BASICS OF CHOOSING PRIME MOVERS FOR CHILLERS.

Hermetic and open-drive are the two broad categories of centrifugal chillers specified today. Hermetic chillers always are driven by electric induction motors. Open machines, however, can be driven by a variety of prime movers. Nearly half the drivers of open-drive chillers are electric motors. This means electric motors assume, by far, the major share of prime-mover duty for centrifugal water chillers. While electric drivers predominate, other types of drivers are available and fill an important need in specific instances. Internal and external combustion engines provide essentially all remaining prime-mover duties. Internal-combustion engines are either reciprocating engines or turbines. Essentially all external-combustion drivers are steam turbines. These can be either back-pressure or condensing turbines. The choice usually depends on other power and energy needs in the system or process.