Defrost system and method for heat pumps

Abstract

A system and method for defrosting an air source heat pump are presented. A defrost conduit extends from the discharge from a system compressor to the outdoor coil. The defrost conduit includes a normally closed defrost valve. When the need for defrost exists, the defrost valve is opened, and warm refrigerant is delivered from the compressor discharge to the outdoor coil to effect defrost of the outdoor coil.

1 . A heat pump system including:
 at least one compressor;   an indoor coil for delivering heat energy to an indoor space to be heated;   an outdoor coil for extracting heat energy from outside air to be used to heat the indoor space;   a conduit system connected between said one compressor and said indoor and outdoor coils for circulating refrigerant from said one compressor to said indoor coil and said outdoor coil and from said outdoor coil back to said one compressor;   a defrost conduit connected between said one compressor and said outdoor coil; and   a defrost flow control valve in said defrost conduit, said defrost control valve being normally closed, and said defrost control valve being opened to deliver refrigerant through said defrost conduit from said one compressor to said outdoor coil to defrost said outdoor coil.   
     
     
         2 . A heat pump system as in  claim 1 , further comprising:
 a detector in said outdoor coil, said detector detecting accumulation of ice on said outdoor coil and generating a defrost signal calling for defrost operation;   a controller, said controller receiving said defrost signal from said detector and generating a signal to open said defrost valve to initiate defrost operation.   
     
     
         3 . A heat pump system as in  claim 2  wherein said detector comprises:
 a light emitting diode;   a phototransistor positioned to receive light from said light emitting diode and generating said defrost signal to said controller as a function of intensity of light from said light emitting diode sensed by said phototransistor.   
     
     
         4 . A heat pump system as in  claim 1  wherein;
 said defrost flow control valve is a combination back pressure and on-off flow control valve.   
     
     
         5 . A heat pump system as in  claim 4  wherein;
 said defrost flow control valve prevents discharge pressure from said one compressor from dropping below a predetermined equivalent temperature level.   
     
     
         6 . A heat pump system as in  claim 1 , further comprising:
 said defrost conduit is connected to deliver refrigerant to a bottom of said outdoor coil during defrost operation to defrost said outdoor coil from the bottom toward a top thereof.   
     
     
         7 . A heat pump system as in  claim 1 , further comprising:
 an accumulator connected in said conduit system between said outdoor coil and said one compressor; and   a heating element in said accumulator, said heating element being activated during defrost operation to increase heat energy of said refrigerant delivered to said outdoor coil to defrost said outdoor coil.   
     
     
         8 . A heat pump system comprising:
 at least one compressor;   an outdoor coil for extracting heat energy from outside air to be used to heat an indoor space;   an indoor coil for delivering heat energy to an indoor space to be heated;   a conduit system for circulating refrigerant fluid from said one compressor to said indoor coil and said outdoor coil and back to said one compressor;   a 4 way valve in said conduit system for reversing flow of refrigerant in said conduit system to change a mode of operation of the heat pump system from heating operation to cooling operation;   a defrost conduit connected between said one compressor and said outdoor coil; and   a defrost flow control valve in said defrost conduit, said defrost control valve being normally closed, and said defrost control valve being opened to deliver refrigerant through said defrost conduit from said one compressor to said outdoor coil to defrost said outdoor coil.   
     
     
         9 . The heat pump system as in  claim 8  wherein;
 refrigerant is delivered to said outdoor coil to effect defrost operation without operation of said 4 way valve.   
     
     
         10 . A heat pump system as in  claim 8 , further comprising:
 a detector in said outdoor coil, said detector detecting accumulation of ice on said outdoor coil and generating a defrost signal calling for defrost operation;   a controller, said controller receiving said defrost signal from said detector and generating a signal to open said defrost valve to initiate defrost operation.   
     
     
         11 . A heat pump system as in  claim 10  wherein said detector comprises:
 a light emitting diode;   a phototransistor positioned to receive light from said light emitting diode and generating said defrost signal to said controller as a function of intensity of light from said light emitting diode sensed by said phototransistor.   
     
     
         12 . A heat pump system as in  claim 8  wherein;
 said defrost flow control valve is a combination back pressure and on-off flow control valve.   
     
     
         13 . A heat pump system as in  claim 12  wherein;
 said defrost flow control valve prevents discharge pressure from said one compressor from dropping below a predetermined equivalent temperature level.   
     
     
         14 . A heat pump system as in  claim 8  wherein:
 said defrost conduit is connected to deliver refrigerant to a bottom of said outdoor coil during defrost operation to defrost said outdoor coil from the bottom toward a top thereof.   
     
     
         15 . A heat pump system as in  claim 8 , further comprising:
 an accumulator connected in said conduit system between said outdoor coil and said one compressor; and   a heating element in said accumulator, said heating element being activated during defrost operation to increase heat energy of said refrigerant delivered to said outdoor coil to defrost said outdoor coil.   
     
     
         16 . The method of effecting defrost operation in a heat pump system, comprising:
 operating at least one compressor to circulate a refrigerant to a first coil to deliver heat energy to an interior space to be heated, and to a second coil to extract heat energy from outside air;   connecting a defrost conduit between said one compressor and said outdoor coil;   positioning a defrost flow control valve in said defrost conduit, said defrost control valve being normally closed; and   opening said defrost control valve to deliver refrigerant through said defrost conduit from said one compressor to said outdoor coil to defrost said outdoor coil.   
     
     
         17 . The method of effecting defrost operation as in  claim 16 , further comprising:
 positioning a detector in said outdoor coil to detect accumulation of ice on said outdoor coil and generate a signal calling for defrost operation;   delivering said defrost signal to a controller, said controller receiving said defrost signal from said detector and generating a defrost signal to open said defrost valve to initiate defrost operation.   
     
     
         18 . The method of effecting defrost operation as in  claim 17  wherein the positioning a detector in said outside coil comprises:
 positioning a light emitting diode in said outdoor coil; and   positioning a phototransistor in said outdoor coil to receive light from said light emitting diode and generating said defrost signal to said controller as a function of intensity of light from said light emitting diode sensed by said phototransistor.   
     
     
         19 . The method of effecting defrost operation as in  claim 16 , further comprising:
 connecting said defrost conduit to deliver refrigerant to a bottom of said outdoor coil during defrost operation to defrost said outdoor coil from the bottom toward a top thereof.   
     
     
         20 . The method of effecting defrost operation as in  claim 16  wherein;
 said defrost flow control valve is a combination back pressure and on-off flow control valve to prevent discharge pressure from said one compressor from dropping below a predetermined equivalent temperature level.   
     
     
         21 . The method of effecting defrost operation as in  claim 16 , further comprising:
 positioning a heating element between said outdoor coil and said one compressor; and
 activating said heating element during defrost operation to increase heat energy delivered to said outdoor coil to defrost said outdoor coil.