Optimizing Ice Thermal Storage to Reduce Energy Cost

Abstract

Thermal energy storage includes a number of technologies that store thermal energy in energy storage tanks for later use. These applications include the production of ice or chilled water at night which is then used to cool the building during the day. Unfortunately, thermal storage may not provide the expected load shifting or the cost saving if not designed or operated properly. This research discusses the optimal design of ice thermal storage (ITS) and its impact on energy consumption, demand, and total energy cost. The emphasis on the use of ITS as an effort to reduce energy costs lies within transferring the time of most energy consumption from on-peak to off-peak periods. Multiple variables go into the equation of finding the optimal use of ITS, and they are all judged with the final objective of minimizing monthly energy costs. This research discusses the optimal design of ITS and its impact on energy consumption, demand, and total energy cost. A tool for optimal design of ice storage is developed, considering variables such as chiller and ice storage sizes along with ice charge and discharge times. Detailed simulation studies using a real office building located near Orlando, FL including the utility rate structure are presented. The study considers the effect of the ITS on the chiller performance and the associated energy cost and demonstrates the cost saving achieved from optimal ice storage design. A whole building energy simulation model is used to generate the hourly cooling load for both the design day and the entire year. Other collected variables such as condenser entering water temperature, chilled water leaving temperature, outdoor air dry bulb and wet bulb temperatures are used as inputs to a chiller model based on DOE-2 chiller model to determine the associated cooling energy use. The results show a significant cost energy saving can be obtained by optimal ice storage design through using the tool proposed in this chapter.