Environmental Engineering Reference
In-Depth Information
Figure 2.20 The different fa¸ade types examined
which corresponds to a low external wind speed. The distance from the inner window
to the outer pane of the double fa¸ade is 0.5m. The following cases were compared
(see Figure 2.20):
Cases W(a) and W(b): Single window fa¸ade, ambient air ventilation. Case W(a)
represents a single fa¸ade consisting of a double-glazed heat protection window
( U
1.5Wm 2 K 1 , g
0.43). In Case W(b), an additional external shading blind
was considered with a shading factor of 90% for the whole year. Ventilation is done
by the ambient air temperature.
Cases F1(a-c): Double fa¸ade, ambient air ventilation. Case F1(a) represents a
double fa¸ade system without shading devices. In F1(b), an additional shading
blind was placed between the panes. The shading factor was also set to 90% for the
whole year. The solar absorption coefficient for the blind was assumed to be 10%
for Case F1(b) and 30% for Case F1(c). Ventilation is also done by the ambient air
temperature.
Cases F2(a-c): Double fa¸ade, double fa¸ade ventilation. Cases F2(a) to F2(c) have
ventilation air coming from the fa¸ade air gap temperature at the outlet opening.
This is symbolized by a tilted internal window.
=
=
The calculated maximum temperature increases in the double fa¸ade range from 3
to 5 K on a hot summer's day with a maximum ambient air temperature of 32 C and
600Wm 2 maximum irradiance (here 2nd September is taken for detailed analysis).
The corresponding volume flow rates are calculated for free convection conditions for
each time step. From the temperature rise and the fa¸ade volume flow, first the total
ventilation gains are calculated, which are produced by the fa¸ade acting like a solar
air collector;
V total ρc ( T outlet T inlet ) /A fa ¸ ade
q vent =
(2.6)
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