Optimal Short-Term Scheduling of Multi-Chiller Plants Considering Energy Requirement of Cooling Towers, Pumps and Chillers

During extremely hot summer days, air conditioning systems are known as major electricity consumers in residential, commercial and industrial sectors. Moreover, high energy requirement of multiple-chiller plants may cause an interconnected power grid be faced with annual on-peak electrical demand, load-generation mismatch, voltage collapse and catastrophic wide area blackout. Therefore, this paper presents a day-ahead economic dispatch model for water cooled multiple chiller systems aiming to minimize total power consumption of cooling towers, pumps and chillers. In addition, refrigeration capacity limit of each chiller and cooling load-generation balance criterion are considered as optimization constraints. On/off status and partial load ratio of each chiller, power consumption of pump/cooling tower/chiller, temperature of chiller outlet water, temperature of cooling tower outlet water, mass flow rate of cooled water, mass flow rate of water flowing in and out of cooling tower are considered as decision variables. Simulations are conducted on a benchmark system with two 550 refrigeration ton (RT) units, four 1000 RT chillers and different cooling load levels over a 24-hour time horizon using generalized algebraic mathematical modeling system (GAMS) software.