Co2 refrigeration unit

Abstract

A refrigeration unit comprises a CO 2 refrigeration circuit having a CO 2 compression stage in which CO 2 refrigerant is compressed, a CO 2 condensation stage having a tank in which CO 2 refrigerant is accumulated in a liquid state, at least one of pressuring means and an expansion stage to direct the CO 2 refrigerant from the CO 2 condensation stage to a CO 2 evaporation stage in which CO 2 refrigerant absorbs energy to refrigerate. A condensation circuit has a second refrigerant being circulated between a second compression stage, a second condensation stage, a second expansion stage and a second evaporation stage. A heat-exchanger unit by which the CO 2 refrigerant from the CO 2 refrigeration circuit is in heat exchange with the second refrigerant in the second evaporation stage such that the second refrigerant absorbs heat from the CO 2 refrigerant to at least partially liquefy the CO 2 refrigerant for the CO 2 condensation stage. A defrost circuit directing defrost CO 2 refrigerant from the CO 2 compression stage to the CO 2 evaporation stage to defrost at least one evaporator of the CO 2 evaporation stage, the defrost CO 2 refrigerant being subsequently returned to the CO 2 refrigeration circuit.

1 . A refrigeration unit comprising:
 a CO 2  refrigeration circuit having a CO 2  compression stage in which CO 2  refrigerant is compressed, a CO 2  condensation stage having a tank in which CO 2  refrigerant is accumulated in a liquid state, at least one of pressuring means and an expansion stage to direct the CO 2  refrigerant from the CO 2  condensation stage to a CO 2  evaporation stage in which CO 2  refrigerant absorbs energy to refrigerate;   a condensation circuit having a second refrigerant being circulated between a second compression stage, a second condensation stage, a second expansion stage and a second evaporation stage;   a heat-exchanger unit by which the CO 2  refrigerant from the CO 2  refrigeration circuit is in heat exchange with the second refrigerant in the second evaporation stage such that the second refrigerant absorbs heat from the CO 2  refrigerant to at least partially liquefy the CO 2  refrigerant for the CO 2  condensation stage; and   a defrost circuit directing defrost CO 2  refrigerant from the CO 2  compression stage to the CO 2  evaporation stage to defrost at least one evaporator of the CO 2  evaporation stage, the defrost CO 2  refrigerant being subsequently returned to the CO 2  refrigeration circuit.   
   
   
       2 . The refrigeration unit according to  claim 1 , wherein the CO 2  evaporation stage has at least medium-temperature evaporators and low-temperature evaporators, with a line directing CO 2  refrigerant exiting the low-temperature evaporators to the CO 2  compression stage, and with the pressuring means upstream of the medium-temperature evaporators to feed CO 2  refrigerant to the medium-temperature evaporators, with another line directing CO 2  refrigerant exiting the medium-temperature evaporators to the CO 2  condensation stage. 
   
   
       3 . The refrigeration unit according to  claim 1 , wherein the CO 2  evaporation stage has at least medium-temperature evaporators and low-temperature evaporators, with a line directing CO 2  refrigerant exiting the low-temperature evaporators to the CO 2  compression stage, and with the expansion stage upstream of the medium-temperature evaporators to feed CO 2  refrigerant to the medium-temperature evaporators, with another line directing CO 2  refrigerant exiting the medium-temperature evaporators to the CO 2  compression stage. 
   
   
       4 . The refrigeration unit according to  claim 1 , further comprising a defrost reservoir between the CO 2  evaporation stage and the CO 2  compression stage to collect the defrost CO 2  refrigerant exiting the defrost circuit, a suction of the CO 2  compression stage connected to the defrost reservoir to collect CO 2  refrigerant in a gas state for the CO 2  refrigeration circuit. 
   
   
       5 . The refrigeration unit according to  claim 4 , wherein a discharge line extends from the CO 2  compression stage to the defrost reservoir to selectively flush CO 2  refrigerant from the defrost reservoir through another line extending from the defrost reservoir to the tank in the CO 2  condensation stage. 
   
   
       6 . The refrigeration unit according to  claim 1 , further comprising at least one dedicated compressor in the CO 2  compression stage to collect at least part of the defrost CO 2  refrigerant exiting the defrost circuit, to compress and discharge the defrost CO 2  refrigerant to the CO 2  refrigeration circuit. 
   
   
       7 . The refrigeration unit according to  claim 1 , further comprising a pressure-reducing valve on a discharge line of the CO 2  compression stage, downstream of a defrost line feeding defrost CO 2  refrigerant to the defrost circuit, to maintain a pressure of the CO 2  refrigerant in the CO 2  refrigeration circuit downstream of the pressure-reducing valve lower than the pressure of the defrost CO 2  refrigerant. 
   
