Capacity Control For Refrigerant System With Multiple Compressors

Abstract

A refrigerant system operates with tandem compressors ( 22, 24 ). A control ( 41 ) for the refrigerant system is operable to change the capacities of each of the compressors dependent upon a load on the system. The control determines the percentage of maximum load capacity currently being utilized by each of the compressors. A compressor with the highest percentage is decreased in capacity should the control determine that excess capacity is being provided. Conversely, the control will increase the capacity of a compressor having a lower percentage, if insufficient capacity is being provided to meet a load on the system.

1 . A refrigerant system comprising:
 at least two compressors, said at least two compressors each having a variable capacity;   an indoor heat exchanger, an expansion device and an outdoor heat exchanger, and a control for controlling a capacity provided by each of said at least two compressors, said control being able to determine whether a capacity provided by said at least two compressors is sufficient to meet a load on the refrigerant system, and increase or decrease the capacity dependent upon this determination, and said control further determining which of said at least two compressors is operating at a highest percentage of its maximum capacity, said control utilizing said determination of which of said compressors is operating at said highest percentage of its maximum capacity when determining which of said at least two compressors to control when said control determines that a change in capacity is desirable.   
   
   
       2 . The refrigerant system as set forth in  claim 1 , wherein said control decreasing a capacity of one of said at least two compressors having a higher percentage if excess capacity is identified. 
   
   
       3 . The refrigerant system as set forth in  claim 1 , wherein said control increasing a capacity of one of said at least two compressors having a lower percentage if insufficient capacity is being provided. 
   
   
       4 . The refrigerant system as set forth in  claim 1 , wherein said percentage is determined by monitoring an actual current leading to a motor associated with each of said at least two compressors, and comparing each said actual current to a rated load for each of said motors. 
   
   
       5 . A method of operating a refrigerant system including the steps of:
 providing at least two compressors, said at least two compressors each having a variable capacity;   providing an indoor heat exchanger, an expansion device and an outdoor heat exchanger, and a control for controlling a capacity provided by each of said at least two compressors;   determining whether a capacity provided by said at least two compressors is sufficient to meet a load on the refrigerant system;   increasing or decreasing capacity dependent upon this determination;   determining which of said at least two compressors is operating at a highest percentage of its maximum capacity; and   said control utilizing said determination of which of said compressors is operating at said highest percentage of its maximum capacity when determining which of said at least two compressors to control when said control determines that a change in capacity is desirable.   
   
   
       6 . The method as set forth in  claim 5 , wherein said control decreasing a capacity of one of said at least two compressors having said highest percentage if excess capacity is identified. 
   
   
       7 . The method as set forth in  claim 5 , wherein said control increasing a capacity of one of said at least two compressors having a lower percentage if insufficient capacity is being provided. 
   
   
       8 . The method as set forth in  claim 5 , wherein said percentage is determined by monitoring an actual current leading to a motor associated with each of said at least two compressors, and comparing said actual current to a rated load for each of said motors.