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Airbrush

A/C for Room Virus Removal

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26 minutes ago, Airbrush said:

However you introduce air into a room (or workspace or sports arena), and how it exhausts, it would be safer for everyone that the air is circulated fast enough to minimize virus hanging around.

Claimed without support.

Faster moving air means the virus can travel further before leaving the room, per the paper I linked to. Meaning you might infect everyone before getting a chance to filter the air.

 

26 minutes ago, Airbrush said:

  Faster air motion means more powerful A/C.  If the bad air exits the room through floor vents it could be piped to the roof and expelled to the environment which will deactivate the virus through wind dilution and UV light from the sun.  The fresh air intakes do NOT need to be treated or filtered for virus.  Just DON'T RECIRCULATE the same air.

Hot air rises, so exiting through the floor isn't always the best option. 

 

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There does seem to be continuing confusion about aerosol spreading of SARS-COV2 virus, with reports out of Wuhan, of detectable traces of virus RNA in cramped, non-ventilated areas of hospitals, markets, and even open air.
But you would have to breathe for 15 min or more, to inhale a single fragment of virus, in open air.

Whether these fragments are viable whole virions, or not, is debatable, as the testing is not that specific ( only looks for certain markers ), and no-one has yet attempted to 'culture', and grow these fragments to check for viability.
Also , viral load comes into play at these small concentrations; how many virus are needed for an infection ?
Indications are that low viral loads result in mild to no infections, that may still test positive.
Larger exposures are needed for serious,symptomatic cases.

A recent case in BC, Canada, had a woman undergo testing 4 times, two positives, one negative, and one inconclusive, so she was diagnosed of having been infected. After quarantine, she was subsequently re-infected, and medical professionals are left wondering if there is no acquired immunity to the virus.

I would first look at the testing procedures, to see what determines an active, viable virus.
And the minimum number of viable virions that determine infection.

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5 hours ago, MigL said:

Whether these fragments are viable whole virions, or not, is debatable, as the testing is not that specific ( only looks for certain markers ), and no-one has yet attempted to 'culture', and grow these fragments to check for viability.

There are studies looking for viability- the data you might have seen where the number of infectious particles reduce under certain condition are conducted with in vitro testing. It is more difficult to try to recover under non-laboratory condition, of course and especially indirect contact is different to assess as there are a lot of variables going into it.

That all being said, the overall pattern is consistent with mostly direct contact exposure, perhaps with additional indirect exposure when folks are not washing their hands, for example. 

5 hours ago, MigL said:

Indications are that low viral loads result in mild to no infections, that may still test positive.
Larger exposures are needed for serious,symptomatic cases.

I am not sure about that one. If you test positive, there are already detectable amount of viral particles in your blood stream at this point you are likely infected. You may be asymptomatic, but your body is already producing particles. If you are just exposed to a few thousand particles indirectly but are not actively producing it is unlikely to identify them (for reference the limit of detection of many kits is around 6 genomic copies of the virus in 1 ul of sample).

While larger exposure is correlated with worse outcomes, it does not mean that only high exposure create serious outcomes. Especially in older folks as well as folks with comorbidities the prediction is worse. While it does not exclude a dose effect, we cannot conclude that it is indeed predominantly (or even significantly) does dependent.

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To clarify, CY, The exposure has to be large enough to overwhelm the immune system for serious outcomes.
'Large enough', is obviously different for different people, according to their age or comorbidities.

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44 minutes ago, MigL said:

To clarify, CY, The exposure has to be large enough to overwhelm the immune system for serious outcomes.
'Large enough', is obviously different for different people, according to their age or comorbidities.

I am not sure whether that is the right way to look at it. Pathogens do not need to overwhelm the immune system by force (though it is one strategy employed by some bacteria). It is sufficient that particles evade detection and start multiplying. The overwhelming part is then from the inside rather than the outside.

So far it is not clear whether a higher initial dose would result in worse outcome under physiological conditions (there is only indirect evidence so far). And conversely it is unclear whether healthy patients can withstand higher doses than sick ones.  

