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SELECTION GUIDE Arduino

CO2 Concentration Monitoring in Greenhouses

DFRobot May 26 2023 2834

Why Monitor CO2 in Greenhouses?

Greenhouse is a man-made structure designed to regulate climate and environment for plant cultivation. It typically contains gases such as carbon dioxide, oxygen, and water vapor. Among these gases, carbon dioxide plays a dominant role and is particularly important in the plant growth process.

 

Monitor CO2 in Greenhouse

 

Positive Effects of CO2 on Plant Growth

CO2 is one of the raw materials for photosynthesis in plants, where plants convert carbon dioxide and water into organic compounds. Adequate levels of CO2 can promote photosynthetic rates, thereby enhancing plant growth. It can also increase crop yield, improve crop quality, and enhance fruit characteristics. Furthermore, appropriate levels of carbon dioxide can enhance plant resilience, such as disease resistance, drought tolerance, and cold tolerance, improving the overall survival ability of plants. CO2 can also reduce plant transpiration, thereby conserving water and allowing plants to grow normally under water-deficient conditions.

 

Positive Effects of CO2 on Plant Growth

 

Negative Effects of CO2 on Plant Growth

However, excessive or insufficient CO2 levels can have various negative impacts. When the CO2 concentration is too high, plant photosynthesis tends to saturate, leading to a decline in nutritional value and overall plant quality. Moreover, if CO2 levels are excessively high, more ventilation may be required in the greenhouse to lower the CO2 concentration, resulting in increased energy consumption and operating costs. On the other hand, when CO2 concentration is too low, the rate of photosynthesis and plant growth decreases. This can lead to increased stomatal opening, increased water transpiration, and restricted plant growth and development, ultimately affecting the taste and nutritional composition of plants.

 

Different plants have different environmental requirements for growth. For example, tomatoes thrive in environments with CO2 concentrations ranging from 800 to 1200 ppm. When the concentration exceeds 1200 ppm, photosynthesis becomes saturated. Prolonged growth under high CO2 concentrations can result in increased sugar content, reduced acidity, decreased vitamin C content, altered taste, accelerated ripening, and decreased storage capacity. On the other hand, when the concentration drops below 800 ppm, photosynthetic rates decrease, leading to reduced fruit quantity and smaller size.

 

Therefore, maintaining appropriate CO2 concentrations is crucial for ensuring healthy plant growth in greenhouses. Understanding and monitoring the CO2 levels in the greenhouse in real-time is of utmost importance.

 

How to Monitor CO2 in Greenhouses

Intelligent Greenhouse CO2 Monitoring System 

An intelligent greenhouse CO2 monitoring system utilizes modern technology to monitor the concentration of CO2 inside a greenhouse. Its main function is to monitor the CO2 concentration in real-time and perform data analysis, enabling farmers to understand the climatic conditions inside the greenhouse and improve the growth efficiency and quality of greenhouse crops.

 

Intelligent Greenhouse CO2 Monitoring System

 

Components of the System

The intelligent greenhouse CO2 monitoring system mainly consists of a CO2 sensor, data collector, wireless communication module, host computer or cloud server, and power module. The CO2 sensor is responsible for monitoring the CO2 concentration in the greenhouse. The data collector receives the data collected by the CO2 sensor. The wireless communication module transmits the processed data wirelessly to the host computer or cloud server. The host computer or cloud server receives the data transmitted from the data collector, performs data analysis and processing, and presents the processed results to the user. The power module supplies power to the system.

 

Operation Process of the System

In the intelligent greenhouse CO2 monitoring system, the sensor continuously collects data on the CO2 concentration in the greenhouse. The data is then transmitted to the data collection module, which uses the wireless communication module to send the data to the server. Upon receiving the data, the server stores it in a database and performs data analysis and processing. Finally, the processed data is presented to the user in a visual format.

 

CO2 Sensor Selection

In the intelligent greenhouse CO2 monitoring system, the selection of CO2 sensors is crucial. When making a specific choice, it is important to understand the selection criteria and the types of sensors available, and then make the best decision based on the specific conditions of the greenhouse environment.

selection of CO2 sensors

 

Selection Criteria for CO2 Sensors

Different types of sensors have different characteristics and suitable applications. Therefore, selecting the right type of sensor will have a significant impact on the monitoring results and plant growth. The following characteristics can be considered:

 

1. Measurement Range

The measurement range of a CO2 sensor is an important factor to consider. Choose a sensor with a suitable measurement range based on the CO2 concentration that needs to be monitored. For example, some sensors have a measurement range of 0-5000 ppm, while others can measure concentrations as high as 100,000 ppm. In general, if the greenhouse is small or the CO2 concentration varies relatively little, such as under natural ventilation conditions where the CO2 concentration may stay between 300-800 ppm, a CO2 sensor with a range of 0-2000 ppm would be sufficient.

