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Energy and Buildings
j ourna l ho me pa g e: www.elsev ier .com/ locate /enbui ld
omparison of passive house construction types using analyticierarchy process
anja K. Kuzmana,1, Petra Groselj a,1, Nadir Ayrilmisb,∗, Martina Zbasnik-Senegacnikc,2
University of Ljubljana, Biotechnical Faculty, Department of Wood Science and Technology, SloveniaIstanbul University, Forestry Faculty, Department of Wood Mechanics and Technology, Bahcekoy, Sariyer, 34473 Istanbul, TurkeyUniversity of Ljubljana, Faculty of Architecture, Slovenia
r t i c l e i n f o
rticle history:eceived 9 November 2012eceived in revised form 28 January 2013ccepted 14 May 2013
eywords:assive house
a b s t r a c t
In this study, in order to determine the advantages and disadvantages of the most common construc-tion materials, different constructions types for passive houses, such as solid wood, wood-frame, aeratedconcrete, and brick, were compared with each other. The analytic hierarchy process (AHP), a widely usedmulti-criteria method, was applied to quantify the comparison. The analysis of different constructiontypes based on quantifying different criteria for passive houses was performed on a case study. The AHPanalysis revealed that the highest ranking criteria came into play here, notably well-being, the psycho-
logical aspect, and functionality in the wood construction considered as one of the most suitable optionsfor passive houses. The AHP analysis can help professionals and future dwellers to make a reasonablechoice on further optimizing and developing a particular aspect of the building process by giving themthe possibility of comparing different alternatives on a common and comprehensive basis. In the lightof the growing importance of energy-efficient building methods, it could be said that wood construction
ly im
would play an increasing
. Introduction
Energy efficiency is essential in the efforts to achieve a 20%eduction of primary power consumption by 2020 [1]. It is widelyecognized that the potential of energy saving in buildings is large.onsidering the tendencies of energy production and price, it
s becoming urgent to reduce energy consumption in buildings.n Europe, the most comprehensive and widely used concept ofltra-low energy, more precisely, the passive house concept wasresented by Dr. Wolfgang Feist of the Passive House Institute [2].
t sets forth the maximum permissible energy consumption for theeating of the building and limits the total primary energy con-umption. In its essence, it is an upgrade of the low-energy housetandard. Passive houses are buildings that ensure a comfortablen-door climate during summer and winter without requiring a
onventional heat distribution system [3]. The passive house stan-ard means that the space heating peak load should not exceed0 W/m2 living area in order to use supply air heating [4]. The
resulting space heating demand will approximately be 15 kWh/m2
but will vary depending on climate [4].The term ‘passive house’ refers to a construction standard that
can be met through a variety of technologies, designs and materialssuch as solid (masonry, concrete, and aerated concrete) and woodstructures. The following considerations are particularly importantwhen choosing the material and the construction type: the con-struction type should be standardized; the construction systemshould be based on natural and environmentally friendly materi-als; the thermal envelope should meet the standards of a passivehouse; the construction should be wind-tight, airtight and diffu-sion open. In order to design and implement a high-quality passivehouse project, attention should be paid to the materials used. Thechoice depends on personal preferences, in particular on the cost.There is a growing movement especially in Germany, Austria andSwitzerland to build passive houses that are based on energy con-servation measures and an efficient mechanical ventilation systemwith heat recovery [4]. Over the past few years, the number of pas-sive houses has been seen a continuous increase in Europe as shownin Fig. 1 [5].
Architects and civil/structural engineers facing with the chal-lenges of climate change have recently focused their efforts
on finding environmentally friendly solutions and constructionmethods that bolster energy efficiency and thus reduce the envi-ronmental burden. The choice of a construction material is the mostimportant decision with long-term consequences for the owner of
M.K. Kuzman et al. / Energy and Buildings 64 (2013) 258–263 259
tdTapccsobhlwnodb
camtrFppassacwb[iCoc
pcntscaatc
Table 1The fundamental scale of analytic hierarchy process (AHP) [19].
