Performances of air source heat pump system for a kind of mal-defrost phenomenon appearing in moderate climate conditions

Developing a new frosting map to guide defrosting control for air-source heat pump units

“…1 2 Fig. 1 Frosting maps developed in two previous studies 3 4 Wang and Chen [17] also proposed a frosting map using simulation results, as shown 5 in Fig. 1 b).…”

“…According to the field test results [15], nearly 68 % of defrosting 4 was unnecessary in a heating season in Beijing, China. For a T-T controlled ASHP 5 unit, mal-defrost mainly resulted from the fact that one important parameter, air 6 humidity, was not taken into account. Both air temperature and humidity affect 7 frosting in an ASHP unit.…”

“…According to Sanders [4], the heating capacity of an ASHP unit 9 can be deteriorated by 35 % under frosting conditions. In the previous studies by 10 Wang et al [5], the heating capacity of an ASHP unit was decreased by 29 % to 57 % 11 when its outdoor heat exchanger was covered by frost. Frosting not only increased the 12 heat transfer resistance and reduced coil's efficiency [6], but could also lead to the 13 shutdown of an ASHP unit [7].…”

“…It serves as a heating and cooling source 4 in many parts of the world [1,2]. However, for an ASHP unit, when its outdoor heat 5 exchanger surface temperature is below both air dew point and freezing point of water, 6 frost will form on the outdoor heat exchanger surface. The experimental results [3] 7 indicated that a frost layer on an outdoor heat exchanger surface can reduce its heat 8 flux by about 40 %.…”

A modeling study on alleviating uneven defrosting for a vertical three-circuit outdoor coil in an air source heat pump unit during reverse cycle defrosting

“…One obvious advantage for using a heat pump unit is that it can provide heating or cooling from one single machine without any major modification [1]. Air source heat pump (ASHP) units used as cooling or heating source for building heating, ventilating and air conditioning installations have been increasingly and widely applied over the recent decades in many parts of the world [2,3]. However, when an ASHP unit operates at a low temperature and high humidity environment, frost can be formed and accumulated over the surface of its outdoor coil [4,5].…”