Influence of control strategy on the energetic performance of an air source heat pump coupled with a solar air collector for domestic hot water in a cold climate

Air source heat pumps (ASHPs) are becoming famous for heating applications, particularly in regions with moderate climatic conditions. However, in colder climates, their efficiency and capacity are reduced significantly and require high auxiliary heating loads. As such, coupling ASHPs with solar energy and energy storage is receiving considerable interest. This study investigates the performance of a solar-assisted air source heat pump for domestic hot water in an extremely cold climate. The operation of the air source heat pump (ASHP) is controlled based on the outdoor temperature and solar radiation. The rated capacity of the ASHP is 2 tons, while the rated minimum outdoor air temperature is −25°C. Since the heat pump capacity reduces at temperatures lower than −10°C, the potential improvement in performance when coupled with an SAC for a lower threshold of ambient temperatures between −10 and −25°C is evaluated. The designed control strategy also includes a lower threshold of solar radiation intensity, i.e. ≥300 W/m2 or ≥200 W/m2 or ≥100 W/m2 or ≥0 W/m2. In addition, the study explores the effect of recirculating air in the SAC on the overall heat pump performance. Results show that the coefficient of performance (COP) of the ASHP increases by 18%, and the heat pump fraction (HPF) is 94% when the heat pump is controlled to work for solar intensities greater than or equal to 300 W/m2 and outdoor temperatures greater than or equal to −25°C. With the same limits, energy savings of 20% are realized. Moreover, the performance improves by 24% when air is recirculated in the SAC at the same conditions. This comprehensive analysis highlights the potential of the control strategy and air recirculation in ASHPs coupled with solar air collectors in cold climates.