Frost suppression performance of an air source heat pump using sensible heat from indoor air to preheat outdoor air

Frost forms on the surfaces of air source heat pump (ASHP) outdoor heat exchangers under heating mode in winter, when the surface temperature of the heat exchanger is lower than both 0°C and the ambient dew point temperature. This can reduce the coefficient of performance (COP) and heating capacity of the ASHP unit. A novel ASHP was examined using two rooms with the same size, orientation, and structure. To test the frost suppression performance of the novel system, two ASHPs of the same size and specifications, but one including a sensible-heat preheating device, were placed in the test platform rooms. By comparing and analyzing field-measured parameters such as COP, heat loss, and frost weight of the two ASHP units, the frost suppression performance of the novel ASHP was evaluated in severe, moderate, and mild frost areas. The results show that when the air conditions were −3.9°C and 98.7% in the moderate frost area and 3.2°C and 96.7% in the severe frost area, the novel ASHP showed significantly improved performance. The frost formation time increased from 25 min to 38.5 min, frost-defrost heat loss decreased by 31.6%–43.7%, frost weight decreased 11.8%–17.4%, and COP increased 7.4%–13.1% compared with those of the conventional ASHP. In the low temperature and mild frost area, when the air temperature was −11.8°C and the relative humidity was 88.8%, the frost suppression effect of the novel ASHP was unapparent.