Hot gas defrost using medium temperature discharge gas

Abstract

A refrigeration system includes evaporators, one or more medium temperature compressors, and a three-way valve positioned downstream from the one or more medium temperature compressors. The three-way valve receives the compressed refrigerant from the medium temperature compressors and directs flow of the received compressed refrigerant to (i) a gas cooler and/or (ii) one or more of the evaporators based on an operation mode of the evaporators. A controller determines that operation of a first evaporator in a defrost mode is indicated and causes the first evaporator to operate in the defrost mode by adjusting the three-way valve to direct a portion of the received compressed refrigerant to the first evaporator.

What is claimed is: 
     
         1 . A method of operating a refrigeration system, the method comprising:
 operating a first evaporator of a plurality of evaporators in a refrigeration mode;   determining that operation of the first evaporator in a defrost mode is indicated; and   after determining that operation of the first evaporator in the defrost mode is indicated, causing the first evaporator to operate in the defrost mode by adjusting a three-way valve positioned downstream from one or more medium temperature compressors of the refrigeration system to direct a portion of refrigerant compressed by the one or more medium temperature compressors to the first evaporator.   
     
     
         2 . The method  claim 1 , further comprising:
 receiving, by a gas cooler of the refrigeration system, refrigerant from the one or more compressors and cooling the refrigerant; and   receiving and storing, by a flash tank, the cooled refrigerant.   
     
     
         3 . The method of  claim 2 , further comprising causing the first evaporator to operate in the defrost mode by:
 closing a first valve located upstream from the first evaporator in refrigerant conduit coupling a liquid outlet of the flash tank to the first evaporator; and   closing a second valve located downstream from the first evaporator in refrigerant conduit allowing flow of refrigerant towards the one or more medium temperature compressors.   
     
     
         4 . The method of  claim 3 , further comprising:
 at least partially opening a third valve located upstream from the first evaporator in refrigerant conduit coupling an inlet of the flash tank to the first evaporator; and   at least partially opening a fourth valve located downstream from the first evaporator in refrigerant conduit allowing flow of refrigerant from the one or more medium temperature compressors to the first evaporator.   
     
     
         5 . The method of  claim 1 , further comprising:
 determining that defrost mode operation of the first evaporator is complete; and   after determining that defrost mode operation of the first evaporator is complete, causing the first evaporator to operate in a transition mode, wherein during operation in the transition mode at least a portion of the compressed refrigerant provided to the first evaporator is provided back toward the one or more medium temperature compressors.   
     
     
         6 . The method of  claim 5 , further comprising causing at least the portion of the compressed refrigerant to be provided back toward the one or more medium temperature compressors by at least partially opening a transition-mode valve. 
     
     
         7 . The method of  claim 5 , further comprising, during operation of the first evaporator in the transition mode:
 determining a pressure associated with the first evaporator;   determining that the pressure is less than a threshold value; and   after determining that the pressure is less than the threshold value, causing the first evaporator to operate in a refrigeration mode.   
     
     
         8 . The method of  claim 1 , wherein, while the first evaporator is caused to operate in the defrost mode, a second evaporator of the plurality of evaporators is caused to operate in a refrigeration mode. 
     
     
         9 . A controller of a refrigeration system, the controller comprising:
 an input/output interface communicatively coupled to a three-way valve positioned downstream from the one or more medium temperature compressors, the three-way valve configured to receive refrigerant compressed by one or more medium temperature compressors, wherein the three-way valve is operable to direct flow of the received compressed refrigerant to one or both of a gas cooler and one or more of the evaporators of the plurality of evaporators based on an operation mode of the plurality of evaporators; and   a processor configured to:
 determine that operation of a first evaporator of a plurality of evaporators of the refrigeration system in a defrost mode is indicated; and 
 after determining that operation of the first evaporator in the defrost mode is indicated, cause the first evaporator to operate in the defrost mode by adjusting the three-way valve to direct a portion of the received compressed refrigerant to the first evaporator. 
   
     
     
         10 . The controller of  claim 9 , wherein:
 the input/output interface is further communicatively coupled to:
 a first valve located upstream from the first evaporator in refrigerant conduit coupling a liquid outlet of a flash tank to the first evaporator, wherein, when the first evaporator is operating in a refrigeration mode, the first valve is open; and 
 a second valve located downstream from the first evaporator in refrigerant conduit allowing flow of refrigerant towards the one or more medium temperature compressors, wherein, when the first evaporator is operating in the refrigeration mode, the second valve is open; and 
   the processor is further configured to cause the first evaporator to operate in the defrost mode by causing the first valve to close and causing the second valve to close.   
     
     
         11 . The controller of  claim 10 , wherein:
 the input/output interface is further communicatively coupled to:
 a third valve located upstream from the first evaporator in refrigerant conduit coupling an inlet of the flash tank to the first evaporator, wherein, when the first evaporator is operating in a refrigeration mode, the third valve is closed; and 
 a fourth valve located downstream from the first evaporator in refrigerant conduit allowing flow of refrigerant from the one or more medium temperature compressors to the first evaporator, wherein, when the first evaporator is operating in the refrigeration mode, the fourth valve is closed; and 
   the processor is further configured to cause the first evaporator to operate in the defrost mode by causing the third valve to open and causing the fourth valve to open.   
     
     
         12 . The controller of  claim 9 , wherein the processor is further configured to:
 determine that defrost mode operation of the first evaporator is complete; and   after determining that defrost mode operation of the first evaporator is complete, cause the first evaporator to operate in a transition mode, wherein during operation in the transition mode at least a portion of the compressed refrigerant provided to the first evaporator is provided back toward the one or more medium temperature compressors.   
     
     
         13 . The controller of  claim 9 , wherein the processor is further configured to cause at least the portion of the compressed refrigerant to be provided back toward the one or more medium temperature compressors by at least partially opening a transition-mode valve. 
     
     
         14 . The controller of  claim 9 , wherein the processor is further configured, during operation of the first evaporator in the transition mode, to:
 determine a pressure associated with the first evaporator;   determine that the pressure is less than a threshold value; and   after determining that the pressure is less than the threshold value, cause the first evaporator to operate in a refrigeration mode.   
     
     
         15 . The controller of  claim 9 , wherein, while the first evaporator is caused to operate in the defrost mode, a second evaporator of the plurality of evaporators is caused to operate in a refrigeration mode.