A balance-point method for assessing the effect of natural ventilation on indoor particle concentrations

A balance-point outdoor concentration was proposed to represent the value of outdoor concentration at which the air exchange between indoor and outdoor does not affect the indoor and outdoor pollutant concentration ratio (I/O). When the outdoor particle concentration is higher than the balance-point outdoor concentration, an increase in the indoor and outdoor air exchange results in a higher indoor particle concentration level and vice versa. Indoor particulate matter concentration and its relationship with outdoor particle concentration for a hypothetical naturally ventilated building are studied using a simple steady-state model. The effects of various factors such as air infiltration exchange rate, ambient particle concentration, indoor source intensity, and human activity on I/O, and the correlation between indoor and outdoor concentration were investigated, and the results compare reasonably well with the results reported in the literature.