The effect of recirculation on air-change effectiveness.

The effect of recirculation on the age of air is described. A new effectiveness measure called the relative air-change effectiveness is defined in such a way that the air distribution pattern in a room may be quantitatively characterized even when the age of the supply air is non-zero. This admits the evaluation of air distribution patterns in single-zone systems that recirculate air, and also multizone systems with or without recirculation. It is shown that the relative air-change effectiveness may be calculated either solely from age of air measurements of from age of air measurements and flow rate measurements. Re-evaluation of previously published experimental data demonstrates how knowledge of the relative air-change effectiveness may change conclusions drawn from experiments in working buildings.