Heat pump system and method of operating

Abstract

A heat pump system operable in a cooling mode, a heating mode and a defrost mode includes a refrigerant compressor ( 20 ), a reversing valve ( 30 ), a first heat exchanger ( 40 ) and a second heat exchanger ( 50 ) disposed in a refrigerant circuit, and a primary expansion valve ( 45 ) disposed in the refrigerant circuit between said first heat exchanger ( 40 ) and said second heat exchanger ( 50 ); said reversing valve ( 30 ) is positionable in a first position for operation of said heat pump system in the cooling mode or defrost mode and is positionable in a second position for operation of said heat pump system in the heating mode; a refrigerant bypass circuit establishes a refrigerant flow path from the refrigerant circuit at a first location upstream of said primary expansion valve ( 45 ) and downstream of said first heat exchanger ( 40 ) with respect to refrigerant flow in the defrost mode to a liquid reservoir ( 70 ) disposed in the refrigerant circuit at a second location downstream of said primary expansion valve ( 45 ) with respect to refrigerant flow in the defrost mode.

1 . A heat pump system operable in a cooling mode, a heating mode and a defrost mode and including a refrigerant compressor, a reversing valve, a first heat exchanger and a second heat exchanger disposed in a refrigerant circuit, and a primary expansion device disposed in the refrigerant circuit intermediate said first heat exchanger and said second heat exchanger, said reversing valve being positionable in a first position for operation of said heat pump system in the cooling mode or defrost mode and being positionable in a second position for operation of said heat pump system in the heating mode, said heat pump characterized by:
 a refrigerant bypass circuit establishing a refrigerant flow path from the refrigerant circuit at a first location upstream of said primary expansion device and downstream of said first heat exchanger with respect to refrigerant flow in the defrost mode to a liquid reservoir disposed in the refrigerant circuit at a second location downstream with respect to refrigerant flow in the defrost mode of said primary expansion valve.   
     
     
         2 . The heat pump system of  claim 1  further characterized in that said second heat exchanger defines a refrigerant collection chamber comprising said liquid reservoir. 
     
     
         3 . The heat pump system of  claim 2  further characterized in that said second heat exchanger comprises a shell and tube heat exchanger having a shell defining the refrigerant collection chamber and a tube bank heat exchanger disposed in the refrigerant collection chamber. 
     
     
         4 . The heat pump system of  claim 1  further characterized in that said liquid reservoir comprises a refrigerant receiver disposed in the refrigerant circuit intermediate said primary expansion device and said second heat exchanger. 
     
     
         5 . The heat pump system of  claim 1  further characterized in that said bypass circuit comprises:
 a bypass refrigerant line interconnecting the refrigerant circuit at the first location upstream of said primary expansion device and downstream of said first heat exchanger with respect to refrigerant flow in the defrost mode in refrigerant flow communication with said liquid reservoir; and 
 a bypass refrigerant flow control device interdisposed in said refrigerant bypass line. 
 
     
     
         6 . The heat pump system of  claim 5  further characterized in that said bypass refrigerant flow control device comprises a flow control valve having a first position in which said bypass refrigerant line is open to refrigerant flow and a second position in which said bypass refrigerant line is closed to refrigerant flow. 
     
     
         7 . The heat pump system of  claim 5  further characterized in that said bypass refrigerant flow control device comprises an open position/closed position solenoid valve. 
     
     
         8 . The heat pump system of  claim 1  further characterized by:
 a flow control valve disposed in the refrigerant circuit upstream of the said first heat exchanger and downstream of primary expansion device with respect to refrigerant flow through the circuit in a heating mode; and 
 a flow check valve disposed in the refrigerant circuit in parallel relationship with said flow control. 
 
     
     
         9 . A method of operating the heat pump system during a defrost mode, the heat pump including a refrigerant compressor, a reversing valve, a first heat exchanger and a second heat exchanger disposed in a refrigerant circuit, and a primary expansion device disposed in the refrigerant circuit intermediate said first heat exchanger and said second heat exchanger, said reversing valve being positionable in a first position for operation of said heat pump system in the cooling or defrost mode and being positionable in a second position for operation of said heat pump system in the heating mode, said method characterized by the steps of:
 initiating switching of said reversing valve from its second position into its first position for operation in the defrost mode;   prior to terminating operation in the defrost mode, passing refrigerant flow from the refrigerant circuit through a refrigerant bypass circuit to a liquid reservoir;   and   initiating switching of said reversing valve out of its first position.   
     
     
         10 . The method of  claim 9  further characterized by:
 providing a flow control valve in said bypass refrigerant circuit, said flow control valve having an open position in which said bypass refrigerant line is open to refrigerant flow and a closed position in which said bypass refrigerant line is closed to refrigerant flow; and in that 
 the step of passing refrigerant flow from the refrigerant circuit through said refrigerant bypass circuit comprises opening said flow control valve. 
 
     
     
         11 . The method of  claim 10  further characterized in that the step of passing refrigerant flow from the refrigerant circuit through said refrigerant bypass circuit by opening said flow control comprises opening said flow control valve in defrost mode when a discharge pressure of said compressor exceeds a first preselected discharge pressure set point. 
     
     
         12 . The method of  claim 10  further characterized in that the step of passing refrigerant flow from the refrigerant circuit through said refrigerant bypass circuit by opening said flow control comprises opening said flow control valve in defrost mode when a frost factor for the first heat exchanger drops to 0%. 
     
     
         13 . The method of  claim 10  further characterized in that the step of passing refrigerant flow from the refrigerant circuit through said refrigerant bypass circuit by opening said flow control comprises opening said flow control valve in defrost mode when the time elapsed in a defrost mode reaches eight minutes. 
     
     
         14 . The method of  claim 10  further characterized by the step of terminating the passing of refrigerant flow from the refrigerant circuit through said refrigerant bypass circuit by closing said flow control valve. 
     
     
         15 . The method of  claim 14  further characterized in that the step of terminating the passing of refrigerant flow from the refrigerant circuit through said refrigerant bypass circuit comprises closing said flow control valve upon expiration of said preselected period of time. 
     
     
         16 . The method as recited in  claim 15  further characterized in that said preselected period of time ranges from one second to forty-five seconds. 
     
     
         17 . The method as recited in  claim 16  further characterized in that said preselected period of time is about five seconds