By Rachel Shafer

At the corner of Seventh and Mission streets, the thin tower of San Francisco’s new Federal Building, home to 1,700 federal employees, reaches 18 stories into the sky. Despite its futuristic flourishes of steel mesh and glass fins and environmentally inspired features, like elevators that stop every three floors (to encourage climbing the extra flights), the building’s most forward-thinking design element may be its simplest: windows that open.

Floors six and up have, in industry parlance, “operable windows.” Employees needn’t breathe conditioned air all day; they can simply reach over and open the window. The cool breezes blowing through these windows are a radical departure from the sealed air-conditioning systems common to most U.S. office buildings built after World War II. The main tower of the new building is designed to consume just 33 percent of the energy of a conventional office building, offering a refreshing trend in energy conservation as well as indoor comfort.

That the federal building has a natural ventilation system at all is partly the achievement of one woman, Berkeley Engineering alumna and architecture professor Gail Brager (M.S.’82, Ph.D.’84 ME). Brager is a researcher in the science of thermal comfort, the study of the environmental and psychological factors involved in an individual’s perception of indoor comfort. Her research and that of her colleagues is accumulating a growing body of evidence that improving indoor environmental quality in various ways—including using operable windows—reduces not just energy consumption, but also employee sick leave and sick building syndrome, the ill health effects sometimes ascribed to sealed, inadequately ventilated buildings.

In the United States, buildings account for more than one third of greenhouse gas emissions, and cooling and mechanical ventilation in commercial buildings account for more than 30 percent of their energy use. So using operable windows to reduce energy consumption could have a potentially significant impact on reducing global climate change.

Brager has spent more than 20 years investigating thermal comfort in offices. In 2004, her research convinced the worldwide organization of air-conditioning engineers, the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), that air conditioning isn’t, well, cool, for every office building. By cracking the proverbial seal, she gave innovative architects and engineers a tool—ASHRAE’s revised Standard 55—to install operable windows under industry-wide approval.

 “Brager’s work is essential to the future of green buildings, especially in the United States,” says Kevin Hydes, former chair of the U.S. Green Building Council (USGBC) and now head of the World Green Building Council. With 15 million new U.S. buildings planned by 2015, the Intergovernmental Panel on Climate Change identifies the building sector as the most promising area for achieving deep cuts in CO2 emissions. In fact, its 2007 Fourth Assessment Report cites Brager’s work as one way to cut those emissions, by reducing our reliance on—what Brager would call our addiction to—air conditioning.

Brager’s fascination with buildings began when, as a mechanical engineering grad student, she landed a job researching passive cooling and indoor air quality in the Environmental Energy Technologies Division at Lawrence Berkeley National Laboratory. After earning her doctorate, she joined the architecture faculty and is now also associate director of Berkeley’s Center for the Built Environment, a 33-member industry-sponsored consortium researching the design and operation of commercial buildings.

“Architects don’t fully understand me, and engineers don’t fully understand me,” Brager says. “I seem to be a research rebel no matter where I am.” In fact, Brager’s ability to maneuver smoothly between the physical and social sciences, between load calculations and psychological evaluations, between working professionals and academics, has given her a unique role.

“Architects have abdicated their historical knowledge of the engineering disciplines that Renaissance and other earlier architects had,” says her colleague, architecture professor Edward Arens. “Architects are trained in the artistic and conceptual side and rely on engineers for the real nitty-gritty of what makes the building work.” Consequently, Arens says, the Department of Architecture has recently begun working with engineering faculty like David Auslander, professor emeritus of mechanical engineering, on green building projects that will help students bridge the gap between the two disciplines.

“Gail is a mechanical engineer who is aware of these things and who is engaged in the ASHRAE process,” Arens adds. “Her knowledge of both fields enables her to deal with problems of buildings and energy use in interesting ways.”

ASHRAE first issued its Standard 55 in 1966, setting a worldwide standard summer temperature range for office buildings of 73 to 79 degrees Fahrenheit. The standard, a range so narrow that only air conditioning could maintain it, was based on laboratory experiments conducted in carefully controlled environmental chambers by the late Danish researcher P. Ole Fanger. Good research? Yes. Good research in an actual office setting? No.