   
       8 . The refrigeration unit according to  claim 1 , wherein the defrost CO 2  refrigerant is circulated in the CO 2  evaporation stage of the defrost circuit at a pressure below 700 Psi. 
   
   
       9 . The refrigeration unit according to  claim 1 , wherein the condensation circuit has a pressure-maintaining line extending from a discharge of the second compression stage to a suction of the second compression stage, the pressure-maintaining line being selectively opened to maintain a minimum operating pressure at a suction of the second compression stage. 
   
   
       10 . The refrigeration unit according to  claim 1 , further comprising a line extending from the CO 2  evaporation stage to the CO 2  condensation stage to direct defrost CO 2  refrigerant from the defrost circuit to the refrigeration circuit. 
   
   
       11 . A refrigeration unit comprising:
 a casing;   a CO 2  refrigeration circuit having a CO 2  compression stage in which CO 2  refrigerant is compressed, a CO 2  condensation stage having a tank in which CO 2  refrigerant is accumulated in a liquid state, at least one of pressuring means and an expansion stage to direct the CO 2  refrigerant from the CO 2  condensation stage to a CO 2  evaporation stage in which CO 2  refrigerant absorbs energy to refrigerate, with at least the CO 2  compression stage, and the CO 2  condensation stage being in the casing;   a condensation circuit having a second refrigerant being circulated between a second compression stage, a second condensation stage, a second expansion stage and a second evaporation stage, at least the second compression stage, the second expansion stage and the second evaporation stage being in the casing; and   a heat-exchanger unit in the casing by which the CO 2  refrigerant from the CO 2  refrigeration circuit is in heat exchange with the second refrigerant in the second evaporation stage such that the second refrigerant absorbs heat from the CO 2  refrigerant to at least partially liquefy the CO 2  refrigerant for the CO 2  condensation stage.   
   
   
       12 . The refrigeration unit according to  claim 11 , further comprising a defrost circuit directing defrost CO 2  refrigerant from the CO 2  compression stage to the CO 2  evaporation stage to defrost at least one evaporator, the defrost CO 2  refrigerant being subsequently returned to the CO 2  refrigeration circuit. 
   
   
       13 . The refrigeration unit according to  claim 11 , wherein the at least one of pressuring means and expansion stage are in the casing. 
   
   
       14 . The refrigeration unit according to  claim 11 , further comprising a ventilation circuit in which circulates a third refrigerant between a third compression stage, a third condensation/gas cooling stage, a third expansion stage and a third evaporation stage, at least the third compression stage, the third condensation/gas cooling stage, and the third expansion stage being in the casing, with the third evaporation stage adapted to be in a ventilation duct to absorb heat from ventilation air. 
   
   
       15 . The refrigeration unit according to  claim 14 , further comprising a heat reclaim stage in a discharge line of the CO 2  compression stage to reclaim heat from the CO 2  refrigerant, the heat reclaim stage comprising a coil adapted to be in said ventilation duct to heat ventilation air. 
   
   
       16 . The refrigeration unit according to  claim 11 , further comprising at least an other one of the refrigeration unit in another one of the casing, the other one of the refrigeration unit being without one of the condensation circuit, and being in heat-exchange relation with the heat-exchange unit of the first one of the refrigeration unit. 
   
   
       17 . A refrigeration unit of the type having a CO 2  refrigeration circuit with a CO 2  compression stage in which CO 2  refrigerant is compressed, a CO 2  condensation stage having a tank in which CO 2  refrigerant is accumulated in a liquid state, an expansion stage to direct the CO 2  refrigerant from the CO 2  condensation stage to a CO 2  evaporation stage in which CO 2  refrigerant absorbs energy CO 2  refrigerate, the CO 2  evaporation stage having at least two evaporators, the refrigeration unit comprising at least one line connected from the CO 2  condensation stage to one expansion valve of the expansion stage, the line diverging into at least two lines each connected to a balancing valve and an own one of the evaporators, such that CO 2  refrigerant expanded by the one expansion valve is directed to the at least two evaporators through the balancing valves. 
   
   
       18 . The refrigeration unit according to  claim 17 , wherein the expansion stage is in a casing with the CO 2  compression stage and the CO 2  condensation stage at a distal location from the CO 2  evaporation stage. 
   
   
       19 . The refrigeration unit according to  claim 18 , wherein the refrigeration unit is retrofitted to existing evaporators. 
   
   
       20 . The refrigeration unit according to  claim 17 , further comprising a defrost circuit directing defrost CO 2  refrigerant from the CO 2  compression stage to the CO 2  evaporation stage to defrost the evaporators, the defrost refrigerant being subsequently returned to the CO 2  refrigeration circuit.