A comparison between the step-up, step down and pulse injection techniques for the measurements of the mean age of air.

A comparison of three injection manners, step-up, step-down and pulse, for determination of the mean age of air was made by using nitrous oxide and sulphur hexafluoride as tracer gases. The concentrations of nitrous oxide and sulfur hexafluoride were simultaneously measured with a dual-channel IR-analyzer. Tests were carried out in a test chamber with air change rates of 3 h-1 and 5 h-1. The tracer gases were injected under three conditions: into the inlet air and directly into the room with and without extra mixing fans. The results suggest that the pulse procedure is as reliable as the two other methods used.