Because of the nature of the research conducted there, the building requires 100% conditioned makeup air. The question is, how do you exhaust hundreds of laboratory workstations to eliminate exhaust re-entrainment, air pollution, neighborhood odors, and noise, yet conform to an extremely tough building code that restricts overall height to only 30 ft?
Keep it short
"That's a tall order for a short building," says Dean Shellenberger, who adds that the California Coastal Commission building height restriction of 30 ft (the building is three stories high), "made it nearly impossible to use conventional centrifugal fans for this application." Shellenberger's firm, Randall Lamb & Associates (San Diego), was responsible for designing the hvac systems for four control areas within the building. Included in this task was design and specification for exhausting the laboratory workstation fume hoods safely, efficiently, and quietly.The building height restriction, as well as building construction, operating, and maintenance costs, presented challenging engineering problems that demanded "thinking out of the box" solutions, according to Paul Eiler, the director of facilities at Syrrx.
Eiler, who is responsible for the company's facilities' construction, retrofitting, and daily operations, worked closely with Shellenberger as well as with Mike Fiorito and Mike Richardson at Custom Mechanical Sales (San Diego), a manufacturer's representative marketing custom hvac equipment for laboratories, universities, hospitals, and many high-tech industries.
In their efforts to go "outside of the box" to meet this unique engineering challenge, they arrived instead at an "inside the box" solution. That is, to use mixed-flow impeller technology systems from Strobic Air Corporation (Harleysville, PA) to exhaust the fume hoods and mount those systems inside the building.
As a result there are virtually no exhaust stacks visible from the property line. In fact, the exhaust stacks at Syrrx extend only about 10 in. above the roof, which is surrounded by a parapet.
In commenting on this installation, Eiler says that, "With that type of height restriction, many times air handlers and exhaust fans must be mounted on mezzanine roofs or on ground floors. With valuable space needed inside this building, the only way we could really accommodate this installation was to put the air handlers in the basement (for recirculating the conditioned air) and mount the laboratory workstation fume hood exhaust fans in the building itself."
He adds that because the exhaust fans couldn't be mounted on the roof of the building, conventional centrifugal fans (with their dedicated, tall stacks) were ruled out.
With regard to the engineering and design issues faced by Syrrx, Eiler says that the length of the ductwork necessary for centrifugal fans (which were evaluated before selecting mixed-flow impeller fans) was "quite long in order to be able to get the necessary pipe diameters away from the building, so as not to cause a lot of turbulence and possible re-entrainment problems.
To make the transition from vertical to horizontal, the elbows, flex connectors, and associated ductwork needed would waste too much valuable space. Also, the inlet configurations for the mixed-flow impeller fans required substantially less space." On the other hand, Eiler continues, "none of these problems existed with mixed-flow impeller systems."
The laboratory workstation fume hoods at Syrrx are exhausted through four sets of two mixed-flow impeller fans each (two fans each mounted on common plenums). Four of the fans in the systems use 25-hp motors (providing 25,000 cfm at 3 in./static pressure [sp]); four use 20-hp motors (20,000 cfm at 3 in./sp). The fans are virtually maintenance free, with the exception of greaseable bearings; there are no pulleys or belts to maintain.
The Syrrx facility requires 100% conditioned makeup air. Eiler says this is a "single path type of situation - no recirculated air at all is allowed back into the building." In addition, all of the mixed-flow impeller fans provide vav capability for efficiency and cost savings.
The sound of silence
The issue of noise generation must automatically be addressed when dealing with workstation fume hood exhaust systems situated inside a building (virtually adjacent to work areas). Shellenberger solved this problem by incorporating unique, fiberglass, reinforced plastic, in-line acoustical silencer nozzles on each exhaust fan.In addition, the areas where the fans are located were insulated with fiberglass on the walls and ceilings. "The ones that are most closely adjacent to the people in offices or workstations use heavier sound insulation material than in other places where the fans were located more remotely," Eiler says. As a result, noise is not a factor, he adds.
Eiler also worked closely with Randall Lamb in the planning stages of the building's entire hvac system. Two of his main concerns for the laboratory workstation fume hood exhaust application were vibration and space requirements. "We knew there wasn't room outside the building for centrifugal fans; the distance to the mechanical yard would have been just too great.
To use conventional centrifugal fans inside the building would have consumed many, many square feet of valuable floor space that had to be dedicated to laboratories," he adds, "and the use of mixed-flow impeller technology permitted significantly more laboratory space rather than consuming it with fan rooms."
The Syrrx facility was officially opened in mid-March. Even with this short experience history, both Shellenberger and Eiler are pleased with the performance of the mixed-flow impeller systems.
The laboratory workstation fume hood exhaust systems at Syrrx are meeting or exceeding expectations. And when you look at the building, you'd hardly tell there's an exhaust system on the roof at all! Which proves a point: While it is always smart to "think outside the box" when facing a difficult design challenge, there are times when the solution is right there for you "inside the box" (or at least inside the building). ES
