14/02/2012

Coated Glass in the Building Industry

Some glasses offer high efficiency solar protection and excellent thermal insulation. With the arrival of new technologies we have modern glasses with excellent thermal insulation and high efficiency solar protection. This type of glasses reflects a certain spectrum of solar energy thanks to a special coating. Often these are incorrectly called glasses with a cover. The coating however may also be of a different kind, and therefore the norm ČSN EN 1096 Glass in the building industry – Coated glass does not use the term cover.
There are two kinds of coatings: Hard coatings (on-line technology, glass susch as Stopsol nebo Sunergy) which are applied on clear or coloured glass online. Soft coatings (off-line technology, glass such as Planibel, Stopray etc.) – this kind of coating is vulnerable to oxidation and is not resistand agains mechanical damage as are hard coated glasses. Soft coated glasses may be used only inside insulating double or triple glass.
We see a trend of increasing the average area of glazing. This increase implies stricter requirements on the thermal technical characteristics of panels and in some cases, demands for a better sun protection to ensure their total energy balance. To ensure all requirements, it is essential that each insulating glass used the coated glass. Characteristics of coatings - thermal insulation Glass as a base material has only a little insulating character.
Figure 1 Influence of glass thickness on the heat transfer coefficient
Coating properties – light and solar protection Coated glass is also able to solve another problem which is overheating of the inside and at the same time ensure sufficient light transmission. The properties of glazing are defined by the aid of a few values – light factors, energy factors and selectivity. Light factors: Light parameters are solely defined to the visible part of solar radiation (from 380 nm until 780 nm). The light transmittation coefficient (Light transmitation – LT) and light coefficient of reflection factor (light reflection – LR) are defined as the part of visible light which goes through the glass or which is reflected back to the exterior. The radiation absorbed to the glass mass is not visible and is generally negligible. Figure 2 Light parameters (light, light reflection coefficient LR, light transmittion coefficient LT, light absorbtion) Selectivity: Solar radiation, which is the visible light, ultraviolet radiation (UV) and infrared radiation (IR) brings heat to the interior of buildings. We can reduce this heat energy without an excessive reduction of light transmission by the use of high efficient low emissive coating on the surface of glass which avoids the transmission of UV and IR and at the same time transmits visible light. Such glazing is called selective. Selective glazing can be expressed by the aid of the quotient of the light transmission coefficient (LT) by the overall factor of solar radiation (SF): Selectivity = light transmission/solar factor Until not so long ago it was accepted that the selectivity of coated glass can reach values from 0 to 2: 0 for opaque glass which does not transmit light 2 was considered as the best possible value for selectivity. Visible light forms 50% of the overall scope of the solar spectrum. Therefore for glazing with LT=50%, SF=25% was considered to be the best possible. With the arrival of new materials and technologies values of higher than 2 can already be obtained. Selectivity is one of the most important parameters which determine the efficiency and performance of glazing. The evolution of „soft“ magnetron coatings Coatings with one layer of silver This is the most basic coating used primarily in regular insulation and double glazing and triple glazing. It is used mainly for ordinary residential construction. The main functional layer in the structure of coating is a layer of silver and metal oxides. The coating is provided with upper cover layer, which protects the individual functional layers from a damage. Coatings with two layers of silver Coatings developed especially for use in commercial buildings. In terms of parameters these coatings were long considered the best and difficult to overcome. The main function layer in the composition of the coating are two layers of silver separated by metal oxides and absorption interlayer. The coating is also provided with a cover layer, which protects particular layers from mechanical damage.
Coatings with three layers of silver: This is a complete and revolutionary innovation in the development of coatings for building applications. It's a coating where three functional layers of silver in combination with other metals and elements are used for the first time.
Author: AGC Glass Europe The article was published in the pilot issue of the Energy self-efficient buildings journal.
Production of glass and environmental protection In 2012 the company AGC received for its products of float glass and soft coated glass a Cradle-to-Cradle certification of the independent organization MBDC. Cradle-to-Cradle (C2C) is a strict program of the organization MBDC which evaluates the overall environmental impact of products over their lifetime. The goal of this inovative approach is to certify producst of companies with the most ecological manufacturing methods and products. By embracing the C2C philosophy and ethics the company AGC became the leader in the glass industry in this area. The AGC group is a true pioneer in introducing the strict ecological goals into into its manufacturing approached and final products. More information about the AGC Glass Europe products can be found on web pages of the company.