The effect of phase change materials used in solar hot water storage tanks on thermal energy storage performance

Thermal energy storage is an energy storage method that enables more efficient use of renewable energy sources. In solar hot water systems, thermal energy is generally stored as sensible heat in the hot water tank. Investigations aimed at increasing the amount of energy stored and improving system efficiency by adding phase change materials (PCM) to the hot water storage tank are an important field of study. In this study, the effects of adding phase change materials to a heat exchanger type of vertical hot water storage tank, which is widely used in solar hot water systems, were systematically analyzed. The analysis was carried out by using three-dimensional numerical models based on computational fluid dynamics. Each component constituting the system was modeled individually and the effects of various parameters were investigated. Firstly, the numerical model developed for the empty tank to which PCM will be added was confirmed by the experimental study, and the system was investigated under various charge-discharge conditions. Then, in order to better understanding of the phase change mechanism, numerical models simulating the melting and solidification process of PCM in a vertical cylindrical tube were developed. The models were verified with experimental studies in the literature and the effects of various parameters affecting the phase change were analyzed. Finally, a numerical model was developed for the mantle tank with PCM. This model was verified with the experimental study and parametric analysis was performed. The effects of PCM were examined in comparison with the empty tank. In the considered system, it was determined that adding PCM into the tank has a positive impact on the thermal energy storage system. It was determined that the tank with PCM provided more hot water of 7.9% than the empty tank under the same conditions.