Heat pump with frost-free outdoor coil

Abstract

A heat pump having an auxiliary outdoor coil equipped with heating means preventing the surface temperature during the heating cycle from falling below 32° C. The heating means comprises an electrical resistance heater in thermal contact with the fins of the outdoor coil such that heat is transferred to the fins by conduction. The system incorporates means to permit functioning immediately upon return to the heating cycle from a cooling cycle even though the pressure in the receiver of the system initially exceeds that in the indoor coil. Additionally, the system incorporates means for protecting the compressor from liquid floodback when changeover occurs from heating to cooling.

I claim as my invention: 
     
       1. In a heat pump, the combination of: an indoor heat exchanger,   first and second outdoor heat exchangers,   a compressor,   a receiver,   conduit means interconnecting said heat exchangers, said receiver and said compressor,   expansion valve means for said indoor heat exchanger and the first of said outdoor heat exchangers,   valve means in the conduit means, said valve means having a first condition in which the output of the compressor is connected through the second of said outdoor heat exchangers, the receiver, the expansion valve means for the indoor heat exchanger and said indoor heat exchanger back to the input of the compressor whereby the indoor and outdoor heat exchangers act as an evaporator and condenser, respectively, the valve means having a second condition in which the output of the compressor is connected through said indoor heat exchanger, the expansion valve means for the first outdoor heat exchanger and said first outdoor heat exchanger back to the input of the compressor whereby the indoor and outdoor heat exchangers act as a condenser and an evaporator, respectively,   .[.electrical resistance.]. heating means in intimate contact with fins on said first outdoor heat exchanger whereby heat can be transferred from the heating means to the fins by conduction, and   means for .[.energizing.]. .Iadd.causing .Iaddend.said heating means .Iadd.to supply heat to the fins .Iaddend.whenever the temperature of the fins reaches a point where frost can form thereon, whereby the fins are maintained free of frost regardless of the ambient temperature.   
     
     
       2. The heat pump of claim 1 wherein said heating means .[.is energized.]. .Iadd.supplies heat to the fins .Iaddend.when the temperature of the fins falls below 32° F. 
     
     
       3. The heat pump of claim .[.2.]. .Iadd.5 .Iaddend.wherein said means for energizing said heating means comprises thermistor means in contact with said fins, and means for supplying electrical power to said heating means when the temperature sensed by said thermistor means falls below said predetermined value. 
     
     
       4. The heat pump of claim 1 wherein said heating means comprises a plurality of heating elements spaced along said one outdoor heat exchanger, each heating element being in intimate contact with the outdoor heat exchanger surface to transfer heat thereto by conduction. .Iadd. 5. The heat pump of claim 1 wherein said heating means comprises an electrical resistance heater, and including means for energizing said electrical resistance heater to supply heat to the fins when the temperature of the fins reaches a point where frost can form thereon. .Iaddend.