Environmental Engineering Reference
In-Depth Information
purposes a pilot drilling has to be carried out that can potentially be used as a well
later.
Heating system
Kompressor
Extraction
Injection
Motor
well
well
Wasser/Wasser-+
Heat pump
Expansionsventil
Clay barrage
Undisturbed groundwater level
Affected groundwater level
Extraction tube
Immersed pump
Filtering gravel layer
Filtering tube
Fig. 9.12
Elementary diagram of a groundwater-heat pump installation (see /9-10/)
Sump tube
One particular problem is the sedimentation of iron ochre in the injection wells.
It occurs very often in oxygen-free groundwater with a low redox potential. Such
groundwater should not get in contact with ambient air. Therefore the entire sys-
tem needs to be closed and be kept under excess pressure all the time, otherwise
water treatment by deferrisation and de-manganesing would be required. Lime
precipitation, however, does not play a role at temperature fluctuations of a maxi-
mum of ± 6 K.
Under certain conditions groundwater heat pumps are possible that exclusively
consist of one or several production wells. Such concepts rule potential problems
with injection wells out. Technically, this requires that the aquifer has enough
newly produced groundwater and that the water can be channelled appropriately
or sunk again. In Germany, such systems are generally not authorised.
Other systems.
Other systems are the utilisation of groundwater with a coaxial
well, the utilisation of pit and/or tunnel water and air preheating or cooling in
near-surface soil.
Coaxial wells.
Coaxial wells ("Standing Column Wells") /9-11/ are positioned be-
tween ground probes and groundwater wells. An ascending tube with a filter at
the bottom end and surrounded by a stack of gravel is built into a borehole. To-
wards the rock, the stack of gravel can be separated with a plastic liner. Water is
pumped from the ascending tube with a submersible pump - in a similar way as in
a groundwater well. It is then cooled down in a heat pump (or heated up) and then
seeps out again through the stack of gravel in the ring section. During the sinking
process the water absorbs heat from the surrounding subsoil or discharges heat
into the subsoil.
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