WG1 - Unresolved technical issues

This task will be divided in two subtasks, regarding the a) design phase and b) installation phase. Both subtasks will consist of preparing a survey and sending it to relevant stakeholders (design offices, constructors). Analysis of survey results will allow listing unresolved issues, classifying them and proposing a road map to address them.

Numerous numerical or analytical methods were studied and developed by different teams to evaluate the behaviour of EGS in terms of heat exchange and energy performance. They rely on different assumptions and approaches and present different complexity levels from the detailed modelling of pipes circuit to the choice of boundary conditions. A necessary step forward to promote the technology towards industry is to provide engineers with a comprehensive comparison of capabilities of available methods, a clear overview of assumptions behind each approach and a summary of the effect that each assumption has on the accuracy of the results. This task aims to gather all this information in a catalogue to drive the practitioners in the choice of the most appropriate solution for their projects.

The complex nature of ground heat transfer around EGS, in addition to their implementation in urban areas, results in design challenges. The first objective of this task is to provide insights of existing methods (guidelines, technical documents) used for the design of EGS, from analytical approaches to numerical ones, to understand their concept and potentiality in order to extrapolate it to the European scale. The second objective is to discuss the possibility of enlarging these methods by taking into account external factors, derived from using different heat source devices at existing buildings. By extension, it is of some interest to discuss the use of design methods at various scales, from the single EGS in interaction with its surrounding ground, to the district scale and city-scale. In particular, the question arising from the scale effect is how these methods perform with the existence of heat island effects. A strong interaction with WG3 will be needed to address the question of hybridisation with other energy sources.