Investigation on the efficiency degradation characterization of low ambient temperature air source heat pump under partial load operation

The heating capacity of air source heat pump increases with the increase of ambient temperature, coupled with the heating demand decreases, resulting in a prolonged partial load operation. The partial load operation of low ambient temperature air source heat pumps applied in cold region is particularly serious. With that also comes an efficiency degradation, taking into consideration that the characterization method of current product standards is not uniform in different countries. In this paper, the mechanism of partial load efficiency degradation was analyzed firstly, the explicit relationship between cycling losses and cyclic time was derived, and a partial load factor characterization method of air source heat pump by coupling start-up loss and stand-by loss was proposed. Secondly, the cycling losses of 3 sets of low ambient temperature ASHPs with different configurations were tested under different ambient conditions by using the intermittent ON-OFF cycles tests method. The magnitude of start-up loss is 2.0%∼17.3% for test ASHPs, and the stand-by loss rises sharply from 4.2 to 8.9% for the test ASHPs as the PLR drops from 0.2 to 0.1. The accuracy of the PLF characterization method was verified, and especially that of the load rate below 0.2 was improved.