Multi-stage refrigerant system with different compressor types

Abstract

Multi-stage refrigerant systems operate with a lower stage compressor of a first type and a higher stage compressor of a second type. In one embodiment, the lower stage compressor type is selected to have the most beneficial characteristics at lower pressure operation, while the higher pressure stage compressor type is selected to have the most beneficial characteristics at higher pressure operation.

1 . A multi-stage refrigerant system comprising:
 at least two compressors, with a lower stage compressor and a higher stage compressor;   a heat rejection heat exchanger for receiving refrigerant from said higher stage compressor, and a heat accepting heat exchanger for delivering refrigerant to a lower stage compressor; and   said higher and lower stage compressors being different compressor types.   
     
     
         2 . The refrigerant system as set forth in  claim 1 , wherein said lower stage compressor and said higher stage compressor are positioned to compress refrigerant in a serial fashion. 
     
     
         3 . The refrigerant system as set forth in  claim 2 , wherein an intercooler is positioned between said lower stage compressor and said higher stage compressor. 
     
     
         4 . The refrigerant system as set forth in  claim 2 , wherein an economizer circuit is provided within the refrigerant system and returns a tapped refrigerant to an intermediate compression point between said lower stage compressor and said higher stage compressor. 
     
     
         5 . The refrigerant system as set forth in  claim 1 , wherein the multi-stage refrigerant system includes two to four stages. 
     
     
         6 . The refrigerant system as set forth in  claim 1 , wherein the multi-stage refrigerant system operates in a transcritical cycle for at least a portion of the time. 
     
     
         7 . The refrigerant system as set forth in  claim 1 , wherein at least one of the multiple stages operates with the CO 2  refrigerant. 
     
     
         8 . The refrigerant system as set forth in  claim 1 , wherein said higher stage compressor and said lower stage compressor are each part of their own closed-loop refrigerant circuit, and wherein refrigerant compressed by said lower stage compressor is delivered into a refrigerant-to-refrigerant heat exchanger, and refrigerant received by said higher stage compressor is delivered from the same refrigerant-to-refrigerant heat exchanger. 
     
     
         9 . The refrigerant system as set forth in  claim 1 , wherein said lower stage compressor is a scroll compressor. 
     
     
         10 . The refrigerant system as set forth in  claim 9 , wherein said higher stage compressor is not a scroll compressor. 
     
     
         11 . The refrigerant system as set forth in  claim 1 , wherein said higher stage compressor is a reciprocating compressor. 
     
     
         12 . The refrigerant system as set forth in  claim 11 , wherein said lower stage compressor is not a reciprocating compressor. 
     
     
         13 . The refrigerant system as set forth in  claim 1 , wherein said different compressor types are selected based on at least one of suction pressure, discharge pressure, equilibrium pressure, pressure ratio, pressure difference, discharge temperature, suction temperature.