Numerical modelling and experimental testing of a thermal storage system with non-spherical macro-encapsulated phase change material modules

Thermal energy storage is a key technology that can support the transformation of our energy system to renewable energy sources. Compared to sensible energy storage systems commonly used in heating, ventilation and air conditioning, phase change material (PCM) based storage systems offer significantly higher storage capacities due to the latent energy of the solid-liquid phase change. In this work, we analyzed a PCM storage using commercially available PCM modules with a special, non-spherical shape. For the future performance analysis of the storage in a cooling application by means of system simulations, a simulation model is needed that enables the correct prediction of the thermal behaviour under different operating conditions. For this purpose, a PCM storage model originally developed for PCM spheres was used and parametrized with regard to the non-spherical module shape. The numerical results agreed well with the results of a series of 19 charging and discharging tests conducted under a wide range of operating conditions. Regarding the thermal power, the highest root mean square error of all tests performed was 0.4 kW for heating and 0.98 kW for cooling, while it was 0.68 K and 0.86 K, respectively, for the in- and outlet temperatures. The observed levels of deviation for the cooling process were generally higher than those for heating, which was due to a quite simple modelling of the supercooling phenomenon.