Volume 25, Issue 5 - September/October 2011

Glass Tech

Building Better Performance
Glazing Can be a Key to Energy and Cost Savings
by Helen Sanders


According to the U.S. Department of Energy (DOE), windows consume 30 percent of building heating and cooling energy and have an even higher impact on peak demand and occupant comfort. Significant improvements are needed in building façade performance, especially if the American Institute of Architects’ 2030 commitment to carbon neutral buildings and the DOE’s 2030 net zero energy goal are going to be met.

There has been some debate recently over whether we need to reduce the use of glass in buildings. This is because, compared to walls, windows have higher heat conduction and higher solar heat gain. However, the most effective way of improving the energy efficiency of the façade is not necessarily to reduce the window-to-wall ratio, but to implement integrated façades that can save energy by optimizing the utilization of natural daylight to offset electric lighting, which accounts for 20 percent of electrical energy usage in buildings. Integrated façades combine automatically controlled dimmable lighting with the appropriate amount of glass in the right locations on the building envelope.

Integration Options
To provide dynamic glare control, dynamic glazings or automated mechanical shades with high-performance conventional glazing may be used. In fact, integrated façades in combination with highly insulating windows with dynamic solar control are key components of the DOE’s road map for zero energy commercial buildings.

Product Selection
Glazing products with increasingly higher performance and capability are becoming available, which allows for performance optimization of integrated façade designs. For example, the use of triple glazing is becoming more prevalent in northern states with U-factors in the range of 0.18-0.23 Btu/ft2.°F when one low-E coating is used (compared with ranges of 0.25-0.29 Btu/ft2.°F for dual pane low-E products with argon). The performance can be increased further by using low-E coatings on two surfaces.

Active Control
For further enhanced energy performance through variable solar control, dynamic glazing products are available and cost competitive with conventional solutions involving mechanical shading. These products provide a dynamic response to the changing exterior environment, providing the means to capture useful daylight when available, yet block the sun’s glare and solar heat when required.

Even though it is not yet 2030, the high-performance glazing products available today when combined with effective daylighting strategies already have the potential to deliver high-performance façades, which maintain the glazed area while improving energy performance and occupant comfort. Additional information about energy-efficient glass and glazing is also available on the Glass Association of North America’s website at

Dr. Helen Sanders is the vice president, technical business development for SAGE Electrochromics and has served as the chair of the Glass Association of North America’s Energy Committee.


Architects' Guide to Glass & Metal
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