Tutorial Ventilation 101

[guest 77721]

A bare 400W bulb in a cabinet will need about 100CFM to cool to 15* of ambient producing 6 ACpM.

The advantage to putting the bulb in the cooltube is to trap most of the heat there and get it the hell out of the box.

100CFM in a cooltube will produce 15*+ exhaust air and maybe a 1-2*F rise in the growbox.

Why subject your plants to 5 ACFM when only 1/5 or less is needed for real ventilation.

BTW, excessive airflow causes stress on the plants by drying them out and causing them to suck up a great deal of water to compensate. If you're running a hydro system then this means more top ups and res changeouts. For soil grower's you'll need to run weaker nutrients and water more often.
.

 

[SmokinSHO]

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[guest 77721]

Wow, that's some major improvements.

I think you can run the hood with 60-40 CFM for 20-30*F exhaust temps with an axial fan. If you can keep the ducts straight and not too long an axial fan would work for you and you could swap out the dayton.

It might be worthwhile to swap the dayton and thermaltake fan around for a trial. I wouldn't be suprised if you end up running two axial fans.

You've really learned a lot from me if you're able to calculate your air flow using exit temps and measuring low flows with trash bags.

It's my experience that 1/2" to 1" of carbon is the right amount for an axial fan. I'd leave it at 1" cause it will last a lot longer.

 

[FlyinHawaiian]

Awesome thread I learned so much! hey Red how effective is your vent gaurd carbon filter? how thick can you fit the carbon in there? I see yours is 14''x6'' they also make a 14''x8'' and even a 30''x6 dual filter Im thinking about using the 14x8. http://www.kevek.ca/products.htm

I think I just might copy your cab design I've gone back and forth on my design so many times but their all way more expensive and not as efficent as your design.

My cab is 20''d,29''w,45''h, plan is 250 hps or cmh air cooled chamber just like your cab but with two 120mm pc fans side by side(not stacked) exhausting the light instead of one.

Do you loose much light reflectifity/intensity without a hood? My cab is the same bright white like yours hopefully thats reflective enough.

 

[guest 77721]

Hey FlyinHawaiian,

I'd say my vent guard filter is only 75% effective with about 3/8" carbon and that's filled right up. I did two grows with it (red's back thread) and it worked well enough when I had a bunch of lollipop sized plants but with two big plants would overpower it in the last two weeks.

On my next grow, I am going to rebuild my two tub filter design. I've found out that with a computer fan, a filter needs to have between 1/2" and 1" of carbon to be effective. This is a proven design from my R2D2 rubbermaid tubs.

Speaking of the R2D2 design, I was able to cool 252W of CFL's using a single 38 CFM fan. You'll be fine using two 120 mm fans.








Here's my air filter design using two Sterilite containers. The small one must fit inside the large one.

The bottom is cut out of the small tub, I left a small rib in the center to support the screening.
Glue the window screen in place with the epoxy.

The lid of the large box is cut so that the small box with fit into it.

Intake holes are cut into the large box and the dryer adapters are fitted onto it. You can just duct tape it to the side if you don't have the adapters. This is probably the first time that duct tape is actually used for it's intended purpose. The flap is removed from the dryer adapter and I use a hack saw to trim off the pipe on one side.

A computer fan and a dryer hose adapter is fitted onto the lid of the small box.

When the filter is all assembled, I take silicone caulking and seal up crack where the small box goes into the large box lid.

My setup uses 1/2 lb of activated charcoal for a filter depth of 1" that I buy at the pet store. The 1" layer is good for the whole grow.

 

[BENJI]

BTW, excessive airflow causes stress on the plants by drying them out and causing them to suck up a great deal of water to compensate. If you're running a hydro system then this means more top ups and res changeouts. For soil grower's you'll need to run weaker nutrients and water more often.
.

Damn it i wish i would of found this thread earlier just finished building my micro cab with 2 130w cfls i used 2 12cm computer fans 1 for the intake and one for exhaust and after killing 4 very rare seedlings i decided to read up about ventilation your quote is exactly what happened to me so i have decided to remove the intake fan and run just the exhaust ill report back in a week or 2 and let u know how i went...

redgreenry you are an absolute lifesaver i love this thread one of the most informative threads here on IC and i thank you for all your hard work..!!!

