Air exchange in the grow room

[Huntington]

I've read that you should size a fan so it can exchange the air in your room within 3-5 minutes. However, how often during an hour do you want to exchange the air? Once an hour? Twice?

For stealth purposes I rather not have the fan run continuously, but I am curious as to what is a sufficient number of air exchanges.

I was taught an air exchange ever 2 minutes when I first started but it's actually more complex than that. You want to exchange the air, in an open system, as fast as possible IMO/IME, while maintaining proper temps while the lights are on as lights off is a different animal and really requires no air exchange if certain parameters are held in check. One thing that will occur lights on is the longer you go between air exchanges the more humidity will rise so even though temps may be in check to your satisfaction RH will go up. Personally I'd rather run at cooler temps with lower RH than higher temps with higher RH and this is more true for me the later I'm in flower. In veg I'd take the higher temps/humidity though.

Also regarding your question it's difficult to say how often you'd need to exchange air to maintain satisfactory CO2 levels because it's not the size of the space but how much canopy you have in that space that will determine how fast the CO2 is depleted.

If stealth is a concern buy oversized fans and slow them down with a speed controller, use insulated oversized ducting, use noise mufflers, hang fans using bungee cords, etc. Also a fan like an Elicent is quieter than the same sized Vortex cause the Elicent is moving less air making it quieter in comparison. More air flowing through the same sized fan housing increases noise.

Good luck!

 

[Calimed]

+1 for 24/7 ventilation, especially if you are running a tent. I just added a new 6 inch canopy fan, and noticed the plants were noticeably happier within a day or two.

 

[Huntington]

You're dealing with a very complex set of influences in a grow room. I keep on telling a friend you are dealing with a dynamic process and not a machine and that's just about the plant...lol. In many instances there is no set answer just general guidelines to follow and you go from there.

I pop in here every few years...till next time...

 

[*mistress*]

As for circulation I always recommend people run an oscillating fan 24/7 so yes I agree that air circulation is important but air exchange lights off is not. I never mentioned circulation...only exchange. I do not see a dehumidifier as providing adequate air circulation in virtually any situation to the point I would not consider it in a discussion about circulation in regards to growing and never have. Circulation is not exchange even though during exchange there is some circulation.

however it is stated, circulated air should be treated for removal of water, voc's (volatile organic compounds) or odors, etc... all circulation in a garden is an exchange of some sort. when watering nutes, ions are exchanged for hydrogen ions, which increase ph... there are no variables in isolation. during circulation, water vapor is carried away... to... well, hopefully an ac or dehumidifier, or the same water vapor pressure, or low vapor pressure defict (high rh) will remain & rate of respiration will slow...
regardless what the 'term' is, if want to use both, ok... air should be circulated & exchanged... ok to expand the topic w/in same subject matter...


this may help clarify importance of gas (air & water vapor) exchange in garden. too much data to re-post here:
Hempy vs. Smart Pots vs. Air Pots
https://www.icmag.com/ic/showpost.php?p=2936454&postcount=12

As for using words guess we'd have to agree on which 'humidity' we are discussing...absolute, specific or relative. Personally I use relative for the sake of discussion and as far as that is concerned...
So yes humidity can be controlled by raising the temperature. It can also be controlled by canopy pruning/trimming.

you cannot avoid the key point of your link...

Key point to remember: Given that the amount of water vapor is held constant, then if you
--reduce the temperature, the relative humidity goes up
--increase the temperature, the relative humidity goes down.

the rate of transpiration is not necessarily linear, no @ a constant level, though there is constant water being released. the amount released depends on temp, avalialble water @ roots, ambient air temps, actual leaf temps & root temps...

so, no, rh cannot be controlled that straight-forward... by adjusting temps, because adjusting temps will adjust amount of water plant transpires & respires...

while the term relative humidity is used by humans, greenhouse engineers & managers, & research stations @ universities use vapor pressure deficit.

this may help detail correlation between rh & vpd...
RH importance
https://www.icmag.com/ic/showthread.php?t=112589

Huntington. see you in next moments...

enjoy your garden!

 

[Redbuddz]

Looking for the same answers

Looking for the same answers

Hello Weimer. I have been surfing the net trying to find the same answers that you were trying to find so I figure I would ask you how you made out with your ventilation problems. as best I could find it seems like you want to change the air in a grow room about 12 times an hour. I'm currently setting up my grow room and I'm trying to figure out what's the best way to set up my ventilation setup and I'm hoping that you will have some good input for me

Bill

 

[Mr Blah]

Hello Weimer. I have been surfing the net trying to find the same answers that you were trying to find so I figure I would ask you how you made out with your ventilation problems. as best I could find it seems like you want to change the air in a grow room about 12 times an hour. I'm currently setting up my grow room and I'm trying to figure out what's the best way to set up my ventilation setup and I'm hoping that you will have some good input for me

Bill

This is an old thread. But you want to exchange the air in your grow twice a minute.
I haven't read this thread just saw how old it was.

 

[theweedman420]

The overall percentage of CO2 in the atmosphere is actually very low, plants need very little of it to survive, and roots need very little actual oxygen.

To look at it from another angle, find me a grow where CO2 deprivation caused an issue, there just aren't any.

yea its called poor bud development

 

[Lazyman]

All else being equal, co2 deprivation- caused poor bud development is about as likely as your first post ever on ICMAG being defensible in any logical manner.