Thermal comfort in ventilated spaces depends mainly on air temperature, air speed and turbulence intensity. Mean air speed is commonly measured with omnidirectional hot sphere sensors, whereas directionally sensitive measurement instruments and CFD-simulations normally give the mean velocity vector. The magnitude of the mean velocity vector in turbulent room air flows can be much lower than the mean air speed due to different time averaging processes. This paper studies the difference both experimentally and theoretically as a function of turbulence intensity.
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.
Login