Fluidized bed air-to-air heat pump evaporator evaluation

Frost formation of air-to-air heat pump evaporator surfaces reduces unit efficiency and restricts application. The use of a fluidized bed heat exchanger as an air-to-heat pump evaporator was investigated to determine if frost accumulation could be eliminated. Experimental investigations were conducted and the following results obtained: (1) frost accumulation was insignificant with fluidized bed temperatures below 32 F and (2) moisture accumulation from condensation resulted in unstable fluidized bed operation when the fluidized bed temperature was above 32 F. Several concepts - maintenance bed temperature below 32 F, reverse refrigerant flow, air-dry bed, nonadhering bed material, and ultrasonics - to solve the moist bed problem were evaluated, with no practical solution being developed. The use of a fluidized bed heat exchanger for air-to-air heat pump evaporators was determined not feasible.