1.4.1 Solar Heat Gain Coefficient
The Solar Heat Gain Coefficient (SHGC) measures how well a translucent or transparent enclousure product blocks heat caused by sunlight.
The SHGC is expressed as a percentage, in decimals between 0 and 1. The lower the SHGC, the less solar heat it transmits. In passive solar design, south-facing windows with high SHGC ratings might be needed to provide a building with heat in the winter. Specific overhangs or window coverings—shades, blinds, mesh screens, and awnings—can also be used to reduce solar heat gain in the summer or as needed. The SHGC needs to be established in conjunction with and under consideration of the Visible Transmittance (VT).
To reduce the SHGC, manufacturers can apply a spectrally selective low-E coating to glazing, typically to the #2 inside surface if using a metallic “soft-coat”. This type of low-E coating can reduce heat loss in the winter as well as solar gain in the summer while still allowing for full light transmittance. Assemblies utilizing two metallic coatings, sometimes called Low-E2, are also available and perform better in the summer and cooling dominated climates. Reflective coatings, tinted glass, fritted glass and exterior shading can also help reduce the SHGC. Energy modeling and cost data are required to analyze first and operational cost savings.
Cost of higher performance glass and exterior shading can be offset by reduced size of mechanical equipment and significant operational cost reductions due to lower cooling loads.
Maximum protection from solar heat without compromising access to daylight and views. Reduced cooling loads.
SHGC requirements need to be established and evaluated in conjunction with requirements for visual transmittance. New vacuum glazing windows transmit as much as two-thirds less heat compared to today’s products.
1.4.2 Visible Light Transmission
5.1.1 Energy Modeling