Page 319 - Defrosting for Air Source Heat Pump

314 Defrosting for Air Source Heat Pump

As assumed, it was 15 years. In addition, the duration of the heating season with frost
formation in a year, T FDH, and the times of the frosting operations in a day, T OT, were
assumed at 60 days and 10 times, respectively. T DC was the duration of a frosting/
defrosting cycle.
In Eq. (10.4), C r, id, fan and C r,od, fan were the running costs of the indoor and out-
door air fans, which could be calculated by,

(10.7)
C r,id, fan ¼ C e,unit P id, fan T Y T FDH T OT T DF
(10.8)
C r,od, fan ¼ C e,unit P od, fan T Y T FDH T OT T DF
During frosting operation of the ASHP unit, the frost accumulated on the surface of the
outdoor coil, which would adversely affect the capacity of outdoor air fan [2,3]. There-
fore, the running cost of outdoor air fan was also calculated by the following equation,

C r,od, fan ¼ C e,unit P ave,od, fan T Y T FDH T OT T DF (10.9)

where P ave, od, fan was the average capacity of the outdoor air fan during frosting,
which could be tested in the experimental study.
Then, using Eqs. (10.5)–(10.7) and (10.9), the total electricity cost at the frosting
operation was,

(10.10)
C r,F ¼ C e,unit P f + P id, fan + P ave,od, fan T Y T FDH T OT T DF
C r, F was also calculated by,

Q id,air,F
C r,F ¼ (10.11)
COP F
where Q id, air, F was the energy supplied to the indoor air at the frosting operation, or
the rated heating capacity, at 6.5 kW, listed in Table 10.1. COP F was the COP at the
relative FEC, which could be calculated at Section 10.2.1.2.
Further, in Eq. (10.4), the electricity cost at the defrosting operation, C r, DF , cov-
ered the running costs of the compressor and indoor air fan. It was,

C r,DF ¼ C r,comp,DF + C r,id, fan,DF (10.12)

Different from the C r, comp, f in Eq. (10.5), the running cost of the compressor during
defrosting, C r, comp, DF , was evaluated by,

C r,comp,DF ¼ C e,unit P DF T Y T FDH T OT T DD (10.13)

where the defrosting power consumption of the compressor, P DF , and the duration of
defrosting in a cycle, T DD , were changing at the working conditions, and calculated
during experiments.