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The
International Journal of Ventilation
Volume 3 No 2 September 2004:
Paper 1: Design Considerations for Roof-Mounted Ventilation Systems
K. Syrios and G.R. Hunt
Department of
Civil and Environmental Engineering,
Imperial College London, London SW7 2AZ, UK.
Abstract
A methodology is presented for
determining the air flow rate through a stack-ventilated single-spaced enclosure
bearing a roof-mounted ventilation tower. We develop a ‘system discharge
coefficient’ which takes into account the pressure losses that occur at the
intake opening of the enclosure, inside the tower and at the outlet opening. The
system discharge coefficient is interpreted as a reduction in the area of the
path that the air flow takes. Based on this reduced area the air flow rate is
then determined. The proposed methodology may be applied to a broad range of
ventilation tower geometries which house typical components. To illustrate how
to apply this technique, we determine the volume flow rate through a tower
connected to a ventilated space; the tower houses a number of common components,
e.g. insect screens, acoustic baffles and louvres. For each component the
pressure losses and the pertinent resistance coefficients are presented and the
most ‘pressure consuming’ components identified. Once identified their
design may then be altered so as to improve air flow rates.
Key words: stack
ventilation, air flow rate, ventilation tower, air flow resistance, component
pressure losses.
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