Cost effective refurbishment approach to achieve energy efficient building: a primary school case study

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1 icccbe 2010 Nottingham University Press Proceedings of the International Conference on Computing in Civil and Building Engineering W Tizani (Editor) Cost effective refurbishment approach to achieve energy efficient building: a primary school case study E. Loh, N. Dawood, T. Crosbie & J. Dean Centre for Construction Innovation Research, Teesside University, UK Abstract Tackling climate change and reducing green house gas emissions is a global aim and a goal to reduce carbon emissions by 60% by 2050 has been set by the UK Government. The construction industry is one of the major sources of the CO2 emissions that cause climate change. Green building construction and upgrading existing buildings present an opportunity to meet the carbon reduction challenge. This paper focuses on building refurbishment because most UK building stock is built and therefore energy efficient building refurbishment will have a larger impact on CO2 reduction than improving the energy performance of new builds. Most of the existing UK building stock does not meet the sustainable buildings requirements of the 21 st century, but the cost of green refurbishment is a major obstacle to the upgrading of these properties. The aim of the research presented in this paper is to develop an approach (focusing on the early design stage) and a decision support system to assist architects in the selection of the most energy efficient material-design combination that also meets stakeholders requirements. The research also demonstrates an approach for enabling sustainable building with minimum upfront investment by considering strategic material procurement and passive design. A case study has been carried out using a primary school project. The initial findings from this case study suggest that a 50% saving in building life cycle energy cost over 40 years can be achieved by using the proposed approach and tools developed in the research presented. The main objective of this paper is to report the material-design selection process using the proposed trade-off tool to achieve cost effective green building refurbishment. To do so it presents an analysis of a primary school case study. Keywords: refurbishment, trade-off, energy efficiency, life cycle cost, early design process 1 Introduction Carbon reduction is a global aim. The built environment is one of the major sources of CO2 emissions. Forecasting the energy performance of a building during the early phases of its design is suggested as a method of informing the development of low carbon buildings (InPro 2007; Loh et al 2009a). In the case of new building construction and building refurbishment energy issues should be incorporated in the early design process. This is because, the greatest opportunity for cost-effective energy measures occurs at the earlier stages of the design process (Schlueter and Thesseling 2009). This paper focuses on building refurbishment, which includes upgrade, major repairs, renovations, alterations, conversions, extensions and modernization of existing buildings (Juan et al 2009). This focus on building refurbishment is important because the replacement rate in UK for existing building

2 stock is less than 0.1% (Siddall 2008). Therefore improving the operational energy performance of buildings during refurbishment offers a much larger opportunity to reduce carbon emissions than improving the operational energy performance of new buildings. However, multi-stakeholder involvement at the early design stage makes the decision making process more complex. This is because those involved in the design of a building often have conflicting priorities. Hence, a trade-off tool is necessary to assist multi-stakeholder decision- making. The research presented in this paper contributes to the simplification of multi stakeholder decision making by developing an environmentally focused decision support system in the form of an Environmental Assessment Trade-off Tool (EATT). This tool allows stakeholders to assess building energy performance and the effectiveness of different design options during the early design stage. The main functions of the EATT are materials and project assessment: Material assessment- EATT analyses the cost benefit of material options in order to generate the best material combination that meets stakeholders requirements. Project assessment EATT analyses and compares the life cycle cost, capital cost and energy performance of different materials and building layouts. Analytical Hierarchy Process (AHP) is the trade-off approach used within the EATT decision support system. AHP was selected because it supports trade-offs with and without tangible values. For example, this approach enables the consideration of aesthetic issues as well as environmental impacts. This feature is important as decision making in reality engages with solid, verbal and subjective elements (Saaty 1980). 2 Literature review 2.1 Decision making using AHP AHP is based on priority theory. The elements of a model are broken down into a hierarchy tree and a numerical value from 1-9 is used to define the importance of each task. This method is usually applied in cases with limited criteria. The benefit of AHP is that it models complex preferences based on specific criteria at the outset of a project enabling a simplification of the decision making process. It allows the subjective and objective judgement of stakeholders to be considered. Hence, AHP can deal with the realities of decision making. AHP has been successfully applied in a wide range of sectors to achieve different types of priorities (Wong and Li 2008; Ho 2008). However, within t buildings construction, cost control is usually the main goal and therefore the least costly alternative will always be shown as the best alternative. Therefore, it is necessary to combine AHP with a cost benefit approach (Saaty 1980, 1995). 2.2 Integration of cost benefit analysis with AHP Cost benefit analysis is a tool commonly used in project evaluation to compare the financial cost of different alternatives. Benefit/ cost AHP analysis (Saaty 1980, 1995) differs from conventional cost benefit analysis in that it incorporates the AHP preference system to draw comparisons between different alternatives. In other word, the benefit/cost AHP method has advantage of supporting the comparison of non-currency units (Wedley et al 2001). Saaty s approach has been widely used to support decision making processes incorporating both benefit and cost issues (Saaty and Cho 2001, Saaty 1994). However, a major weakness in the benefit/cost AHP approach is that users cannot control the benefit/cost ratio. This is because the benefit and cost hierarchy is built separately (figure 1). Wedley et al (2001) tackle this problem by

