A review on energy piles design, sizing and modelling

Boreholes and energy piles coupled with ground source heat pump plants utilize renewable geothermal energy for buildings heating and cooling purposes and need proper design and sizing in order to end up with high plant efficiency. This paper conducted a review of available scientific literature, design standards and guidelines on energy piles performance within the framework of the IEA-ECES Annex 31. Main aspects covered were typical plant solutions, configurations of energy piles and their thermal response test performance, available analytical and numerical models with their main features and application in commercial software and design manuals. Four typical fundamental schemes of geothermal plant with energy piles were found, both suitable for cold and hot climate applications. Properly sized heat pump systems with energy piles were characterized with high overall system SCOP values higher than 4.5, while some case studies reported two times smaller SCOP values that illustrates the effect of proper design and sizing of such systems. The lack of specific heat extraction values which could be determined based on the climate and energy pile application show the need to develop general procedures for early stage energy pile sizing that would allow quick estimates of the heat extraction/rejection potential and system performance with reasonable accuracy for conceptual design. Most of available software is borehole oriented and will fit for energy piles sizing if software supports variable ground surface temperature boundary conditions, which, however is not implemented in most of software packages. Expected software features to be implemented are water advection and multiregional surface boundary heat transfer.