<p>To reduce the significant energy consumption used for heating and cooling in buildings, and the accompanying emissions, ground source heat pump systems are emerging as a promising technology. Making use of the stable deep ground temperatures, they provide the required heating and cooling with efficiencies between 400 – 600%. However, their widespread use is hindered mainly by the higher upfront costs, large land requirements, and low system performance with possible eventual failure owing to changes in the ground temperatures with time when the heating and cooling loads are not the same. Varying heating and cooling loads give different heat extraction and rejection rates into the ground, resulting in&nbsp;a thermal imbalance that leads to reduced system performance. To address this concern and the cost of these systems, the incorporation of ground heat exchangers into building foundations with energy storage is investigated. Because building foundations are not as deep as conventional systems, heat exchangers need to be compact and efficient. The incorporation of energy storage is one way of increasing capacity of compact systems while attaining thermal balance and thereby better performance in both the heating and cooling seasons. To investigate the potential improvements in performance with different backfill material and thermal energy storage, a helical steel pile of 20 m depth has been considered. COMSOL Multiphysics®, based on the finite element method with the heat transfer model and the pipe flow model and ANSYS Fluent with the Realizable k-ε model for explicit modelling of turbulent flow have been used in obtaining the solution to the developed numerical model. The variation of ground temperature with depth was considered using a user-defined interpolation&nbsp;function to investigate the changes in ground temperature with heat injection and removal from the ground. First, the improvement in performance with&nbsp;different enhanced backfill materials was investigated. The considered backfill material are silica sand, concrete and bentonite grouts. Then, the potential for performance improvement with the use of phase change material (PCM) in tube containers placed within the pile is considered. Results show that performance of the energy pile improves as the thermal conductivity of the backfill material increases; as the thermal conductivity increases, heat transfer from the pile to the surrounding ground soil increases. Preliminary results show that the use of PCM gives significant improvements in the heat transfer rate per unit length of the pile. The influence of the PCM on the COP and ground temperature variation with time is a subject of ongoing investigations.</p>

Thermal Performance of a Helical Steel Energy Pile Incorporating Latent Thermal Energy Storage for Ground Source Heat Pump Applications

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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