The potential to source thermal energy from buried infrastructure such as tunnels and metro stations may offer significant potential to reduce the carbon dioxide emissions of heating and cooling, and reduce the costs associated with dedicated drilling for traditional ground-sourced systems. However, this remains a niche approach with few commercial schemes globally, partly due to high initial costs, long payback periods, technical uncertainties and the need to minimise construction risk and delays. To help address these challenges, the energy resource potential, technical and economic barriers and ways of overcoming them were examined for tunnels beneath Manchester and Crewe that were proposed as part of the HS2 Phase 2b railway construction. A worthwhile thermal resource was established, along with enthusiasm for use of the energy by the infrastructure developer and third parties in the vicinity. The economic case is set out, which establishes financial viability but with significant uncertainty based on future market conditions. This demonstrates the need for a supportive future policy environment to encourage the uptake of all available heat sources.
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Subsurface infrastructure assets such as building foundations, tunnels, metro stations and wastewater systems can be used for heat capture and storage alongside their primary function (Lagoeiro et al., 2019; Meibodi and Loveridge, 2021). These so-called ‘energy geostructures’ act as underground heat exchangers. Subject to suitable operational temperature limits, this can facilitate underground storage of waste heat from cooling during summer and the subsequent extraction of that heat from the ground in winter to provide heating. Energy geostructures can also support heating and cooling decarbonisation through enabling access to ground and environmental thermal energy sources that would otherwise be technically or economically inaccessible (Loveridge et al., 2022). Because they avoid the need for dedicated drilling and special-purpose ground heat exchangers, energy geostructures can offer opportunities to reduce the capital costs needed for accessing shallow geothermal energy (Anis Akrouch et al., 2020; Loveridge et al., 2020; Lu and Narsilio, 2019). Energy tunnels are one type of energy geostructure – they involve embedding heat transfer pipes in the linings of tunnels, typically during construction, to extract thermal energy from the earth around the tunnels and from within the tunnels themselves (Adam and Markiewicz, 2009; Franzius and Pralle, 2011).
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