The primary purpose of a laboratory exhaust system is to remove and convey fumes from the fume hoods and laboratory spaces to an area for safe discharge. This requires discharge conditions that allow good dispersion and prevent re-entrainment. Since laboratories are usually designed for once through air ( 100% makeup air with no recirculation), a secondary purpose is energy recovery from the exhaust stream. Laboratory exhaust systems have typically one of two arrangements.
Containment of hazards in a laboratory chemical hood is based on the principle that air drawn through the face area of the hood is sufficient to overcome the many challenges at or near the opening. Challenges to overcome include, but are not limited to, air velocities near the hood, movement of the researcher, people walking past the hood, location of equipment inside the hood, size of the sash opening, and the shape and configuration of entrance conditions. To overcome these challenges, a sufficient face velocity must be maintained.
The heating, ventilating, and air-conditioning (HVAC) system for a laboratory must be designed with consideration for safety, air cleanliness, and space temperature. The primary safety concern is to ensure proper coordination between fume hood exhaust and makeup air supply. Air cleanliness is maintained by properly filtering supply air, by delivering adequate room air changes, and by ensuring proper pressure relationships between the laboratory and adjacent spaces. Space temperature is maintained by supplying enough cooling air to offset the amount of heat generated in the room.
A three-dimensional computational fluid dynamics (CFD) analysis has been used to predict airflow patterns in laboratory fume hoods. The simulation includes bypass fume hood primary operational features including the top and bottom bypasses, front airfoils, and rear-slotted baffles. All results were validated experimentally, and the simulation was found to adequately predict fume hood airflow patterns. The results indicate that fume hood flow patterns are highly dependent on inlet flow boundary conditions so that the computation must include the near field room airflow.
A research program was undertaken by the National Institutes of Health (NIH) to investigate ventilation performance of different laboratory configurations and their effect on the laboratory hood. The intention is to provide a basis for guidelines aimed at maximizing laboratory hood containment.
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