Green Walls May Open New Doors

Tilley (above) worked with University of Maryland Extension viticulture specialist Joe Fiola to determine the right mix of vegetation for his three-year green wall experiment.

Image Credit: Edwin Remsberg

August 28, 2013

While ivy-covered brick walls are a tradition on many college campuses, the plant-covered façades growing at Maryland's research farm serve a more significant purpose than just decoration.

David Tilley, associate professor of environmental science and technology in the College of Agriculture and Natural Resources, is studying green walls and how they might reduce energy consumption. His is the only such U.S. research supported by Green Roofs for Healthy Cities. "I've always been interested in ecosystems and how they can be used to address human problems," says Tilley, whose findings could eventually be used to determine credits toward environmental building certifications.

Commercial green wall products aren't novel, but much of the science behind them has been done in Europe. Tilley's research may help the industry promote the walls' money-saving qualities, as well as their aesthetic appeal, in North America.

"Metrics of the benefits of vegetated green walls and systems have become mandatory for the growth of our industry," says Reuben Freed, chair of the green walls group for Green Roofs for Healthy Cities and director of research and project manager for greenscreen, North America's predominant supplier of green façades.

Greenscreen's product is among those being tested by Tilley and master's student Jeff Price '10. In January, they planted eight varieties of grapes and native plants at the base of 12, 4-by- 8-foot panels. They include rigid, recycled steel systems; stainless steel cable lattices; stainless steel flexible nets; and thick manila ropes.

One goal: to determine if there is a correlation between species that use tendrils, like grapes, and ones that twine, like honeysuckle, and how well they climb the façades.

The testing is being done at the Central Maryland Research and Education Center in Clarksville, Md., where the team rotates the different panels onto the southern walls of two prototype buildings. Vegetation theoretically cools by reflecting solar radiance or turning it into water vapor, so each building is covered with dozens of sensors measuring radiation, temperature and wind speed. Data are collected every 10 minutes using a computerized system, with vital information from "the dead of summer" used to measure peak benefits.

Price will use mathematical modeling this fall to scale findings up to a full-size house. A previous Tilley experiment with green cloaks—vegetation suspended over a building's top—offers promise. Cloaks cooled inside temperatures by 11 degrees during summer, which would cut energy use by 18 percent, or $100 to $200, for the typical, 2,000-square-foot mid-Atlantic home. —KM