Ps This thread would make a great sticky..!!

 

[FlyinHawaiian]

thanks red, ill be making somthing similar to that sterlite container carbon filter.

I have another question tho if someone could confirm this, for my mom/clone chamber I will have 2x 120mm pc fans exhausting with diy mini carbon scrubbers asuming the exhaust holes are 4'' each, for the intake I will need 32 2'' PVC's to get the reccomended 2:1 intake,exhaust ratio correct? thats insane if im reading this correct, I was thinking I could use 8 2''PVC's for the 2:1 ratio, LOL or am I just really high?

 

[gdbud]

FlyinHawaiian,
a 4" hole gives you 12.5 square inches opening X 2 holes = a total of 25 square inches
a 2" hole is 3.14 square inches
25 square inches/3.14 square inches = 8 holes so for the 2:1 ratio you would need 16 holes.

 

[guest 77721]

I made a chart last week and stuck this in one of the early posts.

 

[FlyinHawaiian]

thats the chart I was reading and getting confused, I don't understand the differnce between the ''Area'' and ''Intake Area'' on that chart.

also I don't think pvc elbows are exactly 2'' inside diameter even tho there labeled 2'', I have labled 1 1/2'' pvc elbows that are 1 7/8 inside diameter.

 

[TheMonarch]

This is why I would just use the number on the labels

 

[booghy]

Hey Red, great info and thread!! Can't believe I read through all of it. I'm setting up a cab dimensions are 48"W x 20 1/2"D x 72"H. I plan on using part of the space for a mother/veg chamber and the other for flowering. Flowering will probably be roughly 30"W. I will be running a 400W digital and was just curious what you would recommend for ventilation. I have one of those chinsy duct booster fans, 6" model. I was gonna buy a S & P 100x for my 4" scrubber, then attempt to use the booster fan on a dedicated duct line venting the light. Do you think that fan will be adequate or should I also order the S & P 150 for the light. Or could I get 2 of the 100x and use a reducer to cool the light???

 

[hoosierdaddy]

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.

 

[stellarcollison]

4. Two Stage Cooling/Ventilation with cooltube and scrubber



LIGHTING CFM = 3.16*(Total Watts)/deltaT
where deltaT = 20 to 30*F

VENTILATION = 1 - 5 Min/Ch (Minutes per Air Changes)

Intake Area = 2 x Exhaust Area for EACH section

Fans - Axial for Lighting maximum airflow, minimal pressure loss
Small blower, inline or axial for scrubber

Example: A 400 W HPS in a 3 x 3 x 4 cabinet with a ventilated hood needs 63 - 42 CFM of cooling for . 5 Minutes between Air Changes requires only 7 CFM through the scrubber.

Pros:
unrestricted airflow through lighting allows fan to operate at maximum rated flow
low air flow rates allow for smallest scrubber
use of less expensive fans as design is more efficient
Lighting exhaust deltaT can be 20-30*F while maintaining low grow chamber temps
Much quieter as axial fans operate at 20-30 db compared to 60-70 for centrifugal fans

I'm building 5' x 5' x 8' grow room in a spare room of my house. I'm looking at a 1000w light/hood/ballast combo. The reflector hood has 8" port for cooling the bulb (which is in a cool tube).

At first, I was going to vent the room/filter and hood via 8 or 10" Vortex. I posted my plans on another site and a guy refered me to this thread; telling me to check out, in particular, the Two-Stage vent system.

After reading this thread, I feel a bit overwhelmed and ingorant. I thought I had everything mapped out right, but now I'm reconsidering. I got my previous info from an article on bghydro.com, and through various thread and websites.

I've done the math and found what CFMs I need:
Lighting CFM = 126.4 (for a 25°F rise in ex. temp.)
Ventilation CFM = 40 @ 5 MpAC

I have a few questions:

Intake: what is meant by "EACH section?"

Axial fan to cool the light, and for a filter? Really? Like a comp. fans I saw in this thread...?

