Page 282 - Defrosting for Air Source Heat Pump

276 Defrosting for Air Source Heat Pump

1A 2A 3A 4A 5A

1B 2B 3B 4B 5B

1C 2C 3C 4C 5C

1D 2D 3D 4D 5D
Fig. 9.18 Outdoor coil airside surface conditions during defrosting in the five cases. (1A)
FEC ¼ 93.6% in Case 1, (2A) FEC ¼ 95.6% in Case 2, (3A) FEC ¼ 96.6% in Case 3, (4A) FEC
¼ 93.8% in Case 4, (5A) FEC ¼ 97.5% in Case 5; (1B) 15 s in Case 1, (2B) 15 s in Case 2, (3B)
15 s in Case 3, (4B) 15 s in Case 4, (5B) 15 s in Case 5; (1C) 35 s in Case 1, (2C) 40 s in Case 2,
(3C) 45 s in Case 3, (4C) 64 s in Case 4, (5C) 96 s in Case 5; (1D) 86 s in Case 1, (2D) 93 s in
Case 2, (3D) 95 s in Case 3, (4D) 112 s in Case 4, (5D) 114 s in Case 5.

collected were 805 g in Case 1, 933 g in Case 2, 969 g in Case 3, 1001 g in Case 4, and
1074 g in Case 5, respectively. These experimental results are summarized in
Tables 9.3 and 9.4. It could be demonstrated that the frost accumulation is not propor-
tional to the frosting duration. This also reflects the inaccuracy of a time-based initi-
ation defrosting control strategy. Therefore, experimentally investigating the frost
accumulation influence on RCD performance for an ASHP unit is meaningful.
Fig. 9.19 shows the measured tube surface temperature at the exit of each circuit
and their average values during defrosting in the five cases. It could be found that from