Page 79 - Analysis and Design of Energy Geostructures

Energy geostructures 49

are cast in place. They are characterised by an average length of 26.5 m and a diameter
varying between 0.9 and 1.5 m. Their total length is 8300 m (Pahud and Hubbuch,
2007b). The piles can be characterised as predominantly end-bearing piles because
they rest on a moraine layer.
The energy design process of the energy piles began early in the project: it was
iterative and went hand in hand with the structural design of piles, which changed in
number and sizes with the increasing accuracy and availability of the data typical of
the later phase of a project. The energy piles were monitored over 2 years of opera-
tion (2004 06). The main project contractor was also the direct user and responsible
for system maintenance.
The energy pile system was designed to contribute to both the heating and cooling
supply throughout three successive design stages. In the final stage the heating energy
consumption of the building was estimated to be 2720 MWh/year (Pahud and
Hubbuch, 2007a). A ground source heat pump system was designed to deliver
630 kW (Pahud et al., 1999) and to cover 2312 MWh/year (85%) of the heating
energy consumption (Pahud and Hubbuch, 2007a). The remaining portion of approx-
imately 408 MWh/year (15%) was intended to be supplied by district heating (Pahud
and Hubbuch, 2007a). The cooling energy consumption of the building was estimated
to be of 1240 MWh/year (Pahud et al., 1999). A cooling distribution network was
designed to deliver 690 MWh/year (56%) through the ground source heat pump sys-
tem when the cooling needs might have been simultaneous to the heating needs,
470 MWh/year (38%) by geocooling (i.e. free cooling without heat pump) and
80 MWh/year (6%) by the heat pump used as a cooling machine (i.e. reversed heat
pump) (Pahud et al., 1999).
Ventilation of the building was intended to be achieved with conventional cooling
machines, which supply 510 MWh/year (Pahud and Hubbuch, 2007a). The heat
pump was designed to prevent the fluid temperature dropping under 0 C or exceed-

ing 40 C 45 C(Pahud and Hubbuch, 2007a). The overall system operation mode
was controlled by valves and was monitored by the building automation system every
5 minutes.
Fig. 2.15 presents the monthly energy of the ground source heat pump system,
from October 2005 to September 2006 (Pahud and Hubbuch, 2007a). According to
Pahud and Hubbuch (2007a), the annual heating energy was measured to be
3020 MWh. The heating energy delivered by the ground source heat pump system
was measured to be 2210 MWh (73%) and the district heating contribution was
810 MWh (27%). The annual coefficient of performance of the heat pump was esti-
mated to be 3.9, including the electrical energy for the circulation pumps.
Fig. 2.16 presents the monthly energy of the cooling distribution networks, from
October 2005 to September 2006 (Pahud and Hubbuch, 2007a). According to Pahud
and Hubbuch (2007a), the annual cooling energy was measured to be 1170 MWh.