Factors affecting air flow rates
Air flow rates depend on:
• prevailing wind direction
• average wind speeds (as a guide, use half the average seasonal speed, as wind speeds rarely fall below this value)
• how the site is influenced by daily and seasonal variations in wind such as onshore/offshore winds and how these may change during the day
• building form – whether it enhances or restricts air flow
• surrounding landform and planting – will they obstruct air flow
• orientation and position of window, door, roof ventilator, skylight and vent shaft
• surface pressure coefficients around the building.