Two stage transcritical refrigeration system

Abstract

The invention provides a refrigeration system including a plurality of refrigerated display cases. Each display case has a dedicated evaporator assembly that cools return air by evaporating a refrigerant, and a first stage compressor assembly that is in fluid communication with the respective evaporator assembly to compress the refrigerant to a first pressure corresponding to a first temperature of the refrigerant prior to discharge of the compressed refrigerant. The refrigeration system also includes a second stage compressor assembly that is in fluid communication with the first stage compressor assemblies to compress the refrigerant to a second pressure that is higher than the first pressure, and that corresponds to a second temperature of the refrigerant. The refrigeration system further includes a heat exchanger that is in fluid communication with the second stage compressor assembly to receive the refrigerant from the second stage compressor assembly to reject heat from the refrigerant.

1 . A refrigeration system comprising:
 a plurality of refrigerated display cases, each of the plurality of refrigerated display cases including
 a dedicated evaporator assembly adapted to cool return air from the respective refrigerated display case by at least partially evaporating a refrigerant, and 
 a dedicated first stage compressor assembly in fluid communication with the dedicated evaporator assembly to compress the refrigerant from the dedicated evaporator assembly to a first pressure corresponding to a first temperature of the refrigerant, and to discharge the compressed refrigerant into a discharge main; 
   a second stage compressor assembly in fluid communication with the dedicated first stage compressor assembly of each of the plurality of refrigerated display cases to receive the refrigerant and to compress the refrigerant to a second pressure that is higher than the first pressure, the second pressure corresponding to a second temperature of the refrigerant;   a heat exchanger located remotely from the plurality of refrigerated display cases and in communication with the refrigerated display cases via a fluid main, the heat exchanger including an inlet in fluid communication with the second stage compressor assembly to receive the refrigerant from the second stage compressor assembly to reject heat from the refrigerant to an environment, the heat exchanger further including an outlet in fluid communication with the dedicated evaporator assembly in each of the plurality of refrigerated display cases via the fluid main.   
   
   
       2 . The refrigeration system of  claim 1 , wherein the refrigerant includes a carbon dioxide refrigerant. 
   
   
       3 . The refrigeration system of  claim 1 , further comprising a vessel positioned in fluid communication with the fluid main between the refrigerated display cases and the heat exchanger to separate liquid and gaseous phases of the refrigerant and to supply liquid refrigerant to each dedicated evaporator assembly. 
   
   
       4 . The refrigeration system of  claim 3 , wherein the discharge main is in heat exchange relationship with the refrigerant in the vessel, and wherein the refrigerant in the discharge main is configured to be de-superheated by heat exchange with the refrigerant in the vessel. 
   
   
       5 . The refrigerated system of  claim 4 , further comprising a fluid line in fluid communication with the discharge main between the second stage compressor assembly and the vessel to direct the de-superheated refrigerant from the discharge main toward the second stage compressor assembly. 
   
   
       6 . The refrigerated system of  claim 5 , further comprising a bypass main coupled between the vessel and the fluid line to circulate gaseous refrigerant from the vessel toward the second stage compressor assembly without passing through the fluid main to the refrigerated display cases. 
   
   
       7 . The refrigerated system of  claim 5 , further comprising an outlet line extending between the second stage compressor assembly and the heat exchanger, and a bypass line coupled between the fluid line and the outlet line to circulate gaseous refrigerant from the fluid line to the heat exchanger without passing through the second stage compressor assembly when a temperature of the refrigerant in the discharge main is below a predetermined temperature. 
   
   
       8 . The refrigerated system of  claim 7 , further comprising a check valve positioned in the bypass line and configured to inhibit flow of the refrigerant from the outlet line backward to the fluid line. 
   
   
       9 . The refrigerated system of  claim 1 , wherein the refrigerant includes a critical temperature, and wherein the first temperature is a subcritical temperature and the second temperature includes a transcritical temperature. 
   
   
       10 . The refrigeration system of  claim 1 , wherein the dedicated evaporator assemblies are connected to the liquid main in parallel, and wherein the dedicated compressor assemblies are connected to the discharge main in parallel. 
   
   
       11 . A refrigeration system comprising:
 a low temperature refrigeration circuit configured to circulate a first refrigerant, the low temperature refrigeration circuit including a plurality of refrigerated display cases, each of the plurality of refrigerated display cases having a dedicated evaporator assembly adapted to cool return air from the respective refrigerated display case by at least partially evaporating the first refrigerant, and a dedicated first stage compressor assembly in fluid communication with the dedicated evaporator assembly to compress the first refrigerant from the dedicated evaporator assembly to a first pressure corresponding to a first temperature of the first refrigerant;   a high temperature refrigeration circuit configured to circulate a second refrigerant, the high temperature refrigeration circuit including a second compressor assembly operable to compress the second refrigerant to a second pressure corresponding to a second temperature of the second refrigerant, and a heat exchanger configured to cool the second refrigerant; and   a heat exchanger in communication with the low temperature refrigeration circuit and the high temperature refrigeration circuit to transfer heat from the first refrigerant to the second refrigerant to cool the first refrigerant without mixing the first refrigerant and the second refrigerant.   
   
