Method and apparatus for control of carbon dioxide gas cooler pressure by use of a two-stage compressor

Abstract

A transcritical vapor compression system includes a fluid circuit circulating a refrigerant in a closed loop. The fluid circuit has operably disposed therein, in serial order, a first compressor, an intercooler, a second compressor with a variable capacity, a first heat exchanger, an expansion device and a second heat exchanger. The first compressor compresses the refrigerant from a low pressure to an intermediate pressure. The second compressor compresses the refrigerant from the intermediate pressure to a supercritical pressure. The first heat exchanger is positioned in a high pressure side of the fluid circuit. The second heat exchanger is positioned in a low pressure side of the fluid circuit. The expansion device reduces the pressure of the refrigerant from a supercritical pressure to a relatively lower pressure. Cooling means cools the refrigerant within one of the compressors.

1 . A transcritical vapor compression system comprising:
 a fluid circuit circulating a refrigerant in a closed loop, said fluid circuit having operably disposed therein, in serial order, a first compressor, an intercooler, a second compressor with a variable capacity, a first heat exchanger, an expansion device and a second heat exchanger wherein said first compressor compresses the refrigerant from a low pressure to an intermediate pressure, said second compressor compresses the refrigerant from the intermediate pressure to a supercritical pressure, said first heat exchanger is positioned in a high pressure side of said fluid circuit and said second heat exchanger is positioned in a low pressure side of said fluid circuit, said expansion device reducing the pressure of the refrigerant from a supercritical pressure to a relatively lower pressure; and   means for cooling the refrigerant within one of said compressors.   
   
   
       2 . The system of  claim 1  wherein said cooling means comprises a third heat exchanger in fluid communication with a housing of said one compressor. 
   
   
       3 . The system of  claim 2  wherein said housing of said one compressor includes an internal conduit, said third heat exchanger being configured to circulate a fluid medium through said internal conduit of said housing. 
   
   
       4 . The system of  claim 3  wherein said fluid medium comprises one of oil, water, and forced air. 
   
   
       5 . The system of  claim 1  further comprising a controller electrically connected to said second compressor and operable to vary a capacity of said second compressor. 
   
   
       6 . The system of  claim 5  wherein said controller comprises a means for regulating the pressure of the refrigerant in said first heat exchanger. 
   
   
       7 . The system of  claim 5  wherein the temperature and pressure of the refrigerant at an inlet of said first compressor is substantially unchanged by variations in the capacity of said second compressor. 
   
   
       8 . The system of  claim 5  wherein said intercooler is configured to maintain a substantially constant refrigerant temperature at an inlet of said second compressor while the capacity of said second compressor varies. 
   
   
       9 . The system of  claim 8  wherein the intermediate pressure varies with variations in the capacity of said second compressor. 
   
   
       10 . The system of  claim 1  wherein said cooling means comprises a means for circulating the refrigerant through a housing of said one compressor. 
   
   
       11 . The system of  claim 10  wherein said cooling means comprises a second expansion device in fluid communication with said housing of said one compressor. 
   
   
       12 . The system of  claim 10  wherein said cooling means comprises a flash gas vessel in fluid communication with said housing of said one compressor. 
   
   
       13 - 21 . (canceled) 
   
   
       22 . A transcritical vapor compression system comprising:
 a fluid circuit circulating a refrigerant in a closed loop, said fluid circuit having operably disposed therein, in serial order, a first compressor, a second compressor, a first heat exchanger, an expansion device and a second heat exchanger wherein said first compressor compresses the refrigerant from a low pressure to an intermediate pressure, said second compressor compresses the refrigerant from the intermediate pressure to a supercritical pressure; and   means for cooling the refrigerant within one of said compressors.   
   
   
       23 . The system of  claim 22  wherein said first heat exchanger is positioned in a high pressure side of said fluid circuit and said second heat exchanger is positioned in a low pressure side of said fluid circuit, said expansion device reducing the pressure of the refrigerant from a supercritical pressure to a relatively lower pressure. 
   
   
       24 . The system of  claim 22  wherein said second compressor has a variable capacity. 
   
   
       25 . The system of  claim 22  further comprising an intercooler disposed between said first compressor and said second compressor in said fluid circuit. 
   
   
       26 . The system of  claim 22  wherein said cooling means comprises a means for regulating the pressure of the refrigerant in said first heat exchanger. 
   
   
       27 . The system of  claim 22  wherein said cooling means comprises a means for circulating the refrigerant through a housing of said one compressor. 
   
   
       28 . The system of  claim 27  wherein said cooling means comprises a second expansion device in fluid communication with said housing of said one compressor. 
   
   
       29 . The system of  claim 27  wherein said cooling means comprises a flash gas vessel in fluid communication with said housing of said one compressor. 
   
   
       30 - 34 . (canceled) 
   
   
       35 . A method of controlling a transcritical vapor compression system, said method comprising:
 providing a fluid circuit circulating a refrigerant in a closed loop, the fluid circuit having operably disposed therein, in serial order, a first compressor, an intercooler, a second compressor, a first heat exchanger, an expansion device and a second heat exchanger;   compressing the refrigerant from a low pressure to an intermediate pressure in said first compressor;   compressing the refrigerant from the intermediate pressure to a supercritical pressure in the second compressor;   decreasing a temperature of the refrigerant in the first heat exchanger;   passing the refrigerant through the expansion device and reducing the pressure of the refrigerant in the expansion device; and   selectively cooling the refrigerant within one of the compressor.   
   
   
       36 . A method of controlling a transcritical vapor compression system, said method comprising:
 providing a fluid circuit circulating a refrigerant in a closed loop, the fluid circuit having operably disposed therein, in serial order, a first compressor, an intercooler, a second compressor, a first heat exchanger, an expansion device and a second heat exchanger;   compressing the refrigerant from a low pressure to an intermediate pressure in said first compressor;   compressing the refrigerant from the intermediate pressure to a supercritical pressure in the second compressor;   decreasing a temperature of the refrigerant in the first heat exchanger;   passing the refrigerant through the expansion device and reducing the pressure of the refrigerant in the expansion device; and   selectively cooling the refrigerant between said compressors.