Page 83 - Analysis and Design of Energy Geostructures

Energy geostructures 53

Table 2.1 Economic comparison between the energy pile system with a conventional system
(Pahud and Hubbuch, 2007a).
Heating/cooling system Energy piles Conventional Difference

Investment 670,000 h 80,000 h 590,000 h
Annual cost Capital 46,170 h 5450 h 140,720 h
Maintenance 10,070 h 3170 h 16900 h
Energy 71,660 h 156,180 h 284,520 h
Total annual cost 127,900 h 164,800 h 236,900 h
Thermal energy cost 0.04 h/kWh 0.05 h/kWh

installation, highlights the need for detailed considerations regarding the application of
energy geostructures from the early stages of the design process.
Table 2.1 shows an economic analysis of the considered energy pile system, with
respect to other conventional heating/cooling systems. The analysis shows that the
energy pile system is economically more convenient than a conventional heating/
cooling system. The cost of the investment is paid back in 8 years without taking into
account interest (Pahud and Hubbuch, 2007a).

2.6.4 The Stuttgart-Fasanenhof and the Jenbach energy tunnels
The Stuttgart-Fasanenhof tunnel in Germany and the Jenbach tunnel in Austria are
among the first energy tunnels constructed around the world (cf. Fig. 2.19).
The Stuttgart-Fasanenhof tunnel is a suburban, double-tracked, 380-m-long metro
tunnel, with a 20-m-long thermoactive section (Buhmann et al., 2016). This section
was installed inside the tunnel in 2011. The tunnel ceiling is situated approximately
10 m below the surface throughout its length and is surrounded by marlstone and
mudstone (Buhmann et al., 2016). The tunnel contains two detached thermoactive
sections and is directly connected to a station where a heat pump, an electrical heater,
a heat exchanger for cooling purposes and a main pump for the circulation of heat
exchanger fluid are located and were employed over a 4-year period from 2011 to
2015 (this tunnel operated purely as a test plant) (Berga et al., 2017).
The Jenbach tunnel (which is a part of the Brenner Base tunnel) is a double-
tracked, 3740-m-long railway tunnel, with a 54-m-long thermoactive section (Frodl
et al., 2010). This section was installed inside the tunnel in 2008. The tunnel overbur-
den depth is approximately 27 m and is surrounded by gravel (Franzius and Pralle,
2011). This section supplies the Jenbach municipal town council building heating
needs (this tunnel is in real operation). The tunnel owner is responsible for the main-
tenance of the absorber and pipe system inside the main tunnel while the town coun-
cil is responsible for the whole heat pump system.