Glass Buildings and The Environment

Here is another article from Thomas Hens on designing of glass buildings keeping in mind their impact on environment.

In our last issue, we discussed a number key factors to be taken into account when choosing facade glass. This issue will focus primarily on the environment and demonstrate that designers of glass buildings are also thinking about our planet.

We will be looking at three environmentally friendly construction methods:

  • Insulating buildings: cutting C02 emissions by reducing energy loss via glass.
  • Generating energy: cutting energy consumption by using glass as a construction component as well as to generate electricity.
  • Using sustainable materials and environmentally friendly manufacturing techniques.

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Spray Hard Coat Glass Vs CVD Hard Coat Glass

If somebody tries to sell you cheap reflective glass saying it is “Hard Coated”, the first thing you should ask is “Is it spray hard coat or CVD hard coat?”. Spray hard coat could be termed as a primitive and is relatively cheaper, in this one the chemical composition is sprayed over glass which would be in a semi solid stage (online process). Most cases, the coating tends to be uneven and deposition rate would be poor. In most cases the coated side appears yellowish.

CVD (Chemical vapor deposition in atmospheric pressure) on the other hand is far superior and the latest. Here, the chemical composition is vaporised and then allowed to deposit on semi-solid glass (online coating) in a controlled manner, achieving high deposition rate and the coating would be even. In most cases, the coated side would have a silver appearance.

It would be a disaster if spray coated glasses which come at cheap rates are used (especially when it is mis-sold with the name “Hard coated reflective glass”) in buildings. Below are some pictures for reference.

Spray Hard Coat – Coating peel off

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Soft Coat Glass

Soft Coat Glass, otherwise known as vacuum coated or off-line coated glasses, are manufactured by a process which is entirely different from hard coat glass (discussed in last post). The name soft coat is given because of the susceptible nature of the coating to get peeled off (in single glazing/ monolithic application) when compared to hard coat. However, soft coat glasses can offer a very low solar factor when compared to hard coat glasses.

Manufacturing process involves metal particles being deposited on the glass surface inside a vacuum chamber. The process, otherwise known as Magnetron Sputtering Vapor Deposition (MSVD) is sometimes referred to as Cathodic Vapor Deposition. Some glass manufacturers mention it as CVD coating, just to create a confusion with actual Atmospheric Pressure Chemical Vapor Deposition, mis-interpret it and mis-sell it as hard coat.

During the process, the material to be sputtered is loaded in a high voltage electric circuit, which is followed by the feeding of process gas into vacuum chamber, where plasma is formed. An ion discharge takes place inside the chamber, these positive charged ions gets attracted and collide with the material to be sputtered. This process happens at a very high speed and atoms of the material sputtered gets ejected, which gets accumulated on the glass below. Most widely used metals for sputtering are Silver and Titanium.

Soft coat glasses are generally used in double glazed units, with the coated surface at position 2 or 3, so that the coating is kept protected from peeling off. With the advance in technology, soft coat glasses are now made which can also be used in monolithic form (single glazed) with much improved life for the coating, but still the life of the coating cannot match with that of hard coat glass in monolithic applications.

Soft coat glass also has problems while tempering when compared to hard coat glass. It tends to show up a problem called lensing, which happens because the coated surface of the glass reflects Infra Red radiation and heats up differently than the lower surface (which is heated).



Hard Coated Reflective Glass

Espace rolin fortis, Brussels- Stopsol Silverlight

Hard coated or pyrolytic coated reflective glasses are those in which the coating is applied when the glass is manufactured,i.e. it is an online coating process. In this process of coating, the glass is fused into the glass at 650-700 degree celcius, and on cooling, the coating becomes a part of the glass.

Primary advantage of hard coated glass is the durability, it could also be handled like normal/annealed glass, could be easily heat strengthened, toughened, laminated or curved. These glasses could also be used in single glazing without any fear of losing the coating. Soft coat glasses (to be discussed in the next post) are susceptible to scratch and degradation over time, and requires special handling, hard coated glasses were invented just to counter this problem. Only disadvantage is the variety of colors available when compared to off line coating. Continue reading

What is Float Glass?


Initially, window glasses were made by cutting from large discs of Crown glass. Crown glass is nothing but a large globe of glass, made by blowing molten glass into a crown or a hollow globe. The crown glass is further reheated and spinned out of the globe into large discs, which were then flattened using centrifugal force. These glasses were then cut into desired sizes. There were other methods of making glass as well, like the blown plate, broad sheet, polished plate and cylinder blown sheets, which were all in practice up till the end of the 19th century. 20th century witnessed more advanced processes like rolled plate, machine drawn cylinder sheet, flat drawn sheet, single and twin ground polished plate and float glass. Continue reading