Page 198 - Defrosting for Air Source Heat Pump

192 Defrosting for Air Source Heat Pump

should be further studied. At the same time, the relationship between the FEC and
defrosting performance evaluating indexes could be further analyzed. Second,
when the FEC was calculated, the order of frost mass accumulation on the three cir-
cuits was not fixed. For example, the frost accumulation order in Section 6.3 was at
Circuit 2 > Circuit 1 > Circuit 3 in Case 1, but at Circuit 2 > Circuit 3 > Circuit 1 in
Case 2. Due to the negative effects of the downward flow of melted frost, the
defrosting performance would be different for the two cases with the same FEC
but different frost accumulation mass orders. Therefore, further studies should be car-
ried out considering the frost accumulation mass order. Third, for an ASHP unit, its
frosting duration is much longer than its defrosting duration. The FEC effects on a
frosting-defrosting cycle should be further analyzed before the installation of valves
in each circuit of the outdoor coil was considered in application. Fourth, uneven refrig-
erant distribution may also result in uneven defrosting. Further experimental investi-
gation on the effects of uneven refrigerant distribution during defrosting in an ASHP
unit with a multicircuit outdoor coil should be carried out.

References

[1] Wang W, Feng YC, Zhu JH, Guo QC, Lu WP. Performances of air source heat pump system
for a kind of mal-defrost phenomenon appearing in moderate climate conditions. Appl
Energy 2013;112:1138–45.
[2] Steiner A, Rieberer R. Parametric analysis of the defrosting process of a reversible heat
pump system for electric vehicles. Appl Therm Eng 2013;61:393–400.
[3] Yao Y, Jiang YQ, Deng SM, Ma ZL. A study on the performance on the airside heat
exchanger under frosting in air-source heat pump water heater/chiller unit. Int J Heat Mass
Transf 2004;47(17–18):3745–56.
[4] Seker D, Kartas H, Egrican N. Frost formation on fin-and-tube heat exchanges, Part I:
modeling of frost formation on fin-and-tube heat exchangers. Int J Refrig 2004;27(4):
367–74.