Environmental Engineering Reference
In-Depth Information
ing network is considerably lower than the temperature at the well head, a direct
heat exchanger can optionally be installed in front of the heat pump. Fig. 10.11
illustrates the example of deep well incorporation into a heat supply system.
Exhaust gas
District
heating
system
Heat
pump
Deep
well
Heat pump drive
Fig. 10.11
Incorporation of a geothermal deep well into a heat supply system
The influence of the operating principle on the geothermal capacity mainly de-
pends on the temperature of the heat transfer medium fed into the deep well. The
capacity can therefore be influenced by the aboveground system components inte-
grated within the overall energy provision system as well as by the operating
mode. In times of high heat demand, this allows for an operating modus ensuring
a high share of geothermal energy within the overall heat provided to the cus-
tomer. But very low temperatures of the heat carrier result in an increased tem-
perature gradient within the casing wall and thus within the rocks surrounding the
well in general. Continuous operation under such operating conditions leads to a
considerable reduction in temperature of the surrounding rocks, which may result
in permanently decreased system capacities. Operating mode should thus strive
for a maximum output by keeping the impacts on the underground at a tolerable
level in order to ensure maximum service life (i.e. sustainable operation of the
well).
Since geothermal deep wells are very capital-intensive within heat supply sys-
tems, they should only be designed to cover the base load. In wintertime, peak
load is provided by a conventional fossil fuel-fired boiler permitting also to fur-
ther increase the heating temperature (Fig. 10.11). From an economic viewpoint,
geothermal deep wells should be used at locations where a sufficient heat demand
is given (e.g. small district heating network, large scale individual consumers,
commercial enterprises, local authorities) /10-9/, /10-10/.
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