While this could have developed into a serious health concern, the solution to the problem was ultimately simple, practical, and cost-effective. In fact, it represented a radically different approach to laboratory fume hood exhaust management; and it certainly looks better. That solution is the Strobic Air Tri-Stack laboratory fume hood exhaust system.

While the Tri-Stack solution represents a simple approach to laboratory fume exhaust, arriving at it wasn't easy. It took the efforts of people from two of the university's departments to seek out and evaluate alternatives, ultimately selecting Tri-Stack systems.

To find a solution, Sandy Freund, a mechanical engineer in the Mechanical Section of the Facilities Planning Department, began working with Stuart Kline, manager of Purdue's Radiological and Environmental Management Department. The Facilities Planning Department is involved in virtually all aspects of construction and management at the university; the Radiological and Environmental Management Department works with environmental issues, mainly with regard to atmospheric exhaust and effluent discharge.

In seeking alternative solutions to the problem, Freund discovered Strobic Tri-Stack fans at an ASHRAE show. She was familiar with Tri-Stack through The Scholar Corporation, a Lafayette, IN, architectural and engineering firm. Scholar had incorporated Tri-Stack fan into several of their designs at Purdue including the Lynn Hall addition, Farriery C.T. Lab, and the Lilley Hall renovation.

After all the testing, performance, and specification reviews were completed‹including acquisition/operating cost analyses‹the university decided to buy two Tri-Stack systems. Among the considerations for the installation, according to Kline, were requirements of laboratory exhaust velocity and plume heights, key issues for eliminating the original problem.

This first phase solution incorporating two Tri-Stack systems handles 25 work stations, replacing 25 of the original 80 stacks. Additional fans are anticipated as funding becomes available. Freund said that the 25 work stations are connected to an above-roof plenum which permits convenient access and safety redundancy. "Fans are direct drive to eliminate maintenance intensive belt drives and operate at constant speed. When the fume hoods begin to shut down," Freund said, "ambient air enters through barometric bypass dampers located in the mixing box at the base of each tan. By using unconditioned air from the roof top rather than conditioned air from the lab, we can reduce the make-up air requirements through our supply air handlers," she added.

Mike Carson, senior mechanical engineer, said that an additional six Tri-Stack type manifold systems fans may be installed in four phases to replace the remaining 55 individual laboratory fume hood exhaust stacks.

While the new Tri-Stack installation has met the university's requirements by eliminating the re-entrainment of laboratory work station exhaust fumes in the Agricultural Research and Forest Products buildings, university management is anticipating substantial reduction in maintenance and operating costs in the future as new Tri-Stack type systems begin replacing the aging conventional centrifugal tans and associated stacks.