Refrigeration system with refrigerant charge control

Abstract

A refrigeration system includes a refrigeration subsystem that includes a set of primary compressors operating at a primary suction pressure to compress a refrigerant fluid, evaporators fluidly coupled to the primary compressors, and expansion valves fluidly coupled to the evaporators. The refrigeration system includes a gas cooler/condenser fluidly coupled to the refrigeration subsystem and configured to cool a vapor phase of the refrigerant fluid from the primary compressors to a liquid phase or mixed phase of the refrigerant fluid; a flash tank fluidly coupled to the gas cooler/condenser; and a secondary compressor configured to pump down at least a portion of the refrigerant fluid to the flash tank. The secondary compressor includes a suction side fluidly coupled to an outlet of the flash tank and a discharge side fluidly coupled to an inlet of the gas cooler/condenser.

1 . (canceled) 
     
     
         2 . A refrigeration system, comprising:
 at least one refrigeration subsystem comprising:
 a set of one or more primary compressors operating at a primary suction pressure to compress a refrigerant fluid, 
 one or more evaporators fluidly coupled to the one or more primary compressors through a primary suction conduit and configured to cool an enclosed space, and 
 one or more expansion valves fluidly coupled to the one or more evaporators; 
   at least one gas cooler/condenser fluidly coupled to the at least one refrigeration subsystem and configured to cool a vapor phase of the refrigerant fluid from the one or more primary compressors to a liquid phase or mixed phase of the refrigerant fluid;   a flash tank fluidly coupled to the at least one gas cooler/condenser; and   at least one secondary compressor configured to pump down at least a portion of the refrigerant fluid to the flash tank, the at least one secondary compressor comprising:
 a suction side fluidly coupled to an outlet of the flash tank, and 
 a discharge side fluidly coupled to an inlet of the at least one gas cooler/condenser. 
   
     
     
         3 . The refrigeration system of  claim 2 , comprising an oil return assembly that comprises a refrigerant outlet conduit fluidly coupled to a discharge conduit that fluidly couples the discharge side of the at least one secondary compressor with the at least one gas cooler/condenser. 
     
     
         4 . The refrigeration system of  claim 2 , wherein the discharge side comprises a first discharge side and a second discharge side. 
     
     
         5 . The refrigeration system of  claim 4 , wherein the first discharge side is fluidly coupled to the inlet of the at least one gas cooler/condenser, and the second discharge side is fluidly coupled to a bypass conduit that fluidly couples the flash tank to the primary suction conduit. 
     
     
         6 . The refrigeration system of  claim 2 , wherein the at least one secondary compressor comprises:
 a first secondary compressor comprising a first suction side and a first discharge side; and   a second secondary compressor comprising a second suction side and a second discharge side.   
     
     
         7 . The refrigeration system of  claim 6 , wherein the first suction side is fluidly coupled to the primary suction conduit, and the second suction side is fluidly coupled to the primary suction conduit. 
     
     
         8 . The refrigeration system of  claim 6 , wherein the first and second discharge sides are fluidly coupled to the inlet of the at least one gas cooler/condenser. 
     
     
         9 . The refrigeration system of  claim 6 , wherein the first discharge side is fluidly coupled to the inlet of the at least one gas cooler/condenser, and the second discharge side is fluidly coupled to a bypass conduit that fluidly couples the flash tank to the primary suction conduit. 
     
     
         10 . The refrigeration system of  claim 2 , wherein the flash tank comprises a high level sensor configured to measure a level of the liquid phase of the refrigerant fluid in the flash tank. 
     
     
         11 . The refrigeration system of  claim 2 , comprising a control system communicably coupled to the at least one secondary compressor, one or more pressure transducers positioned in the refrigeration system, and one or more shut-off valves positioned in the refrigeration system, the control system configured to perform operations comprising:
 determining an event occurrence in the refrigeration system; and   based on the determination of the event occurrence, operating the at least one secondary compressor to pump down the portion of the refrigerant fluid to the flash tank.   
     
     
         12 . The refrigeration system of  claim 11 , wherein the operations comprise:
 receiving or identifying one or more fluid pressure values measured by the one or more pressure transducers; and   based on the one or more fluid pressure values, adjusting at least one of the one or more shut-off valves between a closed position and an open position.   
     
     
         13 . The refrigeration system of  claim 11 , wherein the event occurrence comprises a loss of main power to the at least one refrigeration subsystem. 
     
     
         14 . The refrigeration system of  claim 13 , wherein the operations comprise activating an uninterruptible power supply (UPS) electrically coupled to the at least one secondary compressor to provide power to the at least one secondary compressor. 
     
     
         15 . The refrigeration system of  claim 14 , wherein the UPS is not electrically coupled to the one or more primary compressors. 
     
     
         16 . The refrigeration system of  claim 2 , wherein the refrigerant fluid comprises carbon dioxide. 
     
     
         17 . The refrigeration system of  claim 2 , wherein the at least one refrigeration subsystem comprises a medium temperature (MT) refrigeration subsystem. 
     
