Ventilation and/or air purification?
Research and scientists confirm it: Air purifiers protect more effectively against the coronavirus, particulate matter and allergies than just the 'advised' ventilation through an open window!
In all weather conditions, cold or hot, the question can be raised how suitable and effective the window ventilation recommended by the German Ministry of the Environment (UBA) and the Minister of Education and Culture (as well as the Dutch RIVM) is in practice as an infection protection measure.
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Contrary to the view expressed by the German Ministry of the Environment and the Minister of Education and Culture that regular surge ventilation would be sufficient and that there is currently no better technical solution for removing potentially infectious aerosols from classrooms, many scientists and international renowned aerosol experts use high-capacity air purifiers with HEPA filter technology in accordance with EN 1822 – as an effective alternative to window ventilation.
Ventilation is associated with problems
and is only effective under optimal conditions
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The studies and knowledge mentioned by the German Ministry of the Environment mainly relate to room situations, where cross ventilation with opposing windows is possible. Good air exchange only takes place with cross ventilation. However, most buildings and room situations do not offer the right conditions for this.
Often only shock ventilation is possible and no cross ventilation
Most rooms, especially classrooms, only have windows on one side of the room, so that only burst ventilation is possible in these rooms.
The exchange of air with the outside air, however, takes place considerably more slowly with pulse ventilation than with cross ventilation – and this only if there is a sufficiently large temperature difference between the inside and outside air or with sufficient wind strength.
With almost identical temperatures, virtually no air exchange takes place without wind, so that window ventilation in summer and in relatively mild autumn can only provide the protective effect with permanent ventilation! In winter, at the respective temperature difference, a good exchange of air takes place initially, but only for a short time and with a diminishing effect. The cold air supplied from outside cools the interior gradually, so that the necessary temperature difference becomes smaller and smaller.
The result: The air exchange during ventilation almost comes to a standstill
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Mr. Schulte-Mattler, teacher at the Apostelgymnasium in Cologne: "At the moment we have been keeping the windows open for 10 minutes and yet the CO2 content is not falling". Clip WDR broadcast of the program Markt from 18-11-2020 ( https://youtu.be/NXNWN001zUo )
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Ventilation is usually too short, especially in winter, so that it does not get too cold in the room. However, not enough air is refreshed here. This according to Eberhard Bodenschatz, Director at the 'Max-Planck-Institut für Dynamik und Selbstorganisation' in Göttingen Spiegel on the subject of ventilation: "One only needs to determine the temperature difference between inside and outside. Is it 10 °C outside and inside 20 °C, only 50% of the air is refreshed as soon as you measure 15 °C in the interior after ventilation.It is better to avoid areas where ... the temperature does not change during ventilation."
The setup in the TU / e student sports complex
TU EINDHOVEN
Cross ventilation
Is ventilation really enough?
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At an outside temperature of 0 °C in winter, 50% of the aerosols would only be ventilated from the room if the room temperature was only approx. 10°C! The statement of the German Ministry of the Environment in the guideline for ventilation in schools, that the temperature in the room would only cool down by a few degrees with cross ventilation as well as with pulse ventilation, is therefore very doubtful. In order to be able to achieve only the air changes of 3 times recommended by the German Ministry of the Environment in this way, the room would be cooled to 10 °C 6 times per class hour by ventilation.
The statement of the German Ministry of the Environment that ventilation for 3 - 5 minutes every 20 minutes "the room air is completely refreshed three times an hour by fresh air from outside" gives minimal cause for misunderstanding. In the case of surge ventilation in particular, there is no complete, direct exchange of the air in the room, but rather a mixture of the consumed. virus-laden room air with fresh, clean outdoor air. Through this procedure, the virus-laden aerosol particles are therefore not completely vented from the room, as the formulation of the German Ministry of the Environment claims, but just like with air purifiers, the concentration of these is only diluted. With the difference that the capacity of an air purifier is known, reliable and adjustable, while the effectiveness of window ventilation fluctuates greatly depending on the weather situation.
