Totally Tubular Lighting
- By Scott Berman
- January 1st, 2011
School districts implementing daylighting as part of green programs for new or renovated buildings have many choices to make.
Those choices include energy-efficient windows, clerestory windows, roof monitors, light shelves, sloping ceilings, daylight harvesting systems, skylights, architectural elements like light wells and exterior overhangs, among others. Also on the list: tubular daylighting devices (TDDs).
TDDs are metal tubes of varying diameters, for instance 10 inches to 21 inches. They have clear domes at the roof level that collect sunlight and transfer it through a reflective section to an opening at the bottom end equipped with a diffuser. Angle-adapters en route avoid joists, rafters and other obstacles, and there are provisions to collect low-angle sunlight and block UV rays. TDDs integrate with suspended ceiling grids, meeting the ceiling line and appearing like standard lights, or can hang suspended under exposed ceilings. There are options such as lenses, dimmers and automatic controls.
Prices that districts can expect to pay per unit vary depending on make, model, quantities, flashing options and accessories such as tubing lengths, diffusers, dimmers and electric light integration features, which enable units to serve as lights at night. Among the other matters to sort — funding formulas and warrantees.
TDDs, like skylights, provide top light to balance light from exterior wall windows, reduce glare and help provide a natural lighting boost that minimizes the use of electric lights. One manufacturer, Carlisle, calls TDDs “an ideal energy-saving solution for applications where larger industrial skylights may not be cost-effective.”
Proponents depict TDDs as an easier-to-install, more energy-efficient successor to larger, traditional skylights, and as a way to efficiently extend daylight deeply into interiors of buildings. Others, however, have expressed concerns. Take heat transfer and leakage, for example.
Lindsay Walsh, a marketing specialist for large manufacturer Solatube International, acknowledges such concerns and pointed out that they have also been raised about traditional skylights. She said TDDs have less heat gain than skylights or electric lights. As for leakage, flashing options prevent them, Walsh said, the key being to install the TDDs properly. To prevent leakage, it is important to have standardized techniques to integrate TDDs with roofing systems, says Robert Walters, vice president of marketing for another manufacturer, EnTech Solar.
Manufacturers describe a variety of ways TDDs can be used. They may work for spaces where there is “limited access,” such as interior classrooms, Walsh adds, as well as in gymnasiums where there already may be skylights or a translucent wall system, but where another top light source is needed “to turn all the electric lights off.”
Don Poggendorf, vice president of TDD manufacturer Sundome, believes that the tubes work efficiently for either open or suspended ceilings. He emphasizes, however, that building users still need to be vigilant in turning off unneeded electric lights — and that automatic daylight harvesting systems “can make a huge difference” on that score.
“I’m a big fan of them,” John Cavanagh, principal of James S. Wilson Middle School in Millcreek, Penn., says about TDDs installed at his school. The devices, along with clerestory windows, skylights and light baffles, were just part of a comprehensive $25.3-million project to renovate and expand the school in 2006-2007. Geothermal heating and cooling were among the other green steps taken there.
The school uses the aforementioned skylights for its gymnasium and cafeteria, and those clerestory windows, and tubular devices in instruction spaces in every pod. In another application, TDDs at Wilson charge photovoltaic panels that power valves and sensors on hand-washing fountains in lavatories, Cavanagh added. According to a local media report, the overall initiative — again, not just lighting but overall — saved the district $50,000 in electrical bills in 2009.
Some school districts use multi-story TDDs — in other words, devices with shafts that extend for more than one floor, bringing light down from the roof through intervening floors.
At the Renton Secondary School Learning Center in Seattle, a long tube is routed through a mechanical room to help light a computer room below, reported Steve Shiver of NAC Architecture. Multi-story TDDs at the Cherokee County School district in North Carolina span past an upper floor, Architect Maggie Carnevale of Padgett & Freeman reported, to daylight the corridor side of main-level classrooms.