Don't get me wrong, I have a small cab I use for bloom right now. I have three small comp fans exhausting it. Seems to work. Temps in the box rarely move from 75°F. Never measured the exhaust air.​

"a 20-30*F temp rise in the exhaust temps with a 1-2 *F rise in the growbox"
How can that be calculated?

How can unristricted air-flow be achieved if ducting is required to vent hood exhaust out of the room (outside)?

Can you guys please help me out here? I asked these same questions on the other forum and got nothing... I have my shopping list made and planned to take my vacation at the end of this month to build the room. My vacation time has been approved, I've been planning this build for about a yr, the closest hydro shop is a few hours away.... planning is key here, and I'd really like to keep on track.

I'D REALLY APPRECIATE ANY HELP HERE! Thnx in advance. Later on peeps.

SC

 

[guest 77721]

Hey Stellarcollision,

There are lot's of problems with doing a one-pass filter and vent design where all the cooling air is forced through the restriction of a scrubber. I call this a brute force approach. Just try to blow through 2" of carbon, definately not free flowing by any means.

The two stage design is much more elegant as the light cooling air is unrestricted (NO SCRUBBER). You don't need a Inline or Centrifigual blower, just a simple computer type axial fan to get effective air flows.

The cooltube or vented hood keeps all the hot air inside. If you have a glass tube or a wood hood, it works even better than a metal hood because the heat is trapped inside of an insulator.

My comment about 2x Intakes for all sections is for when multiple chambers are employed. For instance having a middle chamber with a 1x vent will be a bottleneck. You have to carry the 2x intakes all the way through.



The best measuring tool is a thermometer. Take measurements of your ambient, grow box temp and exhaust temps. You can work backwards from the ventilation/temp charts to figure out effective airflow.



The lights need 125 CFM for the lights. A S+P mixed vent fan will be a good choice or a Panasonic Whisper. You can get a Can 2600 or 9000 that will work with a 6" axial or a small 4" inline blower to get 40 CFM.

This is a significant improvement over getting a 400 CFM axial blower to force the air through a 200 CFM scrubber to ATTEMPT to get 125 CFM.

The reason I say attempt is that some guys can get a fan/filter combo to work but to be able to engineer it, you need to get out the air flow curves.

I'm building 5' x 5' x 8' grow room in a spare room of my house. I'm looking at a 1000w light/hood/ballast combo. The reflector hood has 8" port for cooling the bulb (which is in a cool tube).

At first, I was going to vent the room/filter and hood via 8 or 10" Vortex. I posted my plans on another site and a guy refered me to this thread; telling me to check out, in particular, the Two-Stage vent system.

After reading this thread, I feel a bit overwhelmed and ingorant. I thought I had everything mapped out right, but now I'm reconsidering. I got my previous info from an article on bghydro.com, and through various thread and websites.

I've done the math and found what CFMs I need:
Lighting CFM = 126.4 (for a 25°F rise in ex. temp.)
Ventilation CFM = 40 @ 5 MpAC

I have a few questions:

Intake: what is meant by "EACH section?"

Axial fan to cool the light, and for a filter? Really? Like a comp. fans I saw in this thread...?

Don't get me wrong, I have a small cab I use for bloom right now. I have three small comp fans exhausting it. Seems to work. Temps in the box rarely move from 75°F. Never measured the exhaust air.
​

"a 20-30*F temp rise in the exhaust temps with a 1-2 *F rise in the growbox"
How can that be calculated?

How can unristricted air-flow be achieved if ducting is required to vent hood exhaust out of the room (outside)?

Can you guys please help me out here? I asked these same questions on the other forum and got nothing... I have my shopping list made and planned to take my vacation at the end of this month to build the room. My vacation time has been approved, I've been planning this build for about a yr, the closest hydro shop is a few hours away.... planning is key here, and I'd really like to keep on track.

I'D REALLY APPRECIATE ANY HELP HERE! Thnx in advance. Later on peeps.

SC

 

[stellarcollison]

Red,
Man, I really appreciate that. I was kind of stressin on this.