Value aij Description
1 Elements i and j are equally important3 Element i is slightly more important than element j5 Element i is much more important than element j
serves reciprocal values of inverse comparisons for aggregation of
Fig. 1. The number of passive houses in 31 countries of Europe.
he building [6]. The scale of the external environmental impactepends on the materials used and the energy sources utilized [7].he theoretical and practical aspects of a passive house’s life cyclend its environment were reported in various research articles androjects. For example, in a recent study Monathan and Powell [8]ompared the embodied carbon in a low-energy affordable homeonstructed using a novel offsite panellised modular timber frameystem, in Norfolk UK with two traditional alternative scenarios. Inther study, Salazar and Meil [9] investigated energy and the carbonalance of two residential house alternatives: a typical wood-frameome of conventional materials and a wood-intensive house. Kak-
auskas et al. [10] compiled passive house complex databases,hich comprehensively described the alternatives from the tech-ical, qualitative, and technological aspects as well as in termsf security and functionality. A system based on these complexatabases allows for a complex analysis of passive house projectsy means of quantitative and qualitative approaches.
Analytic hierarchy process (AHP) has been widely used in woodonstruction studies [11–13]. Smith et al. [11] analyzed factorsffecting the selection of wood as a bridge material using AHPethod, including over twenty criteria. Lipuscek et al. [12] used
he AHP analysis to classify wood products according to the envi-onment burden they presented during the manufacturing process.renette et al. [13] evaluated light-frame wood wall assembliesroviding a methodology for a quantitative evaluation of a set oferformance characteristics. Chauhan et al. [14] demonstrated thepplication of the AHP as a decision-making tool for the housingector. Wong [15] applied the AHP in a multi-criteria analysis toelect intelligent building systems. Liu et al. [16] used the AHP for
method of quantifying the physiological, behavioural and psy-hological portions of the adaptation process. The AHP analysisas also applied as a computer tool for selecting the best com-
ination of building assemblies for each particular design situation17]. Yang et al. [18] used the AHP analysis to weigh the identifiedndicators to assess the energy-efficiency of residential buildings inhina. However, based on an extensive literature search, the AHPr another multi-criteria decision model has not been used to rankonstruction materials for passive houses.
The construction of a passive house is a complex and multidisci-linary field. The decisions are influenced by three main groups ofriteria: economic aspect, environment, and well-being. To ratio-alize the decision-making process and reveal the critical qualityhe attributes application of mathematical models should be con-idered. The primary objective of the study was to identify theriteria having a strong influence on the choice of the material for
passive house. Passive house experts and dwellers have evalu-
ted fifteen criteria from three main groups: the economic aspect,he environment, and well-being. The secondary objective was toompare the different construction types for passive houses, solid
7 Element i is proved to be more important than element j9 Element i is absolutely more important than element j2, 4, 6, 8 Middle values
wood, wood frame, aerated concrete, and brick, on the basis of theselected criteria. The AHP analysis was used for determining themost important criteria and compare construction types. It mayhelp researchers better understand the choice of material for pas-sive house. With the AHP approach, all the criteria, factors andcorresponding elements were arranged in a hierarchic tree andquantified through a series of pair-wise judgements.
2. Methodology
2.1. Analytic hierarchy process (AHP)
The AHP analysis [19] is a widely used multi-criteria decisionmodel for ranking alternatives or selecting the optimal alternativeon the basis of a hierarchical tree structure of goal, criteria, andsub-criteria. The AHP analysis is based on pair-wise comparisonsof the elements on the same level of the hierarchy in respect of theparent element on the higher level of hierarchy. Comparisons cancombine measurable and non-measurable, tangible and intangible,quantitative and qualitative elements. The relative importance ofpair-wise comparisons aij, i, j = 1, . . ., n of elements i and j is evalu-ated on a scale from 1 to 9 (Table 1) and collected in the pair-wisecomparison matrix A = (aij)n×n
. The inverse comparison is assigneda reciprocal value: aji = 1/aij.
