A tool for design decision making - zero energy residential buildings in hot humid climates

S.G. Attia

Research output: ThesisPhd Thesis 4 Research NOT TU/e / Graduation NOT TU/e)

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In this thesis, the development and evaluation of a simulation-based decision aid for Net Zero Energy Buildings (NZEBs) design, ZEBO, was explored. The thesis investigates the ability to achieve informed decision making for NZEB design, in hot climate. Four main questions were posed. Firstly, how to design NZEBs in hot climates? Second, what are the requirements of the BPS decision support tool to be developed? Thirdly, what are the effects of the use of BPS and sensitivity analysis on the decision making of NZEBs? Finally, how to achieve and measure informed decision making for NZEB design? These questions were explored in three corresponding sections: literature review and analysis of the problem, development of the decision aid and evaluation of the decision aid. Whilst the four questions were addressed under the aegis of fairly narrowly-focused studies, consideration was given throughout to their broader implications. The first section, Literature Review and Analysis of the Problem, contains four chapters. The first, chapter 2, presents a review that explored the implications of research problem. The implications of Net Zero Energy Buildings (NZEBs) design in hot climates are discussed. First the chapter reviews the characteristics and classification of hot and humid climates. Then the study context and building typology are defined. Then the anatomy of typical residential buildings performance in Egypt is presented. This is considered as the foundation from which the net-zero target will be reached. The different comfort modes and bioclimatic analysis in hot climates are discussed. Finally, the chapter suggests evaluation criteria of thermal comfort for NZEBs in hot climates. Chapter 3 contains a review on the concepts and definitions of NZEBs for hot climates. The definition of NZEBs is described with a special attention to the importance of passive design strategies. First passive and low energy cooling strategies are presented. Then we explained the idea of mixed-mode and hybrid cooling to achieve a balance between passive and active cooling to avoid discomfort during extreme conditions. Moreover we discussed the implications of scale and urban density on the net-zero targets. The importance of technology and the suitability of a low tech approach versus high tech approach were also discussed because it has a huge impact on the energy performance. Finally, we composed a design methodology and guidelines for NZEB design in hot climates. In chapter 4 a third review is presented and this considers the technologies required in a net-zero residential building in Egypt. This chapter discusses firstly, the active cooling techniques and strategies and explain the different technologies that are suitable in hot climates. Secondly, renewable energy technologies are presented and evaluated according to their performance and fitness in the Egyptian context. Chapter 5 reviews the use of BPS by architects and its ability to support the decision making. The chapter reviews the modelling of NZEB and the integration of building performance simulation to support the design decisions. The review considers the most current simulation software and suggests possible future advances in the use of parametric analysis for decision support. In the second section of this thesis, Development of the Decision Aid, three chapters describe the development of the NZEB decision aid, ZEBO. The first, chapter 6, contains the results of three workshops in Cairo 2010 that aimed to identify the barriers of the use of BPS tools in practice. The workshop activities and discussions highlight the status and difficulties architects encounter in the usage and the needs for BPS tools in the Egyptian context. The chapter first presents a brief overview of the status of the use of BPS in practice then describes the methods used, including, surveys, interviews, tools testing, brainstorming sessions and discussions. In the second chapter of the development section, chapter 7, a field survey was conducted to set a representative simulation model for residential buildings. The development of the benchmark involved surveying almost 1500 apartment in three urbanely dense cities in Egypt. The different energy consumption patterns of two models describing the energy use profiles for air-conditioners, lighting, domestic hot water and appliances in respect to buildings layout and construction. Using EnergyPlus simulation tool the collected surveyed data was used as input for the benchmark. The simulation models were verified against the apartment characteristic found in the survey. The work in this chapter is a foundation for the tool development described in chapter 8. In chapter 8, the prototype of the decision support tool under development, ZEBO is presented. There are two main prototypes that are developed. The previously developed residential benchmark was established coupling sensitivity analysis modelling and energy simulation software (EnergyPlus) as a means of developing a decision support tool to allow designers to rapidly and flexibly assess the thermal comfort and energy performance of early design alternatives. The development embeds the evolving prototypes through