Research on anti-frosting potential of air source heat pump evaporator in hot-summer and cold-winter zone

Abstract

In this paper, the performance curve of a heat pump evaporator under critical frosting conditions was fitted. The functional relationship between the refrigerant evaporation temperature and the absolute air humidity ratio was obtained. In addition, the transfer unit model of the air source heat pump (ASHP) evaporator was established. The inlet air temperature, humidity ratio, velocity, fin pitch, and row number of evaporators were considered as input parameters. The anti-frosting potential of the heat transfer unit was simulated under critical frosting conditions. The results showed that, based on the heating potential of moist air unit mass under critical frosting conditions, the heating potential is at its minimum at an air humidity ratio of 3.39 g/kga. The maximum difference between the minimum temperature on the fin surface and the refrigerant evaporation temperature was found to be only 0.06 °C. The study findings highlighted that controlling the refrigerant evaporation temperature above the critical frosting temperature is an important method to prevent the evaporator from frosting. Under a low temperature environment, with the increase in the fin pitch and the inlet air velocity, the anti-frosting regulation performance of the two tube rows evaporator was found to improve compared to the single tube case. The aim behind increasing the inlet air velocity is to increase the heat transfer temperature difference between the inlet air and the critical frosting conditions. After optimizing the evaporator’s structural and operational parameters, the evaporator’s fin pitch is set according to the ambient air temperature. This was successful in meeting the requirement that the evaporator does not frost most of the time. Moreover, by adjusting the inlet air velocity, the evaporator will not frost at other times. In hot-summer and cold-winter zone, the operation of the ASHP evaporator with no frost can be achieved.