Local air speeds measurement in mechanically ventilated spaces.

Air speeds at the occupied zone were studied experimentally in seven large railway stations of space volume varying from 540- 9076 m3• The spaces are installed with mechanical ventilation systems and the air supply flow rates are from 0.455-23.67 m3 s-1• Results were analyzed by dividing the measured air speeds into different ranges. Statistical data such as the peak  value, mean value, range of the air speeds and the bandwidth are calculated. Values of the percentage of discomfort were calculated and analyzed similarly. Correlation relationships of the variables with the macroscopic numbers describing air flow of the space including the air exchange rate, ventilation rate, the Reynolds number and the modified jet momentum number are studied. Two additional macroscopic flow numbers Xi and X2 defined by considering the range covered by a diffuser discharging air with a large horizontal component are proposed. It is found that both the modified jet momentum number and the new flow number Xi correlate with the air speed at the occupied zone and are recommended to use as an operating parameter on specifying the performance of the ventilation system for the space.