Page 64 - Defrosting for Air Source Heat Pump

Uneven defrosting on the outdoor coil in an ASHP 55

Fig. 3.8 Measured tube surface temperature at the exits of refrigerant circuits in Case 2.

Fig. 3.9 Measured fin surface temperatures at the center of refrigerant circuits in Case 2.

longer for the lower circuit to reach 24°C, so that a defrosting operating was prolonged
and more energy was consumed.
Fig. 3.6 shows the variations of the measured surface temperatures of the fin at the
center point of each circuit. Unlike tube surface temperatures, fin surface temperatures
remained at 0°C during the first 90 s into defrosting. The rise in fin temperature was
later than that in tube surface temperature for 30 s. This was because the tube was in