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International Journal of Geophysics
Volume 2013 (2013), Article ID 916541, 14 pages
http://dx.doi.org/10.1155/2013/916541
Research Article

Measurements and Design Calculations for a Deep Coaxial Borehole Heat Exchanger in Aachen, Germany

1Institute for Applied Geophysics and Geothermal Energy, E.On Energy Research Center, RWTH Aachen University, Mathieustraße 10, 52074 Aachen, Germany
2Institute for Mining Engineering I, RWTH-Aachen University, Wüllnerstraße 2, 52056 Aachen, Germany
3Geophysica Beratungsgesellschaft mbH, Lütticherstraße 32, 52064 Aachen, Germany

Received 21 December 2012; Accepted 24 February 2013

Academic Editor: Jean-Pierre Burg

Copyright © 2013 Lydia Dijkshoorn et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

This study aims at evaluating the feasibility of an installation for space heating and cooling the building of the university in the center of the city Aachen, Germany, with a 2500 m deep coaxial borehole heat exchanger (BHE). Direct heating the building in winter requires temperatures of 40°C. In summer, cooling the university building uses a climatic control adsorption unit, which requires a temperature of minimum 55°C. The drilled rocks of the 2500 m deep borehole have extremely low permeabilities and porosities less than 1%. Their thermal conductivity varies between 2.2 W/(m·K) and 8.9 W/(m·K). The high values are related to the quartzite sandstones. The maximum temperature in the borehole is 85°C at 2500 m depth, which corresponds to a mean specific heat flow of 85 mW/m2–90 mW/m2. Results indicate that for a short period, the borehole may deliver the required temperature. But after a 20-year period of operation, temperatures are too low to drive the adsorption unit for cooling. In winter, however, the borehole heat exchanger may still supply the building with sufficient heat, with temperatures varying between 25 and 55°C and a circulation flow rate of 10 m3/h at maximum.