3359
Geothermal Heat PipeBorehole Heat-Exchangers: Computational Simulation and
Analysis of Measurement Data
Échangeurs thermiques à thermosiphon utilisés en géothermie : simulation numérique et analyse
des mesures
Katzenbach R., Clauss F.
Technische Universität Darmstadt, Institute and Laboratory of Geotechnics, Germany
ABSTRACT: Shallow Geothermal Energy is a very promising alternative to fossil fuels, especially in the Residential and Commercial
sectors, both including the heating and cooling of buildings. Among the available technologies in Shallow Geothermics, the
Geothermal Borehole Heat-Exchanger equipped with a Heat Pipe is a particularly efficient optimization in comparison to
conventional borehole heat-exchanger systems for two main reasons: Due to the gravity and buoyancy driven energy transport in the
borehole heat-exchanger there is no need for a circulation pump. Hence, the consumption of by-energy is significantly reduced.
Furthermore, the temperature distribution within the borehole heat-exchanger is advancing a high energy withdrawal rate much more
than conventional systems. A method has been developed to estimate the heat transport of a Geothermal Heat Pipe Borehole Heat-
Exchanger as computational simulations are used to determine the expected energy withdrawal rate. Furthermore, long-term
measurement data have beencollected from a Geothermal Heat Pipe Borehole Heat-Exchanger installation. The analysis of
measurement data allows proving the functionality.
RÉSUMÉ : L’énergie géothermique de surface comme alternative aux énergies fossiles est une source d’énergie prometteuse, en
particulier dans les secteurs résidentiels et commerciaux incluant le chauffage et la climatisation des bâtiments. Parmi les technologies
disponibles, les sondes géothermiques équipées d’un thermosiphon (conduite de chaleur) sont une solution particulièrement efficiente
en comparaison des traditionnelles sondes géothermiques pour deux raisons principales. Il n’est d’abord pas nécessaire de disposer
d’une pompe de circulation, à cause de la gravité et du transport d´énergie par la flottabilité dans la sonde, diminuant ainsi l’énergie
d’alimentation. Ensuite, la distribution de température dans la sonde géothermique montre une consommation d’énergie moins
importante que pour les systèmes conventionnels. Une méthode a été développée afin d’estimer le transport de chaleur assuré par un
échangeur thermique sur le principe du thermosiphon utilisé en géothermie et des simulations numériques ont été effectuées afin de
déterminer la consommation énergétique du système. Les données ont été collectées à long terme sur une installation utilisant une
sonde géothermique à thermosiphon. L’analyse des données collectées permet de montrer la fonctionnalité de ce type d’installations.
KEYWORDS: shallow geothermal energy, heat pipe, thermosiphon.
1 INTRODUCTION
Geothermal Energy is a very promising alternative to fossile
fuels, especially in the residential and commercial sectors, both
including the heating and cooling of buildings: Almost 50% of
the overall final energy consumption are being unsed for the
tempering of buildings. As using the so-called “Shallow
Geothermal Energy” – the thermal use of soil and groundwater
in the uppermost spoil region for low-temperature applications –
is almost everywhere applicable, decentral and in perfect
conjunction with electirc power from other renewable sources,
various applications scenarios in differenct climate regions,
operational modes and building types in new construction and
the existing building stock allow a wide range and large number
of applications. Among the available technologies in Shallow
Geothermics, the conventional geothermal borehole heat-
exchanger, usually consisting of a double-u loop to circulate the
energy carrying medium is most common. In order to optimize
the overall energy performance of the heat exchanger and
thereby of the entire geothermal facility a heat pipe is being
used as main energy transport element of the borehole heat
exchanger.
A heat pipe is a particularly efficient technology in
comparison to conventional borehole heat-exchanger systems
for two main reasons:
Figure 1: Heat Pipe: Working Cycle
Due to the gravity and buoyancy driven energy transport in
the borehole heat-exchanger a high density of energy transport
can be archived even without using a circulation pump.
Accordingly, the consumption of by-energy is being
significantly reduced.
