Control Indoor Air Quality for Room Comfort

It is often noted that CO2 causes global warming, but keeping track of CO2 concentrations is also an important aspect of preserving indoor air quality. Concentrations of more than 1000 ppm can lead to drowsiness, and long-term exposures can lead to adverse health effects. This example shows how you can control the concentration of CO2 in a room and subsequently check if climate change puts more pressure on the ventilation system.

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Model of a Room with Ventilation

The room consists of a ventilation system that feeds fresh air using a pump. CO2 released by people during breathing increases the CO2 level in the room. The number of people in the room changes throughout the day, and a PI controller is used to maintain the CO2 level below 1000 ppm.
Model of the room with the ventilation system and people.

Simulation of CO2 Levels

The carbon dioxide level inside the room is within the desirable limit. The controller maintains the carbon dioxide level by regulating the amount of fresh air entering the room.
The blue curve on the top plot shows the CO2 level in the room. The red curve on the middle plot shows the CO2 released from people. The orange curve on the last plot shows the mass flow rate of fresh air fed into the room.

Effect of CO2 Emissions

Atmospheric CO2 level measured at Mauna Loa Observatory in Hawaii peaked near 420 ppm in May 2021. This is an increase of 105 ppm from the 315 ppm that was first recorded at the observatory in 1958. It has resulted in an increase in the required mass flow rate of fresh air by about 16 %. Further increase of CO2 level even by a small margin of 30 ppm to 450 ppm (say by 2050) will lead to an increase in the mass flow rates by about 7%, thus putting additional pressure on the room’s ventilation system.
Mass flow rates of fresh air for different CO2 levels in the atmosphere.

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