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Influence of groundwater flow on borehole heat exchangers

The effect of groundwater flow is not taken into account in the design of Underground Thermal Energy Storage (UTES) with borehole heat exchangers. If a borehole heat exchanger crosses an aquifer with a groundwater flow, the expected impact of this flow on the heat exchange process is large. This is because the exchange process changes from a purely conductive to a combined conductive-advective transport, the latter being a lot faster. To investigate the influence of the advective transport due to groundwater flow in a quantitative way, a research project is funded by the Flemish Government, Department of Environment, Nature and Energy, in cooperation with the Belgian Scientific and Technical Centre for the Construction Sector (WTCB) and the Leibniz Institute for Applied Geophysics (LIAG) from Germany. The WTCB is responsible for the measurement of the temperature profile in depth with an optical fibre, to be able to conduct a “Distributed thermal response test”. The LIAG-institute will conduct a Nuclear Magnetic Resonance (NMR) logging in a piezometer tube, to measure the porosity distribution in depth, an essential parameter for advective transport. The research project is divided in two phases: first a controlled experiment will be conducted on one, newly drilled borehole heat exchanger, subjected to a groundwater flow induced by a pumping well at short distance. Second, an existing borehole heat exchanger field will be investigated, which is known to be influenced by a groundwater flow.

Borehole logging before installation of piezometer well tubes:

Installation of the borehole heat exchanger together with the optical fibre: