|Glass Type||Visible Light Transmittance||Ultra Violet Blockage||Relative Heat Gain BTU/HR-SQ FT||Winter U’Value||Winter U’Value w/Argon||Shading Coefficient|
|CLR SINGLE GLAZE*||90%||27%||215||1.11||N/A||0.98|
*Single glazed clear data reported for reference purposes only.
Analysis data supplied by PPG Industries and Cardinal Glass for glass as used in Metropolitan Vinyl Windows and may not apply to products as produced by other manufacturers. Standard design conditions available upon request.
All calculations performed using DOUBLE STRENGTH GLASS with ½ ” air space for a total insulated glass unit thickness of ¾”.
About the glass attributes chart. Here is an explanation of what this information means.
Relative Heat Gain – The total amount of heat gain through a glazing system at NFRC/ASHRAE specified summer conditions, incorporating the U-value and the Solar Heat Gain Coefficient. The conditions are 230 Btu/hr/ft², outdoor temperature of 89°F, indoor temperature of 75°F, and 7.5 mph wind.
[RHG=UsummerX (89 – 75) + SHGC x (230)] Expressed in terms of Btu/hr/ft²
Visible Light % – In the visible spectrum (380 to 720 nanometers), the percentage of light that is transmitted through the glazing relative to the C.I.E. (International Commission on Illumination) standard observer.
UV% – Conventionally, it is considered that UV (Ultra Violet) energy accounts for the majority of fading. This fading potential can affect fabrics, paints, artwork and other materials. To compare like products, UV transmittance (as a percentage) is used to indicate fading potential.
U-Value – The heat flow rate through a given construction expressed in Btu/hr/ft²/°F. Values are normally given for NFRC/ASHRAE winter conditions of 0° outdoor temperature, 70° Btu/hr/ft² indoor temperature, 15 mph wind and no solar load. U – values on this table are expressed in terms of the glass alone and compared to other glazing options.
Here is some additional energy terminology and information.
Argon Gas – Argon is a colorless, orderless, non-toxic, noncorrosive and nonflammable naturally occurring and non-reacting gas. Argon is insert and chemically inactive. Argon lowers the conductive heart transfer across the cavity of the insulated glass unit and improves the U-value.
Emissivity – A measure of a surface’s ability to emit long-wave infrared radiation or room temperature radiant heat energy. Emissivity varies from 0 (no emitted infrared) to 1 (100% emitted infrared). The lower the emissivity, the lower the resultant U-Value.
Low E Glass – Low E glass stands for Low Emissivity Glass. This type of glass coating was developed to provide improved solar heat gain coefficient performance.
Low E² Glass – Low E squared was developed to provide better summer daytime performance with only a slight reduction in visible light transmittance. Because of the excellent winter nighttime and summer daytime performance of Low E², it is becoming the popular choice for many residential window applications.
Sputtered Coatings (Soft Coat) – This is how Low E² is made. The advantage of this coating is that it provides overall qualities of high visible light transmission, neutral color, coating uniformity and low emissivity. This combination provides a nearly invisible coating with the highest level of performance possible.
Pyrolytic Coating (Hard Coat) – As the name implies, these coatings are applied to hot glass. This type of coating gives a “Mid-E” performance ar from that of Low E². It provides rather poor optical quality (color) and consistency of coating. Another disadvantage of pyrolytic coatings is that they exhibit high haze levels compared to that of Low E². Most Low E glass available today on the market is made this way.
Haze – Haze is the percentage of transmitted light which in passing through the specimen deviates from the incident beam by foward scattering. In essence, the higher the haze value, the poorer the product is for clarity. The haze % for Low E² is 0.14 as compared to anywhere from 0.74 up to 1.40 for pyrolytic Mid-E coatings.
Solar Energy Reflectance – In the solar spectrum (300 to 2500 nanometers), the percentage of ultraviolet, visible and near infrared energy from the sun that is reflected from the glazing surface(s).
Solar Energy Transmittance – In the solar spectrum, the percentage of ultraviolet, visible and near infrared energy from the sun that is transmitted through the glazing.
Solar Heat Grain Coefficient (SHGC) – The fraction of incident solar radiation which enters a building as heat. It is based on the sum of the solar energy transmittance plus inwardly flowing fraction of absorbed solar energy on all lites of the glazing. It can be expressed in terms of a window or the glazing alone.
Visible Light Reflectance – In the visible spectrum, the percentage of light that is reflected from the glass surface(s) relative to the C.I.E. standard observer.