissions and wastes;

(ii) Maintenance of the external envelope required during theremaining life of a building and the resulting consumptions,emissions and wastes due to material production, transporta-tion and construction processes;

iii) Retrofit process and the consumptions, emissions and wastesresulting from the material production, transportation andconstruction processes.

The total life of a building is accepted to be 50 years, taking thenormal’ life span defined by EOTA for building products as a ref-rence [19]. Space heating energy consumptions of buildings werealculated by a building energy simulation program, EnergyPlus 4.0,nd the calculated results were then multiplied with a correctionactor in order to achieve more realistic consumption results. Forhis purpose, actual energy consumptions of some selected build-ngs were gathered from the natural gas supply company [20],nd the average energy consumption of the last five years wasompared with the energy simulation results of these buildings.he correction factor of 1.45 was then determined considering theomparison. In the energy consumption calculations, interior airemperature was set to a certain temperature. However, in Turkey,se of thermostatic radiator valves regulating the interior air tem-erature was not common. Therefore, the great distinction among

he actual and calculated consumptions, which caused a correctionactor of 1.45, was found meaningful.

In the energy simulations made for determining the cor-ection factor and energy consumptions of predefined building

rame with insulating glass unit (IGU) is used at windows. The thicknesses (t) of theeceding rows.

types, each apartment was modelled as an individual thermalzone. Internal heat load effects with schedules (occupancy, lightsand equipments), internal mass effects (stairwell walls) andinfiltration/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 todetermine occupancy loads. The activity levels of these people werespecified as 131.8 W/person, and the clothing type was assumed tobe 1 clo in the heating season. Internal air velocity was assumed as0.137 m/s while the infiltration rate was specified as 0.01 m3/s andthe natural ventilation rate was 0.02 m3/s. The heating system wasset to provide a 23 ◦C internal air temperature between 7.00 and24.00 h while 18 ◦C between 24.00 and 7.00 h.

LCA considers the entire life cycle of a product, from rawmaterial extraction and acquisition, through energy and materialproduction and manufacturing, to use and end of life treatmentand final disposal. In an LCA study, there are four stages, whichare goal and scope definition, inventory analysis (LCI), impactassessment (LCIA) and interpretation [22]. The LCIA phase of theLCA approach includes selection of impact categories, categoryindicators and characterization models, assignment of LCI resultsto the selected impact categories (classification) and calculationof category indicator results (characterization) Following these,optionally the magnitude of the category indicator results rela-tive to reference information may be calculated (normalization),and indicator results may be converted using numerical factorsbased on value-choices (weighting). Normalization and weightingprocesses should be performed for achieving a single score [23].However, specific normalization and weighting factors for Turkeyare not present, and thus the Impact 2002+ model, which is animpact assessment model including the aforementioned factors[24], was used to determine the total environmental impacts asa single score. The single score is a dimensionless figure, and it iscalled as the eco-indicator point (eco-point).

Environmental impacts associated with space heating, main-tenance and retrofit processes were calculated by using an LCAbased environmental assessment program, SimaPro 7.1 [25]. TheEcoinvent v2.0 database of the program, which is one of the mostextensive LCI database, was used in the inventory analysis associ-ated with the aforementioned processes [26].

3.3.2. Determination of the economic sustainability performanceSimilar to the determination of environmental performance,

economic performance is determined by comparing ‘total eco-nomic impact of a building type without any retrofit’ with ‘totaleconomic impact of the same building when any of the retrofits isapplied’ by using Eq. (2)

CRi,j = (CIi − CIj) × 100CIi

(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 alter-native planned to be used respectively. A negative value of CRi,jindicates that there is a loss in economic performance rather thana gain when the retrofit alternative is applied.

nd Buildings 74 (2014) 132–140 137

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I. Cetiner, E. Edis / Energy a

Determination of economic impacts is based upon the life cycleost analysis method, and the following items are considered dur-ng the calculations:

(i) Cost of space heating energy consumption during theremaining life of a building type (with or without any retrofits);

(ii) Cost of maintenance processes covering material, transporta-tion and construction costs that are required during theremaining life of a building type;

iii) Cost of retrofits covering material, transportation and con-struction costs.

The amount of space heating energy consumption used for cal-ulating the associated costs were based upon the results obtainedrom EnergyPlus simulations as explained in Section 2.3.3. The unitosts required for the calculations were obtained from IGDAS [20],EDAS [27], ISKI [28] and Petrol Ofisi [29] for natural gas, electricity,ater and gasoline costs respectively, and from constructor firms

or maintenance and retrofits. The net present value approach wassed for determining the present values of the costs that wouldccur in the remaining life of a building. The associated discountate was defined using the constant-dollar analysis approach sug-ested by the U.S. Department of Energy [30]. The discount rate of.71% was determined by finding the difference between the con-umer inflation rates of 2010 [31] and the preceding five years’verage rate of treasury bonds from the Under-Secretariat of thereasury, Republic of Turkey [32].

