Silica nanogel for energy-efficient windows - Nanotechnology in Eco-efficient Construction - page 229

ISO 12567-1) and sound reduction index ( R , EN ISO 10140-2) and they
were compared with conventional glazing with air interspace (same thick-
ness). A U-value of 0.99 W/m 2 K was found for the glazing with granular
aerogel in the interspace. Furthermore, the presence of granular aerogel
increases the sound reduction index values (Fig. 10.14) in all the frequency
ranges (100-500 Hz), but above all in the central range (500-2000 Hz).
Moreover, a weighted sound insulation index R w (EN ISO 717-1, 2007)
equal to 37 dB was obtained for the innovative prototype, 3 dB higher than
that of the conventional window with air in the interspace ( R w = 34 dB),

confi rming good acoustic insulation properties.

10.5 Future trends

Further investigations about highly energy-effi cient windows and skylights
are needed in order to clarify several aspects and to improve some charac-
teristics, such as:

• Aerogel glazings have the lowest potential U-values in the fenestration

market, as low as 0.1 W/(m 2 K) and, due to their very interesting

50

45

40

35

30

25

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20

15

Conventional window,
R w = 34 dB
Window with granular aerogel,
R

10

w = 37 dB

5

Frequency (Hz)

0

10.14 Sound reduction index ( R ) values vs. frequency for the
conventional window and for the glazing prototype with aerogel in the
interspace (Buratti and Moretti, 2012a).