Experimental studies on the airflow characteristics of spaces with mechanical ventilation

Ventilation in the occupied zone was studied experimentally in the waiting area of nine railway concourses in Hong Kong. The performance of the mechanical ventilation systems in those areas was also evaluated by studying the age of air, local air velocity, and carbon dioxide level. The results show that ventilation effectiveness may not necessarily be improved with increasing supply or extraction flow rate. The revised jet momentum numbers for those stations are also calculated and compared with the mean carbon dioxide concentration and the local age of air. It appears that this parameter can be used for evaluating the performance of the ventilation systems. A linear relation is fitted empirically to correlate the mean local age of air with the revised jet momentum number for the nine stations.