1. Common Terminology Emittance Winter U-Factor or U-Value R-Value
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 it’s cold outside, and a lower glass temperature when it’s hot outside will contribute to comfort and energy efficiency.
Guardian Industries Confidential

2. Heat Moves From Where It’s Hot, To where It’s 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. Thermal Imaging Demonstrates Advances In Window Glass Technology
Double Glaze
Std. Clear Glass
Metal Spacer
Double Glaze
Std. Clear Glass
Foam Spacer
Double Glaze
Low-E Glass
Foam Spacer
↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ °F

4. Ozone Layer (20 – 25 KM Above Ground Level)
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 Rays
Visible Rays
Infrared Rays
UVC
100 – 380nm
380 – 760nm
280 – 320nm
UVB
UVA
320 – 380nm
760 – 1,000nm
Si3N4
Sno2
NiCrOx Ag
ZnO
TiO2
Glass
Scratch Resistance
Optical Filter
Adhesive Barrier
Thermal & Solar Performance
Performance Enhancer
Optical Enhancer
Barrier Layer
Glass

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. Retains Furnace Heat, Keeping You Warm When It’s Cold Outside
Low-E Glass Keeps The Heat Where You Want It, Regardless Of The Climate Or Season
Retains Furnace Heat, Keeping You Warm When It’s Cold Outside
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
U-Factor

7. Rejects Excessive Solar Heat, Keeping You Cool When It’s Hot Outside
Low-E Glass Keeps The Heat Where You Want It, Regardless Of The Climate Or Season
Rejects Excessive Solar Heat, Keeping You Cool When It’s Hot Outside
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
SHGC

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

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