Comparison of Portable and Large Mobile Air Cleaners for Use in Classrooms and the Effect of Increasing Filter Loading on Particle Number Concentration Reduction Efficiency

This study focuses on the effect of portable and large filter-based air cleaners (HEPA filters), which became popular indoors during COVID-19 pandemic, their suitability for classrooms (here 186 m3). The decay rates particle number concentration (PNC) were measured simultaneously at up to four positions in room. It was found that different outlet configurations units have an actual PNC removal room when operated same volume flow rates. airflow efficiency (AP) a classroom is quantified with introduced Air Cleaning Efficiency Factor this identify beneficial airflows. In context, filter loading long-term operation cleaning also investigated. emitted sound pressure levels APs are given special attention as critical factor use schools, well power consumption. A total six devices tested—two APs. order achieve necessary rates, three or used one room, while only per When circulation exhibit higher compared At 4–5 h−1, exceeded value 45 dB(A). Two reach below 40 dB(A) whereby both units, positioned rear wall, realize homogeneous dilution air. achieved by directed horizontally height above 2 m diagonally towards ceiling, points into partly sides. On other hand, exclusively sides floor level all achieves lower To investigate influence loading, school period year (190 days 8 h each). For APs, leads changes reduction efficiency, ranging from −3% −34%. not size prefilter main has significant influence, but whether there bypass negatively affects filter. time, it shown type AP, measuring drop across filters readjusting fan, kept rate almost constant (up −3%) over year.