I have a tent i built and that is H5.1'xW3.6'x1.75 for a total of 32.1 cubic feet. My exhaust is a S&P TD-100 inline, rated 101 CFM, and is hung in the top back right corner of tent, with 4" flexible aluminum ducting exiting the tent. My question is, how do I calculate passive intake sizes and positions? Should I have any negative pressure? should the exhaust be all the way at the top of the tent? Thanks for any replies, in advance.
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question about passive intake sizing
- Thread starter potc
- Start date
Palindrome
King of Schwag
Double the size of your active out take
So if your running a 100 mm (4") fan, you should minimum have 2x 100 mm in takes.
Hot air out the top of your tent, and cold air in is IMO not that important. It will pretty much sink to the floor, but it can be used to cool the canopy if needed.
So if your running a 100 mm (4") fan, you should minimum have 2x 100 mm in takes.
Hot air out the top of your tent, and cold air in is IMO not that important. It will pretty much sink to the floor, but it can be used to cool the canopy if needed.
Palindrome
King of Schwag
The placement of cold air intake, you will need a in take!
Could not find a edit post botton.
Could not find a edit post botton.
Mrkline006
Member
So for my room. 12x9x [ceiling8ft] states i should have 173cfm fan running outtake on it? Seems really low? Also. I have a 8inch fan and a 6inch fan does it matter which i use? 6inch runs @440b 8 @ 740. I dont want over kill so any help wohld be great.... Also, its in a garage do i really want the room intaking stale garage air and hot/hunid air in summer and beyond freezing air in winter?help!!
Palindrome
King of Schwag
I always oversize my exhaust, so I can turn the fan up and down with a dimmer, fan controller or what ever it's called. Just make sure it's for ventilation, as most dimmers cut on the front of the AC current. A Fan dimmer, cut's on the back end of the AC current. So it have power to start the fan, even on a low setting.
This way I can adjust my fan, according to the temps outside.
You can hook up a temp controller to a second exhaust fan, that kicks in if your room temp spikes.
Im not sure, but I think your 173cfm. Is what you minimum need to keep your room under negative pressure, but I am not sure.
This way I can adjust my fan, according to the temps outside.
You can hook up a temp controller to a second exhaust fan, that kicks in if your room temp spikes.
Im not sure, but I think your 173cfm. Is what you minimum need to keep your room under negative pressure, but I am not sure.
starke
Well-known member
About one third of the way down page one is a section titled: "Intake Sizing".
https://www.icmag.com/ic/showthread.php?t=112862
https://www.icmag.com/ic/showthread.php?t=112862
Mrkline006
Member
THanks mate.
Mrkline006
Member
That post was.. wow, way out of my league lol.. I know intake needs to be 2x the exhaust.. so 6inch exaust, 12inch of intake.. now for the exchange.. I have a room thats 12x8x9... 864... 865/5 (5min change is the rate of change if i took what i read correctly) makes it just about 173. So do i only need a fan pulling out about 173? or is that JUST to exchange the air? the whole "plants are stressed by too much airflow at 3 ACpM.
The plants only need 5 Minutes per Air Changes (MpAC). That's 0.2 Air Changes per Minute (ACpM)." is what confused me.
you want negative pressure in the tent if you are concerned about smells escaping. exhaust out through a scrubber filter. keep the intake passive. that way any air that leaves the tent is scrubbed for smell. use a strong exhaust that ensures slightly1 more air is being sucked out than can enter through the passive intake hole.
on the other hand, use passive exhaust and put your fans and scrubber on the intake if you do not care about smells and you need to keep pollen from entering the tent use positive pressure in the tent to ensure no outside air is pushed into the tent without being scrubbed.
u can step it up a notch and put scrubbers on the intake and exhaust and adjust power to either exhaust or intake to regulate tent negative/positive pressure.
1 example is if you are breeding and have males in a tent that are producing pollen. you want to protect your other plants from the pollen by using negative and positive pressure differences and scrubbers.
on the other hand, use passive exhaust and put your fans and scrubber on the intake if you do not care about smells and you need to keep pollen from entering the tent use positive pressure in the tent to ensure no outside air is pushed into the tent without being scrubbed.
u can step it up a notch and put scrubbers on the intake and exhaust and adjust power to either exhaust or intake to regulate tent negative/positive pressure.
1 example is if you are breeding and have males in a tent that are producing pollen. you want to protect your other plants from the pollen by using negative and positive pressure differences and scrubbers.
You can see passive intake as a 4" vent opening on the right in the back of the tent. The exhaust is pulled through the scrubber on the left using 2 6" inline can fans. This scrubs all smell from leaving the tent. The difference in outlet/inlet size creates negative pressure which ensures no smell escapes because any air leaving the tent is scrubbed.
Mrkline006
Member
I have a room being built if that makes a difference? as of smell? not TOO concerned about it its in a garage and im on my own land.
all the same concepts will apply. you may have a few leaks here and there depending on construction it may not be as air tight as a zipped up grow tent. my suggestion would be to scrub the intake and the exhaust if you can afford it. use variable power controllers on both intake and exhaust so you can dial them in independently which will allow you to manage air pressure inside. for example you can run exhaust at full power and intake at 75% power to create a slight negative pressure. if you vent your lights outside the space remember that will contribute.
