A key lever to overcome the challenges in the building sector associated with today's extensive use of fossils, such as global warming, is the integration of renewable energy sources such as solar into district heating systems. However, solar energy fluctuates depending on the season and hourly patterns. This points to the importance of seasonal thermal energy storage (STES) systems. Numerical simulations of two STES (tank and pit) were studied. Since the presence of groundwater will reduce the performance of STES, and on the other hand, STES has an effect on groundwater, and the performance of underground tanks with groundwater presence is studied in this paper.
summary
Large-scale seasonal thermal energy storage is an intrinsic element of SDH applications, as it provides considerable robustness to the overall system. Numerical simulation of large-scale STES systems is an alternative to real-world field experiments. In this study, a two-dimensional numerical modeling method for axisymmetric geometry (cylindrical tank and conical pit) is proposed. The method was tested and then showed a comparison of the temperature distribution and storage performance drivers between the two storage options. The results show that the tank is about 4% more efficient than the pit under the given boundary conditions (see Tables 1 and 2). Compiled by Chen Jiaoyun
The same applies when no insulation is used. In addition, a tank without insulation is approximately similar in efficiency to a tank with insulation. The results show that under the given storage capacity and boundary conditions, the storage can only reach stable operation after 5 years. However, this 5-year time period may depend on many participants (e.g., insulation thickness, ground thermal conductivity).
Next, the work highlights the role of hydrogeological conditions on water storage performance through more favourable hydrogeological conditions (no groundwater flow) and extreme conditions (high groundwater flow). Therefore, a three-dimensional numerical model of the tank was established. The results show that heat loss increases significantly when groundwater is present. In fact, when there is no groundwater flowing, only conduction heat is carried from the stored to the surface. On the other hand, if groundwater flow is added, another contribution is added, the convective component. As a result, a wall was introduced to enclose the storage to reduce the impact on groundwater. The different distances from the memory were studied. The conclusion is that the farther away the wall, the better the performance. However, the cost of installing such a structure also plays a role in determining the optimal distance. In addition, future work will focus on model validation of measurement data from real storage plants.
