Cooling The Classics
Inside Mansueto, there are no books in sight. On the surface, that is.
Defying architectural and engineering convention, the University of Chicago (U of C) did the unthinkable: they put 3.5 million volumes, including some of the world’s rarest manuscripts, 45 feet below the Chicago water table and put a greenhouse on top.
Opening in the spring of 2011, the 45,000-sq-ft Joe and Rika Mansueto Library set out to achieve three goals: the underground storage of millions of rare manuscripts, a glass reading environment with access to the manuscripts, and a back-of-the-house conservatory for restoration.
With multiple spaces that each have their own unique HVAC loads, humidity control needs, and conservation requirements, Environmental Systems Design (Chicago) took a tiered approach to mechanical design, providing the Grand Reading Room, the archival storage area, and the preservation laboratories with equally unique mechanical systems.
GRAND READING ROOM
The project’s greatest challenge proved to be creating a reading environment beneath the library’s glass dome that would meet both local and national energy codes, thermal requirements, and the school’s daylighting and operational efficiency goals.
Using computational fluid dynamics (CFD) modeling to determine the right solution for the space, ESD imputed space and occupancy requirements, which include a constant temperature of 75°F with 50% rh (55.1° dewpoint) in summer and 30% rh (41.5° dewpoint) in the winter in the three-story-tall, 8,000-sq-ft open plan Grand Reading Room.
The result was a two-pronged approach to cooling: a perimeter system was designed to directly address the external heat loads from the glass, while an interior system was created to provide local comfort cooling. Maintaining a perfect balance between the two is critical to occupant comfort, since frigid Chicago temperatures create a great conductive loss for the space during the winter and the city’s hot sun results in heat gain during the summer months.
The goal of the perimeter HVAC system is to eliminate unwanted solar heat gain and effectively address the external load. Here’s how it works: round floor diffusers (Figure 1) at the perimeter of the room shoot air up 12 ft along the interior side of the dome to address the heat load at its source. This air will slowly drop down into the occupied zone (6 ft and below), providing additional comfort cooling benefits to the space. Above 12 ft, the unconditioned, unoccupied zone may reach as high as 120°. Not conditioning the unoccupied space above reduces operational costs and minimizes mechanical loads.
The second arm of the cooling system is dedicated to the Reading Room’s comfort cooling. Fourteen kiosk diffusers spread throughout the space provide local lighting and air distribution and serve as informational kiosks to the U of C student body. The kiosks provide a sustainable approach to local cooling by conditioning the immediate air around them. Working together, they are able to maintain a uniform temperature in the space. The kiosks rise over 10-ft-tall and further the desired architectural look, serving no structural purpose in the space.
A single-zone VAV AHU (AHU-8), arrayed-fan wall design with VFDs, chilled water coils served from the central chilled water plant, particulate filters, and demand control ventilation for enhanced IAQ all work together to provide the Reading Room cooling systems with the air supply they need.
The 17,000-sq-ft sub-surface archival area has distinct temperature and humidity criteria required for the preservation of some of the world’s rarest books. Working with conservation specialists, ESD determined lower level archival storage room performance targets of: 60°constant temperature, plus or minus 2°and 30% rh, plus or minus 5%.
Four 15,000 cfm constant volume air handlers with particulate filtration were specified to achieve an effective temperature distribution within the 50-ft. high space (Figure 2). The constant volume AHU (AHU-5) specified provides desiccant dehumidification with high-pressure plant steam for regeneration, HEPA particulate filters, and two stages of gaseous carbon filtration to minimize biological, mechanical, and chemical damage to any materials. The control sequence relies on primary and redundant vault temperature and dewpoint sensors in the space. The humidification is provided by a clean steam generator and reverse osmosis water purification systems.
