Control Of Refrigerant Injection Into A Compressor In An Economized Refrigeration Cycle

Abstract

A method of controlling injection into a compressor in a refrigeration cycle is described. A refrigeration cycle may comprise at least an economizer heat exchanger, a heat rejection heat exchanger, a first expansion device, and a compressor. A discharge port of the compressor is connected to the heat rejection heat exchanger via a discharge line and an injection port of the compressor is connected to the means for compressing. The economizer heat exchanger comprises a first path having an input connected to the heat rejection heat exchanger and an output connected to the first expansion device, and a second path having an input connected to the heat rejection heat exchanger via an economizer valve and an output connected to the injection port of the compressor via an injection line. The economizer valve is regulated based on a superheat level of the refrigerant in the economizer heat exchanger.

What is claimed is: 
     
         1 . A method of controlling injection into a compressor in a refrigeration cycle, wherein the method is performed in a refrigeration cycle, which comprises at least a flash tank configured for receiving a refrigerant and separating liquid refrigerant and vapour refrigerant, and a compressor configured for compressing the refrigerant, wherein the compressor comprises a means for compressing, a suction port and an injection port, which is connected to the means for compressing for at least a time instance of the refrigeration cycle, wherein the flash tank is connected to the injection port of the compressor via an injection valve,
 the method comprising:   determining a pressure in the flash tank;   controlling the injection valve based on the determined pressure in the flash tank.   
     
     
         2 . The method according to  claim 1 , wherein controlling the injection valve comprises:
 if the determined pressure in the flash tank is lower than a first threshold, closing the injection valve.   
     
     
         3 . The method according to  claim 2 , wherein controlling the injection valve comprises:
 if the determined pressure in the flash tank is equal to or greater than the first threshold and lower than a second threshold, at least partially opening the injection valve.   
     
     
         4 . The method according to  claim 3 , wherein opening the injection valve comprises:
 determining, by a proportional integral derivative, PID, controller, a value for an opening degree of the injection valve based on the determined flash tank pressure; and   setting the opening degree of the injection valve to the determined value.   
     
     
         5 . The method according to  claim 3 , further comprising:
 determining whether the compressor is operating; and   wherein opening the injection valve is only carried out, if it is determined that the compressor is operating.   
     
     
         6 . The method according to  claim 3 , wherein controlling the injection valve comprises:
 if the determined pressure in the flash tank is greater than the second threshold, closing the injection valve.   
     
     
         7 . The method according to  claim 1 , the method further comprising:
 determining a pressure at the suction port of the compressor;   determining whether the pressure at the suction port is lower than a third threshold; and   if it is determined that the pressure at the suction port is lower than the third threshold:   closing the injection valve; and   turning off the compressor.   
     
     
         8 . The method according to  claim 1 , the method further comprising:
 controlling the compressor based on the determined pressure in the flash tank.   
     
     
         9 . The method according to  claim 8 , wherein controlling the compressor comprises:
 if the determined flash tank pressure is lower than a fourth threshold, determining, by a PID controller, an operating speed for the compressor and setting the operating speed to the determined operating speed.   
     
     
         10 . The method according to  claim 9 , wherein controlling the compressor comprises:
 if the determined flash tank pressure is equal to or greater than the fourth threshold and lower than a fifth threshold, unloading the compressor; and   if the determined flash tank pressure is greater than the fifth threshold, stopping operation of the compressor.   
     
     
         11 . The method according to  claim 1 , wherein the compressor comprises a discharge port and wherein the refrigeration cycle further comprises a heat rejection heat exchanger, which is connected to the discharge port of the compressor, and an expansion device disposed between the heat rejection heat exchanger and the flash tank, wherein the method further comprises:
 if the determined flash tank pressure is lower than a sixth threshold, setting an opening degree of the expansion device to a predetermined value;   if the determined flash tank pressure is equal to or greater than the sixth threshold and lower than a seventh, setting the opening degree of the expansion device to a value determined by a PID controller based on a first heat rejection heat exchanger pressure mode;   determining that the pressure in the flash tank is equal to or greater than the seventh and lower than an eighth threshold and setting the opening degree of the expansion device to a value determined by the PID controller based on a second heat rejection heat exchanger pressure mode; or   determining that the pressure in the flash tank is equal to or greater than the eighth threshold and lower than a ninth threshold and controlling the opening degree of the expansion device based on fuzzy regulation; or   determining that the pressure in the flash tank is equal to or greater than the ninth threshold and lower than a tenth threshold and controlling the opening degree of the expansion device based on a flash tank pressure regulation mode; or   determining whether the pressure in the flash tank is equal to or greater than the tenth threshold and closing the expansion device.   
     
     
         12 . The method according to  claim 11 , wherein the first heat rejection heat exchanger pressure mode comprises controlling the expansion device based on the temperature of the refrigerant in the heat rejection heat exchanger. 
     
     
         13 . The method according to  claim 11 , wherein the second heat rejection heat exchanger pressure mode (HRHE_mode2) comprises controlling the expansion device based on the temperature of the refrigerant in the heat rejection heat exchanger and the pressure of the refrigerant in the flash tank. 
     
     
         14 . The method according to  claim 11 , wherein the flash tank pressure regulation mode comprises controlling the expansion device based on the pressure if the refrigerant in the flash tank. 
     
     
         15 . The method according to  claim 1 , wherein the refrigerant cycle comprises a by-pass line connected between the flash tank and the suction port of the compressor, wherein the by-pass line comprises a by-pass valve, and wherein the method further comprises:
 determining that the pressure of the flash tank is lower than a eleventh threshold and closing the by-pass valve; or   determining that the pressure of the flash tank is equal to or greater than the eleventh threshold and lower than a twelfth threshold, and determining, by a PID controller, a value for an opening degree of the by-pass valve based on the determined flash tank pressure; or   determining that the pressure of the flash tank is equal to or greater than the twelfth threshold and lower than a thirteenth threshold, and opening the by-pass valve completely; or   determining that the pressure of the flash tank is equal to or greater than the thirteenth threshold and setting an opening degree of the by-pass valve to a predetermined value.