Air movement over the skin in warm humid conditions encourages evaporation of sweat from the skin, causing a cooling sensation and lowering the effective temperature.
WIND GRADIENT
Variation in wind speed as wind speeds increase with the height above the ground, and the smoothness of the ground surface.
As wind passes over hills, there is an increase in wind speed on the windward side and a more sheltered area on the leeward side.
Although towns are “rough” and slow down the wind tail, tall buildings will often deflect strong winds down to a lower level.
Corresponding openings on the leeward side must be carefully located to effect effective cross-ventilation of all areas.
Wind shadows must be anticipated in order to be assured that other areas are not deprived of prevailing breezes.
Buildings should be spaced so that openings do not occur within the wind shadow of the building in front.
Average wind speed in the room will relate to the size of the opening, expressed as a percentage of the wall area, taking either the outlet or inlet, whichever is the smaller.
Wind speed increases rapidly as the percentage opening area increases from 0 to 20%.
Above 30% increase in area, the windspeed does not increase so fast.
The variation in wind direction will alter the direction of the wind shadow, and allowance must be made for these variations.
As a rough guide, the wind shadow will be 5 times the height of the building including the pitched roof.
The length of wind shadow for various shapes of buildings is given in the table, i.e., wind shadow length chart.
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