A two-stage direct-drive variable-speed centrifugal compressor has been developed that delivers identical peak efficiency at a given cooling capacity for both economized and non-economized duty without any hardware adjustment. If the drive system is oversized higher compressor capacity can be achieved by increasing the capacity of the second stage impeller. Actual economizer benefit depends on a number of centrifugal chiller and compressor design choices such as condenser sub-cooling, system piping losses, economizer heat exchanger approach temperature as well as the input work division between first and second stage impeller.
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