 High technology laboratory equipment advancements the last 10 years have far eclipsed the usefulness of conventional heating, ventilating and air conditioning (HVAC) airflow technology in labs. As laboratory equipment such as lasers, electron microscopes and energy-efficient low-flow fume hoods have emerged as major research instruments, it has become evident that today’s labs’ sensitivity to airflow, temperature and noise has become a major building design problem for mechanical engineers. Basically available in laminar (downdraft) or radial (diverging flow) configurations, metal diffusers have limited options in critical environments and haven’t fulfilled researchers’ growing need for more controlled and effective HVAC airflow that doesn’t affect laboratory procedures.
Recently however, the HVAC industry has developed fabric faced diffusers and fabric ductwork that can be customized for airflow, direction, temperature evenness and quietness, thus eliminating the disturbances that sensitive instruments and their processes have experienced in recent years.
A host of educational and industry laboratories have embraced the trend of fabric ductwork and diffusers including University of Louisville, Eli Lilly, Harvard University, Environmental Protection Agency (EPA), Massachusetts Institute of Technology (MIT), University of Nevada—Las Vegas, U.S. Department of Defense, University of Michigan, University of California—Davies, University of Chicago, University of Illinois, University of Michigan, and many others. While a few of the above examples were new construction projects, most of these labs retrofitted to fabric diffusers because their existing critical environment diffusers weren’t delivering a satisfactory airflow performance for the designated research work.
 Case in point is at Harvard University, Cambridge, Mass., Lice Hall. A relatively new lab that was retrofitted to a fabric dispersion device because velocity from two existing 400-cfm radial flow metal diffusers was so turbulent that drafts regularly disrupted papers on countertops, not to mention the resulting negative effects the airflow had on the particle weighing scales used by researchers. Two 2 x 2-foot radial flow metal diffusers were replaced by one 2 x 8-foot fabric-faced diffuser reducing the original 110-fpm discharge velocity down to 35-fpm. Other key benefits included a significant noise reduction while simultaneously generating a more uniform air temperature throughout the space.
Airflow Can Affect Laser Research
The use of fabric air dispersion devices can result from architect or consulting engineer specification or the request of the lab’s researcher. At the University of Chicago, it was all three—the researcher, architect and consulting engineer—that collaborated on the specification of fabric duct for three labs in the $200 million Gordon Center for Integrative Research. The researcher’s request for eliminating airflow noise and uneven temperatures throughout the rooms was answered by architect Peter Pogorski, principal, Ellenzweig, Cambridge, Mass., and consulting engineer, Steve Levin, principal, Bard, Rao + Athanas Consulting Engineers (BR+A), Watertown, Mass., who specified fabric air dispersion for the three labs where the laser-based physics research, such as “Bose Einstein Condensation Reaction” experimentation, is conducted.
The labs use several runs of 18-inch-diameter cylindrical fabric duct suspended from H-Track suspension systems to minimize sway. The ducts incorporate a factory engineered porosity that allows the supply air to flow through the fabric at an even 25-feet/minute velocity compared to intermittent drafts of metal diffusers. The lab maintains a strict 70°F (±1°F) temperature, because the air is dispersed so evenly and slowly that it mixes with the entire volume of the room. In contrast, the higher velocities and metal duct diffusers generally create down-flow drafts that tend to drop to the floor without mixing well with the surrounding room air.
Aiding Fume Hood Validation and Room Pressurization
The even air distribution supplied by fabric duct diffusers actually helps ensure consistent fume hood capture rates. Because commonly applied radial flow metal diffusers tend to discharge air with higher discharge velocities, the resulting turbulence may disturb the natural air draw into the sash of nearby fume hoods. This situation was confronting a lab within Lutz Hall at the University of Louisville, Louisville, Ky. A critical fume hoods did not pass inspections for ANSI/ASHRAE (American National Standards Institute /American Society of Heating Refrigerating, and Air Conditioning Engineers) Standard 110 “Method of Testing for Laboratory Fume Hoods.” The vertical and horizontal turbulent airflow disrupted the uniform draw allowing leakage of the tracer test gasses from the sash of the fume hoods.
To remedy the situation, engineers retained the same 700-cfm per diffuser, but distributed it more evenly with less discharge velocity. The solution was a fabric faced diffuser that replaced the metal radial flow. Now instead of turbulence and divergence, the air flows uniformly based on the shape and porosity of the factory-engineered fabric dispersion panel and is easily drawn into the fume hood. An additional benefit to University of Louisville lab researchers is the fact the airflow is now approximately 10-NC (noise criteria) less with the fabric diffusers, which provides a quieter working environment.
A general rule of thumb for fume hoods is to minimize turbulent supply airflow and balance the supply to provide good air movement to bottom and the top of the sash location. This not only generates poor mixing with existing air and circulation dead spots, but also affects the performance of a fume hood, which typically needs a stable room pressurization and air flow into its vicinity. As observed in smoke testing, conventional laminar flow metal diffusers disperse airflow vertically downward. Radial flow provided an airflow that traverses outward across the ceiling until it hits a wall and then travels down a wall. Flat faced radial flow provides a non-uniform, diverging airflow that when positioned end-to-end, can produce significant turbulent airflow patterns.
Existing lab directors, researchers, or validators that suspect supply airflow problems should call a manufacturer or contractor to review the problems and potentially perform a smoke test, where colored smoke is distributed through the HVAC system to provide a live visual or videotaped account of how the air is distributed. Smoke tests are very common in the HVAC field of air testing and balancing.
The Labs21 Program—sponsored by the EPA and the U.S. Department of Energy (DOE)—encourages laboratories to reduce energy consumption. Consequently, labs are reducing inkling outdoor air by including a variable-air-volume system to better match supply and exhaust air. As airflow decreases or increases, fabric dispersion provides consistent dispersion characteristics.
A second means of savings is being initiated by fume hood manufacturers that reduce energy consumption with equipment that draws less than the current 100-fpm standard, reducing to 75 and even 50-fpm levels. As these decrease, turbulent-causing radial metal diffusers will create more challenges for laboratories seeking ANSI/ASHRAE Standard 110 certification.
Since labs are subject to re-configurations, fabric diffusers such as the Metalpan D-Fuser, which fits over a 2 x 4-foot metal backpan can be replaced with a different air flow pattern to supply the a new configuration. The D-Fuser comes in four airflows:
· Surround Flow: The air flows through a variety of fabric face porosity choices geared to the area’s specified discharge velocity.
· Select Flow: Air is supplied through custom laser-cut vent patterns as well as the fabric to provide a directional control of airflow from one, two, three or all four sides of the fabric face.
Replacing a fabric face takes literally minutes and can be easily performed by maintenance or lab staff employees. The quick release of the fabric face framework also allows for commercial laundering.
Fabric duct and accessories are expected to be the dominant choice of airflow in new and retrofitted labs in the next decade because it appears to be the perfect HVAC solution for the industry’s quest for greater energy efficiency as well as a more effective airflow for research projects/occupants.
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