Enhanced Enclosures

Dual-wall facades, long common in Europe, are finding application in a few U.S. projects, but the concept still seems foreign to most owners and developers.

By Gordon Wright, Contributing Editor

May 1, 2005

Building Design and Construction

After a hiatus of more than 20 years, dual-façade systems, commonly used in European construction, are slowly reemerging in U.S. buildings. Recent examples include the Seattle Justice Center; Levine Hall, on the University of Pennsylvania campus; Genzyme's corporate headquarters in Cambridge, Mass.; and the U.S. headquarters of Canadian-based financial services firm Manulife, in Boston.

Double-wall systems come in several basic types: externally or internally ventilated; internally vented, internally extracted, and coupled to the building's HVAC system; and internally vented and externally exhausted.

Some systems rely entirely on natural ventilation, while others work in concert with mechanical equipment. In general, naturally vented systems are less well suited for use in humid or highly polluted conditions.

The U.S. Green Building Council's LEED rating system and California's Title 24 energy regulations are helping to focus greater attention on dual-wall systems, says Maurya McClintock, associate principal and façade engineer in the San Francisco office of engineer Arup. Both establish a relationship between glazing performance and the amount of glass that can be used.

By virtue of their construction and their integral shading devices, dual-wall systems can provide a greater amount of glazing without violating overall envelope energy requirements. By maximizing the use of glazing while controlling solar heat gain, daylight can be allowed to penetrate more deeply into the building's interior. Without integral sun shading, says McClintock, a dual-wall system cannot achieve its full potential.

McClintock says U.S. dual-façade applications are conceptually similar to what is being done in Europe, but European developers view project costs from the perspective of a much longer life span—30 years or more—than the 3–5 years typically accorded U.S. buildings. Thus, they are more willing to invest in energy-saving options. U.S. clients also want a validation of the system's performance, as well as assurance that the wall system will interface properly with other systems, such as daylighting controls, she says.

Dual-wall systems can be purchased off the shelf or customized for a specific building use and climate. Before a system can be designed, simulations must be created to confirm expected performance. The process is complex, and requires the use of a number of different simulation tools. For example, simulations must be developed in one program in order to obtain input for computational fluid dynamics studies.

"We don't have the kinds of tools that allow us to quickly model a number of variable conditions on a continuum," says Edward Lyon, a senior staff engineer with engineering firm Simpson Gumpertz & Hegar, Waltham, Mass. "We don't have that great model that says, 'I can start at any point in time and model the entire year.'"

A number of U.S. building product manufacturers are reportedly looking at getting into the dual-wall market. However, they would have to compete with Italy's Permasteelisa, whose preeminent market position is due in no small part to its significant research activity on dual-wall construction. Over the past decade, it has spent about $8 million on R&D in this specialty area.

Seattle: Controlling the light path

The 300,000-sf Seattle Justice Center, a recipient of Silver certification in the U.S. Green Building Council's LEED program, was designed by local architect NBBJ and completed in 2002. The $92 million building houses both city courts and police headquarters.

Surrounded on three sides by other buildings, only its southwest side provided the opportunity to introduce direct sunlight, hardly an optimal exposure for solar control.

The 13-story west façade, covering about 18,000 sf, has a 30-inch air space between insulating glass on the interior and single glazing to the outside. Within the cavity are semi-transparent fabric roller blinds that move in unison on each floor and are programmed to extend or retract based on seasonal historical data. The budget did not allow for a solar tracking system.

The width of the cavity was established primarily by OSHA regulations governing accessibility for maintenance.

As initially proposed, the shades would have extended to within two feet of the floor. As a cost-cutting measure, however, they were left six feet above the floor in their lowered position.

Louvers at the top and bottom of the wall are actuated based on the air temperature in the cavity and the building's HVAC operating mode. On cold days they are closed to retain air and create an insulating barrier. On hot days they are opened to vent heat from the building interior. NBBJ thought about incorporating fans, but it was determined that they would not provide a significant benefit.

Kerry Hegedus, the project's glazing designer, says the owner's only complaint—that glare enters the building at certain times of the day—would have been prevented under the initial plan. Roof-level louvers are opened or closed based on the temperature of air in the cavity and the operating mode of the building's HVAC system.

Design parameters for the project were based on historical sun studies, but in two of the last three years, Seattle has experienced a greater than normal number of sunny days. This has accentuated the glare problem because sunlight is entering the building at a lower angle at a time of the year when the blinds are programmed for predominantly cloudy days.