What you say about the "brute force" approach makes perfect sense, that's why I started re-thinking me vent scheme.

The hood I'll be getting is metal. I've been looking at a lot of diff styles and manufacturers, but I think this will work best for my grow. It's only a 1ft² smaller than the are to be illuminated, it's air-cooled, and the bulb is enclosed in a cool-tube as well. I could add glass, but I don't want to diminish light intensity.
It comes with 6" or 8" air ports; which, I guess would be determined by fan size...
Here's a pic:

I read the thread "Great In Line" fanes by FullMetal. Seems a lot of people really like the S&Ps. I've never heard of them. They sound pretty good....

I need 125cfm for the hood/tube. Does that account for the use of ducting? I know, I know... you've already posted the formula, and I hate to ask man, but this here:

Duct Air Flow Calculations

Here's the full formula for calculating the air velocity in a duct knowing the Velocity Pressure

velocity = 4005 * SQRT( velocity pressure) * SQRT (0.075/air density) where 0.075 is the density of air at 68*F

Let's ignore air density for now.

v = 4005 * SQRT (Vp)

To calculate the air flow in a duct, multiply velocity (ft/min) by the area of the duct (ft*ft)

v * A = 4005 * SQRT(Vp) * A

with velocity in ft/min and area in square feet

Flow = 4005 * SQRT(Vp)*A CFM (cubic feet per minute)

That's another language to me... me no comprede senior

The grow room is inside a bedroom and I'll be exhausting both the hood/tube exhaust and grow-room exhaust into the attic (since the air will be scrubbed in the grow room). I'm looking at the TD-125, but it's only 5" and I'm not sure how that would work with 8" ports. Again, I can get the hood with 6" ports, but I want to move as much air as possible through that hood. Guess it's better to have 8" duct flow into a 5" fan, than to have 5" duct flow into an 8" fan...

I want to get that bad boy as close to the canopy as possible. So, should I lower Δ to 10-15°F in the hood exhaust formula?

And just so I'm sure about the in-line fan for the Can filter, is this what you're talking about?
I'm kind of thinging not... and sort of feel dumb for asking. I think hoosier comment on
their lacy of air movement if met with even minute resistance.

I like to have things as close to spec as possible and I have no idea how to account for static pressure
created by ducting and bends. I've looked at your charts and diagrams for hours, my head hurts, LMAO!

Thanks again, I really appreciate the help.

SC

 

[Helis]

Hi RedGreenry! Just wanted to stop in and say thanks for "running" this wonderful thread (and hoosier). It's been a valuable resource while designing, though I do suffer from the "so easy that it gets complicated" trait found in people who like knowledge too much.

Anyway I have a question that I am trying to wrap my brain around. I have a cab which is 6 cu. ft. and has properly sized intake and exhaust holes cut for 2 80mm fans to be used as air movers. After my last run (too much air flow killing plants) I aim to solve a problem, and have come up with the following system:

1) Two (or one) axial fans (80mm, 120v, .25" h2o SP, ~30 CFM) will pull through 1" of carbon and be hooked up to a thermostat set to 4°-5° above ambient. My goal is to have this air extraction process happen as infrequently as possible, thus I would like to get the lights as cool as possible. In fact for one fan to run for 1 minute, it is exchanging the air almost 5 times.

2) The new lighting will be 4 x 55w PL-L bulbs (there is another option, but it is not the discussion of this thread) preferably cooltubed. My question is this if I run each 55w bulb in a separate 2" polycarbonate tube, how much airflow per bulb do you think I need to keep the room's ∆T between 1-4 °F. (Yes another one of those questions).

The formula 3.16*(Total Watts)/deltaT results in 43-173 cfm per bulb, but this applies for cooltube output temps, correct?

I have figured that if each 2 bulbs gets 30cfm (a 3" fan split to two 2" tubes) and each cool tube is 21" in length (0.038 cu ft/tube) then each bulb will get the air over it replaced 395 times a minute. What type of inside-the-cab ∆T am I going to see? Ideally I'd like 1°-2°.

