Glass has been a fascinating material to humankind since it was first made in about 500 BC. At first thought to possess magical properties, glass has come a long way. It is one of the most versatile and oldest materials in the building industry. From its humble beginnings as a window pane in luxury houses of Pompeii to sophisticated structural members in new age buildings, its role in architecture has evolved over the years.
From time immemorial, appearance has been one of the greatest obsessions of humanity. Whether in personal looks, material possessions or natural surroundings, external facades have always been pivotal points of importance. So it is only natural that, even in the construction of buildings, appearance should play a major role. Traditionally, architecture and construction in India has been limited to drab buildings, without any spectacular beauty.
However, recent years have seen the advent of many modern techniques, such as glass construction, to improve this aspect. Especially in the metros and IT parks of the country, it is now quite common to see high-rises with glass glazing, which have a modern and sophisticated look. A number of companies have been offering solutions in glass glazing for the Indian construction industry.
PROPERTIES OF GLASS
This property allows visual connection with the outside world. Its transparency can be permanently altered by adding admixtures to the initial batch mix. By the advent of technology clear glass panels used in buildings can be made opaque. (Electro chromatic glazing)
The U-value is the measure of how much heat is transferred through the window. The lower the U-value the better the insulation properties of the glass– the better it is at keeping the heat or cold out.
Visible transmittance is the fraction of visible light that comes through the glass.
Glass is a brittle material but with the advent of science and technology, certain laminates and admixtures can increase its modulus of rupture( ability to resist deformation under load).
Solar heat gain coefficient:
It is the fraction of incident solar radiation that actually enters a building through the entire window assembly as heat gain.
It is capable of being worked in many ways. It can be blown, drawn or pressed. It is possible to obtain glass with diversified properties- clear, colorless, diffused and stained. Glass can also bewelded by fusion.
Glass is 100% recyclable, cullets (Scraps of broken or waste glass gathered for re-melting) are used as raw materials in glass manufacture, as aggregates in concrete construction etc.
Energy efficiency and acoustic control:
Energy-efficient glazing is the term used to describe the double glazing or triple glazing use in modern windows in homes. Unlike the original single glazing or old double glazing, energy-efficient glazing incorporates coated (low-emissivity) glass to prevent heat escaping through the windows. The air barrier also enhances acoustic control.
The greenhouse effect refers to circumstances where the short wavelengths of visible light from the sun pass through glass and are absorbed, but the longer infrared re-radiation from the heated objects are unable to pass through the glass. This trapping leads to more heating and a higher resultant temperature.
Some More Properties:-
1. It absorbs, refracts or transmits light. It can be made transparent or translucent.
2. It can take excellent polish.
3. It is an excellent electrical insulator.
4. It is strong and brittle.
5. It can be blown, drawn or pressed.
6. It is not affected by atmosphere.
7. It has excellent resistance to chemicals.
8. It is available in various beautiful colours.
9. With the advancement in technology, it is possible to make glass lighter than cork or stronger than steel.
10. Glass panes can be cleaned easily.
Traditionally, architecture and construction in India has been limited to drab buildings, without any spectacular beauty. However, recent years have seen the advent of many modern techniques, such as glass construction, to improve this aspect. Especially in the metros and IT parks of the country, it is now quite common to see high-rises with glass glazing, which have a modern and sophisticated look. A number of companies have been offering solutions in glass glazing for the Indian construction industry.
TYPES OF GLASS
Glass coated with a low-emissivity substance can reflect radiant infrared energy, encouraging radiant heat to remain on the same side of the glass from which it originated, while letting visible light pass. This often results in more efficient windows because radiant heat originating from indoors in winter is reflected back inside, while infrared heat radiation from the sun during summer is reflected away, keeping it cooler inside.
Float glass is also called soda lime glass or clear glass. This is produced by annealing the molten glass and is clear and flat. Its modulus of rupture is 5000-6000 psi. Stronger than Rocky Balboa taking punches from 2000 psi punches man Ivan Drago. It is available in standard thickness ranging from 2mm to 20mm. and has weight range in 6-26kg/m2. It has too much transparency and can cause glare. It is used in making canopies, shop fronts, glass blocks, railing partitions, etc.
