Definition of ventilation efficiency and the efficiency of mechanical ventilation systems.

Discusses air quality and the related definitions of ventilation efficiency. Suggests a definition of efficiency for ventilation systems in residential buildings that takes into consideration how ventilation air spreads within a dwelling. Measurements of the efficiency for exhaust, supply and combined systems show that for combined and supply systems the highest efficiency occurs in those parts where the air is supplied. For these systems efficiency is sensitive to ventilation flow rate, while for the exhaust system the relative efficiency is more or less independent of ventilation flow rate. Finds that in warm-air systems the ventilation efficiency is affected by the positioning of the supply and exhaust registers, the ventilation flow rate and the relative difference between supply air temperature and room air temperature.