Civil Engineering Reference
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compared (Schultz and Jensen, 2008): the annual energy saving was about
1180 kWh/year (19%); in fact, in cold climates the increased heat insulation
of triple glazing with respect to conventional double glazing can be thwarted
by the g value decreasing ( g -value is on the order of 0.4 for a argon-fi lled
triple glazing). Considering a low-energy house, the savings become
700 kWh/year, which correspond to a 34% decrease in space heating
demand.
Commercial applications with monolithic aerogels are not yet available,
but U-values equal to 0.66 W/m 2 K were measured for a prototype of an
evacuated glazing with only 13.5 mm thick aerogel pane (see Section 10.3.2).
Furthermore, translucent insulating materials in glazing can have a major
advantage when they are used in roof applications: the U-values of glazing
systems with adequate layers of translucent nanogel are not dependent on
the inclination to the vertical, while the gas-fi lled glazing with air or gas
(argon or krypton) have a worse behaviour than that expected when they
are used in roofs. The U-value is in fact calculated or measured for a vertical
position, according to the international standards, but when they are hori-
zontal, the warm air meets the colder outer side more quickly when rising,
so an accelerated fl ow arises. The thermal convection in the cavity becomes
higher and the U-value can be more than 50% higher than that measured
or calculated in the vertical, as shown in Fig. 10.12.
In order to characterize the acoustic properties of silica aerogels, the
acoustic attenuation was measured according to the two-thickness method
(Forest et al. , 2001) and it showed that the large granules of aerogels (mean
2.5
Air 16 mm
2.0
Argon 16 mm
￿ ￿ ￿ ￿ ￿ ￿
1. 5
Krypton 10 mm
1. 0
Okagel 30 mm
0.5
Okagel 60 mm
0.0 90
75
60
45
30
15
0
Vertical
Inclination (°)
Horizontal
10.12 Dependence of U-value on the inclination for conventional
glazing and glazing with translucent insulation materials
(Okalux, 2012).
 
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