COST-BENEFIT-ANALYSIS OF A COOLING ENERGY-STORAGE SYSTEM

Since the air conditioner(A/C) load contributes 30% of the peak demand of Taiwan Power Company(Taipower) system during the summer season, load management by clipping AIC load has become one of the most important topics in Taipower system. Since the eutectic salt is a complete inorganic compound with freezing point at 47 degrees F and latent heat 41 Btu/lb, it is a good medium for the energy storage system. In this paper, an A/C system with 1800 RT-HR eutectic salt energy storage tank was built on the campus of National Sun Yat-Sen University (NSYSU) for the demonstration of the cooling energy storage(CES) system. Six operation modes of the CES-system are designed to meet different cooling load requirements. By computer simulation, it is found that 41.1% of the electric peak demand has been reduced and 56% of the energy consumption has been shifted from peak hours to off-peak hours by the CES-system. In this paper, the mathematical model of an eutectic salt CES-system has been developed for the computer simulation of the energy storage system. It is found that the optimal capacity of the storage tank is determined by the off-peak time period and the largest annual electricity charge saving could be obtained by applying the smallest nominal chiller size under the optimal operating conditions. According to the results of the computer simulation and the field test, the payback period of the test system is estimated to be 3.6 years by considering the additional investment cost and the electricity charge saving of the CES-system.