Air exchange in the grow room

[weimer222]

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.

 

[Lazyman]

Air exchange is not super important for lots of grows actually, controlling the temperature with fans hooked to a thermostat will help your girls much more than blowing in a bunch of "fresh" air if it's negatively impacting temperatures. What are your temps?

 

[weimer222]

I live in a northern climate and don't deal with high temps very often. What I am planning to do is run a separate duct line through my air cooled hood to help control temps. I'll split into the duct that exits from the hood and goes back outside, to vent from the room if a maximum temp is reached, but primarily I will use this split to accommodate air exchanges in the room (I have a separate air intake from inside the house to provide fresh air). I guess I am assuming by running the lights at night, and drawing cold air into the hood, I will not have temperature issues except possibly during the July and August, and I still doubt it.

Thus, if heat issues don't really apply, how often do I need to refresh the room air to bring in fresh C02? Is once an hour for 5 minutes sufficient?

 

[weimer222]

Anyone?

 

[Lazyman]

You probably won't need to refresh the room at all, but if you insist then yes, 5 minutes an hour should be sufficient.

 

[weimer222]

Curious as to why you think I won't really need to refresh the room air? True, I will be going in the room once a day, but don't the plants need new C02 and fresh O2?

 

[Guest]

Depend on growing style weimer. Roots use oxygen, above ground system use co2. The above ground system (include leafs) can also take in oxygen from the water vapor collected in the above ground system, but will not get so much into that as it a different topic me think.

It all depend on style of growing and design.

If growing in a hydroponic application with air pumps sending fresh o2 to the rootzone from another space then not so much need for refreshing air given co2 is being supplemented in the grow space. However if this is not the case, then the metabolism of plants/size of space will determine how often you will wish to exchange the air.

Hard to say without some blank fill out.

 

[Lazyman]

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.

 

[Securityfirst]

Why not hang a carbon scrubber and put it on a speed controller? That way you will have fresh air coming through the cracks into your growroom over your plants. The fan will draw it into the room on a slower all day basis. That should be sufficient airflow.

 

[Guest]

True lazyman the co2 level in the natural occur air is "low" aprox 400 ppm. The difference is that in nature the plant have virtually unlimited availability of this 400 ppm due to the openness of nature. There are no barriers, no walls, no poly. There are not a confined space accumulating "stale" air in nature, like in some indoor grows.

Plants need little co2 to survive, this may be very true. However in order to thrive, this is a different case imo. Nowhere in nature is the atmospheric co2 near 1500 ppm, though a dialed in strain will use this higher co2 concentration to it advantage and outpreform it counterpart in an environment without this increased enriched co2.

co2 deprivation aka lack of fresh air. I put a plant in a box with no intake and see how long it go? Then that would just be murder, are you serious?

 

[*mistress*]

plants need & expect @ least 20% oxygen in the environment. they need it just like they need c02...

exchange of gases (oxygen, c02, water vapor) is generally termed respiration. this occurs 24/7...

transpiration primarily only during photosynthesis (lights on)... this is plants pushing out water vapor into atmosphere. occurs when stomata open.

so... when lights are on, plants are uptaking c02, expelling oxygen. they are also expelling water vapor. this is generally referred to as rh by hobbists, but is vapor pressure deficit... they are inverse of ea other. they uptake water from roots & push it out into environment.

air (gas) exchange should occur 24/7, as plant is interacting w/ environment 24/7.

plants regulate use of oxygen by the surrounding temps... they have issues when >than 20% atmosphere is oxygen. leaves have easier acces to oxygen than roots... they require air circulation @ night because they dont produce it in dark.

maybe keep the fans going 24/7...

hope this helps. enjoy your garden!

 

[weimer222]

I'd rather not have the fan running 24/7 for stealth reasons. I am trying to find the balance between replenishing the air in order to bring in more c02, remove moisture from transpiration, etc. and a somewhat quiet grow environment. Although I agree a 24/7 ventilation practice is ideal, I can't imagine it is necessary for a successful grow.

I was doing a search and found an unverified quote that the American Society of Heating, Refrigerating, and Air Condition Engineers recommends a minimum air exchange rate of .35 air exchanges per hour. Now that is for a human environment. In another cannabis forum I heard the recommended number being 30 exchanges per hour. That seems excessive.

I was thinking 1-2 exchanges per hour would be sufficient. Anyone else have good reasoning to the contrary?

 

[whodair]

environments vary greatly. you're gonna have to try and experiment. see how healthy the plants look with/without air exchange.

my friend ran his fan/scrubber for 12hrs the lights were on. i asked him to try 24hr fan scrubber. the improvement was noticeable. almost startling.

 

[*mistress*]

I'd rather not have the fan running 24/7 for stealth reasons. I am trying to find the balance between replenishing the air in order to bring in more c02, remove moisture from transpiration, etc. and a somewhat quiet grow environment. Although I agree a 24/7 ventilation practice is ideal, I can't imagine it is necessary for a successful grow.

I was doing a search and found an unverified quote that the American Society of Heating, Refrigerating, and Air Condition Engineers recommends a minimum air exchange rate of .35 air exchanges per hour. Now that is for a human environment. In another cannabis forum I heard the recommended number being 30 exchanges per hour. That seems excessive.

I was thinking 1-2 exchanges per hour would be sufficient. Anyone else have good reasoning to the contrary?