Regular ventilation increases energy consumption
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Regardless of effectiveness, open windows at low outside temperatures are a pure waste of energy. By ventilating several times per hour, the interior spaces cool down, the important heat energy escapes unused from the window – while the people in the interior are cold. In addition, the supplied outside air must be heated again and again until it is replaced by cold air again during the next ventilation period. This is not only contrary to the efforts of international climate policy. It will also definitely lead to huge additional costs.
Ventilation ensures room temperatures below the legally regulated minimum values
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Employers, as well as schools, have a duty of care for their employees, resp. pupils. They must ensure that they are not harmed by too high or too low temperatures. The health and safety rule A3.5 (German) concretizes healthy room temperatures as follows:
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However, boost ventilation in winter does not only lead to a drop in the indoor temperature by a few degrees, as the German Ministry of the Environment indicates in its infographic "Correct ventilation in daily practice". The indoor temperature drops to values of approximately 15 °C in the shortest possible time and thus lies outside the legally prescribed values.
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Ventilation is "noisy" and disrupts the lesson
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According to the German Ministry of the Environment, road traffic has long been the dominant noise source in Germany. As a result, 2.3 million people in Germany are exposed to levels above 65 dB(A) throughout the day. "Road traffic disturbs or burdens more than half of the German population," states the German Ministry of the Environment and this noise often comes through open windows in the classroom. Education becomes more sensitive to external disturbances and this again leads to a loss of concentration and therefore encounters objections from teachers.
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CO2 is not an indicator for the viral load of the room air
People's CO2 emissions are constant when breathing, when speaking or when singing/shouting about the same. However, the amount of aerosols emitted depends on the number of infected people in the room and their activity.
When speaking or singing, many more aerosol particles are exhaled than when breathing without strain. As a result, the virus load in a room can rise faster than the CO2 value. This example makes it clear why the CO2 measured value does not allow reliable conclusions about the aerosol concentration.
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The German Ministry of the Environment also writes in its "Ventilation recommendations for schools": An increased CO2 concentration cannot provide a definitive answer about virus-laden
aerosols, but it does indicate that there has been no ventilation for too long and this can also increase the risk of infection.
This is also very simple and logical. In 30 healthy students in a classroom, the CO2 concentration rises by a certain value depending on the ventilation conditions. If none of the students are infected, the concentration of virus-laden aerosol particles is low, resp. equal to zero. If several of these 30 students were infected with SARS-CoV-2, the room would already have a virus concentration at a lower CO2 concentration, which would lead to an infection after only a short stay.
The CO2 content also increases depending on the number of people present. For example, if it takes 20 people in a fictitious classroom for 30 minutes to reach 1000 ppm, it would take about 60 minutes for just 10 people. Nevertheless, one of these 10 people would also be infected. Therefore, even with low CO2 values there is a high risk of infection under these conditions.
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Experts warn: Ventilation gives an impression of a sense of safety at the expense of health
Despite strong criticism from renowned scientists, many decision-makers base their guidelines on the scientifically false recommendations of the German Environment Ministry (as well as the Dutch National Institute for Public Health and the Environment), endangering the health of those who have to work or learn with open windows every day. . In addition, numerous studies prove the questionable effectiveness of ventilation alone in the fight against the spread of the coronavirus.
Correct behavior and technical solutions are currently the only effective tools for limiting the contamination rate and thus the costs to the state, the economy and society.
Extensive study by TU Delft yields impressive results
In a comparative test, Dutch researchers from Delft University of Technology investigated how quickly aerosol concentrations in the room can be reduced by boost ventilation and cross ventilation, but also by ventilation installations and air purifiers.
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'Deutsches Zentrum für Luft- und Raumfahrt': Ventilation does not yield the desired result in the fight against the corona virus
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The 'Deutsches Zentrum für Luft- und Raumfahrt': has also examined the effectiveness of the window ventilation recommended by the German Ministry of the Environment in a study.
The problem with window ventilation, according to Prof. dr. ing. Markus Raffel, that "Even with all windows wide open, the air exchange values that would be necessary for the reliable removal of potentially virus-laden aerosols from the room do not arise."
Ventilating every 20 minutes for 5 minutes means: no ventilation 90% of the time
With perfect displacement ventilation, the virus load would on average only be reduced by slightly more than half (55%). In practice (mixing ventilation) much less is achieved!
Solutions
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