Hot gas defrost system using hot gas from low temperature compressor

Abstract

A refrigeration system includes at least one low-temperature evaporator, at least one medium-temperature evaporator, one or more low-temperature compressors, and one or more medium-temperature compressors. A controllable valve positioned downstream from the one or more low-temperature compressors directs flow of refrigerant from the low-temperature compressor(s) to one or both of (i) the medium-temperature compressor(s) and (ii) one or more evaporators based on an operation mode of evaporators. A controller is communicatively coupled to the controllable valve. 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 controllable valve to direct a portion of the received compressed refrigerant to the first evaporator.

What is claimed is: 
     
         1 . A refrigeration system, comprising:
 a plurality of evaporators comprising at least one low-temperature evaporator and at least one medium-temperature evaporator;   one or more low-temperature compressors configured to compress refrigerant received from the at least one low-temperature evaporator;   one or more medium-temperature compressors configured to compress refrigerant received from the at least one medium-temperature evaporator;   a controllable valve positioned downstream from the one or more low-temperature compressors, the controllable valve configured to receive the compressed refrigerant from the one or more low-temperature compressors and direct flow of the received refrigerant to one or both of (i) the one or more medium-temperature compressors positioned downstream from the controllable valve and (ii) one or more evaporators of the plurality of evaporators based on an operation mode of the plurality of evaporators;   and a controller communicatively coupled to the controllable valve, wherein the controller is configured to:
 determine that operation of a first evaporator of the plurality of evaporators 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 controllable valve to direct a portion of the received compressed refrigerant to the first evaporator. 
   
     
     
         2 . The refrigeration system of  claim 1 , wherein the controller is further configured to cause the first evaporator to operate in the defrost mode by at least partially closing the controllable valve. 
     
     
         3 . The refrigeration system of  claim 1 , further comprising:
 a gas cooler configured to receive refrigerant from the one or more medium-temperature compressors and facilitate heat transfer from the received refrigerant; and   a flash tank located downstream from the gas cooler and configured to receive the refrigerant and store at least a portion of the received refrigerant.   
     
     
         4 . The refrigeration system of  claim 3 , further comprising:
 a first valve located upstream from the first evaporator in refrigerant conduit coupling a liquid outlet of the 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;   wherein the controller 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.   
     
     
         5 . The refrigeration system of  claim 4 , further comprising:
 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 coupling the first evaporator to the controllable valve, wherein, when the first evaporator is operating in the refrigeration mode, the fourth valve is closed;   wherein the controller 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.   
     
     
         6 . The refrigeration system of  claim 3 , further comprising a check valve positioned in refrigerant conduit coupling an outlet of the one or more low-temperature compressors to an inlet of the flash tank, wherein the check valve is configured to allow flow of refrigerant from the one or more low-temperature compressors to the flash tank when a pressure difference across the check valve exceeds a threshold value. 
     
     
         7 . The refrigeration system of  claim 1 , wherein the controller 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 refrigeration mode.   
     
     
         8 . The refrigeration system 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 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 controllable valve positioned in refrigerant conduit coupling one or more low-temperature compressors of the refrigeration system to one or more medium-temperature compressors of the refrigeration system; and 
 directing at least a portion of refrigerant compressed by the one or more low-temperature compressors to the first evaporator. 
   
     
     
         10 . The method of  claim 9 , further comprising causing the first evaporator to operate in the defrost mode by at least partially closing the controllable valve. 
     
     
         11 . The method  claim 9 , 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.   
     
     
         12 . The method of  claim 11 , 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.   
     
     
         13 . The method of  claim 12 , further comprising:
 opening 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   opening a fourth valve located downstream from the first evaporator in refrigerant conduit coupling the first evaporator to the controllable valve, wherein, when the first evaporator is operating in the refrigeration mode, the fourth valve is closed.   
     
     
         14 . The method of  claim 11 , further comprising, by a check valve positioned in refrigerant conduit coupling an outlet of the one or more low-temperature compressors to an inlet of the flash tank, allowing flow of refrigerant from the one or more low-temperature compressors to the flash tank when a pressure difference across the check valve exceeds a threshold value. 
     
     
         15 . The method of  claim 9 , 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 the refrigeration mode.   
     
     
         16 . The method of  claim 9 , wherein, while causing the first evaporator to operate in the defrost mode, causing a second evaporator of the plurality of evaporators to operate in a refrigeration mode. 
     
     
         17 . A controller of a refrigeration system, the controller comprising:
 an input/output interface communicatively coupled to a controllable valve positioned downstream from one or more low-temperature compressors of the refrigeration system, wherein the controllable valve is configured to receive the compressed refrigerant from the one or more low-temperature compressors and direct flow of the received refrigerant to one or both of (i) one or more medium-temperature compressors positioned downstream from the controllable valve and (ii) one or more 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 controllable valve to direct a portion of the received compressed refrigerant to the first evaporator. 
   
     
     
         18 . The controller of  claim 17 , wherein the processor is further configured to cause the first evaporator to operate in the defrost mode by at least partially closing the controllable valve. 
     
     
         19 . The controller of  claim 17 , wherein:
 the input/output interface communicatively coupled to:
 a first valve located upstream from the first evaporator in refrigerant conduit coupling a liquid outlet of the 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.   
     
     
         20 . The controller of  claim 19 , 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 coupling the first evaporator to the controllable valve, 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.