Genzyme: Doing double duty

About 32% of the exterior skin of the 12-story, 350,000-sf headquarters of biotechnology company Genzyme Corp. incorporates a double wall. A dual-wall covering the entire exterior was considered, but was rejected because of its cost.

A four-foot-wide air space separates insulated glass on the interior and a single pane-exterior "rainscreen." Glazing rises the full 12 ½-foot floor height, says Christof Jantzen, a principal in the Los Angeles office of project architect Behnisch, Behnisch and Partner, Stuttgart, Germany.

Air rises naturally in the cavity, without any mechanical assist. Outside air enters through scoops on the lower façade and exits at the top. The dual façade, fabricated by SOTA Glazing, Toronto, acts as a thermal buffer that mediates between outdoor and indoor temperatures. On summer nights, cool fresh air is introduced. In cold weather, the sun warms air in the cavity, reducing the load on the building's heating system.

Operable blinds, generally mounted next to the exterior pane, provide two types of shade control. Their upper portion adjusts automatically to solar tracking, while the lower section is controlled by building occupants. Natural light also is brought into the building's full-height atrium with the assistance of seven roof-mounted heliostats.

The building, which has been submitted to the U.S. Green Building Council for Platinum LEED designation, has more than 800 operable windows, in both the dual-façade and single-façade areas.

Jantzen says the double-façade was incorporated to provide usable space as well as energy savings. Employees move their chairs into this loggia space when the weather is pleasant.

N.Y. building was a pioneer—24 years ago

The 200,000-sf Occidental Chemical Center in Niagara Falls, N.Y., is generally acknowledged as the first U.S. building with a dual façade. It was designed by Grand Island, N.Y.-based Cannon Design and completed in 1981.

The system consists of glass walls four feet apart that enclose operable louvers. It saved energy by allowing the building to become transparent when occupied and completely closed off and insulated when vacant. The idea was to keep the building as open as possible during the day, and let it "coast" at night by retaining comfort levels that had been established during the day. The nine-story building is square in plan, with a central core and a column-free interior. Views to the outside were maximized.

The building's rigid white-painted louvers are activated by sunlight falling on a single sensor at the center of each elevation, rather than by a more sophisticated sun-tracking device.

Even with the louvers at their maximum shading setting, enough light is reflected by their white surfaces and through the floor-to-ceiling glass to provide daylighting.

At night and during unoccupied periods, the louvers close, sealing off the air that has been conditioned during the day. For maximum insulating capability, the louvers can be set to abut each other.

The building's annual energy use originally had been projected at 39,000 btu per square foot, but it actually performed at as low as 32,000 btu per square foot, according to Cannon president Mark Mendell.

Occidental sold the building years ago, and it has been largely vacant ever since. Because of its picturesque location within sight of Niagara Falls, there has been talk of converting it into a hotel, but nothing much has happened.

Levine Hall: Lighting a bridge

At 48,000 sf, the six-story Levine Hall at the University of Pennsylvania is a "bridge" building surrounded by older buildings. Its east and west elevations, and a portion of the north elevation, have double-glazed façade.

"We realized we could achieve a nearly fully glazed exterior envelope while meeting or exceeding energy code requirements," says Richard Maimon, associate in charge with project architect Kieran Timberlake Associates, Philadelphia.

The glazing assembly, which extends the full height of the 14-foot-high floors, consists of a double-pane unit on the exterior, which utilizes both transparent and translucent glass, and single glazing on the interior. Air is pulled upward in the cavity by exhaust fans at the top of the wall.

At each level, air enters the interior space via an outlet just above the floor, and is exhausted through ducts located just below the ceiling. Integral blinds are electrically operated but manually controlled, reflecting the owner's desire to give building occupants control over their work areas. The Italian firm Permasteelisa Cladding Technologies was the wall system fabricator.

Manulife: Dual-wall the only option

For the new Manulife Building, a double-wall system was the only option that would optimize the glass area for aesthetic purposes and still meet the requirements of the Massachusetts Energy Code, according to Roberto Bicchiarelli, EVP of fabricator Permasteelisa. He says a European supplier was able to provide a low-e coating on clear float glass, with the right shading coefficient. The 14-story, 420,000-sf facility, designed by Skidmore, Owings & Merrill, opened last fall.

The system has integral vertical blinds. Because the positioning of the blinds depends on actions of individual occupants, the contribution of the blinds to energy savings was not allowed to be factored into energy calculations.