Influence of operating temperature on efficiency of supercooled thermal energy storage

Influence of operating temperature on energy and exergy (available energy) efficiencies of the storage system was evaluated by numerical simulation for a long-term latent heat thermal energy storage system using supercooled phenomena. The supercooled thermal energy storage (super-TES) stores thermal energy at temperatures lower than the melting point of the phase change material, which reduces heat loss from the storage system. The thermophysical properties of disodium hydrogenphosphate dodecahydrate were used for the calculation. From the results of the calculation, we found that super-TES is more advantageous than the conventional latent heat thermal energy storage (LHTES) when the initial temperature of the storage system is close to the melting point of the hydrate. Although the efficiencies of LHTES monotonically decrease with increasing storage temperature, the efficiencies of super-TES reach the maximum when the storage temperature is higher than the ambient temperature. The optimal storage temperature that gives super-TES the maximum efficiency increases with the storage volume and the thickness of the thermal insulation.