A central plant which provides chilled water to a building or group of buildings offers several opportunities for cost reductions through improved control performance using the latest generation of programmable controllers. The annual energy use of a central chilled water plant consisting of one or more centrifugal chillers, chilled and condenser water pumps, and cooling tower fans can be minimized through the use of optimum control strategies which consider total plant energy costs. This paper will define and describe some of these potential optimization routes available to the central plant operator and to the control system specifier. While the techniques described are applicable primarily to an electric-driven centrifugal chiller plant, most are generally applicable to other drive types and refrigeration machines. The paper will also cover some suggestions and possible pitfalls to avoid when interfacing the central plant equipment to a direct digital controller. Lastly, the use of the controller to provide the plant operator with performance feedback in the form of "total KW per TON of delivered chilled water" through its calculation and monitoring capability will be discussed. This capability of many controllers can be used by the plant engineer to improve the plant operation and optimization strategies, as well as pointing the way for achieving further reductions in total plant energy usage.

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