3 incorporating a magnitude adjustment process for the AHP benefit/cost ratio (see figure 1). The idea is to combine the separate benefit and cost hierarchy (proposed by Saaty) into one hierarchy. This approach supports benefit/cost ratio adjustment without losing the original subjective decision making feature of Saaty s AHP. Figure 1: (Left) Saaty s benefit/cost AHP hierarchy, (Right) Structure for benefit/cost AHP with magnitude adjustment In summary, the benefit/cost AHP incorporating a magnitude adjustment process is an ideal approach for supporting decisions during the early design process. This approach prevents a total bias towards build costs in design decisions by allowing stakeholder preferences and lifecycle costs to play a role in design decisions. This approach is therefore used in the development of the Environmental Assessment Trade-off Tool (EATT) presented in this research. This tool use MsExcel and assists group decision making in the selection and procurement of building materials at different stages in the design process (Loh et al 2009b). The output from EATT is not necessarily the most sustainable design approach or the cheapest solution. What it provides is the most cost effective and sustainable design solution that meets the most requirements of stakeholders. Naturally some of the design decisions made are a compromise shaped by the priorities of stakeholders and other constraints. 3 Material-design selection process The process flowchart presented in figure 2 is only applicable to smaller scale building refurbishment projects such as upgrading building facades and renovating the inside of buildings. The refurbishment process for extensive improvement such as constructing a new building block and building extension should follows the design process for new builds but with spatial constraints (Loh et al 2009b). At the beginning of the design process supported by the EATT architects request a BIM model for the existing building so that the team can work on the existing drawings. If a BIM model is not available, then a new BIM model needs to be developed. In the next phase of the process energy simulation is conducted on the existing building in order to benchmark the proposed design. The benchmark process is only carried out for smaller scale refurbishment projects and not in the case of larger scale projects. This is because smaller scale projects mainly involve internal changes and therefore the building foot print will not be change which means the energy data for the proposed design can be compared with the existing building. Wearers in the case of larger scale projects (such as building extensions) will involve a new building footprint and the simulation data based on the original building design will not be appropriate as a benchmark data due to design inconsistency. The next phase of the process involves modelling different internal layouts for the building using BIM tool. Once the internal layout options are designed, a meeting is arranged and the proposal is shown to stakeholders. New ideas input from stakeholders means that it is very likely that a new

4 internal layout is created at this stage. At the same time, a material trade-off is conducted. As an outcome of this meeting with stakeholders, a few sets of material options and layouts are generated. This information is used in the energy simulations conducted in the next stage of the process. After the simulation process for the different design option was conducted, architects are able to view what-if scenario for the different design/materials combinations. However, it is difficult for architects and other stakeholders to finalise the best building design as there are further variables such as building life cycle cost, construction cost, energy performance, etc, that need to be taken into consideration. At this stage the EATT is used to select the final material-building design combination. The best building design is expecting to achieve excellent BREEAM rating as the design criteria in EATT is developed based on BREEAM pre-assessment and green guide to specification. Figure 2, Process flow chart to select the best material-layout combination

5 4 Case study A case study was undertaken using a primary school project access to which was provided by Durham County Council. A focus group was used to verify the approach and processes proposed in this research. A hypothetical approach was adopted in this study due to the fact that the primary school building has only been in existence for five years and the new condition of the school is not ideal for the case of refurbishment. The proposal for the hypothetical study is to assume the building to be operated for 20years and refurbishment is requiring for improving the existing building performance by adopting the proposed tools/process to generate a design solution. Table 1 below is the project specification for the building refurbishment: Table 1: Project specification Project Scope Description Spatial requirement 1) Add 1no. of classrooms, 2) all classrooms have to be located on the south wing, 3) a corridor is required to prevent distraction and noise from the playing field which is next to the classrooms, 4)internal configuration can only be done at the east and south wing, 5) internal improvement should not involve major structural change due to cost constraint Material replacement upgrade external cladding for the whole building and improve the energy efficiency of existing roof Heating cooling Central heating radiators are used in current building and only system maintenance is required The material and design selection process for the case study was presenting below: Generating design alternative Figure 3 illustrates the existing building design and is therefore used as the starting point from which to generate alternative internal layouts in the stakeholders meeting. Two sets of design alternatives were developed as a result of the meeting as presented in table 2. Refurbishm ent for East wing and South wing Figure 3, Floor plan for existing building

