Page 351 - Defrosting for Air Source Heat Pump
P. 351
Appendices
Appendix A: Defrosting efficiency
Defrosting efficiency can be used to evaluate the performance of a defrosting opera-
tion. It is defined as the ratio of the actual amount of energy consumption required to
both melt the accumulated frost and vaporize the retained melted frost to the total
amount of energy available from an outdoor coil during an entire defrosting operation,
as follows:
Q m + Q v
η ¼ 100% (A.1)
d
Q com + Q i, fan + Q i,air
where the energy consumed on melting frost and vaporizing retained water, Q m and
Q v , were evaluated by:
Q m ¼ m f L sf (A.2)
Q v ¼ m v L v (A.3)
where m f and m v are the total mass of the frost accumulated over the outdoor coil
surface and the total mass of the vaporized water, and L sf and L v are the latent heat
of frost melting and water vaporization, respectively. Q com , Q i, fan , and Q i, air are
the energy consumptions by the compressor and supply fan, and the thermal energy
from the indoor air during defrosting, respectively.
