Optimal cool storage capacity for load management

Cool storage is a load management strategy for air conditioning loads, which shifts peak load by storing cooling capacity during off peak period. It allows the customer’s electricity use for cooling to be shifted to off peak period, benefiting both the consumer and the utility. Reduction in peak demand and electricity cost depend on electricity tariff rates, operating strategy, cool storage capacity and climatic conditions. In this paper, a methodology is presented to determine the optimal chilled water storage (CWS) capacity and corresponding operating strategy for the air conditioning loads for different electricity tariffs. This model minimizes the total operating cost of the air conditioning plant by a trade-off between the cost involved for providing the storage and accessories and savings achieved under the specified electricity tariff. A case study for a typical office complex shows that a reduction of 38% in peak demand is possible by adopting the optimal CWS strategy under time of use (TOU) tariff. The corresponding saving in the operating cost for the consumer is 5.9%. The results show that under flat tariffs, the prevalent high consumer discount rates make cool storage unviable. This provides justification for utility intervention in cool storage demand side management (DSM) programs.