Civil Engineering Reference
In-Depth Information
Translucent linear-channel glass systems, Pilkington Profilit
TM
, filled with
Lumira
TM
aerogel were also developed (Pilkington in Europe and TGP America in
the USA) (Technical Glass Products
2012
) with very interesting thermal perfor-
mance: U = 0.19 (low-e with 16 mm Lumira
TM
)—0.21 W/m
2
K (low-e with
25 mm Lumira
TM
) (Fig.
11
c).
The system Okagel
was developed by Okalux (Germany) (Okalux GmbH
2012
) and consists of two glass layers filled with granular aerogel (Fig.
11
d); a
hydrostatic stress is applied to the material, in order to avoid its settling during the
service life. The U-value can decrease down to 0.3 W/m
2
K, and the most famous
application is the British Haley VI Research Station in the Antarctic. In America,
insulated translucent glass units with nanogel
are manufactured from Advanced
Glazings Ltd (Canada): the system called Solera
? nanogel
has a U-value equal
to 0.31 W/m
2
K (76.1 mm configuration) (Advanced Glazings Ltd.
2012
).
High-performance tensile structures could be obtained by incorporating gran-
ular aerogel between two layers of traditional PTFE membranes (Teflon
)
(Fig.
11
e), allowing an increased thermal efficiency without adding significant
weight or creating a barrier to natural light (Birdair
2012
).
Finally, in China, Nano High-tech Co. Ltd developed daylighting panels (TP)
with aerogel particles (Nano High-Tech Co.
2012
). With a thermal conductivity
equal to 0.025 W/m K, they could be used in large buildings as theatres, airport
terminals, exhibition centres, etc. They are hydrophobic, and the light transmission
is in the 40-70 % range, depending on the panel thickness (10-30 mm).
4.2 Windows Prototypes
Double windows with monolithic aerogel (also partially evacuated) in interspace
were considered for decades as alternative to gas-filled conventional systems,
instead of vacuum glazings. The development of monoliths for windows applica-
tion began during the 1980s, thanks to efforts of the Airglass A.B. (Sweden)
(Airglass
2012
). Also thanks to two research projects founded by the European
Commission (HILIT—Highly insulating and light-transmitting aerogel glazing for
window, 1998-2001, and HILIT+ , 2002-2005); transparent insulating silica
aerogel tiles (thickness of about 15 ± 1 mm, 55 9 55 cm
2
) were manufactured at a
pilot scale since 2004. Then, aerogel glazing prototypes were made under vacuum
conditions; a rim seal assured a barrier against atmospheric air and water vapour,
and low thermal bridge effects were obtained. The solar and light transmittances
were optimized by means of low-iron glass covers and antireflection coating. The
optical quality had a minimal disturbance in the view through, except if exposed to
direct non-perpendicular radiation, when the diffusion of the light becomes
significant (Fig.
12
). The centre U-value, measured by means of a hot-plate
apparatus, was equal to 0.66 W/m
2
K, with an estimated thermal conductivity of
0.010 W/m K for the aerogel pane (average thickness 14.8 mm). Moreover, the
solar transmittance is high for windows with monolithic translucent aerogels:
