Assessment of pre-filter systems to control indoor inflow of particulate matter

Abstract

Ventilation systems are installed to introduce outdoor fresh air into indoor environments in an effort to improve indoor air quality. However, as the concentrations of outdoor particulate matter are increasing, additional measures are required to reduce these concentrations in the incoming outdoor air in ventilation systems. This study used a multi-step process to investigate these issues. First, we determined the current status of indoor fine particulate matter (PM2.5) concentrations based on the filter grade of an installed ventilation system. Second, a pre-filter system with guaranteed filtering performance and usability was installed in the outdoor air duct of a ventilation system to compensate for its shortcomings; then, the reduction of indoor PM2.5 concentration was evaluated. To determine whether the filtering performance of the ventilation system was sufficient, the relationships between the indoor–outdoor PM2.5 concentrations and indoor/outdoor PM2.5 concentration ratio were established based on the World Health Organization standard concentrations. The quality of the pre-filter system was tested by installing it in two separate houses that were using the same ventilation system. The results show that based on the filter grade of the European Standards, a fine filter (F grade) or a filter of a higher grade should be used for conventional ventilation systems. By installing a pre-filter system in the conventional ventilation system, the indoor PM2.5 concentration was reduced by 31% and 69% depending on the maintenance of the ventilation system.