     
         18 . A method of operating a refrigeration system, comprising:
 operating at least one refrigeration subsystem of a refrigeration system to cool an enclosed space, the at least one refrigeration subsystem comprising a set of one or more primary compressors operating at a primary suction pressure to compress a refrigerant fluid and supply the refrigerant fluid through one or more expansion valves and to one or more evaporators fluidly coupled to the one or more primary compressors through a primary suction conduit to cool the enclosed space;   operating at least one gas cooler/condenser fluidly coupled to the at least one refrigeration subsystem to cool a vapor phase of the refrigerant fluid from the one or more primary compressors to a liquid phase or mixed phase of the refrigerant fluid;   supplying the liquid phase or mixed phase of the refrigerant fluid to a flash tank fluidly coupled to the at least one gas cooler/condenser;   based on an event occurrence, operating at least one secondary compressor to draw the portion of the refrigerant fluid through a suction side of the at least one secondary compressor that is fluidly coupled at a suction side to an outlet of the flash tank and at a discharge side to an inlet of the at least one gas cooler/condenser;   pumping down at least a portion of the refrigerant fluid drawn through the suction side to the flash tank; and   discharging compressed refrigerant fluid from the at least one secondary compressor through the discharge side to the at least one gas cooler/condenser.   
     
     
         19 . The method of  claim 18 , comprising operating the at least one secondary compressor to draw the portion of the refrigerant fluid through:
 a first branch conduit fluidly coupled between the primary suction conduit and the at least one secondary compressor, and   a second branch conduit fluidly coupled between the flash tank and the at least one secondary compressor.   
     
     
         20 . The method of  claim 19 , wherein the first and second branch conduits are fluidly coupled together upstream of the suction side. 
     
     
         21 . The method of  claim 20 , comprising:
 discharging a portion of compressed refrigerant fluid from a first discharge branch coupled to the at least one secondary compressor to the at least one gas cooler/condenser; and   discharging another portion of compressed refrigerant fluid from a second discharge branch coupled to the at least one secondary compressor to a bypass conduit that fluidly couples the flash tank to the primary suction conduit.   
     
     
         22 . The method of  claim 18 , wherein operating the at least one secondary compressor comprises:
 operating a first secondary compressor to draw refrigerant fluid through a first suction side and discharge compressed refrigerant fluid through a first discharge side; and   operating a second secondary compressor to draw refrigerant fluid through a second suction side and discharge compressed refrigerant fluid through a second discharge side.   
     
     
         23 . The method of  claim 22 , comprising discharging compressed refrigerant fluid from the first and second discharge sides to the at least one gas cooler/condenser. 
     
     
         24 . The method of  claim 22 , comprising:
 discharging a portion of compressed refrigerant fluid from the first discharge side to the at least one gas cooler/condenser, and   discharging another portion of compressed refrigerant fluid from the second discharge side to a bypass conduit that fluidly couples the flash tank to the primary suction conduit.   
     
     
         25 . The method of  claim 18 , comprising determining, with a high level sensor positioned in the flash tank, a level of the liquid phase of the refrigerant fluid in the flash tank. 
     
     
         26 . The method of  claim 18 , comprising:
 determining, with a control system communicably coupled to the at least one refrigeration subsystem, the event occurrence in the refrigeration system; and   based on the determination of the event occurrence, activating, with the control system, the at least one secondary compressor.   
     
     
         27 . The method of  claim 26 , comprising:
 determining one or more fluid pressure values with one or more pressure transducers positioned in the refrigeration system; and   based on the one or more fluid pressure values, adjusting one or more shut-off valves positioned in the refrigeration system between a closed position and an open position.   
     
     
         28 . The method of  claim 26 , wherein the event occurrence comprises a loss of main power to the at least one refrigeration subsystem. 
     
     
         29 . The method of  claim 28 , comprising activating an uninterruptible power supply (UPS) electrically coupled to the at least one secondary compressor to provide power to the at least one secondary compressor. 
     
     
         30 . The method of  claim 28 , wherein the UPS is not electrically coupled to the one or more primary compressors. 
     
     
         31 . The method of  claim 18 , wherein the refrigerant fluid comprises carbon dioxide. 
     
     
         32 . The method of  claim 18 , comprising:
 separating, with an integrated oil separator/reservoir of an oil return assembly, oil from the refrigerant fluid discharged from the secondary compressor; and   transporting at least a portion of the separated oil to the secondary compressor through a conduit fluidly coupled between the secondary compressor and a discharge conduit that fluidly couples the discharge side of the secondary compressor with the at least one gas cooler/condenser.   
     
     
         33 . The method of  claim 32 , comprising:
 storing the separated oil in the integrated oil separator/reservoir that is positioned in the discharge conduit and fluidly coupled to the conduit; and   controlling the transporting of the portion of the separated oil with an oil return valve positioned in the conduit and fluidly coupled to the secondary compressor.