Page 354 - Defrosting for Air Source Heat Pump

350 Appendices

Appendix D: Frosting evenness coefficient

A frosting evenness coefficient (FEC) was used to clearly describe the uneven
defrosting that results when the frost accumulations on the surface of each circuit
are different. It was defined as the ratio of the minimum frost accumulation among
all circuits to the maximum one. In this study, the frost accumulations could be cal-
culated by the melted frost collected from each water-collecting cylinder, with the
water vaporized into the ambient air neglected. For example, as shown in Fig. D.1,
the masses of frost accumulation on the three circuits’ surface are FA1, FA2, and
FA3, respectively. When FA1 ¼ FA2 ¼ FA3, the FEC is 100%, and thus this is even
frosting. If no FA1 ¼ FA2 ¼ FA3, the FEC is not 100%, and that is uneven frosting.
When FA1> FA2> FA3, FEC is the ratio of FA3 to FA1, which is less than 100%.

Fig. D.1 Frost accumulations on the
three circuits’ surface. FA1 Circuit 1 Refrigerant exit (liquid)

FA2
Refrigerant entrance (vapor) FA3 Circuit 2 Water collecting tray

Circuit 3