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By Barbara Knecht and Sara Hart

Continuing Education Use the following learning objectives to focus your study while reading this month’s ARCHITECTURAL RECORD / AIA Continuing Education article. Learning Objective: After reading this article, you will be able to: 1. Discuss high-rise commercial buildings that incorporate natural ventilation in their mechanical systems. 2. Describe methods of incorporating fresh air into commercial buildings. 3. Explain space planning for office buildings with natural ventilation.

The option of installing operable windows in high-rise commercial buildings is rarely, if ever, debated in the U.S. Conventional wisdom preaches that pollution, rain, and noise will infiltrate the envelope if occupants are allowed to open and close windows at will; ambient temperatures will be unstable; energy use will be unpredictable. Operable windows, the argument continues, will add to construction and maintenance costs. And the taller the building, the more vulnerable it will be to all of these negative factors. While it’s true that severe pressure differences and high-wind speeds do complicate building design and operation, there are new ways to mitigate the problems. “There are nine reasons not to provide natural ventilation and one reason to do it,” comments Clark Bisel, senior vice president at Flack and Kurtz in San Francisco, who is, in spite of the drawbacks, a proponent for that one reason: People prefer it. They prefer it because most of them have the option in personal environments. And researchers are suggesting that productivity improves and energy costs go down in buildings where the users have control over temperature and ventilation.

“The more an indoor environment replicates the environment that humans evolved in, the more comfortable people will find it,” states David Bearg, an engineering consultant on Indoor Environmental Quality (IEQ), who is regularly called in to fix what has gone wrong in buildings. However, he is cautious about the challenge that lies in managing the intake of natural pollutants, such as pollen, and man-made ones, such as vehicle exhaust. “The problem is compounded by the increasing use of video-display screens that attract particulates and suppress human blink rates. Airborne particulates can penetrate deeply into the respiratory system. Meanwhile, lower blink rates mean that eyes are more susceptible to irritation.” Mechanical systems are expected to handle heavy pollutants, but the value of user-controlled openings cannot be underestimated.

 

The Nolen Greenhouses at the New York Botanical Garden have state-of-the art HVAC systems. Photography: © Robert Benson Photography

Research by Gail Brager, an associate professor in the Department of Architecture at the University of California, Berkeley, shows that in naturally ventilated buildings people adapt to changes in mean outdoor temperature and are comfortable in a broader range of indoor thermal conditions than are people in air-conditioned buildings. Her research involved field studies of human behaviors and perceptions in indoor environments in 160 buildings on four continents and in various climate zones. Findings showed that the availability of personal control over local conditions played a primary role in shifting people’s thermal expectations.

The research was sponsored by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), and the results were incorporated as the Adaptive Comfort Standard (ACS) to ASHRAE Standard 55, Thermal Environmental Conditions for Human Occupancy in 2004. For now, the standard allows warmer indoor temperatures in naturally ventilated buildings during summer and in warmer climate zones, but only when no mechanical cooling is available. Nevertheless, the findings provide useful data about the experience of working in naturally ventilated buildings.

Brager points out that the narrow range of comfort temperatures required by the traditional version of ASHRAE Standard 55 effectively requires more buildings than necessary to be air-conditioned, and has led to our culture’s addiction to it. Although the requirements were not intended to create a dependency on air-conditioning, it is very difficult to meet the current standard’s definition of comfort without mechanical assistance. The energy costs and environmental consequences of providing constant and uniform temperatures are significant. The potential for energy conservation has spurred interest in expanding natural ventilation to commercial construction, when it is noted that energy costs can easily account for 20 percent or more of a building’s operating costs.