Borehole resistance and vertical temperature profiles in coaxial borehole heat exchangers
2013 (English)In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 102, 665-675 p.Article in journal (Refereed) Published
Ground source heat pump systems are often coupled to the ground by circulating a fluid through vertical Borehole Heat Exchangers (BHEs). The design of a system requires estimates of the ground thermal conductivity and the borehole thermal resistance, which are usually determined by an in situ thermal response test on a completed borehole. The usual test interpretation methods average the inlet and outlet fluid temperatures and use this mean temperature as the average temperature along the borehole length. This assumption is convenient but does not strictly apply. For a coaxial heat exchanger this paper develops an analytical model for the vertical temperature profiles, which can be used instead of the mean temperature approximation to estimate borehole resistance. The model is verified with measured temperatures on a BHE, where an optical technique allows continuous measurements along a coaxial borehole during a distributed thermal response test. A sensitivity study shows that the proposed method corrects errors in the mean temperature approximation, which overestimates the borehole resistance in a coaxial borehole.
Place, publisher, year, edition, pages
2013. Vol. 102, 665-675 p.
Borehole heat transfer, Borehole temperature profiles, Borehole thermal resistance, Ground heat exchanger, Ground-source heat pump, Thermal response test
IdentifiersURN: urn:nbn:se:kth:diva-117833DOI: 10.1016/j.apenergy.2012.08.007ISI: 000314190800072ScopusID: 2-s2.0-84870734806OAI: oai:DiVA.org:kth-117833DiVA: diva2:603232
QC 201302052013-02-052013-02-052013-03-11Bibliographically approved