Improving energy efficiency in buildings through use of glass technology

Low-e, low iron and tinted windows.

Low E-Glass

Low-E, or low emissivity, glass is an energy efficient glass that was developed in the 1980’s. Low-e glass has a coating that increases the reflectiveness and reducing the emissivity of the glass. Glass without a low-e coating may have an emissivity of 0.84 whilst low-e coated glass may have an emissivity of 0.02.

The idea in reducing the emissivity, increasing reflectiveness, is that it reduces the amount of direct solar energy from leaving the building in the winter or entering the building in the summer.
In double glazed units, the low-e coating can be positioned on up to four different positions of the glass from the inside pane to the outside pane dependent on the priorities of the building designer whether the design objective is passive low-e or solar low-e. Passive low-e glass is designed to maximise solar heat gain into a building to provide the effect of passive heating. Solar low-e coatings are designed to reduce the amount of heat that passes into a building for instance in order to reduce air conditioning loads.

Manufacturing low-e glass

The original low-e coatings on glass, known as hard coat low-e, are manufactured using what is termed a ‘pyrolytic’ process. This process occurs whilst the glass is on the float line with the low-e coating fusing to the glass.
Soft coat low-e coatings can be applied off production line in a vacuum chamber at room temperature. Soft low-e coatings have a lower emissivity than hard coat low-e but are more susceptible to damage and so are installed on the inner pane of glass.

Tinted glass

Tinted glass or reflective coatings can be used for architectural appearance and to limit solar gain when used alongside low-e coatings. Tinted glass can be factory made by mixing colour pigments during the float process. Tinted glass works by reducing the amount of light and absorbs the heat and because of this tinted glass almost always requires heat-treatment during manufacture. This is done to reduce potential thermal stress and breakage and can be a reason for failure of the glazed unit.

Reflective coatings are effective at reducing heat gain but also reduce visible light transmission. Low-E coatings reflect solar energy away from the glazing, often without requiring heat-treatment, and generally have lower visible light reflection.

Low iron glass

Low iron glass is visually superior to standard clear glass and is manufactured by reducing the amount of iron in the molten glass. This reduces the green appearance and provides an extra clear look allowing more daylight to penetrate. Allowing more daylight to penetrate a building could reduce the amount of artificial lighting required and reduce lighting energy load when combined with photoelectric lighting controls.

Energy Efficient Glazing

 Improving EPCs through glazing technology