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.

  1. Increase air circulation with fans, especially ones placed near the CO2 gas inlet into the greenhouse.
  2. 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.
  3. 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.

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