Influence of wind on natural smoke and heat exhaust system performance in fire conditions

Abstract

This paper presents the results of a numerical study that examines the influence of wind on the performance of natural smoke and heat exhaust systems employing natural smoke ventilators, natural smoke ventilators equipped with deflectors, wall-mounted ventilators on the back façades of buildings and wall-mounted ventilators on the front façades of buildings. The authors present design methodologies along with traditional methods for estimation of the influence of wind on system performance. In the numerical study, three interchangeable natural smoke ventilation systems are presented and evaluated under different wind conditions. For the worst-case scenario, compared to no-wind conditions, the difference in the resulting flow for roof ventilators is 23,6% lower, while the performance of wall-mounted ventilators is reduced by 37% for tests designed with the same assumptions. This study also shows that laboratory estimates of the flow coefficient cannot be simply extended into an efficiency estimate for a complete system. A case with a commonly made mistake is also presented that shows flow into the building instead of out of it, which means that the system is not working at all. Conclusions regarding currently used design methodologies are given.