Page E2.2 . 05 April 2006                     
ArchitectureWeek - Environment Department
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QUIZ

Health, Care and Comfort

continued

Radiant space conditioning uses the temperature of surfaces such as walls and floors, which tend to have less temperature fluctuation. Studies also show that people in naturally ventilated spaces are psychologically more accepting of a wider warm-cold spectrum throughout the day. So while the stairs and lobby might have a higher or lower mercury reading than the rest of the building, they would feel just as comfortable.

At the same time, heating and cooling strategies constitute just one aspect of the overall building design, and thus must be weighed against other factors. For example, concrete has ideal thermal properties for maintaining a narrow temperature range. But it also has loud acoustic properties when exposed without sound-absorbing coverings. When and where to use concrete in the building is not just a comfort-related decision, but also an aesthetic and economic one.

Balancing such competing concerns is what integrated design is all about. When the developer, architect, contractor, and engineer address these issues together effectively and at an early stage, a building can achieve occupant comfort with greater energy efficiency and at less cost.

Design for Productivity

Whereas a previous generation of architecture may have restricted visual access for fear of occupant distraction and excessive energy use, today we know people are healthier both physically and psychologically when given regular access to daylight, views to the outdoors, and natural ventilation.

Ensuring occupant comfort makes good business sense. Far more money is spent in a typical business on salaries and benefits than on the physical space or on energy and water. As a result, investing in a building's human factors can pay immense dividends. There is a more subtle benefit, too: attractive interior spaces and healthier environments can also help recruit and retain key personnel.

Because the Portland climate is generally mild, the design team for Building One saw an opportunity to use natural ventilation and outside air for free cooling. In particular, we were attracted to cooling down a building prior to each day's occupancy, and then using an economizer cycle during hours of occupancy. Taking advantage of the economizer cycle, in which the HVAC system uses a greater portion of outdoor air when outside temperatures are low and humidity is favorable, can bring about significantly reduced cooling costs.

Our goal, then, was to bring in and filter healthy natural air, and to do so using as little fan energy as possible (instead relying on air pressure and the inherent thermal energy of warm air rising). But a combination of high pressure on the north side of the building from prevailing winds and low pressure to the south made it difficult to move air naturally through the building without a fan assist.

The building depth and layout of the spaces further complicated this. And, because we expect future large buildings to the north and west, we also had to contend with reduced air pressures on the upwind side at ground level shown by a computational fluid dynamics (CFD) model.

Ultimately, we settled on a compromise: to use natural ventilation via the stack effect in stairwells, with microclimate analysis determining inlet and outlet points for vents, and to use fan-forced ventilation for the rest of the building.

This decision also met the need for widely varying uses and air pressure requirements of the interior spaces and rooms. We were also able to incorporate radiant heating and cooling for the atrium at no net cost increase using piping in the first-floor slab.

Design for Health

Nearly 50 percent of River Campus Building One's space is devoted to medical practices. An additional 12 percent consists of outpatient surgery facilities. Maintaining optimal air quality in both spaces was a vital health objective for this project.

Air quality starts with cleanliness, ensured by filtration. Interface specified a MERV-13 (minimum efficiency reporting value) filter for exam and clinic areas that removes more than 90 percent of all particles larger than one micron (about one-fiftieth the width of a human hair). This level of filtration by comparison, a standard building filters about 70 percent of particles above 3 microns with a MERV-8 filter gives cleaner air with relatively few additional costs.

Two core principles guided the mechanical system design: optimum health and reduced energy use. After using CFD analysis to study airflow, Interface selected a displacement ventilation system for the patient examination rooms that achieves both. This approach was also applied to interior office spaces.

Displacement ventilation drops cool air from the high point of an interior wall at relatively low speeds in a waterfall effect. Because cool air is denser than warm air, it pools at floor level. But as it interacts with a warmer object, such as a human body, the air rises. Yet it remains cool enough to cool the space's occupant, with temperatures typically rising from 60 degrees F. (16 degrees C.) at the inlet to 78 degrees F. (26 degrees C.) as it exits on the other side of the room at the ceiling.

Using displacement ventilation, air will cool the doctor and patient primarily, but will not cool the entire space and then reheat the air, as is common. Therefore, less air flow into the room is needed to maintain comfort and, correspondingly, less energy is used: fan energy is reduced by two-thirds and reheat of incoming air is eliminated.

Additionally, displacement ventilation does not require air as cool to achieve that same human comfort. Whereas traditional ventilation systems produce air at 55 degrees F. (13 degrees C.) to bring overall temperature of a space to, say, 75 degrees F. (24 degrees C.), displacement ventilation requires at least 60-degree F. (16-degree C.) incoming air to do roughly the same job.

In the Pacific Northwest, that means it is possible to incorporate outdoor air more often in cooling a building, potentially for hundreds of more hours per year, when the outside air temperature is between 55 and 60 degrees F. (13 - 16 degrees C.).

Another benefit of displacement ventilation is that there are typically fewer contaminants in the air. This was of particular interest to OHSU's physicians, who saw optimal indoor air quality in the clinics as indispensable to their mission of promoting health.

Interface Engineering prepared a computer analysis showing air flow in the displacement ventilation system. We used the same type of airflow analysis done on the macro level outside the building on a micro level here.

From the simulation, one can see how temperatures move through the space, with cold air dropping to the floor, being heated by the body temperatures and then exiting through the return air grille across the room. This results in a more comfortable exam room, with much less air movement and less energy use.

Discuss this article in the Architecture Forum...

Jerry Yudelson, PE, MBA, LEED AP, is associate principal and sustainability director of Interface Engineering and chair of several Greenbuild Conferences. Brian Libby is a Portland, Oregon-based freelance writer who has also published in Metropolis, The New York Times, Christian Science Monitor, and Architectural Record.

This article is excerpted with permission from Engineering a Sustainable World, October 2005.

 

AW

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In this displacement ventilation system, there is a "waterfall" effect, as cool incoming air falls down the walls, pools on the ground and rises as it is heated by people, computers, and lights.
Image: Interface Engineering

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By raising supply air temperatures to 63 degrees F. (17 degrees C.), we create an approach that is more energy efficient and comfortable, with less air movement.
Image: Interface Engineering

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River Campus Building One, currently under construction for Oregon Health Sciences University in Portland, was designed by GBD Architects and Interface Engineering.
Photo: Sally Painter

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Studies at the University of California, Berkeley show that comfortable temperatures rise only slightly as outside temperatures increase, with conventional overhead distribution HVAC systems.
Source: High-Performance Schools Best Practices Manual, Collaborative for High Performance Schools

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UCB studies of buildings with natural ventilation show a much wider band of acceptable temperatures for human comfort.
Source: High-Performance Schools Best Practices Manual, Collaborative for High Performance Schools

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Daylighting design provides light for occupied spaces without glare or unwanted heat gain in summer, while allowing winter sun into the building.
Image: Interface Engineering

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Costs for salaries and benefits dwarf costs for rent and operations. Increasing productivity can increase an organization's income far more than reducing energy costs.
Image: Interface Engineering

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River Campus Building One, OHSU, under construction.
Photo: Sally Painter

 

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