Environmental Engineering Reference
In-Depth Information
fluid production and injection of 80 to 200 kW with a high amount of full load
hours. The additionally produced heat can be integrated within the overall system.
In general, a peak load and back-up boiler fired with fossil fuel energy (e.g.
light heating oil, natural gas) completes the entire heating system. Therefore the
boiler is designed according to the maximum heat load of the overall system.
Geothermal heating stations are designed according to site-specific require-
ments. Due to the multitude of existing impacting factors (such as the characteris-
tics of the geological resources, the geothermal fluid characteristics, the demand
and the consumer behaviour, the (existing) heating network parameters, regionally
influenced prices of fossil or renewable energy carriers, the organisational struc-
ture of the plant operator) general statements can only serve as reference values.
10.1.2
Economic and environmental analysis
The following sections provide an economic and environmental analysis for a
selection of hydro-geothermal heating plants.
Economic analysis.
For all analysed geothermal heating stations geothermal fluid
is produced through one well and, after cooling, is pressed into the reservoir
through another well (Fig. 10.1). The water used within the district heating system
is directly heated up with heat exchangers. The heat can be increased to the de-
sired temperature by means of heat pumps, if required by the reservoir characteris-
tics or to satisfy consumers. The required electricity can be provided by natural
gas-fired or light fuel oil fired CHP stations. The heat produced together with
electricity is additionally fed into the district heating system.
In order to compensate for demand peaks or setbacks, heat insulated water
tanks acting as energy storage are frequently integrated into the overall system. To
cover peak demands or in case of malfunctions, geothermal heating plants are
commonly equipped with a peak-load heating station based on light fuel oil or
natural gas.
Geothermal heating plants for the provision of space heating or domestic hot
water can only cost-effectively be realised and operated with a thermal capacity of
5 MW and more. Out of the demand cases defined in Chapter 1, only the district
heating systems II (DH-II) and III (DH-III) are appropriate for geothermal heat
generation. However, the defined demand cases (i.e. three single family houses
(SFH-I, -II, and -III) and the multiple families home (MFH)) have been consid-
ered for supply by the two district heating systems.
Heat distribution is ensured by a heating network of an average flow tempera-
ture of 70 °C and a return flow temperature of 50 °C. The district heating systems
are designed as plastic-sheathed tubes with a steel medium tube and an indirect
grid connection of the consumer. The latter are additionally equipped with an
intermediate storage for domestic hot water (80 % utilisation ratio).
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