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

States that it is difficult to achieve good mixing in a large space and that the usual methods to evaluate the ventilation system in such large spaces with the age of air measured by tracer gas is not often practicable. Proposes a new method to evaluate this ventilation, based on the normal step-down or decay method. A small control volume of tracer gas is used as opposed to filling the entire space. the local mean age of air is then measured in a study of the transient decay curve of the tracer gas concentration. Considers several positions and uses the ages measured to assess the space ventilation. Describes how field measurements were made to demonstrate the method. In addition the age measured in the control volume is compared with the age measured by thorough mixing of tracer gas in a smaller room.