Page 242 - Defrosting for Air Source Heat Pump

Energy transfer during defrosting 237

10
Circuit 1 in Case 1
Circuit 2 in Case 1
9
Circuit 1 in Case 2
Circuit 2 in Case 2
8
Temperature of ambient air ( o C) 7 6 5 4
Circuit 3 in Case 2

2 3
110 120 130 140 150 160 170 180 190 200 210
Time (s)
Fig. 8.11 Temperature variations of ambient air around each circuit of the outdoor coil.

900
Thermal energy of indoor air
800 MES of indoor coil
Input to indoor air fan
Input to compressor
700
Energy from system outside (kJ) 500 77.94% 80.10%
600

400
300
200
0.82%
100 6.04% 4.50%
0.40%
15.61% 14.58%
0
Case 1 Case 2
Fig. 8.12 Heat supplies during defrosting in the two cases.

The data in Case 2 were always lower than that in Case 1. It looks contradictory
because the total frost accumulated in Case 1 was much more than that in Case 2,
as listed in Table 8.5. However, it mainly resulted from the higher frost density in Case
1, which increased the energy-taken rate during defrosting. More power input to the
compressor was transferred by the refrigerant to the frost via the tube and fins of the
outdoor coil. In addition, the energy input to the compressor was kept small, at lower