Low gwp cascade refrigeration system

Abstract

Disclosed are cascade refrigerant systems for providing cooling of air located in an enclosure that is occupied by or which will be exposed to humans or other animals during normal use, wherein systems includes; (1) a first, relatively low temperature heat transfer circuit having a first evaporator located within the enclosure and a first heat transfer fluid in the low temperature heat transfer circuit; (2) a second heat transfer circuit located substantially outside the enclosure comprising a second heat transfer fluid; (3) a heat exchanger which serves as the condenser in the low temperature circuit thermally coupled with the high temperature circuit by virtue of rejecting heat into the second heat transfer fluid; and (4) in the high temperature loop of a heat exchanger which transfers heat from the second heat transfer fluid exiting from a high temperature condenser to the portion of the second heat transfer fluid which is traveling to the suction side of the compressor.

What is claimed is: 
     
         1 . A heat transfer system for cooling the contents of an enclosure comprising:
 (a) a relatively low temperature vapor compression loop comprising a compressor, an expander and an evaporator in fluid communication in said loop, and a first heat transfer composition in said loop comprising a first refrigerant and lubricant for the compressor, said evaporator being located in said enclosure and being capable of absorbing heat from fluid in said enclosure at about said relatively low temperature;   (b) a relatively high temperature vapor compression loop comprising a compressor, a condenser, an expander, and a suction line heat exchanger in fluid communication in said loop, and a second heat transfer composition in said loop comprising a second refrigerant and preferably lubricant for the compressor, said condenser being capable of transferring heat to a heat sink located outside said enclosure; and   (c) a cascade heat exchanger for condensing said first refrigerant and evaporating said second refrigerant by heat exchange between said first and second refrigerant,   
       wherein said suction line heat exchanger is in fluid communication with said cascade heat exchanger for receiving at least a portion of said second heat transfer composition exiting said cascade heat exchanger and increases the temperature thereof by absorbing heat from said first heat transfer composition exiting said condenser and thereby reducing the temperature of said first heat transfer composition prior to said first heat transfer composition entering said first loop expander. 
     
     
         2 . The system of  claim 1  wherein the first refrigerant has a flammability that is substantially less than the flammability of the second refrigerant. 
     
     
         3 . The system of  claim 1  wherein the first refrigerant has a flammability classified as Al under ASHRAE 34 (as measured by ASTM E681) and the second refrigerant has a flammability that is classified as A2L under ASHRAE 34 (as measured by ASTM E681) or a higher flammability than A2L. 
     
     
         4 . The system of  claim 1  wherein the first and the second refrigerant each have a Global Warming Potential (GWP) that is less than about 150. 
     
     
         5 . The system of  claim 1  wherein each of said compressors and said expanders and said condenser are not located in the enclosure. 
     
     
         6 . The system of  claim 5  wherein the suction line heat exchanger is not located in the enclosure. 
     
     
         7 . The system of  claim 1  wherein said second refrigerant comprises one or more of trans1,3,3,3-tetrafluoropropene (HFO-1234ze(E)), 2,3,3,3-tetrafluoropropene (HFO-1234yf), R-227ea, R-32 and combinations of two or more of these. 
     
     
         8 . The system of  claim 1  wherein said second refrigerant comprises at least about 80% by weight of 2, 3,3,3-tetrafluoropropene (HFO-1234yf). 
     
     
         9 . The system of  claim 1  wherein said second refrigerant consists essentially of HFO-1234ze(E), HFO-1234yf or combinations of these. 
     
     
         10 . The system of  claim 1  wherein said second refrigerant comprises from about 70% by weight to about 90% by weight of HFO-1234yf and from about 10% by weight to about 30% by weight of R32. 
     
     
         11 . The system of  claim 10  wherein said second refrigerant comprises from about 80% by weight of HFO-1234yf and about 20% by weight of R32. 
     
     
         12 . The system of  claim 1  wherein said second refrigerant comprises from about 70% by weight to about 90% by weight of HFO-1234yze(E) and from about 10% by weight to about 30% by weight of R32. 
     
     
         13 . The system of  claim 1  wherein said second refrigerant comprises about 80% by weight of HFO-1234ze(E) and about 20% by weight of R32. 
     
     
         14 . The system of  claim 1  wherein said second refrigerant comprises from about 85% to about 90% by weight of trans1,3,3,3-tetrafluoropropene (HFO-1234ze(E)) and from about 10% by weight to about 15% by weight of 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea). 
     
     
         15 . The system of  claim 1  wherein said second refrigerant comprises from about 88% by weight of trans1,3,3,3-tetrafluoropropene (HFO-1234ze(E)) and from about 10% by weight to about 12% by weight of 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea). 
     
     
         16 . The system of  claim 1  wherein the evaporating temperature of said first refrigerant in said relatively low temperature vapor compression loop is from about −45° C. to about −25° C. 
     
     
         17 . The system of  claim 16  wherein the evaporating temperature of said second refrigerant in said relatively high temperature vapor compression loop is from about −15° C. to about 5° C. 
     
     
         18 . The system of  claim 17  wherein the condensing temperature of said first refrigerant in said relatively low temperature vapor compression loop is from about −5° C. to about −5° C. 
     
     
         19 . The system of  claim 18  wherein the condensing temperature of said second refrigerant in said relatively high temperature vapor compression loop is from about 40° C. to about 50° C. 
     
     
         20 . The system of  claim 19  wherein said first refrigerant comprises carbon dioxide and said second refrigerant comprises one or more of trans1,3,3,3-tetrafluoropropene (HFO-1234ze(E)), 2,3,3,3-tetrafluoropropene (HFO-1234yf), R-227ea, R-32 and combinations of two or more of these.