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Posted (edited)
On 4/28/2020 at 11:34 AM, swansont said:

Found this

https://wwwnc.cdc.gov/eid/article/26/7/20-0764_article#tnF1

Strong airflow is alleged to be the culprit, since droplets travel further. Filtration doesn’t fix that. 

Some basis for the discussion, other than conjecture, is needed.

Hot air rises, so exhaust vents in the ceiling and air intakes through the floor, will speed the replacement of virus-air from an indoor space, and not spread it.  With more powerful fans moving the air faster, and in an upward direction, the virus-air will get sucked out the ceiling sooner.  The outdoor environment will dilute and deactivate the virus.

Edited by Airbrush

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50 minutes ago, Airbrush said:

Hot air rises, so exhaust vents in the ceiling and air intakes through the floor, will speed the replacement of virus-air from an indoor space, and not spread it.  With more powerful fans moving the air faster, and in an upward direction, the virus-air will get sucked out the ceiling sooner.  The outdoor environment will dilute and deactivate the virus.

The worst air has virus droplets and aerosols, effectively slightly and very slightly heavier than air respectively. Drawing air downward will work with that to more efficiently remove the virus rather than keep it suspended, and stronger flows or turbulence in the worst air will be kept closer to your feet than your face, while fresh intake air can enter from higher levels, closer to your face than your feet.

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1 hour ago, Airbrush said:

Hot air rises, so exhaust vents in the ceiling and air intakes through the floor, will speed the replacement of virus-air from an indoor space, and not spread it.  With more powerful fans moving the air faster, and in an upward direction, the virus-air will get sucked out the ceiling sooner.  The outdoor environment will dilute and deactivate the virus.

How realistic is it to expect everyone to re-install their entire HVAC system? At best this would apply to new construction, in places where people don’t mind hanging out in a wind tunnel.

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Posted (edited)
On 5/3/2020 at 12:16 PM, swansont said:

How realistic is it to expect everyone to re-install their entire HVAC system? At best this would apply to new construction, in places where people don’t mind hanging out in a wind tunnel.

There could be a retro-fit.  You can reroute the air intake around the HVAC system when you are not using the A/C for cooling.  Then just fresh air from outdoors is pushed by more powerful fans.  Fans don't use much current.  You won't have cold air from your HVAC system, but you will have clean air from outdoors, just so long it is not very hot outside.  If it is very hot outside, then sorry you are stuck with slow-push A/C fans.  New construction can use more powerful fans.

"Hanging out in a wind tunnel" is an exaggeration.  The air just moves unnoticeably faster, so no matter how large the droplets are that came out when someone coughed or sneezed, the air will exit the room within a few seconds (not a wind tunnel).  That is much better than the virus-air hanging around for M I N U T E S .

Edited by Airbrush

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Posted (edited)
22 minutes ago, Airbrush said:

There could be a retro-fit.  You can reroute the air intake around the HVAC system when you are not using the A/C for cooling.  Then just fresh air from outdoors is pushed by more powerful fans.  Fans don't use much current.  You won't have cold air from your HVAC system, but you will have clean air from outdoors, just so long it is not very hot outside.  If it is very hot outside, then sorry you are stuck with slow-push A/C fans.  New construction can use more powerful fans.

"Hanging out in a wind tunnel" is an exaggeration.  The air just moves a faster, so no matter how large the droplets are that came out when someone coughed or sneezed, the air will exit the room within a few seconds (not a wind tunnel).  That is much better than the virus-air hanging around for minutes.

Agree with the first bold. It may be expensive, but so is not being able to use a building except with significantly reduced capacity.

However, for every velocity of upward airflow there exists a droplet size that has a terminal velocity that matches it. Droplets around that size will be hanging around for a while, supported by that airflow.

Also any sufficiently large building that turns the air over ever few seconds would make for a pretty good (or even excessive) wind tunnel air velocity.

