PSA: Corsi-Rosenthal Air Filters Are a Cheap and Effective Way to Improve Indoor Air Quality
Improving indoor air quality can help with many goals: pandemic preparedness (Covid is definitely airborne), reducing exposure to pollutants/allergens, and respiratory pathogens.
I don’t think there’s much awareness of this inexpensive technology so I thought I would share it with you. In my opinion, these could be in every classroom, workplace, bunker, etc. Seems like low hanging fruit to me.
This is an interesting idea. I’ve got a couple of initial thoughts, all off the cuff.
One consideration in their use is their placement relative to the flow of air in an environment. In indoor scenarios, air will likely flow in a somewhat predictable way based on the design of the ventilation, heat and cooling systems that are installed. A good location to put a filter is at the entrance to the air-return vent because it filters particles out before the air gets recirculated through the system and back into the indoor environment through the inflow vents. However, the point of this design is not to retrofit existing systems with the filter as the systems likely won’t be able to handle the additional resistance to air movement created by the filter. The consequence is that not all the air in the environment will pass through the filter. The placement is, therefore, important to try to maximise the amount of air that is filtered. A location near an air-return vent seems like it would a good starting location.
My concern, from a pandemic preparedness standpoint, is that an insufficient amount of airborne pathogens would be removed and the spread of the pathogens wouldn’t be halted.
From an air quality standpoint, the value seems higher. If you place the box in a good location, it will gradually filter pollutants/allergens out of the air over time. I could see this being particularly valuable for regions of the world where bushfires/wildfires are prevalent and the smoke can hang around for a number of days/weeks. During the Black Summer Bushfires in Australia, the air quality was extremely poor and N95 masks were recommended if you were spending extended time outside.
I recently just heard of attaching a MERV13 filter to a box fan. It would make sense that the 5 filter box design would potentially make the filters last longer, but I wonder if it’s actually more effective at filtering the air than a single filter attached to the back of the fan.
In theory, it would have the same effectiveness as a single filter as a given parcel of air will only pass through a single filter with both designs. To increase the effectiveness of the filtering, you would need to place the filters in series, ie. have two (or more) filters on the back of the fan. However, this would increase the resistance of the filter block and the fan would operate at a lower flow rate. So there’s a trade-off between effective air filtering and effective air flow.