JAMES COOK UNIVERSITY OF NORTH QUEENSLAND
|negative ventilation||positive ventilation|
|NEGATIVE PRESSURE is when the windward or air entrance
of a building is CLOSED and the leeward or opposite side is OPEN.
POSITIVE PRESSURE is the reverse when the front (windward) is OPEN and the leeward is CLOSED.
|For ventilation POSITIVE is the best to create an air flow and air transfer within the building. During destructive storms the NEGATIVE aspect is recommended.|
|Schematic arrangement - extraction rate tests|
|The total pressure of an air stream flowing in a duct is the sum of the static or bursting pressure exerted on the sidewalls of the duct and the impact or velocity pressure of the moving air. With the use of the pitot tube the velocity pressure alone is indicated and the corresponding air velocity determined. Pitot tubes should be used with all ducts with diameters over 4" or 100mm.|
|Raked pitot tube internally designed to measure air flow.|