Static split duct roof ventilators.

Split-duct roof ventilators or windcatchers are used to provide both supply and extract ventilation to the spaces which they serve. However, buildings are often erected in conditions where there is no prevailing wind direction. An investigation into four and six segment windcatchers to determine their relative performances under different wind conditions was undertaken using scale models in a wind tunnel. Conclusions indjciate that six segment windcatchers have a more predictable, reliable performance in uncertain or variablewind conditions. However, a four segment windcatcher that is orientated 45 degrees to the prevailing wind will generate the highest pressure differences and consequently the highest duct speeds in an installation. Further work on strategies for windless conditions are summarized, and scope for further research is indicated.