The personal ventilation (PV) system decreases the pollutant concentration mostly in the microenvironment at the workstation, but it can also increase the contaminant in other zone of the room. Therefore, occupant’s exposure to pollutant depends on the ratio of time occupant stays at the workstation over total time he/she stays in the room. This ratio is named occupied density (OD).

An index, using a modified definition of OD, is developed to compare and quantify the variation in terms of inhaled pollution by occupant in a room with PV in conjunction with a total-volume ventilation system. The index is applied to data collected during full-scale room measurements.

The results show that the index can be used at the design stage for assessment the benefit of PV when applied in practice for office buildings with different OD. It is for example demonstrated that if the occupied density is lower than 0.5 the use of displacement ventilation alone will be advantageous with regard to human-produced contaminates in comparison when it is combined with PV system.