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.