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.

Continue reading

Insulated Glass Units


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Insulated glass unit (IGU), also known as Double glazed unit (DGU) consists of two glass panes separated by dry air with an aluminum spacer. IGU has been in use in many countries since 1960s, except in the middle-east and Asia, … Continue reading

Is Glass Really A Green Building Material?

If somebody says that Glass is a green building material, the straight and honest answer would be a big No! Just because in many high rise green rated buildings, glass has been used extensively, it doesn’t make it a green product in itself. One might have encountered with many architects and glass industry professionals who bluntly promote glass as a green product, then why is this article contradicting that belief? Here is an explanation on why glass is not a green product by itself, but why it is essential for a green rated building. This article is in context of float glass only, which is the most widely used in buildings.

Glass could earn a few green points for the fact that it could be recycled. Broken pieces of glass are added along with the raw materials while glass is manufactured so as to bring down the boiling point and there by reduce the energy consumption. Also if the manufacturing facility is near to the building in construction, that could also fetch a few points for green rating, as the material is locally sourced. Local sourcing of material means less energy consumed for transporting the material.

Glass is extensively used in green buildings to harvest maximum light inside and to reduce energy consumption for internal lighting requirements. When more natural light enters a building, equal amount of heat also enters the building. 50% of the Visual Light Transmittance (VLT) is direct solar energy (ER or DET). So when you are asking for 100% light transmittance, you are getting 50% of heat along with it! If in a building, which is centrally air-conditioned, and if it is clear glass which is being extensively used, energy consumption for internal lighting might get reduced to a significant level, but at the same time energy consumption by the air-conditioner would be enormously escalated. This is where solar control and thermal insulating glasses play a major role.

Solar control glasses let in maximum light and also cuts DET down to a great level. Since 80 to 90% of heat entering a building is solar heat, maximum energy could be saved on lighting and air-conditioning. Apart from direct solar energy, non-solar energy or indirect energy, could also be controlled by using double glazed/ Isulated glass units(DGU / IGU), and thermal insulating glass. A DGU cuts down the heat entering a building due to conduction (glass is a good heat conductor) and convection. A thermal insulating or a low emissivity (Low-e) coated glass can reduce the non-solar heat by cutting down the transmittance of Long Wave Infra Red Radiation (LWIR). LWIR is emitted by objects like trees and furnitures during the night time, which absorb the Short Wave Infra Red Radiation (SWIR). In moderate to cold climate conditions, where heaters are used in buildings, it is better to go for a very low u-value glass, so as to prevent heat loss from the building. In tropical climates, it is better to have a moderate u-value range.

In short, it is not an isolated pane of glass that is green rated or that helps you gain green points, it is the configuration of glass units installed in your building, based on the window to wall ratio, orientation of the building, total glazing area, energy efficiency of the building, and hours of operation of the building occupants.

(Originally written for

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

Non-Solar Heat Control Glasses


Solar and Non-solar heat transfer- IGU

In the previous post, types of heat entering a building was discussed, of which solar heat comprises around 80% and the rest is non-solar heat. It becomes very important to control non-solar heat as well even though it contribute to only 20% heat entering a building, especially in buildings where there is 24 x 7 operations and households, so as to bring down the energy consumption during night time. In this post, non-solar heat and how all to control it will be discussed in detail.

Non-solar heat is mainly transferred in three ways- conduction, convection and radiation, and is measured in terms of U-value (W/m2.K). Continue reading

Solar and Heat Control Glasses


solar and non-solar heat

Glass is used in a building to harvest natural light inside it and there by reducing the internal artificial lighting requirements, in turn saving energy. The two major sources for heat entering the building is solar heat and non-solar heat; solar heat is nothing but the direct solar heat entering the building through visible light, non solar heat is caused by various factors like conduction, convection and radiation. Out of the heat sources, solar heat is the major one and requires more attention, even though the effects of non-solar heat could not be ignored as well, as it plays a major role in certain structures. Continue reading

Thermal Breakage in Glass

There are many instances where the glass panes in a building tends to crack for itself. This could be attributed to various factors like poor quality glazing, but there is also another factor which causes such breakage and is called thermal breakage. Thermal breakage in glass mainly happens due to the high difference in temperature between two points in a single glass pane, resulting in expansion and contraction in the same pane.

The temperature difference as mentioned above could be a result of many factors, such as difference of temperature between inside and outside, solar intensity in the region where building is located, type of glass (whether it is tinted, reflective, etc.), thickness of the glass, internal ventilation, type of glazing done, partial shade on glass, etc. Of all these factors, solar intensity plays a major role and it differs with geographical location, building orientation, seasons, etc. Continue reading