Types of glazing
- One glazing unit;
- Double glazing unit;
- Triple glazing unit.
General information about glass. When one is examining windows, usually attention is drawn to the following components: frame, modes of opening, accessories and fittings, the paint. But often, spontaneously and unconsciously, one misses the glazing (unless it is dirty).
However, glass is an artificial product, which is currently produced using the cutting edge technology and latest developments, so its performance and quality is constantly improving and moving forward. Glass is the essential component of any window. It comprises a very large part of the frame itself, which affects the price, its thermal, safety and other properties. Unfortunately, recently the glazing has not been sufficiently regarded as a quality benchmark.
We understand glass as a natural element that does not require any explanation. However, it should be on the opposite. When ordering windows we should start with the glass and its properties. Also, not many people are aware of the very glass composition. Glass consists of: glaze, silicon dioxide, clean quartz sand mass that accounts for 70/72% of the flow, sodium carbonate or sodium sulphate (about 14%), stabilizer, calcium (about 10%), other oxides, such as aluminium and magnesium which help to improve the physical properties of the glass, especially its resistance to atmospheric factors. These components also determine the glass colour. For example, the addition of cobalt oxide, blue glass is produces; having added chromium oxide – green, and copper oxide gives a blue-green colour. Adding a small amount of very finely cut gold, ruby glazing is achieved.
Glass is not an individual material, but rather an alloy of several matter. The size of standard glass plates (sheets) is about 6,000 x 3,000 mm. All other larger sizes are calculated and produced individually.
Physical properties of glass
- Density. Glass has certain weight (about 2,500 kg/m3), which means that the glass sheet weighs approximately 2.5 kg per square meter, at the thickness of one millimetre. For example, 4 mm thick glass sheet of one square meter weighs 10 kg;
- Load. Glass features high resistance to compression, which is equal to about 1,000 N/mm2 = 10,000 kg/cm2, which means that in order to crush a glass cube, that is 1 cm thick, the load of 10 tons should impact it on one side ;
- Bending. Resistance to flexure highlights the compression of glazing sheet on one plane, where the load and the tensile strength value of glass bend is expressed as follows:
- 40 = 400 N/mm2 kg/cm2 polished glass;
- 120 N/mm2 = 1,200 kg/cm2 (depending on the thickness and type of treatment);
- High-value tempered glass resistance is ensured as both surface planes are tempered during the annealing process;
- Elasticity. Glass is a very elastic material, so that after the “stress” and permanent deformations it returns back into the still position exactly as before deformation. But at the same time glass is a very brittle material, i.e. no ductility, so when the load begins to increase during bending, the glass may break or shatter at any moment;
- Linear thermal expansion. Glass quality is expressed by empirical coefficient that measures the given length of the entire unit elongation, which is equal to 1°C (within the temperature range between 20 and 300°C). Linear thermal coefficient of glass expansion temperature is equal to 9×10-6 = 0.000009. This means that the 2 m long sheets of glass plate heated at the temperature of 40°C increase by 0.72 mm. This helps to better understand the linear thermal expansion coefficient λ values of other materials: wood 4×10-6, masonry 5×10-6, stone, 5×10-6, steel 12×10-6, concrete 14×10-6, alloy 23×10-6, polyvinyl chloride (PVC / plastic) 70×10-6, and to understand the typical “compatibility” between other materials and glass, and taking this into account, to select appropriate compatibilities among wood, aluminium and glass. It is also difficult to match PVC and glass. This factor obviously makes it easier and safer to fit the sealing of glass sheets and wood frame, and to calculate the advantage of transportation, compared with aluminium or PVC;
- Tempered shatterproof glass. Produced by mode of thermal treatment in order to increase its strength. Overall, this glass is about 5 times more resistant than normal glass. For example, the tempered 8 mm thick glass can withstand a fall from a height of 2 m and a strike of 500 g steel ball. For safety reasons such glass is used which when crashing would not injure anybody standing nearby, and would break apart into small pieces with blunt edges, helping to avoid injuries. This is especially important for large structures, internal home or office partitions: internal doors, tabletops, shower enclosures, and so on.
- Advantages of tempered glass:
- Laminated safety glass. Composed of two or more sheets of glass glued together with one or more PVB (polyvinyl butyral) films. In the event of accidental exposure and/or a glass breaking, this film keeps the glass stable until the change in force stops affecting the glass. Often this glass is used in these cases when you need extra protection or when you want the window to remain stable after any physical effects. The glass will always maintain the barrier, whether it is against break-in, accidental collision or even the gun shot or explosion. This is a glass, which will always be suitable for large windows, balconies, stairs, railings, roofs and other environments that require excellent glass stability;
- Solar control. These are the types of glass that reduce the transmission of solar energy (filter against sun rays). Particularly relevant for warm climates or during the summer season with the following factors present:
- high temperature;
- strong and prolonged solar radiation flux;
- high solar intensity and wind speed.
