Window Systems

For schools and universities that have not upgraded their windows in many years, a variety of options are available that can make facilities more comfortable, energy-efficient and more conducive to learning.

The Efficient Windows Collaborative, a coalition of manufacturers; federal, state and local government agencies; and research institutions, has put together a "Tools for Schools" guide that provides administrators with information about the types of windows available and the benefits they offer.

“Different glazing and frame materials and special assemblies can provide insulation value, sun control, and daylight redirection as appropriate for a given room or building,” the guide says.

Glazing options:

  • Tinted glass: It reduces glare from the outdoors and reduces the amount of solar heat transmitted through the glass.

  • Highly insulating glazing: Gas fills and additional glazing layers can further improve a window's insulating value. The additional layers reduce heat loss, as well as visible light transmission and solar heat gain.

  • Laminated glazing: This type of glazing consists of a tough plastic interlayer that is bonded between two panes of glass under heat and pressure. It offers increased protection from the effects of hurricanes or earthquakes. Another benefit is that laminated glass reduces noise transmission, the guide says.

  • “Smart” glazing: This glazing reacts to solar heat gain and glare, and can change from clear to tinted. “Smart glazing could reduce peak electric loads by 20 to 30 percent in many buildings, increase daylighting benefits, and improve comfort and learning environments in schools,” the guide says.

  • Low-e coatings: These improve the insulating properties of window glazing by reducing the amount of heat that is transferred through the glazing. “Of particular value for school buildings are coatings that reflect heat from solar infrared while allowing the visible light spectrum to enter,” the guide says. “These coatings are called spectrally selective.”

  • Reflective coatings: These can be used for greater reductions of glare and solar heat gain. “These coatings can reduce solar heat gain substantially, but visible transmittance usually declines even more, which is problematic if daylighting is desired,” the guide says.

Window-frame options:

  • Aluminum: This material can provide great structural strength, but it has high thermal conductance, which increases the potential for heat loss and condensation. To combat this, aluminum frames often have thermal breaks, which split the frame into interior and exterior parts, joined by a less conductive material.

  • Wood: It has good thermal performance, but is susceptible to rot and can require a lot of maintenance. The guide notes that cladding the exterior face of a wood frame with either vinyl or aluminum creates a weather-resistant surface and can reduce maintenance requirements.

  • Wood/polymer composites: Composites meet or exceed the structural and thermal properties of conventional wood, and are more resistant to moisture and decay.

  • Vinyl: These window frames require little maintenance, do not require painting, and have good moisture resistance. The guide notes that for structural integrity, larger vinyl units often will incorporate metal or wood stiffeners. In changing temperatures, vinyl expands or contracts more than wood, aluminum or fiberglass.

  • Fiberglass: These frames get good thermal performance by incorporating air cavities, which can be filled with insulation. It has a low co-efficient of thermal expansion, which means warping and leaking are minimized in cases of high inside/outside temperature differentials.

The entire guide is at http://www.efficientwindows.org/ToolsForSchools.pdf.

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