Airbrush

What about the fact that the longer you are in contact with a virus in the air, the higher the probability of infection? Just reduce the time of contact. If the airflow is downward, as CharonY suggested, even a slow, steady downward airflow will move the virus, in whatever form, down near the floor. It drops below breathable range in seconds. That is a slow, steady, downward airflow. That will actually push skirts made of tissue paper downward. That would be a big improvement over the virus lingering in the air for hours. There may be a virus residue on the floor, and near the wall exhaust vents, but that can be sprayed with sanitizer after people leave the building. There may even be a way to retro-fit indoor spaces with additional fans to push and pull the air. The business owner may rightfully boast about this to attract employees and customers. Wouldn't you like to work or shop where the air is fresher and cleaner?

Maybe "the last straw" but certainly a perfect political storm. You have a once-in-a-century, global pandemic. You have VERY high unemployment, so lots of people out of work and school. More people than every watching the news on TV. The protesters were upset to begin with and they have plenty of time to protest. More time available for protesting than in decades. Then the murder of George Floyd was so blatant and documented on video. It is horrifying. Then Trump's "law and order" response only poured gas on the fire. Will the White House be surrounded by protesting, angry mobs in the thousands, all the way up to the election in November? I don't see any relief for the White House for a long time.

Then have the airflow moving downward. Fresh air enters thru the ceiling and bad air is sucked out near the floor against the walls. All we are trying to do is reduce the amount of time the bad air hangs around, reducing the probability of infection.

You adjust the fans' speed to move the air as necessary thru experiment. If the force of airflow is balanced with gravity, then all you need to do is slightly increase fan speed to just barely overcome gravity. Right, that is why I would only say the air is replaced quicker than other businesses that have standard A/C. The probability of getting infected indoors is reduced by accelerating air replacement. We will assume that outdoor air is good. Once the bad air get outdoors the virus dilutes and dies from sunlight.

According to Bill Maher there was a study in China that out of 7300 cases of Covid transmission only ONE was outdoor transmission. That means that 99.999% of Covid-19 transmissions occurred INDOORS in China. Yes and the indoor spaces may become ghost towns. The economy won't recover until consumers have the confidence to enter INDOOR spaces. "Build it and they will come" unless consumers are spooked, then they won't come. The USA economy is mostly consumer driven. "...In a study published by the City and Environment Interaction journal, scientists.... argue that the lack of adequate ventilation in many indoor environments -- from the workplace to the home -- increases the risk of airborne transmission of Covid-19. https://www.sciencedaily.com/releases/2020/05/200528115750.htm

Any volunteers for this analysis? "Step right up folks! Come into my new business (restaurant, offices, stores, markets, Disneyland, etc.) and enjoy AAR (accelerated air replacement). My competition has poor, weak A/C that just pushes the air with virus around for an hour before it finally slinks out the ceiling. That gives you plenty of time to get infected right thru your cloth mask. My business, however, has fresh air ALL THE TIME for you to enjoy! We have extra powerful fans to move the bad air out and good air in."

If you enter a building wearing your mask you may get infected right thru the mask! All it takes is one infected person blasting out their "mist" which may linger up to HOURS. If the building had the power to move air up and out (ANY indoor space), you CAN remove the virus from the air. If you don't remove the virus from the room, you will get infected, good luck.

"In fluid dynamics, Bernoulli's principle states that an increase in the speed of a fluid occurs simultaneously with a decrease in static pressure or a decrease in the fluid's potential energy.[1](Ch.3)[2](§ 3.5) The principle is named after Daniel Bernoulli who published it in his book Hydrodynamica in 1738.[3] Although Bernoulli deduced that pressure decreases when the flow speed increases, it was Leonhard Euler who derived Bernoulli's equation in its usual form in 1752.[4][5] The principle is only applicable for isentropic flows: when the effects of irreversible processes (like turbulence) and non-adiabatic processes (e.g. heat radiation) are small and can be neglected." https://en.wikipedia.org/wiki/Bernoulli's_principle Can anyone translate this into common English? How does this disprove my idea of accelerated air replacement (AAR) without a wind tunnel?

No because the air can move much faster thru the vents than it moves thru the room. The air flow can be adjusted by fan speed. You may want to have a wind tunnel after the people are gone, you just turn up the fan speed and empty the indoor space of bad air in a short time. Then during work hours the air is moving upward at a modest speed. If 2 mph blows a skirt up, (it won't unless the skirt is made of tissue paper) then turn it down to 1 mph. The adjustable inlet and exhaust vents push as much air as you need for a modest upward flow of air. With Mr. Bernoulli's speed and pressure, air moves faster thru the vents than thru the room. To compare bad air that lingers in an indoor space for hours because of a few tiny vents which is the current norm, compared to rapid air replacement thru more powerful, adjustable air-flow vents in a few minutes it not a "hand-waving" argument.

