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What does U-value mean?

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The u-value or thermal permeability coefficient corresponds to the k-value, and has replaced it in the course of the European unification. The heat loss that occurs from inside to outside is determined by the u-value per meter and per hour at 1° temperature difference. Metals or conductive materials have a higher and therefore poorer u-value compared to insulating materials. The measuring unit of the u-value is W/mK.
In other words:
• The lower the u-value, the less heat loss.
• The lower the u-value, the better the insulation.
• The more high-quality the windows, the less money is spent.
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Ug-value of window The Ug-values according to DIN 4108 part 4 (also for Europe) replaced the previously valid Uv-values in February 2002. Since March 2003, after publication of the Building Regulation 3/2002, they have also become obligatory building inspection wise. However, it is not just a mere name change, since the thermal permeability coefficient can indeed continue to be calculated in accordance with DIN EN 673, but in many insulating glass constructions the Ug-value differs from the Uv-value and is usually around 0.1 W/m²K higher.

Besides the calculation measurings according to DIN EN 674 or 675 can be done. On the other hand, the excess charges according to the Building Rules List no longer incur, which usally were necessary for the determination of the "official calculated value" or the "Federal Gazette-value".

The following four variables are included to calculate the thermal permeability coefficient: the emissivity of the thermal coating, the gaps between the panes, the type of gas filling and the level of gas fill.
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UV permeability The marking of the UV permeability of ultraviolet radiation occurs in a wavelength range from 280 nm to 380 nm. The radiation of the sun, which contains an ultraviolet radiation from 200 nm to 380 nm, is divided into the following ranges: UVA (380 nm to 315 nm), UVB (315 nm to 280) and UVC (280 nm to 200 nm). The UVC radiation does not reach the earth's surface and the UVB radiation is absorbed by the laminated safety glass. For different uses, a filtration of the UVA radiation by the glass is expected. For a laminated safety glass, the radiation permeability in the UVA range starts at about 360 nm at a total value of approximately 4% * when using a 0.38 mm foil, and about 2% * when using a 0.76 mm foil.

*The data on UV transmission is not binding, but only to be offered as additional information. The PVB foils influence the values of UV transmission, therefore the above mentioned values are taken from the data of the PVB foil manufacturer.
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