Refrigeration system and method of defrosting the same

Abstract

The disclosure provides a method of operating a refrigeration system. The method includes operating a first low-temperature evaporator in a refrigeration mode, where the first low-temperature evaporator receives refrigerant from a flash tank. The method includes operating a second low-temperature evaporator in a refrigeration mode, where the first low-temperature evaporator receives refrigerant from the flash tank. The method includes causing the first low-temperature evaporator to operate in the defrost mode by: closing a first controllable valve in a refrigerant conduit that couples the first low-temperature evaporator to a low-temperature compressor of the refrigeration system, and directing the refrigerant exiting the first low-temperature evaporator to be received by the second low-temperature evaporator.

What is claimed is: 
     
         1 . A refrigeration system, comprising:
 a flash tank configured to receive refrigerant from a gas cooler through a refrigerant conduit, the flash tank configured to store at least a portion of the refrigerant received from the gas cooler;   a first low-temperature evaporator located downstream of the flash tank and configured to receive the refrigerant from the flash tank through the refrigerant conduit;   a second low-temperature evaporator located downstream of the flash tank and configured to receive the refrigerant from the flash tank through the refrigerant conduit;   a low-temperature compressor located downstream of the first low-temperature evaporator and the second low-temperature evaporator, the low-temperature compressor configured to receive the refrigerant from the first low-temperature evaporator and the second low-temperature evaporator through the refrigerant conduit;   a first controllable valve positioned in the refrigerant conduit and downstream from the first low-temperature evaporator, the first controllable valve configured to receive refrigerant from the first low-temperature evaporator and direct a flow of the received refrigerant to: (i) the low-temperature compressor when the first controllable valve is configured in an open position; and (ii) the second low-temperature evaporator when the first controllable valve is configured in a closed position;   a first expansion valve positioned in the refrigerant conduit and located between the flash tank and the first low-temperature evaporator;   a first by-pass valve positioned in the refrigerant conduit and located between the flash tank and the first low-temperature evaporator, wherein when the first by-pass valve is in a closed position the refrigerant flows from the flash tank to the first low-temperature evaporator through the first expansion valve, and when the first by-pass valve is in an open position the refrigerant flows from the flash tank to the first low-temperature evaporator through the first by-pass valve;   a second expansion valve positioned in the refrigerant conduit and located between the flash tank and the second low-temperature evaporator; and   a second by-pass valve positioned in the refrigerant conduit and located between the flash tank and the second low-temperature evaporator, wherein when the second by-pass valve is in a closed position the refrigerant flows from the flash tank to the second low-temperature evaporator through the first expansion valve, and when the second by-pass valve is in an open position the refrigerant flows from the flash tank to the second low-temperature evaporator through the second by-pass valve; and   a controller communicatively coupled to the first controllable valve, wherein the controller is configured to:
 cause the first low-temperature evaporator to operate in a defrost mode by closing the first controllable valve to direct the refrigerant exiting the first low-temperature evaporator to be received by the second low-temperature evaporator; and 
 cause the first low-temperature evaporator to operate in the defrost mode by opening the first by-pass valve to direct refrigerant from the flash tank to the first low-temperature evaporator through the first by-pass valve and closing the second by-pass valve to direct the refrigerant exiting the first low-temperature evaporator to the second expansion valve before the refrigerant is directed to the second low-temperature evaporator. 
   
     
     
         2 . The refrigeration system of  claim 1 ,
 wherein the controller is further configured to cause the first low-temperature evaporator to operate in the defrost mode by opening the first expansion valve to increase a fraction of liquid refrigerant that is received by the first low-temperature evaporator during the defrost mode relative to a refrigeration mode of the first low-temperature evaporator, and   wherein the first controllable valve in the defrost mode directs the refrigerant exiting the first low-temperature evaporator to the second expansion valve before the refrigerant is directed to the second low-temperature evaporator.   
     
