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Sunshine and skylights

Skylights and clerestory windows are brightening daylighting efforts

July 01, 2001 |

Skylights range from utilitarian to high tech, and from strictly functional to solely decorative. However, in the ever-increasing effort to save clients money in energy costs, especially in such high-use applications as lighting, architects and designers are using skylights to bring daylight into their buildings.

The interest in daylighting was conspicuously apparent at last year's Build Boston trade show. When the architect who headed San Francisco-based Pacific Gas & Electric's (PG&E) new daylighting study spoke there, the standing-room-only crowd overflowed into the hallway. The PG&E study — the first comprehensive daylighting study of its kind — showed that daylighting impacts more than energy savings. It indicated that daylighting could increase productivity in manufacturing facilities by at least 25 percent and cut absenteeism rates by up to one half, increase purchases in retail stores by 40 percent and increase students' test scores by 20 percent.

Seeing the light

Daylighting technology — as it pertains to skylights — has improved dramatically in the past few years, not only in the skylights themselves but also in the glazing materials used. For instance, polycarbonate panels manufactured by companies in Switzerland and Israel can now filter out infrared rays — meaning that the same daylighting levels can be reached with a 30 percent reduction in heat gain. Often, however, a simple design feature in a building can allow a designer to utilize daylighting without need for special glass or high-tech skylights.

For instance, the 4,500-sq.-ft. multipurpose building at Marin Country Day School in Corte Madera, Calif., utilized a simple roof clerestory to work in combination with large vertical windows to provide daylighting.

The design team used daylighting models to evaluate alternative building forms for the facility. According to PG&E, a daylighting model can be relatively simple. It should accurately depict the opening size in the skin and approximate the reflectance of the finish materials proposed for the building. When completed, the model is evaluated by placing it outdoors — or in a special chamber called an artificial sky — and oriented in the same direction as the proposed building.

After considering several options, architect Eshrick Homsey Dodge & Davis of San Francisco chose a sawtooth roof form to balance top and sidelight throughout the building. The north-facing clerestory provides diffused light to the interior. By weighing orientation during the design process, extreme glare and heat gain conditions were avoided.

Although the clerestory design is good for daylighting a single, large room, more complex interior layouts require more complex daylighting components. The California State Automobile Association district office in Antioch, Calif., is such a building.

"We started with a hypothetical building that would be considered standard as a base model, and began designing in energy-efficiency measures," says Brian Congleton, owner of Congleton Architects in Carmel, Calif. "However, for these measures to actually be incorporated into the final building, they had to pay for themselves in fuel savings, either in therms of gas or electricity in kilowatt-hours. After taking all these energy-efficiency measures into consideration, energy savings through daylighting came out head and shoulders above all the other measures we either considered, or ultimately used."

Thirty-five prismatic lens skylights were used throughout the building to diffuse light into the work areas, where the ceiling vaults to 15 feet at the center of the building from 10 feet at the perimeter. Light control louvers were used to manipulate the amount of light and heat allowed into the building. Operated by light sensors, these louvers maintain a light level of 80 to 85 foot-candles in order to minimize glare on the computers. Barometric exhaust vents in each skylight provide building pressurization control and exhaust solar heat from the skylight wells to reduce heat buildup throughout the building.

While limiting light and heat may be daylighting concerns in climates such as Antioch's, such is not always the case. Often, it is desirable to optimize the gathering of natural light every day. Some advanced daylighting systems can do both, by using a mirror array that tracks the sun precisely throughout the year — conducting low-angle sunlight efficiently, as well as shading the intense sunlight found at high angles.

This active skylight system was used at an Ace Hardware store in Martinez, Calif. The system incorporates a series of unbreakable mirrors mounted atop a 4-sq.-ft. skylight, an infrared sensor sun-tracking system and a reflective light shaft to actively track the path of the sun from sunrise to sunset.

The skylight tracking system decreases the number of hours electric lights are needed by better capturing low-angle sunlight. The result was a 65 percent annual saving in electric lighting costs, or 4.9 kilowatts per square foot, while interior light levels were increased.

It has become clear that daylighting is an important option for designers to consider. Thanks to new technology, they now have more ways to utilize it than ever before.

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