A prediction model of air-source heat pump system performance with frost-retarded heater

When the air-source heat pump (ASHP) works to provide heating in winter, frost will form on the surface of the heat exchanger as an evaporator in the outdoor unit. The auxiliary electric heater installed upstream of the evaporator is effective in retarding frost growth and extending heating duration, thus conducive to thermal comfort improvement. A prediction model of the ASHP system performance with a frost-retarded heater is presented here. The frosting is embedded into the evaporator sub -model, and the electric heater is included in the system modeling. The model is capable of revealing dynamic variation of system parameters as well as the temporal and spatial distribution of the frost layer. The deviations are within 5% validated with the experiments. Based on the model, the effects of heater power and ambient conditions, including outdoor air temperature, humidity, and initial air velocity, are quantitatively analyzed. Results show that 560 W heater power can retard the frost growth rate by 11.5% and extend the heating duration by 16.2%.