保温材料 Building Envelopes围护结构.ppt

中空玻璃热学参数表 (3) Spectrally selective coating A special category of low-e coating is spectrally selective. This coating is optically designed to reflect particular wavelengths and be transparent to others. Such a coating is commonly used to reflect the infrared (heat) portion of the solar spectrum but admit a higher portion of visible light, creating a window with a low U-factor and low SHGC, but a high VT. (4) Inert gas fill Inert gases are ones that do not react readily with other substances (e.g., argon, krypton). Because these gases have a higher resistance to heat flow than air, they (rather than air) are sealed between the window panes of windows with insulated glazing (and usually a low-e coating) to decrease a window’s U-factor. (5) Heat-absorbing (or tinted) glass Heat-absorbing glass contains special tints that change the color of the glass. Tinted glass absorbs a large fraction of the incoming solar radiation, which reduces SHGC, VT, and glare. Gray and bronze tints reduce the penetration of both visible light and heat into buildings in equal amounts and are the most common colors used. Blue and green-tinted windows offer greater penetration of visible light (higher VT) but also heat (higher SHGC). Heat-absorbing glass reflects only a small percentage of light and therefore does not have the mirror-like appearance of reflective glass. (6) Reflective glass Reflective glass is coated to reflect radiation striking the surface of the glass. The reflective coating usually consists of thin metallic layers and comes in various metallic colors (silver, gold, bronze). Reflective glass reduces the passage of solar radiation through the window, generally blocking more visible light than heat. It reduces SHGC and greatly reduces VT and glare. Reflective glass is most useful in hot climates in which solar control is critical, and it is usually used just for special applications. Reduced cooling energy demands may be offset by the need for additional electrical