Compressor capacity modulation

A capacity modulated compressor comprising:

• a hermetic shell;
• a compression mechanism disposed within said shell, said compression mechanism including a compression chamber defined in part by a moveable member, said moveable member operating to vary the volume thereof;
• a drive shaft rotatably supported within said shell and drivingly coupled to said movable member;
• a suction inlet passage for supplying suction gas to said compression chamber from a source remote from said shell;
• a valve within said suction inlet passage, said valve being actuable between an open position to allow flow of suction gas through said inlet passage and a closed position to substantially prevent flow of suction gas through said inlet passage;
• a controller for cyclically actuating said valve to an open position for first predetermined time periods and to a closed position for second predetermined time periods, the ratio of said first predetermined time period to the sum of said first and second predetermined time periods being less than a given load time constant and determining the percentage modulation of the capacity of said compressor.

A method of modulating the capacity of a compressor forming a part of a cooling system to accommodate varying cooling load conditions comprising:

• sensing an operating parameter of said cooling system, said parameter being indicative of the system load;
• determining a cycle frequency of a maximum duration which will minimize variation in the suction pressure of refrigerant being supplied to said compressor;
• determining a first time period during which suction gas will be supplied to said compressor and determining a second time period during which suction gas will be prevented from flowing to said compressor, said first and second time periods being equal to said cycle frequency;
• and
• pulsing a valve between open and closed positions for said first and second time periods respectively to thereby modulate the capacity of said compressor in response to said system operating parameter.