Facades and Summer Performance of Buildings - Low Energy Cooling for Sustainable Buildings - page 24

inner layers. They obtained good agreement between the measurements and simulated
results. The results showed that the ventilation heat losses duringwinter can be reduced
significantly through air preheating.
Energetic comparisons of a conventional fa¸ade and a double fa¸ade system were
performed by Oesterle et al . (1998). In their conclusions, the authors stated that the
primary energy consumption of mechanical ventilation could be reduced by up to 25%
by temporarily deactivating the fan and using double fa¸ade air. In these cases of no
or only occasional air-conditioning, double fa¸ades may be economical.
Transient simulations of double fa¸ades were undertaken byHausladen et al . (1998).
Their conclusions showed that the ventilation gains during the winter period reduce the
energy consumption significantly. However, especially in summertime, the problem
of overheating requires an air cooling system in order to maintain thermal comfort.
As a result, the marginal energetic advantage is not justified.
Similar investigations were carried out by Kornadt et al . (1999). The authors com-
pared the physical characteristics of a single fa¸ade with different double fa¸ade sys-
tems. The simulations showed that buildings with double fa¸ades consume up to 40%
less heating energy than those with a single fa¸ade. However, in summer the indoor
temperature in rooms with a double fa¸ade systemwas about 8 K higher. Furthermore,
the double fa¸ade system increases the total annual costs in comparison with a single
fa¸ade by approximately 50%. Finally, the remaining advantage of double fa¸ades is
improved sound protection.
An economic solution for a high-rise office building in a city centre was presented
by Blum (1998). His indoor climate concept demonstrates that natural ventilation in
combination with a ventilated cavity wall and with static heating and cooling may be
an alternative to the conventional air-conditioning system. The main advantanges of
a double fa¸ade system lie, in his opinion, in a controlled, natural air-conditioning
especially for extreme external climatic conditions, sound protection, optimization
of indoor illumination by daylight, reduction of energy consumption and reduction of
yearly maintenance costs by up to 50%. The disadvantages are the slight limitation of
thermal comfort in summer and the high investment costs.
Gerhardt and Rudolph (2000) suggested that window ventilation in double fa¸ades
by users in high-rise buildings especially could be replaced by mechanical devices
that reduce the size of the opening automatically depending on the wind speed.
Detailed investigations performed on a double-glazed fa¸ade by Kautsch et al .
(2002) showed good agreement between the fluid flow measurements and CFD sim-
ulations. Their analysis focused on two extreme flow situations in the space between
the fa¸ade layers: free, solar and wind-induced flow in the undisturbed gap between
the primary and the room-side glass fa¸ade, and complex turbulent flow conditions
at the double glazing surface as well as around the side elements between the fa¸ade
layers. In addition to the fluid flow measurements, the thermal situation within the
building was monitored and compared with TRNSYS simulations. These compar-
isons also show reasonable agreement.