Numerical analysis of wind-driven cross ventilation in long buildings

The rule of thumb for effective wind-driven cross ventilation suggested that the length of the building should be less than five times of ceiling height. This study uses a Large Eddy Simulation model to investigate this rule of thumb for buildings of different length. The numerical results reveal that the windward pressure is independent of the building length, but the leeward pressure of short buildings is lower than that of long buildings, because of the reattachment on the roof of the long buildings. Therefore, the ventilation rates of short buildings are higher partly due to the larger pressure difference between the windward and leeward façades. The other reason for the ventilation rate decreases as the building length increases is owing to the friction inside the building. The internal friction can produce a sluggish zone inside the building, and reduce the total flow rate of cross ventilation.