Design considerations of a large central laboratory exhaust.

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. They are either individual, with each hood having its own exhaust fan and stack, or they are central, with multiple hoods served by common fans and stacks. This paper summarizes the rationale used during the design of a large central laboratory exhaust system. Considerations such as wake analysis, diversity, energy recovery, special exhausts, and fan sequencing to maintain stack velocity are presented.