Seasonal Thermal Energy Storage in Abandoned Mines: Transient Numerical Modelling for the ICHS Project

Abandoned, flooded mine workings present a promising opportunity for seasonal underground thermal energy storage (UTES), offering large subsurface water volumes that can hold waste heat from high-performance computing (HPC) systems or other low-grade heat sources and release it during periods of high heat demand. The Immersion Cooling and Heat Storage (ICHS) project at Durham University combines prototype immersion cooling for HPC infrastructure with a feasibility study of using disused mine networks for inter-seasonal heat storage and reuse. ICHS aims to position itself as a living lab that integrates practical technology testing with fundamental research into subsurface thermal storage processes, with the aim of advancing low-carbon heat solutions and facilitating heat reuse within campus systems and beyond.

The potential of flooded mine networks to function as effective thermal stores depends critically on mine water circulation and its interaction with ambient groundwater flow. Advective movement of water between mine workings and surrounding aquifers can lead to significant heat loss or redistribution, thereby influencing storage efficiency, recovery rates, and long-term sustainability of a mine-based UTES system. Accurately quantifying and modelling these coupled flow processes is therefore vital to assess the practical capacity of mine water thermal storage and to develop predictive tools for design and optimisation of real systems.

In seasonal storage schemes, heat is typically introduced into the subsurface during summer months when excess thermal energy is available, and withdrawn in winter to supply space heating via heat pump systems. Such systems can also replenish heat over the summer that was depleted in winter. To model this transient behaviour, we have extended the GEMSToolbox framework (Mouli-Castillo et al., 2024) to support time-dependent injection temperatures and flow rates, enabling simulation of seasonal injection–withdrawal cycles under varying operational conditions.

In this presentation, we (i) introduce the ICHS project, describe (ii) the implementation of transient heat and flow boundary conditions in GEMSToolbox, and (iii) preliminary results that illustrate how mine water–groundwater interactions influence heat dispersion and recovery. These results highlight the importance of capturing coupled flow-heat dynamics in assessments of mine water thermal energy storage (MTES) performance and provide insights into how operational strategies and site characteristics can be tuned to maximise storage efficiency in post-industrial subsurface environments.