Current publications (Rabiah et al. 1989) on the performance of fume hood control systems evaluate the ability of such systems to recover from an upset in face velocity. While these data compare control systems relative to their respective response times, they do not indicate whether the control system is capable of maintaining adequate capture rate of the VAV fume hood. The objective of this study was to find a method to evaluate VAV fume hood control system response time requirements considering the spill of a tracer gas due to the dynamics of fume hood operation. The tests were performed using vertical sash fume hoods with individual variable-speed exhaust fans. Sash movement was found to have the most profound effect on the escape of the tracer gas from the fume hood. For the fume hoods tested, it was noticed that control action was necessary within two to three seconds after the sash position was changed from minimum to full open to prevent any spill of the tracer gas.

KEYWORDS: tracers, gas, variable volume air conditioning, controls, exhaust hoods, comparing, testing.