Why to measure the concentration of carbon dioxide (CO2)

Concentration of CO2 in the air is a good indicator of a stuffy indoor air and corresponds very well with the number of people residing in this space.

There is thus the possibility of ventilation on the basis of the continuous measurement of the concentration of carbon dioxide in the air.

Composition of air of the earth’s atmosphere expressed in percentage is roughly as follows: 78% nitrogen, 21% oxygen, 0.4% water vapour, carbon dioxide 0.04%, the rest create inert gases and other constituents. Carbon dioxide is therefore natural gas constituent of the earth’s atmosphere. The concentration of CO2 in the nature is around 0.04% or 400 ppm (which a common expression is as the number of CO2 molecules in a million molecules; ppm – an abbreviation of the English parts-per-million). A higher amount of CO2 in the outdoor environments occur near roads with high traffic in the vicinity of industrial sites, incinerators, etc..

During the process of breathing the inhaled oxygen is changed to carbon dioxide, the exhaled air of an adult contains about 35 000 to 50 000 ppm CO2 (about 100 times higher concentration than in the outdoor air). Without adequate ventilation then logically increases the concentration of CO2 in the closed areas. The value of concentration of carbon dioxide in the air can therefore be considered as an important indicator of the quality of indoor air.

How much CO2 is too much?

Although carbon dioxide is invisible and odourless, its  increased level is obvious, because of the fatigue and the decrease of concentration. Especially in areas with a higher numbers of people, such as, for example, schools, offices, theatres, health

care facilities, the negative impact of increased CO2 concentration in the air is evident.

The concentration of CO2 to 5000 ppm does not present a serious risk for human health. However, according to research at elevated CO2 concentration occur drowsiness, lethargy, fatigue and decrease of the ability to concentrate and discomfort from stale air. Some studies examine the relation between the increased concentration of CO2 in the air and the decline in productivity and performance.
The recommended concentration of CO2 in the air should be kept at or rather below 1000 ppm.

Examples of CO2 concentration:

  • 360-400 ppm – fresh air in the countryside
  • 800-1000 ppm – recommended level of CO2 in the indoor areas
  • > 1000 ppm – occurring symptoms of fatigue and reduced concentration
  • 5000 ppm – a maximum concentration without health risks
  • 35 000-50 000 ppm – the exhaled air of an adult

How to ventilate?

Current technologies allow easily and relatively cheaply measure the concentration of CO2 in the air and on the basis of obtained values ​​then drive the ventilation systems to ensure a good air quality and simultaneously minimize the energy intensity. Ventilation systems can therefore use the measured values of CO2 concentration for a continuous control of their performance and so maintain the internal concentration of CO2 at or below the required maximum value. Such systems are particularly useful for areas with a variable number of people. Performance of the ventilation then continuously varies depending on the number of people who are in a ventilated area. Based on the measurement of the concentration of CO2 in the air can then modern ventilation systems ensure the optimum air quality in the ventilated areas regardless of the number of people present.


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