The vector of weights w = (w1, . . . , wn) belonging to the ele-ments i = 1, . . ., n can be derived from the pair-wise comparisonmatrix A by the eigenvector method [20]
Aw = �maxw, (1)
where w is the eigenvector corresponding to the maximal eigen-value �max of matrix A.
The inconsistency of matrix A can be measured by theconsistency ratio CRA = CIA/RIn, where consistency indexCIA = (�A,max − n)/(n − 1) depends on the maximal eigenvalue�max of matrix A and the maximal eigenvalue of consistent n × nmatrix, which is n, and the random index RIn, which depends onthe size of the matrix A.
Matrix A is acceptably consistent if CRA < 0.1. If A is not accept-ably consistent there are two possibilities: the decision maker canrevise his judgement or we can improve the consistency of thematrix A by the consistency improving method [21]:
a∗ij = (aij)
�
(wi
wj
)1−�
(2)
where 0 < � < 1. If the adopted matrix A∗ = (a∗ij) is still not acceptably
consistent, we repeat the process of adoption.In the case of more than one decision makers the group vec-
tor of weights should be derived, either by aggregating individualjudgments or individual vectors of weights. For this purpose theweighted geometric mean DEA model (WGMDEA) [22] was usedin this study. It uses weighted geometric mean (WGM), which pre-
individual judgments. It has foundations in the Data EnvelopmentAnalysis (DEA) and uses linear programming for deriving groupweights.
260 M.K. Kuzman et al. / Energy and Buildings 64 (2013) 258–263
Fig. 2. The decision tree for design and construction of a passive house.
on m
mi
m
s
.
2h
acbbttTetr
Fig. 3. Criteria for selection of the most comm
Let a(k)ij
, i,j = 1, . . ., n, k = 1, . . ., m be pair-wise comparisons of decision makers. Let opinions of all decision makers be equally
mportant. First individual judgments are aggregated using geo-
etric mean: m
√∏mk=1a(k)
iji,j = 1, . . ., n. Then linear programme (3)
hould be solved for all wi, i = 1, . . ., n.
max w0 =n∑
j=1
m
√√√√ m∏k=1
a(k)0j
xj
subject ton∑
j=1
⎛⎝ n∑
i=1
m
√√√√ m∏k=1
a(k)ij
⎞⎠ xj = 1
n∑j=1
m
√√√√ m∏k=1
a(k)ij
xj ≥ nxi, i = 1, ..., n
xj ≥ 0, j = 1, . . . , n.
(3)
The maximal values of solutions of linear programmes wi, i = 1, . ., n provide group vector of weights w = (w1, ..., wn).
.2. The decision tree: selecting a construction type for a passiveouse
The objective is to evaluate different types of construction for passive house. The components of the decision tree are goal,riteria, sub-criteria, and alternatives. We focused on finding theest alternative for a passive house. The answer can be obtainedy assessing the criteria that present the core of the decisionree. We decided to choose the most important criteria amonghe collection of many criteria in the first stage of our study.
he criteria of mechanical resistance and stability, fire safety, andnergy efficiency are set forth by construction standards and haveherefore been omitted from the ranking. The remaining crite-ia were combined into tree main criteria groups: the economic
aterials used in a passive house construction.
aspect, the environment, and well-being. Each group containedfive sub-criteria: the economic aspect thus included constructioncosts, maintenance costs, construction speed, prefabrication level,environmental subsidies; the environment included the amount ofembodied energy, life time, end-of-life disposal, locally availablematerial, emissions of material; whereas well-being included rel-ative humidity, health aspect, psychological aspect, functionalityand aesthetics (Fig. 2).
