Reflective Glass

As the SHGC falls in single-pane tinted glazings, the daylight transmission (VT) drops even faster, and there are practical limits on how low the SHGC can be made using tints. If larger reductions are desired, a reflective coating can be used to lower the solar heat gain coefficient by increasing the surface reflectivity of the material. These coatings usually consist of thin metallic or metal oxide layers. The reflective coatings come in various metallic colors-silver, gold, bronze-and they can be applied to clear or tinted glazing. The solar heat gain coefficient can be reduced by varying degrees, depending on the thickness and reflectivity of the coating, and its location in the glazing system. Some reflective coatings are durable and can be applied to exposed surfaces; others must be protected in sealed insulating glass units.

Figure 3-17 illustrates a highly reflective coating placed over a bronze-tinted, double-glazed unit. The emittance of the coating creates modest changes in the U-factor.

As with tinted glazing, the visible transmittance of a reflective glazing usually declines more than the solar heat gain coefficient. Reflective glazings are usually used in commercial buildings for large windows, for hot climates, or for windows with substantial solar heat gains. Reflective glazing is also used by many architects because of its glare control and uniform, exterior appearance.

The reflective coating is applied just like hardcoat Low-E through spraying (Pyrolitic process) during the float glass manufacturing process.

Benefits

Reflects light and heat with a metal oxide coating giving a mirror effect.
Minimizes solar heat gain, and ultraviolet light damage to interior.
Adds daytime privacy.
May be tempered.

Note: Heat absorbing and heat reflective glass can only be used on the exterior lite of a unit in order to avoid a build-up of heat inside the airspace, which will cause thermal stress cracks or seal failure.

Note: Reflective type glass works with the play of light. Example: During daylight hours you can't see inside a building with reflective glass, (only your refection). At night there is just the opposite effect. You can see in, but the people inside can not see out.