Evaluating the energy and micro-climatic effects of large-scale air-source heat pump adoption through urban-resolving Earth system modeling

Air source heat pumps (ASHPs) are an effective measure to building electrification and decarbonization. In heating mode, ASHPs take in heat from the outdoor air to heat the indoors. Wide adoption of ASHPs may then lower urban air temperature and in turn increase heating demand. This positive feedback loop will not only exacerbate cold temperatures, but also lead to higher-than-expected heating energy use through increased heating load (i.e., larger temperature differences between indoors and outdoors) and reduced ASHP efficiencies (which decreases with decreasing temperature). Dynamic modeling of ASHP energy use and the urban climate is therefore needed for comprehensive assessments of ASHP as a climate mitigation strategy and more accurate energy demand projections. Here, we develop an ASHP modeling scheme in the physics-based urban building energy model of Community Earth System Model (CESM2). We explicitly model urban energy balance accounting for the heat removed from urban canyon for indoor heating, and the temperature dependence of ASHPs’ Coefficient of Performance (COP). We focus our analysis on the United States (US) and United Kingdom (UK), two countries with policy incentives to significantly increase ASHP adoption in the coming decades. Preliminary results show comparing with fossil-fuel-based heating, idealized (100%) ASHP adoption reduces winter air temperature by up to 1.0 K and 0.3 K in the US and UK, respectively. This temperature reduction results in an increase of up to 2% in heating load for both countries. Although lower temperatures penalize ASHP efficiency, the primary energy consumption of ASHP is still much lower than fossil-fuel-based heating, highlighting the climate mitigation benefits of ASHP. Under a high-emission scenario, both the urban temperature and the COP penalties are alleviated in the future. Challenges remain in preparing the electricity grid for increased winter demand and improving ASHPs’ cold temperature performance to meet indoor comfort.