Page 116 - Defrosting for Air Source Heat Pump

108 Defrosting for Air Source Heat Pump

28
Circuit 1 Circuit 2 Circuit 3
24
Tube surface temperature at exit ( o C) 16 8 T > T > T 3 187 s 1
20

T was decreasing.
2
1
12

172 s
0 4 95 s 179 s
80 100 120 140 160 180 200
Time (s)
Fig. 4.27 Predicted tube surface temperatures at circuit exits during defrosting in Study Case 3.

C1 C2 C3
Experimental study
170 s 175 s 180 s 185 s 190 s
Δt = 14 s
C1,C2 C3
Study Case 1
170 s 175 s 180 s 185 s 190 s
Δt = 5 s
Δdt = 3 s
C1 C2 C3
Study Case 2
170 s 175 s 180 s 185 s 190 s
Δt = 7 s
Δdt = 7 s
C1 C2 C3
Study Case 3
170 s 175 s 180 s 185 s 190 s
Δt = 14 s
Δdt = –1 s
Fig. 4.28 Analysis on durations for the previous experimental study and the three study cases.

4.3.3 Analysis on heat supply and energy consumption
For an ASHP unit, during RCD, the energy is used to heat the outdoor coil metal, melt
frost, heat the melted frost, heat the cold ambient air, and evaporate the retained water
on the surface of the outdoor coil. In this section, the total energy use for defrosting
was also evaluated for the three study cases, 715.9 kJ for Case 1, 693.2 kJ for Case 2,