The effect of recirculation on ventilation effectiveness parameters.

The effect on ventilation effectiveness parameters of the recirculation of air is investigated. The results of work with respect to air change effectiveness parameters is explained and extended to the effect of recirculation on the contaminant removal effectiveness parameter of local air quality index. It is demonstrated, first with respect to a simple system with one supply and exhaust and then by extension to a system with multiple exhausts, that it is possible to calculate the effect of recirculation by means of a simple algebraic expression. It is explained how the procedure for the computation of ventilation effectiveness parameters by the multi-zonal method may be adapted to include the effects of recirculation.