Technology: Glass coatings for every architectural application
The single glazing that was standard up until the mid 1970s was characterised by high heat loss (Ug = 5.0 W/m2K). Increased use of double glazing brought improved Ug values of an average of 3.0 W/m2K. Further reductions in heat loss followed with the application of modern thin-film coatings. Today double glazing with a Ug value of 1.1 W/m2K with glass thicknesses of 4 mm and a 16-mm argon-filled cavity is regarded as the state of the art. Triple glazing brings the Ug value down to 0.7 W/m2K, with 4 mm-thick glass and two 16-mm argon-filled cavities. In contrast to metals which re-radiate only around 2 to 10 % of the energy they absorb, glass has a high emissivity of ε = 0.85, i.e. over 80 % of the heat is radiated via the surface of the glass. Applying a thin film of metal to the glass significantly reduces emissivity while retaining transparency and permeability to light. The optimum is an ultra-thin film of silver, around 1/100,000 mm thick, or 10 nm. EN 1096 sets out the requirements for coated glass.
