Page 215 - Defrosting for Air Source Heat Pump

The influence of refrigerant distribution on defrosting 209

from Figs. 7.11A and B, the surface conditions at the start of defrosting for each circuit
in the two cases were virtually the same, which agreed well with the data listed in
Table 7.5. Therefore, a similar mass of frost accumulation, frost accumulated at
the same FECs, both higher than 90%. Obviously, different RDEVs make this com-
parative study meaningful.
Figs. 7.12–7.15 show the measured tube surface temperatures at the exits of the
three refrigerant circuits and the measured fin surface temperatures at the centers

28
Circuit 1 Circuit 2 Circuit 3
24 T > T > T 3

Tube surface temperature ( o C) 16 T > T ; T > T 3
2
1
20
1
2
2
12

4 8
181 s 185 s
0
80 100 120 140 160 180 200
Time (s)

Fig. 7.12 Measured tube surface temperatures during defrosting in Case 1.

28
Circuit 1 Circuit 2 Circuit 3
24
Tube surface temperature ( o C) 16 T > T >T 1 T 2 1 >T 3
20

3
2
12

4 8 121 s 170 s
155 s 173 s
0
80 100 120 140 160 180 200
Time (s)
Fig. 7.13 Measured tube surface temperatures during defrosting in Case 2.