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

Frosting Phenomenon and Frost-Free Technology of Outdoor Air Heat Exchanger for an Air-Source Heat Pump System in China: An Analysis and Review

“…Furthermore, Wang and Chen [70] developed a frosting map for the ASHP system using simulation data at an air velocity of 2 m/s (va), and the result is shown in Figure 7. As we can see, this frosting map includes three zones: a non-frosting zone (I), a condensing zone (II) and a frosting zone (III) [63]. The frosting zone III was confined between Ta of −10 °C and 8 °C and between RH of 63% and 100%.…”

“…To obtain accurately and comprehensively the conditions of various frosting pathways, developing a frosting map for the ASHP system is recommended by some scholars. According to the study of Zhu et al [63], when developing the frosting map, it was necessary to do some reasonable assumptions. For example, (1) air cleanliness and the wettability of the surface of air heat exchanger were not included because these parameters were not easily quantified; (2) a constant air flow velocity ranging from 1.5 to 3.5 m/s was set at the inlet of air heat exchanger; (3) the refrigerant mass flow rate was evenly distributed to each circuit; (4) the speed of the compressor was a constant value [63].…”

“…It is well known that frosting is a transient phenomenon along with heat and mass transfer process. This phenomenon is mainly influenced by the parameters as follows: temperature and wettability on the surface of an air heat exchanger, velocity of the inlet air, relative humidity of the inlet air (RH), inlet air cleanliness and temperature (T a ) [62,63]. To obtain accurately and comprehensively the conditions of various frosting pathways, developing a frosting map for the ASHP system is recommended by some scholars.…”

“…The frosting zone III was confined between Ta of −10 °C and 8 °C and between RH of 63% and 100%. According to different frosting rates (Wm), this region III was further divided into five regions to present more details [63]. In conclusion, the range of frosting map depends fundamentally on the air temperature and RH at the inlet of the outdoor air heat exchanger in the ASHP system.…”

Sizing effects on the energy performance of reversible air-source heat pumps for office buildings

“…To evaluate the effect of defrosting cycles during the heating season, the percentage of the heating season in which the outdoor conditions fall within the frosting region [19] (i.e. air temperature below 6°C and relative humidity above 50%), is shown in Table 2 for each location.…”