6 Table 2: Descriptions for design alternatives Design Description alternative Alternative 1 Corridor added at the south wing, remove the left toilet/stores at the south wing to gain bigger footprint for classrooms, existing library move to the staff room at the east wing and the existing library space to be converted into classroom. Alternative 2 Corridor added at the south wing, remove the left toilet/stores at the south wing to gain bigger footprint for classrooms, convert the reception at the south wing into classroom, library extension. Generating material alternative Material preference for the building was selected individually by stakeholders using the EATT in the case presented case there are only three material categories to be upgraded in the primary school. These include replacing the whole roofing, replacing the cladding without structural modification, and demolish/construct internal partition according to the design proposal. After the materials are selected, stakeholders set the standard criteria priority for the project. The materials selected by each individual stakeholder are traded off using the agreed criteria priority to generate the best material combination. In other word, the final decision is the result that consists of the accumulated knowledge/preference from multi stakeholders. Energy simulation The outputs of material combination are then input into the energy simulation software (in this case IES was selected) to simulate the energy performance and the life cycle cost performance of the different material-design combinations. Project analysis/scenario analysis Table 3 presents the simulation results of each of the material-design alternatives. Another materiallayout simulation was also carried out based on the existing building design. The idea is to use this simulation result to benchmark and compare with the proposed material-design alternatives. In this case study, life cycle cost performance was considered more important than the environmental performance (CO2 emission). Therefore, the comparison will focus on the result of the total life cycle cost. The scenario analysis shows that the 40 years life cycle cost of the existing building is higher than other alternatives and alternative 3 has 50% lower life cycle cost than the existing building this is due to using materials with a better energy performance. It is therefore possible to conclude that refurbishing the primary school building as outlined would improve the building life cycle cost performance. Table 3: Simulation result of design alternative and existing building Design alternative Material alternative CO2 emission Capital cost Energy cost-npv Material Total Replacement cycle (materials) cost-npv (40) Alt kgco2/m ,407 64,706 47, , ,722 65,237 53, , ,193 64,786 34, , ,770 61,775 47, , ,070 62,451 52, , ,514 61,801 34, ,114 existing ,781 94,107 25, ,677 life cost

7 5 Summary The research presented in this paper illustrates that the careful selection of materials and building design preconstruction is critical to reducing building life cycle cost and improving the energy performance of buildings. Usually many different stakeholders with different priorities are involved in both the design of new builds and the refurbishment of existing buildings. The challenge for multistakeholder decision making is that everyone has their own perspective. The solution proposed in this research is to use the EATT tool to support the incorporation of both the subjective and objective views of all stakeholders within the decision making process. Reference HO, W. (2008) Integrated analytic hierarchy process and its applications - A literature review. European Journal of Operational Research 186, p INPRO (2007). InPro- a brief overview, JUAN, Y.K., KIM, J.H., ROPER, K., Castro-Lacouture, D. (2009). GA-based decision support system for housing condition assessment and refurbishment strategies, Automation in Construction 18 (2009) LOH, E., DAWOOD, N., DEAN, J. (2009a) Development of RIBA sub-process to assist reduction of building life cycle impact: Integration of RIBA workstage with EU EIA Legislation and ISO14040, paper proceeding for Building Simulation 2009, 27 th -30 th July, University of Strathclyde, Glasgow, UK. LOH, E., DAWOOD, N., CROSBIE, T., DEAN, J. (2009b). Decision support system to assist material procurement and sustainable building design, paper proceeding for 4 th EASY-ECO International conference on Stakeholder Perspectives in Evaluating Sustainable Development, 16 th -18 th Oct, Budapest, Hungary SAATY, T.L (1980). The Analytical Hierarchy Process, McGraw-Hill, New York. SAATY, T.L. (1994) Fundamentals of Decision Making and Priority Theory, RWS, Pittsburgh. SAATY, T.L. (1995). Decision making for leaders, RWS, Pittsburgh. SAATY, T.L. AND CHO,Y. (2001) The decision by the US Congress on China s trade status: A multicriteria analysis, Socio-Economic Planning Sciences 35, SCHLUETER, A., THESSELING, F., 2009, Building information model based energy/exergy performance assessment in early design stages, Automation in Construction, 18(2): SIDDALL, M. (2008). Low Energy and Low Carbon Refurbishment: Towards PassivHaus Retrofits, web accessed on March 2009, WEDLEY, W.C., CHOO, E.U., SCHONER, B (2001). Magnitude adjustment for AHP benefit/cost ratios, European Journal of Operational Research 133, p WONG, J. K. W. & LI, H. (2008) Application of the analytic hierarchy process (AHP) in multi-criteria analysis of the selection of intelligent building systems. Building and Environment, 43,

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This document was downloaded from Please do not use this version for citation purposes. This full text version, available on TeesRep, is the PDF (final version) of: Loh, E. et. al. (2010) 'A framework and decision support system to increase building life cycle energy performance', Journal