Based on the decision tree, in the first phase a questionnaire wasdrafted with paired comparisons of construction criteria in respectof the three criteria groups and the criteria groups with regardto the objective. We sought to establish which criterion is moreimportant for the selection of the construction material for passivehouses and to which extent. Eight experts from the field of archi-tecture, wood science and technology, mechanical engineering, andcivil engineering, along with eight passive house dwellers-users, ofwhich two lived in a wood construction passive house, two in abrick construction, and two in an aerated concrete constructionwere selected. The results were obtained from all eight expertsand from seven dwellers. The transfer of expert knowledge intothe model increased the credibility of the final model.
In the second phase, the first six criteria were selected with thehighest weight by all the interviewees: health aspect, psycholog-ical aspect, functionality, end-of-life disposal material, emissionsof material in their life cycle, and aesthetics. The alternatives wereassessed according to the selected criteria (Fig. 3). The estimates forthe measurable criteria (end-of-life disposal, emissions of materialin their life cycle and functionality) were acquired from the liter-ature whereas the ‘soft criteria’ based on subjective data (healthaspect, psychological aspect and aesthetics) were compared usingAHP scale by two experts.
3. Results and discussion
The results of the evaluation of three criteria groups combined,and experts and dwellers are individually presented in Fig. 4. The
M.K. Kuzman et al. / Energy and Buildings 64 (2013) 258–263 261
uation
mahritw(ad
enwsmgorsoap
Fig. 4. The results of eval
ost emphasis was found for well-being. The results of expertsnd dwellers did not show a major difference in classification;owever, the dwellers weighed well-being more than the envi-onmental aspect. We checked the acceptable consistency of allndividual comparison matrices. The matrix of one expert exceededhe threshold of 0.1 for consistency ratio. His comparison matrixas adopted using � = 0.87 in the consistency improving method
2). The WGMDEA method (3) was used to aggregate the individualssessments and to derive the group priorities first for experts andwellers separately, and then combined.
The interviewees evaluated three criteria groups comparingach other. Eight comparison matrices of four interviewees wereot acceptably consistent. The consistency improving method (2)as performed for those comparison matrices. For each compari-
on matrix, the smallest possible � was used, so that the adoptedatrices were acceptably consistent. Fig. 5 shows the results of
lobal ranking of all criteria for experts and dwellers. The resultsf all interviewees showed that the health aspect had the highestanking while the lowest ranking was found for the construction
peed. As shown in Fig. 6, the health aspect had the highest pri-rity (0.172) for a passive house, followed by the psychologicalspect (w = 0.118), functionality (w = 0.097) and end-of-life dis-osal (w = 0.077), emissions (w = 0.074), and aesthetics (w = 0.069),
Fig. 5. The results of global ranking of al
of three criteria groups.
respectively. Compared to the experts, the dwellers put moreemphasis on well-being. This implies that long-term well-beingshould be a key criterion in the future. The opinions of dwellersand experts diverge mostly in end-of-life disposal while they con-verge on the construction time, prefabrication level, and emissionsof the material in its life-cycle.
3.1. Assessment of alternatives with each criterion
Four different types of construction were studied in this studyand represented as alternatives in the decision tree: solid wood,wood frame, aerated concrete, and brick construction. Each typeof construction was individually assessed for each of the six keycriteria of passive house construction. The values assigned to thealternatives in respect of end-of-life disposal were obtained fromearlier studies [23]. These results show that glued wood/solid wood(w = 0.292) are re-usable, brick is partially re-usable (w = 0.250)whereas aerated concrete is re-usable to an even lesser extent(w = 0.167). The value of alternatives in respect of the emissions
was assigned on the basis of results yielded from a study [24]comparing various types of construction (aerated concrete, brick,and wood) and the amount CO2 released during construction. Inwood construction, the use of CO2 is greater during the growth of
l criteria for experts and dwellers.