Multi-story units are also at use in seven prototype energy-efficient elementary schools in the Douglas County School District in Colorado. The daylighting approach there: sidelighting through windows and/or clerestories combined with TDDs, including some with tubing that extends for two floors, according to architect Paul Hutton. Hutton says he prefers TDDs because “they don’t leak, the thermal impact is negligible, and they cost far less than any other overhead daylight technique.”
“Daylighting has been a great addition to our district,” says Lee P. Smit, energy manager for the Douglas County district. Bearing in mind that daylighting is just part of a range of energy-efficient measures, those prototype schools are using 40 kBtu per square foot annually, as opposed to 72 kBtu per square foot annually in other district buildings, according to Smit.
There also have been energy savings at LEED Gold-certified Manassas Park Elementary School in Virginia, which includes daylighting with TDDs as part of a broad array of environmentally friendly features. Although Wyck Knox of VMDO Architects cannot quantify Manassas Park’s energy savings from lighting alone, energy use overall is 42 percent less than that of an adjacent, similar school from 1999. The 1999 building is energy efficient anyway, meeting the ASHRAE 90.1 2004 energy code, and is well-lit, but has no daylight harvesting, skylights or TDDs, Knox explained. Manassas Park Elementary, on the other hand, has TDDs, energy-efficient windows, sloping ceilings to make the most of ambient light and automatically adjusted light sensors. Knox reports, incidentally, that on a typical day at the school, “usually only about half of the lights are on.”
Manassas Park principal Stacey Mamon could not be reached for comment, but has praised the natural light in her school as a morale-booster. Knox, on the other hand, considers TDDs to be “a no-brainer,” and “the easiest and most cost-effective way to get the LEED certification point for Indoor Environmental Quality Credit 8.1, Daylighting.”
On another point, “Retrofit jobs create their own variables” for daylighting projects, says Lisa Maycroft of GMB Architecture + Engineering. The firm worked with the Zeeland Public School district in western Michigan to add daylighting with TDDs to a recent lighting and roofing renovation project at Roosevelt Elementary School.
Zeeland District Assistant Superintendent Don Van Ginhoven says the district is “very pleased with the results.” No projections yet on energy savings, he said, but “we have been able to shut down a significant number of lights…(and) we know there will be savings.” He added that, “we were a bit nervous about using these (TDDs), but the installation went very smoothly.” In this case, the designers had to deal with ductwork and conduits in order to bring the devices into the interior.
TDDs are handy, Knox explains, because pipes and wiring can be re-routed to accommodate them or, if not, shafts available with “newer TDDs can do 90-degree turns to avoid them (pipes and wiring).”
That being said, “existing ducts to remain can be a challenge for renovations — especially if a large trunk line to distribute conditioned air is over the corridor ceiling,” Knox points out. Corridors “are usually areas in dire need of natural light,” he adds. By the way, sunlight in Manassas Park’s corridors is also boosted with wall-mounted mirrors.
Two renovated school buildings in Buckingham County, Va., employ TDDs in another VMDO project. Knox’s colleague Kelly Callahan reports that the devices are in long, double-loaded corridors, as well as “existing gymnasiums, a new computer lab and a community meeting room.”
Light in that meeting room is boosted by tubes “that extend through the floor above,” through long shafts, Callahan said. Instead of imbedding them within walls, “we chose to express these shafts by encircling them with custom millwork fins and computer lab stations,” she says. Elsewhere, tubes help light “classrooms, break-out spaces, administrative areas and assembly spaces,” explains Callahan. She also points out that if TDDs are used in assembly rooms, there should be a dimmer so the space can be darkened for presentations.
Callahan points out another aspect: If the devices are conspicuous, they can “become a learning tool for the children,” she adds. At Manassas Park, by the way, signs explain how various features throughout the school are saving energy, another way to take advantage of a teaching and learning opportunity.
TDDs are one of the options schools can explore with qualified experts as part of comprehensive daylighting strategies. Daylighting, in turn, can play a key role in districts’ broader, concerted efforts to make their buildings as energy efficient and conducive to learning as possible. Finally, as the U.S. Green Building Council puts it, “green schools cost less to operate, freeing up resources to truly improve students’ education.”
Scott Berman is a Denmark-based freelance writer with experience in educational topics.