Greening a greenhouse

Nothing seems greener in an urban setting than a garden conservatory—an indoor space dedicated to growing countless varieties of plants, acting as a natural haven for visitors. And often nothing is greener, as long as green doesn’t refer to energy efficiency.

Greenhouses by nature are poor energy performers, says Jim Smith, head of Montgomery Smith Inc. in Burlington, Ky. Despite recent advances in sustainable design, greenhouses remain one of the most inefficient structures.

“For office and residential spaces, architects have made tremendous strides with energy conservation,” Smith says. “But you can’t do that with a totally glass-clad and encased envelope. We don’t have those opportunities to hit [energy efficiency] goals in a greenhouse merely because of the definition of the building.”

Greenhouses are completely monolithic glass-enclosed spaces that suffer from tremendous heat gain. To make it livable for plants and semicomfortable for human visitors, heating and cooling systems have to run almost year round.

In addition, indoor gardens can’t rely on any efficient glazing materials because of the effect they have on plant growth, Smith says.

High-performance coatings, tints, frits and any other changes to the surface of the glass limit portions of the light spectrum and affect photosynthesis. “There are even arguments against insulating glass, because of the way the light spectrum bounces off the second layer,” he says.

The Phipps Conservatory and Botanical Gardens in Pittsburgh, built in 1893, faces those exact inefficiency issues. Despite challenges to make a greenhouse green, the board of directors and officials from Phipps made efficiency a top goal when they began the $36.6 million project to add four buildings to the complex, says Richard Piacentini, executive director for Phipps.

“The board was going through its strategic plans and came to the decision that sustainability and green should be the primary goal at Phipps,” Piacentini says. “It makes sense; we’re a botanical garden and should be promoting green practices. We’re reinventing Phipps a century later as the greenest garden.”

The four buildings include the welcome center, production greenhouses, tropical forest and special events pavilion.

Welcoming LEED
The 1960s Modernist architectural trends were hard on the Phipps Conservatory. Architects of the age built a pavilion entrance for the then 70-year-old complex that fit the era: simple, Modernist and sleek, with clean lines and harsh geometric edges.

“It was a very utilitarian design and so out of step with the Victorian conservatory,” Smith says. “It was an empty and awkward space, and one of our huge goals was to replace it with a structure that was sympathetic to the domes and curves of the original building.”

The center accomplished that and more with its welcome center that opened in March 2005.

The 11,000-square-foot structure mirrors the center’s original design and is set below grade, allowing the historic buildings to be seen from the entry. In addition, the light-filled space serves as an open and welcoming environment for visitors with its gift shop, café and art gallery, Smith says.

The most important attributes of the welcome center are its energy efficiency and sustainability. The center’s green design reduces energy costs by 40 percent, giving it a Silver rating from the U.S. Green Building Council’s Leadership in Energy and Environmental Design program.

One major element of the design is the glazing. The atrium features insulating units with low-emissivity glass and a ceramic frit from Viracon of Owatonna, Minn. “The roof cuts out 50 percent of the daylight coming through, reducing cooling loads,” says Joel Bernard, project architect from IKM Architects in Pittsburgh.

A wall of laminated, insulating glass from PPG Industries of Pittsburgh runs the length of the courtyard on the front face of the center. Combined with the natural light from the dome, “we have plenty of daylight coming through, enough to override electrical lighting systems that are controlled by light sensors,” Bernard says.

The dome also features operable glazing units for ventilation and cooling, Bernard says. “The vents are at the top of the dome and the base of the dome, and tied into the air conditioning system. When hot air builds up, the vents will open,” he says.

The only area of the welcome center that requires air conditioning is the lower level because the dome is cooled through natural ventilation.

Other non-glass green elements of the welcome center include its complete reliance on wind power; use of no- or low-volatile organic compounds for paint, adhesives and other products; and heating pipes under the entrance walkway that use steam to warm the sidewalks, eliminating the need for plows or de-icing chemicals.

All welcome center functions are controlled by an Argus fully integrated environmental control system. The Argus computer system opens and closes vents and makes other alterations in building functions based on temperature, weather conditions, and wind direction and speed. The Argus system is active in the welcome center, as well as the other new buildings in the conservatory.

Growing sustainability
The production greenhouse complex was the second piece completed in Phipps’ major renovation. The 36,000 energy-efficient growing space opened in early 2006.

While the greenhouses require single-pane clear glass to foster early plant growth, they feature several efficient and sustainable elements to limit energy use. Temperature, lighting and watering is all computer-controlled, and vents allow for natural ventilation.

