Poor and stale air in classrooms is a problem. The ability to concentrate decreases, headaches, mood disorders and fatigue occur and the efficiency of teaching suffers.

In addition, recent studies conclude that poor air quality promotes the spread of viruses, germs and bacteria.

Frequent ventilation as a solution also has its disadvantages. Students near the windows may quickly become hypothermic, and emissions such as noise and dust enter the classroom. Heating efficiency also suffers.

Indoor CO₂ concentration is a key indicator of air quality.

The Committee on Indoor Guideline Values states a room air concentration of up to 1,000 ppm (parts per million) CO₂ as harmless. In reality, the concentration already decreases noticeably from 800 ppm. By way of comparison, the current level of CO₂ in the atmosphere – including fresh air – is around 400 ppm on average.

Up to now, the actual indoor air concentration has been recorded at best on a random basis – and before the start of the Corona pandemic, often not at all. Measurements by the accident insurance fund NRW¹⁾ in 380 classrooms showed concentrations of over 2,000 ppm in some cases – according to the classification, this is considered hygienically unacceptable. This is primarily because viruses in particular can spread optimally in such a room climate.

With a CO₂ sensor in the control circuit of the ventilation system, this condition is a thing of the past. The installation is inexpensive and can be carried out quickly, the costs are minimal.

By controlling ventilation systems according to demand, various advantages can be realized. For example, energy savings through optimal operation of the equipment, a constant high quality of breathing air and uniform air distribution without excessive temperature fluctuations.

Conclusion

Continuous recording of air quality with a CO₂ sensor integrated into the control loop ensures optimum plant utilization, improved air quality and thus a better learning climate.

Thanks to simple and cost-effective installation, the retrofitting of such sensors can be realized without great effort.

Thick air in meetings, employees freezing and sweating next to each other in open-plan offices or stale air in classrooms – unfortunately, these are still everyday occurrences today.

Headaches, mood disorders and signs of fatigue are the result.
But insufficient ventilation also encourages the spread of pathogens.

Ultimately, the only remedy is to replace the room air with fresh air.
with fresh air.

An essential indicator for the quality of the air is the CO₂ concentration.

For fresh air, this value is around 400 ppm (parts per million). Values of up to 1,000 ppm are considered acceptable, but restrictions on performance can be detected as low as 800 ppm. A CO₂ sensor is ideal for continuous measurement. In conjunction with existing ventilation systems, the sensor enables optimal control of ventilation performance.

The most obvious way to exchange indoor air seems to be opening windows and doors. But that’s not always an option – especially on the 20th floor of a modern office building. But even where windows are present, this type of ventilation is definitely associated with disadvantages.

For example, to exchange the entire volume of air in an office of 10 m² , cross-ventilation is required for at least 5 minutes per hour. In a classroom it is already significantly longer. This means completely open windows and doors with a corresponding draught.

With tilted windows, even 30-60 minutes must be allowed for. This is neither realistic nor energetically reasonable in everyday life.

In addition to conventional ventilation, various technical systems are in use

• mobile air cleaners
• permanently installed ventilation systems
• decentralized systems or
  fan-window combinations

For the evaluation of the system efficiency, ventilation and air purification effects are often considered equally. However, the decisive factor for the quality of indoor air is the concentration of CO₂ – which depends exclusively on ventilation.

For example, room air filters, which have been frequently encountered since the Corona pandemic, offer a perfectly acceptable effect in filtering viruses or bacteria. However, constantly circulating the room air does not change its CO₂ content and therefore often proves to be less effective.

Permanently installed room air systems offer not only considerable heat recovery but also the advantage of being combined with filters. However, such systems are very expensive and often difficult to operate equally optimally for all areas. Retrofitting is rarely an option because of the considerable construction effort involved.

Decentralized ventilation systems perform best in tests. These units are permanently installed on exterior walls or the ceiling, but operate independently for a specific room or area. These units are inexpensive to retrofit and provide optimal ventilation performance with low energy consumption.

Conclusion

Continuous measurement of air quality with a CO₂ sensor is a basic requirement for controlling any ventilation system.

Mobile circulators with HEPA filters work reliably against viruses, but do nothing to improve air quality.

Relatively simple and inexpensive to install are decentralized ventilation systems or fixed-fan combinations in conjunction with CO₂ sensors. This form of ventilation provides the best results.