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.
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.