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| Titel |
Spatial resolution of subsurface anthropogenic heat fluxes in cities |
| VerfasserIn |
Susanne Benz, Peter Bayer, Kathrin Menberg, Philipp Blum |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250103574
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| Publikation (Nr.) |
 EGU/EGU2015-8698.pdf |
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| Zusammenfassung |
| Urban heat islands in the subsurface contain large quantities of energy in the form of elevated
groundwater temperatures caused by anthropogenic heat fluxes (AHFS) into the subsurface.
Hence, the objective of this study is to exemplarily quantify these AHFS and the generated
thermal powers in two German cities, Karlsruhe and Cologne. A two-dimensional (2D)
statistical analytical model of the vertical subsurface anthropogenic heat fluxes
across the unsaturated zone was developed. The model consists of a so-called Local
Monte Carlo approach that introduces a spatial representation of the following
sources of AHFS: (1) elevated ground surface temperatures, (2) basements, (3)
sewage systems, (4) sewage leakage, (5) subway tunnels, and (6) district heating
networks.
The results show that district heating networks induce the largest local AHFS with values
larger than 60 W/m2 and one order of magnitude higher than the other evaluated
heat sources. Only sewage pipes and basements reaching into the groundwater
cause equally high heat fluxes, with maximal values of 40.37 W/m2 and 13.60
W/m2, respectively. While dominating locally, the district heating network is rather
insignificant for the citywide energy budget in both urban subsurfaces. Heat from
buildings (1.51 ± 1.36 PJ/a in Karlsruhe; 0.31 ± 0.14 PJ/a in Cologne) and elevated
GST (0.34 ± 0.10 PJ/a in Karlsruhe; 0.42 ± 0.13 PJ/a in Cologne) are dominant
contributors to the anthropogenic thermal power of the urban aquifer. In Karlsruhe,
buildings are the source of 70% of the annual heat transported into the groundwater,
which is mainly caused by basements reaching into the groundwater. A variance
analysis confirms these findings: basement depth is the most influential factor to
citywide thermal power in the studied cities with high groundwater levels. The
spatial distribution of fluxes, however, is mostly influenced by the prevailing thermal
gradient across the unsaturated zone. A relatively cold groundwater temperature
combined with a high ground surface temperature (GST) and a high groundwater level
promote elevated fluxes. Overall, 2.15 ± 1.42 PJ and 0.99 ± 0.32 PJ of thermal energy
are annually transported into the shallow groundwater of Karlsruhe and Cologne
due to AHFS. This is sufficient to sustainably cover 32% and 9% of the annual
residential space heating demand of Karlsruhe and Cologne, respectively. Furthermore,
extracting this energy could also keep groundwater temperatures from rising any further. |
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