Page 169 - Defrosting for Air Source Heat Pump

Frosting evenness coefficient 163

0
Fin in Case 1 Fin in Case 2
–2

–4
Fin surface temperature ( o C) –10
–6

–8

–12
–14

–16
0 500 1000 1500 2000 2500 3000 3500 4000
Time (s)

Fig. 6.12 Measured average fin surface temperatures at the center of the three circuits during
frosting in the two cases.

4.8
Case 1 Case 2

4.4

4.0
COP (/) 3.6

3.2

2.8
0 500 1000 1500 2000 2500 3000 3500 4000
Time (s)
Fig. 6.13 COP variation of the ASHP unit during frosting in the two cases.

pressure drop increased. This resulted from the heat transfer between the ambient air
and the refrigerant becoming hard as frost accumulated on the surface of the outdoor
coil. And this agrees well with the temperature decrease of the refrigerant, as shown in
Figs. 6.6 and Figs. 6.7. Due to the higher FEC in Case 2 than that in Case 1, the trends
of increasing and decreasing in Case 1 were bigger than those in Case 2.