Improving thermal performance of groups of energy screw piles with phase change materials

Underground thermal storage systems have potential to play an important part in the transition to renewable energy. Studies on combining building foundations with thermal storage are often limited to concrete piles, especially when involving phase change materials. In a recently published work, the authors presented a novel energy pile built using a screw pile filled with phase change materials. While the previous work considers all energy screw piles with same pile fillings, meaning a trade-off of low thermal conductivity and high heat capacity, screw piles in this work have two different functions: one screw pile filled with grout acts as the heat exchanger (energy pile) and its neighbour, filled with Phase Change Materials, act as a thermal battery (thermal storage pile). U-loop pipes are embedded only into the energy piles and connected to a Ground Source Heat Pump, so thermal energy from buildings will be stored in both the ground and the thermal storage piles. Numerical results show that this system can store up to 189.8 MJ/m3 heat energy during one year of operation. The Coefficient of Performance of the heat pump increases slightly, up to 3.4 %, which results from an improvement of the cooling mode performance.