Hybrid Compressor System and Methods

Abstract

An apparatus ( 20 ) has a centrifugal compressor ( 24 ), a positive displacement compressor ( 26 ), a first heat exchanger ( 32 ), and a second heat exchanger ( 36 ). A plurality of valves ( 70, 72, 74 ) are positioned to provide operation in at least two modes. In a first mode, refrigerant is compressed in the positive displacement compressor and the centrifugal compressor at least partially in parallel. In a second mode, refrigerant is compressed in the positive displacement compressor and the centrifugal compressor is offline. In a third mode, refrigerant is compressed in the positive displacement compressor and the centrifugal compressor at least partially in series.

1 . An apparatus ( 20 ) comprising:
 a centrifugal compressor ( 24 );   a positive displacement compressor ( 26 );   a first heat exchanger ( 32 );   a second heat exchanger ( 36 ); and   a plurality of valves ( 70 ,  72 ,  74 ) positioned to provide at least two of:
 operation in a first mode wherein:
 refrigerant is compressed in the positive displacement compressor and the centrifugal compressor at least partially in parallel; 
 
 operation in a second mode wherein:
 refrigerant is compressed in the positive displacement compressor; and 
 the centrifugal compressor is offline; and 
 
 operation in a third mode wherein:
 refrigerant is compressed in the positive displacement compressor and the centrifugal compressor at least partially in series. 
 
   
     
     
         2 . The apparatus of  claim 1  wherein:
 the positive displacement compressor is a screw compressor. 
 
     
     
         3 . The apparatus of  claim 1  wherein:
 the centrifugal compressor has a rated maximum capacity; and 
 the positive displacement compressor has a rated maximum capacity of 100-150% of the rated maximum capacity of the centrifugal compressor. 
 
     
     
         4 . The apparatus of  claim 1  wherein:
 the plurality of valves are positioned to provide all three of said modes. 
 
     
     
         5 . The apparatus of  claim 1  wherein:
 the plurality of valves are positioned to provide at least the first mode and second mode. 
 
     
     
         6 . The apparatus of  claim 1  being a chiller wherein:
 the first heat exchanger is part of a condenser unit; 
 the second heat exchanger is part of a cooler; and 
 an expansion device ( 34 ) is positioned between the condenser and the cooler. 
 
     
     
         7 . The apparatus of  claim 1  wherein the plurality of valves comprises:
 a first valve ( 70 ) between the centrifugal compressor and the first heat exchanger; 
 a second valve ( 72 ) along a bypass ( 90 ) extending from a location ( 92 ) between the centrifugal compressor and the first valve to a location ( 94 ) between the second valve and the screw compressor; and 
 a third valve ( 74 ) between the second heat exchanger and the positive displacement compressor. 
 
     
     
         8 . The apparatus of  claim 1  further comprising:
 a controller ( 40 ) programmed to automatically switch between said at least two modes. 
 
     
     
         9 . The apparatus of  claim 8  wherein:
 the controller is programmed to automatically switch between said first mode and said second mode. 
 
     
     
         10 . The apparatus of  claim 9  wherein:
 said controller is programmed to switch from said first mode to said second mode responsive to a decrease in load and from said second mode to said first mode responsive to an increase in load. 
 
     
     
         11 . The apparatus of  claim 10  wherein:
 the controller is programmed to switch to said third mode responsive to calculating a high requirement for lift. 
 
     
     
         12 . An apparatus comprising:
 a centrifugal compressor ( 24 );   a positive displacement compressor ( 26 );   a first heat exchanger ( 32 );   a second heat exchanger ( 36 ); and   means ( 70 ,  72 ,  74 ) for providing at least two of:
 operation in a first mode wherein:
 refrigerant is compressed in the positive displacement compressor and the centrifugal compressor at least partially in parallel; 
 
 operation in a second mode wherein:
 refrigerant is compressed in the positive displacement compressor; and 
 the centrifugal compressor is offline; and 
 
 operation in a third mode wherein:
 refrigerant is compressed in the positive displacement compressor and the centrifugal compressor at least partially in series. 
 
   
     
     
         13 . A method for operating a vapor compression system ( 20 ) having a centrifugal compressor ( 24 ) and a positive displacement compressor ( 26 ), the method comprising at least two of:
 operating in a first mode wherein:
 refrigerant is compressed in the positive displacement compressor and the centrifugal compressor at least partially in parallel; 
   operating in a second mode wherein:
 refrigerant is compressed in the positive displacement compressor; and 
 the centrifugal compressor is offline; and 
   operating in a third mode wherein:
 refrigerant is compressed in the positive displacement compressor and the centrifugal compressor at least partially in series. 
   
     
     
         14 . The method of  claim 13  wherein:
 the system is operated in the second mode from a minimum load condition to an intermediate load condition; and 
 the system is operated in said first mode at loads above said intermediate load condition. 
 
     
     
         15 . The method of  claim 14  wherein:
 in the first mode, load variation is principally accommodated by the positive displacement compressor. 
 
     
     
         16 . The method of  claim 13  wherein:
 operation is based on a combination of required capacity and required lift and wherein some-to-all of:
 in a high required lift, the system is operated ( 306 ) in the third mode; and 
 at low required lift, some-to-all of:
 at low capacity:
 the system is run ( 320 ) in the first mode; and 
 at high head the system is run ( 322 ) in the third mode; 
 
 at intermediate capacity:
 at low head, the system is run ( 330 ) in the third mode with essentially constant positive displacement compressor capacity and the centrifugal compressor at variable capacity; and 
 at high head, the system is run ( 322 ) in the first mode with the centrifugal compressor at essentially constant capacity and the positive displacement compressor at variable capacity; and 
 
 at high capacity, the system is run ( 340 ) in the first mode with both compressors providing variable capacity. 
 
 
 
     
     
         17 . The method of  claim 13  wherein:
 the positive displacement compressor and the centrifugal compressor are both electrically powered by variable speed drives. 
 
     
     
         18 . The apparatus of  claim 12  wherein:
 the positive displacement compressor and the centrifugal compressor are both electrically powered by variable speed drives. 
 
     
     
         19 . The apparatus of  claim 1  wherein:
 the positive displacement compressor and the centrifugal compressor are both electrically powered by variable speed drives.