Miniature sensor for good air: Page 2 of 4

December 03, 2019 //By Hicham Riffi
The CO2 concentration is a key indicator of the quality of the indoor air. Good air means less drowsiness and more productivity, while too high a concentration of CO2 indoor means poor air quality, often due to inadequate air conditioning and air recirculation. This can lead to health issues including the well-documented sick building syndrome (SBS) towards which other indoor toxins can contribute, such as fine dust, mould, pollen, germs or even asbestos.

But there are many other applications, including in vehicle CO2 monitoring to regulate the air quality in the driver's cab or in the entire vehicle interior. In agriculture, the sensor is used to control the concentration of CO2 in greenhouses in order to achieve higher yields and cost savings. Sensors are also used in medical applications including capnometry, a method for measuring the CO2 content of a patient's exhaled air in real time, especially useful in the field of anaesthesia.

Industrial use cases include the detection of CO2 leaks in the vicinity of CO2 gas sources such as dry ice reservoirs, storage tanks or underground gas sources. Smart cities can correlate CO2 emission sources to drivers’ density for traffic management.


Todays’ CO2 sensors

Today NDIR (non-dispersive infrared) sensors are widely used, especially in building automation. However, they are relatively large, expensive and therefore can only be used to a limited extent. Such a sensor, consisting of an IR light source, sampling chamber, spectral filter as well as reference and absorption IR detectors, provides true and accurate CO2 measurements. However, in addition to purely aesthetic aspects, it is not suitable for installation in mobile devices, thermostats or other smart home components in the living room, primarily because of its higher cost and lower integration capability due to its form factor (significant size).

There are currently no comparable solutions on the market that can perform such true and accurate CO2 measurements and that are cost effective at the same time. Although there are so-called eCO2 sensors to detect various indoor pollutants, these are not good alternatives to NDIR sensors. An eCO2 sensor does not perform real measurements; it uses algorithms to calculate an equivalent CO2 value. This involves assuming that the CO2 level is caused primarily by the persons present. As a result, it provides an estimate based on numerous assumptions. Consequently, with this eCO2 value, the regulation of the indoor air quality can only be performed on the basis of this potentially inaccurate information.

This leads to air-conditioning systems consuming an unnecessary amount of energy or not ventilating properly at all, precisely when it is needed. As a result, air quality is not effectively improved and users lose confidence in products that work with such eCO2 sensors.

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