The potential of shallow geothermal energy in Norway and Portugal: optimized borehole design for two different climate conditions

Shallow geothermal energy offers a promising, renewable and sustainable solution for both heating and cooling buildings. However, the performance of these solutions is strongly affected by local ground properties and climatic conditions. This study evaluates the potential of shallow geothermal systems by optimizing borehole designs for two distinct geological and climatic settings, using a real university building in Aveiro, Portugal, as the case study. Real measured data on ground properties, borehole specifications and building loads have been integrated to enhance the accuracy of the models as well as the findings. This study has mainly contributed through numerical analysis in the following three aspects: a systematic comparison of the required borehole depth and the energy consumption of the heat pump under heating- and cooling-dominant conditions, comparison of four different bore field geometric configurations over multiple operational horizons to assess the impacts on borehole design depth and conducting detailed parametric analysis on impact of single-parameter and combined effects of key parameters on required borehole depth. Significant differences in the borehole depth requirements were observed between these two locations. The findings emphasize that the maximum entering fluid temperature, the grout thermal conductivity and the U-tube pipe diameter are crucial parameters. The best parameter combination reduces borehole depth by up to 58%, highlighting the substantial influence of design variables on BHE system efficiency. These design-oriented insights provide a valuable framework for climate-adaptive, configuration-aware and long-term-resilient BHE system design, thereby improving energy efficiency and sustainability across two distinct European climatic settings.