Very High Performance Glazing In Traditional Framing

Apr 02, 2012

For many centuries the benefits of daylight and vision through a single pane of residential clear glass far outweighed any discomfort from winter heat loss, condensation (or even icing), and any excessive summer heat gain from direct sunshine. The advent of low emissivity (Low-E) coatings (reducing the emissivity of glass from 0.8 down to about 0.1) controlled this major heat transfer mode and caused the vacuum unit to be re-invented to further reduce the overall heat transfer of double glazing.

It is not widely recognized that two types of Low-E coating are available: high solar IR transmitting; and solar IR blocking (by reflection or absorption). Residences from Seattle to NYC and north, including Denver and Salt Lake City, can typically achieve a net annual energy benefit from the free passive solar heating of high solar IR transmitting windows. Residences to the south of that line, and most large commercial buildings throughout North America have greater air conditioning loads than heating loads and so benefit from solar IR blocking glass.

Today’s VIG (composed of 2 plies of 3 mm (1/8 in.) glass, with Low-E coating(s) and a 0.7 mm (0.03 in.) gap supported by spacers on 25 mm (1 in.) centers) with high or low solar IR transmission, addresses all these heat gain and heat loss issues with a single piece of 6.5 mm (1/4 in.) thick glazing. Vacuum insulating glass can provide better insulation than plain, sealed triple glazing. A vacuum unit has a fraction of the weight of multilayer sealed units, fits into existing historic frames and sashes, and has the clear, non-reflective appearance of original traditional glass.

Christopher J. Barry (Pilkington NA Inc.)
Presented at: 
Building Enclosure Science & Technology (BEST3) Conference
Published & professionally reviewed by: 
Pilkington NA Inc.
Building Enclosure Technology & Environment Council (National Institute of Building Sciences)

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