usability testing. Participating architects, architectural engineer and architecture student tested the tool using the system usability scale method. The usability testing was mainly implementing the system usability scale. Two prototypes were tested and significant shortcomings were identified during the process. Consequently, significant alterations were made to later prototype of the tool, in particular the inclusion of sensitivity analysis features which allowed designers to see the impact of parametric variations. From the results of this study, decision aid usability testing was found to comprise of two distinct processes: firstly the involvement of users in the development processes, and secondly their responses to prototypes up until the final version. Accordingly we developed suggestions for the third prototype In the third section of the thesis, Evaluation of the Decision Aid, two chapters describe the evaluation of ZEBO. The first, chapter 9, is reporting the results of three design case studies for NZEBs. The aim of the case studies was to evaluate the effect of ZEBO on knowledge, decision attitudes and patterns, the components of informed decision making, defined as knowledge in the presence of attitudes that are congruent with subsequent decisions. Three design workshops were organized early 2011 in Cairo to design and develop three case studies. This chapter focus on the setting of the case studies and describe the design objectives, design teams, workshop structure and process. The final design outcomes of the different design iterations are reported. In chapter 10, the relationship between the usage of ZEBO and informed decision making is examined and validated in greater detail. The outcome data from the usability study, combined with detailed information about the design performance of participants improved designs, allowed us to examine the effect of sensitivity analysis on decision making. The key finding from this research was that sensitivity analysis features embedded in ZEBO was found to promote informed decision making. The use of ZEBO and DesignBuilder resulted in an increase in knowledge uptake between 35 and 87 percent compared to the pre-workshop knowledge. Also the use of BPS tools improved the energy performance of the original design by 40 to 64 percent. More importantly, 78.8 percent of participants recognize the importance of BPS tools in informing the decision making and 71.2 percent recognize the importance of BPS tools in guiding the decision making of NZEBs design. Then we analysed the tools limitations and the reasons behind the lack of confidence (44.2 percent) and lack of ability (51.9 percent) to achieve NZEBs design using ZEBO and other BPS tools. Based on the feedback provided during the group discussion participants considered the complexity of design and the limitation of the used tool to address all design objectives including, cost, aesthetics, visual comfort, time, and budget, etc. real barriers. Participants expected that the tool can enrich creativity through flexible 3D modelling using more design like medium or tools and allow the interpretation of the results to understand the building performances. In conclusion, in chapter 11 of the thesis, the results and conclusions from the three sections of the thesis are discussed. After outlining the rationale for the thesis, the results of chapters 2 to 10 are described. Then, the findings are interpreted and critiqued from a number of perspectives, including methodology, and with respect to the wider literature. According the research findings there are four factors that promote or inhibit the uptake of BPS as decision support in architectural practice: 1) interactional usability, 2) decision support (intelligence), 3) users’ skills and 4) contextual integration. All four of these factors apply to the uptake of ZEBO. Interactional usability and decision support could help understand the human computational interaction between the tool and the user for modelling. The third factor, users’ skills, could be used to clarify the educational requirements for the use of ZEBO. The fourth factor; the contextual integration could be explored in terms of the incorporation of a tool such as ZEBO in a climatic and building context. Theoretically, it is possible to develop BPS tools that support the design of NZEBs and address factor 1, 2 and 4. However, the success of the design will be always dependent on the users’ skills factor. I conclude at the end of this thesis that the need for a simulation-based decision aid remains undiminished. The need for a simulation-based decision support is growing daily. A generation of simulation-savvy architects is now necessary, for whom NZEB design is of increasing relevance. They and following generations will demand easily sable, reliable, simulation based information in order to help them with one of the most difficult and complex processes of NZEBs design. Informed decision making remains the key, and this needs to be developed and evaluated further.
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • KU Leuven
  • De Herde, A., Promotor, External person
  • Grätia, E., Promotor, External person
  • Bodart, M., Promotor, External person
  • Hensen, Jan L.M., Promotor
Award date7 May 2012
Place of PublicationLouvain
Print ISBNs978-2-87558-059-7
Publication statusPublished - 2012


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