Abstract:
The natural ventilation testing methodology developed at the University of
Technology, Sydney (UTS) to distinguish a ventilators flow rate performance due to
wind siphonage as distinct from stack effect (temperature / pressure differentials) is
detailed in this paper. From experimental data the percentage of exhaust flow rate
contributable to either stack effect or wind siphonage of various devices and designs
can then be combined to achieve the total exhaust rate possible under the
environmental/climatic conditions likely to be experienced.
Variations in temperature and pressure may not be adequately accounted for in wind
tunnel test procedures and a steady state airconditioned environment is required so as
to reduce any discrepancies that may be attributable to temperature and pressure
differentials.
The testing of ventilators must adhere to aerodynamic principles and an ideal test
procedure is the comparison to the perfect bell mouth. The coefficient of discharge
(Cd) at a given wind speed would be = Q actual / Q (bell mouth).
The perfect bell mouth is not a standard ventilation shape so a more practical
approach to testing was chosen. It was decided to compare ventilators relative
performance to an unimpeded 300mm diameter open pipe set 200mm high above the
subjective roofline as the base standard.
Experiments with various manufacturers’ ventilators were undertaken, comparing
them to, the relative performance of an unimpeded 300mm diameter opening, the
results are disclosed in this paper.
New advanced ventilation designs are described, such as the long volume turbines and
improved wind directional vanes, with increased exhaust flow rates. Product
innovation and improved performance led to the commercialisation of new products
such as the Wind Directional Skylight Ventilator and the roof siphon that utilises the
hot air in the roof space to drive the natural ventilation process.
