Plea2004 - The 21th Conference on Passive and Low Energy Architecture. Eindhoven, The Netherlands, 19 - 22 September 2004 Page 1 of 5
A Multi-Criteria Decision-Making Method for the Retrofitting of Designated Buildings in Thailand Aumnad Phdungsilp and Ivo Martinac Sustainable Building Systems Group Department of Energy Technology Royal Institute of Technology 100 44 Stockholm, Sweden Tel.: +46 8 790 7840, FAX: +46 8 411 23 23 E-mail: [email protected]
ABSTRACT: Energy use in the building sector in Thailand is controlled by the Energy Conservation Promotion Act 1992 (ECP Act, 1992). This regulation defines and sets limits for four parameters related to energy efficiency in designated buildings. These are Overall Thermal Transfer Value (OTTV), Roof Thermal Transfer Value (RTTV), lighting, and air-conditioning requirement. However, this regulation does not explicitly consider or relate to other relevant aspects including resource use, environmental impacts, life-cycle cost, indoor climate, building functionality or architectural design issues. To achieve overall sustainability in buildings, these factors must be taken into consideration. The main purpose of this paper is to introduce a multi-criteria decision-making (MCDM) method as an aid in evaluating retrofitting solutions for buildings. This concept is envisioned to assist design teams and their clients in finding wholesomely sustainable retrofitting solutions. Conference Topic: 2 Design strategies and tools Keywords: multi-criteria decision-making (MCDM), sustainable buildings, retrofitting
BACKGROUND The success of sustainable urban development is explicitly dependent on the building sector. Sustainable buildings rely predominantly on the assessment and integration of different design and operation stages. The environmental friendly and sustainable building process is an interdisciplinary task. Only the close teamwork of people from different building related disciplines makes it possible to face the challenge of answering these questions and real life problems. In Thailand, the energy used by the building sector is controlled by the Energy Conservation Promotion Act (ECP Act.), which was promulgated by the Royal Thai Government in 1992. The aim is to promote energy conservation and the development of renewable energy in a comprehensive way. Buildings covered by the Act are entitled “Designated Building” and defined as those that are not royal buildings or palaces, embassies or consulates, offices of international organizations, or any other established by the agreement between the Thai and foreign governments, ancient places, temples or buildings for religious purposes, meeting the following requirements: • A building or buildings under the same address which are allowed by any energy distributor to install an electricity metering device, one or more transformers with a combined capacity of 1,000 kW or 1,175 kVA or more.
A building or buildings under the same address consuming commercial energy including electricity and steam from the time period January 1 to December 31 of the past year with a total volume of energy amounting 6 to 20*10 MJ or more of equivalent electrical energy. Currently, there are 1,646 designated buildings situated in the country. According to the Department of Energy Development and Promotion (DEDP), the designated buildings are divided into six categories, i.e. office, hotel, hospital, department store, academic institution and miscellaneous . The regulation defines and sets limits for four parameters related to energy efficiency in buildings. These parameters are: 1) Overall Thermal Transfer Value (OTTV); 2) Roof Thermal Transfer Value (RTTV); 3) lighting load for the building illumination; and 4) air-conditioning standard requirement. Regarding the OTTV, it is devised as a measure relating to thermal performance of the building envelope in air-conditioned buildings. A set of calculation procedures and property values are provided for evaluating the OTTV of a building as a part of the by-laws of the Act. The OTTV formulation has been discussed in earlier literature . The OTTV of the exterior walls of air-conditioned 2 areas in a building should not exceed 45 W/m for 2 new buildings and 55 W/m for existing buildings, while the RTTV should not exceed 25 W/m2 in both cases . It is therefore essential to reduce external heat gains through the building envelope for those
Plea2004 - The 21th Conference on Passive and Low Energy Architecture. Eindhoven, The Netherlands, 19 - 22 September 2004 Page 2 of 5
buildings having OTTV and/or RTTV exceeding this regulation. This can be done by retrofitting the building envelope. An envelope retrofit can reduce the cooling load and can lead to the reduction of air leakage. With a reduced cooling load from the envelope retrofit and improved in lighting efficiency, the size of a replacement air-condition can be smaller. However, the regulation has not considered other aspects such as resource use, environmental loading, life cycle cost, indoor climate, functionality, and architectural expression. In order to produce sustainable buildings, these factors must be taken into consideration. The main purpose of this paper is to introduce the multi-criteria decision-making (MCDM) method to aid the design team when evaluating solutions for retrofit buildings. The potentials for sustainable energy used in existing buildings are immense. Methods to produce a means for the retrofit, enabling the design team and client to better understand and handle holistic sustainable buildings are being designed. This method is based on IEA Task 23 – Optimization of Solar Energy Use in Large Buildings, suggesting a structured approach for evaluating design alternatives based on the scoring and weighing techniques. Therefore, it can help the design team in organizing information required for decision-making and promoting sustainable solutions for sustainable buildings. This paper is a theoretical analysis and has not been fully implemented in a real life retrofit building.