- The window screened with solar radiation filter is a way to control the flow of solar energy, which leads to a significant increase in room temperature, commonly known as the “greenhouse effect.” In order to buffer this phenomenon, it is recommended to use solar control glazing panes.
How does selective glazing:
This means two advantages. First it ensures solar control on the outer glazing. Second – a weak radiation on the inside surface of glazing unit.
In winter, solar radiation reflects unnecessary UV rays letting in the required amount of heat, and transmitting inside little radiation. In this way, the premises takes the required heat from the environment and allows you to have a large portion of the sun light.
During summer, sun control filter filters out the sun’s rays and thus limits the heat and infrared rays that heat the room. Currently, the latest means of solar protection can let in up to 60% of solar rays (light), buffering harmful UV and infrared rays emanating from the sun.
In practice, the impact is felt because of the decreased to approximately 60% of the sunlight falling through the glass. This means saving energy for air conditioning during the summer season.
Warm glass. Warm Glass – is a U value. Thermal insulation is particularly relevant during the cold winter season; if the U-value is low, then the inside temperature of the glass surface will remain higher and so will reduce the so-called “cold glass effect” effect, which will enable the following advantage:
- no unpleasant cold sensation from the glass;
- reduced dew effect / condensation on the windows;
- significantly reduced the environmental and residential heating costs.
U – value is thermal comfort, better glass insulation, more practical use of heat. These are the advantages that will have a positive impact not only in the cold season (winter), but will also soften the effects of summer heat, since the glass surface remains cool.
In order to increase the effectiveness for U-value to the maximum, it is necessary to choose certain glasses with selective coating.
The selective is a material which the inner glass is coated with. If it is a two-glass pane unit, it is laid on the first glass, if a three-glass pane unit – then on the second. The material prevents outward radiation of heat.
Heat reflection is created by heating devices indoors. It is reflected due to the low radiation selective, coated on the glass. Thus, the heat is stored indoors to the maximum. Selective features a low radiation coefficient, but conducts heat energy and a larger share of sunlight into the room.
There is a practical effect felt – significantly reduced heating costs.
The condensation phenomenon can be the reason to wall or glass moisture. It is condensation of dew on “cold” items, otherwise referred to as a “dew point”. When the outdoor temperature is lower than the inside, when there are cold things stored with high relative humidity present, water condenses on the coldest parts of the surrounding area. This is a very common phenomenon in the corners or junctions. So warm glass allows avoiding such an effect, of course, if there is no too high relative humidity in the home.
Thermal insulation is a glass protection against two different temperatures in the operating environment. As through any other type of material, so heat exchange occurs through the glass. Both through warm (inside or outside of the building) and colder (inside or outside of the building) glass. But in any case, the glass surface must remain clear that the solar ray transmission could take place as intended by the glass formula and would ensure the difference between the indoor and outdoor temperatures.
Heat exchange can take place in three propagation modes:
- Energy is transferred between two bodies that are in direct contact with one another. Because of temperature difference in the environment, thermal conductivity of the glass is λ = 1.0 W / (m • K);
- Convection is when heat is transferred through the solid surface radiation in liquid or gas streams;
- Radiation is the heat transfer that occurs between two bodies through radiation, with prevailing electromagnetic irradiation of different temperature, transmitted at the infrared wavelength, greater than 5 mm, and proportional to the radiation of the surface. At low radiation, heat exchange is poor. For normal glass r = 0.89 (r – is the thermal convection, the equivalent used in construction industry), and few glasses may feature particularly low radiation coefficient (also called “low-E”) e <0.10;
Most importantly, the lower the U value, the lower the heat loss is, and to the contrary – higher thermal insulation (insulating power). One glass (4 mm thick) heat transfer coefficient is equal to U = 5.8 W / (m2 • K).
In order to increase thermal insulation and to reduce U-value, usually, as a starting point, it is common to use double glass units, which are inter-connected with a thermal frame and arranged to the greatest distance. This is done so that the gas mixture that is used to fill the gap between the glass units would set up the “insulating glass”, which would reduce the U-value. Standard double glass unit is 4 (4mm thick glass) + arg. (argon – gas filler) x 16 (space between the panes) + 4 (4mm thick glass) U = 2.7 W / (m2 • K). If you want to achieve even better results, then three or even four glass units are used, and these can be also filled with other gases, such as krypton (but this type of gas is very expensive). The warmest packages glass units are the ones whose interior is free of any gas. However, today’s technology does not produce a sufficient amount of such holdings.
Light and UV rays – Solar control. When solar energy reaches the earth, the rays create the wavelength of electromagnetic radiation, which is between 0.28 and 2.50 micron, 1 micron (μ) = 10-6 m. The light sensation felt by people is only due to the radiation. After such solar energy passes inside the room through the glass, it is absorbed by the interior objects and the walls that are heated. They, in turn, re-radiate (mostly infrared rays – more than 5 m) the heat, thus creating the heat effect, otherwise known as the “greenhouse effect.” In order to avoid overheating, one can use glass with a limited solar energy transmission ratio, otherwise known as the “solar control” glass, which allows to buffer part of solar radiation to the maximum, block the UV rays and also allows to maintain certain lighting with natural light, depending on the formula of glass panes and glass configuration.