If you read this, thank you! Same goes to anyone else with input

Helis

 

[guest 77721]

Hey StellarCollision,

That looks like a nice hood. It would probably be easier to connect up to a 6" outlet with a 5" to 6" reducer on the fan. The fan will work at rated flow with an increase in duct size.

The CFM calculations are for the heat extraction. On the plus side, the losses due to ducting are minimal unless you have really long runs. It's more important to install your ducting with smooth curves instead of sharp corners. Flexible ducting with all the ridges will create a loss where solid ducting won't.

Here's a link to the duct loss calculations. http://www.engineeringtoolbox.com/duct-friction-pressure-loss-d_444.html

That fan is an axial duct fan. The home depot versions produce about 75 CFM at 0.1 inwc. A common inline blower used here is a Vortex that will produce 0.75 to 1.0 inwc.

 

[guest 77721]

Hey Helis,

I'm assuming you're buiding a 2 stage vent design.



1) 5 ACPM is only 1.2 CFM in a 6 cuft cab. That's next to nothing. I'm getting about 15 CFM using a computer fan and about 1sqft of filter area with a depth of 1". I'd increase the carbon depth to lower your airflow and make the filter more effective at the same time. That's easier than switching with a thermostat.

2) Running the lights inside a cooltube will keep the heat out of the box. The airflow at 20* to 30*F heat rise through the cooltube will limit the growbox temp to +1 to +2 degrees.

220W (4 x 55) needs is 20 to 35 CFM through the cooltubes for a 20 to 30 rise in exhaust temps. At 70* ambient the hottest the tubes will get will be 100* and that will raise the box temps up 1-4*F. That's why you can get away with 5 MpAC.

3) I'd recommend sectioning off the lights using a piece of glass rather than installing 4 tubes and having to duct them all together.

Hi RedGreenry! Just wanted to stop in and say thanks for "running" this wonderful thread (and hoosier). It's been a valuable resource while designing, though I do suffer from the "so easy that it gets complicated" trait found in people who like knowledge too much.

Anyway I have a question that I am trying to wrap my brain around. I have a cab which is 6 cu. ft. and has properly sized intake and exhaust holes cut for 2 80mm fans to be used as air movers. After my last run (too much air flow killing plants) I aim to solve a problem, and have come up with the following system:

1) Two (or one) axial fans (80mm, 120v, .25" h2o SP, ~30 CFM) will pull through 1" of carbon and be hooked up to a thermostat set to 4°-5° above ambient. My goal is to have this air extraction process happen as infrequently as possible, thus I would like to get the lights as cool as possible. In fact for one fan to run for 1 minute, it is exchanging the air almost 5 times.

2) The new lighting will be 4 x 55w PL-L bulbs (there is another option, but it is not the discussion of this thread) preferably cooltubed. My question is this if I run each 55w bulb in a separate 2" polycarbonate tube, how much airflow per bulb do you think I need to keep the room's ∆T between 1-4 °F. (Yes another one of those questions).

The formula 3.16*(Total Watts)/deltaT results in 43-173 cfm per bulb, but this applies for cooltube output temps, correct?

I have figured that if each 2 bulbs gets 30cfm (a 3" fan split to two 2" tubes) and each cool tube is 21" in length (0.038 cu ft/tube) then each bulb will get the air over it replaced 395 times a minute. What type of inside-the-cab ∆T am I going to see? Ideally I'd like 1°-2°.

If you read this, thank you! Same goes to anyone else with input

Helis

 

[Helis]

Thank you! I already have the lightroom sectioned off by glass, I was hoping to win back some headroom by going cooltube though (2" of lighting instead of 4"). Looks like I'll hack apart the cab a bit and raise the glass 1", and put a line of PC fans bowing over their bases. Also I will open the exhaust space for the lights more to allow them to flow freely.

1.2 CFM is very little. I will thicken my filter and will run only one of my AC fans pulling through it. Would be nice to have better odour control. If this all goes well, I might consider a sealed environment with CO2 during the hotter summer months.

I can't thank you enough... I'll be sure to stop back in in a few weeks to let you know how temps are running with the new setup.

Cheers!