Co2 refrigerant system with tandem compressors, expander and economizer

Abstract

A refrigerant system utilizes an expander that provides a more efficient expansion process and recovers at least a portion of energy from this expansion process. At least a portion of refrigerant that has been at least partially expanded in the expander is tapped and passed through an economizer heat exchanger. In the economizer heat exchanger, the tapped refrigerant cools a main circuit refrigerant increasing its thermodynamic potential. Further, a compression section is provided with at least two compressors operating in tandem and allowing for multiple stages of unloading. By selectively utilizing one or more of the tandem compressors, the economizer cycle, and the expander, the refrigerant system can achieve very efficient operation and provide enhanced control flexibility, in particular, for the CO 2 refrigerant system operating in the transcritical cycle.

1 - 30 . (canceled) 
   
   
       31 . A refrigerant system comprising:
 at least two compressors operating in tandem, said compressors compressing refrigerant and delivering it downstream to a first heat exchanger, refrigerant passing from said first heat exchanger through a first pass of an economizer heat exchanger, and then to an expander, refrigerant expanding in said expander, and said expander recovering at least a portion of energy from the expansion process of said refrigerant, and said recovered energy utilized to assist in driving of at least one of the refrigerant system components;   a second heat exchanger positioned downstream of said expander, and refrigerant passing from said expander through said second heat exchanger, and then back to said at least two compressors; and   a portion of refrigerant being tapped at a location where it has been at least partially expanded in said expander, and passed through a second pass of said economizer heat exchanger to cool refrigerant in a main refrigerant circuit, said tapped portion of refrigerant then being returned to at least one of said at least two compressors.   
   
   
       32 . The refrigerant system as set forth in  claim 31 , wherein said tapped portion of refrigerant is returned to both of at least two compressors. 
   
   
       33 . The refrigerant system as set forth in  claim 31 , wherein said at least two compressors have at least one common manifold. 
   
   
       34 . The refrigerant system as set forth in  claim 31 , wherein said at least two compressors are of different sizes. 
   
   
       35 . The refrigerant system as set forth in  claim 31 , wherein at least one of said at least two compressors consists of at least two separate stages. 
   
   
       36 . The refrigerant system as set forth in  claim 31 , wherein said expander has separate expansion stages for the main and tapped refrigerant flows. 
   
   
       37 . The refrigerant system as set forth in  claim 31 , wherein there are at least three of said compressors operating in tandem. 
   
   
       38 . The refrigerant system as set forth in  claim 31 , wherein said tapped portion of refrigerant being returned to at least one of said at least two compressors. 
   
   
       39 . The refrigerant system as set forth in  claim 31 , wherein said refrigerant is CO2. 
   
   
       40 . The refrigerant system as set forth in  claim 31 , wherein said refrigerant system operates in a transcritical cycle for at least a portion of the time. 
   
   
       41 . The refrigerant system as set forth in  claim 31 , wherein said refrigerant system operates in a subcritical cycle for at least a portion of the time. 
   
   
       42 . The refrigerant system as set forth in  claim 31 , wherein said at least two compressors can be controlled individually or in combination with each other. 
   
   
       43 . The refrigerant system as set forth in  claim 31 , wherein the economizer circuit can be selectively actuated. 
   
   
       44 . The refrigerant system as set forth in  claim 31 , wherein more than two sequential compression stages and more than two economizer circuits are utilized. 
   
   
       45 . The refrigerant system as set forth in  claim 31 , wherein said recovered energy is utilized to at least partially drive at least one of said at least two compressors. 
   
   
       46 . The refrigerant system as set forth in  claim 31 , wherein said recovered energy is utilized to assist in driving at least one of said at least two compressors. 
   
   
       47 . The refrigerant system as set forth in  claim 31 , wherein said recovered energy is utilized to assist in driving a shaft for said at least one of the refrigerant system components, or to generate electricity to assist in driving said at least one of the refrigerant system components. 
   
   
       48 . A method of operating a refrigerant system comprising the steps of:
 (1) providing at least two compressors operating in tandem, said compressors compressing refrigerant and delivering it downstream to a first heat exchanger, refrigerant passing from said first heat exchanger through a first pass of an economizer heat exchanger, and then to an expander, refrigerant expanding in said expander, and said expander recovering at least a portion of energy from the expansion process of said refrigerant, and said recovered energy utilized to assist in driving of at least one of the refrigerant system components;   (2) providing a second heat exchanger positioned downstream of said expander, and refrigerant passing from said expander through said second heat exchanger, and then back to said at least two compressors; and   (3) tapping a portion of refrigerant from a location where it has been at least partially expanded in said expander, and passing it through a second pass of said economizer heat exchanger to cool refrigerant in a main refrigerant circuit, said tapped portion of refrigerant then being returned to at least one of said at least two compressors.   
   
   
       49 . The method as set forth in  claim 48 , wherein said tapped portion of refrigerant is returned to both of at least two compressors. 
   
   
       50 . The method as set forth in  claim 48 , wherein said at least two compressors have at least one common manifold.