Of all building materials only glass can protect from the environmental impact while at the same time providing the opportunity to observe the outside world. Variety of glazing types enable one to choose the desired light that enters through the window, characteristics. Key indicators describing the window light characteristics are as follows:
- Light transmittance coefficient (LT) – the ratio of light transferred to the room with the falling light beam;
- Light reflectance coefficient (LR) – the ratio of light reflected outwards with the falling light beam;
- Solar factor (g) or total transmission – share of total solar energy falling within the premises. This is the sum of solar energy that is directly transmitted, absorbed and reflected into the premises.
The bigger the light transmission coefficient of the window, the more of daylight enters into the room.
Light is actually very important to all living organisms and their quality of life. The most important thing is that a certain output of light makes the environment even more comfortable. Glazing in the window frame acts as a “filter”. It can magically tame and soften the intensity of light at home, so that it can be exploited as needed. Window glazing is always carrying a grandiose control of light contact with the outside world. In the design of buildings, one usually wants to see large windows. The most preferred area should be from 35% to 45% of the total facade area. It is important, where you will be fitting the windows. One should consider whether they will facing the north, where there is the minimum of sunlight received, or the south, where one can take advantage of the sunlight and make use of it in the winter.
We use special programs to help you select optimal glass and allows you to get the right amount of natural light into the building.
Glass and safety. Glass can perfectly protect against theft or vandalism. Of course, it is equally important to evaluate window frames, which are manufactured according to strict safety requirements and are regulated by legal acts. Window production technology enables to achieve the features protecting those standing around from accidental breakage, which currently is the most relevant to protection against any strokes.
The level of protection depends on the two materials, as follows:
- Laminated glass;
- Tempered glass.
These glasses protect from:
1. Accidental damages. Usually these are the risky places in the facades, windows at knee height and doors. That is what the definition of “safe glass” is used for. This may be tempered or laminated glass.
2. Risks of objects falling on the roof windows. Laminated glass protects against accidental falls and glass damage after a collision.
3. Vandalism, theft, or similar hazards. Such blows as attempts to break in with an axe, a hammer or crowbar.
4. Firearm. This kind of protective effect must meet international and local regulations in accordance with EN1063, which defines seven classes in order to cover virtually all needs of security against all weapons.
Laminated glasses feature high compression strength, but low resistance to bending, therefore can usually shatter into many small and sharp fragments that can cause a variety of health impairment. To avoid this, you can use glass with high resistance. In other words, instead of ordinary glass the tempered glass is used rather. This creates additional security.
Glass and acoustic insulation. Major advantage of the window with silent glazing is that it protects against the outside noise. Sound insulation is defined by the index, which is perceived in different frequencies (low, medium or high – in the amplitude from 50 to 5000 Hz). Noise assessment is expressed in decibel scale – dB. One glass panel features sound insulation, which is 10 and 15 dB, for example, when the glass is 4 mm thick, the critical frequency corresponds to 3000 Hz, and 13 mm thick plaster board corresponds to 3200 Hz. By increasing the thickness of the glass (as one glass or laminating), and increasing gaps in the glass units (the wider the better), it reduces the intensity of the sound, and mutes low-frequency noise (particularly typical for road traffic noise).
Usually a comfortable sound level should not exceed 35 dB intensity during the day, and 30 dB at night.
Sound, as it is known, consists of different-frequency sound waves, therefore even the slightest body (material) during the fall or movement causes so-called critical vibration excitation frequency, in which more or less all the bodies vibrate (and thus transmit the sound). This is how one or another kind of sound strength, in other words, noise is caused. With information in hand about the environment that surrounds the building, and sound measurement data, we can easily select the appropriate glazing units that will protect against extraneous and unnecessary sound emanating from the environment.
Sound attenuation is highly influenced also by the window frame, the type of material it is made. Physiologically, the windows manufactured from aluminium or PVC manufactured conduct (or vibrate) more than those made of wood (as well the type of wood is important), because wood is thick enough, not a hollow profile (like PVC or aluminium). For this reason, the same glazing unit in wooden windows will be more efficient and feature better protection against sound than windows made of aluminium or PVC. However, what is important about wooden windows is how they are assembled, and in what way the glazing is fitted in window frame, and how it is filled with silicone.
In conclusion it may be recalled that sound is made up of many frequencies. The frequency type, from low to high, determines the nature of noise or sound intensity. Frequency is expressed in hertz – Hz (vibrations per second). The higher the frequency, the more oscillations are transmitted per second.
To mute the noise it is not enough to just increase the thickness of the glazing. Such increase in thickness of the glass only moves the noise peak to different frequencies.
To mute the noise there are films used between the glass panes, laminated from one or more layers. They ensure good sound insulation and reduce the vibration of the glass or the construction itself.