Design of plane energy geostructures based on laboratory tests and numerical modelling

• Energy geostructures are an up-coming technique for the thermal utilisation of the ground.
• A semi-analytical calculation model was developed based on thermal resistances.
• This model was implemented in the 3D software code (SHEMAT-Suite).
• Computing times can be reduced significantly by using the new approach.
• The verified new model was used for an extensive parameter study.

Energy geostructures are an up-coming technique for the thermal utilization of the ground. Due to the complexity of the system, it is necessary to apply numerical simulations for a proper design of plane energy geostructures. However, varying scales, different heat transfer mechanisms, and a missing rotational symmetry require complex numerical models and long computing times.This motivated the authors to develop a semi-analytical calculation model based on thermal resistances. This model was implemented in the general 3D coupled heat and flow transport code SHEMAT-Suite. Large-scale laboratory tests were carried out for verification and validation of the model. The results from the novel numerical approach were compared with results from the laboratory and with results from a fully discretized finite element model. All comparisons show a good agreement. As expected, computing times are significantly smaller than for fully discretized numerical models. Thus, the new approach is suitable for the design of plane energy geostructures. The new model was used for an extensive parameter study. As a result, the flow rate in the heat exchanging system, the ground temperature, the groundwater flow, the pipe arrangement in the structural element and the structure of the element were identified as the decisive parameters.