Facades and Summer Performance of Buildings - Low Energy Cooling for Sustainable Buildings - page 32

Air-conditioned room

|-------- Test façade -------- |

outer
pane

shading
blind

double
window

Ventilated
air curtain

Cooling box

Solar
simulator

Incoming
radiation G int

External
radiation
G ext

Secondary
heat
emission

q cool = G int + q i

Fan

Heat
exchanger

Figure 2.3 Schematic representation of experimental set-up

In the cooling box, the transmitted energy is exactly compensated by the cooling
power transferred via a heat exchanger so that the box temperature stays constant (see
Figure 2.3). Consequently, the required cooling energy corresponds to the transmitted
radiation plus the secondary heat flux from the inner pane. To avoid transmission heat
loss through the well-insulated box walls, the temperature of the ambient room is as
close as possible to the temperature level within the test chamber. In order to reach
convective heat transfer coefficients that correspond closely to the standard values
given in the German standard DIN 4108-4 (2002) (outside 25Wm − 2 K − 1 , inside
7.7Wm − 2 K − 1 ), ventilators generate a controlled flow on both sides of the fa¸ade. The
set-up is based on a calorimetric reference method developed by a German research
consortium (Sack et al ., 2001).
The dimensions of the test fa¸ade are 2.6m 0.7m. In the case of a double fa¸ade

system, the distance from the inner layer to the outer panemay be varied by up to 0.8m.
Surface temperatures are determined by thermocouples as well as PT100 sensors.
All sensors were shielded from direct irradiance. All air temperatures are integrated
over 3m long Ni1000 sensors. The external irradiance is averaged from pyranometer
measurements at 65 locations over the whole fa¸ade area. The maximum deviation
from the mean value is 14% (see Figure 2.4). The system needs approximately 5 hours
to reach steady-state thermal conditions.

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