Environmental Engineering Reference
In-Depth Information
466
10.2.2
Economic and environmental analysis
Compared to hydro-geothermal heat generation systems, deep well heat supply
systems are almost location-independent as such deep well systems are character-
ised by a closed circuit system (i.e. closed system). Such systems consist of a well
and the pertaining completion, a heat exchanger which usually includes a heat
pump and a fossil fuel-fired peak load plant. Depending on the consumer struc-
ture, an additional heat distribution network may be required. The following para-
graphs contain an economic and environmental assessment of such systems.
Economic analysis.
Within the following explanations we assume a 2,800 m
geothermal deep well with a total thermal capacity (including the fossil fuel-fired
peak load boiler) of 4 MW. Furthermore, a heat demand according to the small
district heating system (DH-II) of approximately 26 TJ/a off consumer or
32.2 TJ/a off plant is assumed (see Chapter 1.3). The geothermal capacity
amounts to approximately 500 kW. The system is equipped with a heat pump to
provide the required inlet temperature to the heating network. The heat pump is
characterised by a coefficient of performance (COP)
of 4 and has an electricity
demand of approximately 600 MWh/a. The share of heat delivered by the heat
pump referring to the overall provided heat amounts to almost 44 % (i.e. ap-
proximately 10.5 TJ/a geothermal heat are integrated within the overall system).
The fossil energy-fuelled peak load plant has a thermal capacity of 6 MW (to en-
sure supply security) and an overall efficiency of 92 %.
Heat is supplied to a new housing estate by a small district heating network
(DH-II) (heating network temperature 70/50 °C, 15 % network losses, 1,800 full
load hours; Chapter 1.3). Two options are analysed: the drilling of a new well
(reference system I) and the use of an existing well (reference system II). How-
ever, one should keep in mind that it is not very likely to find an existing well
useable to be extended as a deep well close to customers. The technical lifetime of
such a plant amounts to approximately 22 years.
Within the following explanations the investment costs, the operation costs and
the heat provision costs are discussed.
Investment costs.
Table 10.3 illustrates the investment costs of the analysed sys-
tems. Besides drilling of a new well the costs are mainly dominated by the com-
pletion of the well (downhole part). Compared to these expenses, the costs for
heat exchanger, heat pump and peak-load plant are relatively low. Additionally,
high costs are caused by the heat distribution network (Table 10.3).
Operation costs.
The operation costs are mainly due to the use of auxiliary energy
(electrical energy for running the pump for the heat carrier circulation, fossil fuel
required for operating the peak load plant (separately indicated in Table 10.3) and
electrical energy required for the heat pump). Further expenses are given by main-
tenance, repairs, and miscellaneous costs. The total annual costs amount to ap-
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