Not surprisingly, devising an hvac system for such a facility proved a major challenge. Bill Freeman, senior project engineer for Hellmuth, Obata + Kassabaum (HOK), the architectural firm that designed the lab, said the project involved interfacing a very complex and detailed engineering system into an existing structure."

UP AND COMING
Located in the heart of downtown Atlanta, Georgia State University (GSU) ranks as the second-largest institution in the University System of Georgia, with 23,000 students.

The school's traditional strengths have been law, business, and education, but it has branched out to new areas in recent years. The sciences have taken on increased importance as GSU set out to become a leading urban research university.

The concept for the Viral Immunology Center came about when the Georgia Research Alliance allotted $3 million to build a facility, much of the funding coming from the Georgia lottery. The alliance was formed to promote biotechnology in the state. One of the goals was to bring in world-class scholars to enhance the state's educational system.

GSU set out to recruit Dr. Julia Hilliard, a leading expert in the herpes B virus, from the Southwest Foundation for Bio-medical Research in San Antonio, Texas, to head the new center. School officials knew they would need a state-of-the- art lab to entice Hilliard. As it turns out, Dr. Hilliard not only made the move, she also brought her team of scientists.

Funded by National Institutes of Health grants, the Viral Immunology Center is one of only four or five labs in the country rated Biosafety Level-4 (BSL-4), and the only one currently in a university setting. As part of the Department of Biology in the College of Arts & Sciences, it occupies 3,000 sq ft on one floor of the six-story Natural Science Center building. The center also includes a BSL-3 lab, a grade less strict than the BSL4, and several-thousand square feet of BSL-2 labs.

The lab's research focuses on the herpes B virus, found in most rhesus macaque monkeys. They transmit it to humans through a bite or scratch, and this poses a risk to the thousands of workers who handle primates, including zookeepers and biomedical lab technicians. The virus is 70% lethal to humans, with survivors suffering severe nerve damage.

Dr. Richard Henkel, associate research professor at the center, says, "It's not a public health risk but an occupational risk." Henkel explains that viruses are easy to kill, as they break down when exposed to air, heat, and light, but they pose a threat to researchers as they handle fluid samples containing the virus.

Viruses such as herpes B are handled in an environment that meets requirements for BSL-4, the strictest of four lab designations given by the U.S. Department of Human Services in conjunction with the Centers for Disease Control and Prevention (CDC) and the National Institutes of Health (NIH). BSL-4 involves dangerous and exotic agents that pose a high risk of life-threatening disease, for which there is no vaccine or therapy.

If not housed in a separate building, a BSL-4 lab must occupy a completely isolated zone with specialized ventilation and waste management systems.

Work with viruses must either take place inside a Class III biological safety cabinet, or workers must wear full-body, air-supplied, positive-pressure personnel suits the so-called "suit room" approach. GSU chose to use a safety cabinet because it's simpler and less costly.

The center's biological safety cabinet is a totally enclosed, 30ft-long unit made from 12-ga stainless steel and 3/s-in. laminated safety glass. As a ventilated, air-tight enclosure, it operates under negative pressure and can withstand 3 in. wc of pressure.

It's also known as a "glove box," because scientists reach inside it through arm-length rubber gloves attached to a sealed front panel to manipulate, grow, and study viruses.

DESIGN CHALLENGES
HOK's Lab Focus Group, headquartered in Atlanta, designed the lab. The group specializes in labs and similar hightech projects, and has become known for its lab design work.

Jon Crane, a vice president at HOK and director of its Science and Technology Focus Group, cites two challenges the job presented.

First, the time frame stipulated by GSU put the project on a fast track. "It had to be designed and bid within a fourmonth period," Crane recalls. Then they wanted it constructed six months later to be able to recruit Dr. Hilliard et al.

The other challenge was finding room for an energy recovery unit on the roof which, as part of an existing lab, was cluttered with exhaust stacks.

The hvac system represented a whopping 30% of the project budget (actually a typical figure for labs of this type). Requirements for BSL-4 labs stipulate that room air be 100% exhausted and that all exhaust pass through HEPA filtration. Supply and exhaust air streams must be balanced to ensure flow into the lab, and this must be monitored, alarmed, and interlocked to ensure negative pressure.

