Velocity Based Defrost and Frost Inhibition of Evaporator Coils of Heat Pump

Abstract

Researchers in the past have reported various methods to either retard frost formation or minimize energy expenditure during defrosting, but the methods reported in this paper is novel. Use of air flow during heating and defrosting cycles has not been studied and reported so far. The effect of using air flow during heating and defrosting cycles of heat pump were investigated experimentally. In the heating cycle, it is found that at higher air flow velocities, it is possible to retard the rate at which frost grows on the evaporator coils of the heat pump. Changing the air velocity from 0.8 m/s to 2 m/s caused a significant reduction in the frost growth rate. The ΔT of the working fluid for the 2 m/s experiment stayed at least 0.5 ∼ 1.0 °C more than the corresponding value of the 0.8 m/s experiment for the entire 90 minute duration of the heating cycle. In the defrost cycle, it is found that using air flow in the direction opposite to the normal air flow on the evaporator coil provides an energy saving opportunity by increasing the time interval between subsequent defrosting. It was seen that a reduction of 1 ∼ 2 defrost cycle was possible in 1 hour of operation, depending on the level of frost formation.