Page 70 - Defrosting for Air Source Heat Pump

Uneven defrosting on the outdoor coil in an ASHP 61

Fig. 3.12 Airside surface conditions of the outdoor coil during defrosting in three cases.
(A1) 0 s; (A2) 100 s; (A3) 130 s; (A4) 150 s; (B1) 0 s; (B2) 100 s; (B3) 130 s; (B4) 150 s;
(C1) 0 s; (C2) 100 s; (C3) 130 s; (C4) 150 s.

As observed from Fig. 3.12A1, B1, and C1, the surface conditions at the start of
defrosting for the three cases were virtually the same. From Fig. 3.12A2, B2, and
C2, it can be seen that frost melting started 100 s into defrosting, and no melted frost
flowing downward may be observed at this stage. Furthermore, as seen from
Fig. 3.12A3, at 130 s into the defrosting operation in Case 1, the frost melting on
the surface of Circuit 1 was quicker than that on the surface of Circuit 2 while the
melted frost flowed downward from Circuit 1 to Circuit 2. On the other hand, the frost
melting on the surface of Circuit 3 was later than that on the surface of Circuit 2
because the melting frost flowing downward to Circuit 3 was more than that to
Circuit 2. However, as seen from Fig. 3.12B3 for Case 2 and C3 for Case 3, the state