The concentration of carbon dioxide (CO2) in the air is a good indicator of the breathability of indoor air and correlates very well with the number of people living in these enclosed spaces. Therefore, ventilation based on continuous measurement of the carbon dioxide concentration in the air is an option.
The composition of the air in the Earth’s atmosphere, expressed as a percentage, is approximately 78% nitrogen, 21% oxygen, 0.4% water vapour, and 0.04% carbon dioxide. The remainder consists of noble gases and other components. CO2 is therefore a natural gaseous component of the Earth’s atmosphere. Its concentration in nature is about 0.04% or 400 ppm (Parts Per Million).
Higher concentrations of CO2 occur in the outdoor environment:
The process of respiration changes inhaled oxygen into carbon dioxide. The exhaled air of an adult contains on average about 45 to 50 thousand ppm CO2 (about 100 times higher concentration than in outdoor air). Without adequate ventilation, the concentration of CO2 logically increases in enclosed spaces. The value of the carbon dioxide concentration in the air can therefore be considered an important indicator of indoor air quality.
Although carbon dioxide is invisible and odourless, its elevated level is obvious. It causes fatigue and loss of concentration, headaches… Particularly in areas with large numbers of people, such as schools, offices, theatres, medical facilities, the negative impact of increased CO2 concentration in the air is very noticeable.
The recommended airborne CO2 concentration should be maintained at or around 1,000 ppm.
Current technologies allow easy and permanent measurement of CO2 concentration. The values obtained can then be used to control ventilation systems to ensure good air quality and reduce energy consumption for heating, ventilation and air conditioning indoors. Ventilation systems can therefore use the measured CO2 concentration values to continuously control their performance and keep the indoor environment comfortable. Such systems are particularly useful for spaces with variable occupancy. Ventilation performance is then continuously varied depending on the number of people in the ventilated space. By measuring the CO2 concentration in the air, modern ventilation systems can then ensure optimum air quality in the ventilated space, regardless of the number of people present.