Facades and Summer Performance of Buildings - Low Energy Cooling for Sustainable Buildings - page 31

nodes and through ventilation gains, if the fresh air is supplied by the fa¸ade. The
total energy transmission or g -value of a glazed fa¸ade adds the contributions of
transmission and secondary heat flux and is defined as

q i
G

g = τ + (2.5)

where τ is the short-wave transmission coefficient of the whole fa¸ade system, G
the incident external irradiance and q i the secondary heat flux from the inner glazing
surface to the room. Especially when using shading devices inside the room or in a
fa¸ade gap, secondary heat fluxes are difficult to calculate. Often g -values are only
estimated, which is a real problem for cooling load calculations and consequently the
design of the cooling supply system. The solar simulator test rig at the University of
Applied Sciences in Stuttgart provides the possibility of experimentally determining
the overall energy transmission coefficient of fa¸ade systems up to 2.6m in height.

Experimental Set-up

The simulator contains 15 Hg lamps of 1000W electrical power each in a planar
arrangement (see Figure 2.2). For special applications, the lamp field of the solar
simulator can be rotated from a horizontal to a vertical position. To avoid a temperature
increase in the room, each of the five lamp fields is mechanically ventilated and the
heat discharged to ambient air. A ventilated air curtain between the light source and
the test fa¸ade prevents long-wave heat exchange between the hot cover glass of the
lamps and the outer fa¸ade surface. The temperature of the air curtain can be adapted
to the surrounding temperature.

Figure 2.2 Photo of the test fa¸ade and solar simulator