Hollow glass wall blocks are manufactured as two separate halves and, while the glass is still molten, the two pieces are pressed together and annealed. The resulting glass blocks will have a partial vacuum at the hollow center. Glass bricks provide visual obscuration while admitting light
Certain additions to the glass batch mix can add color to the clear glass without compromising its strength. Iron oxide is added to give glass a green tint; sulphar in different concentrations can make the glass yellow, red or black. Copper sulphate can turn it blue. Etc.
Toughened (or tempered) glass is a type of safety glass that has increased strength and will usually shatter in small, square pieces when broken. It is used when strength, thermal resistance and safety are important considerations. Using toughened glass on automobile windshields would be a problem when a small stone hits the windshield at speed, as it would shatter into small squares endangering the driver and passengers. In commercial structures it is used in unframed assemblies such as frameless doors, structurally loaded applications and door lites and vision lites adjacent to doors. Toughened glass is typically four to six times the strength of annealed glass.
This type of glass is tempered, may have distortions and low visibility but it breaks into small dice-like pieces at modulus of rupture of 3600 psi. Hence it is used in making fire resistant doors etc. They are available in same weight and thickness range as float glass.
This type of glass is made by sandwiching glass panels within a protective layer. It is heavier than normal glass and may cause optical distortions as well. It is tough and protects from UV radiation (99%) and insulates sound by 50%. Used in glass facades, aquariums, bridges, staircases, floor slabs, etc.
A recent (2001 Pilkington Glass) innovation is so-called self-cleaning glass, aimed at building, automotive and other technical applications. A nanometre-scale coating of titanium dioxide on the outer surface of glass introduces two mechanisms which lead to the self-cleaning property. The first is a photo-catalytic effect, in which ultra-violet rays catalyse the breakdown of organic compounds on the window surface; the second is a hydrophilic effect in which water is attracted to the surface of the glass, forming a thin sheet which washes away the broken-down organic compounds. This type of glass is hydrophilic i.e. The water moves over them without leaving any marks and photocatylitic i.e. they are covered with Nanoparticles that attack and break dirt making it easier to clean and maintain.
By adding a polyvinyl butyral layer, shatter proof glass is made. This type of glass does not from sharp edged pieces even when broken. Used in skylight, window, flooring, etc
Double Glazed Units:
Insulated glazing, or double glazing, consists of a window or glazing element of two or more layers of glazing separated by a spacer along the edge and sealed to create a dead air space between the layers. This type of glazing has functions of thermal insulation and noise reduction. When the space is filled with an inert gas it is part of energy conservation sustainable architecture design for low energy buildings.
These are made by providing air gap between two glass panes in order to reduce the heat loss and gain. Normal glass can cause immense amount of heat gain and upto 30%of loss of heat of air conditioning energy. Green, energy efficient glass can reduce this impact.
This type of glass can control daylight and transparency effectively. These glass are available in three forms- photochromatic (light sensitive lamination on glass), thermochromatic (heat sensitive lamination on glass) and electrochromatic (light sensitive glass the transparency of which can be controlled by electricity switch.) It can be used in meeting rooms and ICUs
Glass wool is a thermal insulation that consists of intertwined and flexible glass fibers, which causes it to “package” air, and consequently make good insulating materials. Glass wool can be used as filler or insulators in buildings, also for soundproofing.
A 1994 innovation for insulated glazing is evacuated glass, which as yet is produced commercially only in Japan and China. The extreme thinness of evacuated glazing offers many new architectural possibilities, particularly in building conservation and historicist architecture, where evacuated glazing can replace traditional single glazing, which is much less energy-efficient.
An evacuated glazing unit is made by sealing the edges of two glass sheets, typically by using a solder glass, and evacuating the space inside with a vacuum pump. The evacuated space between the two sheets can be very shallow and yet be a good insulator, yielding insulative window glass with nominal thicknesses as low as 6 mm overall. The reasons for this low thickness are deceptively complex, but the potential insulation is good essentially because there can be no convection or gaseous conduction in a vacuum.
