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Before NFRC standardized energy efficiency ratings, each manufacturer developed their own methods. They often published misleading claims on their products' energy efficiency. For example, many manufacturers published center-of-glass u-factors rather than entire-unit u-factors, even though most of the heat loss occurs around the edges of a window.
A typical installation of insulated glass windows with uPVC frames. Possibly the earliest use of double glazing was in Siberia, where it was observed by Henry Seebohm in 1877 as an established necessity in the Yeniseysk area where the bitterly cold winter temperatures regularly fall below -50 °C, indicating how the concept may have started: [2]
In the United States, the efficiency of air conditioners is often rated by the seasonal energy efficiency ratio (SEER) which is defined by the Air Conditioning, Heating, and Refrigeration Institute, a trade association, in its 2008 standard AHRI 210/240, Performance Rating of Unitary Air-Conditioning and Air-Source Heat Pump Equipment. [1]
Window insulation reduces heat transfer from one side of a window to the other. The U-value is used to refer to the amount of heat that can pass through a window, called thermal transmittance, with a lower score being better. [1] The U-factor of a window can often be found on the rating label of the window.
R-values expressed in I-P units are approximately 5.68 times as large as R-values expressed in SI units. [14] For example, a window that is R-2 in the I-P system is about RSI 0.35, since 2/5.68 ≈ 0.35. In countries where the SI system is generally in use, the R-values will also normally be given in SI units.
The use of this rating scheme was extended to public and commercial sector in 2007 and from 2012 the operational rating is mandatory for both residential and commercial buildings. The rating system consist of a scale ranging from A to E basis, where A represent the most efficient and E represent the least efficient rating.
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Shading coefficient (SC) is a measure of thermal performance of a glass unit (panel or window) in a building. It is the ratio of solar gain (due to direct sunlight) passing through a glass unit to the solar energy which passes through 3mm Clear Float Glass. [ 1 ]