     
         3 . The refrigeration system of  claim 1  further comprising:
 a second controllable valve positioned in the refrigerant conduit and located between the flash tank and the first low-temperature evaporator, wherein when the first low-temperature evaporator is operating in a refrigeration mode the second controllable valve is open; 
 a third controllable valve positioned in the refrigerant conduit and located between the flash tank and the second low-temperature evaporator, wherein when the second low-temperature evaporator is operating in a refrigeration mode the third controllable valve is open; and 
 a fourth controllable valve positioned in the refrigerant conduit and located downstream from the second low-temperature evaporator, the fourth controllable valve configured to receive refrigerant from the second low-temperature evaporator and direct the flow of refrigerant to: (i) the low-temperature compressor when the fourth controllable valve is configured in an open position, and (ii) the first low-temperature evaporator when the fourth controllable valve is configured in a closed position, 
 wherein the controller is further configured to cause the first low-temperature evaporator to operate in the defrost mode by causing the third controllable valve to close. 
 
     
     
         4 . The refrigeration system of  claim 3 , wherein the controller is configured to cause the second low-temperature evaporator to operate in a defrost mode by opening the first controllable valve, closing the second controllable valve, opening the third controllable valve, and closing the fourth controllable valve. 
     
     
         5 . The refrigeration system of  claim 3  further comprising:
 a first check valve positioned in a portion of the refrigerant conduit that directs the refrigerant exiting the first low-temperature evaporator to mix with the refrigerant entering the second low-temperature evaporator, wherein when the first low-temperature evaporator is operating in the defrost mode the first check valve is configured to allow the refrigerant to flow from the first low-temperature evaporator to the second low-temperature evaporator; and 
 a second check valve positioned in a portion of the refrigerant conduit that directs the refrigerant exiting the second low-temperature evaporator to mix with the refrigerant entering the first low-temperature evaporator, wherein when the first low-temperature evaporator is operating in the defrost mode the second check valve is configured to restrict the refrigerant flowing from the second low-temperature evaporator to the first low-temperature evaporator. 
 
     
     
         6 . The refrigeration system of  claim 1 , wherein the controller is further configured to determine that the defrost mode of the first low-temperature evaporator is complete, and after determining that the defrost mode is complete, cause the first low-temperature evaporator to operate in a refrigeration mode. 
     
     
         7 . A method of operating a refrigeration system, the method comprising:
 operating a first low-temperature evaporator in a refrigeration mode, wherein the first low-temperature evaporator receives refrigerant from a flash tank;   operating a second low-temperature evaporator in a refrigeration mode, wherein the first low-temperature evaporator receives refrigerant from the flash tank; and   causing the first low-temperature evaporator to operate in a defrost mode by:
 closing a first controllable valve in a refrigerant conduit that couples the first low-temperature evaporator to a low-temperature compressor of the refrigeration system; 
 directing the refrigerant exiting the first low-temperature evaporator to be received by the second low-temperature evaporator; 
 opening a first by-pass valve positioned in the refrigerant conduit, wherein the first by-pass valve is located between the flash tank and the first low-temperature evaporator, and when the first by-pass valve is open the refrigerant flows around a first expansion valve located between the flash tank and the first low-temperature evaporator and through the first by-pass valve; and 
 closing a second by-pass valve positioned in the refrigerant conduit, wherein the second by-pass valve is located between the flash tank and the second low-temperature evaporator, and when the second by-pass valve is closed the refrigerant flows through a second expansion valve located between the flash tank and the second low-temperature evaporator. 
   
     
     
         8 . The method of  claim 7 , wherein operating the first low-temperature evaporator in the defrost mode further comprises:
 opening a first expansion valve positioned in the refrigerant conduit, wherein the first expansion valve is located between the flash tank and the first low-temperature evaporator, and wherein opening the first expansion valve increases a fraction of liquid refrigerant that is received by the first low-temperature evaporator during the defrost mode relative to a refrigeration mode of the first low-temperature evaporator; and   directing the refrigerant exiting the first low-temperature evaporator to a second expansion valve positioned between the flash tank and the second low-temperature evaporator.   
     
     
         9 . The method of  claim 7 , wherein operating the first low-temperature evaporator in the defrost mode further comprises:
 passing the refrigerant through a second controllable valve positioned in the refrigerant conduit located between the flash tank and the first low-temperature evaporator;   closing a third controllable valve positioned in the refrigerant conduit and located between the flash tank and the second low-temperature evaporator; and   passing the refrigerant through a fourth controllable valve positioned in the refrigerant conduit and located downstream from the second low-temperature evaporator, and when the fourth controllable valve is open the refrigerant is directed to the first low-temperature evaporator.   
     
