Thermal Storage Options for HVAC Systems

Abstract

With the ever-increasing cost of electricity and the high demand charges levied by utility companies, thermal storage for cooling is rapidly becoming a widely recognized method to lower cooling costs. There are three maior types of thermal storage systems: • Ice Storage: This utilizes the latent heat of fusion of ice for thermal storage. During off-peak periods, the refrigeration system is used to build ice. The ice is melted to produce chilled water when cooling is required. • Chilled Water Storage: Chilled water is generated and stored during off-peak periods and used for cooling during on-peak hours. Since this method is based on the specific heat of water rather than the latent heat of fusion of ice as in ice storage, it requires about 4 times the storage capacity of an equivalent ice storage system. • Salt Storage: This system utilizes eutectic salts which freeze and melt around 47°F. Existing chillers can be easily retrofitted for salt storage or chilled water storage. For ice storage systems, a direct refrigerant system or glycol chillers are suitable. This paper discusses the details of each system, their advantages and disadvantages, and application.