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About Low-E Glass / Window


As it is known, glass material is one of the most common materials used in a wide variety of areas in the construction field. One of the most important reasons for this is that the ability of glass to provide better daylight illumination and thermal comfort of building interiors over time is constantly improving. One way to achieve this performance is with Low-E coatings that help provide passive control of sunlight.

In order to understand the Low-E coating better, it is important to understand the solar energy spectrum, in other words, the energy coming from the sun. Because, within the total energy coming from the sun, it also includes wavelengths that can adversely affect human health and material.

As you can see in the table on the side, the sun is located in different parts of the spectrum as ultraviolet (UV) (ultraviolet) light , visible light and infrared (infrared ( IR )) light. The difference between these three is determined by their wavelengths.

  • Ultraviolet (UV) (ultraviolet) light : It causes indoor materials such as fabric and wall coverings to fade and lose their color over time. The wavelength range is between 310-380 nanometers.

  • Visible beam: Wavelength range lies between 380-780 nanometers.

  • Infrared (infrared (IR)) ray or heat energy is transmitted to the building as heat energy and its wavelength starts from 780 nanometers.

Low-E coating glass has been developed to reduce the UV and IR rays passing through it without reducing the visible light quality.

When heat or light energy is absorbed by the glass, either the direction of action is shifted by air movements or it is radiated away again by the glass surface. The ability of a material to spread energy is called emissivity. Generally, highly reflective materials have low emissivity. Dark, black colored materials have high emissivity. Decreasing the spreading ability in window elements increases the glass insulation feature. For example, while an uncoated glass emissivity ability is 0.84, with a sun-controlled coating the glass coating emissivity ratio can be reduced to 0.02. In other words, these coatings are of great importance in order to prevent the heat in the house from being dissipated by the glass.

Low-E lenses contain microscopically thin clear coatings - thinner than a human hair - that can reflect unwanted IR rays or energy. This feature is beneficial in the following way: During the winter period, the indoor heat energy tries to escape to the cold area, while the Low-E window stays inside due to its ability to reflect the heat back. Thus, heat loss is prevented and efficiency is increased. For example, thanks to the silver thin coating of the part of the glass facing the interior of the building, the indoor temperature is preserved, it prevents the occurrence of heat difference between the parts close to the window and the other interior, and the user comfort is increased in every part of the house.

Generally, there are two different types of Low-E coated glass. These are Passive Low-E coating and Solar controlled Low-E coating.

Passive Low-E coated glasses should be preferred in very cold climates . Because, while it allows some of the IR rays to enter the building in winter, it allows the building to heat (thanks to the outer surface feature), while it prevents heat energy loss thanks to its ability to reflect the indoor heat (inner surface feature).

Most of the solar controlled Low-E coated glasses will be more appropriate to use in humid and hot climates, especially in commercial center buildings, when the air conditioner is operating for a long time.

Both types of glass, passive or solar controlled Low-E glasses , provide the opportunity to achieve good performance. The following terms are used to measure the effectiveness of Low-E glasses:

  • U-Value (U Value) (Heat transmission coefficient): This evaluation indicates how much heat loss the window will cause. That is, the lower this value means, the more heat loss can be reduced.

  • Visible Light Transmittance (VLT): Indicates how much light has passed.

  • Solar Heat Gain Coefficient (SHGC): The smaller this coefficient value, the lower the solar heat input.

  • Sun-Light Ratio (Light to Solar Gain) (LSG): Indicates SHGC / VLT value.

Advantages of using Low-E glass / windows:

* For the reasons we mentioned above, the building's indoor energy conservation is ensured, energy consumption is reduced and energy savings are achieved . That is, the air conditioner used to cool the house in the summer and the energy used to heat the house in the winter can be better controlled, so a more affordable bill comes.

* It allows more outdoor glass coating, therefore factors such as sunlight and scenery can be increased, increasing indoor user comfort . At the same time, the electricity bill can be reduced as the lighting can be met more naturally.

* It prevents the formation of cold / hot areas in the parts of the building close to the windows. For this reason, by keeping the temperature values at the same levels in almost every part of the house, the area usage capacity is increased.

Another important issue to be aware of;

It should not be forgotten that the window joints are well insulated and controlled.

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