     
         10 . The method of  claim 9 , further comprising:
 causing the second low-temperature evaporator to operate in a defrost mode by opening the first controllable valve, closing the second controllable valve, opening the third controllable valve, and closing the fourth controllable valve.   
     
     
         11 . The method of  claim 9 , wherein operating the first low-temperature evaporator in the defrost mode further comprises:
 passing the refrigerant exiting the first low-temperature evaporator through a first check valve positioned in the refrigerant conduit, wherein the refrigerant passing through the first check valve is directed to mix with the refrigerant entering the second low-temperature evaporator; and   restricting the refrigerant exiting the second low-temperature evaporator from flowing to the first low-temperature evaporator using a second check valve positioned in a portion of the refrigerant conduit that directs the refrigerant exiting the second low-temperature evaporator to mix with the refrigerant entering the first low-temperature evaporator.   
     
     
         12 . The method of  claim 7  further comprising:
 determining that the defrost mode of the first low-temperature evaporator is complete; and 
 causing the first low-temperature evaporator to operate in a refrigeration mode. 
 
     
     
         13 . A controller of a refrigeration system, the controller comprising:
 a network interface circuit communicatively coupled to a first controllable valve positioned in a refrigerant conduit and downstream from a first low-temperature evaporator, the first controllable valve configured to receive refrigerant from the first low-temperature evaporator and direct a flow of the received refrigerant to: (i) a low-temperature compressor when the first controllable valve is configured in an open position; and (ii) a second low-temperature evaporator when the first controllable valve is configured in a closed position; and   a processor operably coupled to the network interface circuit and configured to cause the first low-temperature evaporator to operate in a defrost mode by:
 closing the first controllable valve to direct the refrigerant exiting the first low-temperature evaporator to be received by the second low-temperature evaporator; 
 opening a first by-pass valve positioned in the refrigerant conduit, wherein the first by-pass valve is located between a flash tank and the first low-temperature evaporator, and when the first by-pass valve is open the refrigerant flows around a first expansion valve located between the flash tank and the first low-temperature evaporator and through the first by-pass valve; and 
 closing a second by-pass valve positioned in the refrigerant conduit, wherein the second by-pass valve is located between the flash tank and the second low-temperature evaporator, and when the second by-pass valve is closed the refrigerant flows through a second expansion valve located between the flash tank and the second low-temperature evaporator. 
   
     
     
         14 . The controller of  claim 13 , wherein the controller is further configured to cause the first low-temperature evaporator to operate in the defrost mode by:
 opening a first expansion valve positioned in the refrigerant conduit, wherein the first expansion valve is located between the flash tank and the first low-temperature evaporator, and wherein opening the first expansion valve increases a fraction of liquid refrigerant that is received by the first low-temperature evaporator during the defrost mode relative to a refrigeration mode of the first low-temperature evaporator; and   directing the refrigerant exiting the first low-temperature evaporator to a second expansion valve positioned between the flash tank and the second low-temperature evaporator.   
     
     
         15 . The controller of  claim 13 , wherein the controller is further configured to cause the first low-temperature evaporator to operate in the defrost mode by:
 passing the refrigerant through a second controllable valve positioned in the refrigerant conduit located between the flash tank and the first low-temperature evaporator;   closing a third controllable valve positioned in the refrigerant conduit and located between the flash tank and the second low-temperature evaporator; and   passing the refrigerant through a fourth controllable valve positioned in the refrigerant conduit and located downstream from the second low-temperature evaporator, and when the fourth controllable valve is open the refrigerant is directed to the first low-temperature evaporator.   
     
     
         16 . The controller of  claim 15 , wherein the controller is further configured to cause the second low-temperature evaporator to operate in a defrost mode by opening the first controllable valve, closing the second controllable valve, opening the third controllable valve, and closing the fourth controllable valve. 
     
     
         17 . The controller of  claim 13 , further comprising:
 determining that the defrost mode of the first low-temperature evaporator is complete; and   causing the first low-temperature evaporator to operate in a refrigeration mode.