Page 344 - Defrosting for Air Source Heat Pump

Technoeconomic performances 339

were at 1.9, 2.9, 4.5, and 7.6 years, respectively. That means that before the ASHP unit
works 8 years, more than 80% of the initial cost could be recovered. After 15 years, the
initial cost becomes only 10% of the total cost. It is also confirmed that the total cost is
mainly decided by the running cost. After the trays and valves are installed, the total
cost could significantly decrease. To clearly show the additional initial cost effect on
the total cost during operation of an ASHP unit, Fig. 10.28 shows proportions of the
additional initial cost of the total cost in the 15 operating years in three typical cases.
As shown, the curve of Case D6 was the lowest because its additional cost was the
smallest, only 15 CNY for the three water-collecting trays. Therefore, after the ASHP
unit worked 5 years, 10 years, and 15 years, the proportions of the additional initial
cost of the total cost remained very small, at only 0.409%, 0.028%, and 0.020%,
respectively. However, the line of Case D8 was always the highest because its addi-
tional initial cost was the most, 165 CNY for trays and valves. Although the propor-
tions in Cases D7 and D8 were much bigger, when the ASHP unit worked for 5 years,
the additional initial costs became less than 0.6% of the total cost. This also reflects the
dominant role of the running cost on the economic analysis of an ASHP unit. In addi-
tion, this figure shows that the additional initial cost had a minute effect on the total
cost. When the ASHP unit is changed to another one with a higher-rated power, the
running cost difference between the traditional and modified ones would be larger,
implying that more money could be saved by installing valves and trays in the mul-
ticircuit outdoor coil due to operational performance improvements and less energy
consumption after modification. Thus, the modification of the multicircuit outdoor
coil should be fully considered when designing or optimizing a bigger scale residential
ASHP unit or some commercial ones. For example, the rated heating capacity of the
ASHP unit is much higher than 6.5 kW, as used in this study.
In this study, the electricity unit price was assumed to be 0.9 CNY/kWh. Propor-
tions of the initial cost of the total cost in the 15 operating years with an electricity unit
price variation from 0.7–1.1 CNY/kWh were discussed and presented in Fig. 10.29.
As seen, the trend is decreasing as the electricity unit price increases. It is easy to
understand that the operation cost is affected by the electricity price. At the same time,
the difference of D6 and D4 is decreasing, from 0.83% with the unit price at 0.7 CNY/
kWh to 0.59% with the unit price at 1.1 CNY/kWh. That means that as the electricity
unit price increases, the additional initial cost effect on the total cost becomes smaller.
If the electricity unit price decreases, we should also consider this modification for two
reasons: (1) more energy could be saved with a higher-rated power ASHP unit. These
running costs are much higher than that of the investment of modification; and (2) the
environmental factor, as more energy saved leads to reducing environmental pollu-
tion. It is well known that environmental problems have a big negative influence
on our life and society. Therefore, modifications should be fully considered no matter
whether the unit price of electricity decreases or increases. This also demonstrated the
fundamental meaning of this study.
In this section, a technoeconomic analysis study on frosting/defrosting operations
for an optimized ASHP unit, with trays and/or valves installed with its outdoor coil,
was conducted and the results are reported. After the water-collecting trays and/or val-
ves were installed, the economic performances of an ASHP unit were effectively