Page 328 - Defrosting for Air Source Heat Pump

Technoeconomic performances 323

the valves were installed. Therefore, the valve effect on cooling operation perfor-
mance should be further studied.
Fig. 10.11 shows the total costs in the two cases in the 15 operating years. As the
fundamental assumptions show, the total costs kept increasing in line. As shown in
Fig. 10.11, after 1 operating year, the running cost relationship of the two cases
was at D3>D4. That means the payback of the first cost is less than 1 year. When
the system operations were 5, 10, and 15 years, the total costs in the two cases were
31,156.43 CNY and 29,530.42 CNY, 54,312.86 CNY and 50,910.84 CNY, and
77,469.29 CNY and 71,747.93 CNY, respectively. Their differences and ratios in
the values of Case D3 were $243.85 and 5.22%, $510.19 and 6.26%, and $776.54
and 6.68%, respectively. Clearly, their differences and ratios were both increasing
with the operation duration.
However, in practical application, the maintenance costs increased the total run-
ning cost, which was assumed to be about 10% of the total first cost per year added.
Also, the operating performances of the ASHP unit would decrease as time goes by,
which was also assumed at a 10% per year range. The practical total costs’ curves in
the two cases were also shown in Fig. 10.11, using dash lines. Clearly, the difference
between the two cases would be increased a lot as time goes by. This figure plays an
important role in the budget guiding work of equipment procurement. To clearly show
the difference of total costs in the two cases and its change as time progresses, the ratio
of the difference was calculated and shown in Fig. 10.12. This value was the ratio of
the total cost difference in the two cases and the system operating duration. As shown,
at the first 5 years, the ratio was increasing rapidly. The difference between years 1 and
5 was about 120.00. At the second five operating years, the difference became to about
15.00. The curve kept increasing slowly. However, the difference was only 5.00 at the
third 5 operating years. The ratio was nearly not increased. That means that the valves
effects on the total cost were mainly shown at the first 5 years. When an ASHP unit
worked after 10 years, the total cost still saved a lot after the ASHP unit had installed
valves. However, the effects on economic performance were not as obvious as the
first years.
Fig. 10.13 shows the proportion of the first cost in the total cost in the two cases in
their 15 operating years. At the life span of an ASHP unit, their relationship showed
D4>D3. This also confirmed that the installation of valves could save more money in
an ASHP unit’s application. As shown in this figure, when the proportions were 50%,
40%, 30%, and 20%, the operating time was about 1.9 years, 2.8 years, 4.5 years, and
7.6 years, respectively. That means that after the ASHP unit worked 8 years, the first
cost only accounted for less than 20% of the total cost. In Case D3, the duration was
about 6.9 years. That means that using the same running cost, the system can work
0.7 years longer in Case D4. When it works 15 years, the first cost becomes only about
10% of the total cost. It is also confirmed that the total cost is mainly decided by the
running cost. To clearly show the additional first cost effect on the total cost during the
operation of the new ASHP unit, Fig. 10.14 shows the proportion of additional first
cost in total cost in the 15 operating years. As shown, after the new ASHP unit works
5 years, 10 years, and 15 years, the proportions of additional first cost in total cost
changed from 1.84% to very small values, at only 0.5%, 0.3%, and 0.2%, respectively.