Centrifugal Compressors - Performance

Packaged water cooled centrifugal compressors are available in sizes ranging from 85 tons to over 5,000 tons. Larger sizes, typically those 1,200 to 1,500 tons and larger are shipped in sub-assemblies. Smaller sizes are shipped as a factory-assembled package. While some smaller air-cooled centrifugal models are manufactured, they are largely exported to the Middle East and other arid areas where water is simply not available for HVAC condensing use, even in cooling towers.

The centrifugal compressors mentioned here will be using HCFC-123, HCFC-22 and HFC-134a. This usually calls for semi-hermetic designs, with single or multi-stage impellers. Two manufacturers (Carrier and McQuay) offer semi-hermetic gear driven models. Trane offers multi-stage direct drive semi-hermetic units. York offers an integrated open-drive geared design.

Chillers using ammonia as the refrigerant are not generally available with centrifugal compressors. Only open drive screw or reciprocating compressors are compatible with ammonia, largely because of its corrosive characteristics and reactions with copper.

The selection of single stage, multi-stage, open or hermetic designs is largely a function of individual manufacturer preference and the application. For example, centrifugal compressors are limited in their compression ratio per impeller. Therefore, applications calling for high temperature lifts (such as with ice thermal storage) may require multi-stage designs.