This project demonstrated an advanced thermal energy storage system—Latent Energy Storage System (LESS)—that utilizes an engineered bio-based polymeric gel to store latent energy in a heat exchanger. This approach to thermal storage can deliver substantial savings for the Department of Defense (DoD) not only in energy costs but also in infrastructure, equipment, and operational maintenance costs. The technical objective was to demonstrate at the Army National Training Center (NTC) at Ft. Irwin, CA the potential for an engineered phase change material (PCM) to store thermal energy at pre-determined temperatures, providing a minimum of 20% plant peak demand energy reduction, 25% plant energy cost savings (based on time of use rates) and, when replacement is due, a 40% reduction in chiller sizing.
The project expanded the use of PCM into large-scale thermal energy storage systems, such as heat exchangers, for the control of electrical peak demand loads. LESS is a modular, self-contained system of thermal energy storage capable of storing and redistributing thermal energy at any predetermined temperature between -50°C to +150°C. This new technology uses the well-established principle of the latent heat of fusion when changing phase from liquid (gel) to solid. The system is based on the re-purposing of established polymer and carbon steel heat exchanger technology used extensively in the ice storage and solar thermal hot water industries. The system comprises an atmospherically vented tank, in which heat exchangers are fully immersed in a cross-linked polymeric matrix gel, specifically engineered for either high or low temperature storage. At the core of the LESS concept is an organic material derived from agricultural bi-products. The material is food grade, non-toxic, non-flammable, and developed from a renewable supply source.
By implementing LESS at the selected site, the project has successfully validated PCM’s potential to provide in excess of 7.4% reduction in energy usage and 20% reduction in peak energy demand usage and 43% reduction in energy cost for DoD chilled water-cooling systems. The overall cooling and heating cost savings potential for DoD plants and facilities using LESS can be up to 43% depending on rate structure. The average system payback was estimated at 8 years. Furthermore, unlike traditional thermal storage systems, PCM-based storage allowed for the full integration of energy storage into existing facilities without the need to replace existing equipment or installation of new inefficient glycol-based systems.
PCM-TES technologies can face some implementation issues to market entry, these can be identified under the following categories: 1. Market readiness; 2. Containment vessel design; 3. PCM manufacturing costs in general as a thermal storage medium; 4. While PCM-TES remains an emerging technology, manufacturing cost of the PCM remains the key issue as the raw materials cannot be purchased or manufactured as a commodity product and remain a custom order.