The first sign that the Blue Ridge Parkway Visitor Center boasts a green focus can be found on its roof or, more accurately, roofs.
Prickly pear cactuses, columbine, grasses, goldenrod and other native plants crown the sloped roof of the Visitor Center’s exhibition hall and the flat roof that tops the rest of the building, at Parkway Milepost 384 near east Asheville.
The living roof is just one of a host of environmentally friendly features that helped the 13,000-square-foot building achieve gold LEED status when it opened to the public in spring 2008.
Built to resemble a barn with an attached shed, the building’s green components also include passive-solar Trombe walls, radiant-floor heating, high-efficiency heating and cooling systems, motion-sensor-activated office lighting, on-demand hot water, a passive drainage system for the parking lot and a pair of cisterns that capture and recirculate rainwater.
Five years in, National Park Service officials now have a clear picture of just how well those green elements have performed, and they offer a frank assessment of what has worked — and what hasn’t.
“It’s been several years of trial and error and learning as we go, but overall, it’s a good building,” says Brandon Hensley, National Park Service maintenance mechanic who also serves as building operator.
All told, the Visitor Center cost $9.8 million, Hensley says, which includes engineering and architectural-design fees, site preparation and building construction.
Trombe walls: too efficient?
The building — made of concrete, steel, glass and wood — packs a visual punch, especially in its soaring exhibit hall, which features exposed laminate beams, a stuffed and mounted bear that appears caught in mid-trot, a motion-sensor-tripped mountain music display, blocks for children to try their hands at arch construction and more. There’s even a small theater outfitted with high-definition surround sound.
From an environmental standpoint, one of the most impressive elements might be the 30-foot-tall bank of passive-solar Trombe walls on the building’s south side. The structure works by allowing the sun’s rays to pass through a glass window, which heats an air pocket between the window and a poured concrete wall. The superheated air heats the concrete, which then provides radiant heat to the building’s interior.
“In the winter, they’re making radiant heat for nothing,” Hensley says of the walls. “In the winter, they’re awesome.”
The Trombe walls (eight in all) are a big reason why the Visitor Center’s heating costs are 50 percent less than they would be for the same-size conventional building, he says.
Yet despite their wintertime efficiency, Hensley says, the Trombe walls became problematic in the summer by overheating the building, even with sun-blocking shade screens and mechanical cooling efforts. During the summer, air-conditioned air is pumped into the walls’ air pockets to force the hot air through vents to the outdoors — which is supposed to eliminate the radiant-heat effect.
“But by no means was it doing that,” Hensley reveals.
In fact, efforts to cool the Trombe walls in the summer ended up reducing the building’s overall energy savings. Still, the combined heating-and-cooling costs come in at 30 percent less than a same-size conventional building, he says.
About a year ago, officials sought to address the problem by replacing the undersized air-conditioning chiller plant with a new split pump. They also bought higher-quality fans for the exhibit hall and lowered them to better circulate air. Though the new equipment does a better job, Hensley doesn’t yet have the data to show exactly how well it’s doing. He’d be satisfied, however, if combined heating and cooling costs were 45 percent lower than a conventional building.
Many paths to energy savings
On the plus side, other energy-saving features of the Blue Ridge Parkway Visitor Center have largely performed as expected, including the building’s radiant-floor heating. Water heated by a propane gas-fired boiler is piped throughout the concrete floors, keeping them between 72 and 75 degrees during the heating season. Once the floors reach the proper temperature, the system turns itself off.
“It keeps that concrete from cooling down,” Hensley explains. “You don’t want it to fall down and have to heat it up.”
Hensley seems particularly jazzed by the ERU (energy recovery unit) in the basement that brings in 100 percent outside air, boosting air quality in the building. It also boasts an energy-recovery wheel, which sends heated air back near the intake to preheat the outdoor air that will then run through the system.
“Without this recovery wheel, this whole system would be very inefficient,” Hensley notes.
Another area of efficiency is found in the air-handling unit’s spanning capabilities. If the air needs to be heated about 1 to 5 degrees, the system is programmed to use the boiler. If more heat is needed, up to about 15 degrees, the split pump is deployed. Beyond that, the boiler kicks on.
“You don’t typically see spanning in air-handling units,” Hensley says.
Because the boiler is pulse-fired — meaning it’s not putting out a steady stream of gas — it, too, is more efficient, he notes. And if the outside air temperature is greater than around 65 to 68 degrees, the boiler shuts itself down.
The hot-water system also is designed for efficiency. The upstairs restrooms and janitor’s closet use a small hot-water heater. But the employee kitchen and downstairs restrooms use on-demand hot water, in which an electrical heating element heats the water when the faucet is turned on.
“That way, you’re not keeping hot water,” Hensley says.
The high-tech lighting system also yields significant energy savings, he adds. Motion sensors in the offices and restrooms turn on the lights when someone enters the room, with the lights gradually increasing in brightness.
“The sudden start of any output is what drains energy,” Hensley says.
In the offices, the artificial lighting automatically dims as natural light increases. And in the downstairs conference room, a panel of switches allows for four levels of brightness, depending on the needs of the occupants.
Up on the roof
The living roofs atop the Visitor Center are doing precisely what they’re intended to do — reduce the urban heat index — though they, too, have also presented their share of challenges.
“As far was what we’re getting out of our roof, we’re getting 100 percent of what we want,” Hensley emphasizes. But keeping the plants alive on top of the building has been a “significant challenge,” he admits, estimating that about 70 percent of the flora has died over the past five years.
Part of the difficulty lies in the National Park Service’s requirement that only native plants can be used. And the native plants that thrive in the shady, damp conditions of the surrounding woods — such as trillium or bloodroot — won’t survive summers on the hot, full-sun environment of a roof.
The roofs are irrigated by a pair of cisterns that capture and recirculate rainwater, but the water drains so quickly through the 4-inch-deep potting-soil mix, especially from the sloped roof, that it’s still difficult to keep the plants hydrated.
“It’s an extreme environment,” Hensley notes.
Park Service officials have come to realize that a garden roof, one with beautiful blooms, isn’t feasible using native plants.
But with the help of National Park Service plant ecologist Chris Ulrey, they’re steadily trying out different types of native plants — such as the sun-loving prickly pear cactus — that will sustain themselves with minimal spot watering. Fire pinks are next on the list to try, though finding seeds, which have to be collected by hand, will present its own hurdle.
Growing in popularity
Apart from the environmental pat on the back from receiving gold LEED status, the Visitor Center has apparently won approval from the public. More and more people visit each year, with about 1,300 people per day trekking through the building during the latest peak leaf season, notes maintenance worker Bob Rothweiler.
And with the kinks largely worked out, Hensley’s estimation of the building and its systems also has grown over the past five years.
“Overall, we’re fully satisfied, absolutely,” he says.
Other green features
- placing the building to have the least environmental impact
- low-emission interiors and formaldehyde-free wood harvested within 500 miles from the site
- a passive-drainage system for the parking lot, which traps silt in ditches instead of draining the sediment into the woods
- porous patio pavers
- a bike rack
- car-pooling spaces for the public
Architect: Lord, Aeck & Sargent, Atlanta lordaecksargent.com
Builder: Perry Bartsch Jr. Construction Co., Asheville, pbjrconstruction.com
Living roof company: American Hydrotech, Chicago hydrotechusa.com
Tracy Rose is an Asheville-based freelance writer and editor.