advances in glazing materials
Current Options In Widow's Energy Efficiency 5Understanding How Energy Moves Through Windows 5Tomorrow's Options for More Efficient Windows 81. How energy flows through windows: Radiation 6 2. How energy flows through windows: Convection ..............................................6 3. How energy flows through windows: Conduction..............................................74. Three Routes to Switchable Windows. 10Until recently, clear glass was the primary glazing material used in windows. Althoughglass is durable and allows a high percentage of sunlight to enter buildings, it has very littleresistance to heat flow. During the past two decades, though, glazing technology has
How much does energy cost: in Califiornia for example where the rate for electricity per kilowatt-hour will be the most expensive in the nation, one can justify spending a lot more on energy efficient windows than if you live in Colorado where is cheap. Visible Light Transmittance - A measure of the amount of that portion of the total solar radiation visible to the human eye. Infrared Radiation - Invisible radiation that humans perceived as heat. Three Routes to Switchable WindowsLawrence Berkley Laboratory's Selkowitz thinks that electrochromics should be far easier to sell than low-e, or emissivity, windows, which already appear in more that 25 percent of the new commercial and residential windows. But the energy performance of hard-coat low-e films is slightly poorer thanthat of soft-coat films. Gray- and bronze-tinted windows reduce the penetration of both light and heat intobuildings in equal amounts (i. This first generation of superwindows nowavailable have a center-of-glass R-value of 8 or 9, but have an overall window R-value ofonly about 4 or 5 because of edge and frame losses. The coatings typically face air spaces within windows and reduce heat flow-betweenthe panes of glass. (Wilson, 1993)Spectrally Selective CoatingsSpectrally selective (optical) coatings are considered to be the next generation of low-e technologies. Your microclimate: One might live in a part of the country that is generally warm, but your house might be in a cold spot-for example, on the noth side of a hill where is it always windy. Soft-coat low-e films degrade whenexposed to air and moisture, are easily damaged, and have a limited shelf life, so they arecarefully applied by manufacturers in insulated multiple-pane windows. Heat- absorbing glass reflects only a small percentage of light and therefore does not have the mirror-like appearance of reflective glass. Glass absorbs radiant heat, or long wavelength infrared radiation, warming up in the process. (Wilson, 1993)Tomorrow's Options for More Efficient WindowsSuperwindows"Superwindows" now coming on the market can attain high thermal resistance by combining multiple low-e coatings; low-conductance gas fills; barriers between panes, which reduce convective circulation of the gas fill; and insulating frames and edge spacers.
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