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New Developments in near-surface geothermal energy systems
Nouveaux Développements dans les systèmes géothermiques proches à la surface
Ziegler M., Kürten S.
Geotechnical Engineering, RWTH Aachen University
ABSTRACT: The geothermal utilization of the ground is a future oriented and environmental option to gain heat. In most cases
borehole heat exchangers (BHE) are used. However, in the last years several researches which focussed on the development of new
technologies are carried out. The Chair of Geotechnical Engineering (RWTH Aachen University) investigated new applications for
the near-surface geothermal energy sector. In this regard, the geothermal utilization of smouldering mining dumps as well as the
development of thermo-active seal panels are two main research topics. For both systems the description of the heat transfer between
the geothermal system and the ground are important for an effective plant design. Mostly, the existing calculation models are based on
the formulation of thermal resistances. For symmetric systems (such as a BHE) several approaches exist. However, these approaches
cannot be transferred to plane structures directly. Therefore, a new model for plane structures is presented in this paper.
RÉSUMÉ : L’utilisation géothermique du sol est une option environnementale et orientée vers le futur pour obtenir de la chaleur.
Dans la plupart des cas on utilise des sondes géothermiques; cependant, dans ces dernières années, plusieurs recherches orientées vers
le développement de nouvelles technologies ont été réalisées. Le Département de l’Ingénierie Géotechnique (RWTH Aachen
University) a fait des recherches sur des nouvelles applications pour le secteur de l’énergie géothermique proche à la surface. À cet
égard, l’utilisation géothermique de terril couvant, ainsi que le développement de panneaux thermoactifs scellés sont deux des
principaux thèmes de recherche. Pour tous deux systèmes, la description du transfert de la chaleur entre le système géothermique et le
sol est importante pour une conception effective de l’équipement. La plupart des modèles de calcul existants sont basés dans la
formulation de résistances thermiques. Pour des systèmes symétriques (comme un BHE) il y a de nombreuses approches. Pourtant,
ces approches ne peuvent pas être transférées directement à des composants de grande étendue. Un nouveau modèle pour des
composants de grande étendue est présenté dans cet exposé.
KEYWORDS: Geothermal Energy, Heat Transfer, Earth-Coupled Structures, Thermal Resistance, Numerical Simulation.
1 INTRODUCTION
The use of geothermal energy has been increased over the past
years in Europe. Mostly, borehole heat exchangers (BHE) or
horizontal ground heat exchangers (horizontal loops) are
installed in the ground to gain heat. In some cases existing
earth-coupled structures are thermally activated, e.g. piles,
diaphragm walls or ground slabs (e.g. Brandl 2006). New
developments focus on the thermal utilization of underground
structures especially tunnels (e.g. Pralle et al. 2009, Adam and
Markiewicz 2009). The main advantage of these systems are the
low installations costs comparing to common geothermal
systems due to the combination of structural and geothermal
elements.
At the chair of Geotechnical Engineering at RWTH Aachen
University new applications for the geothermal use of the
ground are investigated. The geothermal utilization of
smouldering mining dumps as well as the development and
testing of new thermo-active seal panels are two main fields of
research. For both systems an integrated approach has been
carried out to enlarge the efficiency of respective systems.
In this paper the two research topics will be introduced.
Furthermore, suitable models for the description of the heat
transfer between the geothermal system and the ground will be
shown for each topic.
2 GEOTHERMAL UTILIZATION OF SMOULDERING
MINING DUMPS
Mining dumps are a common occurrence in coal-mining areas.
Less well known is the fact that in many old dumps
smouldering fires exist. Due to a poor processing technique in
the past the amount of residual coal is high. In conjunction with
a low compaction spontaneous combustion occurs.
N
Field 3
T = 221°C
max
HS 1
HS 2
HS 3
HS 5
HS 6
Field 2
T = 426°C
max
Field 1
T = 74°C
max
TP 3
TP 5
TP 4
TP 2
TP 1
HS
Hot Spot
Temperature Gauge
(existing)
Test Pit
Heat Exchanger Field
Figure 1. Schematic view of the smouldering mining dump
