Method and apparatus for applying dual centrifugal compressors to a refrigeration chiller unit

A condenser for use in a refrigeration chiller having first and second centrifugal compressors, an evaporator, and first and second expansion devices for expanding a refrigerant passing therethrough, comprising:

• a shell through which the refrigerant is passed;
• a plurality of heat transfer tubes extending through said shell, said heat transfer tubes extending throughout substantially the entire length of the interior of said shell;
• a divider within said condenser shell that separates the condenser into first and second condensing chambers, said divider having a cross section substantially the same as the cross section of the shell and having a plurality of holes through which the plurality of tubes extend;
• and
• a valve in fluid communication with each of said first and second condenser chambers for selectively operating to equalize or not equalize the pressures in the two chambers.

A method of operating a dual centrifugal compressors in a closed refrigeration chiller, the method comprising the steps of:

• providing a tube and shell condenser with first and second condensing chambers through which extend a common bundle of heat exchanger tubes, said condenser including a valve in fluid communication with the first and second condenser chambers;
• selectively applying refrigerant to the shell portion of the first chamber of the heat exchanger by a first centrifugal compressor,
• selectively applying refrigerant to the shell portion of the second condenser chamber by a second centrifugal compressor,
• completing a first refrigeration circuit by flowing refrigerant from the first condenser chamber, through an expansion device, and into an evaporator, in fluid communication with the first centrifugal compressor;
• completing a second refrigeration circuit by flowing refrigerant from the second condenser chamber, through an expansion device, and into an evaporator, in fluid communication with the second centrifugal compressor, and
• opening the valve when only one of the compressors is on and closing the valve when both of the compressors are on.