Mrkline006
Member
Do I need a powered intake? or would a passive system suffice? as for exhaust will just be vented outside my place, which is not much worry i live behind a forrest lol.. i may look into filter for intake whether its a passive one or not. even some type of hepa filter over a passive opening be okay? or need something better?
You may be concerned about airborne pathogens. You can infect your garden with bud rot mold or powdery mildew by sucking in unfiltered air from outside. Certain times of year the spore count will be higher than other times of year. Another factor is male pollen from a neighboring farm. Either way it is safest to scrub the intake. When you place a scrubber on the intake, you will reduce the airflow, which will then require a fan to keep things moving at a good rate. In theory if your exhaust was strong enough, you could pull enough air through a scrubber passively. You will have to show us what scrubber you want to use and we can tell you what the requirements might be to have it work properly. Some scrubbers require quite a bit of pull to keep things moving. Others require less depending on size. You could put a very small scrubber on the intake or even some time of HVAC air filter. Choices are endless for you. If you are setting this up for the long run... I would absolutely filter the intake for pollen,spores, allergens, etc. This is the best way to ensure clean air inside your garden which is key for long term success.
If your #1 concern is keeping pathogens like spores out of your garden, remember that you will want positive air pressure. This means you are trying to inflate your grow space like a balloon with more air going in than can escape out. Do this by pulling harder through your intake and letting the exhaust remain passive or under powered compared to the intake. If you have positive air pressure in the grow, the random spores from outside will not be able to freely and passively float inside to your grow from the outside because all air from inside your grow will be flowing out of any cracks in the construction. This may cause an odor issue if air escapes through cracks rather than through your exhaust scrubber but if you aren't worried about the smell it's not a big deal.
Mrkline006
Member
I currently have 1 8inch fan (740CFM), 2 6inch (440CFM) and a small 6 inch duct fan (200 CFM or so) would this be enough for a 12x9 room?> as for scrubber, i would just go look at good HVAC filters from just a hardware store, should be good? I dont have a make or model on hand to think of but i wouldnt just get like a wool sock lol
We need to know how tall the room is as well. Give us a #x#x# for width x depth x height. Your fan is rated 740 Cubic Feet per Minute. Your room is 12 x 9 I assume feet and that would make 108 square feet. If your room is 10 feet tall that makes 1080 Cubic Feet. Your 740CFM fan would evacuate the entire room in just over a minute. Any filters or scrubbers could reduce this volume by slowing down the airflow through the filter. If your CFM is equal going in and out - you will have neutral air pressure in your room. If your CFM going out is more than in, you will have negative pressure. So on and so on.
Hardware store HVAC filters will work great. You can get all types of quality filters and build a custom frame or box to mount it. Make sure you seal the joints and cracks to ensure no leaks around the construction.
Hardware store HVAC filters will work great. You can get all types of quality filters and build a custom frame or box to mount it. Make sure you seal the joints and cracks to ensure no leaks around the construction.
Mrkline006
Member
Thought I had the entire dimension in my first comment sorry... its 12x9x 8 tall.. i could always add the 200 CFM to in 740 if extra is needed. or get another fan.
You did list the height actually sorry about that so yeah do the math on 12x9x8 is 864 cubic feet. Depending on your setup, you do not need to replace the air inside your room every minute. If you put a scrubber on your 740CFM fan, you may only get 600CFM out of the exhaust. That would replace the air in your space every 90 seconds or so. If you need to exhaust HEAT from your grow space, you may want to replace the air every minute or even twice or more times per minute. You'll have to see what your needs will be. On the other hand, if you supplement your grow space with CO2 then you will not want to exhaust the CO2 out before it has had an effect on your plants. If you use CO2, you may want a controller to maintain ppm (800-1500ppm CO2) for example and then set to exhaust the air when humidity builds up or on a timer to refresh the grow space air on a fixed schedule.
You should default to more airflow when making a decision on HVAC. Always overbuild. You can put the fans on a variable controller to dial the power back if you have too much air exchange. I would go ahead and use 2 separate 740CFM exhaust fans or upgrade to 1 larger CFM fan. Now that you can calculate your cubic feet in your grow space, you can calculate your air exchange. Question is how quickly do you want to exchange the air? As said above, at least once a minute if not twice or 4 times a minute should be enough as long as you are not struggling with heat issues or humidity issues.
You should default to more airflow when making a decision on HVAC. Always overbuild. You can put the fans on a variable controller to dial the power back if you have too much air exchange. I would go ahead and use 2 separate 740CFM exhaust fans or upgrade to 1 larger CFM fan. Now that you can calculate your cubic feet in your grow space, you can calculate your air exchange. Question is how quickly do you want to exchange the air? As said above, at least once a minute if not twice or 4 times a minute should be enough as long as you are not struggling with heat issues or humidity issues.