.3.3. Determination of the overall sustainability performanceThe overall performance of any retrofit is determined by using

q. (3)

Pi,j =((

NRi,j × mn

)+(

CRi,j × mC

)100

)(3)

here SP is the sustainability performance (−), NR is the environ-ental performance (−), CR is the economic performance (−), m is

he importance ratio (%). The indices i and j are the building typend the retrofit alternative planned to be used respectively, and

and c indicate the environmental and economic performancesespectively. The sum of mc and mn is 100. The method used to findhe overall performance bases on weighted-sum method used in

ulti-objective decision making. It is preferred because a simplevaluation with only two criteria (i.e. environmental and economicerformances) was intended.

Following the determination of the most comparable build-ng type and observation of the individual environmental andconomic performances of retrofits, the importance ratio of envi-onmental performance relative to economic performance isefined by the user for determining the overall performance ofach retrofit alternative. However, whenever the most compara-le building type considerably varies from the actual building forome of the characteristics, it is beneficial to select the second (orhe third, if necessary) comparable building type, and evaluate itserformance results for understanding the effect of change in theharacteristic on the points achieved. The retrofit alternative thatas the highest overall performance represents the most efficientlternative depending on the importance ratios defined by the user,nd the one that has the lowest overall performance represents theeast efficient alternative. Theoretically, the highest overall per-ormance is 100, which is only possible when the environmentalnd economic impacts of a retrofitted building type are both zero.

owever, among all building types investigated, the highest overalloint achieved is 50.78, when the importance ratios of environmen-al and economic performances were selected to be equal to eachther.

building.

4. Example application

A residential building located in Uskudar Municipality of Istan-bul was chosen for presenting the application of the proposedmethod. It is one of a number of buildings in a housing developmentzone, and all the surrounding buildings have a similar number ofstories. A photograph showing the south and west facades alongwith a schematic floor plan and section of the building are given inFig. 2.

The first step in evaluating the efficiency of retrofits on the envi-ronmental and economic sustainability of a building is to select themost comparable building type considering its characteristics. Forthis purpose, information on the characteristics of the aforemen-tioned 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 screenshotshowing the filtering process is given.

The plan type, orientation, number of stories, external wallmaterial and its thickness, roof form, window frame and glazingtype, and stairwell location of the most comparable building typeselected for evaluating the efficiency of the retrofits are exactly thesame as the actual building under evaluation. Only building age,area of one storey, WWR and distance to the surrounding build-ings are different. The area of one storey is smaller, and the WWRis bigger than those of the actual building. It is 230 m2 and 20% atthe selected building type for the floor area and WWR, respectively,while it is 309.58 m2 and 16.29%, respectively, at the actual build-ing. The age of the selected building type is one year less than theactual building (21 years old). The actual building is at a distanceof 12 m from the surrounding buildings in front, and 7 m in rear.However, these distances are 20 m and 4 m, respectively, for theselected building type.

Following the selection of the most comparable building type,the environmental and economic performance results, which aregiven in Table 4, were observed in the database separately for eachpredefined retrofit alternative. Calculated environmental and eco-nomic impact values, which are not present in the database, are alsoadded to Table 4. These results clearly indicate that the sustaina-bility performance decreases as the environmental and economicimpacts increase.

According to the environmental performance results,retrofitting of all elements has the highest performance (approx-imately 49–51 points), mainly due to the reduced space heatingenergy consumption. When all elements are retrofitted by usingXPS for instance, the total consumption during its remaining lifereduces from 6,186 MWh to 2,865 MWh. Thermally insulating theexternal wall and projected floor, and thermally insulating the rooffloor yield 33–35 points and 11.16 points, respectively. Thermallyinsulating the floor above the unheated basement has the lowest

performance with only a gain of 2 points, which is considerablyminor when compared to that of other retrofit alternatives. Forthe retrofit alternatives that allow the use of different thermal

138 I. Cetiner, E. Edis / Energy and Buildings 74 (2014) 132–140

Table 3Characteristics of the building used in the example application.