2. REFERENCE BUILDING An example illustrating how a MCDM method can be used in a retrofit building in order to meet the regulations stipulated by the building energy code while considering other aspects in creating sustainable buildings, has been examined. The information gained from this method can be utilized for other purposes such as declaring the environmental status of the building, enabling property owners to inform tenants of the environmental requirements, in addition to the management of operational maintenance. It was decided that focus on a specific application would do more to enhance the understanding of the approach than a general discussion. A model building, which is representative of a typical configuration of a commercial office in Thailand, was selected as the basis for determining the proposed MCDM approach for retrofit buildings. This reference building model has been developed based on energy audit information . As mentioned earlier, each designated building is required by law to engage a consultant in order to conduct the energy audit. Information obtained from a large number of energy audit reports on commercial buildings was used to construct the building model. The shape of the model is a rectangle with the smaller facades facing east and west. The opaque walls of the building typically comprise cement plastered brick work. Single glazing is predominantly used. Table 1 illustrates the details of the model, which has incorporated the most
common features of the type of office building in Thailand. The length and width are comparable, so that the area of each floor is large and the ratio of total wall area to total floor area is relatively small. Table 1: Details of the reference building model . Number of stories 2 Total area of opaque wall (m ) Total area of glazing (m2) 2 Total area of roof (m ) Total area of floor (m2) Ratio of wall area to floor area Ratio of window area to wall area, WWR Shading coefficient of glazing, SC Overall coefficient of heat transfer for 2 wall, Uw (W/m .K) Overall coefficient of heat transfer for 2 roof, Ur (W/m .K) Solar absorptance of wall and roof surfaces, αw, αr Annual average OTTV (W/m2) Interior temperature, Ti (oC) 2 Number of occupants per 100 m Number of working day per week Working hours
12 3,883 3,051 1,421 12,567 0.55 0.44 0.64 2.96 1.84 0.4 62.32 25 7 5 8:00–17:00
3. METHODOLOGY The MCDM method proposed by IEA Task 23 consists of two main phases . In the first phase, the team decided on the criteria to be used and determined its relative importance. It was recommended to organize them into 5 to 8 main criteria each with sub-criteria. This should be done before alternative designs to retrofit building are created. In the second phase, the team applied the method in an attempt to judge the relative merits of their alternatives. This was done by determining scores for each alternative, each criterion, using measuring scales defined in the first phase. It could also be useful to perform computer simulations to determine criterion such as energy use. The scores are then aggregated into several overview presentations. The star diagram is employed to show the results of the evaluation. A diagram was produced for each alternative. By visually inspecting these diagrams, the team could attain an immediate perception of the overall situation. In general, the method can be conducted in a user-friendly 7-step procedure. The first three being carried out in the phase one, while the last four are carried out in the second phase. • Step 1: selecting the main design criteria and sub-criteria. • Step 2: developing measurement scales for the sub-criteria. • Step 3: generating alternative solutions. • Step 4: weighing the main criteria and subcriteria. • Step 5: predicting performance. • Step 6: aggregating scores.
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Step 7: analysing results and making decisions. During this process, criteria may be added, removed or reformulated. The proposed method requires numeric manipulation, such as interpolating in tables, computing averages, normalizing a set of values, and plotting graphs. These can be accomplished by hand or spreadsheet software in order to assist in the process. The second alternative is using software MCDM-23, which is developed by IEA Task 23 . 3.1 Criteria used The following team members were chosen to evaluate the obtained criteria: • Tika Bunnak, Ph.D., Asst. Prof., Faculty of Engineering, Dhurakijpundit University, Bangkok, Thailand. • Chuntana Kunchornrat, School of Energy and Material, King Mongkut’s University of Technology Thonburi, Bangkok, Thailand. • Paulina Bohdanowicz, Ph.D. student at Sustainable Building Systems Group at the Department of Energy Technology, Royal Institute of Technology, Stockholm, Sweden. • Vlasta Zanki, Ph.D. student at Sustainable Building Systems Group at the Department of Energy Technology, Royal Institute of Technology, Stockholm, Sweden. • Aumnad Phdungsilp, Ph.D. student at Sustainable Building Systems Group at the Department of Energy Technology, Royal Institute of Technology, Stockholm, Sweden. It was assumed that the sustainable building would consider emphasizing low environmental loading, satisfactory indoor environment, pleasant appearance, excellent functionality and suitable economics. The authors therefore proposed a list of main design criteria and sub-criteria designated by the IEA Task 23  Additionally, the energy performance criteria with sub-criteria: OTTV and RTTV were added, due to regulation requirements (Table 2). Life cycle cost was not included because of the lack of available data. The team also decided to omit the environmental loading criterion since gas emissions are primarily associated with energy use this could account for the resource use criterion. Annual energy and water consumption were included in the resource use, however, it was impossible to obtain data on land and material consumption. Energy performance was comprised of OTTV and RTTV. The remaining criteria including indoor climate, functionality, and architectural expression, determined as proposed by Task 23. 3.2 Generation of alternative solutions Different alternatives were structured according to the options for energy conservation in office buildings as suggested by consultants and agencies in accordance with the ECP Act. It was decided to do an evaluation of 3 alternative solutions according to the following: • Alternative 1: energy savings from roof and wall insulation. The improvement of roof
insulation by the addition of 25 mm fiber glass to roofs and the addition of 20 mm air gap + 9 mm gypsum board to walls. Alternative 2: energy savings from the addition of double-glazing and overhang. Changing single glazing to double-glazing (SC=0.18). Alternative 3: energy savings from integrated roof-wall glazing retrofit. Adding 25 mm fiber glass to roofs and 20 mm air gap + 9 mm gypsum board to walls. Improvement of glazed windows by adding a film (SC=0.18).
