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Strategies for Success: Window Systems

As an education facility ages, many of the systems and equipment that make up the building begin to break down. When school windows stop functioning the way they were designed to, facilities can be vulnerable to energy waste, security breaches and building deterioration.

The good news for institutions that need facility renovations is that today's window systems offer much better energy efficiency and security measures than those installed in schools a generation ago.

Low-emissivity (low-e) glass has a special coating applied that allows light to come through, but reflects much of the heat that otherwise would flow through the window into or out of the building. The rate at which a window lets heat flow through is expressed by the “U-factor.” The lower the U-factor, the more energy-efficient a window is. Double-pane windows with an inert gas such as argon between the panes also will enhance a window's ability to keep heat from entering or leaving a building.

Another way to upgrade the energy efficiency of a window system is to apply window film to the glazing. Low-e coatings are applied while a window is being made, while film can be applied to existing windows. The film can bolster safety and energy efficiency. It not only will reduce the amount of solar heat and ultraviolet rays that penetrate the building, but also will make the window more shatter-resistant. When such film was introduced years ago, its effectiveness often was undermined because the film was too reflective and could be scratched easily, but the latest products do not succumb to those problems.

The U.S. Department of Energy's Energy Design Guidelines for High-Performance Schools offers these guidelines for choosing appropriate window glazing:

  • For windows oriented east and west and not externally shaded, the best choice is to use a tinted glazing with low-e or low-e with argon.

  • If a window is north-facing or well shaded by overhangs or other building elements, tinting is not recommended.

  • For windows close to the floor, comfort becomes more critical, and low-e windows are a good choice.

  • If windows are above lightshelves or in roof monitors as part of a daylighting strategy, the best choice typically is clear double glazing or clear double glazing with argon.

In addition to the type of glass installed, the frame used in a window system can affect its durability and energy efficiency.

“Frames are available in metal, wood, vinyl, composite, and fiberglass,” says the U.S. Department of Energy's Best Practices Manual for High-Performance Schools. “Metal frames conduct the most heat and must have a thermal break for good performance. Insulated vinyl and fiberglass frames have the lowest U-factor.



Percentage by which a typical school's energy bill could be reduced if it were made energy-efficient.


Amount that could be saved each year if school facilities used energy more efficiently.


Number of additional teachers that could be hired if school facilities used energy more efficiently.


Percentage of a typical school's energy use that goes for lighting.

Source: U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy

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