PCMs, Salt Hydrates, Thermal Energy Storage, Latent Heat, Phase Change
Phase change materials (PCMs) with desirable phase change temperatures can be used to provide a constant temperature source or sink for diverse applications. As such, incorporating PCMs into building materials, equipment, or appliances can shift and/or reduce the energy load. The motivation of this work is to identify low-cost inorganic salt hydrate PCMs that can complement current building systems and designs. Two key challenges to incorporating PCMs into building materials are 1) maintaining desirable thermal properties at large scales, and 2) developing cost-effective systems that are easily incorporated into existing structures and systems. In this work, we present an analysis of inorganic salt hydrates with phase change temperatures in the range of 5-60°C, targeted towards both space heating and cooling. The properties of the salt hydrates are compared with common waxes over the same temperature range. The results showed that salt hydrate systems such as sodium thiosulfate pentahydrate, NaS2O3·5H2O, has a latent heat as high as 201 kJ/kg at a phase change temperature of 48°C which is comparable to some paraffin waxes (213 kJ/kg at 52.5°C). At a density of 1.73 g/cm3, sodium thiosulfate pentahydrate has an energy density of 347 J/cm3 (paraffin waxes, 170 J/cm3). Moreover, it was found that salt hydrates are generally less costly per unit energy in contrast to common waxes with typical salt hydrate costs in the range of 0.001-0.01 $/kJ. This analysis shows the potential of salt hydrate PCMs for developing low-cost heating and cooling thermal energy storage systems to meet a range of applications.