Naturally Cool Enclosure
It's five o'clock in the morning, and a small group of Loyola University Chicago students are nestled into plush leather chairs along the east-facing glass wall in the campus's new digital library building.
These students didn't drag themselves out of bed at the break of dawn to cram for finals or finish a paper. Instead, they wanted to grab the best seat on campus to watch the sun emerge from the depths of Lake Michigan.
Watching the sun rise has become something of a ritual for Loyola students ever since the Richard J. Klarchek Information Commons opened in January. Built just steps from the water's edge on the university's Lake Shore Campus nine miles north of the Loop, the four-story, 70,500-sf digital library offers breathtaking views of Lake Michigan. Expanses of crystal-clear, low-iron, argon-filled glass reach three stories high and nearly 140 feet across the building's east and west façades, creating unobstructed, almost panoramic views of the lake to the east and the historic campus to the west.
The $32 million facility was built on once-cherished green space that was Loyola's last remaining wide-open vista of the Great Lake. Since the university had grand plans to build on the space as part of a $500 million campus expansion program, the Building Team did the next best thing to preserving the lawn and its awe-inspiring views—by making the structure virtually see-through.
“We knew we had to do something special,” says Devon Patterson, AIA, principal with local design architecture firm, Solomon Cordwell Buenz. “Here we are planning this building on green space in the middle of campus that was going to block views of the lake. We wanted to create a building where students felt as if they were sitting in that green space.”
SCB led a collaboration with structural engineer Halvorson and Partners, MEP engineer Elara Engineering, and contractor Pepper Construction (all local firms), as well as German-based climate engineer Transsolar Klima Engineering, to develop a design scheme that placed the glass-clad, open-plan digital library between limestone precast “bookends” that house traditional classroom space for the university. The bookends mimic the scale, detail, and material of the surrounding historic structures, down to ancient inscriptions on the limestone façade and traditional clay tile roofing, helping to link the contemporary library to its landmark neighbors.
Placing what is essentially a glass box on the shore of Lake Michigan necessitated a climate-control scheme that would keep the interior spaces comfortable through Chicago's extreme seasonal temperature swings without having to “write a blank check to the energy company,” says Patterson. “The challenge was coming up with a cutting-edge design that allowed a high level of transparency while simultaneously driving down energy costs.”
Based on Transsolar's detailed climate analysis of factors like year-round temperature, wind speed, and solar radiation impact, the design team developed a complex, highly engineered solution that relies on passive climate control approaches, including natural ventilation, to heat and cool the building. The system, as modeled by Transsolar, has the potential to cut energy use in the building by 52% over ASHRAE 90.1-99 minimum requirements.
Once thought to be suitable only for buildings in moderate climates like San Diego or San Francisco, passive climate control using natural ventilation is proving to be beneficial even for structures in harsh environments like Chicago's. Loyola, for instance, will be able to utilize outdoor air (with no mechanical assistance) to cool its digital library nearly one-third of the year—114 days to be exact, according to the climate models.
The building operates in four basic modes, based on the season and weather conditions.
One mode is for moderately cool days, when humidity levels are low and the outdoor temperature is anywhere between 50-68 F. In this mode, the glass library is cooled using 100% outdoor air. With input from a rooftop weather station, the building automation system automatically opens rows of small operable windows located along the top of each floor on the east and west façades. Cool air off the lake enters the building through the east-facing windows and travels along the precast concrete ceilings, effectively cooling the space below without creating drafty conditions. At the same time, a double-skin glass façade on the west elevation—a first in Chicago—uses negative pressure to naturally “pull” the warm air from the interior and exhaust it out automated glass dampers at the top of the glass cavity system.
“The prevailing winds moving over the top of the double-glass wall cavity create a vacuum or negative pressure at the top of the cavity, which actually pulls the warm air out and naturally enhances the air flow throughout the interior space, so we're not relying totally on stack effect,” says Patterson. The building will operate in this “natural” mode for 52 days a year on average.
On warmer days (68-75 F), the second mode comes into play, and the building's radiant ceiling system kicks on to provide supplemental cooling in conjunction with the outdoor air. An integrated loop of radiant PEX tubes embedded in the precast concrete ceiling slowly circulates unconditioned 60-68 F water supplied from the university's nearby chilled water plant. Once cooled, the concrete ceilings hold the cold thermal energy and slowly release it over time. “The slabs eventually reach about 62-70 degrees, so they're not freezing cold, but occupants can feel the temperature difference,” says Patterson.
Even in this “hybrid” mode, which will operate about 62 days a year, the university will realize considerable savings in cooling costs due to the highly energy-efficient radiant ceiling system, which uses just 1/20th the energy of a traditional forced air mechanical system, says Patterson.
The third mode comes into play during Chicago's hot, humid summers, when the temperature can swing from 75 F to 95 F in short order. Then, for about 50 days of the year, the building operates in full cooling mode The east-facing operable windows are closed while the west windows remain open to exhaust the warm air out of the interior through the double-wall system. A combination of the radiant vaulted ceiling system and underfloor air distribution with displacement ventilation works to cool the interior from above and below.
Finally, during the other 202 days of the year, when temperatures can range from subzero to 50 F, the natural ventilation system is shut down, and the building kicks into heating mode. Hot water from the building's boiler system is pumped through the radiant tubing in the vaulted concrete ceiling, heating up the ceiling slabs, while the UFAD system gradually delivers warm air to the space.
To help reduce solar heat gain in all four operational modes, automatic blinds on the east and west elevations track the sun's movement and retract as needed.
While it's too early to tell if the digital library will actually achieve a 52% reduction in energy over ASHRAE 90.1-1999, the building's immense popularity among the students certainly indicates that passive climate control with natural ventilation is a viable method for heating and cooling buildings in harsh climates like Chicago's.
“There's such a demand among students to get into this building that the library building next door is constantly packed with people waiting for spots to open up,” says Patterson. “University officials are wondering where all these students went to study before.”