Laboratory exhaust stacks should be designed with sufficient height and exit momentum to avoid re-entry of exhaust and possible air quality problems, and the design should be evaluated before construction. One evaluation method is presented in this paper that combines dilution prediction equations from the 1997 ASHRAE Handbook - Fundamentals (1997) and a dilution criteria of Halitsky (1988). This method is less conservative than a geometric method in the ASHRAE Handbook and is less costly than wind-tunnel modeling. The method should only be applied to relatively simple building geometries with no larger buildings adjacent to them.

A planned change to the ASHRAE equations, which would result in larger stacks being necessary, is discussed. Further investigation of this change is recommended using comparisons to wind tunnel data.

Units: Dual