Facades and Summer Performance of Buildings - Low Energy Cooling for Sustainable Buildings - page 34

In a second experiment, an external shading blind was used which reduces the
incoming radiation to 17% (aluminium lamella, 80mm, ρ = 0 . 76, colour RAL 9010).

With an overall optical transmission of 9% (considering the blind as well as the thermal
protection glazing) and a calculated secondary heat flux of 30Wm − 2 , the calculated
g -value is 13% and thus close to the measured value of 15%.
Compared with the unshaded heat-protecting glazing the internal surface temper-
ature is now 6 K lower at 21.3 ◦ C. The experiment was done under the following
boundary conditions: external irradiance: 535Wm − 2 ; external heat transfer coefficient
25Wm − 2 K − 1 ; internal heat transfer coefficient: 10Wm − 2 K − 1 , room air temperature
21.9 ◦ C; cooling box temperature 19.9 ◦ C.
Several repetitions of the measurements showed that the calorimetric method
achieves an accuracy of 6%.

Double Fa¸ade Energy Transmittance

5 . 8Wm − 2 K − 1 )was
placed in front of the shading blind corresponding to a double-glazed fa¸ade ventilated
by natural convection.
The calculated overall transmission was 0.06, and the comparison between mea-
sured and calculated g -values showed similar results (measured: 0.10; calculated:
0.09). The boundary conditions were as follows: external irradiance 590Wm − 2 ;
external heat transfer coefficient 25Wm − 2 K − 1 ; internal heat transfer coefficient
10Wm − 2 K − 1 ; room air temperature 21.3 ◦ C; cooling box temperature 20.5 ◦ C. The
measured temperatures agree well with the calculated results (see Figure 2.6). In this
case of buoyancy-driven flow, the Nusselt correlation as well as the Reynolds number
are as in Olsson's work (Olsson, 2004). Table 2.2 summarizes the measurement results

Finally, an additional single 6mm pane ( τ = 0 . 8, g = 0 . 83, U =

Figure 2.6 Temperature levels in a double fa¸ade with natural convection and a shading element
between the double glazing