Page 67 - Defrosting for Air Source Heat Pump

58 Defrosting for Air Source Heat Pump

effect on defrosting performance should also be further studied, and thus its negative
effects could be finally fixed for an ASHP unit.
This section reports on an experimental study on the effects of the downward
flowing of melted frost due to gravity over a vertical three-circuit outdoor coil surface
on the defrosting performance of an experimental ASHP unit during RCD. A detailed
description of the experimental ASHP unit is first presented. This is followed by
reporting various experimental conditions and experimental results. Finally, based
on the experimental results, a quantitative analysis on the impacts of the downward
flowing of the melted frost due to gravity on the defrosting performance is reported.

3.3.1 Experimental setup
The experimental ASHP unit used in this section is also placed in the environmental
chamber, which is the same as the previous section. The difference is the outdoor coil,
here a three-circuit outdoor coil, as shown in Fig. 3.11. In fact, we designed a five-
circuit outdoor coil at first, but only two circuits were used in the previous section.
But here, we used the top three circuits, and thus the outdoor coil was correspondingly
adjusted. That means that, compared with the previous two-circuit outdoor coil, the
three-circuit one has a total heat transfer area that is 1.5 times larger. The specifica-
tions of the tailor-made three-circuit outdoor coil are summarized in Table 3.4.
Table 3.5 summarizes the measuring accuracy for various sensors/instruments used
in the experimental ASHP unit, and the calculated relative standard errors for the three
calculated parameters of total energy supply for defrosting, total energy consumption
during defrosting, and defrosting efficiency, respectively.

Fig. 3.11 Location of valves on the three-circuit outdoor coil.