Errors in the measurement of local and room mean age using tracer gas methods.

Local and room mean ages of the air in a room may be measured by three versions of the tracer gas technique; which are the pulse method, the tracer step-up up method and the tracer decay method. The values of mean age obtained are of course subject to errors in the measurement of the tracer gas concentrations. The sensitivity of the three methods to errors in the tracer gas concentration is not the same, and in some cases can be very large. In order to examine this problem, test measuremenb have been carried out in a model room using the three difEerent methods. The results obtained from these tests were then compared with each other, and with theoretical data, which was generated with differing levels of error. It has been found that the step-up method was the least reliable and local and room mean ages generated using this method varied substantially from mean ages measured using the other two tracer gas techniques,