Numerical analysis of the prototype of the high-temperature thermal energy storage based on sand bed

Heating accounts for more than 60 % of the final energy consumed by buildings in EU countries. As new buildings are required to meet a zero-carbon standard, technical solutions are being sought to reduce heat demand and maximize the use of renewable energy. One of the possible solutions is the implementation of seasonal heat storage systems that can be charged using solar energy. The main goal of the study was to analyze the operation of a long-term, high-temperature heat storage using a sand bed and distinguish the parameters affecting its efficiency. In addition, the work aimed to show the feasibility of using such a storage in different charging schedules and the method of discharge through an air heat exchanger. As part of the research, a laboratory prototype consisting of an insulated tank filled with 300 kg of sand was developed. This prototype was used to perform the experiments required to validate the numerical model. The model, created in the ANSYS Workbench 2024 R2 environment, was then used to perform further analysis aimed at increasing the efficiency of the tested system. The results showed that the low thermal conductivity of sand prolonged high temperature retention and minimised heat losses, especially with thicker insulation. Analysis showed that positioning the heaters closer to the tank axis reduced heat loss, but required monitoring to avoid temperatures above ∼1073 K. In addition, control logic was implemented to prevent the heaters from overheating the sand. Various charging schemes - continuous, off-peak G12 and photovoltaic based - demonstrated the flexibility of the system under changing energy price tariffs and renewable availability. Discharge tests used airflow in a pipe heat exchanger, where higher velocity increased power output but caused faster local cooling. The proposed solution could be cost-effective, environmentally friendly and suitable for both building heating and industrial processes, highlighting its potential for scalable, long-term energy storage.