Unfortunately, evacuated glazing does have some disadvantages; its manufacture is complicated and difficult. For example, a necessary stage in the manufacture of evacuated glazing is outgassing; that is, heating it to liberate any gases adsorbed on the inner surfaces, which could otherwise later escape and destroy the vacuum. This heating process currently means that evacuated glazing cannot be toughened or heat-strengthened. If an evacuated safety glass is required, the glass must be laminated. The high temperatures necessary for outgassing also tend to destroy the highly effective “soft” low-emissivity coatings that are often applied to one or both of the internal surfaces (i.e. the ones facing the air gap) of other forms of modern insulative glazing, in order to prevent loss of heat through infrared radiation. Slightly less effective “hard” coatings are still suitable for evacuated glazing, however.
Furthermore, because of the atmospheric pressure present on the outside of an evacuated glazing unit, its two glass sheets must somehow be held apart in order to prevent them flexing together and touching each other, which would defeat the object of evacuating the unit. The task of holding the panes apart is performed by a grid of spacers, which typically consist of small stainless steel discs that are placed around 20 mm apart. The spacers are small enough that they are visible only at very close distances, typically up to 1 m. However, the fact that the spacers will conduct some heat often leads in cold weather to the formation of temporary, grid-shaped patterns on the surface of an evacuated window, consisting either of small circles of interior condensation centred around the spacers, where the glass is slightly colder than average, or, when there is dew outside, small circles on the exterior face of the glass, in which the dew is absent because the spacers make the glass near them slightly warmer.
The conduction of heat between the panes, caused by the spacers, tends to limit evacuated glazing’s overall insulative effectiveness. Nevertheless, evacuated glazing is still as insulative as much thicker conventional double glazing and tends to be stronger, since the two constituent glass sheets are pressed together by the atmosphere, and hence react practically as one thick sheet to bending forces. Evacuated glazing also offers very good sound insulation in comparison with other popular types of window glazing.
Why Is Glass – Indispensible?
• Glass is an indispensable part of all buildings purely because of its unmatched qualities.
• Freedom from conventional building shapes, with unmatched aesthetics.
• Does not deteriorate, corrode, stain or fade.
• Transparent to visible light.
• Helps to maintain clean environment because of zero degeneration.
• It can be recycled indefinitely- structure does not deteriorate through the process.
• Glass is a pure and sustainable material.
• Helps to maintain hygienic environment with easy maintenance
• Glass touches various components of a building like :-
Ø External Façade
Ø Internal partition
Ø Shop fronts
Ø Glass floors
Ø Decorative application in interiors
Ø Fire resistance
Ø And many more…
Why Glass is important in energy conservation..
Ø For a standard building, Windows contribute approx. 41% of the total heat transfer
Ø This is for a WWR of 15% and naturally more the WWR, more will be the heat gain
Ø Right selection of glazing will positively impact the energy requirement of the building.
Glass – A Green Building Material
Right Selection of Glass
Ø Use tempered, heat strengthened or laminated glass
Ø Use Laminated Glass
Ø Select the types of lamination according to safety requirement & safety norms
For Sound Insulation
Ø Use laminated glass with special acoustic interlayer
Glazing Selection process:-
Effective Aperture Approach-Keep EA between 0.2 and 0.3. Larger windows will permit more light hence low-VLT glazing will do.
Bigger windows require better glazing.
Choose products with least SHGC and U value and optimum VLT.
Vary glazing selection by façade
Determine an optimum set of values for U-value, solar heat gain coefficient, and visible transmittance through more rigorous computer modeling with whole building simulation programs
Do’s in Indian context
• Add overhead shading
• Add internal shading
• Have more windows on North and South facades
• Use glazing with Optimum VLT ; low SHGC and U value
• Use dark tinted glass at visible height and clear at higher levels
• Use EA between 0.2 to 0.3
• Add light shelves to interiors
• Use high windows (ventilators in naturally ventilated buildings)
Don’t in Indian context
• Do not use glass with very low U value and moderate SHGC.
• Do not assume dark tinted glass brings solar control
• Do not use un-insulated frames
• Do not use Tempered glass as safety glass
• Do not use IGU as sound insulation glass