Abstract: A multiple chiller control system includes a temperature controller TC, a data base and optimizer DBO, and a plurality of driven-servo loops DSL1, DSL2, . . . DSLn. The temperature controller and the data base and optimizer monitor various parameters of the chilled water system. At periodic intervals, the system determines and stores the current values of these parameters. From this data, and from data determined from operator-selected signals supplied to the temperature controller, the temperature controller determines if a change in total operating capacity is required. If this determination is affirmative, the temperature contoller supplies a request for a system capacity adjustment to the data base and optimizer, which then proceeds to select the chillers to be operated and to adjust the capacity of the chillers so selected.