Evaluating age from arbitrary forms of injection functions of tracer

The age of the air in a room is normally determined either from a pulse res ponse or from a step change response (up or down). There are a certain numb er of problems involved in applying these two theoretical models, especiall y those associated with the duration of the injection, which must either be infinitely short or infinitely long. A hybrid method that consists of inje cting a known quantity of tracer for a given time offers the advantages of both methods. The equation for calculating age is exact, regardless of the type of flow considered, and is derived from the expressions already establ ished for a pulse response to which a correction is included to account for the tracer generation function. If a rectangular pulse is used for the inj ection, the solution is particularly simple.