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. 1. Introduction Before 2004, RWTH-Aachen University planned to install a deep borehole heat exchanger (BHE) to use geothermal energy for heating and cooling of its new “SuperC” student service centre. In summer time the large roof should provide shade, while in winter the sun should irradiate the glass-front, passively heating the building. Solar cells on the roof should generate the electricity for driving the pump of the borehole heat exchanger. The deep coaxial borehole heat exchanger is a closed system where cold water flows down in the outer pipe, heats up, and rises in the inner pipe. The borehole RWTH-1 of the RWTH-Aachen University reached a depth of 2500？m and was intended to provide the thermal power for heating and cooling as a BHE. The temperature of the outlet inner pipe should have a temperature of at least 55–80°C over a period of 30 to 40 years to drive the climate control adsorption chiller during summer time. In winter the geothermal water will heat directly the building. The borehole was drilled in spring 2004 before construction of the building (Figure 1). The site is located in the urban center Aachen at a distance of about 500？m from the “Imperial Cathedral,” frequently referred to as the final resting place of Charlemagne, and its vicinity of the famous thermal springs of 60°C. Figure 1: Mobile drill rig in the center of the city Aachen. The borehole
References
[1]
B. Oesterreich, U. Trautwein, and S. Lundershausen, “Die geothermiebohrung RWTH-1,” VAG—Vereinigung Aachener Geowissenschaftler e.V. Infoblatt 2005.
[2]
S. Signorelli, Geoscientific investigations for the use of shallow low-enthalpy systems [Ph.D. thesis], ETH Zürich University, Zurich, Switzerland, 2004.
[3]
Anonymous, Akkupyc Manual, Micromeritics Instrument Corporation, Norcross, Ga, USA, 1997.
S. Speer, Design calculations for optimising of a deep borehole heat-exchanger [M.S. thesis], Institute of Applied Geophysics, RWTH Aachen University, Aachen, Germany, 2005.
[6]
G. Knapp, J. Gliese, and H. Hager, “Geologische Karte der Nordlichen Eifel 1:100 000,” Tech. Rep., Geologischen Landesamt Nordrhein-Westfalen, Krefeld, Germany, 1980.
[7]
B. Oesterreich, “Petrographische beschreibung der RWTH-1 kernsektionen,” Tech. Rep., Geologischer Dienst North Rhein Westphalen, Krefeld, Germany, 2005.
[8]
R. Pechnig and U. Trautwein, Log Interpretation in the RWTH-1 Borehole, vol. 67, Jahrestagung der Deutschen Geophysikalischen Gesellschaft, Aachen, Germany, 2007.
[9]
L. Dijkshoorn and R. Pechnig, Physical Properties in the Carboniferous and Devonian Rocks Drilled in the RWTH-1, vol. 67, Jahrestagung der Deutschen Geophysikalischen Gesellschaft, Aachen, Germany, 2007.
[10]
Ribbert, “Die bohrung RWTH-1- regionalstratigraphische einordnung und deutung,” Tech. Rep., Geologischer Dienst North Rhein Westphalen, Krefeld, Germany, 2006.
[11]
J. Sch？n, Handbook of Geophysical Exploration: Physical Properties of Rocks, vol. 18, Elsevier, Waltham, Mass, USA, 1996.
[12]
Anonymous, “Superc entwurfplannung, unterlagen zur hu-bau,” Tech. Rep. 33239, Arup GmbH, New York, NY, USA, 2004.
[13]
J. Quirein, J. Garden, and J. Watson, “Combined natural gamma ray spectral/litho-density measurements applied to complex lithologies,” in Proceedings of SPE Annual Technical Conference and Exhibition, pp. 1–14, New Orleans, La, USA, September 1982.
[14]
V. ？érmak, L. Bodri, L. Rybach, and G. Buntebarth, “Relationship between seismic velocity and heat production: comparison of two sets of data and test of validity,” Earth and Planetary Science Letters, vol. 99, no. 1-2, pp. 48–57, 1990.
[15]
L. Rybach, “The relationship between seismic velocity and radioactive heat production in crustal rocks: an exponential law,” Pure and Applied Geophysics, vol. 117, no. 1-2, pp. 75–82, 1978.
[16]
C. Bücker and L. Rybach, “A simple method to determine heat production from gamma-ray logs,” Marine and Petroleum Geology, vol. 13, no. 4, pp. 373–375, 1996.
[17]
C. Clauser, Numerical Simulation of Reactive Flow in Hot Aquifers, Springer, Berlin, Germany, 2003.
[18]
A. Beck, “Methods for determining thermal conductivity and thermal diffusivity,” in Handbook of Terrestrial Heat Flow Density Determination, R. Haenel, L. Rybach, and L. Stegena, Eds., Kluwer Academic Publishers, Norwell, Mass, USA, 1988.
[19]
H. D. Vosteen and R. Schellschmidt, “Influence of temperature on thermal conductivity, thermal capacity and thermal diffusivity for different types of rock,” Physics and Chemistry of the Earth, vol. 28, no. 9–11, pp. 499–509, 2003.
[20]
C. Clauser, “A climatic correction on temperature gradients using surface-temperature series of various periods,” Tectonophysics, vol. 103, no. 1–4, pp. 33–46, 1984.
[21]
R. Schellschmidt, S. Hurter, A. F？rster, and E. Huenges, Atlas of Geothermal Resources in Europe, Office for Official Publications of the European Communities, Brussels, Belgium, 2002.
[22]
H. Karg, Untersuchung des Temperatursfeldes im Untergrund der Region Aachen-Maastricht-Lüttich [M.S. thesis], RWTH-Aachen University, Aachen, Germany, 1995, Applied Geophysics and Geothermal energy Lochnerstrae 4–20, Haus B Geb？ude No. 154/1, D-52056.
[23]
M. Verkeyn, Bepaling van de Warmestroomdichtheid in Belgi？- een verkenning naar de mogelijkheden en de beperkingen (Detemination of the Specific Heat Flow in Belgium with possibilties and limitations) [M.S. thesis], Kath. University Leuven Belgium, Department Geology-Geography, Historical Geology Redingenstraat, Leuven, Belgium, 1995.
[24]
L. Dijkshoorn and C. Clauser, “Relative importance of different physical processes on upper crustal specific heat flow in the eifel-maas region, central europe and ramifications for the production of geothermal energy,” Natural Science, vol. 5, no. 2, pp. 268–281, 2013.
[25]
F. Summa, L. Benner, and F. Otto, Tagung für Ingenieurgeologie, Erlangen, 2005, Geothermie unter geotechnischen und wirtschaftlichen aspekten.
[26]
T. Kohl, R. Brenni, and W. Eugster, “System performance of a deep borehole heat exchanger,” Geothermics, vol. 31, no. 6, pp. 687–708, 2002.
[27]
Anonymous, Kusiflex; Das Extrem Flexible Leitungssystem, Kusimex Infothek, 2005.
[28]
E. Simmelink and K. Geel, “Sustainable tomatos are growing on geothermal heat,” Tech. Rep., TNO, Brussels, Belgium, 2008.
[29]
W. van Leeuwen, N. Buik, M. Gutierrez-Neri, A. Lokhorst, and G. Willemsen, Eds., Subsurface Spatial Planning for Geothermal Heat Production in, Greenport, Westland-Oostland, The Netherlands, 2010.
