Experimental and model validation of a phase change material heat exchanger integrated into a real building

Latent heat thermal energy storages (LHTES) are a promising technology witha wide range of applications in the framework of energy efficiency improve-ment. Phase change materials provide a big storage capacity, but their thermalconductivities are always extremely low. The use of finned tube heatexchangers is nowadays the best solution to enhance PCMs thermal perfor-mances. This allows significant charging and discharging rates. The majorchallenge concerns the balance between thermal performances and high mate-rial costs. A proper design of the heat transfer surfaces is essential to limit thesystem overall cost. Two different heat exchangers solutions, with radial andlongitudinal fins are here examined. The design of the LHTES is performed bydeploying a simplified FEM numerical model specifically developed for theapplication. A validation procedure based on laboratory tests with a smallLHTES prototype was also carried out. The obtained results confirmed the reli-ability of the numerical model and justify its adoption as a tool for the designphase. The FEM model allows to effectively simulate the system thermalbehaviour and assess the impact of the different HEX geometrical parameterson thermal performances. Based on this information it was possible to performthe optimization of the heat transfer surfaces and to derive the best heatexchanger layout in terms of material usage. The results showed that the solu-tion with longitudinal fins is the most efficient, with 215 kg of steel lessrequired for the realization of the finned heat exchanger.