   
       12 . The refrigeration system of  claim 11 , wherein the first refrigerant and the second refrigerant include carbon dioxide refrigerant. 
   
   
       13 . The refrigeration system of  claim 11 , wherein the first refrigerant is circulated in a subcritical refrigeration cycle. 
   
   
       14 . The refrigeration system of  claim 11 , wherein the low temperature refrigeration circuit further includes a low temperature receiver disposed between and in fluid communication with each dedicated evaporator assembly and the heat exchanger to separate liquid and gaseous phases of the first refrigerant and to supply liquid refrigerant to each dedicated evaporator assembly. 
   
   
       15 . The refrigeration system of  claim 11 , wherein high temperature refrigeration circuit further includes a high temperature receiver disposed between and in fluid communication with the heat exchanger and the heat exchanger to receive the cooled second refrigerant and to direct the cooled second refrigerant to the heat exchanger. 
   
   
       16 . The refrigeration system of  claim 11 , wherein the high temperature refrigeration circuit further includes an accumulator disposed between and in fluid communication with the second compressor assembly and the heat exchanger to separate liquid and gaseous phases of the second refrigerant and to supply gaseous phase second refrigerant to the second compressor assembly. 
   
   
       17 . The refrigeration system of  claim 11 , wherein the heat exchanger is operable as a condenser for the first refrigerant, and wherein the heat exchanger is operable as an evaporator for the second refrigerant. 
   
   
       18 . The refrigeration system of  claim 11 , wherein the second refrigerant is circulated in a transcritical refrigeration cycle. 
   
   
       19 . A refrigeration system comprising:
 a plurality of refrigerated display cases, each of the plurality of refrigerated display cases including a dedicated evaporator assembly adapted to cool return air from the respective refrigerated display case by at least partially evaporating a refrigerant;   at least one first stage compressor assembly in fluid communication with the dedicated evaporator assemblies to compress the refrigerant from the dedicated evaporator assemblies to a first pressure corresponding to a first temperature of the refrigerant;   a second stage compressor assembly in fluid communication with the at least one first stage compressor assembly to receive the compressed refrigerant and to compress the refrigerant to a second pressure that is higher than the first pressure, the second pressure corresponding to a second temperature of the refrigerant;   a heat exchanger located remotely from the plurality of refrigerated display cases, the heat exchanger including an inlet in fluid communication with the second stage compressor assembly to receive the refrigerant from the second stage compressor assembly and to reject heat from the refrigerant to an environment;   a vessel positioned between and in fluid communication with the dedicated evaporator assemblies and the heat exchanger to separate liquid and gaseous phases of the refrigerant;   a liquid main fluidly coupled to the dedicated evaporator assemblies and to the vessel, the liquid main configured to supply liquid refrigerant to each dedicated evaporator assembly; and   a gas main fluidly coupled to the second stage compressor assembly and to the vessel, the gas main configured to direct gaseous refrigerant from the vessel to the second stage compressor assembly without passing through the dedicated evaporator assemblies.   
   
   
       20 . The refrigeration system of  claim 19 , wherein the refrigerant includes a carbon dioxide refrigerant. 
   
   
       21 . The refrigerated system of  claim 19 , wherein the refrigerant includes a critical temperature, and wherein the first temperature is a subcritical temperature and the second temperature includes a transcritical temperature. 
   
   
       22 . A refrigeration system comprising:
 a closed coolant loop configured to circulate a coolant fluid, the coolant loop including a supply main, a distribution main, a discharge main, a heat exchanger fluidly connected to the discharge main and the supply main and in communication with an environment to reject heat from the coolant fluid into the environment, and at least one coolant pump fluidly connected to the distribution main and the discharge main to pump the coolant fluid to the heat exchanger and through the coolant loop; and   a plurality of refrigerated display cases coupled to the coolant loop, each of the plurality of refrigerated display cases including
 a dedicated evaporator assembly adapted to cool return air from the respective refrigerated display case by at least partially evaporating a refrigerant, and 
 a dedicated refrigeration unit coupled to the evaporator assembly, the evaporator assembly and the refrigeration unit in fluid communication with each other and defining a closed transcritical refrigeration circuit, the refrigeration unit including a compressor assembly in fluid communication with the evaporator assembly to compress the refrigerant from the evaporator assembly, and a heat exchanger in fluid communication with the compressor assembly and with the evaporator assembly, the heat exchanger in heat exchange relationship with the coolant loop to reject heat from the refrigerant to the coolant fluid.