Why do we measure Carbon dioxide inside buildings?

We spend half of our lifetime at work or school. In addition, when going to the cinema, shopping mall, gym, etc. we spend most of the time in closed spaces, but do we think about the air quality and how it can affect us? How can we be sure that air quality in those places is not adequate? How can we measure it and what can happen if nobody cares about it? Hopefully, this article will answer these questions.

What is CO2?

Carbon dioxide is a greenhouse gas that is a natural component of air and it is harmless in small quantities. It consists of one part carbon and two parts oxygen. Its level in an air sample is measured as parts per million (ppm).
Usually, the outdoor air has about 380 ppm, it is higher in the city centres, near vehicle traffic areas and industry.
Indoor levels of CO2 are elevated in comparison to the outdoor. People exhale carbon dioxide, which is why the level will be higher in crowded spaces if the ventilation is not working properly. Each exhale contains about 35 000 to 50 000 ppm.

Why measure it?

Without a CO2 sensor, we are not capable to assess if the HVAC system is delivering the recommended minimum quantities of outside air to the building. There is a possibility to calculate the amount of fresh air that should be delivered but the problem is when the number of people inside the room is constantly changing. The problem will occur when more people than calculated enters the room and CO2 levels get higher than it should be.
Also, it is inefficient to set all parameters in the HVAC system to constant. Imagine that the ventilation works the same when there are 10 or 30 people inside the office. To control and make sure that people inside the building have good conditions and the ventilation, heating, air conditioning is working efficiently we need to measure the CO2 levels.

What are the guidelines for ventilation?

There are various codes and standards for office spaces, schools when it comes to CO2 levels. Each country can have its standard. In many sources, we can find that the CO2 concentration should be below 1000ppm, and for perfect conditions around 800ppm – regarding ASHRAE (the American Society of Heating, Refrigeration, and Air Conditioning Engineers.

How do high levels of CO2 impact people?

There are some typical effects when ppm level is high:

  • Poor cognitive performance
    Now we have many studies and researches on how a low level of fresh air can affect cognitive functions. Research in schools checked that better air quality lead to higher scores on tests and faster problem-solving tasks. [1]
    Another study has shown that CO2 levels can reduce brain activity. In this research, people were inhaling 5% CO2 and then scientists using magnetic resonance checked the brain activity. [2]
  • Low productivity
    Since there are research showing that our brain activity is lower and we may have problems with higher cognitive functions, it will affect our productivity. One of the researches shows that people can work 60% faster in lower CO2 concentrations. [3] It seems that proper maintenance of the HVAC system may increase business revenue.
  • Drowsiness, increased heart rate and blood pressure, headache
    High CO2 levels in the blood can cause several problems, from headaches to loss of consciousness, depending on the overall health. [4]
    In the table below there is an explanation of how the CO2 level can affect peoples’ health: [5]

Do high CO2 levels help in viruses transmission?

Since the start of the Covid-19 pandemic, scientists were investigating the ways the virus spreads. It took many months to confirm that high levels of CO2 help in virus spreading. A new study was published in the journal Environmental Science and Technology Letters.
The conclusions are that, when indoor CO2 levels in a gym dropped from 2 800 to 1000 ppm, the risk of Covid-19 transmission dropped to one-quarter of the original risk.

How can we measure the level of CO2?


The easiest and the only way is to include CO2 sensors in the HVAC systems. There are different types available on the market. CO2 value can be used then by heating, ventilation and air-conditioning to automatically adjust the volume of outside air, to maintain indoor CO2 levels at the proper value.
In iSMA products, we have an iSMA-B-LP panel that can have a temperature, humidity and CO2 sensor inside. This kind of solution is perfect for office spaces, schools, public buildings. It not only reads the values from the sensors but gives the user a possibility to control the temperature in space/room, fan speed and more depending on the HVAC application.