Winter  2006


Metal Matters

    Energy Drives Window Designs
By Mike Manteghi and Mike Hill

The energy codes vary greatly from state to state and have caused changes in window design and manufacturing. The design challenge is meeting the needs of many states that have adopted and enforce different building and energy codes. The International Code Council (ICC) strives to integrate all building codes into a universal standard for both the commercial and residential industries.

The two main criteria that must be met with energy codes are the U-value of the thermal property and solar heat gain coefficient (SHGC). High-performance windows with low U-value result in inside glass surface temperatures much closer to the room air temperature. It is imperative that products perform optimally to reduce heat gain. In addition, energy efficient windows also help reduce condensation. Windows with warm-edge technologies reduce condensation on the frame or at the edge of the glass. 

The Office of Energy Efficiency and Renewable Energy is leading the drive for development and deployment of sustainable energy technologies. Estimates are that the technologies and practices supported by its program have saved Americans $10-15 billion in energy costs over the past decade. These savings continue to mount as new energy technologies developed by the program for buildings, transportation, utilities, and industry are put to use and as research continues.

According to a study by the Energy Research and Development Administration, the buildings with the poorest energy efficiency are those built between 1940 and 1975. Older buildings were found to use less energy, and require fewer weatherization improvements, because they were built with a sense of comfort and they maximized natural sources for heating, cooling, lighting and ventilation. Today, builders continue to achieve energy savings in historic buildings without jeopardizing the architectural and historical qualities.

These elements continue to be important in window design:

Color and glazing;
Reflective glass;
Light-to-solar ratio;
Window-to-wall ratio.

The desirable color qualities of daylight are best transmitted by neutrally colored tints that alter the color spectrum to the smallest extent. 

As much as possible, the use of reflective glass or low-E coatings with a highly reflective component should be avoided. They reduce the quality of the view and the mirrored effect is unpleasant to occupants after dark.

The use of high-performance and selective low-E glazing reduces the visual light transmission (VT) proportionately less than do reflective coatings or tints. Dividing the VT by the SHGC is a good rating of the performance of the glass. If the result is less than 1.0, the glass is a poor choice for visual quality and daylighting. If the result is higher than 1.55, it is a high-performance option. 

For view and a positive connection to the outdoors, people prefer a minimum 20 to 30 percent ratio of window area to wall area. Glazing the wall areas below desk height (0-30 inches above the floor) offers little or no benefits for daylighting an office or view for the occupants. 

Research and development groups are constantly exploring new ways to improve the glass and framing system of the windows because both can affect the integrity of the unit to provide long-term superior insulation. New technologies such as high performance and dynamic glazing and enhanced framing materials are increasing the energy efficiency of fenestration products for future requirements.

The DOE is pushing to ultimately get zero energy buildings by the year 2025. As a result, the U-value of the overall product and SHGC will be monitored closely. There is a trend toward high-performance glass and the use of more glass in the future to brighten buildings and residences.

Mike Manteghi, is director of research and development for TRACO and a board member of the National Fenestration Rating Council (NFRC). Mike Hill is architectural services manager for TRACO.


Architect's Guide to Glass & Metal
Copyright 2006 Key Communications Inc. All rights reserved. No reproduction of any type without expressed written permission.