262 M.K. Kuzman et al. / Energy and Buildings 64 (2013) 258–263
on of c
tpwwbcessmfawatATmi((ss
3
ocTonwTshsa
F
Fig. 6. Priority ranking for the selecti
rees used for material than the emissions produced during woodrocessing and construction [25,26]. The results show that solidood construction yields least emissions (w = 0.333), followed byood frame construction (0.250), aerated concrete (w = 0.250), and
rick construction (w = 0.167), respectively. The weighting coeffi-ients of alternatives according to the functionality criterion werestimated based on the indicators such as construction design,pan possibility, multi-storey construction, system solutions, andurface efficiency, and evaluated on the basis of the survey by Kuz-an [27]. In terms of the functionality, the solid wood and wood
rame construction are the best (w = 0.286), closely followed by aer-ted concrete (w = 0.265). The brick construction had the lowesteight coefficient value for functionality criterion (w = 0.163). The
lternatives were pair-wise compared by two experts accordingo the soft criteria of psychological aspect, aesthetics, and health.ll individual comparison matrices were acceptably consistent.he assessments of two experts were aggregated by the WGMDEAodel (3). The solid wood construction had the highest aesthet-
cs potential (w = 0.483), followed by wood frame constructionw = 0.322), brick construction (w = 0.126), and aerated concretew = 0.069), respectively. The psychological and health aspects wereimilar to the aesthetic potential: the classification of types was theame and the weights differed slightly.
.2. Results of the decision tree
The importance of each criterion (as weights) according to thebjective (from the first stage) and alternatives regarding eachriterion was individually combined by the decision tree (Fig. 6).he priorities of each construction material type (alternative) werebtained through the matrix multiplication of weights of alter-atives and vector of priorities of the criteria. The final prioritiesere normalized so that the sum of all priorities equals one.
he final weights of different types of construction materials arehown in Fig. 7. The weight of solid wood construction was the
ighest (w = 0.415), followed by the weight of wood frame con-truction (w = 0.293), the weight of brick construction (w = 0.152),nd the weight of concrete (w = 0.140), respectively. As a result, the
ig. 7. The final priority ranking of different construction types for a passive house.
onstruction type for a passive house.
wood construction was found to be the best material for passivehouses among the construction materials. The advantages of woodas a construction material with lower embodied global warmingpotential, embodied carbon, positively associated with well-being,aesthetic and eco-friendliness, and realistic end-of-life disposaloptions.
4. Conclusions and further work
This case study showed the application results of AHP methodcould be used for analyzing the decision criteria related to a pas-sive house. Based on the findings obtained from the study, it canbe said that the AHP analysis is one of the most suitable models forcomparing different construction types used in a passive house. Ourmodel revealed that the highest ranking criteria in decision-makingwere health and psychological aspects, functionality and end-of-life disposal, emissions, and aesthetics, apart from load capacity,fire safety and energy efficiency. The analysis showed that wood asa renewable raw material was one of the best choices for energy-efficient construction because it is also a good thermal insulator, hasgood mechanical properties, and ensures a comfortable indoor cli-mate. The AHP analysis method can help professionals and futuredwellers to make a reasonable choice on further optimizing anddeveloping a particular aspect of the building process by givingthem the possibility of comparing different alternatives on a com-mon and comprehensive basis. Moreover, it can identify the weakand strong aspects of using a material for a passive house and thusopen up a new dimension to the promotion and marketing of pas-sive wood houses by allowing a better appreciation of the impact ofindividual parameters on other performance criteria. The findingsof AHP analysis can be further integrated into strategies to increasethe usage of wood as a construction material. The links between theselected criteria remained unexplored. Future research will inves-tigate the underlying link between the criteria, notably by using theanalytical network process (ANP). In the future study, to make reli-able evaluation or comparison, proven tools will be used to examinethe construction materials in terms of different angles in additionto human judgement.
Acknowledgement
The financial support provided by the research programmetitled Wood and Lignocelluloses Materials, financed by the Slove-nian Ministry of Higher Education and Science, is gratefullyacknowledged.
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