Page 314 - Defrosting for Air Source Heat Pump

Technoeconomic performances 309

Table 10.5 Experimental results of the four defrosting cases
Item Parameters Case D1 Case D2

1 FEC 82.6% 96.6%
2 Total frost accumulation 878 g 881 g
3 Defrosting duration 205 s 185 s
4 Total power inputs to compressor and indoor air fan 124.6 kJ 107.6 kJ
5 Energy from indoor air 666.1 kJ 541.2 kJ
6 Condition shown in Fig. 10.2 (A) (B)
7 Shown in Fig. 10.4 (T1) (T2)

FEC 3 ¼82.6%. This condition was reached by fully opening the valves, and this case
works as the ASHP unit without valves installed in this economic analysis study.
Some experimental results of the two defrosting cases were listed in Table 10.5.
Their total frost accumulations were 878 and 881 g, which were nearly the same.
The frosting durations were all 60 min, but their defrosting durations were 205 and
185 s, respectively. To undertake this economic analysis work, the total power input
to compressor and indoor air fan and the thermal energy from the indoor air were also
calculated and presented.

10.2.1.2 Assumptions and calculation conditions

To economically analyze the frosting and defrosting performances of the new ASHP
unit with valves installed, four kinds of assumptions were given: (1) fundamental
assumptions, (2) frosting assumptions, (3) defrosting assumptions, and (4) cooling
assumptions. The first one was assumed for all operating seasons, and the following
three kinds for different operating seasons. Additionally, in order to clearly show the
frosting and defrosting influence on economic performance of the modified ASHP
unit, a typical severe cold city, Harbin in China, was taken as the operation location.
(1) Fundamental assumptions
In this economic analysis, the following fundamental assumptions were first given:
i. Maintenance costs of equipment were neglected.
ii. Running cost of solenoid valves was neglected.
iii. Service life of the ASHP unit was assumed at 15 years.
iv. In the whole service life of an ASHP unit, three seasons were divided: heating season with
frost formation, heating season without frost formation, and cooling season.
v. Durations of the three operating seasons were constant, and assumed as the climate of
Harbin in northeast China.
vi. Heating season was from Nov. 1 to Mar. 31, when the minimum average air temperature
o
was lower than 0 C (Shown in Fig. 10.5).
vii. Cooling season was from Jun. 1 to Jul. 31, when the maximum average air temperature
o
was higher than 26 C (Shown in Fig. 10.5).
viii. In heating season with frost formation, a frosting/defrosting cycle was assumed at 70 min.