Evaluation and simulation of cost saving operation for thermal storage HVAC system

Three indices are introduced in order to evaluate cost saving operation of chillers using nighttime low electric power rates for thermal storage systems with water tanks. A storage tank discussed here is a multi- connected complete mixing type, which is widely used in Japan. The indices are calculated with some measured data. In this paper, definitions of the indices are described, and one of evaluation results in actual office buildings is shown. Moreover, differences among the indices applied to simulation results are compared under several combinations of chiller capacity, tank capacity and set point temperature in the tank for chiller on/off control. As a result, these indices give us useful information if operation of thermal storage HVAC system can be more economical.