Refrigeration apparatus

Abstract

A refrigeration apparatus uses supercritical range refrigerant, and includes a multi-stage compression mechanism, a heat source-side heat exchanger, a usage-side heat exchanger, a switching mechanism switchable between cooling and heating operation states, and a second-stage injection tube. The second-stage injection tube branches off refrigerant, which has radiated heat in the heat source-side heat exchanger or the usage-side heat exchanger, and returns the refrigerant to the second-stage compression element. Refrigerant is prevented from returning to the second-stage compression element through the second-stage injection tube at least during a beginning of a reverse cycle defrosting operation, which is performed to defrost the heat source-side heat exchanger by switching the switching mechanism to the cooling operation state.

1 . A refrigeration apparatus that uses a refrigerant that operates in a supercritical range, the refrigeration apparatus comprising:
 a compression mechanism having a plurality of compression elements arranged and configured so that refrigerant discharged from a first-stage compression element of the plurality of compression elements is sequentially compressed by a second-stage compression element;   a heat source-side heat exchanger using air as a heat source and being arranged and configured to operate as a radiator or evaporator of refrigerant;   a usage-side heat exchanger arranged and configured to operate as a evaporator or radiator of refrigerant;   a switching mechanism arranged and configured to switch between
 a cooling operation state in which the refrigerant is circulated through the compression mechanism, the heat source-side heat exchanger, and the usage-side heat exchanger in order, and 
 a heating operation state in which the refrigerant is circulated through the compression mechanism, the usage-side heat exchanger, and the heat source-side heat exchanger in order; and 
   a second-stage injection tube arranged and configured to branch off the refrigerant, which has radiated heat in the heat source-side heat exchanger or the usage-side heat exchanger, and to return the refrigerant to the second-stage compression element   the second-stage injection tube being arranged and configured such that refrigerant is prevented from returning to the second-stage compression element through the second-stage injection tube at least during a beginning of a reverse cycle defrosting operation, which is performed to defrost the heat source-side heat exchanger by switching the switching mechanism to the cooling operation state.   
     
     
         2 . The refrigeration apparatus according to  claim 1 , wherein
 the at least the beginning of the reverse cycle defrosting operation is a time period from a start of the reverse cycle defrosting operation until a predetermined time duration elapses, and the predetermined time duration is set according to a length of a refrigerant tube between the usage-side heat exchanger and the switching mechanism.   
     
     
         3 . The refrigeration apparatus according to  claim 1 , wherein
 the at least the beginning of the reverse cycle defrosting operation is a time period from a start of the reverse cycle defrosting operation until a temperature of the refrigerant in the usage-side heat exchanger decreases to a predetermined temperature or lower.   
     
     
         4 . The refrigeration apparatus according to  claim 1 , wherein
 the at least the beginning of the reverse cycle defrosting operation is a time period from a start of the reverse cycle defrosting operation until a pressure of the refrigerant in the intake side of the compression mechanism decreases to a predetermined pressure or lower.   
     
     
         5 . The refrigeration apparatus according to  claim 1 , wherein
 the refrigerant that operates in the supercritical range is carbon dioxide.   
     
     
         6 . The refrigeration apparatus according to  claim 2 , wherein the refrigerant that operates in the supercritical range is carbon dioxide. 
     
     
         7 . The refrigeration apparatus according to  claim 3 , wherein the refrigerant that operates in the supercritical range is carbon dioxide. 
     
     
         8 . The refrigeration apparatus according to  claim 4 , wherein the refrigerant that operates in the supercritical range is carbon dioxide.