Table 2: The design criteria use Criteria Resource Use Energy Performance Indoor Climate
Sub-criteria Annual water consumption Annual energy consumption OTTV RTTV Air quality Lighting (including daylight) Thermal comfort Acoustic Functionality Flexibility Maintainability Public relations value Identity Scale/proportion Integrity/coherence Integration in urban context
3.3 Scales and weighing of criteria Measurement scales were constructed as quantitative and qualitative values. The quantitative values were used for criteria that could be measured directly with numbers, such as annual energy consumption, OTTV, and RTTV. Qualitative values were used to characterize how well a building scheme rated against particular criteria where the rating was more a matter of judgement, not normally subject to quantification. Finally, all criteria were ultimately converted to a qualitative scale, using a scale of 1 to 10. Table 3 illustrates an overview of the scales that were used for the different criteria. Table 3: Measurement scales Score
Energy consumption (kWh/m2/yr.)
8 7 6 5 4
160 200 240 260 300
55 60 70 80 90
25 30 40 50 60
Resource use Indoor climate Functionality Architectural 10-excellent 9-good to excellent 8-good 7-fair to good 6-fair 5 accept to fair 4-Min. accept
The criteria was evaluated among the team members using a questionnaire on a scale from 4 to 10 (bigger is better, 4 being the minimum acceptable or less preferred). The preliminary weight criteria is illustrated in Figure 1. It has been shown that the total amounted to approximately 20 %.
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Alternative 1 Architectural quality 19%
Resource use 10
Resource use 22%
8 6 Architectural quality
Functionality 18% Energy performance 21%
Indoor climate 20%
Alternative 2 Resource use 10 8 6
Figure 1: Result of criteria assessment. 3.4 Performance prediction and results The performance prediction was conducted using estimations based on rules of thumb and the experience and knowledge of the team members. The only tool was a calculator. No computer simulations were performed. Some predictions were subject to long discussions with the experts, especially those related to architectural aspects. The results of criteria assessment and performance prediction were entered into the MCDM-23 software. Star diagrams illustrating the score for different alternatives were produced as shown in Figure 2. The total weighed scores for the alternative solutions with the contributions of the different criteria indicated are shown in Figure 3. A star diagram indicated the evaluation of each alternative performance. Alternative 1 has the overall score of 7.79 while alternatives 2 and 3 scored 7.46 and 8.03 respectively (Fig.3). Alternative 3 scored the highest of the resource use and energy performance criterion. This is due to the renovation of roof and wall insulation as well as the improvement of glazed windows. Indoor climate scored low on alternative 2. Almost no distinction between alternative 1 and 3 was observed. For functionality and architectural quality, virtually no differences between the 3 alternatives were detected.
Alternative 3 Resource use 10 8 6
Figure 2: Star diagrams for the 3 alternative solutions 10 9 8 7 6
Architectural quality Functionality
The application of the MCDM method to the retrofit of a designated office building has been studied. Based on a reference building in Thailand. The model building was constructed from the national energy audit information. The results illustrate that alternative 3 (energy savings from integrated roof-wall glazing retrofit) appear to be the best proposal. Alternative 1 (energy savings from roof and wall insulation) and 2 (energy savings from adding double-glazing) produce approximately equal values. It can be concluded that whole building retrofit is more efficient than adopting individual options.
Energy performance Resource use
t t. 1 2 3 e e e en cp tiv tiv tiv ell ac a a a c . rn rn rn in Ex te te te M Al Al Al
Figure 3: Total weighted scores The team members found this method to be the most advantageous for retrofit as well as new building design. However, it may be beneficial to include economic criterion in order to evaluate the cost effectiveness of each alternative solution.
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REFERENCES  Coordinating Office for Energy Conservation, Department of Energy Development and Promotion. Energy audit reports of designated commercial buildings and of small government buildings during 1995-2001, DEDP, Ministry of Science Technology and Environment, Thailand.  S. Chirarattananon, P. Rakwamsuk and J. Kaewkiew, A proposed building performance standard for Thailand: An introduction and a preliminary assessment. In: Proceedings of the ASHRAE Far East Conference on air-conditioning in humid climate, Kuala Lumpur, November 1989.  S. Chirarattananon and J. Taweekun, A technical review of energy conservation programs for commercial and government buildings in Thailand. Energy Conversion and Management 44 (2003), 743762.  www.iea-shc.org/task23/