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

Abstract

Latent heat thermal energy storages (LHTES) are a promising technology with a wide range of applications in the framework of energy efficiency improvement. Phase change materials provide a big storage capacity, but their thermal conductivities are always extremely low. The use of finned tube heat exchangers is nowadays the best solution to enhance PCMs thermal performances. This allows significant charging and discharging rates. The major challenge concerns the balance between thermal performances and high material costs. A proper design of the heat transfer surfaces is essential to limit the system overall cost. Two different heat exchangers solutions, with radial and longitudinal fins are here examined. The design of the LHTES is performed by deploying a simplified FEM numerical model specifically developed for the application. A validation procedure based on laboratory tests with a small LHTES prototype was also carried out. The obtained results confirmed the reliability of the numerical model and justify its adoption as a tool for the design phase. The FEM model allows to effectively simulate the system thermal behaviour and assess the impact of the different HEX geometrical parameters on thermal performances. Based on this information it was possible to perform the optimization of the heat transfer surfaces and to derive the best heat exchanger layout in terms of material usage. The results showed that the solution with longitudinal fins is the most efficient, with 215 kg of steel less required for the realization of the finned heat exchanger.