Would a ceiling mounted air cleaner help with coronavirus?

[Roger Feeley]

My daughter is on the board of our local preschool. They are trying to figure out how to open next school year. Getting 2 year olds to wear masks is obviously a big deal so they are trying to think up other things to do.

Another approach is to filter the ambient air. Say we have a room that’s 20’x30’x10’ high so 6000 cubic feet. Jet air cleaner ads-1000 moves over 1000cfm so 10 changes per hour. As sold, these things filter to 1 micron.

The actual virus is much smaller but the virus travels in a droplet that should be caught. I have some non-woven polypropylene used in n-95 masks and could are a pre filter from that.

thoughts?

[Matt Day]

Highly doubtful. Someone asked the same question a while back.

Spread of the virus is droplets from speech or sneezes/coughs and close contact, so an air filter on the ceiling won’t catch that.

[Frank Pratt]

I did a fair bit of reading on just this subject. The virus is small enough to pass, but a virus on it's own won't last long. Airborn, they are almost always in droplets that they were breathed, sneezed, or coughed out with. They can travel a fair distance. Those droplets are caught by HEPA filters. So yes, HEPA filtration will help, the more, the better. Don't bother with anything less than HEPA though. That 1 micron stuff wouldn't do much.

Big Ass Fans just announced a UV option for some of their fans. It is aimed up from the fan so it won't fry people's eyeballs.

[Aaron Rosenthal]

Might be interesting to find out what size a HEPA filter screens.
I was given to understand HEPA will filter to 3 microns, and the Covid-19 virus is closer to 1 micron.

[Roger Feeley]

I hunted around yesterday to see what hepa would do. It’s around a half micron. For what it’s worth one source said hepa is equal to 17-20 on the MERV scale.

[Ole Anderson]

Went to the dentist office yesterday. Big changes. One of them was that each treatment room now has a "Hospital Grade" floor mounted recirculating HEPA filter.

[Frank Pratt]

HEPA is 99.97% of particles down to .3​ microns.

An interesting thing about particles that are smaller than that is that a HEPA filter will still catch most of them because they are so light that they are subject to Brownian motion. The particles zig-zag around so much as they pass into the media that they bump into it & get stuck.

[David L Morse]

HEPA is 99.97% of particles down to .3​ microns.

An interesting thing about particles that are smaller than that is that a HEPA filter will still catch most of them because they are so light that they are subject to Brownian motion. The particles zig-zag around so much as they pass into the media that they bump into it & get stuck.

HA! I was just about to post about diffusion capture when you're edit showed up. Glad you added that.

But, since I gathered some stuff for the post I guess I'll show it anyway.

An interesting chart:

435735

That chart is from here (https://www.tsi.com/getmedia/4982cf03-ea99-4d0f-a660-42b24aedba14/ITI-041-A4?ext=.pdf).

This (https://www.tandfonline.com/doi/pdf/10.1080/00022470.1980.10464592) for even more as well as an introduction to Most Penetrating Particle Size (MPPS).

Also, the size of the COVID-19 virus particle is usually reported as 0.12 micron.

[Bill Dufour]

My dentist has a small portable box fan air cleaner in the waiting room. It has a filter and a internal uv light. I am not sure if it is better to have calm air and let the virus settle and die or to kick the air around with a fan and try to filter it before you breathe it. A lot of air motion will keep it airborne longer.
Bil lD.

[Frank Pratt]

HA! I was just about to post about diffusion capture when you're edit showed up. Glad you added that.

But, since I gathered some stuff for the post I guess I'll show it anyway.

An interesting chart:

435735

That chart is from here (https://www.tsi.com/getmedia/4982cf03-ea99-4d0f-a660-42b24aedba14/ITI-041-A4?ext=.pdf).

This (https://www.tandfonline.com/doi/pdf/10.1080/00022470.1980.10464592) for even more as well as an introduction to Most Penetrating Particle Size (MPPS).

Also, the size of the COVID-19 virus particle is usually reported as 0.12 micron.

Thanks for posting that David. I hadn't seen the graph before & it illustrates very well.

[Kev Williams]

As I understand it (meaning, I may be wrong ;) ) - covid-19 isn't airborne enough, I assume because it's expelled wet. So if a hepa filter would work, you'd want it low, NOT on the ceiling.

And back in May I read this article below about a guy who's working on a portable virus detector. I found it very interesting as it seems very do-able. I've seen or heard nothing more of this since. Give it a read... :)

https://www.ksl.com/article/46750908/u-professor-developing-portable-reusable-covid-19-test

[Mike Soaper]

"As I understand it (meaning, I may be wrong ) - covid-19 isn't airborne enough, I assume because it's expelled wet. So if a hepa filter would work, you'd want it low, NOT on the ceiling. "


I saw a report that explained how several (8?) occupants in a restaurant contracted covid because 2 infected people were sitting near the hvac supply duct/register, it seems their droplets were carried via airflow to 3-4? tables downstream and those folks got covid.

