Abstract
Around 20% of the total primary energy use in the United States is for thermal demands of buildings, such as space cooling, dehumidification, and space heating. Low-grade geothermal energy is abundant and could effectively satisfy these thermal demands. However, low-grade geothermal energy is underused because geothermal fluids have an energy density too low to justify transportation between the existing resources and buildings. The mobile sorption-based thermal battery (MSTB) system was thus developed to store the low-temperature heat using three-phase (vapor-liquid solution-solid crystal) sorption technology with a much higher energy density than a geothermal fluid provides. The energy density of an MSTB is over 6 times that of conventional hot water, enabling economical long-distance transport of low-temperature heat for thermal end uses. This can alleviate peak demand on the electricity grid by offsetting space-conditioning loads, improving the reliability and resilience of US energy systems. High energy density, fast crystallization, and crystal dissolution of the sorption material are critical to the viability and performance of the MSTB system. Therefore, the design and operation of MSTB systems must ensure effective generation and dissolution of the salt crystals inside the MSTB. To achieve this target, this study developed a prototype MSTB and its testing apparatus, and experimentally investigated the prototype MSTB. The crystallization and dissolution performance were also theoretically defined and quantified. The experimental results showed that the prototype MSTB was able to achieve an energy storage density of 903.0 kJ/kg and a maximum discharge rate of 1.3 kW. This study proves the feasibility and high performance of the MSTB concept, which is helpful to further study and development of the MSTB system.
