Suction superheat conrol based on refrigerant condition at discharge

Abstract

A relationship is developed between a discharge condition of a refrigerant leaving a compressor, and the suction superheat or refrigerant quality. By relying upon measurement and control of the discharge condition, the present invention is able to achieve very low suction superheat values. Controlling the operation to very low suction superheat values results in augmented refrigerant system performance.

1 . A refrigerant system comprising:
 a compressor, said compressor having a suction inlet line and a discharge outlet line;   a compressed refrigerant passing from said compressor downstream to a heat rejection heat exchanger and then downstream to an expansion device;   an evaporator positioned downstream of said expansion device; and   a sensor for sensing a condition of a discharge refrigerant leaving the compressor and   a control utilized to control a refrigerant thermodynamic state at a location between the expansion device and the compressor based upon the sensed condition of the discharge refrigerant.   
     
     
         2 . The refrigerant system as set forth in  claim 1 , wherein said sensed condition is the discharge temperature of the refrigerant. 
     
     
         3 . The refrigerant system as set forth in  claim 2 , wherein said refrigerant thermodynamic state is at least one of the suction superheat or refrigerant quality. 
     
     
         4 . The refrigerant system as set forth in  claim 1 , wherein said sensed condition is the discharge superheat of the refrigerant. 
     
     
         5 . The refrigerant system as set forth in  claim 1 , wherein said location is between the evaporator and the compressor. 
     
     
         6 . The refrigerant system as set forth in  claim 5 , wherein a relationship is found between at least one of the discharge temperature and discharge superheat, and at least one of the suction superheat and refrigerant quality at a location between the evaporator exit and the compressor inlet. 
     
     
         7 . The refrigerant system as set forth in  claim 6 , wherein said relationship is essentially linear. 
     
     
         8 . The refrigerant system as set forth in  claim 6 , wherein said relationship is periodically checked by varying said suction superheat value during refrigerant system operation. 
     
     
         9 . The refrigerant system as set forth in  claim 6 , wherein said relationship for at least one of suction pressure and discharge pressure is stored in the system controller memory. 
     
     
         10 . The refrigerant system as set forth in  claim 9 , wherein a control retrieves said relationship from said memory. 
     
     
         11 . The refrigerant system as set forth in  claim 9  wherein said relationship is a lookup table. 
     
     
         12 . The refrigerant system as set forth in  claim 9 , wherein said relationship is determined experimentally. 
     
     
         13 . The refrigerant system as set forth in  claim 12  wherein said relationship is determined during unit operation. 
     
     
         14 . The refrigerant system as set forth in  claim 9 , wherein the relationship is determined analytically. 
     
     
         15 . The refrigerant system as set forth in  claim 1 , wherein the sensed condition is used to achieve suction superheat values equal to or less than 2° F. 
     
     
         16 . The refrigerant system as set forth in  claim 1 , wherein the sensed condition is used to achieve suction superheat values equal to or less than 4° F. 
     
     
         17 . The refrigerant system as set forth in  claim 5 , wherein said suction superheat is calculated based on the difference between the saturated temperature and measured temperature sensed between the evaporator and compressor. 
     
     
         18 . The refrigerant system as set forth in  claim 17 , wherein said suction temperature is measured by a temperature sensor. 
     
     
         19 . The refrigerant system as set forth in  claim 18  wherein said sensor is one of the thermistor or thermocouple type. 
     
     
         20 . The refrigerant system as set forth in  claim 17 , wherein said saturated temperature is measured by a temperature sensor located within the evaporator. 
     
     
         21 . The refrigerant system as set forth in  claim 17 , wherein said saturated temperature is calculated based on the pressure measurement. 
     
     
         22 . A method of operating a refrigerant system including the steps of:
 providing a compressor, said compressor having a suction inlet line and a discharge outlet line;   passing a compressed refrigerant from said compressor downstream to a heat rejection heat exchanger and then downstream to an expansion device;   passing the refrigerant to an evaporator downstream of said expansion device;   sensing a condition of a discharge refrigerant leaving the compressor; and   controlling a refrigerant thermodynamic state at a location between the expansion device and the compressor based upon the sensed condition of the discharge refrigerant.   
     
     
         23 . The method as set forth in  claim 22 , wherein a relationship between said refrigerant thermodynamic state at a location between the expansion device and the compressor and said sensed condition of the discharge refrigerant used for the control is determined experimentally. 
     
     
         24 . The method as set forth in  claim 22 , wherein a relationship between said refrigerant thermodynamic state at a location between the expansion device and the compressor and said sensed condition of the discharge refrigerant used for the control is determined analytically. 
     
     
         25 . The method as set forth in  claim 22 , wherein the sensed condition is used to achieve suction superheat values equal to or less than 2° F.