Glass Technology for Hot Climates
Window Performance in Cooling-Dominated (Hot) Climates
Creating Energy Efficient Window Performance in Cooling-Dominated (Hot) Climates
Window Performance in Cooling-Dominated (Hot) Climates
Windows in cooling-dominated climates transmit solar heat energy to the interior of the home. This energy from the sun comes in the form of short-wave infrared energy, which is transmitted through the glass and is absorbed by the floors, walls, furniture, people, etc. This energy is then re-radiated by the floors, walls, etc., as long-wave infrared energy or heat. (This is why your arm feels warm when placed next to a sunny window.)
This transmittance of solar heat through glass is measured by the term solar heat gain. Solar heat gain occurs during daylight hours only and is concentrated along a home’s east, south, or western-facing elevations.
Many cooling-dominated climates have weeks or even months where direct solar heat can raise interior home temperatures above the desired interior temperatures.
Solar heat transfer through windows occurs primarily in the glass area by the process of transmittance. Shading coefficient (SC) and solar heat gain coefficient (SHGC) measure the amount of solar energy transmitted by the glass. A lower SC or SHGC means less solar energy is transmitted through the glass and reaching the interior.
A small portion of solar heat transfer can occur through the window sash and frame by conduction (where the frame transfers the solar heat energy from the exterior side of the frame to the interior frame side).
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Creating Energy Efficient Window Performance in Cooling-Dominated (Hot) Climates
There are a number of glass-related options that window manufacturers can use to design energy efficient windows in cooling-dominated climates. Most of these approaches involve glass technology that reduces the transmission of direct solar energy through the glass. There are two glass categories that window manufacturers can use:
· Solar-Control Tinted Glass
Solar-control tinted glass can be used in a single-pane application or an insulating glass unit application. All tinted glasses provide some degree of glare control and provide a faint color appearance. Tinted glasses typically block the solar energy by absorbing the solar heat and re-radiating it outside as well as inside. When used in an insulating glass unit (with the tinted glass glazed to the outside), most of the heat re-radiated towards the inside is captured in the airspace and not transmitted to the interior of the home.
Tinted glasses available from PPG in residential thicknesses include Solarbronze®, Solargray®, Optigray®, Graylite®, Solexia™ (formerly Solex®), Azuria™ (formerly Azurlite®), and Atlantica™ (formerly Solargreen®). All of these tinted glasses can be combined with a PPG Low-E glass product to construct a higher performance insulating glass unit.
· Solar-Control Low-E Glass
Solar-control low-e glass must be used in an insulating glass unit. In addition to blocking more of the direct solar energy, it also improves thermal insulation (lower insulating glass unit u-values), which helps keep cool air inside and hot air outside.
Solarban® 60 is a solar control low-e glass from PPG.
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