Page 220 - Defrosting for Air Source Heat Pump

214 Defrosting for Air Source Heat Pump

45
o
T = 43.2 C Case 1
40 1, max o
T = 40.9 C Case 2
2, max
35
Temperature difference ( o C) 25 T > T 2
30
20
1
15
10
5
25 s
0
30 s
–5
0 25 50 75 100 125 150 175 200
Time (s)
Fig. 7.19 Temperature difference of the indoor coil at the entrance and exit during defrosting.

improved by evenly adjusting the refrigerant distributed into each circuit for an ASHP
unit, with MFDF along the surface of its multicircuit outdoor coil.
Fig. 7.20 presents the measured refrigerant volumetric flow rate during RCD in two
experimental cases. As shown, the compressor discharge pressure suddenly increased
at the start of the defrosting operation. First, the internal diameter of the electronic
expansion valve (EEV) was very small. Second, the system operation at the frost

1.6
Case 1 Case 2
1.4
Refrigerant volumetric flow rate (L / min) 1.0
1.2

0.8
0.6

0.4
0.2
2
160 s
0.0 Fluctuation 74 s R > R 1 152 s Fluctuation
0 20 40 60 80 100 120 140 160 180 200
Time (s)
Fig. 7.20 Measured refrigerant volumetric flow rate during defrosting in two cases.