%0 Journal Article
%T Measurements and Design Calculations for a Deep Coaxial Borehole Heat Exchanger in Aachen, Germany
%A Lydia Dijkshoorn
%A Simon Speer
%A Renate Pechnig
%J International Journal of Geophysics
%D 2013
%I Hindawi Publishing Corporation
%R 10.1155/2013/916541
%X 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¡ãC. In summer, cooling the university building uses a climatic control adsorption unit, which requires a temperature of minimum 55¡ãC. 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¡ãC at 2500£¿m depth, which corresponds to a mean specific heat flow of 85£¿mW/m2¨C90£¿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¡ãC 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¨C80¡ãC 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¡ãC. Figure 1: Mobile drill rig in the center of the city Aachen. The borehole
%U http://www.hindawi.com/journals/ijge/2013/916541/