| 摘要 |
A refrigeration unit comprises a CO2 refrigeration circuit having a CO2 compression stage in which CO2 refrigerant is compressed, a CO2 condensation stage having a tank in which CO2 refrigerant is accumulated in a liquid state, at least one of pressuring means and an expansion stage to direct the CO2 refrigerant from the CO2 condensation stage to a CO2 evaporation stage in which CO2 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 CO2 refrigerant from the CO2 refrigeration circuit is in heat exchange with the second refrigerant in the second evaporation stage such that the second refrigerant absorbs heat from the CO2 refrigerant to at least partially liquefy the CO2 refrigerant for the CO2 condensation stage. A defrost circuit directing defrost CO2 refrigerant from the CO2 compression stage to the CO2 evaporation stage to defrost at least one evaporator of the CO2 evaporation stage, the defrost CO2 refrigerant being subsequently returned to the CO2 refrigeration circuit.
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