Investigation of the occupant thermal behavioural settings and overheating in a hot-dry climate in Australia

• Occupant thermal behaviours in homes in a hot dry climate in Australia were investigated. • Results are used to derive cooling and heating setpoint and trigger temperatures. • Actual setpoint temperatures were found to be different from those used in energy rating tools. • Results are also used to develop overheating criteria and temperature thresholds for this climate. • Many houses were found to be overheated when air-conditioning was not in use. This paper presents the findings from a study to investigate occupant thermal behavioural settings and the criteria for potential overheating of houses in a hot-dry climate in Australia. Occupant thermal behavioural settings refer to the thresholds of the thermal conditions that trigger the occupants to take actions to achieve thermal comfort as well as the times of these occurring. Overheating is defined as the extent to which a space exceeds an upper threshold of an acceptable thermal condition. The study was conducted from June 2023 to February 2024, involving 30 households in Port Pirie, Port Augusta and Whyalla of South Australia. The methodology to calculate overheating is based on the Effective Temperature (ET*), used as the index to assess the degree of overheating, and outdoor mean monthly temperature. The results showed that the actual average cooling setpoint temperatures were lower than the assumptions in the Australian Nationwide House Energy Rating Scheme (NatHERS). Trigger point temperatures were also found to be lower than NatHERS’ assumed trigger point temperature. These results indicate that houses in this climate zone that have been rated by NatHERS could use more cooling energy than predicted. The results also showed that houses that have met the minimum star rating requirement according to NatHERS can still experience overheating when the air-conditioning is not in use. Findings from the study are expected to contribute to the improvement of the occupant behavioural settings in NatHERS and the inclusion of overheating calculations in the Australian National Construction Code.