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logo LGM logo LGM GEOTH logo LGM geothermal Shallow geothermy

Bertrand François

Selçuk Erol

Collaboration Robert Charlier (ULg)

Frédéric Nguyen (ULg)

Vincent Ficquet (OREX)

Vincent Lejeune (Geolys)

Vincent Lemort (ULg)

Stephanie Staquet (ULB)

Noel Huybrechts (CSTC)

Christian Trêve (CFE)

With increasing worldwide energy consumption, improvement and assessment of renewable energy sources is significant nowadays. Geothermal energy, one of the renewable energy sources, is the form of energy stored as heat in the underground, and within a range of 0-400m depth stored heat is categorized as shallow geothermal energy. Beside some traditional applications (e.g. bathing and recreation), this energy can be used for instance in space heating and cooling, and commonly this type of utilization is referred to as direct use.

One of the most common used ground source heat pump (GSHP) technologies, closed-loop systems, comprise a vertical (or horizontal) borehole heat exchanger (BHE) installed inside a borehole and a heat pump that circulates a solution of water or anti-freeze mixture through the buried pipes. Thus, the stored heat in the subsurface is transferred across the pipes. The total of the length of the BHE is based on the required amount of energy and the type of underground.


geothermal modeling

Figure 1. Scheme of a vertical double-U-pipe BHE.


Due to the complexity of the thermal fluxes, groundwater and subsurface conditions, analytical methods are mostly not sufficient to describe and analyze the operation of GSHP systems. In the objective of maximizing the thermal transfer between the pipes and the ground, the geometry of the borehole heat exchanger and the properties of the grouting material must be optimized.

To evaluate and optimize the performance of the geothermal system, the global problem is decomposed into two sub-problems: the near-field behaviour (at the level of the borehole heat exchanger) and the far-field behaviour (in the surrounding ground). Each problem is addressed from the double point of view of experimental developments and numerical analysis:

- Near field response: Laboratory tests aims at characterizing the thermal properties of the grout and the pipe geometry, and the responses within the wells, while a detailed analysis of these results is performed through finite element numerical modeling.

- Far field response: In the coming months, a full-scale in-situ borehole heat exchange will be fully instrumented by temperature, stress and pore pressure sensors, in the main borehole but also in two additional measuring borehole in the vicinity of the heat exchanger. The obtained results will be then analysed through numerical simulations in order to evaluate the performance of the system.

  • This study is funded by the Walloon Region through the ERABLE project (GeoTherWal project) with a collaborative work between four partners: Université de Liège (Prof. R. Charlier, Prof. F. Nguyen), Université Libre de Bruxelles (Prof. B. François), OREX (Ir. V. Ficquet), Geolys (Ir. V. Lejeune).