Page 315 - Defrosting for Air Source Heat Pump

310 Defrosting for Air Source Heat Pump

40
Maximum Average Minimum
30 26°C
Air mean temperature (°C) 10 0 0°C
20

–10

–20 Heating season Cooling season Heating season

–30
1 2 3 4 5 6 7 8 9 10 11 12
A typical year (month)
Fig. 10.5 Duration of heating season and cooling season at Harbin [19].

ix. In a frosting/defrosting cycle, frosting duration was fixed at 60 min., and the defrosting
durations of the four typical cases were constant.
x. In a frosting/defrosting cycle, two periods of 3–4 min for compressor shutdown were left
for safety.
xi. At each stage, the system COP and defrosting efficiency were constant.
xii. All ambient air parameters, such as air temperature and relative humidity, were constant at
fixed operating seasons.
xiii. The unit price of electricity for residential use was assumed at 0.9 CNY/kWh.
xiv. For the case without valves installed, the FEC was fixed at 75.7%.
xv. For the case with valves installed, the FEC was fixed at 96.6%.

(2) Frosting assumptions
In order to calculate the running cost of the ASHP unit at the frosting stage, the system
COP and indoor heat supplied should be obtained. Therefore, the following assump-
tions were further given.
i. Durations of heating season with frost formation and heating season without frost forma-
tion were both assumed at 60 days in a year.
ii. In heating season with frost formation, 15 operating cycles were assumed in a day.
iii. In heating season without frost formation, the duration of frosting operation was assumed
at 12 h in a day.
iv. When the ASHP unit works at the heating season with frost formation, the system COP was
assumed at the value of COP in 60 min.
v. When the ASHP unit works at the heating season without frost formation, the system COP
was assumed at the value of COP in the first 10 min.