Environmental Engineering Reference
In-Depth Information
Figure 18.6.1 System structure of a transparently insulated wall.
such that the maximum values of the solar-induced heat flow reach the inside when
the direct solar gains through the windows have already decreased and outside tem-
peratures are falling. In addition, the thermal characteristics of the entire building play
a role; however, above all it is the heat-storing capability of the interior structural
elements that aids in the avoidance of overheating.
For example, an external wall even with 10 cm external insulation under German
climatic conditions will still exhibit annual heat losses of over 30 kWh per square metre.
However, with the application of transparent thermal insulation, this same wall acts
as a solar collector during the heating season and produces around 50-100 kWh m 2
of useful heat for the building.
The heat transfer coefficient of an external wall insulated with transparent insula-
tion results from the total of the thermal resistances of the existing external wall and
the transparent insulation, with layer thickness s TTI and heat conductivity λ TTI of the
transparent insulating material, layer thickness s wall and heat conductivity λ wall of the
external wall and also the heat transfer coefficients inside h i and outside h o .
G
U eff
=
U wall TTI
η 0
(18.6.1)
T i
T o
The wall absorber (see Figure 18.6.1) is characterized by the absorption coefficient
α and the transparent insulation by the diffuse total energy transmission factor g d .
The U-values of 10 cm TTI are typically about 0.8 W m 2 K 1 , which are lower
than the best double-glazed heat-protection glass, but still twice as high as the heat
 
Search WWH ::




Custom Search