Preliminary studies on a new method for assessing ventilation in large spaces

Conventional methods of evaluating the ventilation system in large spaces using the age of air measured by tracer gas might not be practical. It is difficult to achieve ‘well-mixed’ condition throughout the huge space; and the cost of discharging large volume of tracer gas is too expensive. A new method for evaluating the ventilation in large enclosed spaces is proposed. This is based on the conventional step-down or decay method. Instead of filling up the entire hall with tracer gas, only a small control volume is considered. Tracer gas is discharged into this control volume with the ‘local’ mean age of air measured by studying the transient decay curve of the tracer gas concentration. Several positions are considered and the ‘ages’ measured can be used to evaluate the ventilation in the big hall. Field measurements were made in two big halls for illustrating the method. Further, the age measured in the control volume is compared with the age measured by thorough mixing of tracer gas in a smaller room.