In November 2007, Chicago hosted the Washington, D.C.-based U.S. Green Building Council’s annual Greenbuild International Conference and Exposition, the world’s leading gathering of green-building designers and experts. Attendance was the largest ever, with more than 22,000 individuals assembling for five days of conferences, presentations and tours. Chicago was the perfect host for the event as one of the nation’s premier cities for sustainable design and construction practices. (For more information about Chicago’s environmental endeavors, see eco-structure’s October 2007 issue.)
Located about 45 miles (72 km) northwest of Chicago is Elgin, Ill., home to Judson University and its new Harm A. Weber Academic Center, the school’s first green building. Judson University is a 1,200-student evangelical Christian college nestled along the Fox River. The academic center, which became operational in August 2007, is drawing national attention as one of the first highereducation facilities to feature a fully integrated hybrid-passive-natural-ventilation design along with a handful of other high-performance features. The school currently is seeking a LEED Silver rating from USGBC.
A post-occupancy review was conducted by Tacoma, Wash.-based BCRA, a regional architectural and engineering firm and specialist in sustainable-building design. The review was commissioned to determine whether the hybrid-ventilation-system design is realizing the modeled predictions. Using building modeling to determine what may be possible and by collecting live building measurements with scientific equipment, a comparison can be made between the original design intent, predictions and reality.
THE ACADEMIC CENTER
The Harm A. Weber Academic Center was designed by Short & Associates, London, in collaboration with local architects-of-record Burnidge Cassell Associates. Short & Associates is respected worldwide for its design of energy-efficient and innovative structures. The design considered the proposed building’s shape and orientation to Tyler Creek, a tributary of the Fox River; climate; environmental strategies; and the building program.
The center consists of 88,000 square feet (8175 m2) on four floors and is comprised of two main structures that meet at a central atrium, which serves as a stairwell and passageway. The northernmost structure, known as the “block,” houses the main library on levels two and three and architecture studios on level four. A basement is reserved for storage and utilities. The southernmost structure houses offices while the “bowtie” in the middle provides space for classrooms, laboratories and galleries.
The southern office wing utilizes a ventilation design in which air is introduced and exhausted through the perimeter, also known as edge-in, edge-out. The theory behind this concept is based on introducing cool air at the lowest level and using the shape of the interior spaces, along with pressurization from air temperatures, to draw and exhaust naturally buoyant warm air out through the top of the structure.
The BCRA analysis focuses on the block. At the center of the block, a light well extends through levels two, three and four and serves as the main air duct for the center-in edge-out ventilation design. Cool air is drawn into a plenum between the basement and first floor from the perimeter and enters the light well. The stack effect moves air upward through the light well to each floor, and air is admitted to the occupied spaces as needed by mechanized louvers. Air then travels through occupied spaces to the exterior walls and enters the ventilation stacks where its buoyancy propels it to the stack termini at the roof level.
The Chicagoland area is located on relatively flat plains, where weather can be severe. The metropolitan area is subject to strong northerly winds from Lake Michigan and experiences average summer highs of 84 F (29 C) and winter lows of 15 F (-9 C). Because such a varied climate is challenging for passive ventilation, extensive computer modeling was performed in the design phase by the Institute of Energy and Sustainable Development at De Montfort University, Leicester, England, with the dynamic thermal model Esp-r. Airflow behaviors were simulated using CFX computational-fluid-dynamics software. The BP Institute for Multiphase Flow at the University of Cambridge, England, explored the likely effects of introducing heat-producing elements and proposed photovoltaics into and adjacent to exhaust air paths using water bath models incorporating heating elements.
According to a report released in 2005 by Keelan P. Kaiser, AIA, and Dr. David M. Ogoli for USGBC’s Chicago Chapter, these original calculations had predicted “… passive ventilation with neither heating nor cooling would be possible for 29 percent of occupied hours, and for 23 percent of such hours, ventilation pre-heating would be required.” Additionally, the entire structure was calculated such that “… the predicted annual energy cost should be 43 to 47 percent less than the standard U.S. building … the mechanical plant should only be needed 48 percent of the occupied hours of the year.”
