question about passive intake sizing - Growroom Designs & Equipment - International Cannagraphic Magazine Forums

potc · 01-25-2018, 09:33 AM

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.

Palindrome · 01-25-2018, 05:07 PM

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.

Palindrome · 01-25-2018, 05:09 PM

The placement of cold air intake, you will need a in take!

Could not find a edit post botton.

Mrkline006 · 01-30-2018, 03:00 PM

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 · 01-30-2018, 03:29 PM

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.

starke · 01-30-2018, 05:11 PM

About one third of the way down page one is a section titled: "Intake Sizing".

https://www.icmag.com/ic/showthread.php?t=112862

Mrkline006 · 01-31-2018, 04:50 PM

Quote:

Originally Posted by starke

About one third of the way down page one is a section titled: "Intake Sizing".

https://www.icmag.com/ic/showthread.php?t=112862

THanks mate.

Mrkline006 · 01-31-2018, 05:29 PM

Quote:

Originally Posted by starke

About one third of the way down page one is a section titled: "Intake Sizing".

https://www.icmag.com/ic/showthread.php?t=112862

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.

2011rex87 · 01-31-2018, 05:51 PM

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.

2011rex87 · 01-31-2018, 06:26 PM

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.

01-25-2018, 09:33 AM	#1
potc Newbie Join Date: Jan 2018 Posts: 1	question about passive intake sizing 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.
	Quote

01-30-2018, 05:11 PM	#6
starke Member Join Date: Aug 2015 Location: Between Key West and Perdido Key Posts: 669	About one third of the way down page one is a section titled: "Intake Sizing". https://www.icmag.com/ic/showthread.php?t=112862 __________________ “We've all heard that a million monkeys banging on a million typewriters will eventually reproduce the entire works of Shakespeare. Now, thanks to the Internet, we know this is not true.” ~Robert Wilensky "Spread the knowledge, be humble if you don't know, be helpful if you do, if you are wrong, admit it quickly and emphatically, and overgrow the world." (SuperWeed 2017) "Always keep in mind that when the hearse pulls up to pick you up, there is no trunk or luggage rack on that bitch." (Author unknown) Current Grow: https://www.icmag.com/ic/showthread....343153&page=20 Page 20 forward
	Quote

01-31-2018, 05:51 PM	#9
2011rex87 Banned Join Date: Jan 2018 Posts: 93	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.
	Quote 1 members found this post helpful.

01-25-2018, 05:07 PM	#2
Palindrome Member Join Date: Jan 2018 Location: Republic State of Banana Posts: 193	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.
	Quote

01-25-2018, 05:09 PM	#3
Palindrome Member Join Date: Jan 2018 Location: Republic State of Banana Posts: 193	The placement of cold air intake, you will need a in take! Could not find a edit post botton.
	Quote

01-30-2018, 03:00 PM	#4
Mrkline006 Member Join Date: Oct 2017 Posts: 113	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!!
	Quote

01-30-2018, 03:29 PM	#5
Palindrome Member Join Date: Jan 2018 Location: Republic State of Banana Posts: 193	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.
	Quote

01-31-2018, 06:26 PM	#10
2011rex87 Banned Join Date: Jan 2018 Posts: 93	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.
	Quote