Daylight Savings: Window Systems Deliver Light and Reduced Energy Costs

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Sponsored by Guardian Industries Corp., MechoShade Systems, Inc., Pella Corporation, and Technical Glass Products (TGP)

Window Considerations

In achieving daylight-friendly windows, the following areas should be carefully explored and analyzed:

Window Design. Generally, windows on the north and south faces receive moderate, constant light throughout the day rather than extreme glare in the morning and afternoon. Placing windows at eye level allows for a view to the outdoors. Shading windows at and above eye level avoids excessive brightness and direct sunlight streaming in on visual tasks. These and other basic design principles should be fully understood and applied.

The extensive use of natural light streams through strategically placed window systems at the Dorothy K. Vallier Environmental Learning Center, reducing the need for artificial light.

Schlitz Audubon Nature Center, Milwaukee, WI; The Kubala Washatko Architects, Inc.; Photo courtesy of Pella Corporation

 

Thoughtful examination of window placement was critical in the design of the Dorothy K. Vallier Environmental Learning Center at the Schlitz Audubon Nature Center, the first new construction Gold LEED-certified building in Wisconsin. "The windows were a huge decision," says Joel Krueger, Green Building Specialist / Associate / Project Architect, of the Kubala Washatko Architects, Inc. who was the key architect on the project. "In designing a building, you tend to look at the sun. Then, you want to combine the openings with the views and vistas. It all works together at the same time. You also have to decide what needs to operate or be fixed and what types of windows are needed," he says.

Window Glazing. According to the Efficient Windows Collaborative, there are three approaches to improving the energy performance of glazing products. The glazing material may be tinted to block out unwanted solar energy. Coatings may be applied to the surface of the glazing material. Reflective coatings and films, or low-emittance (Low-E) coatings were developed to improve both heating and cooling season performance. Alternatively, double- or triple-glazed windows may be assembled and films or gas fills inserted between the layers. "Typically, an architect selects the glass first and then proceeds to consider the various shading options," points out Zeimetz.

Framed by Steel

TGP's headquarters incorporate a steel-framed curtain wall.

Typically, there's so much focus on the type of glass used, that it can be easy to overlook ways that framing can support daylighting. The strength of the frames affects how large an uninterrupted glazed area can be provided. The size of the frame profile also determines how crisp and clean sightlines are, and defines the extent of cast shadows.

American designers are accustomed to working with aluminum frames for windows, doors, and curtain walls, but steel curtain wall is popular in Europe with a strong track record of successful installations.

Modern steel frames are approximately three times stiffer than aluminum, enabling large glazed free spans with fewer horizontal and vertical framing members, yet they can be customized around various curtain wall shapes, members, spans, anchoring conditions, etc. And steel framing systems also have significantly lower potential for heat gain and loss. Compared to aluminum, steel conducts about 74 percent less heat. In an indoor ski area in Dubai, the aluminum framed curtain wall was replaced with steel frames. Despite the temperature difference between the cooled interior and an adjacent indoor eating area, there was no condensation on the steel frames, a common problem with some aluminum frames.

Photo courtesy Technical Glass Products (TGP)

 

Shading Options. Interior, exterior and between-the-glass shade options can protect windows not otherwise shaded from the sun. According to the Florida Solar Energy Center, exterior shades catch the sun and reflect some of it away from the window. Because some exterior shades are partially transparent, a portion of the incident radiation will pass through to the window, with the rest absorbed by the shade and carried away from the window by radiation and airborne convection currents. Exterior or interior awnings and light shelves above or below windows can block sun and bounce light up to the ceiling, allowing it to penetrate deeper into the space and controlling glare.

At the Gregory Bateson Building, in Sacramento, California, motorized external shades help protect occupants from the sun's rays and heat.

©2009 MechoShade Systems, Inc.; Architecture: Sim Van der Ryn; Photography: Ed Asmus

 

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Originally published in Architectural Record
Originally published in June 2009

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