In the 1970s and ’80s, as public awareness of energy consumption widened and architects and engineers who favored natural ventilation began to challenge Standard 55, ASHRAE decided to reexamine the research methodology behind it. Brager proposed a series of field studies using laboratory-grade instruments and rigorous survey methods to assess actual building occupants’ responses to thermal environments in both air-conditioned and naturally ventilated buildings. ASHRAE funded Brager’s team (which included Arens and architecture professor Cris Benton), working in the temperate Bay Area, followed by other teams applying her methods in different climates and cultures.

Brager teamed up with Richard de Dear, a thermal comfort researcher now at Australia’s Macquarie University, to collect the raw data and build a meta-database analyzing the behavioral, psychological and physiological responses to various indoor thermal conditions of approximately 20,000 workers in more than 160 buildings worldwide. The resulting paper, published in 2000 in the ASHRAE Journal, sent the thermal comfort research community into a tailspin.

“We discovered that people in air-conditioned environments became addicted to that narrow temperature range,” Brager says. “They dressed the same year-round because they were dressing for the indoors. They had no control, so when conditions deviated from what they were used to, they screamed loudly.” On the other hand, the data showed, workers in naturally ventilated buildings preferred a greater temperature range because they had control over their conditions. They could open or shut a window.

“Control matters,” Brager says. “When people have control over a stimulus, they accept and, in fact, prefer a wider range of that stimulus compared with when somebody else is pushing the button.” In fact, according to environmental construction website greenbuildings.com, giving employees control over their office air can reduce sick leave by as much as 30 percent.

Brager’s research held up under peer scrutiny, becoming known as the “adaptive model of thermal comfort.” But, knowing that true change in the building industry could come about only by modifying Standard 55, she began agitating for a revision, not an easy sell to air-conditioning professionals.

After all, operable windows have their drawbacks. They introduce noise, wind, odors, potentially poor air quality and additional cost as well as safety and security concerns. Operable windows don’t automatically cool a building; they require careful placement and holistic design. And human behavior is unpredictable; occupants leave windows open when they shouldn’t and keep them closed when they should be open. Co-workers must agree on what’s acceptable.

“Passive ventilation scares engineers who like a lot of control,” Brager says. “As soon as you add pesky people who actually want to open the window and control the thermostat, it drives engineers crazy!”

Dan Int-Hout, chief engineer at the air distribution device company Krueger, chaired the Standard 55 committee. He recalls that Brager’s campaign generated a great struggle within ASHRAE. “But she had so much data that we couldn’t ignore it,” he says. “In the end, design engineers, manufacturers and thermal researchers alike agreed that it was a reasonable approach.” In 2004, ASHRAE revised Standard 55 to accommodate a more flexible definition of thermal comfort.

Europe, Australia and Japan are well ahead of the United States in implementing operable windows; code in some European countries actually requires them for ventilation. While no nationwide statistics are available on new U.S. buildings with operable windows, Int-Hout believes the number remains very small. Peter Alspach, Brager’s former student and a mechanical engineer with Arup, the engineering firm for the SF Federal Building, thinks the trend is catching on.

“People are looking at operable windows for all sorts of reasons, such as occupant satisfaction, climate change, energy savings and financial savings,” Alspach says. “In certain markets like San Francisco and Seattle, if you don’t know how to build a natural ventilation system, someone else is going to get the job.”

Brager is now investigating mixed-mode building, a hybrid strategy that combines operable windows with mechanical cooling systems. She’s focusing on strategies—how and when to open windows versus when to power on the AC—to determine best practices. Her group developed an online database of mixed-mode buildings as a resource for engineers and architects in different climate zones (www.cbe.berkeley.edu/mixedmode/index.html).

Operable windows will never completely replace thermal controls, Brager concedes. Some buildings—like labs, museums, hospitals and prisons—will always require full control over indoor environments. Certain climates will always require air conditioning in summer; but, she says, using less of it in spring and fall can go a long way toward conserving energy resources.

“The true achievement of her work will be to convince the 330 million users of North American building space in this, the most consumptive place on Earth, that we can do more with less,” says Kevin Hydes of the World Green Building Council.

Can we open a window and forgo air conditioning? We might have to dress differently but, as engineers know, the best solution is sometimes the simplest. Brager’s real victory may be in opening our minds as well as our windows.

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For more on air conditioning, see "Man-made weather" changes a landscape.

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Rachel Shafer is managing editor of Engineering News, the College’s semiweekly student newsletter, and associate editor of Forefront.