I've written a post about air distribution. It seems like a technical and minor aspect of air quality, but it's extremely important. So much of the misinformation and bad decisions during the pandemic relate to misunderstanding air distribution.
1/15
https://t.co/EEdJ4mfn4h
Air distribution refers to how air mixes and is supplied throughout the space. You can get clean air into a room, but you only care about what people are breathing in. When that clean air bypasses people and gets exhausted, it's a useless waste of energy.
2/15 https://t.co/COXi2JIyRo
The goal in the vast majority of ventilation systems is to have the air properly mixed. It ensures the clean air dilutes all the pollutants and there are no spaces with higher pollutant concentration. A proper design with diffusers can achieve this.
3/15 https://t.co/ya2PFNd2j0
Often corners are cut and no air distribution is installed. If the supply and return are on the same side of the room, distribution effectiveness is 50%, meaning the ventilation is only half as effective as advertised. Here's an example of no air distribution.
4/15 https://t.co/tUX8x8kTmq
If a system was designed without proper air distribution, fans are the effective tool to mix the air. Ceiling fans are the best, but pedestal fans work too. Avoid creating direct currents between people.
5/15 https://t.co/AEq9Ms0vSs
Checking the ventilation system does not tell you if the air is properly distributed in the space. You need to measure pollutants in the space for that. The best tool and most obvious one is monitoring CO2. Here's a full intro.
6/15
https://itsairborne.com/intro-to-monitoring-co2-20f191dd8f60
You can also do a study where you measure the pollutant decay in the space. It's easiest to do it with dry ice and a CO2 monitor. It's explained here on page 16 https://schools.forhealth.org/wp-content/uploads/sites/19/2020/10/Harvard-Healthy-Buildings-program-How-to-assess-classroom-ventilation-10-30-2020.pdf-EN.pdf
7/15 https://t.co/hJQLBVsk2i
The last tool is a fog study that can identify all the dead-zones in a space where air is not being cleaned and pollutant concentration can increase.
https://t.co/KEFPJPCJ7A
8/15
Short range transmission is higher risk because there is a higher virus concentration in that location - it's an air distribution issue. Good air mixing, like with a ceiling fan, can reduce the virus concentration in that area and mitigate short range transmission.
9/15 https://t.co/FibTGtXHkN
Concerns about "blowing the virus around" are nonsense, because it is already being blown around. Air travels around a room, even if you can't feel it or see it. The goal is to make sure there is clean air supplied to the room and it is diluting the pollutants.
10/15
HEPA filters, which use fans, can help mix the air in the room. They do not have effective distribution by themselves since the supply and return are so close to each other. Think of them as working with and augmenting the ventilation system.
11/15
There's no concern about HEPA filters "drawing the virus closer to you". They pull in air from the room that is mixed. Because of poor air distribution, the air close to the HEPA filter will likely have lower pollutant concentrations.
12/15
Personal HEPA filters aren't necessarily effective in general. If you have it blowing on your face, it will reduce the amount of virus you will be inhaling, depending on the distance. Comfort is an issue with doing this as a long term strategy. Test from @CleanAirStars .
13/15 https://t.co/c7RkzgXikw
For personal air outlets on planes, the air mixes with the space pretty quickly, so they do not provide significant protection. Advice from ASHRAE is they are not necessarily recommended, but not discouraged.
14/15
https://www.ashrae.org/file%20library/technical%20resources/covid-19/ashrae-transportation-c19-guidance.pdf https://t.co/TPUkdfaj8y
Plexiglass barriers interfere with air distribution, increase virus concentration and consequently increase risk of disease transmission. Air distribution effects should be studied if barriers are considered for use.
15/15 https://t.co/zMrFhMnJdl
