Residential geothermal air-conditioning: Inhabitants' comfort, behaviour and energy use

How do occupants' behaviour and expectations influence energy use for residential geothermal air-conditioning? This detailed study of 40 homes with geothermal AC in Sydney, Australia, during the period 2019–20 covers one of hottest Australian summers and increased daytime occupancy over the winter due to working from home during Covid-19 lockdowns. Monitored data are analysed for ground source heat pump (GSHP)-AC energy, occupancy, indoor conditions, as well as a snapshot resident feedback captured during hot and cold spells. Findings indicate that the homes built to comply with 2011 energy efficiency standards maintain indoor temperatures within 10–12°C of peak summer and minimum winter temperatures, without AC. A general preference to adopt adaptive strategies such as ceiling fans and appropriate clothing before deploying AC is evident for moderately hot and cold days. A heightened dependence on AC is seen for extreme days. However, a significant number of houses adhere to a narrow range of acceptable temperatures, thereby increasing the take-up of GSHP-AC and energy consumption. The replacement of conventional AC with alternate technologies is not a one-stop solution in, and of, itself. There is a need for improved building low energy design and construction based on a better understanding of occupant behaviour and energy consequences. POLICY RELEVANCE Although geothermal systems offer potential energy savings (especially in extreme conditions) and their potential for seamless technological replacement of conventional AC in homes, the findings suggest GSHP-AC is not a one-stop solution to reduce dependence on AC. The study reveals that the unconstrained use of GSHP-AC can increase energy consumption and squander energy savings achieved through its technological efficiency. The 'conditioned' expectations of inhabitants, stimulated by a lower tolerance of 'imperfect' conditions and availability of heating and cooling on standby, can lead to increased dependence and usage. In an increasing warming world, more stringent guidelines are needed for thermal performance and design to mitigate residual discomfort and transform occupant practices. These must also be supported with occupant education and engagement to ensure the design intent is realised.