CO₂ traffic lights can be used to monitor the air quality in closed rooms. A system with several sensors, developed by Computing Science students, can track the distribution of carbon dioxide in lecture theatres or classrooms across the board.
Proper ventilation has become a key issue in schools, universities and offices during the pandemic: "Intensive, professional ventilation of building interiors ensures effective removal of excreted viruses and thus reduces the risk of infection in rooms that are used by several people," according to a recommendation from the German government.
The concentration of carbon dioxide gas in indoor air is a good indicator of when an air exchange should take place. Elevated values can be detected using so-called CO₂ traffic lights, the central component of which is a carbon dioxide sensor. If the values are high, a yellow or red light comes on - just like a traffic light.
Regular supply of fresh air
Until now, individual CO₂ sensors have usually been used to monitor the quality of the air we breathe in a room. A group of Computing Science students at the university have now developed a system that monitors the CO₂ values at several points simultaneously and thus provides a more accurate picture of the condition of the room air. "For example, you can use it to track how a cloud of fresh air moves through the room," says Computing Science expert Prof Dr Oliver Theel.
The team, consisting of seven students from the subjects of Computing Science, Business Informatics and Computer Science Teaching, started from scratch last semester in a course led by Theel and presented a fully functional system at the end. At the centre of the system are several sensors that measure the CO₂ concentration at short intervals and report the values to a so-called data sink. This software, programmed by the students, stores the measured values in a database and displays them graphically as coloured dots on a spatial map according to a traffic light principle. The precise measured values can also be exported from the database and displayed and analysed in the form of curves, for example. The system is suitable for testing ventilation concepts in larger rooms under real conditions, the students reported in their final presentation.
"What's new about the students' system is that the CO₂ distribution can be tracked in many places at the same time and the development can then be replayed in fast motion," says Theel, Head of the System Software and Distributed Systems department. This makes it possible to analyse very precisely whether a ventilation concept is working - or what specific measures can be taken to improve it.
Values in real time
To measure the CO₂ concentration, the team used commercially available sensors that measure carbon dioxide levels with high accuracy using infrared light. They combined these sensors with small single-chip computers, so-called microcontrollers, their own power supply, LED lights and other components to form so-called sensor nodes. The small boxes can be positioned anywhere in the room. Each sensor node displays the current CO₂ concentration at its position via the LED traffic light system and also sends the precise measurement data to a laptop in the same room via Wi-Fi. There, the graphically processed values can be displayed in real time.
The team has already used the system to check the ventilation concept of a laboratory room at the university. With success: the measurements showed that the CO₂ values in the room, in which up to five people were present, never reached the critical range over a period of several hours, even when the windows were temporarily tilted. The plan is to use kits with several sensor nodes in schools after the summer holidays so that ventilation concepts can be evaluated and, if necessary, optimised together with the school authorities. "In principle, the system can also work with 70 or 700 sensor nodes without requiring any changes to the hardware or software," reports Theel.
The students applied for the necessary funding for materials and accessories from the university's own teaching programme forschen@studium, which promotes active research by students.
