Buhl Community Park and the "Cloud Arbor" structure in front of the Children's Museum of Pittsburgh opened June 23, 2012. One child is spied running through a shroud of fog, while another is clearly more intrigued by the acrobat. The mist has a cooling effect without getting people wet.
Photo: Eliza Bachelder, Children's Museum of Pittsburgh

Buhl Community Park at Allegheny Square on Pittsburgh's Northside sits in front of the Children's Museum of Pittsburgh. The park was a $6.5 million collaborative effort between the museum, Andrea Cochran Landscape Architecture of San Francisco (recipient of the 2014 Smithsonian Cooper-Hewitt National Design Award for Landscape Architecture), site artist Ned Kahn and Koolfog. Funds for park renovations came from private
donors, corporations and foundations, including $3 million from the Heinz Foundation, and $1 million from the Buhl Foundation.

The park design of Andrea Cochran Landscape Architecture respects and highlights the historic importance of the site, while bringing renewed vigor to the plaza. The park is within Allegheny Commons, part of a tract of land just north of where the Allegheny River and Ohio River meet, which was established by the Commonwealth of Pennsylvania in 1783 to establish Allegheny City. Pittsburgh annexed Allegheny City in 1907. Allegheny Center, the hub of Allegheny City, had the Children's Museum, the Buhl Planetarium and the Carnegie Free Library, among other amenities.

However, the area deteriorated steadily from during the depression and into the 1950s. An urban renewal project ensued, razing hundreds of buildings and eliminating what had been a walkable business district. In its place was an enclosed mall that opened in 1965, and a below street-level Allegheny Square Plaza devoid of greenery. By the 1990s, the mall had failed, but was successfully converted to an office complex.

 

The fog system is designed for varying cycles of use. At the launch, it was set
to cycle for 15 seconds every 10 minutes. Water usage at that setting is about 33 gallons per hour.
Photo: Ned Kahn




There are 64 stainless steel, 3-inch dia., 32-ft. tall poles, however, the poles positioned within a center spherical band on the ground plane create the cloud effects. The most upper and lower portions of the spherical band have 4 poles with 18 nozzles each; the upper-middle and lower-middle sections of the sphere have 8 poles with 24 nozzles each; and the center band of the sphere has 12 poles with 22 nozzles, for a total of 528 nozzles. Each nozzle required machining holes in the poles. The nozzles are flush to the pole surface for a clean aesthetic look. Integrated into the poles is stainless steel tubing with nozzle adapters. To prevent freezing, heat trace and insulation wraps the atomization lines. Everything was inserted and fastened within the poles prior to arriving on site. All the poles were angled inward at installation to facilitate the
desired cloud effect.
Photo: Chris Siefert, Children's Museum of Pittsburgh

Today, Allegheny Commons and Buhl Community Park are once again the public gathering area it once was for Allegheny City. Important design features for Buhl Park are bioswales and native plantings. The landscape architects assembled and managed a large team of designers and engineers to meet the challenges of building this park, which emphasized species native to the area's waterways, woodlands and meadows, while processing the plaza's stormwater.

The park offers a central plaza with tables and chairs, a large meadow of native grasses, benches, natural bluestone walls, rain gardens for storm water management, bike racks and drinking fountains for people and pets. Pittsburgh wanted a prominent centerpiece for the plaza, something to capture attention and the imagination. How did Ned Kahn come up with idea for his art piece? "There is already so much solid-looking architecture surrounding the site," he explained. "I started thinking about the opposite, something that would maybe suggest the ghost of a building, that would dematerialize and dissolve into the landscape and the atmosphere."

The translation of that concept is the arresting rise of 64 stainless steel, 32-ft. tall poles from the plaza, a piece of public art by Ned Kahn called "Cloud Arbor," made possible through a gift from the Charity Randall Foundation.

Koolfog notes that when the wind conditions are calm, the fog nozzles "sculpt a spherical cloud, spinning and rising in the winter and spinning and falling in the summer. As the wind picks up, the spherical shape becomes distorted. The intent is to create "a porous environment that merges with the atmosphere, blurring the boundary between atmosphere and architecture." The museum created a $400,000 endowment to help pay for the upkeep of Cloud Arbor.
Photo: Ned Kahn

Koolfog is responsible for the "clouds." The company specializes in outdoor cooling and humidification,
fog effects, outdoor heaters and scenting systems to make outdoor areas more comfortable and engaging. Fog effects are generally generated by either heated or chilled fog machine systems. The heated kind use inert gas or an electric pump to bring mineral oil or glycol based "fog juice" into a heat exchanger where it vaporizes.
Chilled fog machines employ dry ice, which create thick clouds that hang around close to the ground, but dissipate as they rise.

Koolfog, by contrast, uses high-pressure pumps and water, couple with high-pressure misting and humidification nozzles engineered to deliver water particles sized for evaporation. Some nozzles can produce a fog that quickly evaporates, so as to keep the surrounding area dry.

Emanating from the poles are misting clouds that rise, swirl about and eventually fall onto those who seeks their cooling precipitation. Although the original design specified a completed internal circle of poles affixed with fog nozzles to produce a solid spherical shape, the team decided the same visual effect could be produced using much less water. The solution was to "core" out fog nozzles from the inner most poles creating a hollow sphere.

Beneath the Fog
The fog system has a 400-gallon soft water atmospheric tank for water storage and recirculation, and two Koolfog Atacama 12-gpm high-pressure pumps with filtration to protect from debris and sediment. The system controls are co-located with the pumps in an equipment room interfaced with the museum's building management system. Two main high-pressure flexible hoses rout water from the pump to a manhole adjacent to the Cloud Arbor. From there, each line is split through a distribution manifold and routed underground to the stainless steel tubing networks that service the individual rows of poles, ultimately pressurizing to 1000 psi as water emits through the fog nozzles.

About the Site Artist
Ned Kahn of Ned Kahn Studios, Sebastopol, Calif., is the artist behind Cloud Arbor. His site art replicates the forms and forces of nature, which can be classified in five categories: fire/light, fog, sand, water, wind. His prolific work is seen across the U.S. and in Canada, Germany, Switzerland, Netherlands, Singapore, Australia, China, United Arab Emirates.