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Bars and restaurants can also easily procure mobile air filter systems.
However, the government does not promote such emergency measures
Photo: Ben Hasty / MediaNews Group / Getty Images
Winter is coming.
But no matter how well a house is insulated: It could get cold in many rooms.
Because the Federal Environment Agency recommends airing indoors to prevent infection with the coronavirus.
In schools, students could soon be taught with hats and gloves, and red wine and pasta should also be fresh in bars and restaurants.
The only way out of this winter corona dilemma is with air filter systems.
They can be used to catch coronaviruses from the air - without the annoying ventilation.
To be fairly safe from Corona and still in the warm - a real dream at these times.
What could be more obvious than the quick retrofitting of all public facilities, shops and restaurants with the Wunder machines?
But the obvious is more complicated than expected: The Federal Ministry of Economics has launched a funding program for room air systems.
This should come into force next week, contribute 40 percent of the costs and "increase the protection against infection", as the BMWi writes in response to a request from SPIEGEL.
But Minister Peter Altmaier's laudable initiative completely ignores reality.
Too cumbersome, too tedious
In any case, scientists like Christian Kähler, who have been dealing with aerosol particles and their spreading and mixing in space for years, are of this opinion: "This will not save a single life," says the physicist from the Institute for Fluid Mechanics and Aerodynamics at the University of the Federal Armed Forces in Munich MIRROR.
His criticism: the ministry only subsidizes stationary ventilation systems that have to be drawn into walls and ceilings, which is a laborious process.
"It takes at least two years to get permits for such systems in public buildings," said Kähler.
Therefore, the program is limited to 2024.
"This funding program is of no use to anyone this winter or next."
Retrofitting of already installed air systems is hardly possible, explains the researcher.
To do this, very extensive and expensive modifications would have to be made to the systems and this would also require a permit, which cannot be obtained so quickly.
The only way out: Mobile filter systems
According to researchers like Kähler, the quickest way to make rooms safer is therefore mobile air purifiers.
However, these are not sponsored by the government.
"This is clearly the wrong industry being provided with state funds," says Kähler.
The mobile devices are half a meter to one meter in size and can be placed immediately in any room.
They usually suck in the air from below and then blow it back into the room through a special filter.
Advantage: There is no need for renovation work or tearing open walls.
Before the corona pandemic, the systems were mainly used to clean the air, for example from pollen, in order to protect allergy sufferers.
They have been used for decades in hospitals and microbiological laboratories with particularly sensitive filters.
Several studies now recommend the air filter against corona viruses.
Scientists from the Goethe University in Frankfurt am Main tested the devices in classrooms.
These would have reduced the virus concentration in a classroom by 90 percent within half an hour.
The risk of infection is reduced by a factor of six if there is a “super spreader” in a room with an air purifier, the scientists write.
"The use of mobile devices is certainly quicker and easier to implement in the current situation," explains study author Joachim Curtius.
"Corona can never be 100 percent secure, but the filters reduce the risk."
Air purifier with virus function
Up until now, room air filters with a "virus function" were rare.
The reason: That was simply not necessary before Corona.
Allergenic pollen, for example, are significantly larger than corona air particles.
In order to filter these out, the devices must capture particles that are smaller than a micrometer.
In addition to the normal filters against the coarse dirt, so-called HEPA filters (for: "High Efficiency Particulate Air") of quality level H13 or H14 are required.
At the Bundeswehr University, the physicist Christian Kähler and his team tested such highly sensitive devices a few months ago.
The researchers wanted to know whether aerosols contaminated with corona viruses really stick to the filters and are not whirled back into the room.
Aerosols are constantly in our air.
For example, they enter our environment when we exhale, sneeze and cough.
Coronaviruses attach to these airborne particles and continue to spread.
In Kähler's study, the researchers tested the room air filter of a device from Trotec and came to the conclusion that it can intercept aerosol particles down to a size of 0.1 to 0.3 micrometers very reliably.
In a room of 80 square meters - for example a medium-sized restaurant or bar - the concentration of aerosols can be reduced to a "low level" "within a short time".
However, such devices also cost around 3000 euros.
According to information on their websites, buyers have to wait weeks for some models.
When buying a device, you should pay less attention to the price than to three criteria, explains Kähler.
Otherwise the systems were simply of no use:
The size of the room is important.
Basically, the following applies: The device must be able to filter six times the volume of the room.
With a room of 200 cubic meters, a system must be purchased that can filter 1200 cubic meters per hour.
The device must have a HEPA filter of class H13 or H14.
The model should be as quiet as possible, otherwise there is a risk that it will be switched off more often for noise reasons.
Now it is up to the countries
Researcher Curtius thinks it makes sense to use several small devices.
That covers the room better than a large device.
In addition, the pre-filters have to be cleaned regularly.
The Federal Association of Consumers agrees with the researchers' recommendations.
In addition, care should be taken that the systems do not work with ozone, as this would pollute the air with harmful substances.
However, the air filters are only a supplement to ventilation, according to the association.
Kähler sees it differently.
For the scientist, room air filters are always more efficient than tearing open the windows.
That is why he can only shake his head at the handout from the Federal Environment Agency on the subject of "Ventilation in schools": "There is simply a lack of fluid mechanics competence."
Ventilation is inefficient in two respects: A lot of energy is wasted.
At the same time, the air would not be exchanged sufficiently.
"Even the low ventilation target set by the Federal Environment Agency (three air changes per hour) will not be achieved in practice," says Kähler.
Due to the dangerousness of the virus, the recommendation of three air changes is too low.
"Air purifiers are indispensable for real protection against indirect infection in winter," says Kähler.
In addition, he advocates transparent protective walls between children in schools.
Since the federal government does not subsidize mobile air filters, the federal states now have to take action: Bavaria was the first federal state to announce that it would purchase the devices for schools.
But here too, restaurants, hotels or bars are left out again.
The German Hotel and Restaurant Association is at least calling for the federal funding program to be expanded.
When it comes to mobile room filters, the association is rather cautious: It is said that one cannot assess whether mobile room air purifiers are actually able to clean the room air in practice because the movement of people strongly influences the air flows.
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