Tadem compressor operation

Abstract

A refrigerant system operates with tandem compressors. As is known, one or more of the tandem compressors can be shut down at part-load operating conditions when lower refrigerant system capacity is required. A control periodically engages at least one shut down tandem compressor for a short period of time. This increases the refrigerant mass flow of refrigerant throughout the refrigerant system to ensure that oil travels through the system and is not retained in the system.

1 . A refrigerant system having a compressor unit comprising:
 a plurality of tandem compressors, said plurality of tandem compressors utilized for compressing a refrigerant, and delivering the refrigerant throughout the refrigerant system, and to at least one heat rejection heat exchanger, an expansion device and at least one evaporator; and   a control for operating said refrigerant system having capability to shut down at least one of said plurality of tandem compressors to provide unloading of the refrigerant system, and said control periodically moving into an oil return mode by engaging at least one shutdown compressor for at least one short period of time to increase refrigerant mass flow rate and facilitate oil return.   
     
     
         2 . The refrigerant system as set forth in  claim 1 , wherein said plurality of tandem compressors have both a common suction manifold and a common discharge manifold. 
     
     
         3 . The refrigerant system as set forth in  claim 1 , wherein said plurality of tandem compressors have at least one of a common suction manifold and a common discharge manifold. 
     
     
         4 . The refrigerant system as set forth in  claim 1 , wherein the compressor unit incorporates at least one economized tandem compressor. 
     
     
         5 . The refrigerant system as set forth in  claim 1 , wherein the compressor unit incorporates at least two economized tandem compressors also having a common intermediate manifold. 
     
     
         6 . The refrigerant system as set forth in  claim 1 , wherein the compressor engagement is controlled based on a safety device or sensor feedback. 
     
     
         7 . The refrigerant system as set forth in  claim 6 , wherein the sensor is an oil level sensor. 
     
     
         8 . The refrigerant system as set forth in  claim 1 , wherein compressor engagement is based on at least one environmental or operating control parameter. 
     
     
         9 . The refrigerant system as set forth in  claim 8 , wherein the control parameter being a shutdown time for at least one of the shutdown compressors. 
     
     
         10 . The refrigerant system as set forth in  claim 9 , wherein an additional control parameter is included, and is at least one of a saturation suction temperature, suction pressure, evaporator secondary fluid temperature, oil temperature, and suction temperature. 
     
     
         11 . The refrigerant system as set forth in  claim 1 , wherein the short period of time is predetermined. 
     
     
         12 . The refrigerant system as set forth in  claim 1 , wherein the short period of time is defined by at least one of the following control parameters: saturation suction temperature, suction pressure, evaporator secondary fluid temperature, oil temperature, suction temperature, temperature variations in the conditioned environment, humidity variation in the conditioned environment. 
     
     
         13 . The refrigerant system as set forth in  claim 1 , wherein said control engages a shutdown compressor after a predetermined period of time has elapsed with said at least one compressor being shut down. 
     
     
         14 . The refrigerant system as set forth in  claim 13 , wherein the elapsed shutdown period of time is between 30 minutes and 12 hours. 
     
     
         15 . The refrigerant system as set forth in  claim 1 , wherein the short period of time is between 10 seconds and 10 minutes. 
     
     
         16 . The refrigerant system as set forth in  claim 13 , wherein said at least one compressor being engaged for a plurality of short periods of time in sequence. 
     
     
         17 . The refrigerant system as set forth in  claim 1 , wherein said engaged at least one compressor is again shut down after it has been engaged for a short period of time. 
     
     
         18 . The refrigerant system as set forth in  claim 1 , wherein multiple compressors are brought online in sequence. 
     
     
         19 . The refrigerant system as set forth in  claim 1 , wherein multiple compressors are brought online simultaneously. 
     
     
         20 . The refrigerant system as set forth in  claim 1 , wherein multiple compressors are shutdown in sequence. 
     
     
         21 . The refrigerant system as set forth in  claim 1 , wherein multiple compressors are shutdown simultaneously. 
     
     
         22 . A method of operating a refrigerant system including the steps of:
 providing a compressor unit comprising a plurality of tandem compressors, said plurality of tandem compressors compressing a refrigerant, and delivering the refrigerant throughout the refrigerant system, and to at least one heat rejection heat exchanger, an expansion device and at least one evaporator; and   controlling said refrigerant system to shut down at least one of said plurality of tandem compressors to provide unloading of the refrigerant system, and periodically moving into an oil return mode by engaging at least one shutdown compressor for at least one short period of time to increase refrigerant mass flow rate and facilitate oil return.   
     
     
         23 . The method as set forth in  claim 22 , wherein the compressor engagement is controlled based on a safety device or sensor feedback. 
     
     
         24 . The method as set forth in  claim 22 , wherein compressor engagement is based on at least one environmental or operating control parameter. 
     
     
         25 . The method as set forth in  claim 22 , wherein the short period of time is defined by at least one of the following control parameters: saturation suction temperature, suction pressure, evaporator secondary fluid temperature, oil temperature, suction temperature, temperature variations in the conditioned environment, humidity variation in the conditioned environment.