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Thermal Efficiency Comparison of Borehole Heat Exchangers with Different Drillhole Diameters
GeoZentrum Nordbayern, Friedrich Alexander University Erlangen Nuremberg, Bayern 91054, Germany
Rheinland, LGA Bautechnik GmbH, Tillystr. 2, 90431 Nuremberg, Germany
* Author to whom correspondence should be addressed.
Received: 10 May 2013; in revised form: 8 July 2013 / Accepted: 22 July 2013 / Published: 19 August 2013
Abstract: Thermal efficiency of borehole heat exchangers (BHE) is of crucial importance for the design and optimization of ground source heat pump (GSHP) system. This paper investigates thermal efficiency of a BHE with three drillhole diameters: 121 mm, 165 mm and 180 mm. The BHE was installed in a GSHP system of an office building located in Nuremberg, Germany. Thermal properties and hydraulic properties of the ground where the BHE was installed have been measured by thermal response tests as well as pumping tests. Furthermore, the evaluation of thermal performance is made possible by monitoring operation of the GSHP system. Using the recorded data, thermal exchange rates have been calculated and compared in a daily period as well as a seasonal period. The daily statistics indicate that the thermal exchange rate of the BHE increases with larger drillhole diameter. For the seasonal cooling performance, the amount of thermal exchange of BHE with 165 mm and 180 mm diameters was found to be 3.2% and 7.1% larger than that of the BHE with 121 mm diameter, respectively. These findings provide helpful suggestions for the design of future GSHP systems to achieve higher energy-efficiency.
Keywords: ground source heat pump system; borehole heat exchanger; drillhole diameter; thermal efficiency
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MDPI and ACS Style
Luo, J.; Rohn, J.; Bayer, M.; Priess, A. Thermal Efficiency Comparison of Borehole Heat Exchangers with Different Drillhole Diameters. Energies 2013, 6, 4187-4206.
Luo J, Rohn J, Bayer M, Priess A. Thermal Efficiency Comparison of Borehole Heat Exchangers with Different Drillhole Diameters. Energies. 2013; 6(8):4187-4206.
Luo, Jin; Rohn, Joachim; Bayer, Manfred; Priess, Anna. 2013. "Thermal Efficiency Comparison of Borehole Heat Exchangers with Different Drillhole Diameters." Energies 6, no. 8: 4187-4206.