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Why Control CO2 Levels at Night in Plant Grow Rooms?
In this article, we outline 5 reasons why you may consider turning off the CO2 supply at night via your CO2 monitor and controller.
How to Fix GasLab® Software Not Detecting Your CO2 Sensor
Having trouble connecting your CO2 sensor to GasLab® Software? Learn how to fix driver issues, install the correct FTDI USB-to-UART drivers, and restore communication.
Temperature Change Impacts Oxygen Sensors
If you work with gases like we do at CO2Meter, you already know that the ideal gas law PV=nRT shows that absolute gas concentration decreases as temperature increases. This relationship is important to anyone measuring oxygen levels during combustion, fermentation, distillation or algae production.
But like they say, “a picture is worth a thousand words.”
That’s what we discovered when we measured the change in oxygen gas levels in a sealed environment using our UVFlux 25% Oxygen sensor and Gaslab software. Using the built-in RS232 protocol, the UVFlux sensor samples both the oxygen level and the temperature inside the sensor once per second.
Over several minutes we raised the temperature of the sample from 24C to 34C, and were able to see in real-time the oxygen concentration in the sample drop from 20.6% to 19.8%.
click image on right for larger view.
Note the internal sensors components are corrected for operating temperature over the range. No compensation is made for the temperature of the gas being measured. Also note the change in oxygen level measured slightly lagged behind the change in temperature.
In addition to temperature, the % relative humidity will have an impact on the oxygen concentration in a sample. At the same pressure and temperature, a volume of oxygen at 100% humidity will contain less oxygen molecules than if there were no water.
Constant CO2 Level in Greenhouse
Controlled CO2 gas inflow and improved air mixture can help maintain optimum CO2 levels in small indoor greenhouses or grow rooms. These were the lessons learned after working with a client who was attempting to control the CO2 levels in a group of 3 10x20” greenhouses.
The client wanted to maintain different consistent CO2 levels in each greenhouse to test the effects on the plants inside. To control the CO2, he used our iSense 1% CO2 Level Controller, a more industrial version of our Day Night CO2 Monitor & Controller for Greenhouses.
In one test greenhouse, the CO2 controller was set to turn on a CO2 Tank Regulator with Solenoid Valve at 700ppm and turn it off at 1,400ppm. While the controller correctly turned the regulator on at 700ppm, the CO2 levels were overshooting 1,400ppm before switching off the solenoid on the regulator. As a result, the clients was seeing wild swings of CO2 levels instead of the consistent level required for his experimentation.
After looking at his CO2 levels vs. time graphs, we noticed a pattern of a quick rise in the level of CO2, followed by slow drops. This lead to the conclusion that the greenhouse was being quickly flooded with CO2 before the CO2 sensor in the controller had a chance to react to the change in CO2 levels.
In other words, the problem was being caused by inefficient air mixture in an enclosed area.
In a perfect world the CO2 flow rate could be set to exactly match the CO2 loss. However, in the real world, minimum and maximum level switches are required to turn the regulator on and off to keep the CO2 levels within a specified range.
We suggested three changes to the client’s setup to help solve his problem.
- Increase air circulation with fans, especially ones placed near the CO2 gas inlet into the greenhouse.
- Make a CO2 delivery tube like industrial greenhouses with propane CO2 systems use. Drill small holes in a long piece of flexible tubing that runs the length of the greenhouse, then hang the tubing above the plants. Since carbon dioxide is heavier than normal air, it will naturally mix as it falls.
- This decreases the amount of CO2 released between the time the room reaches the optimum CO2 level and the controller senses it. In addition, a good regulator with flow control not only limits the amount of CO2 that is released, but it maintains a consistent level of flow as the CO2 is used and the tank pressure changes.
Using our suggestions, the client will be able to maintain a more consistent CO2 level in the test greenhouses in order to complete their experiments.
Gas Sensor Response Time Increases with Length of Tubing
CO2 sampling sensors in a react at different rates depending on the length of the tubing used between the source gas and the sensor.In a closed loop system.