Located 50-ft below the surface in a small doughnut at the center of the archival area are eight air-handlers. Four serve their neighboring archival space, and the other four serve the Grand Reading Room’s perimeter cooling system. Another underground space, located between Mansueto and Regenstein Libraries, hosts five more air handlers. One serves the archival area and the other four service the Grand Reading Room’s interior kiosk system and the preservation and conservation spaces on the ground floor.
PRESERVATION AND CONSERVATION
Assuming 6,000-sq-ft of the ground level, the library’s Preservation Department is made up of the conservation and digitalization laboratories. The conservation lab includes special paper washing sinks, fume hoods for chemical treatments, bookbinding equipment, and flexible workstations that help conservationists preserve original artifacts. In the digital technology lab, large-format digital cameras create high-resolution digital images of unique book and paper materials that are too fragile for traditional conservation treatments or frequent handling. To-gether, the labs allow the library to conserve collections for future generations, while providing worldwide access to digitized collections online. Both laboratories serve all campus libraries, handling materials in both the general and special collections.
The ground floor preservation labs have a performance target of 75° and 45% rh (52.2° dewpoint) year-round. The constant volume air handler selected (AHU-11) provides dehumidi-fication from the central chilled water plant, HEPA particulate filters, and two stages of gaseous carbon filtration to address biological, mechanical, and chemical damage. The area is also served by two lab fume exhaust hoods with bag in, bag out HEPA filtration. Each lab has a dedicated reheat coil and clean steam humidifier for individual zone control.
An engineering and architectural first, the University of Chicago’s Joe and Rika Mansueto Library will lead its class in innovation, efficiency, and conservation, raising the bar for tomorrow’s university libraries. A formal dedication ceremony for the library was scheduled for November 2011. ES
Designing The Glass Dome
Controlling sunlight and glare in the 8,000-sq-ft Grand Reading Room while still preserving the beauty of the glass dome design required innovative engineering.
Working with architectural designers Murphy/Jahn (Chicago), ESD analyzed the thermal characteristics and energy performance of a number of different frit patterns applied to different types of high-performance glass. Finding the right, but delicate, balance between allowing daylighting and blocking solar heat gain was crucial. Forging new territory together with a number of glass manufacturers, hundreds of different glass scenarios were developed, followed by extensive energy and CFD modeling using various combinations of the fritted glass coatings and shading devices to determine which one provided the optimal performance for the space.
The result is a high-performance, insulated, low-E, fritted glass that incorporates 57% shading at the upper area of the dome, with a ceramic frit 1/8-in. dot pattern that creates 80% opacity on its external surface. Designed to reject 73% of the solar heat while admitting 50% of the visible light, the Grand Reading Room is a comfortable reading and working environment flooded with daylight.
Supported by a light steel grid made of 6-in.-diameter high strength structural steel tubes spaced at approximately 6 ft in each direction and anchored to the building’s concrete ring beam, the dome glass is supported above the steel tube grid at each intersection.
The dome was constructed in six phases. First, its European manufacturer assembled the structural steel frame into sections overseas before being shipped to the site. Scaffolding was built over the ground floor to facilitate construction. The elliptical shape rose in tiers after which the structural steel frame was installed. The glass’ aluminum frame support was installed and finally the glass and its sealants.
Chicago fire code requires every facility to be fully sprinklered, so fire protection was integrated within the structure of the dome. Sprinkler pipes curve with the dome under the glass (see photo).
Book And Manuscript Storage Retrieval
The University of Chicago’s Mansueto Library hosts the largest automated storage and retrieval system (ASRS) in the country. The 17,000-sq-ft lower level archival storage area has space for 3.5 million volumes in a area extending 45 feet below the Lake Michigan water table.
Volumes are shelved by size rather than library classification in vault-like metal storage boxes, taking up just one-seventh of the space of regular stacks. Not accessible to visitors or most staff, the volumes are retrieved within minutes of ordering at the circulation desk by a robotic crane. Each manuscript is scanned when it is requested and removed from its location and as it is returned to the ASRS so that the Library’s computerized system can track materials at all times.