Page 253 - Defrosting for Air Source Heat Pump

248 Defrosting for Air Source Heat Pump

16
o
14.0 C
14 Case 1 13.8 C
Measured air temperature difference ( o C) 10 8 6 4
o
12
Case 2

2

0
0 20 40 60 80 100 135 s 140 140 s 180 200
120
160
Time (s)
Fig. 8.19 Measured air temperature differences between the inlet and outlet of the indoor coil.

Fig. 8.20 Energy input to the compressor during defrosting in the two cases.

The data in Case 2 were always lower than those in Case 1. It looks contradictory
because the total frost that accumulated in Case 1 was much more than that in Case
2, as listed in Table 8.8. However, it mainly resulted from the higher frost density in
Case 1, which increased the energy taken rate during defrosting. In addition, the
energy input to the compressor was kept small, at lower 3.0 kJ, at 0–86 s in Case 1
and 0–100 s in Case 2. It is demonstrated that at the start of defrosting, little energy