Energy and Environmental Performance Assessment of a Solar Thermal Energy Storage System for Building Heating Supply with an Approach to Reducing Energy Consumption and Greenhouse Gas Emissions

The increasing use of solar energy for building thermal demands, due to intermittent solar radiation and mismatch between production and consumption, requires efficient energy storage systems. Maintaining stratification and controlling the thermocline are essential for improving stored-energy quality. Despite numerous studies on thermal storage tanks, the combined effects of inlet hydrodynamic and thermal conditions on thermocline behavior and the performance of turbulence models remain insufficiently explored. This study evaluated the thermal and hydrodynamic behavior of a thermal energy storage tank and identified suitable operating conditions. Numerical simulations predicted temperature and velocity fields using the k-ε and RNG k-ε turbulence models. The effects of inlet temperature, flow rate, and Archimedes number on temperature distribution and stratification were assessed, and numerical results were compared with experimental data. Both models agreed reasonably with experimental results; however, the RNG k-ε model predicted the temperature gradient and thermocline thickness more realistically because of its lower numerical diffusivity. Increasing the Archimedes number improved agreement between numerical and experimental results. The thermocline advanced over time, while its thickness increased because of conductive heat transfer. Controlling inlet flow rate to maintain constant fluid temperature produced more favorable stratification than variable inlet temperature conditions. Appropriate inlet design also reduced internal mixing and improved thermocline formation. Therefore, the RNG k-ε model, coordinated control of inlet temperature and flow rate, and inlet geometry optimization can support more efficient design and operation of solar energy storage systems in buildings.