Optimal window designs for Australian houses

Abstract While energy-efficient window designs have been available for decades, their uptake in the Australian residential sector has been slow. This is partially due to inadequate policies and a scarcity of research about the optimal designs across different climate zones around Australia. This study addresses this gap by investigating the impact of different window designs on the annual energy loads of a house for all eight Australian capital cities covering diverse climate zones. The analysis focussed on two types of double glazing: uncoated; and coated with low-emittance films for improved thermal insulation (U-value) or lower solar heat gain. The results show that while low-emittance double glazing provides superior performance, the low solar gain option should only be installed in sunnier climate zones. The thermal performance of different frames (timber, aluminium, thermally broken aluminium and uPVC) was also analysed. The best performance is provided by timber and uPVC frames – especially for the sunnier climate zones, where uPVC frames provide the most energy savings for cost. This paper highlights the need for a more nuanced understanding of windows and their performance in delivering improved performance of housing. It also demonstrates limitations of current policies and modelling software that must be addressed to improve outcomes.