Experimental investigation of heating performance of air source heat pump with stable heating capacity during defrosting

•An air source heat pump prototype with stable heating capacity was developed.•The defrosting process had little effect on the operation of the heat pump cycle.•The heating capacity during defrosting only decreased by approximately 20%.•By optimizing, the heating capacity decay during defrosting can be within 10%. Traditional air source heat pumps with reverse defrosting and hot gas bypass defrosting methods significantly decrease the heating capacity and even extract heat from the user side, resulting in low indoor thermal comfort. In this study, an air source heat pump prototype was developed that used multiple air source heat exchangers linked with anti-icing fluid pipelines to extract heat from the outdoor air and alternately defrost one of the air source heat exchangers by transferring a small portion of the heat from the indoors, thus achieving stable heating to the user side during defrosting. Its performance was tested in an enthalpy difference chamber, and optimization was predicted based on the test results. The results showed that under the most severe frosting condition, with an outdoor temperature of 1 °C and a relative humidity of 95%, the heating capacity decay rate to the user side during defrosting was only 20%. After optimization, the heating capacity decay rate during defrosting could reach within 10%, and the coefficient of performance under nominal operating condition (outside temperature of −2 °C, supply water temperature of 35 °C) and the heating season performance factor were 3.38 and 4.05, respectively, when used for heating the radiation floor in hot summer and cold winter regions. The principles and results provided in this study can be applied to air source heat pumps with different heating capacity requirements during defrosting.