4477 (RP-1002) -- Effect of Fin Staging on Frost/Defrost Performance of a Two-Row Heat Pump Evaporator at Standard Test Conditions

Three two-row heat pump evaporators (outdoor coils) were tested on a residential heat pump to determine whether fin staging would slow frost growth and improve heat pump frosting/defrosting performance. The base coil had a uniform fin density of 20 fins per in. (8 fins per cm) on both rows. Two fin staged coils were examined. The first (Case One) had fin spacing on the first and second rows of 15 fpi (6 fins/cm) and 20 fins/in. (8 fins/cm), respectively .The second (Case Two) had fin spacing on the first and second rows of 15 fpi (6 fins/cm) and 25 fpi (10 fins/cm), respectively. Frosting/defrosting performance was evaluated at 35ºF (1.7ºC) and 82% RH. Frost growth on the leading edge of the first row was measured. Frost mass was estimated from psychrometric measurements across the evaporator. Steady state cooling and heating tests were also performed. The Case One staged coil improved frost/defrost COP 8% over the base case, while the Case Two coil improved 4%. The Case One coil had a 63% longer frost/defrost cycle time compared to the base case, while Case Two had a 76% longer cycle time. Both staged coils delayed frost growth on the leading edge of the evaporator fins even though psychrometric measurements indicated an increase in moisture removal. These trends suggested that staging was successful in moving frost growth to locations away from the leading edge of the first row. The heat pump was also tested with each of the three coils at standard steady-state cooling and heating conditions. Cooling and heating capacities and efficiencies were similar with all three coils.

Units: Dual