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The issue of indoor air quality is once again receiving greater attention as a result of the Corona pandemic. This is because ventilation dilutes indoor concentrations of coronaviruses and minimizes the risk of infection. But good indoor air quality is not only important to protect against aerosols and thus viral illness. Air quality is also crucial for the ability to concentrate, as well as successful learning and teaching.

For pandemic control, the Federal Office of Public Health recommends that rooms where people from different households are present should be particularly well ventilated. To ensure that people do not forget to ventilate, sensors can be used to measure the air quality. In addition, valuable data on the quality of indoor air can be collected.

Measurement indicators

The most important indicator of indoor air quality is CO2. The CO2 content in the air is measured in parts per million (ppm) or in percent by volume. A CO2 concentration that is too high can have consequences: Already from a value of 1200 - 1500 ppm, i.e. 0.12 - 0.15% carbon dioxide content in the air, general well-being can deteriorate. Reduction of the ability to concentrate, drowsiness, inattentiveness or headaches can occur as a result.

In addition to the CO2 emitted by industry, every human being also releases CO2 naturally. On average, a person exhales about 15-20 liters of air per hour during sedentary work, thus adding more than a hundred times the amount of carbon dioxide. Over the course of a day, this corresponds to the amount emitted by a small car traveling ten kilometers. Just one person's breath can raise the CO2 content within a room to 1000 ppm. Which corresponds to the maximum air-hygienic value according to Pettenkofer's comfort limit.

Other indicators of a good indoor climate are temperature, relative humidity, air pressure and volatile organic compounds (VOCs). Since it is extremely difficult to trace complaints back to individual VOCs, the totality of volatile compounds in indoor air is measured, known as Total Volatile Organic Compuds (TVOC).

Sensors

The basis for determining indoor air quality are sensors that record and reproduce measured values. For this purpose, there are various manufacturers, which achieve different measured values and accuracies. Some devices have to be connected to a power supply, others are battery operated. Both variants offer advantages and disadvantages. Different solutions from Teneo IoT, Milesight and Decentlab are presented and compared later in the text, under Products.

Visualization of a carbon dioxide measurement on ax-track.

To visualize the measured data, there are different solutions from supplier to supplier. Some devices show the measured values directly on a display or indicate limit value violations using a traffic light system (green, orange, red). Other devices require a platform on which the data is visualized (for example, with our in-house solution ax-track). This can be used to send automated notifications by mail or short message to inform affected persons. Analyses of the measured data are also possible via these platforms. Based on this data, future room planning (number of people per room size) and/or ventilation intervals can be optimized.

Products

For the monitoring of the room climate, there are various solutions from different providers. Which solution makes sense where and which additional devices are needed for it, is described in the following section.

CO2 stoplight

The Stoplight from Teneo-IoT measures the CO2 content, temperature and humidity. The stoplight works on the traffic light principle and changes color when the measured CO2 content in the air exceeds the specified standards.

As soon as the traffic light turns yellow, this is an indication that the air quality has deteriorated, giving people enough time to take action. As soon as the traffic light changes to red, this means that immediate ventilation is required or the area must be vacated. In addition to the signaling function using LEDs, the traffic light also has wireless communication based on LoRaWAN or WiFi, making it possible to log measurement data and issue notifications as well.

The sensor is connected to the power and thus has an unlimited functional life. However, the placement in the room is limited by the required network connection.

Milesight AM107

The Milesight AM107 consists of multiple smart sensors specifically designed to measure indoor climate. It provides accurate carbon dioxide measurement from 400 to 5000 ppm and displays the result directly on an e-ink screen.

Unlike the CO2 stop light, the display is not as obvious and therefore not visible to everyone in the room. This allows, for example, a teacher to take action without the students knowing the exact reason. Exaggerated or even panic reactions of the students can be avoided.

The sensor is battery operated and can therefore be used in any room, even without a power supply. Using LoRaWAN capability, automated messages or actions, such as turning fans on and off, can be triggered.

Decentlab - Indoor Ambiance Monitor

Decentlab's Indoor Ambiance Monitor measures volatile organic compounds (VOCs) in addition to CO2 levels.

An additional integrated PIR motion sensor measures the activity level in the room and therefore provides further data for future intelligent ventilation.

The sensor is battery powered and features LoRaWAN. To view the measured data, an additional solution is required, such as the ax-track platform. Alarms, notifications and statistics can be set up individually via the platform and viewed at any time in a mobile app.


Conclusion

Monitoring indoor air quality in practice makes sense for a variety of reasons. On the one hand, if the indoor air quality deteriorates, you are automatically notified and thus reminded in good time to ventilate the room or even to leave it. On the other hand, the measurement data can be collected on IoT platforms and thus used for future room occupancy, ventilation distances or even for monitoring teachers (how often was the air quality borderline).

adnexo will help you to find the right sensor for your application.
Just contact us by mail at: [email protected] and visit our website www.adnexo.ch.