[ Page 5 of 7 ]

By Nancy B. Solomon, AIA

Although Croxton agrees that the east-west axis made sense when passive solar design was in its infancy, he argues that technological advances over the years—specifically, high-performance glazing that lets in the visible light spectrum while filtering out hotter infrared rays, plus continuously operating light sensors and dimming ballasts that minimize energy usage when daylighting is plentiful—has changed all this. His research—through previous projects and computer modeling—suggests that, when designed correctly, a building oriented along the north-south axis can actually benefit, in terms of both energy efficiency and indoor environmental quality, from its more abundant and varied daylighting.

The organization of the 47,300-square-foot building is straightforward: The main entrance near the center of the west facade leads to a central, skylit circulation spine that runs north-south. On a sunny day, a beam of light cascades down the atrium’s open staircases to mark solar noon. The brightly lit vertical space is flanked on both sides by classrooms, laboratories, staff offices, and student facilities. Multiple bridges on the second and third floors connect the two sides.

 

Austin Resource Center for the Homeless (ARCH), Austin, Texas This 26,800-square-foot municipal building (top) by LZT Architects exhibits numerous sustainable strategies. A “stack-cast tilt-frame” structural system (below) reduces the amount of formwork required while increasing the quality of the concrete finish, thereby reducing the total amount of materials needed for the job. Photography: © Thomas Mcconnell Photography

Because of the orientation, daylight control is highly sophisticated. On the east and west facades, the architects specified large exterior windows with spectrally selective glazing to admit abundant visible light while blocking solar heat gain. Interior solar screens installed just above eye level can reduce light transmission by 97 percent when deployed.

Above the solar screen is a system of extruded aluminum louvers that bounce light toward a sloping ceiling. The carefully crafted geometry allows daylight to penetrate significantly deeper into the building for longer periods of time than would be possible in a similarly proportioned building oriented east-west at the same latitude.

Coupled with artificial lighting that is controlled by photosensors and dimming ballasts, this careful manipulation of natural light saves a significant amount of energy by greatly reducing the need for electrical illumination. But Croxton argues that the benefits go far beyond the simple economics: “The power of the building is that you can live a day in nature.” Occupants on either side of the building enjoy half a day with abundant diffused light—the most ideal form of illumination—and half a day with the delightful variations in light conditions that occur as the sun traverses the sky between zenith and horizon. Connecting to the latter—nature’s own circadian rhythm—allows occupants to experience what Croxton describes as “the most primitive, deep-seated aspects of comfort.”