Multi-objective optimisation of a prefabricated house in Australian climate zones

Abstract

Quantitative evaluations of indoor environmental quality (IEQ) along with energy efficiency are amongst the key features of environmentally sustainable buildings. Buildings are responsible for a significant portion (nearly 40%) of the world’s total energy consumption and GHG emissions. On the other hand, operational phase contributes to the greater part of the building’s energy consumption. Along with energy efficiency, IEQ is another aspect that has been attracting significant attention in the field of sustainable building design. People spend about 90% of their time indoors. Therefore, the comfort levels and satisfaction of indoor environment can easily affect the quality of their daily life. The IEQ parameters considered in this thesis include thermal comfort, visual comfort, auditory comfort and indoor air quality (IAQ). While prefabrication offers substantial benefits to the construction industry through quality assurance, time savings and waste reduction, it tends to transform the construction process and components which can affect the buildings’ performance in both positive and negative ways. Understanding the effects of the prefabricated building components on energy performance and IEQ will inform the design decisions which can lead to the creation of more sustainable buildings with high quality. Although previous research has focused on the benefits and limitations of prefabrication in housing, there has been little quantitative analysis on how various envelope components may affect several performance parameters including energy consumption and IEQ of residential buildings. Along with that, there is still a lack of systematic design methods and decision support which can lead to design solutions to improve both sustainability and affordability aspects. These issues constitute the main knowledge gaps, leading to the identification of the research aim as: ‘The aim of this thesis is to optimise the envelope components of a prefabricated house to minimise thermal discomfort hours (TDH), daylight unsatisfied hours (DUH) and life cycle costs (LCC) while meeting the requirement of Australian National Construction Code (NCC) on energy efficiency and IEQ performance’. The focus of this study is on a prefabricated house in various Australian climates. Building performance optimisations with multi-objectives in early stages of design have been conducted to minimise LCC while maintaining the satisfactory indoor environment. A framework was developed to conduct multi-objective optimisation of a selected residential building. The framework is the structure developed for conducting multi-objective optimisation in early design stages through a number of sequential rational steps. The steps include model development, model validation, sensitivity analysis, development of component’s library and multi-objective optimisation. As the result of optimisations, the optimal combinations of envelope components were presented in the form of Pareto optimal solutions. The optimal solutions achieved 27-31% savings in LCC compared to the baseline while the reductions for TDH varied between 6% and 55%. As a result of trade-offs, the selected compromised solutions in each climate could achieve better reductions for either TDH, LCC or both.The optimal solutions, as well as recommended best compromised solutions, provided useful insight and decision support towards the design solutions that minimise LCC while providing satisfactory indoor environment. The developed framework for building optimisation in early stages can be used by designers and building performance simulation practitioners across any types of buildings.