The evolution of the geothermal potential of a subsurface urban heat island

Abstract

Meeting the rising energy demands of cities is a global challenge. Exploitation of the additional heat in the subsurface associated with the subsurface urban heat island (SUHI) has been proposed to address the heating demands. For the sustainable use of this heat it is crucial to understand how SUHIs evolve. To date, there have been no comprehensive studies showing how temperature anomalies beneath cities change over time scales of decades. Here, we reveal the long-term increase of temperatures in the groundwater beneath Cologne, Germany from 1973 to 2020. The rise in groundwater temperature trails atmospheric temperature rise in the rural areas and exceeds the rise in atmospheric temperature in the urban center. However, the amount of heat that is currently stored each year in the thin shallow aquifer reaches only 1% of the annual heating demand. The majority of the anthropogenic heat passes by the vertical extent of the aquifer or is discharged by the adjacent river. Overall the geothermal resource of the urban ground remains largely underused and heat extraction as well as combined heating and cooling could substantially raise the geothermal potential to supply the city’s demand.

The silent impact of underground climate change on civil infrastructure

“…Harvesting such thermal power via geothermal technologies would contribute to only 0.5% of the annual heating consumption of the largest buildings of the Loop (i.e., 8 GWh vs. 1824 GWh as estimated through the simulations performed in this work and previously published data 56 , respectively). Comparable results have been previously reported for other cities 43 . The limited size of heat-emissive surfaces in contact with the ground relative to the large size of the space conditioning surfaces of buildings in the Loop is the reason for the relatively small heating potential associated with the harvesting of waste heat in the considered district.…”

“…Subsurface temperature rises can also cause transportation infrastructure and public health issues, such as overheated subway rails that force trains to slow down or stop to avoid incidents with significant economic costs associated with the delay of public transportation services, and extreme air temperatures underground that cause thermal discomfort and heat-induced diseases, such as heat cramp, dehydration, hypertension, asthma, and heatstroke 13,[30][31][32][33][34][35][36][37] . On the contrary, subsurface temperature rises represent an opportunity, as geothermal technologies can harness and reutilize additional heat from the ground [38][39][40][41][42][43][44] .…”

Einführung in das Verbundvorhaben Easyquart

“…Insbesondere in neuen Quartieren kann es zu einer langfristigen Änderung der Untergrundtemperaturen (i. d. R. Anstieg) unabhängig durch die Nutzung Oberflächennaher Geothermie kommen. Dieser als "urbane Grundwasserwärmeinsel" beschriebene Effekt (Balke 1974;Böttcher und Zosseder 2022;Zhu et al 2010) und seine Auswirkungen auf das geothermische Potenzial sind Gegenstand zahlreicher Untersuchungen (Arola und Korkka-Niemi 2014;Hemmerle et al 2022;Zhu et al 2010). Vor allem gilt es aber, mögliche Veränderungen der Grundwassertemperatur durch die Errichtung von Gebäuden und Versiegelung von Oberflächen (z.…”

A New Type in TRNSYS 18 for Simulation of Borehole Heat Exchangers Affected by Different Groundwater Flow Velocities

“…Heating ventilating air-conditioning (HVAC) systems such as groundwater and air heat pump systems coupled to borehole heat exchangers (BHE) have been used increasingly because they are among the cleanest and most energy efficient heating/cooling systems for houses, multi-residential buildings, public offices, or farms [1][2][3][4][5][6]. Because of the incentives for these systems by the Italian government, often the design of ground source heat pump (GSHP) systems is not adequate and superficial.…”