Maybe not on the ceiling but how about under a raised floor?, like a big sanding station, it might draw the droplets down before they can go lateral as normal? Probably not practical though, cleaning under the floor would probably be a difficult, and dangerous for those wearing pointy high heeled shoes

[Roger Feeley]

I wondered about the raised floor idea. Computer rooms have raised floors so they can direct cooling air.

Funny story. On of our operations guys kept disappearing during his shift. Turned out he was slipping under the raised floor from time to time for a quick nap. I had been around for quite some time. I thought it was only justice that I didn't tell him that the place where he napped was where the raw sewage backed up.

[Mike Soaper]

sorry, duplicate post

[Mike Soaper]

I think if the ceiling also had similar overhead perforated supplies it would help the airflow in the room to be mostly downward vertical (kind of laminar) perhaps causing less lateral spread of covid etc, Once under the perforated floor the air could be ducted to a filter before being sent back to the ceiling supplies and then back into the room. I think balancing the airflow so that all areas get equal airflow would be a challenge.

I probably wouldn't have told that operator either. I once had a small divisional server room with 4 server racks, shared with telco and a network rack. I once found one of the network guys catching a nap there.

About the nastiest IT site I saw was before upgrading a Polycom video conference system. The equipment to be replaced was in a conference room desk high cabinet with a vent cut in the top for cooling. The cabinet top had become a place for food and drink, the cooling slot had became a place for spilled food to go and was sometime taken as a trash receptacle, all of that was found by mice which caused quite the mess.

[Roger Feeley]

A raised floor in a restaurant would be very hard to keep clean. One dinner with my 2 year old grandson and you can see why. They don't call him Hurricane Charlie for nothing. We see him as living proof that the earth is not flat. If it were, Charlie would have knocked everything off the edge.

However, imagine returns built into walls beneath the booths and such. The air comes from the ceiling (filtered of course) and proceeds in a general downward path to many returns along the walls, under raised booths or other imaginative places. I'm thinking of a restaurant around us where all the booths are raised a bit. I don't know why they did it but that raised floor under the booths would make a dandy plenum.

[Mike Soaper]

A raised floor in a restaurant would be very hard to keep clean. One dinner with my 2 year old grandson and you can see why.

Been there, when my 3 daughters were toddlers and we would go out to eat, sometimes I felt I had to leave a big tip or we would be banned from the place.:)

[Jerome Stanek]

I think it would help spread it by moving the air around

[Roger Feeley]

I think it would help spread it by moving the air around
Jerome, in my imagination, the air moves from many holes in the ceiling straight down to many holes near the floor. The objective would be that air would not move horizontally at all. It’s an interesting thought. Somehow, I suspect that it’s not possible.

[Jerome Stanek]

Jerome, in my imagination, the air moves from many holes in the ceiling straight down to many holes near the floor. The objective would be that air would not move horizontally at all. It’s an interesting thought. Somehow, I suspect that it’s not possible.

It is just like a screen if the air is moving fast the screen will act as a solid

[Frank Pratt]

It is just like a screen if the air is moving fast the screen will act as a solid

???? Not sure at all what point your making here.

[Frank Pratt]

I was in a very large theater where the the entire space under the sloped seating area was a huge return air plenum. Supply air came from diffusers at the ceiling level & flowed out through grills in the floor that were every few feet. Seems like a good design that would minimize viral spread.

[Wade Lippman]

In NYS they will not allow malls to open until they have MERV13 filters on the AC. So far none have complied. That's all I know.

[Roger Feeley]

My high school was built in 1928 and the auditorium seated 2409 people. There was a raised air inlet under about every 4th seat. So I imagine that the space beneath seats was probably a giant plenum. I was there in the ‘70s and the building wasn’t air conditioned. I don’t remember the auditorium being hot.

[Kev Williams]

Jerome, in my imagination, the air moves from many holes in the ceiling straight down to many holes near the floor. The objective would be that air would not move horizontally at all. It’s an interesting thought. Somehow, I suspect that it’s not possible.
Many stores/business have 'air curtains' instead of actual doors that you're probably familiar with, they force warm air straight down from overhead blowers into floor vents which are under a vacuum condition. The air door is an effective barrier between outside air and inside air, both of which get caught in the downward airflow rather than moving sideways into each others air space. Very effective as invisible insulation, but I can't imagine how to apply it to purifying the air..? People with the virus continually shed the virus, no boundaries :(

[John Stankus]

Jerome, in my imagination, the air moves from many holes in the ceiling straight down to many holes near the floor. The objective would be that air would not move horizontally at all. It’s an interesting thought. Somehow, I suspect that it’s not possible.

That is basically how the semiconductor fabs I used to work in were set up. The cleanrooms had a perforated grid floor, a very large space above with airhandlers and filters and a very large space below to collect the air below. I forget the actual specification but it was something like less than 0.1 particles per cubic meter or some such. The were pretty restrictive about photos, so I never got a picture of myself in a bunny suit (I looked like a giant marshmallow actually:)). The cleanroom was a great place to hide out in allergy season though. Pretty expensive setup to build for a retail situation.

John