Filter type

Ventilation systems usually have a filter through which the air about to be supplied to your room will be passed. Filter efficiency is usually reported in terms of a MERV (Minimum efficiency reporting value) number. Higher MERV numbered filters are better at filtering out small droplets and particulates from the air. The filter, by eliminating virus laden particles from recirculated air, adds to the volume of outdoor air being supplied to your room in terms of virus free air. We add the fraction of filtered outdoor air as an added measure of outdoor air ventilation when doing the calculations.

We have included a list of filters with the following specifications of filtration efficiency for particles in the range of one to three microns. Particles in this size range are generated plentifully by occupants, even when just breathing, and they are also more likely to carry the viruses.