In houses systems of heating, conditioning and lighting consume about 67% of all consumed electricity.
In Russian climate conditions in a typical home through Windows lose up to 50% of energy for heating. Proper installation of energy efficient Windows can help to eliminate air leakage and minimize the need for heating, cooling and artificial lighting.
- Heat loss through the glass occur due to the radiation.
- Heat loss through the structure that separates the glass and through the window frame occur due to the heat.
- Due to the movement of air in the space between the panes the heat loss occurs by convection.
- Between moving or opening parts of the frame heat loss occurs through air infiltration.
Energy-efficient Windows. Key indicators
There are indicators such as , by means of which it is possible to estimate the heat loss through the window. This figure could apply to all window construction (glass, frame etc.), or just the glass. A small value of U-factor indicates that a window has good heat-insulating properties, and thus more energy efficient. The value of U-factor of 0.30 or lower is considered very good.
characterizes the fraction of solar heat energy that passes through the window. For areas with cold climates are more suitable for Windows with a high SHGC value (> 0,55) (i.e., for Russia it is better to use such a window), while in areas with a hot climate it is better to use Windows with a low SHGC (<0,40).
— measured in m3 of air passing through m2 of the window area. The lower the number, the less air will pass through cracks in the Assembly. Manufacturers of low-quality Windows can omit this parameter. Windows should have the metric value leaks at least 0,02788 m3 per minute per m2 of the window.
— determines the ability of a window to resist condensation on the inside of the glass. The higher the number, the better.
characterizes the amount of visible light that can pass through the window. VT can vary from 0 to 1, where 0 means completely darkened the window, and 1 corresponds to the transmittance of the entire visible spectrum. A high value of VT can improve natural lighting and reduce the need for artificial lighting. If tinted glass or coated glass are not spectral-selective (spectral selective coating, pervious to visible light, but do not pass infrared radiation) that they can reduce the transmittance of visible light. To the spectral selective glazing are low-e glass Low-E which will be discussed further.
characterizes the ability of glass to pass the light of the sun and not to let the heat flow. The LSG ratio is the ratio of visible light transmittance VT the gain coefficient SHGC solar heat. The high value of LSG suggests that through the window is a lot of light and a small amount of heat.
To provide comfort and warmth, the most acceptable are Windows with two or more Windows, the maximum energy savings provide Windows that are made of different distances between the plates.
is the glass coated with the coating of metal oxide, which prevents the passage through it of thermal radiation (radiation with longer wavelengths), while permitting visible light (radiation with shorter wavelengths), the Addition of the coating Low-E provides additional insulation and can be the equivalent of an additional pane of glass. Coatings to protect from condensation on the inside of the Windows, and the fading of fabric, paper, or wood furniture.
such as argon or krypton can significantly improve the insulating properties of Windows as they are a better insulator and sound insulator than air. Manufacturers may use a mixture of gases, as argon is less expensive, and krypton is a more effective insulator.
Also recently received the technology of electrochromic Windows or smart glass, which in the future may be very popular, as it allows better use of sunlight. Glasses change its optical properties when passing an electric current through them, this allows you to control their opacity depending on the lighting and the preferences of the person.
Measures to ensure energy efficiency of Windows are not limited to the installation of Windows with good features. The use of curtains, blinds, plants can help to keep cool in the summer, when the sun is high in the sky. Possible in the design of the Windows in the house need to consider the location and climatic features of the area. For example, in colder climates, Windows with a high SHGC value should primarily go to the South, so that through them penetrated more heat in the winter, when the sun is low on the horizon.
On the other hand, through Windows that face North, as a rule, passes more light than heat. Properly placed Windows can reduce the need for artificial lighting, allowing greater penetration of sunlight. For natural lighting of premises, where it is impossible to install horizontal window or it is necessary to increase the luminance, it is possible to consider different systems, for example, light guides and lamps.
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