CFD STUDY OF ASHRAE 110 FUME HOOD TEST
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For years laboratories were known for their high operating costs due to requiring significantly more airflow than typical building spaces. An office space typically requires around 2-3 air changes per hour where a laboratory will require 6-12 air changes per hour. As more knowledge has been gained about containment, there is an ever-growing need for safety, and as this need for safety has grown, so too has the need for more ventilation. Today laboratories are full of ventilated products, and as a result, operating expenses are through the roof, literally. Exhausting conditioned air has always been just thought of as the cost of safety but with costs ranging from $3-9 per CFM-yr, designers began looking for ways to cut the cost without compromising safety. Thus, major innovations were made in the field, leading us to where we are today with the industry’s Low Exhaust Volume (LEV) fume hoods.
Low Exhaust Fume Hoods
To overcome the issue of high energy costs in laboratories, the industry has developed energy efficient LEV fume hoods. SEFA 1 – 2010, Laboratory Fume Hoods divides LEV fume hoods into two categories: Low Flow Fume Hoods and Low Velocity Fume Hoods.
Low Flow Fume Hoods are hoods that reduce the exhaust volume by reducing the size of a sash opening.
Low Velocity Fume Hoods are hoods that reduce the exhaust volume by reducing the face velocity a hood operates at. Low Velocity Fume Hoods can operate as low as 60 FPM and pass ASHRAE 110 – 2016, Methods of Testing Performance of Laboratory Fume Hoods containment testing.
Innovative design features like efficient bypasses, baffle configurations, aerodynamic low profile airfoils, and radiused fascias grant an equivalent or greater level of safety to LEV fume hoods compared to conventional fume hoods. A comparison of the features of both conventional and low exhaust volume hoods are presented below:
Part of the reason LEV hoods can safely operate at lower face velocities is that face velocity by itself is not the only indicator of how well a fume hood contains air.
There are four main factors that must be taken into account when selecting a face velocity:
design of the hood
location of the hood within the laboratory
quality of the supply air distribution
work practices of the user
The standard governing laboratory ventilation is ANSI/AIHA Z9.5 – 2012, American National Standard for Laboratory Ventilation. ANSI/AIHA Z9.5-2012 recognizes that LEV hoods can perform at face velocities as low as 60 FPM, whereas conventional fume hoods are only recommended to operate as low as 80 FPM. The ANSI/AIHA Z9.5 – 2012 recommendation is based on the optimization of those four factors through proper design and work rules.
In some cases, local and state codes dictate a specific face velocity that must be followed unless special permission is given. Even then, the design features of LEV fume hoods are capable of providing improved safety and containment despite operating at a face velocity typical of conventional fume hoods. Using an LEV hood at lower sash opening and lower face velocities will yield higher levels of safety and energy efficiency.
Wilburn is an Industrial Hygienist and Product Designer at Kewaunee Scientific.