For the purposes of natural-ventilation design, two important factors to consider are the thermal mass of the structure and cooling-load profiles. The building is constructed primarily of concrete, providing high thermal-mass capabilities, a key component of the hybrid-ventilation-system design.
In early 2007, another series of calculations and airflow models was undertaken by Dianne Ahmann and John Reynolds, both of the University of Oregon, Portland. This modeling was performed using the Ambiens module of Thermal Analysis Software and provided a prediction of airflow pathways for a 3.3-foot- (1-m-) thick sectional slice through the building. The results of the study concluded that “... under design high conditions, night ventilation of thermal mass should be able to remove a substantial portion of the cooling load in June, only about one-third of the cooling load in July, and all of the cooling load in September.”
For one week in August 2007, BCRA performed an in-depth study of thermal and airflow properties of the block. During this time the building primarily was in its mechanical mode, meaning the air was being mechanically cooled; however, a central design innovation was using the same infrastructure for naturally and mechanically driven airflows for greatest efficiency.
Temperature and relative humidity were measured with data loggers for the duration of the study throughout levels three and four and vertically next to the light well from levels one to four. The data then were used to produce psychometric charts specific to each level. Infrared thermography also was utilized to visualize thermal-behavior patterns and determine relative-temperature gradients. Because airspeeds were low, less than 40 feet per minute (12 m per minute), and mean radiant temperatures differed little from air temperatures, less than 7 degrees F (4 degrees C) difference, operative temperatures were calculated as the mean of the air and mean radiant temperatures according to ANSI/ASHRAE Recommendation 55-1992 R, “Thermal Environmental Conditions for Human Occupancy” for comparison with the updated version, ASHRAE 55-2004, “Thermal Environmental Conditions for Human Occupancy,” thermal-comfort zone. Airspeeds were measured with anemometers or, for high speeds, fan-type weather meters; airflow directions were determined with flutter-strip apparatus and glycerol bubbles.
The field study supported the prior modeling analysis of the hybrid-ventilation strategy. Airflow pathways from the plenum into the light well and then into the individual levels followed those intended by Short & Associates and predicted by the TAS Ambiens model. However, airflows did not exit level four as intended and predicted, and the airflow relationship between the block and bowtie was unexpected with the bowtie providing abundant conditioned air to the block through double-door and stairwell connections.
Level four was operating as a low-pressure zone, and thermal comfort was not being achieved according to ANSI/ASHRAE Standard 55-2004. Level four’s ventilation strategies were being compromised by an open operable window and lack of a seal around the warm, pressurized greenhouse at the top of the light well. These airflow anomalies have simple remedies. Of greater concern was the pressure differential established at the communication of the block and bowtie. This short-circuiting of the block’s ventilation system will need to be analyzed and corrected to ensure optimal efficiency and greater thermal comfort.
Currently, the building is undergoing “fine tuning,” and BCRA will assess the progress this spring.
BUILDING ON SUCCESS
The Harm A. Weber Academic Center is an exciting and inspiring example of energy-efficient building design in the U.S. Although it has not yet reached its optimum energy savings, the building still is operating at a higher efficiency than other buildings of similar size and type—it can only get better through the fine-tuning process.
As noted in the 2005 report, “it will serve as a regional model for energy efficiency and alternative methods of building design. It will also serve as a living laboratory for engineers, architects, students and the public for years in the future.” Most importantly, the building “…will require less energy to operate and will very likely be an enjoyable place to study and teach.” In and of themselves, these results make the academic center a success and champion of efforts in green architecture.
“Low energy architecture for a severe U.S. climate: Design and evaluation of a hybrid ventilation strategy,” Energy and Buildings, Volume 39, Issue 1, January 2007, by Kevin J. Lomas, Malcolm J. Cook and Dusan Fiala
Dale Anderson is principal of Tacoma, Wash.-based BCRA, a regional architectural/engineering frim and a specialist in sustainable-building design. Lee Durston is a building-science specialist with BCRA who conducts diagnostic studies of envelops and performance characteristics. Diane Ahmann is a visiting scientist with BCRA and employee of the Energy Studies in Building Laboratory at the University of Oregon, Portland. The authors can be reached at (253) 627-4367.