CO2 Sensor | What is it and how do you use it?

A CO2 sensor measures the concentration of carbon dioxide (CO2) in the air in “parts per million (ppm).“

CO2 Sensor Installation

The installation and positioning of the CO2 sensor are important because there are various microclimates in a greenhouse. Attach the sensor with a tie-wrap or rope to a tripod and place it among the plants:

• • When only one sensor is available, the best place to position it is in the center of a greenhouse or section. (Lee et al., 2019).

• • When using multiple sensors, more distribution is possible to get a better overview of the temperature and humidity in the greenhouse. (Bhujel et al., 2020).

Do’s and Don’ts when Installing a Sensor

• • Place the sensor between the lower and upper leaves, depending on what needs to be measured.

• • Install the sensor in a location that is representative of most of the plants, for example, not along an aisle.

• • Do not place the sensor near a location where CO2 is injected.

• • Use a radius of one meter of plants around the sensors. This minimizes the edge effect.

Analyzing CO2 Sensor Data

Every five minutes, the CO2 sensor sends the values to MyLedgnd.

Here, you get an immediate overview of the progression of these values throughout the day. At the same time, you can analyze multiple sensors simultaneously to gain insight into the differences in values between different areas of the greenhouse.

In image 1, it is clearly visible that around 18:00, the yellow line is significantly higher compared to the green line. This is because the yellow line sensor is located close to the CO2 diffuser, resulting in a different microclimate.

Image 1: The CO2 value for the yellow line is too high because it is located too close to the CO2 diffuser. This results in a different microclimate.

What conclusions can you draw from the measured data?

The CO2 values are interesting to compare with other data, such as:

• • Leaf temperature: To observe the effect of the CO2 concentration on the opening and closing of the stomata, compare the leaf temperature with the data from the CO2 sensor. A normal plant response to a higher CO2 concentration is to partially close the stomata.

    Time: It is important to keep track of the CO2 levels in the air within the greenhouse. This applies to both a greenhouse with CO2 supplementation and one without supplementation.

For a greenhouse with CO2 supplementation, it is important to monitor whether the levels remain consistent with the set ppm value. Several factors can cause this not to be the case:

1. Too little CO2 is being injected.
2. The distribution of CO2 in the greenhouse is suboptimal.
3. The CO2 sensor is placed too close to the area where CO2 is injected.
4. The windows are open too wide, causing a lot of CO2 to be lost
5. The plants are very active and absorb a lot of CO2.

For a greenhouse without CO2 supplementation, it is also important to monitor CO2 levels. This is mainly to ensure that the CO2 levels do not drop too much during the day. Through measurements by the CO2 sensor, it becomes clear whether enough fresh air is entering through the windows to refresh the air.

Advice from Ledgnd

CO2 sensors are an excellent way to quickly gain insight into CO2 variations across different microclimates in the greenhouse. For the best insights, we recommend conducting measurements for CO2, as well as leaf temperature and VPD, to make the comparisons described above.

References

Bhujel, A., Basak, J. K., Khan, F., Arulmozhi, E., Jaihuni, M., Sihalath, T., … & Kim, H. T. (2020). Sensor Systems for Greenhouse Microclimate Monitoring and Control: A Review. Journal of Biosystems Engineering, 45(4), 341-361.

Lee, S. Y., Lee, I. B., Yeo, U. H., Kim, R. W., & Kim, J. G. (2019). Optimal sensor placement for monitoring and controlling greenhouse internal environments. Biosystems Engineering, 188, 190-206.