Development and validation of the numerical model of an innovative PCM based thermal storage system

Because of the high costs of experimental tests in the real conditions of buildings, numerical simulation, developed analytical methods and different modelling studies are needed to predict the behaviour and results of phase change materials (PCMs) usage in buildings in order to optimize the thermal energy storage techniques and to make them more efficient and cost-effective. The aim of this study is to develop a numerical model reproducing the behaviour of an innovative water-PCM heat exchanger for cooling purposes particularly created for HIKARI, the first positive energy, mixed use district in France. Once numerically calibrated and experimentally validated, this model was used to optimize the system's technology applying Genetic Algorithms methods. The model presented in this article was developed based on the heat balance approach and solved using the finite difference method. It was validated both numerically, using a Computational Fluid Dynamics model and experimentally using both the results of an innovative experimental prototype designed and constructed in laboratory conditions and HIKARI in situ monitoring results. The Normalized Mean Bias Error and the Coefficient of Variation of the Root Mean Squared Error, used to analyse the validation results, show that the choice of the heat balance approach provided a valid model able to reproduce the PCM-water heat exchange with high accuracy.