1/ All gr8 points made by @Poppendieck. Knows his stuff! I've recommended in several forums, including today, to stick to proven technologies. In the case of portable air cleaners, that means those with HEPA filters. As Dustin says, avoid "add ons". Stick to HEPA. (more)
2/ Any portable air cleaner (PAC) that is worth considering should have a stated Clean Air Delivery Rate (CADR). Those that do not, probably don't for a reason. The CADR is usually certified (in North America) by AHAM - aham.org. (more)
3/ CADR is the product of 2 numbers (eta x Q). Eta is the single-pass removal efficiency for a pollutant (fraction of pollutant removed with one pass through a PAC). Q is the volumetric flow rate of air (e.g., standard cubic feet per minute [scfm]) through a PAC. (more)
4/ Some PACs not based on HEPA filtration may have a relatively large eta but very low value of Q. Companies that sell these have touted their high removal efficiency (despite a low & unstated CADR). Efficient but not effective! You are not told that part of the story.
5/ For a HEPA-based air cleaner you can take the CADR & multiply it by 60 to get cubic feet per hour. Then divide by room volume (floor area x ceiling height). The resulting value has units of per hour (i.e., 1/hr), the same units as outdoor air exchange rate. (more)
6/ So, you can think of a PAC as delivering an equivalent additional outdoor air exchange rate (hence Clean Air Delivery Rate). Example, if the actual air exchange rate is 2/hr and you have a CADR*60/volume = 2/hr it is like you just doubled outdoor air exchange rate. (more)
7/ If the mean removal pathways for particles in an indoor environment are outdoor air exchange (ventilation) and a PAC, in previous example the particle levels in air would be reduced by 50% relative to just ventilation. If there is recirculation through an HVAC system (more)
8/ with filtration in the unit, the PAC will still reduce particle levels but not with the same impact (as there are now three major removal mechanisms). For a typical K-12 classroom or large bedroom, etc., look for PAC w/ HEPA that have CADR > 300 scfm for ... (more)
9/ smoke (very small particles). If it has a high CADR for these particles it will do well for 1 micron and greater particles that contain viruses.
I hope that this is helpful.
There will be a short quiz in twitter class tomorrow.
I hope that this is helpful.
There will be a short quiz in twitter class tomorrow.
