CO2, temperature, and humidity monitoring sustain IAQ


Maintaining indoor air quality involves controlling pollutants from various sources using mechanical ventilation and air conditioning systems. Davide Di Dia and Giovanni Bonesso from CAREL share how monitoring CO2, temperature, and humidity ensures a healthy environment and provides comfort in diverse indoor settings.

What are the primary sources of indoor and outdoor air pollutants, and how can indoor air quality be maintained?

The sources of indoor air pollutants may be biological, such as human respiration, which releases pathogenic particles such as viruses and bacteria. Mould can also proliferate in environments with high relative humidity, releasing spores. Other sources of pollutants are human activities like cooking food, direct combustion indoors and raising dust. Finally, there are sources of pollutants deriving from the materials used to construct the building and its interiors, which release volatile organic compounds (VOCs) into the environment.

The main sources of outdoor pollutants are vehicular traffic, industries, heating systems, agriculture, and natural emissions, such as desert dust and pollen.

The substantial difference between indoor and outdoor pollutants involves the substances released by human respiration. In outdoor environments, these particles are quickly diluted in the atmosphere, but in closed indoor spaces, they can reach high concentrations and be a source of airborne diseases (e.g., COVID).

Indoor pollutants can be diluted through controlled mechanical ventilation and air conditioning systems, which filter out the pollutants from the outdoor air and thus deliver clean air into the building. This clean incoming air, together with appropriate humidity conditions, guarantees the well-being of occupants and ensures healthy indoor spaces.

How can CO2 concentration control indoor air quality in varied environments?

Varied indoor environments consequently require different types of IAQ control. Classrooms tend to have a high density of occupants who spend relatively little time inside. In offices, occupant density usually is lower, while the time spent inside is higher, spanning the entire working day. In healthcare facilities, the situation depends on the department, which may have different needs in terms of the type of patients and the treatments provided. However, very similar pollutants can be found in these environments.

Except for some sources of pollution that are typical of the specific environment, such as chalk in schools and printers in offices, a significant portion of the pollutants present are due to the respiration of occupants. Humans emit CO2 while breathing, which is not harmful in low concentrations. CO2 concentration is technically easy and economical to measure; for this reason, it can be considered the reference parameter for setting the operating conditions of ventilation and air conditioning systems. Diluting the CO2 concentration means dilution of the total pollutant load.

How do controlled mechanical ventilation and air conditioning systems maintain indoor air quality and energy efficiency in buildings?

Controlled mechanical ventilation and air conditioning systems allow air from outside with a low CO2 concentration (450 ppm) to be delivered into buildings, whether offices or private homes. The air is then conditioned to guarantee the ideal temperature and relative humidity. The rooms inside buildings can be equipped with temperature, relative humidity, and CO2 sensors, such as CAREL’s DPWQ, to minimise energy consumption and manage ventilation correctly.

These sensors send the parameters to the ventilation system’s electronic controller, CAREL K. Air, which manages the incoming and exhaust air flow rates in the different building rooms. The control algorithms synchronise the various components of the ventilation system, such as dampers, heat exchangers, and humidifiers. They are designed to maximise energy savings.

Monitoring and maintaining the right relative humidity (RH) temperature and CO2 values are also important. In colder times of the year, indoor relative humidity is often very low (<25%), and this phenomenon could be amplified by a ventilation and air conditioning system.

RH values lower than the optimal range of 40–60% lead to dryness of the mucous membranes in the respiratory system. This weakens the human body’s defences and makes us more vulnerable to viruses and bacteria. Furthermore, dry air causes sensations of discomfort, such as dry skin and eye irritation.

Through monitoring temperature, RH, and CO2, indoor air quality can be kept constant, guaranteeing a healthy environment for all building occupants.

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