*photosynthesis*
occurs in
only those cells of green plants & a few bacteria which contain chlorophyll
raw materials
water & carbon dioxide
time of occurrence
only when light shines on the cell
energy
stored by process
matter
results in an increase in the weight of the plant
products
oxygen & organic materials

*respiration*
occurs in
all living cells
raw materials
oxygen & organic substances, ieg, glucose
time of occurrence
continuously, night & day
energy
released by the process
matter
results in decrease of weight of plant or animal
products
carbon dioxide & water

respiration occurs 24/7...

the hvac stats may be good for the inverse of that forumla, as they are generally trying to evacuate c02 & other gases from areas of human activity... though hvac standards to be familar w/...

there are threads on icmag about sound insulation. they/the garden itself can be sealed & acoustically muffled.

the requirement is not that much though, just keep gentle breezes going from bottom--up, & laterally across canopy... 'whisper' type fans work well... so do cheapo clip fans...

enjoy your garden!

 

[Huntington]

Although I agree a 24/7 ventilation practice is ideal, I can't imagine it is necessary for a successful grow.

24/7 ventilation is not necessary for a successful grow in an open system. Only thing you need to control lights off are humidity (mainly IMO) then temps. Lights on you want to exchange the air as often and much as possible making sure temps stay in range...primarily. The faster the air exchange the better you will control humidity...typically.

 

[*mistress*]

24/7 ventilation is not necessary for a successful grow in an open system.

...Only thing you need to control lights off are humidity...

The faster the air exchange the better you will control humidity...

...

enjoy your garden!

 

[Huntington]

Just to be clear, since quoting can take things out of context, with lights off and no air exchange humidity can easily be controlled with a dehumidifier if properly sized. Temps are super easy to control lights off when there's no air exchange. With lights on in an open system a dehumidifier is basically useless and humidity is more dependent on air exchange...typically. The slower the air exchange the greater the RH cause of plant respiration but then you have to take into consideration the ambient humidity of the incoming air. Running an open system in Biloxi is for sure gonna be different than running the same setup in Eastern Oregon. Another factor in RH, especially lights off, is when temps drop cause RH goes up with the exact same air. Colder air can not hold as much moisture. Keeping things on the warmer side can help.

 

[*mistress*]

Just to be clear, since quoting can take things out of context, with lights off and no air exchange humidity can easily be controlled with a dehumidifier if properly sized. Temps are super easy to control lights off when there's no air exchange. With lights on in an open system a dehumidifier is basically useless and humidity is more dependent on air exchange...typically. The slower the air exchange the greater the RH cause of plant respiration but then you have to take into consideration the ambient humidity of the incoming air. Running an open system in Biloxi is for sure gonna be different than running the same setup in Eastern Oregon. Another factor in RH, especially lights off, is when temps drop cause RH goes up with the exact same air. Colder air can not hold as much moisture. Keeping things on the warmer side can help.

a dehumidifier is a fan that draws in air & squeezes out water...
a different way of saying air circulation is required @ night, or more accurately, 24/7...

not every gardener has sealed room w/ coins for dehumidifier... alternative is continuous, or steady air flow across canopy.

it is transpiration that releases water into atmosphere, not respiration.

if temps are raised @ night (can be ), then most definitely need fans/ac/dehumidifer on, as there is faster condensation in higher temps w/out a fan extracting moisture held in it.

actually, warmer temps excite water molecules more than cooler temps...

Keep in mind though the reality of the situation: If air temperature increases, water vapor temperatures does too. This results in a higher saturation (or maximum) vapor pressure. If there isn't enough vapor in the air to meet the maximum, evaporation occurs as the atmosphere strives to reach balance. If air temperature decreases, the saturation vapor pressure decreases as well. If there is more vapor present than this maximum value can support, the condensation occurs as the atmosphere strives to reach balance.

enjoy your garden!

 

[bostrom155]

Nice write up Mistress

 

[Huntington]

a dehumidifier is a fan that draws in air & squeezes out water...
a different way of saying air circulation is required @ night, or more accurately, 24/7...

not every gardener has sealed room w/ coins for dehumidifier... alternative is continuous, or steady air flow across canopy.

it is transpiration that releases water into atmosphere, not respiration.

if temps are raised @ night (can be ), then most definitely need fans/ac/dehumidifer on, as there is faster condensation in higher temps w/out a fan extracting moisture held in it.

actually, warmer temps excite water molecules more than cooler temps...

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.

If temps are raised you only need an ac if they go over a certain threshold and not just because you've raised temps. Same goes for a dehuey...you don't need one just because temps are raised. Temps and humidity can be manipulated within a certain range before requiring equipment such as an ac or dehuey.

There's more condensation at lower temperatures not higher temperatures because of the colder air's inability to hold moisture. In this instance water vapor returns to a liquid state.

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...

Relative humidity depends on two factors: the amount of moisture available, and on the temperature.So you can have a change in relative humidity in one of two ways: 1) Change the amount of water vapor available; if there is liquid water present, for instance, a lake, you can have an increase in relative humidity by evaporation from the surface of the lake. This is pretty obvious. You’re adding water vapor, so the humidity increases.
2) The other way is to change the temperature of the air, while holding the water vapor constant. Even though there is no water source, and no water vapor is added, a lowering of air temperature results in a rise of relative humidity. This is automatic. The amount of water vapor that could be present at saturation is less at the lower temperature, so the existing amount of water vapor represents a higher percentage of the saturation level of the air. Similarly, a rise in temperature results in a decrease in relative humidity, even though no water vapor has been taken away.

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.

So yes humidity can be controlled by raising the temperature. It can also be controlled by canopy pruning/trimming.