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1 Common Terminology Emittance The ratio of the radiant flux emitted by a specimen to that emitted by a blackbody under the same conditions. This is expressed.

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Presentation on theme: "1 Common Terminology Emittance The ratio of the radiant flux emitted by a specimen to that emitted by a blackbody under the same conditions. This is expressed."— Presentation transcript:

1 1 Common Terminology Emittance The ratio of the radiant flux emitted by a specimen to that emitted by a blackbody under the same conditions. This is expressed as a number between zero and one. A lower emittance value indicates reduced radiative heat flow. Winter U-Factor or U-Value A measure of the amount of non-solar heat that is transferred through a window. This is usually expressed in units of Btu/hr-sq ft- °F. A lower U-Factor indicates greater resistance to heat flow and better insulating performance. R-Value A measure of the resistance of a window to non-solar heat transfer. It is the inverse of a U-Value (R= 1/U). A higher R-Value indicates greater resistance to heat flow and better insulating performance. Solar Heat Gain Coefficient The amount of the solar heat that is passed through a window. This is expressed as a number between zero and one. A lower SHGC indicates that less solar heat is transmitted through the window. Visible Light Transmission The amount of day light that is passed through a window. This is usually expressed as a percent. Ultraviolet (UV) Transmission The amount of the UV portion of the solar spectrum that is passed through a window. This is expressed as a percent. A lower UV transmission percent indicates greater protection of home furnishings from fading. Room-Side Glass Temperature This is the temperature of the glass surface that you can touch from the inside of your home. A higher glass temperature when its cold outside, and a lower glass temperature when its hot outside will contribute to comfort and energy efficiency.

2 2 Heat Moves From Where Its Hot, To where Its Not Radiation losses occur through the window glass and represent about 66% of total heat loss in a standard window Low-E glass dramatically reduces radiation heat loss Conduction losses in windows occur primarily through the edges of the glazing and through the sash and frames Changes in sash and frame construction, use of warm edge spacer material, and the use of inert gasses have reduced conductive heat loss Convection losses occur due to air movement caused by temperature fluctuation Air Leakage is a significant contributor to heat losses Window design and installation technique must be carefully managed to minimize air leakage

3 °F Double Glaze Std. Clear Glass Metal Spacer Double Glaze Std. Clear Glass Foam Spacer Double Glaze Low-E Glass Foam Spacer Thermal Imaging Demonstrates Advances In Window Glass Technology

4 4 Si3N4 Sno2 NiCrOx Ag ZnO TiO2 Si3N4 Glass Sno2 NiCrOx Ag ZnO Scratch Resistance Optical Filter Adhesive Barrier Thermal & Solar Performance Performance Enhancer Optical Filter Adhesive Barrier Thermal & Solar Performance Performance Enhancer Optical Enhancer Barrier Layer Glass Low-E Coatings Are Comprised Of Carefully Tuned Layers, Providing Thermal, Solar and Optical Properties. Ozone Layer (20 – 25 KM Above Ground Level) Gamma Rays X-Rays Ultraviolet RaysVisible RaysInfrared Rays UVC 100 – 380nm380 – 760nm 280 – 320nm UVBUVA 320 – 380nm 760 – 1,000nm

5 5 Low-E Coatings Have Changed Glass From An Energy Liability To An Energy Asset Standard glass has a high emissivity Furnace-generated heat moves freely from in to out. Solar heat moves freely from out to in. Low-E coated glass has a low emissivity Furnace-generated heat is retained. Solar heat is rejected. Low-E coatings act like a filter to manage heat transfer Some energy wavelengths pass through, while others are rejected Furnace energy (long wave radiation) Solar energy (short wave radiation)

6 6 Retains Furnace Heat, Keeping You Warm When Its Cold Outside U-Factor Low-E Glass Keeps The Heat Where You Want It, Regardless Of The Climate Or Season Escaping long wave energy (furnace energy) leads to discomfort associated with heat loss Better insulating performance (lower U-factor) minimizes home heat loss when outdoor temperatures are lower than desired indoor temperatures

7 7 Rejects Excessive Solar Heat, Keeping You Cool When Its Hot Outside Low-E Glass Keeps The Heat Where You Want It, Regardless Of The Climate Or Season SHGC Unwanted short wave energy (solar energy) leads to discomfort associated with excessive heat gain Low solar gain (lower SHGC) low-E eliminates overheating when outdoor temperatures are higher than desired indoor temperatures

8 8 Reduces Damaging UV Rays, Protecting Home Furnishings UV Low-E Glass Transmits Natural Daylight And Reduces Damaging UV Radiation Transmits Natural Daylight, Brightening Your Home And Your Mood Visible Light

9 9 The Evolution of Window Glass as Positively Impacted Comfort, Energy Efficiency, and the Life-Span of Typical Home Furnishings Heat loss has been reduced Heat gain has been reduced Day light has been maintained Fading and deterioration have been reduced


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