From the outside, Princeton Theological Seminary's new library, under construction in Princeton, N.J., looks a lot like other scholarly research libraries on stately campuses. But looks in this case are deceiving. The new structure, when completed next year, will play a significant role in preserving one of the world's largest and oldest collections of theological books—second only to the Vatican Library in Rome.

"People come from all over the world to see these priceless collections," says German Martinez Jr., PTS director of facilities and construction. Martinez oversees construction of the 94,000-sq-ft library, which includes a sophisticated HVAC system designed with the rare books and artifacts, some thousands of years old, in mind.

Tight control of temperature and humidity is critical in preventing paper and other materials from deteriorating. Thus, the HVAC system was one of several factors that ultimately led PTS to decide to demolish its 53-year-old Speer Library in 2010 and replace it with this new, as-yet-unnamed library that will be larger and more technologically advanced. Speer had outlived its usefulness, especially considering that the seminary's other library adjacent to Speer—the Henry Luce III Library—holds the special collections in four controlled-access "book box" rooms and is itself in need of an upgrade. The HVAC system, located in the new structure but connected through a new atrium by ducts and piping to Luce, will serve both libraries.

Plans for construction, which began in October 2010, call for first building the replacement library, which includes the 3,041-sq-ft atrium linked to Luce by a 2-in. caulk joint. When this project is completed in March 2013, renovation work will begin on Luce.

The new structure is three stories above grade and one below, with mechanical space consuming the entire 9,000-sq-ft top floor as well as 2,500 sq ft of the space below grade. It will include a small section for collections; offices; reading rooms; and 17.6 miles of browsable compact shelving that is able to hold much more material than conventional library shelving.

The weight of the shelving equipment and media is nearly 4 million lb and presented its own construction challenges, says Greg Ondick, project manager with construction manager Barr & Barr. "This is not a conventional library; it's all high density," he says. "The standard load for a library would be about 150 pounds per square foot, but this [with the heavier shelving] must carry a load of about 300 pounds per square foot."

The envelope of the building is tight," Martinez says. About 90% of the structural steel frame is wrapped in quartzite with a band of granite around the bottom. The wall system contains an 8-in. stone shelf, 2.5 in. of insulation, 0.25 in. or more of drain mat and the 5-in. outer stone layer.

"There's a large amount of glazing on the building, especially the southwest exposure, which was done to bring in natural light," Martinez says. He estimates that the glazing covers at least 25% of the structure.

Taking advantage of natural light was important for the new structure, as well as for the atrium. The 62-ft-high atrium's ceiling, itself an expansive focal point of the new construction, uses a Solatube daylighting system that includes 25 skylights spaced randomly to capture light. The skylights also save energy "because you don't need as many lights," Martinez says.

The atrium's roof includes smoke-controlled fans that interlock with windows on the lowest level that will open in case of a smoke-related emergency. This system presented its own challenges because, if there were a smoke-related emergency, about 66,000 cu ft per minute of air would flood the building through the windows, says Jason Fierko, Ewing Cole lead mechanical engineer on the project. "But, because the building is mostly buried at the lowest level, we would have had limited levels where we could take in air."

The solution was to take in as much air as possible from the lowest level as well as the first floor, and rig the front doors to automatically open in case of emergency, Fierko says.

The atrium's roof also includes large heavy beams that had to be lifted with a 250-ft boom crane and placed to hang over the Luce library in a type of cantilever. "We're not actually connected to Luce," Ondick says. "We're completely isolated by that 2-inch joint, but we hang over Luce by up to five feet in some locations."

Concerned about heating the atrium's large open space in winter, the project team added an in-floor radiant heating system to warm the floor slab, Fierko says.

There is also a small solar array located on part of the new structure's roof. The array will generate about 76 kilowatts of power to meet some of the new building's energy needs, Martinez says.

Inside the new structure, the browsable shelving will be installed from below grade to the second floor, with the entire third floor, which wraps the atrium on two sides, consumed by mechanical space. The mechanical space is accessible by a hydraulic elevator that runs from below grade. "There's a lot packed into the [mechanical] spaces," Martinez says.

Indeed, if PTS's two libraries combined were a grand cathedral, the mechanical spaces in the new structure would be their meeting hall and the HVAC system their podium. "This is above and beyond the traditional HVAC system," Fierko says.

"This is a special system with redundancies built in in case of failure," Martinez says. It includes backup variable speed drive chillers, backup circulating pumps for both hot and cold water and a backup reheat system for dehumidification. But the process of deciding on the new systems was based in no small part on the needs of Luce library and its special collections.

Luce currently has two mechanical rooms and three air-handling units, one of which serves the four temperature- and humidity-sensitive book boxes. The outdated air-handling units are not designed to meet the temperature and humidity needs of the book boxes, Fierko says. "The humidity swings from, say, 20% in the winter to up to 60% in the summer; that really degrades [archival material] quickly," he adds.

Plans call for that old system to be demolished and replaced with two new air-handling units in the new building "so all of the air-handling systems will be centralized in one location," Fierko says. The air-handling system uses a dual-enthalpy wheel unit to reduce energy use and stabilize the humidity level. The team is at present nearly ready to make this changeover.

A dehumidification unit, located on the fourth floor, has constant-volume distribution to keep airflows up and improve filtration in the book boxes, Fierko says. It also includes two types of coils: a chilled water cooling coil served from a chilled water plant, located in the below-grade space, for primary cooling, and a dual-circuited refrigerant direct-expansion coil, downstream from the first coil, located in the dehumidification unit.