Tutorial Ventilation 101

[Dignan]

Red-

I haven't grown indoors for a few years and my previous grow was of "brute force" design, as you like to say. I had the luxury of doing that in the other garden because it was in a basement with no security/stealth concerns.

Well, I'm building a new closet and a new mother/veg cab and this thread has been a godsend man. Thank you so much.

I *think* everything is making sense and have come up with this rudimentary drawing of my plans. Would you mind glancing it over and just let me know if there are any glaring errors or miscalculations?

The flowering closet will be 6' tall, 4' wide, 20" deep. The upper shelf is how the closet comes from the factory; removing/moving it would require modifications. Not counting this upper shelf, the actual grow area is about 55 CF.

I have a nice piece of lantern glass that I plan to make into a cooltube, but I would be willing to consider partitioning off the 400W HPS with glass the way you do in your cabinet, but I just can't think of a good work-around for the fact that my scrubber (which is 2' long... big DIY one...) will be in the upper chamber and I'd have to somehow run ducting THRU the section housing the HID.



Thanks and

 

[stellarcollison]

A common inline blower used here is a Vortex that will produce 0.75 to 1.0 inwc.

I'm just not understanding the 0.75 to 1.0 inwc. and for whatever reason, I'm not understanding how to match fans and filters to achieve the desired CFM.
Sorry to be a bit redundant; sometimes it takes me a bit to understand things...

I was looking at the Can 9000 on Can's website, and it says that a 4" axial computer fan will have an exhaust CFM of 47. Correct me if I'm wrong, but wouldn't that work for my purpose? I mean, it seems logical.... I'm trying to achieve 40, and 47 would result in 4.2MpAC.

Really don't know why I'm having such a hard time wrapping my head around this....

And for the hood, it would seem the more air that flow through it, the better.

So, here's what I'm thinking... I should go ahead with the S&P TD Series Inline Fan.($150) for 8 inch round duct - 538/476 cfm (high/low) for the hood, and if the 4" fan wont work, that I should get the S&P TD 100x Series Inline Fan ($77) for 4 inch round duct - 135/100 cfm (high/low) to exhaust the room.

Here's how I'm thinking I should exhaust the room and hood:

 

[stellarcollison]

Ok, I found how to calculate the SP created by a filter.

Take the max CFM of the fan at .0 sp, then divide by the max recirculating CFM of the filter, ex:

S&P TD-100x, set to low, has a max CFM of 100 @ .0 sp.
Add a Can Filter 33; which, has a max recirculating CFM of 400.
100/400 = .25
The S&P 100x operating @ .25 sp (.25 sp is the max for this fan) would be reduced from 100 CFM to 48 CFM.
So the fan ?would? exhaust at 48 CFM

That sound about right?

 

[gdbud]

I'm just not understanding the 0.75 to 1.0 inwc. and for whatever reason,

the pressure created by a fan is measured in inwc (inches of water column) which means if you take a fan add a length of duct to it drill a hole into the duct and fit a tube to the duct then add water to the duct then turn the fan on you will see the water level in the tube rise 1 inch that would be 1 inwc.

 

[stellarcollison]

Ya, gbud... I worded that wrong. I know what inwc means, I didn't know how he was getting those numbers. I figured it out though.

Thanks anyways man.

 

[Dignan]

One more question:

Bigger ducting is better-- get it; makes sense.

What's the best option if a person uses, say, 8" ducting (I don't plan on it, but hypothetically) but the run of ducting has portions that reduce to smaller diameters?

For instance, I can make my passive intake for my cooltube any size I want, no problem there. But then my cooltube itself (the glass portion) reduces down to about 4.5" diameter, and the exhaust fan (a 4.5" 110 CFM Dayton axial) reduces down to about 5".

Does it make the most sense to just keep the ducting itself 5", or is there an advantage to increasing to 8" the portions that are able to be increased?

Peace-

Dig

 

[ITryToGrow]

Does it make the most sense to just keep the ducting itself 5", or is there an advantage to increasing to 8" the portions that are able to be increased?

You won't get more CFM. It's like a chain is never stronger than its weakest link type of thing.

However, the larger duct helps with silencing the sound of air rushing thru the ducting.

Hmm, does that make sense or should I word it differently?

 

[Dignan]

You won't get more CFM. It's like a chain is never stronger than its weakest link type of thing.

