Carbon dioxide refrigeration system and a method of operating the refrigeration system

Abstract

A refrigeration system including one or more first compressor(s) for compressing a carbon dioxide (CO 2 ) refrigerant, a main heat rejection system for cooling the CO 2 refrigerant, one or more high pressure expansion device(s) for reducing the pressure of the CO 2 refrigerant, a receiver for storing the CO 2 refrigerant, one or more high pressure expansion device(s), an evaporator and a receiver pressure regulating device. The refrigeration system further includes an auxiliary refrigeration system including an auxiliary compressor arranged to compress at least part of the CO 2 refrigerant and thereafter to direct the compressed CO 2 refrigerant to a heat rejection system.

1 . A refrigeration system for transferring heat, wherein the refrigeration system comprises:
 a main refrigeration system comprising:
 one or more first compressors for compressing a carbon dioxide (CO 2 ) refrigerant; 
 a main heat rejection system for cooling the CO 2  refrigerant discharged from the one or more first compressors; 
 one or more high pressure expansion devices for reducing pressure of the CO 2  refrigerant discharged from the main heat rejection system; 
 a receiver for receiving the CO 2  refrigerant from the one or more high pressure expansion devices; 
 one or more low pressure expansion devices for reducing the pressure of a liquid phase of the CO 2  refrigerant from the receiver; 
 an evaporator for evaporating the liquid phase part of the CO 2  refrigerant from the one or more low pressure expansion devices and thereafter directing the evaporated liquid phase part of the CO 2  refrigerant to a suction side of the one or more first compressors; 
   an auxiliary refrigeration system comprising:
 an auxiliary compressor arranged to compress at least part of a vapour phase of the CO 2  refrigerant from the receiver to generate compressed CO 2  refrigerant and to direct the compressed CO 2  refrigerant to a heat rejection system, wherein a nominal maximal volume rate of flow of the compressed refrigerant of the auxiliary compressor is less than 10% of the nominal maximal volume rate of flow of compressed refrigerant of the one or more first compressors. 
   
     
     
         2 . The refrigeration system according to  claim 1 , wherein the one or more first compressors are arranged to compress the CO 2  refrigerant from the vapour phase of the CO 2  refrigerant to a supercritical phase and wherein the main heat rejection system is arranged to cool supercritical CO 2  refrigerant discharged from the one or more first compressors. 
     
     
         3 . The refrigeration system according to  claim 2 , wherein the one or more high pressure expansion devices are arranged to reduce the pressure of the CO 2  refrigerant in the supercritical phase, after being discharged from the main heat rejection system, wherein the one or more high pressure expansion devices are further arranged to decompress the CO 2  refrigerant to a subcritical state. 
     
     
         4 . The refrigeration system according to  claim 1 , wherein the receiver is arranged to receive subcritical CO 2  refrigerant from the one or more high pressure expansion devices. 
     
     
         5 . The refrigeration system according to  claim 1 , wherein the auxiliary compressor is arranged to either compress at least part of the vapour phase of the CO 2  refrigerant from the receiver to a supercritical phase and thereafter to direct the compressed CO 2  refrigerant to an auxiliary heat rejection system or compress at least part of the vapour phase of the CO 2  refrigerant from the suction side of the one or more compressors to a supercritical phase and thereafter to direct the compressed CO 2  refrigerant to the main heat rejection system. 
     
     
         6 . The refrigeration system according to  claim 1 , wherein the auxiliary compressor is arranged to direct the compressed CO 2  refrigerant to the main heat rejection system. 
     
     
         7 . The refrigeration system according to  claim 1 , wherein the main heat rejection system is arranged to allow for cooling of the CO 2  refrigerant discharged from the auxiliary compressor and to allow the CO 2  refrigerant to be led through the main heat rejection system, when the main heat rejection system is off. 
     
     
         8 . The refrigeration system according to  claim 1 , wherein the auxiliary compressor is arranged to direct the compressed CO 2  refrigerant to an auxiliary heat rejection system. 
     
