Civil Engineering Reference
In-Depth Information
coating in the inner position. The solar transmittance, evaluated by means
of the solar factor, is high for windows with monolithic translucent aerogels:
the direct solar transmittance measured in the laboratory for a monolithic
window prototype (15 mm aerogel) was higher than 75% (Jensen
et al.
,
2004) but, at the same time, the U-value was equal to the best triple-layered
gas-fi lled glazing units (U
0.6 W/m
2
K). The net average energy balance
on the window depends in fact on both the U-value and solar factor, in
which case monolithic aerogel prototypes in evacuated conditions were
better than the other highly insulating glazings (Fig. 10.11), especially in
very cold climates such as in northern Europe: the improvements due to
monolithic aerogel windows in a typical Danish single-family home were
underlined by Schultz and Jensen (2008). A wide range of
g
-values can be
found in the manufacturers' technical data for daylighting systems with
granular translucent aerogels, depending on the external retaining layers
(glasses, low-e glasses, PMMA, polycarbonate) and on the total thickness
(see Tables 10.1 and 10.2).
Nanogel windows are excellent in the thermal insulation of buildings
because of the very low thermal conductivity of transparent or translucent
silica aerogel. As shown in Table 10.2, a wide range of U-values can be
obtained for commercial products with translucent aerogels: the U-value
can be as low as 0.48 W/(m
2
K) for polycarbonate solutions (polycarbonate
sheets with Lumira
TM
aerogel, thickness
<
50 mm, RODA, Germany),
whereas U-values in glass solutions can be about 0.20 W(m
2
K) (translucent
linear channel glass systems Pilkington Profi lit
TM
fi lled with 25 mm Lumi-
ra
TM
aerogel, Technical Glass Products, USA). The energy consumptions
with triple-layered argon-fi lled glazing and with aerogel glazing were
=
Net energy balance (kWh/m
2
)
75
50
25
0
-25 -50 -70 -100
0.8
-125
-150
Aerogel
glazing
0.7
0.6
0.5
-175
-200
0.4
0.3
-225
-250
0.2
0.1
0
0
0.5
1
1. 5
U-value (W/m
2
K)
2
2.5
3
10.11
Energy balance (kWh/m
2
) for window glazing as a function of
U-value and solar factor. The curve represents the typical relationship
for window glazing systems, the aerogel glazing position is shown by
the star (Jelle
et al.
, 2012).
Search WWH ::
Custom Search