Experimental characterisation of sub-cooling in hydrated salt phase change materials

Phase change materials (PCMs) allow storage of large amounts of energy within a narrow temperature range via their latent heat. This is useful for applications where the outside environment swings above and below the nominal temperature range, enabling the design of passively regulated thermal systems. This short communication presents an experimental characterisation of two proprietary hydrated calcium chloride-based salt materials designed for maintaining temperatures of 25-30 °C for building/enclosure temperature stability. It was found that materials' thermal performance is critically influenced by their rate of cooling. Using a T-history method, the experiments revealed that these salts undergo high specific enthalpy changes across a broad temperature range (e.g. up to 1 MJ/kg, which is 5-10 times their latent heat), but that up to 10 °C of sub-cooling and long nucleation times are possible, depending on their rate of cooling. This communication reveals that careful operation is needed to ensure that these materials achieve control within the desired temperature range.