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Project Code [2022-Geothermica-458_C2G]
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Project title
Galleries to Calories (G2C)
Primary Funding Agency
Geological Survey Ireland
Co-Funding Organisation(s)
Lead Organisation
University College Dublin (UCD)
Project Abstract
Galleries to Calories (G2C) demonstrates for the first time the use of legacy mine workings as
recycled heat storage and transport networks to provide managed sustainable regional recharge of
low enthalpy (< 40�C) geothermal heat present naturally in the subsurface, to make it available for
regional heat pump extraction. G2C demonstrates the storage, transport, and recycling of waste
industrial heat in extensive legacy mine workings southeast of Edinburgh, Scotland, and assesses its
potential application in European and US coal and mineral mines.
A primary aim of G2C is to install a field test site where the hydraulic and heat transport
characteristics of the legacy mine workings can be investigated in detail through the provision of both
an injection and extraction borehole at two different locations within the mine workings, and the
establishment of a demonstration of the technology. The project design is based around the need to
provide a working prototype of up to 9 MW of cooling for a national computer facility. The heat
geobattery concept is that the cooling is provided using mines water in a closed loop heat exchanger
at the surface, and an open loop heat exchange in the mine workings. Once this heat is distributed
and stored in the subsurface, various heat pump technologies in different surface geographical
locations can be employed to recover it. The recycled heat will augment the natural geothermal heat
present and sustainably replenish the natural heat extracted through the heat mining using heat pump
technology.
Static heat storage in mine workings and various aquifer thermal storage schemes is currently stateof-the-art and either being investigated or trialled at a local scale in a number of countries (e.g.,
Verhoeven et al., 2014; Adams et al., 2019; Bao et al., 2019; Monaghan et al., 2021; Walls et al.,
2021). Additionally, there are several examples of mine water discharge from legacy mine workings
being used by community and small district-scale developments to heat 10s - 100s of properties. The
fundamental issue is that although the amount of low-grade geothermal heat present in the
subsurface is extensive, the resource is the result of thousands of years of heat conduction from deep
within the earth and storage, influenced by the prevailing paleo-surface temperature conditions. The
actual deeper subsurface heat recharge rate or outward heat flux is of the order of mW/m2.
G2C undertakes a full feasibility study of heat injection and subsurface transport, including in-depth
geological, hydrogeological and geochemical site characterisation, quantitative assessment of the
dynamic processes initiated by the widespread temperature changes to the subsurface, assessment
of the sustainable thermal resource management for different development scenarios, determination
of the best techniques for monitoring heat distribution, development of socially based economic
models, investigation into the legal aspects of subsurface heat ownership as a basis for facilitating the
establishment of equitable and sustainable business models and technical consideration of its wider
application to European and US coal and mineral mines.
Grant Approved
�76,264.00
Research Theme
Climate Solutions, Transition Management and Opportunities
Initial Projected Completion Date
31/08/2025