Refrigerant system with cascaded circuits and performance enhancement features

Abstract

An improved refrigerant system incorporates at least two circuits arranged in a cascaded relationship. Preferably, the upper circuit utilizes a hydrocarbon refrigerant and preferably the lower circuit utilizes CO 2 refrigerant. Preferably, the CO 2 circuit mainly operates in a subcritical region. To improve the efficiency and capacity control of the cascaded refrigerant system, at least one of the circuits is equipped with performance enhancement features such as, for example, an economized function provided by a flash tank or economizer heat exchanger. Additional enhancement features can also include a liquid-suction heat exchanger and bypass function.

1 . A refrigerant system comprising:
 at least one pair of circuits operated in a cascade fashion, with a first circuit including a first compressor compressing a refrigerant and delivering the refrigerant to a heat rejection heat exchanger, refrigerant passing from said heat rejection heat exchanger through an expansion device, and then to a refrigerant-to-refrigerant heat exchanger, refrigerant from said refrigerant-to-refrigerant heat exchanger being returned to said first compressor;   a second circuit, said second circuit including a second compressor, said second compressor delivering refrigerant to said refrigerant-to-refrigerant heat exchanger, refrigerant from said refrigerant-to-refrigerant heat exchanger passing through an expansion device, and then through said heat accepting heat exchanger;   said refrigerant-to-refrigerant heat exchanger providing heat transfer communication between said first circuit and said second circuit;   said first circuit utilizing a first refrigerant, and said second circuit utilizing a second refrigerant; and   at least one additional performance enhancement feature incorporated in at least one of said first circuit or said second circuit.   
   
   
       2 . The refrigerant system as set forth in  claim 1 , wherein said additional performance enhancement feature is an economizer. 
   
   
       3 . The refrigerant system as set forth in  claim 2 , wherein the economizer function is provided by an economizer heat exchanger. 
   
   
       4 . The refrigerant system as set forth in  claim 2 , wherein said economizer function is provided by a flash tank. 
   
   
       5 . The refrigerant system as set forth in  claim 2 , wherein a bypass function is also incorporated into the refrigerant system. 
   
   
       6 . The refrigerant system as set forth in  claim 5 , wherein the economizer and the bypass function are both included in the first circuit. 
   
   
       7 . The refrigerant system as set forth in  claim 5 , wherein the economizer and the bypass function are both included in the second circuit. 
   
   
       8 . The refrigerant system as set forth in  claim 2 , wherein the economizer is included in the first circuit. 
   
   
       9 . The refrigerant system as set forth in  claim 2 , wherein the economizer is included in the second circuit. 
   
   
       10 . The refrigerant system as set forth in  claim 1 , wherein the additional performance enhancement feature is a liquid-suction heat exchanger. 
   
   
       11 . The refrigerant system as set forth in  claim 10 , wherein an economizer is also included in the refrigerant system. 
   
   
       12 . The refrigerant system as set forth in  claim 11 , wherein the liquid-suction heat exchanger and the economizer are both included in the first circuit. 
   
   
       13 . The refrigerant system as set forth in  claim 11 , wherein the liquid-suction heat exchanger and the economizer are both included in a second circuit. 
   
   
       14 . The refrigerant system as set forth in  claim 10 , wherein the liquid-suction heat exchanger is included in the first circuit. 
   
   
       15 . The refrigerant system as set forth in  claim 10 , wherein the liquid-suction heat exchanger is included in the second circuit. 
   
   
       16 . The refrigerant system as set forth in  claim 1 , wherein said first refrigerant is hydrocarbon. 
   
   
       17 . The refrigerant system as set forth in  claim 1 , wherein said second refrigerant is CO2. 
   
   
       18 . The refrigerant system as set forth in  claim 1 , wherein said first refrigerant and said second refrigerant are the same refrigerants. 
   
   
       19 . The refrigerant system as set forth in  claim 1 , wherein said first refrigerant and said second refrigerant are different refrigerants. 
   
   
       20 . The refrigerant system as set forth in  claim 1 , wherein at least one circuit from said pair of circuits itself is represented by a pair of circuits. 
   
   
       21 .- 42 . (canceled)