Photo ©Tom Heidrick
Ballard High School, Huxley, Iowa, has 18,000 square feet of high-performance glass.

High-Performance Design

Oct. 1, 2012
Advanced techniques in high-performance glass can contribute to sustainable school construction.

For years, educators and architects have understood the benefits of incorporating daylight into building design. However, within the last 10 years, significant technological advancements have improved the glass used in buildings. These advancements have contributed to sizable energy savings and created more enjoyable spaces for students and educators.

The following techniques and advancements in high-performance glazing can be incorporated in new construction projects, or the replacement of existing glass. These techniques are common, and "building decisions should be made within the context of the whole building as a single functioning system, rather than as an assembly of distinct parts," according to "Tips for Daylighting with Windows: The Integrated Approach," from the Lawrence Berkeley National Laboratory.

These techniques and advancements include:

  • Tinted glass. Many glass tints and colors are available, including green, gray, bronze and blue. Low-iron glass has become more popular over the last few years, and is "clearer" or less green in appearance than standard clear glass. By using a glass type that is not clear or low-iron, schools will be letting in less light and lowering the solar heat gain coefficient (SHGC) — effectively reducing the amount of solar heat entering the building. This is important because 40 to 50 percent of the total energy consumed by buildings is for producing electric light and removing the heat it produces.

  • Low-E coatings. Low-E, or low-emissivity coatings have been around for decades, and hundreds of low-E coatings are available. They have become more commonplace in schools over the last 10 to 20 years because of building codes that require high-performance glazing to meet higher energy requirements.

    There essentially have been three generations of low-E coatings, and each is unique in performance and appearance. The original coatings were reflective — their properties mimicking their name. They have low visible light transmission (VLT) and excellent SHGCs. The next generation of coatings shifted away from highly reflective to more transparent. These were low-E coatings with very high VLT and higher SHGC values.

    Having a higher amount of visible light also increases the amount of heat entering the building. The latest generation of coatings falls somewhere in the middle. These coatings have average degrees of reflectivity and performance values.

    One additional coating that should be mentioned is called a triple silver low-E coating. Within this coating, three layers of silver are used. It has extremely good solar performance, along with higher visible light transmission values. The silver provides a slight green appearance in the low-E coating. The more layers of silver that are used, the greener the coating appears. A low-iron glass substrate can be used with triple silver coatings to minimize this slight green appearance.

    A few issues should be considered when determining which low-E coating to use. Performance is one factor, but the appearance of the coating may play an equally important role. Each coating has a unique appearance, lending itself to specific designs.

    A third factor might be the size of the openings. With an increase in glass sizes, a lower VLT might be used compared with a project where smaller windows are used. Schools should be cautious when selecting glass with a higher VLT in any instance. There always is a possibility for issues related to glare when specifying high VLT coatings. A high-VLT coating on smaller windows might create areas inside the space with very contrasting areas of light and dark.

    When applied to the various glass substrates, low-E coatings should provide a balance between visible light transmission and solar energy control. A coating can reduce heat gain by about 50 percent compared with a similar unit that has no a coating. Reducing the heat gain in turn will lower a building's energy costs.

  • Silk-screened ceramic fritting. The process of silk-screen printing on glass has been around for more than two decades, and it is used for two primary reasons: to increase the performance of glass that is used in schools, and for the visual effect it provides to the appearance of the glass. The paint used is ceramic-based, and once applied, must be fired to the glass. The glass is then run through a heat-treating furnace, and the paint essentially becomes part of the glass. Most manufacturers have standard line, dot or hole patterns, and offer them in a variety of standard colors including white, black and multiple grays. Most offer the capabilities for custom patterns and colors.

    One benefit of adding a ceramic frit to glass is that it may reduce the number of bird collisions with the glass. Although ongoing testing is necessary to further review the effectiveness of the various silk-screen patterns and coatings — such as those with low, medium and high levels of reflectivity — it is evident based on the testing done thus far that silkscreen patterns can be an effective way to reduce bird collisions with glass.

    In addition, by adding the silk screen, the solar performance of glass is improved. Adding a silk screen will reduce the VLT and SHGC, again leading to a potential savings in energy costs compared with a similar glass type without a silk-screen.

  • Laminated glass. Laminated glass also has great potential to improve certain areas of building performance. It will help reduce the amount of ultraviolet (UV) light that passes through the glass. UV is the portion of the spectrum that fades fabrics and finishes.

    Laminated glass typically will have less than 1 percent UV transmission. Using it also is an excellent way to improve acoustic performance in an insulating laminated makeup. A standard 1-inch insulating unit has a Sound Transmission Class (STC) rating of 35, compared with a standard insulating laminated unit, which has an STC of 42 resulting in a 20 percent improvement.

    Studies have shown that reducing the amount of outside noise will improve a student's ability to focus. Finally, laminated glass typically is used in areas where codes dictate safety glazing.

Daylighting benefits

Multiple studies have shown that a student's health and test scores are bolstered by improved daylighting. Improved daylighting is not the maximizing of daylight, but rather "right-sizing" the amount of daylight for a specific building or space.

The four techniques covered above combine to make up a high-performance glass system. Each solution is unique — there is not a "one solution fits all" for a high-performance glass. Designers need to consider the comprehensive options of architectural glass before coming to a solution that will satisfy and sustain.

Lawrence is an architectural design specialist with Viracon, Owatonna, Minn. He can be reached at [email protected].

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