Derives formally two air diffusion efficiency measures, the displacement efficiency and the removal efficiency, using a control volume/conservation of mass approach. States the generalised forms of these measures come from a common origin, proposed to be called the transfer efficiency, and include system-level effects. Discusses factors influencing the evaluation of these measures, including recirculation, time constants, internal generation flow rate and location of the control volume. Sates the improved forms of the efficiency equations are equally applicable to tracer gas concentration growth and decay experiments. States that two new measures, the system displacement efficiency and the system removal efficiency, evaluate the combined characteristics of the air handler and the room overflow patterns.

KEYWORDS: Indoor, air quality, efficiency, air diffusion, ventilation, performance