HI-02-15-2 -- The Influence of a Rooftop Structure on the Dispersion of Exhaust from a Rooftop Stack PDF

In a previous study, the dispersion of exhaust from a three-story building was evaluated using field and wind tunnel experiments. Low dilution values obtained at some rooftop receptors were attributed o a rooftop structure located upwind of the stack. In the present study, wind tunnel experiments were performed to determine he impact of he structure on the plume. The results show that dilution at various receptors increases significantly when the structure is removed, due likely to an increase in plume rise. The amount of increase in dilution depends on the momentum ratio, M (the ratio of exhaust velocity to wind speed), and wind direction. The results indicate that, depending on its interpretation, the ASHRAE geometric design method for rooftop stacks may lead to unconservative design when rooftop structures are present.

Units: Dual