A Frost-Less Heat Pump

Abstract

There are two major concerns associated with heat pump applications in heating season operation. One is that periodic defrosting is required when the ambient temperature is below 4.4°C (40˚F), and the other is the “cold blow ” effect (delivery of air at less than body temperature) that compromises indoor thermal comfort. Conventional defrosting by cycle reversing has an inherent energy penalty because it absorbs heat from the indoor air during the defrosting period. A new frost-less heat pump technology has been developed at Oak Ridge National Laboratory. If a moderate amount of heat is added to the refrigerant stream in the accumulator, the suction pressure and temperature can be raised. As a result, frost accumulation on the outdoor coil is retarded. Most of the heat added to the accumulator will be delivered to the indoors in the form of a higher heat pump supply air temperature, reducing the cold blow effect. The frequency of defrosting cycles can be drastically reduced, estimated, based on the temperature bin method, by a factor of five (5) in the Knoxville, Tennessee area in the ambient temperature range from 0 to 4.4°C (32 to 40°F). The new technology also includes a new energy-efficient defrosting scheme. When the ambient