Passive Cooling Strategies - Low Energy Cooling for Sustainable Buildings - page 75

The results indicate that two air exchanges per hour are simply not sufficient to
remove the daily internal loads, despite reasonably cool night temperatures of 20 ◦ C
or lower. Detailed measurements of one section of the building (one of eight exhaust
air fans with a volume flow of 5250 m 3 h − 1 ), carried out by the University of Applied
Sciences in Offenburg, showed that average nightly COPs varied between 5 and 10.

Mechanical Ventilation in the eb ok Building

The ebok building in Tubingen uses active ventilation for supply and exhaust air.
During the night a volume flow of up to 4000 m 3 h − 1 of ambient air is injected into the
building for cooling purposes, which corresponds to two air exchanges per hour as in
the SIC building. As can be seen in Figure 3.15, the cooling loads of the day cannot
be fully removed during night-times, resulting in room temperatures above 26 ◦ Cin
the morning hours of the second week. This means a drop of only 2-3 K compared
with the preceding evening.
A maximum of 147Wh m − 2 per night of internal loads is removed during the eval-
uated time (last two weeks of June 2005) while the average is about 85Wh m − 2 per
night. The peak cooling power is nearly 14 kWwith an average of 7 . 4 kW. Mechanical
night ventilation obviously requires electrical power for the fans, which is significant
even if highly efficient fans are used. In the ebok building, the mean COP for night ven-
tilation during the two-week measurement campaign in 2005 was 4.0, with maximum
values of 6.0 (see Figure 3.16). The design power of the fans for summer ventilation
was 300W for a total daily volume flow of 2000 m 3 h − 1 and 1100W for night venti-
lation with 4000 m 3 h − 1 total flow rate. Measurements of the installed system showed
that at 2066m 3 h − 1 supply air flow and pressure drops of 123 Pa in the supply and
84 Pa in the exhaust channel, the power consumption was 200W for the supply fan

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Ambient air temperature
Room air temperature

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June July

Figure 3.15 Ambient air and room temperatures in the ebok building during summer 2005