Page 129 - Defrosting for Air Source Heat Pump

122 Defrosting for Air Source Heat Pump

Table 5.3 Measurement/calculation errors of system parameters
Measurement/
Item Parameter calculation error Unit

1 Air dry-bulb temperature at upstream of 1 (K-type °C
the outdoor coil thermocouple)
2 Air wet-bulb temperature at upstream of 0.1 (PT100, class A) °C
the outdoor coil
3 Air temperature at downstream of the 0.2 (hygrosensor) °C
outdoor coil
4 Air relative humidity at downstream of the 1.0% (hygrosensor) –
outdoor coil
5 Air flow rate passing through the outdoor 3% (flow hood) –
coil
6 Temperatures of tube/coil and fin surfaces 1 (K-type °C
thermocouple)
7 Refrigerant pressure 0.3% (pressure –
transmitters)
8 Refrigerant volumetric flow rate 1.6% (variable area –
flow meter)
9 Mass of the melted frost collected 0.1 (weighing scale) g
10 Temperature of the melted frost collected 1 (K-type °C
thermocouple)
11 Total energy supply for defrosting 1% (calculated) kJ
12 Total energy consumption during 1% (calculated) kJ
defrosting
13 Defrosting efficiency 0.15% (calculated) –
14 Defrosting evenness value 5.9% (calculated) –

temperature, 24°C in this section [11, 12, 14, 18]. To supply enough energy for
defrosting and keep the ASHP unit working safely, the indoor air fan during defrosting
remained operational at a lower speed. However, the outdoor air fan was turned off or
turned to blowing at the opposite direction as the same air quantity in different exper-
imental cases, which was controlled by the inverter (Model: KASUGA KIDEN
INVERTER, KKVF-F204ESB). Table 5.3 summarizes the measuring accuracy for
various sensors/instruments used in the experimental ASHP unit, and the calculated
relative standard errors.

5.2.1.3 Experimental cases
A series of experimental works using the experimental ASHP unit have been carried
out to study the defrosting performance for an ASHP unit with a horizontally installed
multicircuit outdoor coil. In order to obtain meaningful experimental results, it was
necessary to ensure that the frost that accumulated on the surface of the three circuits
was even at first. For an ASHP unit with a multicircuit outdoor coil, it is hard to make