Selective glazing
From Swikipedia
Introduction
About two-thirds of the heat escaping through double-glazed windows does so through radiation. Originally, low-e was intended to reduce heat loss by blocking heat radiating from objects inside the house. This is called far infrared energy. Scientists have devised new "selective" coatings that also help block solar heat streaming through the glazing. Solar heat includes energy from visible light and invisible heat called near infrared radiation.
While solar heat gain is helpful for some buildings, it's a problem for others. Blocking solar heat gain has been important in commercial buildings for decades. The windows of mirrored office towers block much of the sun's heat, but also much of the light and views. Selective glazing allows more visible light to penetrate. This means that daylight can be used instead of electric light and the occupants of the building can see the view.
Spectrally selective glazing is window glass that permits some portions of the solar spectrum to enter a building while blocking others. This high-performance glazing admits as much daylight as possible while preventing transmission of as much solar heat as possible.
Brief Description
By controlling solar heat gains in summer, preventing loss of interior heat in winter, and allowing occupants to reduce electric lighting use by making maximum use of daylight, spectrally selective glazing significantly reduces building energy consumption and peak demand. Because new spectrally selective glazings can have a virtually clear appearance, they admit more daylight and permit much brighter, more open views to the outside while still providing much of the solar control of the dark, reflective energy-efficient glass of the past. They can also be combined with other absorbing and reflecting glazings to provide a whole range of sun control performance.
Because of its solar heat transmission properties, spectrally selective glazing benefits both buildings in warm climates where solar heat gain can be a problem and buildings in colder climates where solar heat gains in summer and interior heat loss in winter are both of concern. The energy efficiency of spectrally selective glazing means that architects who use it can incorporate more glazing area than was possible in the past within the limitations of codes and standards specifying minimum energy performance. When spectrally selective glazing is appropriately used, the capacity of the building's cooling system might also be downsized because of reduced peak loads.
Spectrally selective glazings screen out or reflect heat-generating ultraviolet and infrared radiation arriving at a building's exterior surface while permitting most visible light to enter. Spectral selectivity is achieved by a microscopically thin, low-emissivity (low-E) coating on the glass or on a film applied to the glass or suspended within the insulating glass unit. There are also carefully engineered types of blue- and green-tinted glass that can perform as well in a double-pane unit as some glass with a spectrally selective low-E coating. Conventional blue- and green-tinted glass can offer some of the same spectral properties as these special absorbers because impurities in tinted glass absorb portions of the solar spectrum. Absorption is less efficient than reflection, however, because some of the heat absorbed by tinted glass continues to be transferred to the building's interior.
Spectrally selective glazings can be used in windows, skylights, glass doors, and atria of commercial and residential buildings. It may not provide reduced glare control even if solar gain is reduced. This technology is most cost effective for residential and non-residential facilities that have large cooling loads, high utility rates, or poorly performing existing glazing (such as single-pane clear glass or dark tinted glass).
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