Comparative analysis of charging and discharging characteristics in novel cold and hot simultaneous energy storage tanks

Energy storage technology is instrumental in reducing energy costs and crucial for balancing demand and supply. This study proposes a cold and hot simultaneous energy storage tank (CAHSEST) for the first time, although its heat transfer characteristics are not yet clear. The objective is to explore the heat transfer properties of CAHSEST. Utilizing computational fluid dynamics (CFD) software, three-dimensional models for five distinct tanks were developed and comparative analyses were performed focusing on temperature distribution, velocity distribution, thermocline thickness and storage efficiency. The findings indicate that tanks with separated cold and hot water (cases 3–5) exhibit significantly better stratification than those with mixed water (cases 1 and 2), showing higher energy storage efficiency. At a heating time of 3600 s, cases 3 and 5 shows higher heat charging efficiency than other cases. In addition, case 3 achieves the highest cold discharging efficiency of 90.25 %, whereas case 2 has the lowest, at only 15.94 %. Overall, case 3 emerges as the optimal configuration. This research offers technical assistance for the design and understanding heat transfer characteristics of CAHSEST, and provides new directions for achieving long-term heat storage and short-term cold storage.