Filtration efficiency and ventilation performance of window screen filters

Efficient natural ventilation is an important approach to maintaining indoor air quality. However, owing to the increasing concentration of outdoor particulate matter (PM), natural ventilation without filtration results in the introduction of outdoor particles in buildings, thus increasing indoor exposure to PM. Indoor PM concentration is determined by the particle removal efficiency of window screen filters. In this study, using an experimental chamber and an actual building, the particle removal performance of window screen filters was evaluated for their potential application. To investigate the relationship between the outdoor and indoor concentrations of particles with diameter size ≤ 2.5 μm (PM_2.5), and to evaluate the efficiency of the window screen filters in removing such particles, the window screen filters were installed in a full-scale test room. The results obtained showed that the average PM_2.5 indoor/outdoor (I/O) ratio was within the range 0.24–0.72, and varied with the performance of the window screen filter. An analysis of the correlation between the ventilation rate and the air exchange rate (AER) showed that the I/O ratio increased as AER increased. Additionally, the particle size removal efficiency (PSE) of the window screen filters varied considerably with increasing particle diameter (0.3–10.0 μm), ranging from 0 to 82.4%, and the PSE results showed trends that were similar to those of PM_2.5 removal efficiency based on the measurements performed in the test room. Therefore, window screen filters can be used to reduce the indoor concentration of outdoor particles.