Low gwp cascade refrigeration system

Abstract

A refrigeration system having a low stage and a high stage circuit. Each stage having a compressor, an evaporator or a condenser. The low stage includes a low stage refrigerant comprising R744. The high stage includes a high stage refrigerant having a GWP less than 500. The system further includes a heat exchanger configured to transfer heat from the low stage refrigerant to the high stage refrigerant allowing the circuits to provide cooling in two stages.

What is claimed: 
     
         1 . A refrigeration system for an enclosed structure capable of sheltering personnel comprising:
 a high stage refrigeration circuit including a high stage compressor, a condenser, a high stage expansion device, wherein the high stage refrigeration circuit circulates a high stage refrigerant having a GWP less than 500;   a low stage refrigeration circuit including a low stage compressor, a low stage expansion device, and an evaporator, wherein the low stage refrigeration circuit is configured to circulate a low stage refrigerant comprising R744;   wherein the evaporator is configured to be located within the enclosed structure and the condenser is configured to be located outside the structure;   a primary heat exchanger configured to transfer heat from the low stage refrigerant to the high stage refrigerant; and   wherein the low stage refrigeration circuit further comprises a supplemental heat exchanger to reduce the heat of the low stage refrigerant prior to entering the heat exchanger.   
     
     
         2 . The refrigeration system of  claim 1 , wherein the supplemental heat exchanger is integrated into the high stage condenser. 
     
     
         3 . The refrigeration system of  claim 1 , wherein the supplemental heat exchanger desuperheats the low stage refrigerant. 
     
     
         4 . The refrigeration system of  claim 1 , wherein the low stage refrigeration circuit further includes a discharge pipe downstream of the low stage compressor, wherein the discharge pipe carries the low stage refrigerant to the supplemental compressor. 
     
     
         5 . The refrigeration system of  claim 4 , wherein the discharge pipe is upstream of the heat exchanger. 
     
     
         6 . The refrigeration system of  claim 1 , further comprising a thermal energy storage reservoir surrounding the primary heat exchanger, the thermal energy storage reservoir configured to receive heat from the low stage refrigerant to control the temperature of the low stage refrigerant during a power outage. 
     
     
         7 . A refrigeration system for an enclosed structure capable of sheltering personnel comprising:
 a high stage refrigeration circuit including a high stage compressor, a condenser, a high stage expansion device, wherein the high stage refrigeration circuit circulates a high stage refrigerant having a GWP less than 500 and a flammability classification of A1, A2 or A2L;   a low stage refrigeration circuit including a low stage compressor, a low stage expansion device, and an evaporator, wherein the low stage refrigeration circuit is configured to circulate a low stage refrigerant comprising R744;   wherein the evaporator is configured to be located within the enclosed structure and the condenser is configured to be located outside the structure;   a heat exchanger configured to transfer heat from the low stage refrigerant to the high stage refrigerant; and   wherein the heat exchanger further includes a thermal energy storage reservoir configured to receive heat from the low stage refrigerant to maintain the temperature of the low stage refrigerant during a power outage.   
     
     
         8 . The refrigeration system of  claim 7 , wherein the low stage refrigeration circuit further comprises a low stage refrigerant receiver downstream of the heat exchanger. 
     
     
         9 . The refrigeration system of  claim 8 , wherein the thermal energy storage reservoir surrounds either the receiver or the heat exchanger. 
     
     
         10 . The refrigeration system of  claim 7 , wherein the high stage refrigeration circuit further comprises a high stage refrigerant receiver. 
     
     
         11 . The refrigeration system of  claim 7 , wherein the thermal energy storage reservoir includes a blend of phase change materials with a melting point of 28 to 64 degrees Fahrenheit. 
     
     
         12 . The refrigeration system of  claim 7 , wherein at least one of the low stage compressor and the high stage compressor includes parallel compressors. 
     
     
         13 . A refrigeration system for a building, wherein the system comprises:
 a high stage refrigeration circuit including a high stage compressor, a condenser upstream of the high stage compressor, a high stage refrigerant receiver downstream of the condenser, a high stage expansion device downstream of the high stage refrigerant receiver, wherein the high stage refrigeration circuit circulates a high stage refrigerant comprising R471A;   a low stage refrigeration circuit including a low stage compressor, an evaporator upstream of the low stage compressor, a low stage expansion device upstream of the evaporator, and a low stage refrigerant receiver upstream of the low stage expansion device, wherein the low stage refrigeration circuit is configured to circulate a low stage refrigerant comprising R744;   wherein the evaporator is configured to be located within the building and the condenser is configured to be located outside the building; and   a heat exchanger downstream of the low stage compressor and upstream of the high stage compressor configured to transfer heat from the low stage refrigerant to the high stage refrigerant.   
     
     
         14 . The refrigeration system of  claim 13 , wherein the low stage refrigeration circuit further comprises a supplemental heat exchanger to reduce the heat of the low stage refrigerant prior to entering the heat exchanger. 
     
     
         15 . The refrigeration system of  claim 14 , wherein the supplemental heat exchanger is integrated into the high stage condenser. 
     
     
         16 . The refrigeration system of  claim 13 , further comprising a thermal energy storage configured to receive heat from the low stage refrigerant to control the temperature of the low stage refrigerant during a power outage. 
     
     
         17 . The refrigeration system of  claim 16 , wherein the thermal energy storage reservoir includes a blend of phase change materials with a melting point of 28 to 64 degrees Fahrenheit. 
     
     
         18 . The refrigeration system of  claim 16 , wherein the thermal energy storage reservoir includes a blend of fats or oils with a melting point of 65 to 79 degrees Fahrenheit. 
     
     
         19 . The refrigeration system of  claim 16 , wherein the thermal energy storage reservoir surrounds the heat exchanger. 
     
     
         20 . The refrigeration system of  claim 16 , wherein the thermal energy storage reservoir surrounds a receiver, wherein the receiver is located in the low stage refrigeration circuit.