According to Henkel, the secondary objective was to maintain a pleasant atmosphere for researchers working long hours in the lab. The system has a dedicated energy recovery unit, which handles all the supply and exhaust in the BSL-3 and BSL-4 sections of the lab, including that for safety cabinets and occupied spaces. HOK chose a Des Champs "Wringer Plus-4" packaged rooftop ventilation dehumidification unit with heat recovery. The unit uses two heat pipe heat exchangers in conjunction with open-wire electric heat and a 25 ton, air-cooled condensing unit feeding a DX coil.

In summer, one heat exchanger uses heat recovery to precool inlet air to 69 degrees F; the cooling coil cools it to 45 degrees F, and the second heat exchanger reheats it to 67 degrees F. In winter, both heat exchangers are used to heat inlet air to 64 degrees F.

A unique feature of the energy recovery unit is that it mates with two "Tri-Stack" fans made by Strobic Air Corp., with one fan operating at a time and the other serving as a backup. These are designed as an alternative to the belt-driven centrifugal fans commonly used for lab fume hood exhaust; they also replace tall stacks with guy wires. Bill Freeman at HOK explains, "It's a little more effective at disbursing the exhaust airstream than other systems."

Air enters the Tri-Stack fan through a plenum at the bottom, and a motor-driven impeller forces it upward. A windband and nozzle create a jet effect to generate discharge velocities ranging from 3,000 to 6,600 fpm, compared with 1,000 to 3,000 fpm for stack designs. This draws in outside dilution air to mix with exhaust fumes, allowing for additional momentum to penetrate the roof recirculation region and prevent exhaust air from recirculating through the makeup air inlet.

Crane says they chose the Wringer-Plus because of its energy recovery feature, in view of the requirement to exhaust 100% of the air.

The fast-track nature of the project also played a role in the air handler selection, according to Crane, because "It caused us to rethink how procurement was done."

They bought the energy recovery unit with the Strobic fans as a unit before the contractor came on board. "It wouldn't have been here on time if we hadn't." Additionally, the compact nature of the energy recovery unit with fans was helpful in mounting the equipment.

AIR FLOWS ONLY ONE WAY
In explaining the negative pressure in the lab, Freeman says, "A pressure hierarchy makes the BSL-4 space the most negative, so you have a migration of airflow from the clean to the dirty." In the BSL-4 section, 0.22-in.wc negative pressure is maintained relative to adjacent corridors, while in the BSL-3 section, 0.05 in. wc is maintained. The air handler accomplishes this by moving supply air at 3,735 cfm and exhaust air at 4,235 cfm.

The system features ample redundancy, an important factor in areas like downtown Atlanta. Despite the minuscule risk of spreading viruses through the air, Henkel says it still helps to have overkill in the system to allay public fears. "The system is set up so it can't go positive if the exhaust fan shuts off, the supply fan does also," Henkel states. Two automatic alarms, monitored by the building automation system, signal when differential pressure goes out of spec.

When it comes to nicely exhausting air outside, stacks Henkel says, "The filters provide the main feature of safety." Exhaust air goes through four filters in the room to decontaminate it before it leaves the building.

As an added safety feature, double-wall, stainless steel ducts carry exhaust and supply air to and from the air handler.

AIR CHANGE RATES
HOK designers used Biosafety in Microbiological and Biomedical Laboratories, published by the CDC and NIH, as a guideline for determining the number of air changes required in the lab, as this is the main criteria used in the industry.

They went with the minimum number of air changes to minimize the impact of exhausting 100% of the space air, and this resulted in 10 changes/hr.

Engineers chose to go with a constant-volume system, typical for high-containment microbiological labs, because the supply and exhaust don't vary much. Crane says, "Your entire system stays balanced at a constant volume level.

"We thought if we introduced any variable-volume components, they would cause headaches maintaining the pressure relationships." Air valves in the supply and exhaust streams modulate flow to maintain proper pressure, and these also compensate for filter loading.

Because safety cabinets in the BSL-3 area of the lab aren't 100% exhausted, this section was handled differently. The cabinets have thimble connections, which allow operators to run the central system continuously yet turn the safety cabinets on and off. When you and turn the cabinet off, the air goes through the thimble connection, rather than through the hood, so they don't need to be run constantly.

The ventilation system runs 24/7 (except during planned maintenance shutdowns every six months). A diesel generator on the ground floor stands ready to supply emergency power in case of a power outage. Henkel says the cutting-edge technology used in the Viral Immunology Center represents a vast improvement over other BSL-4 labs around the world.

Tom Gibson is a freelance writer in Roanoke, VA. He can be reached uia e-mail at progress@grev.net.