Building characteristics Existing state

City/municipality Istanbul/UskudarDistance to the surrounding buildings (m) Front and back: ∼12 rear: ∼7Plan type Rectangular 14.50 × 21.35 = 309.58 m2

Orientation of the facades with long sides E–WBuilding age 21Number of stories (excluding basement) 5Exterior wall material and its thickness (cm) Brick–13.5Thermal insulation condition of the exterior wall, roof and ground floor UninsulatedRoof form Hipped roofWWR–average of different orientations (%) 16.29Window frame material, glazing and glass type Most of them are PVC framed double glazed with float glass, and few of them are

timber framed single glazed with float glass.Stairwell location and its thermal properties In the centre, unheated and uninsulated

g the

iu

i

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W

Fig. 3. A screenshot showin

nsulation materials, the highest gains are achieved when XPS issed, followed by EPS and RW, respectively.

According to the economic performance results, apart fromnsulating the floor above the unheated basement and insulating

able 4nvironmental and economic sustainability performances of predefined retrofit alternati

Retrofit alternative Retrofit material(s)

Insulating exterior wall and projected floor XPS

EPS

RW

Insulating roof floor GW

Insulating floor above unheated basement XPS

EPS

RW

Insulating all elements XPS

EPS

RW

hile determining the performance points, PVC double glazing already present at the bu

filtering process for WWR.

the all elements with RW, all other retrofit alternatives have aneconomic performance ranging between 8 and 18 points, whichis considerably lower than the environmental performance. Ther-mally insulating the floor above the unheated basement with RW

ves.

NI (eco-points) CI (TRY) NR (points) CR (points)

239.07 170320.24 35.36 18.42243.86 171934.41 34.06 17.65246.41 192332.43 33.37 7.88328.57 19017.56 11.16 8.99360.63 209466.30 2.49 −0.33362.17 209601.22 2.07 −0.39362.54 213687.78 1.97 −2.35179.97 188061.34 51.34 9.93185.64 189608.37 49.81 9.19188.52 219229.73 49.03 −5.00

ilding is accepted to complete its life span and then be replaced.

I. Cetiner, E. Edis / Energy and Buildings 74 (2014) 132–140 139

Table 5Overall sustainability performances when different importance ratios are used.

Retrofit alternative Retrofit material(s) Overall sustainability performances for differentenvironmental/economic importance ratios (%)

30/70 50/50 70/30

Insulating exterior wall and projected floor XPS 23.50 26.89 30.28EPS 22.57 25.86 29.14RW 15.53 20.63 25.73

Insulating roof floor GW 9.64 10.07 10.51Insulating floor above unheated basement XPS 0.52 1.08 1.65

EPS 0.35 0.84 1.33RW −1.05 −0.19 0.68

rl

rostduef

sabaewTws

cifsi

cwina

ae

TS

Insulating all elements XPS

EPS

RW

esults in a small economic loss up to 2 points, and thermally insu-ating the all building with RW causes a bigger loss of 5 points.

The second step in evaluating the efficiency of predefinedetrofit alternatives is by determination of the importance ratiof environmental sustainability performance relative to economicustainability performance. In the database, in default, the impor-ance ratios of environmental and economic performances areefined equally as 50%. As mentioned before, it is possible for theser to select different importance ratios. Overall performances ofach retrofit alternative when different importance ratios are usedor environmental and economic performances are given in Table 5.

When importance ratios of environmental and economicustainability performances are selected to be equal to each other,ll retrofit alternatives increase the overall sustainability of theuilding to some extent, except for thermally insulating the floorbove the unheated basement with RW. In general, insulating alllements provide the highest gain, followed by insulating externalall and projected floor, and insulating roof floor, respectively.

hermally insulating the floor above the unheated basementith XPS or EPS has a minor effect on increasing the overall

ustainability of the building.As given in Table 4, thermally insulating all elements with RW

auses a loss of 5 points in the economic performance while theres a considerable gain of 49.03 points in the environmental per-ormance. Therefore, a positive value can be achieved for overallustainability performance, which indicates a gain. It is the same fornsulating the floor above the unheated basement with XPS and EPS.

The effect of changing importance ratios can be observed in thease of insulating the floor above the unheated basement with RW,here the loss in economic performance is higher than the gain

n environmental performance. When the importance ratio of eco-omic performance is decreased to 30%, a positive value indicating

gain can be achieved for overall performance (Table 5).Situations observed at insulating all elements and the floor

bove unheated basement with RW show that, apart fromvaluating the overall performance, it is important to evaluate

able 6ustainability performance results of the second comparable building type.

Retrofit alternative Retrofit material(s) NR

Insulating exterior wall and projected floor XPS 29EPS 28RW 27

Insulating roof floor GW 10Insulating floor above unheated basement XPS 1

EPS 1RW 1

Insulating all elements XPS 46EPS 44RW 43

a Numbers within the parenthesis indicate the importance ratios of environmental and

22.35 30.63 38.9121.37 29.50 37.6211.21 22.01 32.82

environmental and economic performances separately if a gainis requested for each performance. In addition, depending on theusers’ priorities (i.e. environmental vs. economic gain) a gain or lossin the overall performance can be observed for the same retrofitalternative.