Air moving upward at 2 mph is equal to about 3 feet per second. Will air moving upward at 3 feet per second blow a skirt up? I doubt it. The idea is to not allow the virus float around for hours or even minutes indoors. If you can move air up over people's heads in a few seconds I suppose that decreases the risk of getting infected.

Thanks for the correction. That means in a room 10' x 10' with 9 exhaust vent fans, 9" radius each, in the ceiling you will have 3.14 x 9^2 = 3.14 x 81 = 254 square inches/144 = 1.77 square feet of venting area per vent, times 9 vents in the ceiling = about 16 square feet of venting area per 100 square feet of indoor space. Don't you think the air is passing through such a broad exit it can move at 2 mph? Then you have whatever number of intake vents you need to equalize the volume of air being sucked out the ceiling through 16 square feet of venting area per 100 square feet. I just thought it would be more comfortable working with a cool breeze on my ankles. The more floor vents you have the more air you can move without blowing skirts up. Just adjust the air inflow fans speed, size, and number to achieve moving air upward at 2 mph.

Please explain what you mean. I thought a circular venting area would be pi X diameter. What's with the "squared /4"?

Sorry for the miscommunication. My intention was to say that when someone sneezes, with AAR the water droplets will be lifted over people's heads in a few seconds, removing most threat of infection. It will actually take minutes for ALL that air to travel out of the ceiling suction vents. But remember in the 10' x 10' room you have almost half the ceiling area (42 square feet) is venting used air. Lots of air can move out at a slow speed. You can have fewer intake vents blasting air into the room along the room's perimeter near the floor. These can match the same air flow as the exhaust vents. People may experience wind blowing near their feet, but it won't blow skirts up. Also when we sneeze at 100 mph the droplets will not bounce off the walls. The droplets meet air resistance that causes the mist to mushroom into a larger area so air resistance increases even more with distance from the sneeze, decreasing droplet speed dramatically, slowing the mist to well under 100 mph. "The lighter droplets are deflected [upward] over the heads of people after the sneeze droplets travel about 10 - 15 feet" by the upward motion of air moving 2 mph. As to the size of the rooms, I'm thinking of AAR for larger, commercial spaces like hospitals, warehouses, offices, factories, businesses, or the homes of the wealthy.

A large area of small fans do not inherently give rise to different flow rates than a large fan. You can have one giant fan moving the SAME amount of air as many smaller fans. I only thought it would be impracticable to build such a large fan. Cheaper to use a number of smaller ceiling-suction-vent-fans. The speed of air will be greater near a nozzle constricting the area that the air is passing thru. For example, if you have a room of 100 square feet (10' x 10'), you can have about 9 ceiling vent fans with a diameter of 18 inches or 1.5 feet. Area of each circular vent is PI X diameter (3.142 x 1.5' = 4.7 square feet per vent). Times 9 ceiling fan vents (9 x 4.7 = 42) square feet of vent area. That means almost half the square footage of the ceiling will be venting area circles sucking out the used air. With that much venting area you can move a lot of air slowly. You can have air entering the room faster around the perimeter near the floor. What is a "WAG"? You are misunderstanding my proposal. Air is not "only around for a few seconds." In a few seconds the droplets projected from a sick person will float above the heads of people. It would take several minutes for all the air in the room to be removed. I have never heard of AAR (Accelerated Air Replacement) have you? Did I just invent the term? In the future engineers will be considering AAR in new construction I suspect.

False. 100 mph only near the sneezing nose or coughing mouth. After a few feet the water droplets slow down RAPIDLY due to air resistance. Heavy droplets fall to the floor in one second. The lighter droplets are deflected over the heads of people after the sneeze droplets travel about 10 - 15 feet. I have seen high-speed video analysis of droplet projection from coughing, sneezing, or shouting. The droplets do NOT travel across the room, only about 15 feet. Even if they did travel across the room, it would not matter since the bad air would be over people's heads in seconds. After only a FEW seconds of AAR (Accelerated Air Replacement) the strong suction fans in the ceiling will suck the air upward at about 2 mph. If you have enough fans, of adequate diameter, sucking air out the ceiling, turning at the proper rate, you can adjust the vertical air flow so all the air in the room leaves in a few minutes without a wind tunnel. You can move the air in a vertical direction over the heads of people in a few seconds. Also, you can catch Covid-19 by droplets reaching your eyes! So you need eye protection as well as an N95 mask.

Not the same area. By having many fans you can increase the total area of the openings that the air is passing thru. That slows down the air flow even though the same amount of air is expelled. You could also have one giant fan the size of the ceiling turning slowly, pushing air out a giant hole 50 feet in diameter, but that is not practical for construction.

Air moves faster through an air duct when you constrict the duct. Water flows faster out a hose when you constrict the nozzle. Having many smaller ceiling vent fans EXPAND the size of the exit. When you increase the size of the exit door, more people can flow through the door walking, not running.

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. 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?

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.

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

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. 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. 😃

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 .

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.

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. 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.