Impacts of underground climate change on urban geothermal potential: Lessons learnt from a case study in London

Asal Bidarmaghz; Ruchi Choudhary; Guillermo Narsilio; Kenichi Soga

doi:10.1016/j.scitotenv.2021.146196

Impacts of underground climate change on urban geothermal potential: Lessons learnt from a case study in London

Sci Total Environ. 2021 Jul 15:778:146196. doi: 10.1016/j.scitotenv.2021.146196. Epub 2021 Mar 6.

Authors

Asal Bidarmaghz¹, Ruchi Choudhary², Guillermo Narsilio³, Kenichi Soga⁴

Affiliations

¹ School of Civil and Environmental Engineering, University of New South Wales, Sydney, Australia. Electronic address: a.bidarmaghz@unsw.edu.au.
² Department of Engineering, University of Cambridge, Trumpington Street, CB2 1PZ, UK; Data-centric Engineering, Alan Turing Institute, UK.
³ Department of Infrastructure Engineering, University of Melbourne, Parkville, Australia.
⁴ Department of Civil and Environmental Engineering, University of California, Berkeley, USA.

PMID: 33714806
DOI: 10.1016/j.scitotenv.2021.146196

Abstract

While urban underground is being increasingly used for various purposes, two concerns should be addressed with respect to the urban underground climate change: i) how much energy has been stored in urban subsurface due to the heat rejection from underground heated spaces (such as tunnels and basements) and ii) how much of the thermal demand of a city or district can be supplied by harvesting this accumulative thermal energy in the ground. However, our understanding of the temperature rise in the ground and of the geothermal potential of urban subsurface is still limited. This paper quantifies the geothermal potential for a 12 km² densely populated borough in central London by considering the spatio-temporal temperature variation in the ground owing to continuous rejection of heat into the ground, coupled with the effect of geothermal extraction capacity. A large-scale transient semi-3D geothermal subsurface model of the site is developed, and the thermal interaction between underground heated spaces, geothermal energy extraction systems and the ground and groundwater are simulated. The concurrent heat rejection and extraction processes in the subsurface are computed so that the most influencing parameters of the subsurface on its geothermal potential are identified. Results show that up to 50% of the borough's total heat demand can be supplied via geothermal installations leading to around 33% reduction in CO₂ emission. The geothermal extraction efficiency in sand and gravel primarily depends on the ground conditions such as the thickness of the permeable layer and the groundwater flow regime. In impermeable ground such as clay, however, the underground built environment such as heated spaces have shown to have a significant impact on improving the geothermal extraction efficiency.

Keywords: Borehole heat exchangers; Geothermal potential; Large-scale numerical modelling; Subsurface temperature; Subsurface urban heat island; Underground climate change.