Interview by Heike A. Batzer
How can you protect yourself from virus transmission indoors? A question that, in view of the corona pandemic and the hope of the return of face-to-face teaching, moves students, parents and teachers before the new school year, but also the municipalities that are thinking about purchasing technical filter devices for the classrooms. This Thursday, the vacation committee of the district council will decide that for the secondary schools in the district. Kai Sannwald from the Munich company Sunny Air Solutions specializes in advising companies, medical facilities, restaurants, schools and retailers on the choice of ventilation system, regardless of manufacturer. In the SZ interview, he explains what to look out for when choosing a device.
SZ: How does indoor air have to be cleaned so that you can come together in a virus-safe way? Please explain in this context what air filters, air purifiers, air purifiers and ventilation systems are.
Kai Sannwald: The top class are the air conditioning systems, known as RLT systems. They provide for a permanent exchange of air. If you want to retrofit existing properties with it, the costs are immediately in the six-digit range, because it is a massive structural intervention. The others are mobile air filters or air purifiers, they aim to absorb dust, pollen or odors. The third category is air purifiers. They denature – as they call it – bacteria, molds, yeasts, Sars-CoV-2 viruses.
Which air purifier is the right one? The elementary school in Neubiberg in the Munich district was one of the first to equip its classrooms with the appropriate equipment. That was already at the end of last year.
(Photo: Claus Schunk)
Why is it not enough to open the windows at regular intervals?
The most relevant criterion is the disinfection of the air, and for that you need an air envelope. Air conditioning systems make that perfect, in theory ventilation also works. But you cannot permanently ventilate in schools, for example. I remember my daughter’s class when the students were sitting in the classroom in winter clothes. And just tilting the window is not enough, there is no exchange of air.
What kind of air purifiers are suitable for schools?
There are the Hepa filter systems, in which the sucked in room air is pressed through a narrow filter and then blown out again. But this creates a noise problem, because these systems need strong fans and they are loud. Also, when the filters are full, they must not be disposed of with household waste because of the virus contamination. So far, the Federal Environment Agency had only recommended such HEPA filter systems. Now it also considers the use of air purifiers with UV-C light tubes to be justified. This technology has been used in operating theaters for surface disinfection for 20 years. It has now been adopted in closed devices. They are quieter than HEPA filters.
What is important when choosing a device?
The spatial situation is important. It is about two questions: How many people are there in the room? And: how big is the room volume? This depends on which air change is sensible. Also about whether an office is blocked by partition walls that have a negative effect on air circulation. Let us take the music hall at the school as an example: There you have to plan with a significantly higher air exchange rate than in a normal classroom with frontal teaching because there is singing.
What else do you have to consider?
An important factor is the volume of the devices. I have seen a device in the staff room – but not connected to the power, because otherwise it was so loud that no one could work. Or in gastronomy: It makes a difference whether I set up the device at the bar or in the large kitchen, where it’s loud anyway. Attention should also be paid to the safety of the installation – especially in a daycare center, for example -, the design, the safety of the devices themselves and their performance. Because the individual device can have a great performance, but still be unsuitable if the fans are too weak and the cleaned air does not blow out properly.
Where do you get your expertise from?
You have to deal with it. Above all, it is important that tests are carried out in the respective room situation. We have a certification company on hand with whom we work out test scenarios. Our claim is: We take care of the individual situation with manufacturer-neutral advice.
What does a company or municipality have to spend in order to get decent quality air purifiers?
For an average classroom in which, say, 20 students receive frontal teaching, they have to calculate around 3500 euros.
Since politics started promoting the purchase, the demand has risen sharply. Can you get all the devices here at all? The new school year starts in three and a half weeks.
The Bavarian Prime Minister Markus Söder announced at the end of the school year that all classrooms should be equipped by the end of the summer vacation. That is not possible! We currently have a global shortage of raw materials, and so ventilation systems are made up of different components. And when the demand completely explodes, as it is now, you can’t simply multiply production x-fold quickly. A large provider, for example, says that the delivery time for schools is currently eight weeks.
Hopefully, when the pandemic is over, will the devices be useless again?
Disinfection always makes sense, for example with flu viruses. Think of the year when there were 25,000 flu deaths. With such devices, companies can also aim to reduce sickness-related absenteeism. 4.8 percent of sick days in companies are caused by virus and bacterial infections. Disinfection is part of a clean hygiene concept and therefore makes sense.