RP-809 -- Evaluation of Optimal Control for Ice Storage Systems

Report / Survey by ASHRAE, 1995

Full Description

Thermal energy storage systems are effective in reducing the operating cost of cooling equipment. By operating the refrigeration equipment during off-peak hours to recharge the storage tank and discharge it during onpeak hours, a significant fraction of cm-peak electrical demand and energy consumption is shifted to off-peak periods. Cost savings are obtained because utility rates favor leveled energy consumption patterns.

Two types of thermal energy storage media exist: single-phase and two-phase. Chilled-water systems are single-phase as the contents of the tank is cooled without undergoing a phase change. Eutectic salt systems employ a salt that changes from the dissolved to solid state at a temperature above the freezing point of water. These two-phase systems provide a high storage density without the need for operating the chiller at low evaporator temperatures but require the usage of expensive chemicals. Ice storage systems feature a high storage density using a cheap storage medium, i.e. water, but require the chiller to operate at lower efficiencies when making ice. This research deals exclusively with the characteristics and performance of ice storage systems.