Page 318 - Defrosting for Air Source Heat Pump

Technoeconomic performances 313

Stage 1: Heating season with frost formation Stage 2: Heating season without frost formation
Part 1: Frosting period • Compressor electricity consumption
• Compressor electricity consumption • Indoor air fan electricity consumption
• Indoor air fan electricity consumption • Outdoor air fan electricity consumption
• Outdoor air fan electricity consumption
Stage 3: Cooling season
Part 2: Defrosting period
• Compressor electricity consumption • Compressor electricity consumption
• Indoor air fan electricity consumption • Indoor air fan electricity consumption
• Indoor thermal energy consumption • Outdoor air fan electricity consumption

Fig. 10.6 Running costs of ASHP unit in three seasons in a year.

of the ASHP unit. Therefore, the total first costs in the two cases were 8000 CNY in
Case D3 and 8165 CNY ($1224) in Case D4, respectively.
(2) Running cost
As shown in Fig. 10.6, the running costs of the ASHP unit in a year were calculated in
three seasons. At Stage 1, the running cost contains the frosting period and the
defrosting period. At the first period and Stages 2 and 3, the running costs came from
electricity consumption on the compressor and the indoor and outdoor air fans. At the
second period, the outdoor air fan was turned off. However, indoor thermal energy
would be consumed during defrosting, which came from the ambient air during the
frosting operation. Therefore, the corresponding electricity cost of indoor thermal
energy consumption was contained.

Stage 1: Heating season with frost formation
At this stage, the total running cost, C r, FDH , includes three parts of the electricity cost:
(1) electricity cost at the frosting operation, C r, F , (2) electricity cost at the defrosting
operation, C r, DF , and (3) corresponding electricity cost of indoor thermal energy con-
sumption during the defrosting operation, C r, ITE, DF . This could be expressed as:

(10.4)
C r,FDH ¼ C r,F + C r,DF + C r,ITE,DF
where the electricity cost at the frosting operation could be obtained by,

C r,F ¼ C r,comp,F + C r,id, fan,F + C r,od, fan,F (10.5)

here, C r, comp, F was the running cost of the compressor at the frosting operation:

(10.6)
C r,com,F ¼ C e,unit P F T Y T FDH T OT T DF
C e, unit was the unit price of electricity. P F was the heating capacity of the ASHP unit at
the frosting operation, which could be tested in the experiment. In this study, the rated
heating power consumption was 1840 kW, as listed in Table 10.1. T Y was the service
life of an ASHP unit, which is dominated by the level of maintenance work.