Influence of roof topology on the air distribution and ventilation effectiveness of wind towers

The performance of wind towers, which depends on external wind speed, is often reduced when still air conditions prevail. As a solution to this, this research used a combination of Computational Fluid Dynamics (CFD) and wind tunnel tests to evaluate the influence of five different roof configurations - flat roof, pitched roof, narrowed roof, curved roof and tilted curved roof - on the ventilation performance of commercial wind towers to identify the potential of accelerating wind passively to enhance natural ventilation within a building's microclimate. This assessment was carried out by analysing the static pressure, supply air velocity, supply flow rate, mean age of air and air change effectiveness which were computed for each model and compared against the CIBSE Environmental Design Guide and ASHRAE 129 set standards. This was followed by the evaluation of supply flow rates under varying wind directions from 0 degrees to 90 degrees. The results revealed that the narrowed roof produced an air change effectiveness of 0.96 and flow rates greater than 10L/s/person when the wind direction was prevalent at 0 degrees and 45 degrees, thus being the only roof that complied with the recommended guidelines. Conclusively, roof design being a strong influential factor upon wind properties is a keystone which, if meticulously designed, can be used to passively enhance the air distribution and ventilation effectiveness of wind towers. (C) 2016 Elsevier B.V. All rights reserved.