Geothermal Cooling - Low Energy Cooling for Sustainable Buildings - page 96

OU EX

FC

Seminar room

AM SU FC

Foyer

Earth
heat
exchanger

Figure 4.13 Systemdrawing of horizontal heat exchanger coupled to themechanical ventilation system
(AM = ambient air; SU = supply air; EX = exhaust air; OU = outlet air)

157m 2 activated concrete floor are conditioned by geothermal energy. Five vertical
borehole heat exchangers of 80 m each supply cooling and heating energy with an
air-based distribution system for the seminar room. The fan is designed for a volume
flow of about 5100 m 3 h − 1 . The geothermal cooling system as the cooling supply
for the ventilation system is only operated when needed, say if a lecture or seminar
takes place. If ventilation air cooling is not required, cooling energy is delivered to
the floor cooling system in the lobby (see Figure 4.13). This combination has proven
to be crucial for achieving reasonably long operating hours and thus an economical
performance of the system. Only 233 hours for fresh air cooling was counted for the
seminar room in 2005 compared with 2289 hours for the floor activation and 856 hours
for winter air preheating.
Ventilation systems are often responsible for high electricity consumption. A close
analysis of the operating hours showed that manual switching of the ventilation system
by the users was not effective, as the system was often left on during the night (see
Figure 4.14).
In the present system the ventilation system can operate at two levels with a power
consumption of 1 . 36 kW for the first level and 2 . 7 kW for the second level. In the first
three months of 2005, a total electricity consumption of 1985 kWh was measured. If
the ventilation system had been switched off during the night, savings up to 42% could
have been achieved (see Table 4.1).
In 2006, the ventilation system was still on several times during the night, which
was necessary to maintain the room setpoint temperature at 17 ◦ C. The main problem