Edited by J.C.MacSwell

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19 hours ago, Airbrush said:

There could be a retro-fit.  You can reroute the air intake around the HVAC system when you are not using the A/C for cooling.

Retro-fit assumes you have a compatible geometry. What if the ductwork is in the walls?

 

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19 hours ago, Airbrush said:

There could be a retro-fit.  You can reroute the air intake around the HVAC system when you are not using the A/C for cooling.  Then just fresh air from outdoors is pushed by more powerful fans.  Fans don't use much current.  You won't have cold air from your HVAC system, but you will have clean air from outdoors, just so long it is not very hot outside.  If it is very hot outside, then sorry you are stuck with slow-push A/C fans.  New construction can use more powerful fans.

"Hanging out in a wind tunnel" is an exaggeration.  The air just moves unnoticeably faster, so no matter how large the droplets are that came out when someone coughed or sneezed, the air will exit the room within a few seconds (not a wind tunnel).  That is much better than the virus-air hanging around for M I N U T E S .

Most commercial places have ventilation systems that do up to 10-20 air changes per hour. A restroom might do 30. That means the air hangs around for minutes

https://www.engineeringtoolbox.com/air-change-rate-room-d_867.html
https://en.wikipedia.org/wiki/Air_changes_per_hour

Which means that you need a flow rate that is much higher if you want air to only hang around for seconds. That's not "unnoticeably faster"  

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Posted (edited)

Covid-19 is like a dress rehearsal for even more deadly pandemics.  Covid-19 is bad enough, but in the future you may have more contagious and more deadly viruses escaping into human society.  In such a world you better have good AHC if you want to do things indoors.  Either that or "herd immunity" after tens or hundreds of MILLIONS of deaths.

How fast the air is replaced in a room, warehouse, or sports arena depends on the NUMBER of exhaust and intake vents.  If you have only a few vents there will be "wind tunnels."  But if you have MANY vents to exhaust and intake air, you distribute the wind tunnel effect so the overall effect is a slow upward motion of perhaps a couple of miles per hour.  Maybe that is fast enough to move the air upward.  In a few seconds the virus-air is already above the heads of people, and moving upward.

On 5/7/2020 at 8:00 AM, J.C.MacSwell said:

...However, for every velocity of upward airflow there exists a droplet size that has a terminal velocity that matches it. Droplets around that size will be hanging around for a while, supported by that airflow.

As the warm air moves upward it accelerates evaporation of water droplets, making them lighter and thus maybe not hang around so long.  The lighter-weight and heavier-weight droplets may get quickly separated.   Maybe the heavier droplets will fall to the floor and the lighter droplets carried upward. 😃

Edited by Airbrush

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10 minutes ago, Airbrush said:

In such a world you better have good AHC if you want to do things indoors. 

Not all diseases are transmitted through the air 

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2 minutes ago, Strange said:

Not all diseases are transmitted through the air 

Yes but we need to be prepared for diseases that are transmitted through the air.  We were not prepared. 😲

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3 minutes ago, Airbrush said:

Yes but we need to be prepared for diseases that are transmitted through the air.  We were not prepared. 😲

I'm not convinced that moving the air around more is a good plan. Is there any evidence for this? Personal protection may be more appropriate and is known to work.

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35 minutes ago, Airbrush said:

Yes but we need to be prepared for diseases that are transmitted through the air.  We were not prepared. 😲

Do you imagine our preparedness will protect us from a disease that evolves beyond that? We can't sanitise the world and still live in it...

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1 hour ago, Airbrush said:

 

As the warm air moves upward it accelerates evaporation of water droplets, making them lighter and thus maybe not hang around so long.  The lighter-weight and heavier-weight droplets may get quickly separated.   Maybe the heavier droplets will fall to the floor and the lighter droplets carried upward. 😃

My concern is with the ones in between. Unless there is reason to believe droplets that size are acceptably safe, and I can't see how that is likely.