     
         9 . The refrigeration system according to  claim 1 , wherein the auxiliary refrigeration system further comprises one or more auxiliary high pressure expansion devices for expanding the CO 2  refrigerant received from the main heat rejection system. 
     
     
         10 . The refrigeration system according to  claim 1 , further comprising one or more control systems for controlling operation of the auxiliary refrigeration system, including the auxiliary compressor, based on one or more inputs. 
     
     
         11 . The refrigeration system according to  claim 1 , wherein the refrigeration system comprises one or more measuring devices for measuring a value representative of a pressure and/or temperature of the refrigeration system and providing an input accordingly to one or more control systems of the refrigeration system. 
     
     
         12 . The refrigeration system according to  claim 1 , wherein the auxiliary refrigeration system comprises a control for controlling a flow of CO 2  refrigerant to the auxiliary compressor. 
     
     
         13 . The refrigeration system according to  claim 1 , wherein the auxiliary refrigeration system comprises a control comprising one or more pulse width modulation (PWM) valves, and wherein a control system of the refrigeration system is arranged to control the operation of the one or more PWM valves based on one or more inputs representing a pressure and/or temperature of the refrigeration system. 
     
     
         14 . The refrigeration system according to  claim 1 , wherein the auxiliary refrigeration system is arranged to be powered by an auxiliary power supply separate from a power supply of the main refrigeration system. 
     
     
         15 . A method of operating a refrigeration system in the event a main refrigeration system of the refrigeration system being off, wherein the refrigeration system comprises:
 a main refrigeration system comprising:
 one or more first compressors for compressing a carbon dioxide (CO 2 ) refrigerant; 
 a main heat rejection system for cooling the CO 2  refrigerant discharged from the one or more first compressors; 
 one or more high pressure expansion devices for reducing pressure of the CO 2  refrigerant discharged from the main heat rejection system; 
 a receiver for receiving the CO 2  refrigerant from the one or more high pressure expansion devices; 
 one or more low pressure expansion devices for reducing the pressure of a liquid phase of the CO 2  refrigerant from the receiver; 
 an evaporator for evaporating the liquid phase part of the CO 2  refrigerant from the one or more low pressure expansion devices and thereafter directing the evaporated liquid phase part of the CO 2  refrigerant to a suction side of the one or more first compressors; 
   an auxiliary refrigeration system comprising:
 an auxiliary compressor arranged to compress at least part of a vapour phase of the CO 2  refrigerant from the receiver to generate compressed CO 2  refrigerant and to direct the compressed CO 2  refrigerant to a heat rejection system, wherein a nominal maximal volume rate of flow of the compressed refrigerant of the auxiliary compressor is less than 10% of the nominal maximal volume rate of flow of compressed refrigerant of the one or more first compressors; 
   wherein the method comprises:
 detecting a value representing pressure and/or temperature of the refrigeration system by a measuring device and providing an input accordingly to a control system; 
 controlling operation of the auxiliary compressor and if present, a control of the auxiliary refrigeration system, by the control system based on the input. 
   
     
     
         16 . The refrigeration system according to  claim 1 , wherein the nominal maximal volume rate of flow of compressed refrigerant of the auxiliary compressor is less than 5% of the nominal maximal volume rate of flow of the compressed refrigerant of the one or more first compressors. 
     
     
         17 . The refrigeration system according to  claim 1 , wherein the nominal maximal volume rate of flow of compressed refrigerant of the auxiliary compressor is less than 1% of the nominal maximal volume rate of flow of the compressed refrigerant of the one or more first compressors. 
     
     
         18 . The refrigeration system according to  claim 1 , wherein the nominal maximal volume rate of flow of compressed refrigerant of the auxiliary compressor is less than 0.5% of the nominal maximal volume rate of flow of the compressed refrigerant of the one or more first compressors. 
     
     
         19 . The refrigeration system according to  claim 10 , wherein the one or more inputs represent a pressure and/or temperature of the refrigeration system. 
     
     
         20 . The refrigeration system according to  claim 8 , wherein the auxiliary refrigeration system further comprises one or more auxiliary high pressure expansion devices for expanding the CO 2  refrigerant received from the auxiliary heat rejection system.