Low Cost CO2 Sensors Comparison: Photo-Acoustic vs NDIR
This article has been updated in September 2024 with new information about the Infineon photo-acoustic sensor as well as the performance of photo-acoustic sensors outdoors.
The first method via TVOC sensors is extremely unreliable. Some TVOC sensors like the Sensirion SGP30 estimate CO2 via organic components in the air. When you breathe out, you add organic components to the air which these sensors pick up and try to calculate a corresponding CO2 ppm value. The problem is that also other indoor sources like deodorizers add these chemical components to the air and thus the estimated CO2 rises -even though nobody might be in the room. We strongly advise against using TVOC sensors for CO2 estimation and thus will also not analyse it further in the rest of this article.
Both NDIR as well as photo-acoustic sensors are much more accurate than eCO2 from TVOC sensors as these sensors measure the CO2 directly and both are based on the absorption principle of gases. Different gases absorb light at specific ranges of wavelengths. So if the light is tuned at a certain wavelength and a receiver measures the incoming light levels, the rate of absorption can be calculated and with this the concentration of the gas established.
