Heat pump system having a defrost mechanism for low ambient air temperature operation

Abstract

A heat pump system includes a hot gas bypass defrost mechanism which enables normal heat pump operation at low ambient air temperatures, and may be used for heating swimming pools. The bypass defrost mechanism is activated by sensing a drop in compressor suction line pressure, which occurs at low ambient temperatures when frost forms on an evaporator in the heat pump, which disrupts normal heat pump operation. The defrost mechanism includes a circuit that redirects a portion of hot refrigerant discharged by a compressor directly to the evaporator, thereby bypassing other heat pump components and defrosting the evaporator.

1 . In a heat pump including a compressor; a condenser; a compressor discharge line connecting said compressor to said condenser; an expansion device; a condenser discharge line connecting said condenser to said expansion device; an evaporator; an expansion device discharge line connecting said expansion device to said evaporator; a suction line connecting said evaporator to said compressor; 
 and a by-pass valve having an inlet, which is in fluid communication with said compressor discharge line, and an outlet, which is in fluid communication with said expansion device discharge line, the improvement comprising:    controlling means for controlling said by-pass valve so as to adjust said by-pass valve between an open position and a closed position in response to pressure in said suction line.    
   
   
       2 . The heat pump of  claim 1 , wherein said by-pass valve is a capacity control discharge valve.  
   
   
       3 . The heat pump of  claim 2 , wherein said controlling means includes an equalization tube extending between said capacity control discharge valve and said suction line.  
   
   
       4 . The heat pump of  claim 3 , wherein said valve moves into its said open position in response to the suction line pressure dropping below a selected value associated with frost formation on said evaporator, whereby refrigerant flowing from said compressor discharge line to said evaporator causes the evaporator to defrost.  
   
   
       5 . The heat pump of  claim 4 , wherein said selected suction line pressure value is 60 psi.  
   
   
       6 . The heat pump of  claim 1 , wherein said by-pass valve is a solenoid valve.  
   
   
       7 . The heat pump of  claim 6 , wherein said controlling means includes a pressure switch adapted to sense pressure in said suction line, said pressure switch being electrically connected to said solenoid valve.  
   
   
       8 . The heat pump of  claim 7 , wherein said solenoid valve moves into its said open position in response to the suction line pressure dropping below a selected value associated with frost formation on said evaporator, whereby refrigerant flowing from said compressor discharge line to said evaporator causes said evaporator to defrost.  
   
   
       9 . The heat pump of  claim 8 , wherein said selected suction line pressure value is 60 psi.  
   
   
       10 . In a heat pump including a refrigerant circuit having a compressor; a condenser; a compressor discharge line connecting said compressor to said condenser; an expansion device; a condenser discharge line connecting said condenser to said expansion device; an evaporator; an expansion device discharge line connecting said expansion device to said evaporator; and a suction line connecting said evaporator to said compressor; the improvement comprising: 
 a defrost circuit including a valve having an inlet and an outlet; an inlet line in fluid communication with said compressor discharge line and said inlet; an outlet line in fluid communication with said outlet and said expansion device discharge line; and controlling means for controlling said valve so as to adjust said valve between an open position and a closed position in response to pressure in said suction line, wherein said valve moves into its said open position in response to the pressure in said suction line dropping below a selected value, whereby refrigerant flowing from said compressor discharge line to said evaporator causes the evaporator to defrost.    
   
   
       11 . The heat pump system of  claim 10 , wherein said valve is a capacity control discharge valve.  
   
   
       12 . The heat pump system of  claim 11 , wherein said controlling means includes an equalization tube in fluid communication with said suction line and said valve, said equalization tube being adapted to communicate the pressure in said suction line to said valve.  
   
   
       13 . The heat pump system of  claim 10 , wherein said valve is a solenoid valve.  
   
   
       14 . The heat pump system of  claim 13 , wherein said controlling means includes a transformer electrically connected to said solenoid valve, and a switch disposed in said suction line and electrically connected to said transformer.  
   
   
       15 . A method for defrosting an evaporator of a heat pump which also includes a compressor; a condenser; a compressor discharge line connecting the compressor to the condenser; an expansion device; a condenser discharge line connecting the condenser to the expansion device; an expansion device discharge line connecting the expansion device to the evaporator; a suction line connecting the evaporator to the compressor; and a by-pass valve having an inlet, which is in fluid communication with the compressor discharge line, and an outlet, which is in fluid communication with the expansion device discharge line, the method comprising the steps of: 
 selecting a pressure value associated with the formation of frost on the evaporator;    monitoring the pressure in the suction line;    opening the by-pass valve when the pressure in the suction line drops below the selected value, thereby allowing a flow of refrigerant from the compressor, through the by-pass valve and into the evaporator, wherein the refrigerant is of a temperature sufficient to defrost the evaporator;    continuing to monitor the pressure in the suction line; and    closing the by-pass valve when the pressure in the suction line returns to the selected value.