Ventilation designers should provide the tallest possible exhaust stacks so that effluent exit velocity can be minimized in order to save energy. The concept of "available dilution" helps determine the amount of contamination one can expect from an exhaust stack configuration of a given exit velocity and height. The minimum stack height above the roof should be at least 10 ft (3.0 m) as per ANSI Z9.5. However, the stack height, after correction for downwash, must also protrude above any flow recirculation cavity or obstructions, such as those typically caused by variation of roof levels, architectural fences, penthouses, and roof-mounted equipment. [Petersen, 2000] [Neuman, 2000] [D'Cruz, 1999] [Petersen, 1999] [Wilson, 1998] [Wilson, 1983; Industrial Ventilation..., 1995; ANSI… Z9.5:p.5, 1992]
Manifolded vs. individual exhausts
