A novel hybrid design algorithm for spiral coil energy piles that considers groundwater advection

This paper presents a novel hybrid design algorithm for spiral coil energy piles that considers groundwater advection. The design algorithm considers the groundwater advection effect using an analytical model. During this study, the accuracy of the analytical model was verified for its design application using a finite element (FE) numerical model, and the effect of groundwater advection on the design results was investigated. According to these results, groundwater advection attenuates thermal interference between piles, as well as long-term ground thermal resistance, which contributes to the economical design of energy piles. Moreover, when there is an extreme disparity between cooling and heating loads, hybrid design was achieved using hourly building energy load data calculated by the design builder program. Hybrid design decreases the total heat exchanger length of the energy piles, and reduces the entering water temperature (EWT) variance caused by heat interference. Furthermore, the pile arrangement can influence the impact caused by separation distance. For a square arrangement of piles, the shorter the separation distance, the less the effect from the hybrid system. In contrast, for a linear arrangement of piles, there is no influence caused by the separation distance, and generally, a high reduction rate of heat exchanger length is shown.