Refrigerant system with economizer, intercooler and multi-stage compressor

Abstract

A refrigerant system is provided with a multi-stage compression system. An intercooler is positioned between at least two compression stages to cool a refrigerant, by heat transfer interaction with a secondary fluid, after it has been compressed in the lower compression stages to some intermediate pressure. The intercooler enhances refrigerant system performance, improves compressor reliability, and extends operational envelope. Further, at least one economizer circuit is incorporated into the refrigerant system that returns the economized refrigerant flow at the location between at least two compression stages.

1 . A refrigerant system comprising:
 at least two compression stages connected in series with respect to a refrigerant flow, a condenser positioned downstream of said at least two compression   stages, an expansion device positioned downstream of said condenser and an evaporator positioned downstream of said expansion device, refrigerant passing through said at least two compression stages, to said condenser, to said main expansion device, to said evaporator, and then returning to a lower compression stage of said at least two compression stages; and   an economizer circuit incorporated into the refrigerant system, said economizer circuit including an economizer heat exchanger for receiving a portion of refrigerant tapped from a liquid line in the main circuit, and expanded to an intermediate pressure, said tapped expanded refrigerant cooling a refrigerant flowing in said liquid line through said economizer heat exchanger, and said tapped refrigerant   then being returned to an injection point intermediate said at least two compression stages, and an intercooler heat exchanger positioned between said at least two compression stages.   
   
   
       2 . The refrigerant system as set forth in  claim 1 , wherein at least two compression stages are represented by separate compressor units. 
   
   
       3 . The refrigerant system as set forth in  claim 1 , wherein at least two compression stages are represented by compression members within the same compressor. 
   
   
       4 . The refrigerant system as set forth in  claim 1 , wherein there are at least three of said compression stages, and said injection point for said tapped refrigerant and said intercooler are positioned between different compression stages. 
   
   
       5 . The refrigerant system as set forth in  claim 4 , wherein said intercooler is positioned between higher compression stages and said injection point is positioned between lower compression stages with respect to refrigerant flow. 
   
   
       6 . The refrigerant system as set forth in  claim 4 , wherein said intercooler is
 positioned between lower compression stages and said injection point is positioned between higher compression stages with respect to refrigerant flow.   
   
   
       7 . The refrigerant system as set forth in  claim 1 , wherein said injection point for said tapped refrigerant and said intercooler are positioned between the same compression stages. 
   
   
       8 . The refrigerant system as set forth in  claim 7 , wherein said intercooler is positioned downstream of said injection point with respect to refrigerant flow. 
   
   
       9 . The refrigerant system as set forth in  claim 7 , wherein said intercooler is positioned upstream of said injection point with respect to refrigerant flow. 
   
   
       10 . The refrigerant system as set forth in  claim 1 , wherein said tapped refrigerant is tapped from a location upstream of said economizer heat exchanger. 
   
   
       11 . The refrigerant system as set forth in  claim 1 , wherein said tapped refrigerant is tapped from a point downstream of said economizer heat exchanger. 
   
   
       12 . The refrigerant system as set forth in  claim 1 , wherein said refrigerant system operates for at least for a portion of the time in the transcritical cycle. 
   
   
       13 . The refrigerant system as set forth in  claim 1 , wherein said refrigerant system operates for at least for a portion of the time in the subcritical cycle. 
   
   
       14 . The refrigerant system as set forth in  claim 1 , wherein said refrigerant system utilizes CO 2  as a refrigerant. 
   
   
       15 . The refrigerant system as set forth in  claim 1 , wherein a relative position of said intercooler and said injection point with respect to refrigerant flow is at least partially defined based on at least one of a temperature of a source for a secondary fluid supplied to the intercooler and relative importance of capacity and efficiency provided by the economizer circuit. 
   
   
       16 . The refrigerant system as set forth in  claim 1 , wherein an absolute position of said intercooler and said injection point with respect to compression stages is at least partially defined based on at least one of discharge temperature, environmental conditions, required refrigerant system efficiency, required refrigerant system capacity, required unloading options and a temperature of a source for a secondary fluid supplied to the intercooler. 
   
   
       17 . A method of operating a refrigerant system comprising the steps of:
 (1) providing at least two compression stages connected in series with respect to a refrigerant flow, a condenser positioned downstream of said at least two compression stages, an expansion device positioned downstream of said condenser and an evaporator positioned downstream of said expansion device, refrigerant passing through said at least two compression stages, to said condenser, to said main expansion device, to said evaporator, and then returning to a lower compression stage of said at least two compression stages; and   (2) providing an economizer circuit incorporated into the refrigerant system, said economizer circuit including an economizer heat exchanger for receiving a portion of refrigerant tapped from a liquid line in the main circuit, and expanded to an intermediate pressure, using said tapped expanded refrigerant to cool a refrigerant flowing in said liquid line through said economizer heat exchanger, and said tapped refrigerant then being returned to an injection point intermediate said at least two compression stages, and positioning an intercooler heat exchanger between said at least two compression stages.   
   
   
       18 . The method as set forth in  claim 17 , wherein there are at least three of said compression stages, and said injection point for said tapped refrigerant and said intercooler are positioned between different compression stages. 
   
   
       19 . The method as set forth in  claim 18 , wherein said intercooler is positioned between higher compression stages and said injection point is positioned between lower compression stages with respect to refrigerant flow. 
   
   
       20 . The method as set forth in  claim 18 , wherein said intercooler is positioned between lower compression stages and said injection point is positioned between higher compression stages with respect to refrigerant flow. 
   
   
       21 . The method as set forth in  claim 17 , wherein said injection point for said tapped refrigerant and said intercooler are positioned between the same compression stages. 
   
   
       22 . The method as set forth in  claim 21 , wherein said intercooler is positioned downstream of said injection point with respect to refrigerant flow. 
   
   
       23 . The method as set forth in  claim 21 , wherein said intercooler is positioned upstream of said injection point with respect to refrigerant flow. 
   
   
       24 . The method as set forth in  claim 17 , wherein said tapped refrigerant is tapped from a location upstream of said economizer heat exchanger. 
   
   
       25 . The method as set forth in  claim 17 , wherein said tapped refrigerant is tapped from a point downstream of said economizer heat exchanger. 
   
   
       26 . The method as set forth in  claim 17 , wherein said refrigerant system operates at least for a portion of the time in the transcritical cycle. 
   
   
       27 . The method as set forth in  claim 17 , wherein said refrigerant system operates at least for a portion of the time in the subcritical cycle. 
   
   
       28 . The method as set forth in  claim 17 , wherein said refrigerant system utilizes CO 2  as a refrigerant. 
   
   
       29 . The method as set forth in  claim 17 , wherein a relative position of said intercooler and said injection point with respect to refrigerant flow is at least partially defined based on at least one of a temperature of a source for a secondary fluid supplied to the intercooler and relative importance of capacity and efficiency provided by the economizer circuit. 
   
   
       30 . The method as set forth in  claim 17 , wherein an absolute position of said intercooler and said injection point with respect to compression stages is at least partially defined based on at least one of discharge temperature, environmental conditions, required refrigerant system efficiency, required refrigerant system capacity, required unloading options and a temperature of a source for a secondary fluid supplied to the intercooler.