What is the bare minimun for ventilation?

[Dalaillama]

I haven't found clear answer for this one. In this case I mean what is needed for sufficient CO2 and O2 for plants?

If we think that the grow room is a cold shed that is insulated. Outside of the shed is about -5 to 30F degree temperatures. Insulation is made quite air tight to prevent heat loss. In this kind of situation you don't have to worry about excessive heat and it is even preferred not to vent once warmed air too often.

I have seen this kind of setup that seemed otherwise functioning perfectly. Only problem was that grow was very slow. Could it be that plants didn't receive enough fresh air?

Is there anyone here with something like described above and have encountered problems with reduced growth rates?

 

[intotheunknown]

air only holds a certain amount of co2... a small percentage, somewhere in the .04% range i believe. (not exactly positive on that number) so if youre NOT constantly moving air in and out, i would say yes... a slower growth rate would be the result of very low co2 content.
if your room is sealed, you would need to be adding co2.

 

[Harry Gypsna]

The rule of thumb most grow books will tell you is that the ventilation system needs to be able to completely change all the air in the room/tent/cab, within 2-3 minutes or 20-30 times an hour.
So you measure up your space, multiply length x width x height, and choose a fan capable of moving that much air.

 

[FlowerFarmer]

Bare minimum...

I was always taught once every 5 minutes.
Always shot for once every 2-3 minutes until the preachings of Heath, DHF, and the a like..


Now I shoot for as much as possible (2x PER minute)... and treat intake "lung" air throughout the seasons when necessary.

 

[farmari]

You could buy a co2 meter to test if the co2 levels drop.

 

[intotheunknown]

myself, I constantly vent. 24/7
I do lower and raise fan speeds per day/night cycles. less air movement during the night and more during the day. also depending on temps.

 

[LeeROI]

Maybe the setup in the OP caused high humidity before CO2 depletion became a factor?

 

[Dalaillama]

Thanks for quick replies guys and girls.

I'm keeping this once per 5 minute as a reference. It is also mentioned in the "ventilation 101" sticky of this forum.

However these plants are very small Only 2 to 3 inches tall, under 10 nodes and quite small leaves. Space is about 9m3 which is 318 cubic feet. My intuition says that they cannot consume that much CO2 at the moment. Still CO2 is very small percentage of air so it could be consumed quite quickly. Maybe this must be solved with empirical tests if nobody have not tested this yet.

Testing this is problematic in cold climate. If air is changed rapidly heating costs sky rockets. Second is air drying. If you heat very cold air to room temperatures humidity drops very low. You might need quite efficient humidifier which needs regular refills.

I guess somebody have studied the subject of plant CO2 consumption. I don't if that kind of studies are available in the net. Maybe I just look around. It would be interesting to know..

CO2 meter would be very handy. If somebody knows reasonable price yet accurate meter please let me know.

 

[Granger2]

With the cold you're talking about, I would suggest a sealed room w/CO2, and the option to air cool your lamps if needed, using a closed loop. Outside air never entering the room, flowing only thru lamps, then back outside. Good luck. -granger