Measurements ith tracer gases were performed, together with more classical temperature and air velocity measurements, on various ventilation systems installed in the test chamber of Sulzer Infra, in Winterthur. The test chamber was arranged to simulate an office room, with heat generated form computers and occupants, Moreover, the contaminants from one occupant was simulated with a tracer gas. This document addresses the measurement of the age of the air and of the contaminant removal effectiveness at various locations.