As a non-engineer not working in this space, I can’t say much but I’ve had a lot of similar thoughts (ceiling mounted, outer casing, non-HEPA). I do have my question about your design (and GPT o4-mini-high is pretty skeptical), wondering whether the fan really draws all the air through the filters. This design also doesn’t work well in smaller rooms? I personally like “fandeliers” or ceiling-mounted CR boxes that include lighting and actually look decent.
I agree that there seems to be a lot of improvement up for grabs, and I would love to see a company start innovating here and—most importantly—scale up production.
The problem, however, seems like it would be demand: air purifiers aren’t in high demand, and consumers don’t notice the difference between high and low CADR (they do notice noise). A company could bet on creating a large, cheap stockpile to sell off at high prices during an epidemic, but I imagine it’d be hard to get investors on board for that. This space probably needs market-shaping, such as advance market commitments or indoor air quality regulations (e.g. mandated PM2.5 levels) creating demand.
I do have my question about your design (and GPT o4-mini-high is pretty skeptical), wondering whether the fan really draws all the air through the filters.
Ah, good post! I should probably just have refrained from commenting on the design given my limited knowledge. For benchmarking purposes, perhaps these designs are better than the one from Wirecutter:
wondering whether the fan really draws all the air through the filters
It doesn’t need to. If only 90% goes through each time, it’s incredibly effective, since it’s getting through all the air in the room many times each hour.
I think to some extent the skepticism is warranted due to a mix of reduced airflow via restriction and the unknown q of bypassed airflow. Measuring airflow in a few locations with an inexpensive anemometer would be sufficient to allay these concerns, but using particulate as a proxy doesn’t seem quite as strong
Isn’t particulate what we care about? The purpose of the filters is to get particulate out of the air, and the controlled experiment Jeff did basically measures that. If air mixing is the concern, ceiling fans can mix air far more than required, and you can just measure particulate in several locations anyway.
It’s an OK experiment, but there could be other reasons for air exchange in the room that vary quite widely. Building infiltration would exchange air with outdoors and varies quite a bit with outdoor conditions. It’s also not very difficult to measure airflow so I don’t see many disadvantages to doing so
Btw this might sound trivial, but for people with a central ducted HVAC system it’s quite common for the central fan to pressurize/depressurize rooms with closed doors, which in some cases will be the largest driver of infiltration. So simply having an AC or furnace cycle on and off during the experiment would be quite bad for the results.
Good point! I’m used to houses with the older systems (steam, forced hot water) that are common in the Northeast and wasn’t thinking about this effect.
As a non-engineer not working in this space, I can’t say much but I’ve had a lot of similar thoughts (ceiling mounted, outer casing, non-HEPA).
I do have my question about your design (and GPT o4-mini-high is pretty skeptical), wondering whether the fan really draws all the air through the filters.This design also doesn’t work well in smaller rooms? I personally like “fandeliers” or ceiling-mounted CR boxes that include lighting and actually look decent.I agree that there seems to be a lot of improvement up for grabs, and I would love to see a company start innovating here and—most importantly—scale up production.
The problem, however, seems like it would be demand: air purifiers aren’t in high demand, and consumers don’t notice the difference between high and low CADR (they do notice noise). A company could bet on creating a large, cheap stockpile to sell off at high prices during an epidemic, but I imagine it’d be hard to get investors on board for that. This space probably needs market-shaping, such as advance market commitments or indoor air quality regulations (e.g. mandated PM2.5 levels) creating demand.
When I tested the prototype it worked well: https://www.jefftk.com/p/ceiling-air-purifier
Now that I know more about how these fans move air, I think it would work even better if the filters extended slightly lower.
Ah, good post! I should probably just have refrained from commenting on the design given my limited knowledge. For benchmarking purposes, perhaps these designs are better than the one from Wirecutter:
https://housefresh.com/quiet-air-purifiers/
It doesn’t need to. If only 90% goes through each time, it’s incredibly effective, since it’s getting through all the air in the room many times each hour.
I think to some extent the skepticism is warranted due to a mix of reduced airflow via restriction and the unknown q of bypassed airflow. Measuring airflow in a few locations with an inexpensive anemometer would be sufficient to allay these concerns, but using particulate as a proxy doesn’t seem quite as strong
Isn’t particulate what we care about? The purpose of the filters is to get particulate out of the air, and the controlled experiment Jeff did basically measures that. If air mixing is the concern, ceiling fans can mix air far more than required, and you can just measure particulate in several locations anyway.
It’s an OK experiment, but there could be other reasons for air exchange in the room that vary quite widely. Building infiltration would exchange air with outdoors and varies quite a bit with outdoor conditions. It’s also not very difficult to measure airflow so I don’t see many disadvantages to doing so
Btw this might sound trivial, but for people with a central ducted HVAC system it’s quite common for the central fan to pressurize/depressurize rooms with closed doors, which in some cases will be the largest driver of infiltration. So simply having an AC or furnace cycle on and off during the experiment would be quite bad for the results.
Good point! I’m used to houses with the older systems (steam, forced hot water) that are common in the Northeast and wasn’t thinking about this effect.