Before specifying efficient heating and cooling equipment, it’s important to do what we can to reduce heating and cooling loads. Insulation is one of the key products to consider here, but because there are so many insulation products on the market, we look for additional benefits. Examples include cellulose insulation with recycled content, mineral wool insulation with no flame retardants, and fiberglass insulation with no formaldehyde binders. Other products in this area are high-performance windows and glazings, products that contribute to building airtight envelopes, products that reduce thermal bridging, and window-retrofit products.
With products in this area under constant development, we are always refining our approach. For example, as we have learned about insulation products with hazardous flame retardants and blowing agents that have high global warming potential, we have removed those products from GreenSpec, pending manufacturing changes. We encourage building professionals to pressure manufacturers for those changes through specification language and purchasing decisions.
Pilkington Energy Advantage
Pilkington Energy Advantage is a hard-coat (pyrolytic), low-e glass with an emissivity of 0.15. In a double-pane unit, a SHGC of 0.7 is achieved. This is an excellent glazing for use in passive solar buildings on southern orientations where solar gain needs to be high.
In commercial buildings, architects have long specified the thermal, structural, and aesthetic properties of glazing.
With residential windows, designers and builders have also become involved in specifying glazing, as advanced glazings have become available since the 1980s that reduce heat loss and regulate solar heat gain. It is even becoming common practice with high-performance buildings to specify different glazings for different orientations--choosing glazings that block most of the solar heat gain for east and west windows while choosing glazings transmit more solar gain on the south for passive solar heating.
Key properties to consider when specifying glazing include the following.
Solar heat gain coefficient (SHGC) is a value from 0 to 1 that indicates the ratio of solar heat gain coming through the window to the incident solar energy striking the window. High-SHGC glass (over 0.33 SHGC) is beneficial for passive solar heating, while lower numbers are essential for cooling-load avoidance.
U-factor is the rate at which heat moves through a window or glazing system for a given temperature difference; not including direct solar gain or air leaks. High-performance buildings are pushing for lower and lower U-factors: less than 0.30 is recommended in most situations, and whole-window values as low as 0.13 are possible.
Visible light transmittance (VLT) is a value from 0 to 1 that indicates the amount of visible light transmitted through the glazing. Higher VLT glass looks clearer—anything below 0.40 starts to appear noticeably gray.
GreenSpec lists glazing that offers strong energy performance properties for a variety of applications. Careful selection of glazing for specific applications is critical for optimum energy performance and building comfort. Some glazing listed by GreenSpec allows these performance properties to change based on user desires or ambient conditions. GreenSpec also lists glazing products that help minimize bird collisions or deliver other environmental benefits.
LEED Credits
EAc1: Optimize Energy Performance
EAp2: Minimum Energy Performance
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