However, the larger duct helps with silencing the sound of air rushing thru the ducting.

Hmm, does that make sense or should I word it differently?

Thanks. Makes fine sense the way you worded it.

I'm not looking for more CFMs exactly; what I suspect is that air moving through a smaller duct, then expanding into a larger chamber, then constricting back down to a smaller duct... seems like when it expanded in the larger chamber the static pressure would increase due to turbulence. No?

 

[sneakinman13]

hey there. i have a few questions for you guys...

my floors in my basement are rising. i put plastic on the floor. and the basement is sealed.....

for vent i have.....

8 inch active intake>ducting/hoods>10 inch exaust

^ thats just to cool my lights.
i also have a

6 inch active intake for fresh air. with a 10 inch fan connected to my can filter.

now from everything i just read. it seems as if i dont need the active intakes???? if this is tru. how do i fix this problem? the intake isnt 2 times the exaust. so do i take out my intake fans and just cut the squares to my exaust size or double my exaust size?

and if i do that do i still run ducting into the room or do i just leave those holes.....

and if this is tru. would this mean i dont neen any intake fans??
im a bit lost and trying to grap here....

the basement is 24 feet long by 14 feet wide. i have 8 k in lighting.

and when i go down to the basement it looks like the room is sucking my panda film in towards the basement?

if someone could walk me threw this as easily as possible i would really be gratefull. thanks

 

[ITryToGrow]

I'm not looking for more CFMs exactly; what I suspect is that air moving through a smaller duct, then expanding into a larger chamber, then constricting back down to a smaller duct... seems like when it expanded in the larger chamber the static pressure would increase due to turbulence. No?

Take a look at post #11 (by Red), explains some of the intake issues and static pressure.

What you can do is to put a fine mesh net where the ducting goes from large to small.

Like this:

It's used in the auto-industry. It helps "straighten" out the air-flow. This is to make sure that the air-flow (air masse) sensor get's an honest reading since turbulent air gives false readings.

 

[hoosierdaddy]

The turbulence are less restrictive than the walls of a smaller duct would be.
No matter what...the smallest orifice in the train, no matter where it is in the path, is the restricting factor and dictates the volume of air.
The screen will indeed restrict turbulence, but at the expense of volume.

 

[ITryToGrow]

The screen will indeed restrict turbulence, but at the expense of volume.

True dat!

It's like you can't keep the cookie and eat it too...

 

[FlyinHawaiian]

FlyinHawaiin, the "area" is the actual area of the duct itself, as in 6" duct has 28.3 inches of open area. The "intake area" is a figure of how big the exhaust should be when using that size duct. What Red has done is double the area of the passive intake of what the area of the exhaust duct is.
And I think you will find that a 2" pipe indeed is 2" inside diameter.
According to Reds chart you need 18 2" pvc pipes to make the intake, however that is a complete double of the exit duct, as explained above. It is a good rule of thumb for growers to size the intake to double the exhaust...however, if things are good in the room one could use an intake figure that is 10-20% (as opposed to 100% as in the chart) larger than the exhaust and will be fine.

thanks lol I feel kinda dumb now, I wasn't thinking the intake area was well the intake area....

I have another question now, does anyone know the sq " intake area of an 8x8 darkroom louver? I think I remember reading these vents block 1/2 the air flow? is that true?, so that equals a 4''square hole, so 16sq'' of intake a good guess? thats not much

 

[sneakinman13]

my question is on page 22. please help!

 

[guest 77721]

Hey sneakinman,

Are your temps ok with your system right now?

The reason the panda film is sucking inwards is from negative static pressure. You want to have a bit of negative pressure inside the room so the outside air enters the room. Positive pressure will push stinky air out of the room through cracks so your grow will smell and give you away. There's lot's of discussions on where the fans should go on the intake or exhaust side depending on how you want to control leakages.

With any ventilation system, you will have slight positive or negative pressurization. Do you have a real problem or is it that your Panda film needs more support?

I can't tell by your description where your intake air is coming from. I would recommend taking all of your air from outside using two 8" ducts for passive intakes.

I would recommend using a 10" or 12" intake duct with the lights cooling duct connected to it and an active intake fan connected to it to provide fresh air to the room. This would give you an active/passive system.


