Correlation of air change efficiency with Archimedes number in a ventilated test room.

The "step-down" tracer gas technique was used to evaluate experimentally in a mechanically ventilated test room the effect of varying thermal boundary conditions, inlet flow rates, and inlet - exhaust grids position on the Air Change Efficiency (ACE) values. The paper shows that the measured global ACE values are strongly correlated to the Archimedes number (Ar). Reynolds number becomes influent only for Ar tending to zero and in this area a marked discontinuity has been observed, suggesting that switching from cooling to heating may produce a relevant variation on the performance of the ventilation system.