choader

I've started putting together my new cab in earnest and need some hep to finish buying what I need. The goal is to finish this over Christmas.

Let's start with the proposed setup.

Rubbermaid 3749 - 17cu ft w/3sq ft floorspace, 67" tall
600W HPS EYE (ballast outside cab) and cool tube

6" active intake : pulling air from the house. approx 15' run pulling, 8' push. temps 70f-80f.
6" exhaust : pulling air from the cab. approx 15' run pull, 1' push
all lines are 6" insulated, flexible duct.

I have a fantech FR140 (214cfm) and need to purchase another fan. 3 questions.

1. which side should the FR140 be on? Intake or exhaust?
2. given the answer to #1, what size should the 2nd fan be?
3. how can I convert my setup into some approx backpressure numbers?

During my last grow, I was in about 50cu ft with the same light. Used passive intake and had the ballast inside the cab. The FR140 was able to keep up nicely as the exhaust fan but it also had about 1/2 the currently planned run and no push ducting.

I've looked at the backpressure curves of the fantech fans but I can't seem to convert my setup into backpressure. If I could, I'd use the curves.

Hope this makes sense. I appreciate your help.

Choader

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slowthestone

hey hey choader...

I ran into fan curves accidentally when I noticed a fan I was installing, fitting, testing...dropping it down barely more than couple inches...it went from pulling air to pushing.

Gave me a decent 'wtf' for a few minutes till hitting the Google switch.

Fan Curve FAQ

choader

Great link slow!! Props for that.

So if I've got this right from your link...............

23' of flexiducting
3' of rigid duct
1 bend = 2m flexiducting
Intake grill = 20Pa

Being conservative, I've got 10m of ducting at 1.5-3.5Pa/m (I'll use 3.5) of backpressure with 250Pa=1" static water pressure.

That equals 55Pa which is .22" static water pressure on the fan. Derate this down to 75% which is .3". Still not bad at all.

Interesting...............

Choader

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afterburner

Depends on your intake temperatures, are they that constant year round? do you have any future plans for expansion/adding light?

I say get the biggest fan you can afford. 350cfm + And use a speed controller to slow her down if needed.

If your using a scrubber you want to keep negative pressure on the room so having a larger fan on exhaust is preferable.

-afterburner

choader

Good point afterburner, I didn't think about a carbon scrubber. Not sure if I'll need one. Plan to have 3 plants flowering (max) and exhaust out of the attic gable grill. This is 20ft off the ground.

Also, if I add a carbon scrubber, it will make the exhaust job harder than intake thus needing the bigger fan. I've got a speed controller and will get one with the new fan too. I'm looking at the FR150. 6" duct, 263cfm. Maybe the FR160 or FX6XL but that jumps in $$ and current draw. Need to keep current down. However, they are 289cfm and 392cfm respectively.

As for temps, yes, I'll be pulling from the house which is always between 70f-80f. Cab will be in the garage with ducting running thru the ceiling. I don't plan on expanding. In fact, this is smaller than my last setup and I'm trying cram a 600W HPS EYE in there!

More to ponder...............

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ltsystems

i would go with only 1 air exchange blower, 1 blower pushing and 1 pulling air dont = 2x power. then get a high volume low pressure duct fan "much cheeper than the higher pressure blower needed for the room/filter". that is used only to cool a sealed lite i.e. the growroom air and the lite cooling air are seperate.

slowthestone

I'm sensing some geekness in here.

So maybe you fellas might dig this +pressure review. A pdf thats very in-depth (pictures too)

Characterizing Positive Pressure Ventilation

knna

I think you need more extraction than you think.

In order to extract all the heat produced by a 600w, you need near 1000CFM. 300CFM likely increase the cab temp by 3,5-4ºC, but in a small cab like yours, thermal steady state would be higher. And im talking about true flow.

To control heat in such small space, you need to invest in a good exhaust, more taking into account to 20' ducting. If you can take the air from outside, or mantain a window slighty open, in order to have lower temps in the room, things would be a lot easier. Ambient temps over 70F give you too little margin. If you can achieve room temps about 60-65F, then extracting from the cooltube with a 300-350CFM exhaust would be enough (or using cold air from outside).

Then, you will only need a small fan to renove the air in the cab, with passive intake (or small fan+passive intake).

PD: now i see your last post. Garage temps should be lower, isnt it? Taking the air for the cooltube from outside should be enough then.

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choader

I know I need good extraction and I think the new blower will do the trick. It will be a Fantech 150, 160 or 6XL. Leaning toward the 6XL.

Intake air will come from the closet in my bedroom which is just on the other side of the wall. That wall separates the bedroom closet and the garage. Make sense? I won't be using outside air. I'll vent into the attic and out the gable. Will also be able to dial back the intake fan to ensure neg pressure cab. I expect cabinet temps to be ~80f.

Anyone have any other thoughts on which fan to put where or which of the fans listed above would be best?

Thanks.

Choader

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knna

I believe the 6XL would be the best choice. Maybe the 160 work fine, consider the cost diff, but as more extraction the best.

I you arnt concerned about smells, i dont understand why you want a negative pressure. It reduces the fans efficiency strongly. I suggest to use a small intractor plus passive intake and a 12cm PC fan as extractor (without ducting), and use the 6XL only to pull from the cooltube, taking the air for this from the garage (not the cab), to avoid a too low humidity. In other words, splitting the cooling circuit from CO2 renovation circuit.

Have you thought in letting some passive intakes in the garage? (for example, letting the garage door 1" over floor). This will provide you lower ambient temps in the garage, allowing you to use the Fantech 160 and providing fresh CO2. Then you just need to do the duct to the attic.

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