Refrigeration System

Abstract

A pressure regulating valve ( 71 ) is connected to the discharge side of a low stage compressor ( 55 ) to make the pressure in the suction side of high stage compressors ( 11, 12 ) lower than the pressure in a dome of the low stage compressor ( 55 ). Further, an oil return path ( 72 ) is connected to the dome of the low stage compressor ( 55 ) at one end and to the suction side of the high stage compressors ( 11, 12 ) by bypassing the pressure regulating valve ( 71 ) at the other end. With this configuration, refrigeration oil accumulated in the dome of the low stage compressor ( 55 ) is returned to the high stage compressors ( 11, 12 ).

1 . A refrigeration system having a refrigerant circuit ( 6 ) including a low stage compressor ( 55 ) and high stage compressors ( 11 ,  12 ) which are connected in series to perform a two-stage compression refrigeration cycle, wherein 
 the refrigeration system ( 1 ) comprises an oil return means ( 70 ) for returning refrigeration oil from the low stage compressor ( 55 ) to the high stage compressors ( 11 ,  12 ).    
   
   
       2 . The refrigeration system of  claim 1 , wherein 
 the low stage compressor ( 55 ) is configured to accumulate the refrigerant oil in a high-pressure part thereof and    the oil return means ( 70 ) is configured to return the refrigeration oil accumulated in the high-pressure part of the low stage compressor ( 55 ) to the high stage compressors ( 11 ,  12 ).    
   
   
       3 . The refrigeration system of  claim 2 , wherein 
 the oil return means ( 70 ) is provided on the discharge side of the low stage compressor ( 55 ) and includes a pressure reducing means ( 71 ) and an oil return path ( 72 ),    the pressure reducing means ( 71 ) making the pressure in the suction side of the high stage compressors ( 11 ,  12 ) lower than the pressure in the high-pressure part of the low stage compressor ( 55 ) and    the oil return path ( 72 ) being connected to the high pressure part of the low stage compressor ( 55 ) at one end and to the suction side of the high stage compressors ( 11 ,  12 ) by bypassing the pressure reducing means ( 71 ) at the other end.    
   
   
       4 . The refrigeration system of  claim 1 , wherein 
 the low stage compressor ( 55 ) is configured to accumulate the refrigeration oil in a dome thereof where the pressure is high and    the oil return means ( 70 ) is configured to return the refrigeration oil accumulated in the dome of the low stage compressor ( 55 ) to the high stage compressors ( 11 ,  12 ).    
   
   
       5 . The refrigeration system of  claim 4 , wherein 
 the oil return means ( 70 ) is provided on the discharge side of the low stage compressor ( 55 ) and includes a pressure reducing means ( 71 ) and an oil return path ( 72 ),    the pressure reducing means ( 71 ) making the pressure in the suction side of the high stage compressors ( 11 ,  12 ) lower than the pressure in the dome of the low stage compressor ( 55 ) and    the oil return path ( 72 ) being connected to the dome of the low stage compressor ( 55 ) at one end and to the suction side of the high stage compressors ( 11 ,  12 ) by bypassing the pressure reducing means ( 71 ) at the other end.    
   
   
       6 . The refrigeration system of  claim 2 ,  3 ,  4  or  5 , wherein 
 the low stage compressor ( 55 ) includes a plurality of low stage compressors ( 55   a ,  55   b ,  55   c ) connected parallel to each other,    the oil return means ( 70 ) is configured to return the refrigeration oil from one of the low stage compressors ( 55   a ) to the high stage compressors ( 11 ,  12 ), the one of the low stage compressors ( 55   a ) being in charge of returning the refrigeration oil to the high stage compressors ( 11 ,  12 ), and    the oil return means ( 70 ) includes oil delivery paths ( 67   a ,  67   b ) for sending the refrigeration oil to the low stage compressor ( 55   a ) in charge from the other low stage compressors ( 55   b ,  55   c ) than the low stage compressor ( 55   a ) in charge.    
   
   
       7 . The refrigeration system of  claim 1 , wherein 
 an oil separator ( 64 ) is provided on the discharge side of the low stage compressor ( 55 ) to trap the refrigeration oil discharged from the low stage compressor ( 55 ) and    the oil return means ( 70 ) includes a pressure reducing means ( 71 ) and an oil return path ( 72 ),    the pressure reducing means ( 71 ) being closer to the high stage compressors ( 11 ,  12 ) than to the oil separator ( 64 ) to make the pressure in the suction side of the high stage compressors ( 11 ,  12 ) lower than the pressure in the oil separator ( 64 ) and    the oil return path ( 72 ) being connected to the oil separator ( 64 ) at one end and to the suction side of the high stage compressors ( 11 ,  12 ) by bypassing the pressure reducing means ( 71 ) at the other end.