Some relations revisited in tracer gas analyses using numerical methods.

Tracer gas measurements have Jong been used to quantify the performance of ventilation systems by exploring such scales as the air exchange efficiency, the local mean age of the air, the residence time distribution and so on. The present work deals with a numerical reexamination and calibration of some relations previously derived from tracer gas analysis. The relations revisited include the approximated local air age in terms of the local, instant tracer concentration using the step-up and step-down methods, and the equations for the mean cumulative age distribution and for its frequency distribution. A mixing ventilation flow is employed in the numerical examination. The availability of these relations for practical tracer gas analyses is discussed and they are shown to be useful for efficient tracer measurements.