Page 82 - Analysis and Design of Energy Geostructures

52 Analysis and Design of Energy Geostructures

Figure 2.18 Monthly extracted and injected energy as well as inflow and outflow temperature
associated with the energy extraction and injection for the energy pile system at Zürich Airport.
Redrawn after Pahud, D., Hubbuch, M., 2007a. Measured thermal performances of the energy pile
system of the dock midfield at Zürich Airport. In: Proceedings of European Geothermal Congress.
Bundesverband Geothermie.

system, from October 2005 to September 2006. According to Pahud and Hubbuch
(2007a), the injected energy corresponds to the geocooling production of 620 MWh.
This production represents 41% of the 1500 MWh extracted by the Ground Source
Heat Pump System. The measured maximum and average thermal powers extracted
from the energy piles are of 272 and 245 W/m, respectively. The annual heating
energy extracted from the energy piles is 2183 kWh/m. The measured maximum
and average thermal powers injected in the energy piles are 33 and 16 W/m, respec-
tively. The annual cooling energy injected in the energy piles is 74 kWh/m. The
overall system efficiency, that is the ratio between the thermal energy delivered by the
system (for heating and cooling) and the total electric energy required to run it (all the
circulation pumps, the heat pump and the reversed heat pump), was estimated to be
5.1 (Pahud and Hubbuch, 2007a). This efficiency could be improved to 5.7 by lower-
ing the delivered cooling energy in the cooling distribution (thus using geocooling
only) and the electric consumption of the pump (Pahud and Hubbuch, 2007a).
In this project the design values were close to the measured ones (Pahud and
Hubbuch, 2007a). This fact, in conjunction with the success of the energy pile