The increasing deployment of ground-source heating and cooling systems relies on understanding, characterising and predicting the thermal and hydraulic behaviour of the subsurface across scales, from laboratory and experimental studies to field applications. Closed- and open-loop systems depend on interactions between heat transport, groundwater flow, geological heterogeneity, and the thermal and hydraulic properties of the subsurface. Understanding these processes is essential for system design, operation, optimisation, long-term performance and sustainability.

This session focuses on ground-source heating and cooling through numerical modelling, field observations, monitoring, experiments and case studies. We welcome contributions on:

• Numerical methods for coupled thermal, hydraulic, mechanical and chemical processes, including finite-difference, finite-volume, finite-element and mixed-dimensional approaches for complex subsurface systems;
• Model calibration, parameter estimation, sensitivity, uncertainty and approaches for improving confidence in subsurface thermal models;
• Exploratory and experimental testing, including thermal response tests and approaches for characterising subsurface properties;
• Monitoring and field observations, including thermal, hydraulic and geophysical monitoring;
• Integration of numerical modelling with monitoring, experimental data and field observations for system characterisation, prediction and performance assessment;
• Field-scale case studies of open- and closed-loop systems, including borehole heat exchangers, aquifers and mines;
• The influence of geological heterogeneity, fractures, faults, groundwater flow and other subsurface processes on system performance;
• System design, optimisation and long-term operation, including interactions between subsurface systems and surface infrastructure such as heat pumps and district heating and cooling networks;
• Innovative approaches to harnessing the subsurface for sustainable heating and cooling across diverse geological, climatic and operational settings.

The session brings together modelling, experimental, monitoring and applied approaches to subsurface heating and cooling. By connecting numerical and experimental methods, it will foster exchange on how to better characterise, design, monitor and operate ground-source systems, while identifying opportunities and challenges for their wider deployment.