Could residential air-source heat pumps exacerbate outdoor summer overheating and winter overcooling in UK 2050s climate scenarios?

The UK government promotes heat pumps to replace gas boilers in the residential sector as a vital part of its strategy to achieve Net Zero by 2050. As climate change intensifies, heat pumps, traditionally used for heating, will also play a role in cooling to address indoor heat risks that threaten public health and increase energy demands. However, air-source heat pumps (ASHPs) might unintentionally exacerbate summer overheating and winter overcooling in residential neighbourhoods. This study uses a multi-scale modelling approach, combining SUEWS and EnergyPlus, to assess the impact of ASHPs on outdoor temperature in two idealised UK low-rise residential neighbourhoods under 2050s climate scenarios. Results show that in summer, ASHPs increase median anthropogenic heat emission by up to 19.3 W m^-2 and raise local median 2 m air temperature by up to 0.12 °C in an idealised London neighbourhood. In winter, replacing gas boilers with ASHPs for heating reduces anthropogenic heat emissions by up to 11.1 W m^-2 and lowers local air temperatures by up to 0.16 °C in London. The research shows that conventional waste heat calculations from air-conditioning can overestimate anthropogenic heat emissions by up to 86 %, and cooling entire building rather than just occupied rooms can increase energy consumption by 68 %. Although temperature changes will vary across UK cities, the response of air temperature to anthropogenic heat change is generally consistent. The study enhances understanding of role of ASHPs in the UK's net zero target for 2050, highlighting the importance of balancing outdoor and indoor thermal comfort when considering the wide use of ASHPs.