A Case Study to Investigate Free Heating Potential of BTES Systems

Thermal energy constitutes an important part of energy-need in buildings. Renewable and efficient technologies reduce the amount of energy usage and the environmental impacts of buildings. One of the most promising technologies is the ground source heat pumps charged by solar thermal systems. For the climate change and zero carbon targets, free heating is the best solution, despite its high initial costs. In this study, the free-heating potential of a borehole thermal energy storage (BTES) is investigated for a Nordic city when concentrated solar thermal collectors (CSTC) are used for thermal charge. A BTES with ten boreholes of 150 m depth, positioned on a concentric double circular geometry, is considered for the first five years of operation. The radii of the circles are optimized to maximize the seasonal coefficient of performance (SCOP). Comsol and OpenGeoSys are used for numerical calculations. Annually, the ground is first charged by solar energy and then used for free-heating of 20 standard houses. When the averaged borehole surface temperature goes below a critical temperature for free-heating, heat pump mode is considered. SCOP values and the percentage of free-heating are examined. A considerable free-heating potential is seen even for a Nordic city when CSTC are used.