Page 140 - Defrosting for Air Source Heat Pump

Investigation of effect on uneven defrosting performance 133

Table 5.5 Durations for the tubes and fins and the DECs in the three cases
Item Parameter Case 1 Case 2 Case 3 Figs. Unit

1 Duration for tube 173 186 199 5.8–5.10 s
of Circuit 1
2 Duration for tube 182 186 204 5.8–5.10 s
of Circuit 2
3 Duration for tube 186 186 196 5.8–5.10 s
of Circuit 3
4 DEC for tube 93.01% 100% 96.08% – –
surface
temperature
5 Duration for fin of 185 187 205 5.11–5.13 s
Circuit 1
6 Duration for fin of 190 188 207 5.11–5.13 s
Circuit 2
7 Duration for fin of 195 187 205 5.11–5.13 s
Circuit 3
8 DEC for fin 94.87% 99.47% 99.03% – –
surface
temperature

be higher. Meanwhile, the DEC could be used as one index to evaluate the defrosting
performance for an ASHP unit with a multicircuit outdoor coil.
To clearly and comparatively study the effects of wind blowing on melted frost,
Table 5.6 listed all the different durations and their differences in Case 2 and Case
3. The starts of all the tube surface temperatures leaving 0°C in the two cases were

Table 5.6 Different durations and their differences in Case 2 and Case 3
Item Parameter Case 2 Case 3 Difference a Figs. Unit

1 Start of all the tube 90 90 0 5.9, s
surface temperatures 5.10
leaving 0°C
2 Start of all the fin 90 100 10 5.12, s
surface temperatures 5.13
leaving 0°C
3 Start of one tube 106 115 9 5.9, s
surface temperature 5.10
reaching 3°C
4 Start of one fin surface 101 114 13 5.12, s
temperature 5.13
reaching 3°C
5 Temperature of the 9.6 4.2 5.4 5.9, o C
tube surface increased 5.10
during 40 s
Continued