Good point with respect to evaporation. I think that is considered in the duration of the risk from airborne droplets.

https://onlinelibrary.wiley.com/doi/full/10.1111/j.1600-0668.2007.00469.x

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21 hours ago, Strange said:

I'm not convinced that moving the air around more is a good plan. Is there any evidence for this? Personal protection may be more appropriate and is known to work.

One thing that is generally accepted with respect to avoiding airborne viruses is that being outside is considered better than being inside most buildings.

Obviously a big part of that is ventilation by somewhat random dilution typical of outside conditions. 

So more of the same and more make up air might help. The key is to make sure that it does .

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Posted (edited)
On 5/11/2020 at 6:10 AM, Strange said:

I'm not convinced that moving the air around more is a good plan. Is there any evidence for this? Personal protection may be more appropriate and is known to work.

If you have about one ceiling exhaust vent per square meter of ceiling area, and have a fewer number of fresh air inflow vents near the floor, you can make the air move upward at a modest speed, not a "wind tunnel," and not move it "around."  The heavier droplets and lighter droplet should separate quickly.  The idea is to suck the bad air up and out the ceiling before it can infect someone.

Personal protection of a mask, except the R95 mask, does not screen out virus in the air.  It primarily prevents the wearer from spreading droplets.

Personal protection is known to work and having better air replacement in public indoor spaces also could work.  Hospitals, factories, warehouses, any kind of work spaces, would benefit from having steady air replacement.  Companies can boast of how high their air replacement is to attract workers.  Any businesses can boast of having accelerated air replacement.

Edited by Airbrush

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17 minutes ago, Airbrush said:

If you have about one ceiling exhaust vent per square meter of ceiling area, and have a fewer number of fresh air inflow vents near the floor, you can make the air move upward at a modest speed, not a "wind tunnel," and not move it "around."  The heavier droplets and lighter droplet should separate quickly.  The idea is to suck the bad air up and out the ceiling before it can infect someone.

How about some math/modeling to back up this claim

 

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Nothing technical, but here is an interesting article based on some Canadian Engineers considering the problem. There does seem to be some disagreement as to how much the spread is airborne, other than immediately from droplets being probably most significant, but they are primarily concerned with the control that ventilation can improve on:

https://www.thechronicleherald.ca/news/canada/covid-19-likely-spread-by-building-ventilation-say-canadian-researchers-working-on-an-hvac-fix-442278/

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I wonder if this discussion has lost focus on the fact that , for much of the world, "air conditioning" means opening the door.

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49 minutes ago, John Cuthber said:

I wonder if this discussion has lost focus on the fact that , for much of the world, "air conditioning" means opening the door.

We have focused more on mechanical ventilation. Here is a WHO publication to natural ventilation for health care settings if you are interested.

https://apps.who.int/iris/bitstream/handle/10665/44167/9789241547857_eng.pdf;jsessionid=39488D09F98E3FB5C175C9CC2225AD4B?sequence=1

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Posted (edited)
On 5/12/2020 at 12:24 PM, John Cuthber said:

I wonder if this discussion has lost focus on the fact that , for much of the world, "air conditioning" means opening the door.

Exactly, that is why I have a problem with my original title, since A/C is not the issue.  The issue is moving bad air out of the indoor space and bringing fresh air in.  It has nothing to do with A/C or filtering or treating air.  You don't need to filter or treat fresh air from outdoors.

On 5/12/2020 at 9:30 AM, swansont said:

How about some math/modeling to back up this claim

Any volunteers for math modeling?  If you have many vent fans sucking air out the ceiling (like one fan per square meter), rather than one big fan that creates a wind tunnel, you distribute the motion over a greater area, increase the area of the air moving upward and out the ceiling.  Therefore no wind tunnel.  This will be better than nothing in a world where deadly pandemics can pounce on us at any time.  A fan is not a very expensive, or sophisticated device, but installing so many of them will be more expensive.  Will such installation be prohibitively expensive?

Edited by Airbrush

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