 

2. Accuracy

Accuracy refers to the deviation between the measurement result and the actual value. Generally, higher accuracy leads to more precise measurement results. Since greenhouse environments have higher CO2 concentration requirements, it is necessary to choose a sensor with high accuracy, typically with an accuracy requirement of ±50 ppm or lower.

 

3. Response Time

Response time refers to the time it takes for the sensor to detect a change in CO2 concentration and output the measurement result. For applications that require real-time response, response time is a crucial indicator. CO2 concentration in the greenhouse can change with plant respiration and photosynthesis, so it is important to choose a sensor with fast response speed, typically within 1 minute or faster.

 

4. Stability

Stability of a CO2 sensor refers to its long-term measurement performance. The higher the stability of the sensor, the more reliable the measurement results. In greenhouse scenarios, it is important to choose a sensor with high stability. Additionally, the sensor's lifespan and maintenance costs should also be considered.

 

5. Price

The price of CO2 sensors varies depending on brand, model, accuracy, etc. Choose a sensor that offers good value for money based on actual needs.

 

6. Power Consumption

Power consumption refers to the energy consumed by the sensor during operation. Generally, choosing a sensor with low power consumption can extend battery life, reduce maintenance frequency, and improve the availability and cost-effectiveness of the sensor in the greenhouse.

 

7. Other Features

Some CO2 sensors may have additional features such as a display screen, alarm function, specific output signal types, specific interface types, temperature and humidity compensation, etc. Choose a sensor with the appropriate features based on actual requirements.

 

In conclusion, the best choice for a CO2 sensor would be one that combines high accuracy, low power consumption, fast response time, high stability, and good value for money.

 

Classification of Carbon Dioxide Sensors

There are various types of CO2 sensors, and understanding the types of CO2 sensors is helpful for selection. Common CO2 sensors can be categorized into electrochemical, infrared, and photoacoustic based on their working principles. The principles and general characteristics of each type are as follows:

 

Sensor TypePrincipleGeneral Characteristics
Electrochemical SensorConverts CO2 concentration into an electrical signal through electrochemical reactions
  • High accuracy
  • Good long-term stability
  • Requires chemical materials such as electrolytes and electrodes
  • Affected by humidity and temperature
Infrared SensorMeasures CO2 concentration by detecting the absorption of specific wavelengths of infrared light by CO2 molecules

Non-dispersive infrared (NDIR) sensor:
 

  • High accuracy
  • Good stability

Dispersive infrared sensor:
 

  • High power consumption and larger size
  • Less interference from other gases
  • Suitable for atmospheric and remote measurements
Photoacoustic SensorMeasures CO2 concentration by detecting the absorption of specific wavelengths of light by CO2 molecules or the interaction between CO2 molecules and vibration or sound waves
  • High sensitivity and fast response
  • Sensitive to light sources and ambient light interference
  • Affected by environmental noise and interference
  • Suitable for specific application scenarios

 

Best CO2 Sensors for Greenhouses

In greenhouse environments, factors such as area, cultivated plants, and building materials have an impact on the selection of CO2 sensors, and the choice can be made based on the actual situation.

 

Greenhouse Factor

Key Considerations

CO2 Sensor Selection

​​AreaSmall area (occupying an area <100 square meters):Measurement range、accuracyNDIR sensor
Medium area (occupying an area of 100-1000 square meters):Measurement range, accuracyNDIR sensor or electrochemical sensor
Large area (occupying an area >1000 square meters):Measurement range, accuracy, power consumption, priceElectrochemical sensor or dispersive infrared sensor
​Cultivated PlantsPlants with high CO2 requirements (such as tomatoes, cucumbers, peppers, and other C3 plants and vegetables):Measurement range, accuracy, power consumptionNDIR sensor
Plants with low CO2 requirements (such as Begonia, Equisetum, ferns, and other C4 plants and some shade-tolerant plants):Measurement range, stabilityNDIR sensor or electrochemical sensor
​Building MaterialsMaterials with good CO2 retention performance (double or multi-layered glass, polycarbonate panels, polyethylene film):Stability, accuracyNDIR sensor
Materials with significant CO2 loss (single-layer glass, transparent plastic film, metal materials):Accuracy, response timeNDIR sensor or electrochemical sensor
​Ventilation SystemWell-ventilated system (sufficient ventilation, even air distribution, good controllability):Response time, stability, accuracyNDIR sensor or electrochemical sensor
Weak ventilation system (insufficient ventilation, uneven air distribution, lack of flexibility in control):Measurement range, accuracyNDIR sensor or dispersive infrared sensor
​Lighting SystemMore artificial light sources used:Respon​se timeNDIR sensor or electrochemical sensor
Primarily natural lighting:StabilityNDIR sensor or dispersive infrared sensor
​Control SystemUsed in conjunction with automated control system:Accuracy, response time, stabilityNDIR sensor or electrochemical sensor
No automated control system:Accuracy, stabilityNDIR sensor or dispersive infrared sensor
​LocationIndoor environmentAccuracy, response timeLight-acoustic sensor, infrared sensor, or electrochemical sensor
outdoor environmentAccuracy, response time, stability, power consumptioninfrared sensor, or electrochemical sensor

