Sensgreen Knowledge Base

Carbon Dioxide (CO2)

What is Carbon Dioxide (CO2)?

Carbon Dioxide (CO2) is an odorless and non-flammable gas that’s generated naturally as a part of human metabolism. That’s why the indoor level of CO2 is dependent on various factors such as the number of people in the building, occupation time of the area, size of the room, and the amount of fresh air entering the site. Other than human sources, CO2 can be generated by the combustion of carbon fuel like cars and buses.

green cloud icon with co2  written in it
two green windows with red covid-19 figures showing indoor-covid-transmission-risk

Carbon Dioxide as Covid Transmission Risk Indicator

According to a very recent study, the infection risk of SARS-CoV-2 (Covid-19) is also proportional and highly related to the CO2 levels in an area, and thus monitoring the CO2 levels and minimizing the amount of it in especially commonly used shared areas is a substance of very high concern. Additionally, the transmission risk of Covid-19 is much easier in indoor environments than outdoors. It's also stated that keeping the CO2 levels as low as possible will reduce the risk of transmission. ¹

It is observed that if an influx of people makes CO2 jump from 800 to 1600, the risk of Covid transmission triples.  ²

Effects of CO2 on Performance

Another research study focusing on IEQ (indoor environment quality) of green and conventional buildings and its effects on an objective measure of human cognitive function performance showed that, in green buildings, the cognitive performance of the occupants was 61% better with lower CO2 and VOC levels independently associated with the scores. ³

In addition to cognitive performance effects, CO2 levels can also affect other mental functions. In a study, in better-ventilated classes, student's test scores were higher up to 15% in comparison to classrooms with lower ventilation rates. ⁴

Impact of  carbon dioxide on human decision making
Impact of  CO2  on human decision-making performance. Error bars indicate 1 SD. image retrieved from
Head figure with two circles around it showing Carbondioxide Causes Dizziness


Head figure with red vawes in it showing Carbondioxide Causes Headache


Head figure with red dots and points in it showing Poor Decision Making

A decrease in cognitive abilities

human spine model with some red parts showing bone demineralization

Bone Demineralization

Other Effects of Carbon Dioxide on Human Health

ASHRAE has recommended indoor CO2 levels not exceeding 1,000 ppm in densely occupied spaces. There is strong evidence that CO2 concentrations are frequently near or above the levels in schools and office spaces. It’s easy to see why indoor air quality is an emerging topic. ASHRAE(American Society of Heating, Refrigerating and Air-Conditioning Engineers) Atlanta, GA: ASHRAE; 2010. ANSI/ASHRAE Standard 62.1-2010: Ventilation for Acceptable Indoor Air Quality.)

According to the Minnesota Department of Health’s website, long-time exposure to high levels (5,000 ppm) of CO2 may cause nausea, dizziness, headache, and other symptoms. At higher (40,000 ppm) levels can cause asphyxiation since it replaces the oxygen in the blood, but CO2 poisoning is very rare. ⁵

In another article released by Nature Sustainability, new evidence suggests that chronic CO2 exposure may cause inflammation, a decrease in cognitive abilities, behavioral changes, and even bone demineralization and kidney calcification in longer durations. (Jacobson, T.A., Kler, J.S., Hernke, M.T. et al. Direct human health risks of increased atmospheric carbon dioxide. Nat Sustain 2, 691–701 (2019).


CO2 and Ventilation

HVAC System (Heating, Ventilation, and Air Conditioning) is responsible for 50-65% of energy usage in commercial and public buildings. ⁶ Demand Controlled Ventilation (DCV) is a ventilation strategy that manages the ventilation according to CO2 levels of different rooms.  DCV control logic could lead to 9% to 33% HVAC energy savings on a source energy basis compared with the non-DCV baseline. Most of the buildings are managed based on predefined scenarios, and systems cannot adapt themselves to real-life conditions during the day. This leads to an excessive amount of energy waste in buildings. 

One example demonstrates the evidence of CO2-controlled room ventilation. The exhaled air of a human contains up to 40,000 ppm CO2. In one hour a person breathes out 15 liters of CO2. Thus in a classroom with a volume of 200 m³ occupied by 25 pupils the CO2 concentration increases in one hour by 1,875 ppm! ⁸

Only 22% of the recently constructed or renovated classrooms met recommended minimum ventilation rates.⁹ Sensgreen's IAQ monitoring solutions help you to optimize the HVAC systems and save energy by tracking the most important IAQ parameters including CO2 and, take actions based on the data with the power of AI analytics.

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