Page 72 - Defrosting for Air Source Heat Pump

Uneven defrosting on the outdoor coil in an ASHP 63

Fig. 3.14 Measured tube surface temperatures at the exits of refrigerant circuits in Case 2.

Fig. 3.15 Measured tube surface temperatures at the exits of refrigerant circuits in Case 3.

100 s into the defrosting operation, and thereafter, the tube surface temperatures
increased steadily from 0°Cto24°C. The tube surface temperatures of the three cir-
cuits reached 24°C at 172, 182, and 186, respectively. In Case 2, as shown in Fig. 3.14,
the time for the surface temperature at the exit of the two up-circuits to reach 24°C was
nearly the same at 174 s, and that for Circuit 3 was a little longer at 180 s. However, as
shown in Fig. 3.15, in Case 3, the surface temperatures at the exits of the three circuits