SE-14-C023 -- Optimal Model-based Control of Chiller Tower Fan and Cooling Water Pump PDF

A general component-based chiller plant model is developed. Each component is modeled from first principles and/or empirical relations selected to be valid over a wide range of operating conditions, speed and load. The components include single-stage centrifugal compressor, shell-and-tube evaporator and condenser, cooling tower with variable-speed fan and cooling water pump. The modeled chiller uses R134a as refrigerant and both heat exchangers carry water inside with refrigerant outside the tubes. Methods are developed to reliably identify physical model parameters from operational data. The component-based model predicts plant COP given cooling load and conditions, and the cooling tower fan and cooling water pump speeds or flow rates. By decoupling the evaporator, balance-of-plant performance becomes a function of load and evaporating and wet-bulb temperatures, to be useful when chilled water flow is beyond operator control. A performance map generated by the plant model is embedded in the objective function of an optimization problem that determines the optimal combination of cooling tower fan speed and cooling water pump speed for any load and operating condition by grid search method.