Short-Term Co-Optimization of Multi-Chiller Plants and Ice Storage System

During extremely hot summer days, air conditioners 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 co-optimization of water cooled multiple chiller systems and ice storage unit aiming to minimize total power consumption of cooling towers, pumps, chillers, ice making and melting processes. In addition, the refrigeration capacities of chillers and ice storage unit and the cooling load-generation balance criterion are considered as optimization constraints. On/off states and partial load ratios of chillers and ice storage unit, power consumptions of pumps/cooling towers/chillers/ice making mode/ice melting process, temperature of cooling tower outlet water, mass flow rate of cooled water, mass flow rate of water flowing in and out of cooling tower, time and amount of generation and consumption of ice, and state of charge of ice storage tank at each hour are considered as decision variables. Simulations are conducted on a benchmark system with two 550 refrigeration ton (RT) units, four 1000 RT chillers, 2000 RT ice storage capacity, and different cooling load levels over a 24-hour time horizon using generalized algebraic mathematical modeling system (GAMS) software.