Enhancing the performance of solar water heating systems: Application of double-layer phase change materials

An efficiently designed thermal energy storage (TES) tank is critical for enhancing the efficiency of solar water heating systems (SWHSs). This study describes the development of a hybrid sensible-latent TES tank in which a double-layer phase change material (PCM) with different melting points is integrated. To study its performance, a mathematical model of the SWHS with the hybrid tank was established in TRNSYS software. The results showed that when the volume of tank per unit area of solar collectors was in the range of 33.3-66.7 L/m2, the heat collection of the hybrid tank increased by 7.0%-15.6% and the heat supply increased by 7.6%-16.9% compared to that of the tank without the PCM. However, the effect of adding the PCM to the tank diminished when the volume of the tank was increased. The hybrid tank with the double-layer PCM achieved a twofold benefit of extending the heat supply time and maintaining a relatively high supply temperature compared to the tank with only a single-layer PCM. The effect of the hybrid tank on the thermal performance of the SWHS was prominent for the full-day and nighttime heating modes but was not significantly observed for the daytime heating mode.