In a greenhouse, light-acoustic sensors are relatively suitable for indoor environments, while electrochemical sensors depend on some other factors. Among the types of infrared sensors, NDIR CO2 sensors are a commonly used and versatile type. NDIR stands for Non-Dispersive Infrared Gas Analyzer, which utilizes the absorption characteristics of infrared light to measure gas concentration. It typically consists of an infrared light source, sample chamber, detector, and signal processing circuitry. This sensor can rapidly and accurately measure CO2 concentration without being affected by other gases. Additionally, it has low power consumption, long-term stability, and is suitable for long-term monitoring in greenhouse environments.

 

Furthermore, there are various models and brands of NDIR CO2 sensors available. Let's take the DFRobot Infrared CO2 Sensor (SEN0220) as an example to understand the meaning of its parameters. You can find the sensor at this link: Gravity: UART Infrared Carbon Dioxide Sensor (0-50000 ppm).

 

Typically, the atmospheric concentration of CO2 is around 400 ppm, and common CO2 sensor ranges include 0-2000 ppm, 0-5000 ppm, and others. The measurement range of this sensor is 0-50000 ppm, which falls into the wide range category. It has an accuracy of ±50 ppm, indicating high precision. The response time is less than 30 seconds, indicating a fast response. It also exhibits excellent stability, high sensitivity, and low power consumption, making it a standard CO2 sensor suitable for greenhouse scenarios. For more information and guidance on selecting CO2 sensors, you can refer to this article: https://www.dfrobot.com/blog-1487.html.

 

Installation and Deployment of CO2 Sensors

After selecting a suitable CO2 sensor, proper installation and deployment are necessary to effectively monitor CO2 concentration in a greenhouse. Correct installation and deployment ensure the accuracy and stability of the sensor, enabling accurate data acquisition and control in an intelligent greenhouse system. The following steps can be followed as a reference:

 

1. Determine the monitoring location

The sensor should be placed in the most representative area inside the greenhouse, typically on the walls or ceiling at the height of plant growth. This ensures measurement of CO2 concentration around the plants. Avoid placing the sensor near ventilation ducts, exhaust pipes, or areas with high human activity to prevent interference from fresh external air, which may result in inaccurate data within the greenhouse.

 

2. Install the sensor

Before installing the sensor, ensure that the installation location is flat and that the screws, expansion tubes, and other materials meet safety requirements. Additionally, some sensors may need to be connected to a power source or other devices. Follow the guidelines provided by the sensor manufacturer to ensure proper connections during installation.

 

3. Connect the sensor

Connect the sensor to the data collector of the monitoring system to read the CO2 concentration data and transmit it. The connection method may vary depending on the type of sensor, so carefully read the sensor's instructions for guidance.

 

4. Calibrate the sensor

Before using the sensor, calibration is necessary to ensure accurate CO2 readings. Some sensors have automatic calibration features, while others require manual calibration. Check the accuracy and measurement range of the sensor before calibrating. The calibration process should be performed according to the instructions provided by the sensor manufacturer, usually involving the use of specific calibration tools or software.

 

5. Configure the monitoring system

After installing and connecting the sensor, configure the monitoring system to start reading CO2 concentration data. Thresholds can typically be set, so that when the CO2 concentration exceeds or falls below the set thresholds, the system will generate alerts or automatically adjust the CO2 levels inside the greenhouse.

 

6. Monitor and maintain the sensor

After the sensor is installed, regularly monitor the sensor's measurement results and periodically clean it to maintain accuracy. Regularly check and replace the sensor batteries to ensure proper functioning.

 

Summary

In the greenhouse, building an intelligent greenhouse CO2 monitoring system and selecting a suitable CO2 sensor are crucial for monitoring CO2 concentration and promoting plant growth. When selecting a CO2 sensor, factors such as measurement range, accuracy, response time, stability, price, and power consumption should be considered. In greenhouse scenarios, it is recommended to use versatile NDIR (Non-Dispersive Infrared) CO2 sensors, and light-acoustic sensors can also be considered for indoor greenhouses. Once you have the appropriate CO2 sensor, proper installation and deployment are necessary to achieve optimal monitoring results.

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