However, the greenest aspect of the production greenhouses is the use of stainless steel, aluminum or hot-dip galvanized steel for supports and framing, Bernard says. In the galvanizing process, a zinc coating is applied to the metal to prevent corrosion. Aluminum and stainless steel act similarly.

“In greenhouses, you expect after 15 or 20 years to have to go through a major overhaul,” Bernard says. “Phipps didn’t want something disposable, so we used these metal materials. We expect these greenhouses to last for 35-50 years.”

Breaking boundaries
Phipps took big botanical risks with the tropical forest conservatory, completed in conjunction with the special events pavilion in December 2006. Going against traditional greenhouse design, the conservatory features IG units in the 12,000-square-foot roof, greatly improving thermal performance of the space.

“The first decision was to have the roof slope,” Bernard says. “The maximum volume of sunlight comes through the south face of the building, and we calculated through computer modeling that there wasn’t a lot of beneficial sunlight coming through the roof. So, we could use IGUs on the roof.”

The south side is a slightly curved wall of 4-foot-by-8-foot clear, monolithic glass. Designers added a heat retention curtain along the wall to provide thermal insulation in the winter and at night, shade during the summer and to prevent convective and radiant heat loss.

The decision to use IGUs on the roof presented huge challenges when it came to framing, Smith says.

Greenhouse framing suppliers provide systems for single-glazed units. So, designers had to look to commercial curtain wall suppliers to find frames. “It was quite a headache finding something that could support that much weight,” Smith says. “It was completely out of the realm of the greenhouse industry, but the commercial industry weren’t used to operable vents.”

The structure required operable roof IGs and narrow framing systems to ensure frame members didn’t obstruct sunlight. “A cumbersome frame structure blocks the plants, and that was something our design team was hugely aware of,” Smith says.

Naturalite Skylight Systems, part of The Vistawall Group in Terrell, Texas, worked with the Phipps design team to build a custom roof system that responded to both concerns.

Just as in the welcome center, the roof vents in the tropical forest conservatory also are computer-controlled based on a fluid dynamics study by Architectural Energy Corp. of Boulder, Colo. The study found that if every other row of roof glass opened, it could naturally cool the building.

“Typical conservatories have one or two vents open at the top and one or two below,” Piacentini says. “The idea is to draw hot air out the top and cool air low—the chimney effect—but it doesn’t work that well. Our analysis showed that if every other row opens up, they would be effective.”

The vents work in conjunction with earth tubes to cool the building, Piacentini says. Six earth tubes, 24-inch concrete tubes that are 300 feet long and 15 feet below grade where the earth is 55 degrees year round. The tubes replace the need for HVAC in the building. A vacuum effect occurs as hot air exits the roof vents, pulling cooled air into the conservatory.

The tropical forest also features the first fuel cell in the world for a conservatory. The Siemens 5kW Solid Oxide Fuel Cell is a state-funded prototype that produces electricity from natural gas, uses wasted captured heat to heat the water system and reduces emissions.

On top of design challenges, glass installers also faced hurdles during construction, says Emery Lukacs, project manager for contract glazier D-M Products Inc. of Bethel Park, Pa. The building’s location on a hillside presented the most issues.

“Cranes are normally set outside a building. But we didn’t have the space to do it, because the site is right on a hillside,” Lukacs says. “We had to put the crane inside the building and reach through the skylights to install most of the south wall.”

The hillside location also exposed glaziers to harsh cold and winds during the wintertime construction. “There were days when the wind was too fierce to work with the cranes, so we’d have to shut down,” Lukacs says.

The special events pavilion, adjacent to the tropical forest, was built at the same time. The 6,750-square-foot space also features a south wall of glass.

PPG Industries provided its Solarban 70 high-performance glass for the curtain wall.

Vistawall Architectural Products supplied the curtain wall system for both the tropical forest glass wall and the special events pavilion façade.

Green today and tomorrow
“We look at all of these buildings individually—the welcome center, the tropical conservatory, the special events hall and the production greenhouses—and see that Phipps has really started to carve out a reputation as a green garden. And that is directly tied to how we work with glass,” Piacentini says.

Renovation and new building at Phipps will continue indefinitely with green at the forefront, though no exact timeline has been set, Piacentini says. 

The biggest project is the education-administration building, a 24,000-square-foot complex that will connect to the conservatory through a covered skywalk. Refurbishments also are planned for the original greenhouse buildings that will make the spaces much more efficient.

“With all these developments, we can easily say Phipps is the most energy efficient conservatory in the world,” Piacentini says.