Testing the applicability of CIBSE overheating criteria to Australian subtropical residential contexts

Abstract

Overheating is widespread across diverse building typologies. In the context of global warming, it is becoming increasingly problematic in naturally-ventilated dwellings in which air-conditioning is not an available option. Whilst CIBSE TM59 offers the most widely used overheating assessment criteria for naturally-ventilated homes, the criteria have not been rigorously tested against real-world observations made beyond temperate regions of the UK. With an aim to examine the applicability of the CIBSE TM59 overheating criteria to subtropical residential contexts, statistical analysis was performed on thermal comfort field data collected from 162 dwellings in Australia. Our dataset consisted of indoor temperature observations recorded in living and sleeping spaces across the two-year monitoring period, accompanied by householders' subjective evaluation of thermal comfort (both daytime and nocturnal) and sleep quality. The results of our analysis identified a significant gap between the overheating assessment criteria and actual householders' experience of thermal conditions in their homes. Whilst most of our sample dwellings were deemed ‘overheated’ according to CIBSE TM59, approx. 80 % of daytime and nocturnal thermal sensations collected from the householders indicated they were comfortable. Especially in bedrooms, CIBSE's static 26 °C upper temperature threshold was found to be too stringent to be applicable to naturally-ventilated homes in subtropical regions of Australia. Our analysis demonstrated that sleep thermal comfort and sleep quality remained unaffected well beyond CIBSE's 26 °C limit. This study calls for further research in diverse climatic, housing, demographic and cultural contexts.