Centrifugal chillers can have one, two or three stages of compression. Single-stage compressors are more compact and simpler in design than multistage units. Single-stage compressors have no interstage efficiency losses, as multistage compressors do. But single-stage compressors require geared drives, which add complexity to the chiller design and reduce efficiency. Multi-stage units can be geared or direct drive.
Multistage machines offer better stability over a wider operating range.
A direct-drive chiller has fewer moving parts and operates at lower speeds. Direct-drive design eliminates energy losses associated with the use of gears. One manufacturer offers a chiller with two smaller compressors to improve part-load performance. One of the compressors running at or near full load can handle part-load conditions. Factors to consider There is no single factor that can be used to decide which centrifugal chiller to buy.