Optimizing the selection and combined operation of multiple air-source heat pumps for sustainable heating systems

A common concern is that air-source heat pumps (ASHP) perform poorly when operating at partial load. This issue arises due to the disparity between the unit's heating capacity and the actual heating load of the building. This work introduces a new, generally applicable method to determine the optimal combination of air-source heat pump units and provides an optimum unit selection scheme. It proposes two definitions: the average unit load rate throughout heating season (ALR) and the comprehensive nominal heating capacity throughout heating season (Qoa), and develops a formula to intuitively demonstrate how different unit selection schemes affect the ASHPs' performance on an annual basis. The results of the final calculations demonstrate that the best performance is achieved by selecting five units with varying nominal heating capacity. Compared to conventional selection schemes with the identical units for their nominal heating capacity, the average unit load rate throughout entire heating season rises from 81% to more than 95%, and the yearly average coefficient of performance (COP) rises by 6%.