Hey guys, you're right on about the use of screens and grills to reduce turbulance. Take a look in your homes and offices wherever there is duct exhaust it will be covered by a grill. This is to straighten the airflow to reduce the vent noise.

There is a tradeoff between airflow and noise as the grill or screen will present a small pressure drop. On an exhaust vent, the area is increased to compensate because flow is always sqrt(pressure)*area.

hey there. i have a few questions for you guys...

my floors in my basement are rising. i put plastic on the floor. and the basement is sealed.....

for vent i have.....

8 inch active intake>ducting/hoods>10 inch exaust

^ thats just to cool my lights.
i also have a

6 inch active intake for fresh air. with a 10 inch fan connected to my can filter.

now from everything i just read. it seems as if i dont need the active intakes???? if this is tru. how do i fix this problem? the intake isnt 2 times the exaust. so do i take out my intake fans and just cut the squares to my exaust size or double my exaust size?

and if i do that do i still run ducting into the room or do i just leave those holes.....

and if this is tru. would this mean i dont neen any intake fans??
im a bit lost and trying to grap here....

the basement is 24 feet long by 14 feet wide. i have 8 k in lighting.

and when i go down to the basement it looks like the room is sucking my panda film in towards the basement?

if someone could walk me threw this as easily as possible i would really be gratefull. thanks

 

[booghy]

Hoping for anyone that will help. My cab's dimensions are 24" wide by 20" deep by 5-6' tall. The plan is to run 2 S&P TD-100x fans, one directly for cooling the light and one to run with a 4" Phresh filter. Do you think the fans will be adequate for my cooling and scrubbing purposes?? Or should I step up the fans to a 6" model.

 

[Dignan]

Red- I noticed in your cabinet thread that the intake and the exhaust for the light cooling stage are right next to each other. In designing my new cabinet (still just on paper... I posted the plans for your review a page or two back) I have been trying to keep my intakes and exhausts on opposite sides of the cabinet so that the intake isn't taking in the hot air that's being exhausted.

Not so much of a concern, in your experience?

 

[stellarcollison]

you need to get out the air flow curves.

How did you make those charts?

 

[grasspass]

fan noise ignored

fan noise ignored

I know some one with a small grow box that is trying to keep it secret from his teen kid. The box sounds like a computer fan. The kid can stand next to the box and not notice the fan. Maybe because the house has , heating fan , video game fan , computer fans , people get conditioned to ignore fans. Smell is a different story. This guy took plants out of the scrubber equipped box to water them and the kid noticed pot smell on the other side of the house. Smell will not be ignored.

 

[sneakinman13]

so you say i should use 2, 8'' inch passive intake. meaing ducting with no fans? from the same area i get my fresh air.

right now i have my lights set like this. 8 inch max fan intake 10 inch can fan exaust. should i flip that???

also the panda film door i made. sucks inward towards grow. but the floor in the grow room itself rise's ...

my temps are ok i belive. its a pretty big area so thats not a huge problem. least for winter

but im worried about the floors rising and smell leaking... right now in veg it doesnt smell until i open the panda door. so i think its doing the right thing...

idk let me kno if you need any more info. im trying to fix this asap..
thanks for your time

Hey sneakinman,

Are your temps ok with your system right now?

The reason the panda film is sucking inwards is from negative static pressure. You want to have a bit of negative pressure inside the room so the outside air enters the room. Positive pressure will push stinky air out of the room through cracks so your grow will smell and give you away. There's lot's of discussions on where the fans should go on the intake or exhaust side depending on how you want to control leakages.

With any ventilation system, you will have slight positive or negative pressurization. Do you have a real problem or is it that your Panda film needs more support?

I can't tell by your description where your intake air is coming from. I would recommend taking all of your air from outside using two 8" ducts for passive intakes.

I would recommend using a 10" or 12" intake duct with the lights cooling duct connected to it and an active intake fan connected to it to provide fresh air to the room. This would give you an active/passive system.


Hey guys, you're right on about the use of screens and grills to reduce turbulance. Take a look in your homes and offices wherever there is duct exhaust it will be covered by a grill. This is to straighten the airflow to reduce the vent noise.

There is a tradeoff between airflow and noise as the grill or screen will present a small pressure drop. On an exhaust vent, the area is increased to compensate because flow is always sqrt(pressure)*area.