Environmental Engineering Reference
In-Depth Information
problems. Glass capillaries are much more temperature- and UV-resistant but also
mechanically not very stable. The recycling ability of glass, which is also possible with
PMMA, is advantageous. On the other hand, polycarbonates are recyclable only with
high energy expenditure and with quality losses.
For glazing systems with smaller thicknesses of 2-3 cm, aerogels are suitable.
Aerogels are highly porous, open-pored solids made of silica gel that consist of
more than 90% air and 10% silicate and exhibit a very low heat conductivity
( λ
0.02 W m 1 K 1 ). Aerogels can easily be poured into the cavity of double-glazing,
are not inflammable, and are easy to dispose of and recycle. Significant disadvantages
include a light transmission only about half that of capillary materials and a sensitiv-
ity to water. Aerogel material absorbs water that penetrates into the edge network of
double-glazing and the sensitive structure is broken down by capillary forces.
Transparent heat-insulating systems are mainly used in two types of construction:
mullion-transom or element construction with framed TTI panel elements. To avoid
dirtying of the TTI materials, the external covers usually consist of highly transparent,
iron-poor single glass panes. Element constructions are characterized by a higher degree
of prefabrication, which has a potential for cost-reduction. From the outside, it is
often impossible to distinguish between element and a mullion-transom construction
installation.
Shading mechanisms such as blinds or shutters are preferably inserted between the
outside windowpane and the TTI material. Lamella type systems can also be used in
front of the façade and are highly reliable when movements between open and closed
positions are minimal or when maintained in a lowered position.
Heat-insulating compound system construction with frameless direct installation.
The transparently plastered capillary structures are supplied with a fabric for attaching
the plaster to the conventional insulation and fastened to the external wall with a black
adhesive that serves as an absorber.
=
18.8 HEAT STORAGE BY INTERIOR BUILDING ELEMENTS
The heat storage capacity of the interior components is decisive for the degree of
useful energy produced by both passive solar use via windows and transparent heat-
insulating systems. Heating demand can only be reduced if solar gains do not lead
to overheating of the interior. The heat storage capacity of interior components can
be roughly estimated from the storage mass, the thermal capacity and the possible
rise in temperature of the storage mass. Thus, for example, a solid concrete wall
with a thickness d of 30 cm, a heat capacity c of 1kJkg 1 K 1 and a gross density ρ
of 2100 kg m 3 can store, with a rise in temperature of 5 C, 0.875 kWh of heat per
square metre of surface.
Q
A =
2100 kg
kJ
kgK ×
3150 kJ
m 2
0 . 875 kWh
m 2
(18.8.1)
ρdcT
=
m 3 ×
0 . 3m
×
1 . 0
5K
=
=
This approach assumes that the component is completely warmed or cooled to the
temperature levels forming the basis of the calculation. It also assumes very high heat
 
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