Optimizing CO2 mass flow control in indoor hydroponic systems

Controlling CO2 in indoor growing environments is an effective way to improve crop yield. The optimal concentration of CO2 for most plant species is around 1000 PPM. Here, we discuss the use of mass flow control to regulate CO2 levels and improve indoor growing processes.

Using CO2 gas to boost indoor plant yields

Monitoring and maintaining an indoor CO2 concentration of around 1,000 PPM will maximize the yields of most crops by up to 50%. However, this must be precisely controlled, as concentrations of CO2 at 2,000-5,000 PPM can cause headaches and nausea and at 50,000 PPM can lead to loss of consciousness or even death. Therefore, if CO2 is supplemented, precautions must be taken to continuously and accurately raise, lower, and monitor CO2 levels.

The main components to control CO2 levels in indoors hydroponics systems include the following:


CO2 is released from the gas source as needed based on set points from the CO2 monitor while amounts of total CO2 gas and their flow rates are controlled using flow meters and controllers. For optimal CO2 control, Alicat’s M and MC-Series devices offer gas control and measurement to ±0.5% of reading or ±0.05% of full scale, a control range of 0.01-100% (10,000:1 turndown), and a flow range up to 5,000 SLPM.

To eliminate separate flow controllers for inflowing and for outflowing CO2, Alicat’s MCD-Series of bidirectional gas mass flow controllers provide a process solution where CO2 can be simultaneously added and removed.

Using CO2 gas as a natural pesticide

Another less common application for CO2 in indoor hydroponic farming systems is as a food-safe natural pesticide. At concentrations of 40% or higher, 400,000 PPM, CO2 can kill all different types of bugs within 7-15 days and as quickly as 60-120 hours for some species. When used indoors as a fumigant, CO2 reduces levels of oxygen, thus bugs die from asphyxiation.

To add the CO2 for fumigation, flow controllers and pumps are used, thus reducing the air’s concentration of oxygen. After the process is complete, pumps and flow controllers remove CO2 until the CO2 monitor returns back to an optimal concentration for plant growth around 1,000 PPM.

Pairing Alicat mass flow controllers with CO2 monitors

Alicat’s mass flow controllers offer multiple solutions for communicating with CO2 monitors to fully automate the previous processes. Alicat’s devices can work with PLCs, allowing for pairing with CO2 monitors, providing a wide range of customizable control possibilities. For example, to reduce the chance of accidental human exposure to dangerous levels of CO2, when connected to a PLC, an alarm output can be set to trigger at different concentrations of CO2, notifying a central system when the process falls outside of tolerances, shutting off (or turning on) the Alicat mass flow controllers.

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M/MC mass flow meters and controllers that ship in just 3-5 business days.
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