Frost accumulation on the outdoor coil of a heat pump one of the basic concerns about heat pump operation. Defrosting by cycle reversing is energy consuming, compromises indoor thermal comfort, and causes excessive and unnecessary use of electric resistance heating.

By adding a moderate amount of heat to the refrigerant stream in the accumulator, the evaporator coil temperature can be raised by several degrees. This concept can be used retard frost accumulation on the outdoor coil of the heat pump and, thus, keep the coil clean. The frequency of defrosting cycles can be drastically reduced by a factor of five in the Knoxville, Tennessee, area. This study describes the development a frost-less heat pump.

Also discussed is a new defrosting technology that does not rely on heat taken from the conditioned space of the house by adding heat to the liquid refrigerant in the accumulator. The accumulator becomes an evaporator, providing heat for coil defrosting. In this system, the indoor fan is not energized during the defrosting period. Two-phase refrigerant flowing through the indoor coil will remain two-phase as it enters the accumulator where it then boils. An obvious advantage is that there will not be a cold blow phenomenon during the defrosting period. Energy consumption is modest--around 1 kW-- compared to an average of 10 kW resistant heating coil fully energized.

Test data on several engineering units showed that the frost-less concept and the new defrosting scheme worked expected. Results are presented in this paper.

Units: I-P