2.1 Coating Types
Special coatings can be applied to a float glass surface to make it reflective to short wave radiation from the sun and/or long wave radiation from heat inside or outside the building. These coatings are known by a variety of terms, but there are two main types:
- Pyrolytic Coatings
A coating applied on line at high temperature during the float manufacturing process. Also known as on line or hard coatings.
- Sputtered Coatings
A coating applied off line in special equipment, also known as off line, vacuum, or soft coatings.
Traditional reflective glass has a mirror-like appearance and reflects and absorbs a major proportion of the sun’s direct short wave solar radiation. The degree of reflectivity is dependent on the type of coating and the orientation of the glass. The use of reflective glass is more popular in commercial glazing as it provides superior solar control performance to clear or tinted glass products, and thus improves the energy efficiency of the building.
Low Emissivity (Low E) coatings are traditionally clear and are designed to reflect long wave radiation. They are available in both pyrolytic and sputtered coatings and the performance varies. Some modern reflective glass products have Low E coatings to reflect long wave radiation as well as the sun’s short wave radiation.
In addition, self cleaning coatings are available but these are not reflective, nor Low E. Some special glasses have a sputtered Low E coating applied to the rear surface of a self cleaning coated glass. New developments include UV and scratch resistant coatings such as Climaguard SPF and DiamondGuard SRG. Contact Metro GlassTech for more information.
The building designer should consider several issues when deciding on reflective and coated glass such as:
- The aesthetics of a reflective glass in relation to the coating reflectivity and orientation of the building. Reflective products can offer the designer a multitude of colour options to enhance or transform a building’s appearance.
- The performance of the glass to reduce heat gain and cooling costs. Reflective glasses offer superior heat gain performance over tinted glass but this is at the expense of reduced natural daylight levels in a building. In general, reflective glass offers lower UV and visible light transmittance than tinted glass.
- The ability of the glass to reduce heat loss and heating costs. This can be improved by using Low E coatings or Insulating Glass Units or both.
- The protection of the coating from damage during construction or cleaning (refer Section 11.5.4 Metro Protect).
Glass alone will not provide all the answers in the design needs of a building. Orientation, overhangs, shading devices and window size all have a bearing on how well a glass product can perform.
2.2 Pyrolytic Reflective
A pyrolytic coating is a metal oxide coating applied on line during the float manufacturing process. The coating is fused into the glass surface at high temperature making it extremely hard and durable. Since the coating is durable it can be glazed to the outside (surface 1) or inside (surface 2) of the building. It can be handled and cut like standard float glass and processed into heat strengthened, toughened, laminated, curved glass and Insulating Glass Units. These products are also known as an ‘on line’ or ‘hard coat’ reflective glass.
The most common types are the Stopsol and Eclipse ranges. They are available in a range of colours, such as clear, grey, bronze and shades of blue and green. Some manufacturers have different types of pyrolytic coatings, such as Glaverbel, who offer Stopsol Classic, Supersilver and Silverlight coatings.
Coated glass colours do change when viewed at different times of the day, depending on the weather, surrounding reflections, building orientation and the angle at which the glass is viewed. In addition the appearance is distinctly different if the coating is glazed outside on surface 1 or inside on surface 2. Therefore it is recommended that either a mock-up and/or an on-site visit to a completed building is undertaken when selecting a glass type.