Development and Validation of the Water Pit Numerical Model for Seasonal Thermal Energy Storage

Seasonal thermal energy storage (STES) can effectively mitigate the supply and demand imbalance of solar energy between winter and summer. Large-scale water pit thermal storage systems require efficient and accurate computational simulations to avoid investment waste. This study proposes a simplified numerical analysis method and establishes a cylindrical underground pit with a total volume of 11 304 m³ to describe the operation of a STES system. The model establishes a one-dimensional heat transfer model for the water body and a two-dimensional heat transfer model for the soil, separately solving for the water and the soil temperature field. The two models are connected through the temperature boundary at the pool wall to simulate the entire system. To comprehensively verify the accuracy of the numerical simulation model, validation was conducted under standby, charging, and discharging modes. The results indicate that the developed model has good accuracy and reliability. Under the standby mode, the temperature error of the five water layers in the sandbox test is less than 10%, with the highest accuracy in the middle and lower-middle water layers, with an average absolute error of 1.75% and 1.24%, respectively. Under the charging mode, the average relative error is 1.57%, and the average temperature error is 0.44 ℃. Under the discharging mode, the average relative error is 0.46%, and the average temperature error is 0.24 ℃.