The last step is the selection of an efficient retrofit alternativeand depends on the objective/priorities of the user:

• If the importance ratios of environmental and economic sustaina-bility performances are equal to each other, the most efficientretrofit alternative will be insulating all elements with XPS, andit is the same when the importance ratio of environmental per-formance is considerably higher;

• If the importance ratio of economic sustainability performanceis considerably higher than that of environmental performance,then the most efficient retrofit alternative will be insulatingexternal wall and projected floors with XPS.

In addition, as the method is based upon evaluating the over-all sustainability performance of predefined building types, somecharacteristics of the most comparable building may vary consid-erably. Therefore, as aforementioned, it will be beneficial to analysethe results of a second comparable building type before deciding onthe efficient retrofit alternative. In the example application chosen,the floor area of the case building is considerably different fromthose of other building types. Therefore the results of the secondcomparable building, which has a floor area of 420 m2 (Table 6), areconsidered during the last phase, and it is observed that the mostefficient retrofit alternatives for different priorities do not changewhen the floor area increases. In addition, comparative evalua-tion of the sustainability performance results given in Tables 4–6

shows that the sustainability performance of each retrofit alter-native decreases as the floor area increases. Therefore it is safe toassume that the actual sustainability performance of the case studybuilding would be somewhere between these points.

CR SPa (70/30) SPa (50/50) SPa (30/70)

.59 12.74 24.54 21.17 17.80

.50 12.16 23.60 20.33 17.06

.83 2.02 20.09 14.93 9.76

.26 7.91 9.56 9.09 8.62

.56 −2.07 0.47 −0.25 −0.98

.50 −2.01 0.44 −0.26 −0.96

.29 −5.07 −0.62 −1.89 −3.16

.27 3.49 33.44 24.88 16.32

.71 2.74 32.12 23.73 15.33

.79 −12.33 26.95 15.73 4.51

economic performances respectively.

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40 I. Cetiner, E. Edis / Energy a

Other distinctions between the actual building and selecteduilding type were WWR and distance to surrounding buildings.t is important to note that during a real application, the effects ofarying WWR should also be studied. However, in the current statef the database, it is not possible to evaluate the effect of vary-ng distances to surrounding buildings, which will be considered inuture research.

. Concluding remarks

This paper introduces a method developed for evaluating theetrofits applied to the building elements of existing detachedesidential buildings with a natural gas-fired central heating sys-em to increase their environmental and economic sustainabilityy reducing space conditioning energy consumption during theiremaining life. It excludes structural and services systems’ retrofits.n environmental terms, it is based on the LCA approach. There-ore, it considers not only space conditioning energy consumptionnd resulting emissions, but also the resulting effects of materialroduction and construction processes for retrofitting and main-enance processes. In economic terms, similarly, costs associatedith construction and maintenance operations are considered, asell as the cost of space conditioning. The overall sustainabilityerformance calculated by considering both environmental andconomic performances together is used to determine the efficientetrofit alternatives depending on the priorities of the user. Withhese features, the method differs from other methods consideringnly use period energy consumptions or treating environmentalnd economic effects separately.

The evaluation procedure of the method is based on selecting theost comparable building type for a particular building under con-

ideration, and evaluating the effectiveness of predefined retrofitlternatives. This approach allows for estimating the gain or loss inhe performance without making detailed energy and environmen-al impact simulations for a specific building, which would be costlyspecially in the case of privately owned apartment buildings. In itsurrent state, the database of the method covers detached residen-ial buildings located in Istanbul, with a natural gas-fired centraleating system. Building types were defined by field and archiveurveys. Energy consumption and environmental impacts of eachuilding type were determined by computer simulations. In the cal-ulations, space cooling energy was not included since currently its not a common practice in Istanbul.

This method is designed to be used by building owners, usersr architects in order to decide which retrofit alternative(s) isore suitable for their buildings in the usage period, considering

he overall sustainability results pertaining to the predefinedlternatives. However, some definitions and explanations shoulde given as a manual for them to select the most comparable build-

ng type and to determine sustainability importance ratios. Theatabase can be evolved by considering different cities, buildingharacteristics, and life cycle inventory data that will be generatedor Turkey.

cknowledgement

This paper presents the method generated in the researchroject numbered 108K418 supported by The Scientific and Tech-ical Research Council of Turkey (TUBITAK).

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