where Ce is the pollutant concentration in exhaust air, CS the
pollutant concentration in supply air and CP is the mean contaminant
concentration in the occupied zone. If Cp is the concentration
at breathing level, then the ventilation effectiveness can be used to
assess the efficiency of contaminant removal from the breathing
zone. This index is indefinitely large when Cs and CP are equal.
However, to evaluate the ability of the ventilation system in
reducing the concentrations of pollutants at a point in time, the
absolute ventilation efficiency, which is expressed as given below
has been used