Window Materials & Assemblies: Emerging Technologies
Insulation-filled Glazings | Evacuated Windows | Smart Windows | Building Integrated Photovoltaics
Insulation-filled Glazings
There are several options for highly insulating windows with aerogel, honeycombs, and capillary tubes located between glazing panes. These materials provide diffuse light, not a clear view. Some of these materials are used in Europe for passive solar applications.
Aerogel is a silica-based, open-cell, foam-like material composed of about 4 percent silica and 96 percent air. The microscopic cells of the foam entrap air (or another gas if gas-filled), thereby preventing convection while still allowing light to pass. The cell sizes are smaller than the mean free path of air/gas molecules, thus reducing conduction to values below those of pure conduction for the air/gas. Long-wave thermal radiation is virtually eliminated due to the multiple cell walls through which long-wave infrared radiation must be absorbed and reradiated. The particles that make up the thin cell walls slightly diffuse the light passing through, creating a bluish haze similar to that of the sky.