Low emissivity coated glass speaks to what is low emissivity coated glass and why use low emissivity coated glass.
This glass will improve the thermal performance substantially by the use of what is referred to as low e coating. Low e coatings are ultrathin, virtually transparent and almost colourless metallic coatings that selectively reflect solar radiation of different wavelengths.
They have a high visible light transmittance and depending on the particular coating, a low transmittance for some or all types of infra radiation developed heat. Low e coated glass is most commonly used as one of the two lights in double glazing, where it offers several benefits.
By reducing the radiant transfer of heat between individual lights, the overall thermal transmittance of the glazing unit is reduced to the extent that low e double glazing can meet or exceed the thermal performance of ordinary triple glazing. By reflecting the majority of the infrared component of solar radiation, low e double glazing can simultaneously provide high visible light transmittance with low solar heat gain, allowing such units to achieve the highest light to solar gain ratios of any insulated glass type.
By varying the properties of the low e coating and by combining it with different types of tinted glass, the performance characteristics of the glazing unit can be tailored to meet different needs. For buildings dominated by wintertime heating, low e units with high U factors which minimizes heat loss, and high solar heat gain coefficients, which promote wintertime solar heat gains, may be selected.
For buildings dominated by cooling loads, units with low solar heat gain, to minimize solar heating and lower visible light transmittance are used. Like laminated glass, low e coated glass has low UV radiation transmittance, a benefit to interior finishes and furnishings. Though less common, low e coated glass may also be used is single or triple glazing to improve the thermal performance of these glass types.
When specifying glass with any type of coating whether low e glass or reflective coated glass, it is necessary to specify on which glass surface the coating is to be located. By convention, glass surfaces are numbered starting from the exterior side of a glazing and working inward.
In single glazing and working outward, the outward face is surface number 1 and the inward face is surface number 2.
In double glazing the outward face of the outer glass light is surface number 1 and the inward face of this light is surface number 2, the outward face of the inner glass light is surface number 3, and its inward face is surface number 4.
In low e double glazing, the low e double glazing, the low e coating is most commonly located on the number 2 surface, although, where a high solar heat gain coefficient is desired, it may be located on the number 3 surface instead.
Low e coatings can also be applied to very thin membranes of transparent plastic. One or two of these plastic films can be installed within the centre of the airspace or gas space of a double glazed unit, stretched tight, parallel to the sheets of glass, where they act as virtually weightless additional glazing elements. Combined with selective properties of the low e coating, thermal performance values ranging from R-6 to R-20 are claimed by manufacturers of these films.