The conventional wisdom on artificially increasing CO2 saturation in a grow space is to try to hit a target range of 1200 PPM-1500 PPM. There are many ways of accomplishing this task: CO2 tanks and regulators, using CO2 burners on propane or natural gas, or utilizing a natural decomposition process like Exhale bags. I’ve even used the off-gas from my brewery to enrich the CO2 levels in a small cultivation space!
But I digress…
I’ve spent the last few years experimenting with lower CO2 levels and optimizing photosynthesis. What I have discovered is that if I stay in the 900-1000 PPM range, I find my yields are no bigger than when I go to the 1200 PPM or even 1500 PPM range.
I’m curious if/what other growers here on GNET have found…please let me know!
If you are planning on running CO2 tanks or propane/NG burners, I’d seriously consider running at a lower level, Bryan. You’ll save a lot of money in the cost of ongoing maintenance in the course of even the first year of operation. Consider the savings over several years running at a lower level.
This is a conversation worth having in this industry and in any CEA-related ag business.
We run 750# exterior tanks and keep levels around 1100ppm. Running any higher has not shown any additional yield. We believe this setup and level to be the most cost effective and lowest risk. Burners bring other risks that outweigh the benefits.
I’m glad you brought up the danger factor that accompanies burners! Thanks for mentioning that point, Shane!
Always consider staff issues when bringing in CO2 to your cultivation facility. Rolling big CO2 tanks around poses its own series of risks to your staff. We found we were able to minimize the risks associated with tanks by installing a large central CO2 tank that served the whole facility. We plumbed individual feed lines to each and every cultivation space to supply the rooms with CO2 via 3/4 inch line with simple inline valves and solenoids to be able to turn on/off the function. Individual environmental controllers operated the solenoids to maintain CO2 levels at proper setpoints.
We were able to accomplish much by utilizing the central tanks: minimizing risk associated with rolling large, heavy tanks; minimizing time that staff had to roll tanks to and from the delivery truck and hook up regulators periodically; we were also able to minimize the security/contamination issue typically associated with having non-staff personnel in the building. The delivery truck pulls up to the building, fills the tank from the exterior, then sends the accounting department an invoice. Simply magical.
All factors considered, the central CO2 tank was a good idea for our facility.
We went down the same path, from moving 50# tanks around with a handtruck to an exterior plumbied in big tank that we don’t have to touch. Also, the regulators here in Portland are, how do i say this nicely, fing nuts and changed the rules along the way. Basically, they used to allow as many 50# tanks as you wanted inside then they changed to 100# aggregate inside maximum before they have to be put in their own C1D1 room. Putting the tanks outside was really our only option at that point for growing and extracting. So we also have a 1400# liquid tank outside thanks to the city($$$$). In the long run the whole setup is ideal and cost effective, but the up front costs are much, much higher.
By the way, has anyone else noticed how much CO2 has gone up in the last two years? I think we are at $0.33/ pound delivered to our tanks.
Id like to add another benefit of C02. You can run your rooms at higher temperatures , around 80 degrees as opposed to 72ish . With plenty of C02 available the plants Stomata will partially close , conserving water and lowering the canopy temp in doing so.
This is very true! I always advise growers in arid or desert climates prone to high temperatures to enrich with CO2 to allow for a little additional forgiveness in temperature fluctuations.
I grow outdoors so it’s not my issue, but at what level does CO2 become toxic to humans and how does a small cap grower monitor that level? I’d hate to give mouth to mouth resuscitation to Rover because he wandered into the grow room and keeled over.
OHSA says 8 hours at 5000 ppm is acceptable. We have a monitor mounted on the outside entrance of the CO2 enriched room that has both audible and visible alarms. When the alarm event happens, it triggers a filtered exhaust fan to evacuate air rather quickly, along with an filtered intake. Reality is that there is no way to get the room to even 5000 ppm with the volume of our CO2 system capacity. We also had to install a door switch that kills the CO2 supply when someone enters the room. Signage is also required at entrance to enriched room. Bottom line was an extra $15k system that will never be used for a 40 light room.
That’s cool, I didn’t realize that the mechanism behind increased water use efficiency at elevated CO2 levels is the stomata not opening as wide! Happy to learn any new physiology! But don’t you think less transpiration actually allows canopy to become hotter if anything? Less evaporative cooling, right? The plants will just lose less water through smaller openings - so they can handle higher temperatures where they would normally be losing water faster than they could absorb it (and have to shut down completely).
c02 actually helps them regulate water use more efficiently, which keeps them from expelling too much water , stressing, and drying up to quickly. It also helps the enzyme RuBisCO kick the photosynthesis into high gear allowing the plant to be more productive and increase biomass beyond normal limits. This is where proper lvls of C02 come into factor .
Working at this “higher” level keeps the plant from stressing under higher heat and light intensity.
I’m about to start adding CO2 in a 40’ x 24’ room. By my calculations (you’re welcome to correct me) with a 20’ ceiling I have about 19,200 cf, and thus require about 19.2cf or 2 pounds of CO2 to fill to 1,000ppm. With 4-5 fills per day I figure will use about 90-110 pounds per month
My Q for this group is if I should even consider 50 or 75 pound tanks?
A fixed tank refilled by a gas company (Airgas? others?)
5-10 new Exhale bags every month (they claim to last 6 months so I would have 30-60 at any given time)?
I’ve think I have ruled out burners due to heat, but if you want to convince me I’d love to hear from you. I have a 7 ton commercial A/C and another older 2.5 ton condenser that isn’t really needed at the moment.
