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Why CO2 an Indicator of Indoor Air Quality?

A Heating, Ventilation and Air-conditioning System, HVAC regulates indoor air for the comfort of occupants and with energy saving in perspective. Indoor air is exchanged through recirculation and replacement. Indoor air that is high in Carbon Dioxide, CO2 is exhausted while diluted with outdoor fresh Oxygen, O2.


Indoor combustion appliances and building occupants consume O2 and release CO2. Hence, indoor CO2 is presumably higher than natural outdoor. In an urban environment, congested with industries, vehicles, and sources of combustion, CO2 in the outdoor air could possibly be higher. We need a greener environment that replenishes and balances the O2 density.


Higher CO2 in relative to O2 in confined buildings with high occupancies such as schools, industrial, workplaces, and offices is correlated to a reduction in productivity. People become lethargic, suffer difficulty focusing, and sense the discomfort of stale air, known as Sick Building Syndrome.

ASHRAE 62 provides a general guideline of recommended outside air per person (CFM per person) measured in relative to CO2 differential. CO2 will likely increase in an occupied space by the end of the day in a low ventilation environment. Measuring CO2 is complicated but thanks to technology, CO2 monitoring devices, built-in or separate have now been widely applied in buildings. These devices usually also measure other important IAQ parameters such as temperature, relative humidity, PM2.5, and TVOC.


In summary, to address Sick Building Syndrome is to reduce pollutant sources, increasing ventilation, performing air purification, and creating Occupational Safety and Health awareness.

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