Airflow/cooling question

[Batboy]

I got my cab up and running last night and have a cooling question.

The cab is 29 cubic feet and I'm running a 6" S&P TD-150 inline fan (293 cfm) pushing air through a 6" Hydrofarm cooltube and then out a 6" outflow flange at the top. I've got 2 6" round passive intake holes cut at the bottom back of the cab. Airflow is very good and even with a tiny bit of air escaping from the cooltube, a ton of air is flowing out of the top. Intakes are working and when I put a paper towel over one, it was sucked into the cab.

Ambient temp (where the intakes are sucking in from) is 71F. With the fan on 50%, the cab was steady at 81F. When I cranked the fan to 100%, and there was a definite difference in noise and airflow, the cab temp dropped a whopping 1 degree, to 80.

I am really hoping that this is a fixable design flaw, and not a fan problem. I haven't yet added my filter to the intake side of the fan, so I know that static pressure will only decrease when that happens. The only fix I can think of is that I need another hole for intake. I thought that 2 6 inchers would be enough, but maybe not? If this is the problem, would adding a 3" do it or should I cut another 6"? I hesitate to cut more holes in the cab because I'm having a tough time lightproofing them.

Anything else that I'm not thinking of that may help cool this sucker another 5 degrees or so? I am really itching to get this grow started, but I want to get the temps and airflow situated before I get dirty.

 

[~fvk~]

Get a Vortex or something similar. My impression is that S&P's are quiet, but not the best for restricted air flow? I might be wrong though, it's been awhile since I researched fans. You'd also be better off pulling the air out, instead of pushing it. Are you using a carbon filter dude?

 

[FreezerBoy]

With the fan on 50%, the cab was steady at 81F.

81º ain't bad. How big is the lamp? May I ask how you got the fan to run at 50% as the fans 2 speeds are 220 and 290 cfm? Any ducting will add resistance. Any chance you can use smooth PVC?

 

[Batboy]

Get a Vortex or something similar. My impression is that S&P's are quiet, but not the best for restricted air flow? I might be wrong though, it's been awhile since I researched fans. You'd also be better off pulling the air out, instead of pushing it. Are you using a carbon filter dude?

I researched the shit out of the fan choice and decided on S&P because of the noise factor, knowing that I was giving up some pulling power because of the mixed vent design versus centrifugal. Everyone that I've spoken to has said that the vortex is probably the best inline centrifugal, but it sounds like a jet engine.

I haven't connected a carbon filter yet, but I have one and will eventually hook it up. I was under the impression that if I wasn't willing to use 2 different fans (1 for exhaust and 1 for cooling), then the best method for reducing odor was to pull through the filter and then push through the light and out the cab. The idea being that any suction after the filter risks sucking in smelly air and exhausting it. In my setup, the filter and fan are [will be] very close; after the fan, any leaks in the duct or cooltube will simply push smelly air back into the cab and not out in the real world. Wrong?

81º ain't bad. How big is the lamp? May I ask how you got the fan to run at 50% as the fans 2 speeds are 220 and 290 cfm? Any ducting will add resistance. Any chance you can use smooth PVC?

I should have mentioned it's a 400w HPS.

Perhaps 50% is a little misleading. I've got the S&P wired for high speed and then dialed my S&P speed controller to a spot that is roughly halfway between the highest and lowest settings.

I thought that hard ducting was louder, which I'm trying to avoid. Also, wouldn't that mean that I'd have to rearrange things every time I wanted to raise or lower the light? Do you really think that my inability to get the temps under 10 degrees over ambient is a function of the fan, and not something more easily fixed, like intake volume?

 

[FreezerBoy]

Hard may be louder (don't know) I was thinking purely of resistance. As ~fvk~ mentions, the S&P just doesn't suck like a centrifugal. If you could put the fan at the end of run so all air is sucked, that would help .. some.

If you don't want to do a separate cool tube line, I'd suggest a DIY scrubber with a 1/2 inch thick carbon bed rather than the 1-2 inch thick core that many are designed with. Obviously, it would need refilling more often but, I did this for my TD 100X and its lasted through two 75 day flowering periods and is still effective.

 

[SmokinSHO]

...

 

[qbert]

I was under the impression that if I wasn't willing to use 2 different fans (1 for exhaust and 1 for cooling), then the best method for reducing odor was to pull through the filter and then push through the light and out the cab. The idea being that any suction after the filter risks sucking in smelly air and exhausting it. In my setup, the filter and fan are [will be] very close; after the fan, any leaks in the duct or cooltube will simply push smelly air back into the cab and not out in the real world. Wrong?

In principal, I believe you are correct on these points.

Also seems like you have enough intake space.

Interested to know if that temp sensor is in the light or the shade.

Is that S&P usable throughout the entire range of the speed control, or does it get funky towards the low end (noises, vibrations, etc)?

 

[BLUNToPOTomuss]

To me if you have an ambient temp of 71 at the intakes it seems as if your fan just isnt strong enough to exhaust at the proper rate for cooling your bulb.

Your cab is just short of twice my size(16cuft with a 400 also)..... but my numbers worked for me so maybe if you tweek them a bit you can get them to work for you also.

I used .3 cfm per watt to cool the bulb

plus an extra 100CFM for added intake and circulation.

then add another 50-100CFMs for the loss due to the scrubber.

I also put 2 4'' fans and 1 6'' fan inside the cab.

My ambient temps are 75-78 and I cant get my cab +2 degrees above ambient WITHOUT turning off a couple of inside fans.

So I would suggest 133CFM for bulb cooling, 100CFM for added circulation/intake and an additional 50-100 for scrubber loss.

bringing your total 1 fan CFM of 280-350CFMs. looking at your post that is what you are using! That leads me to believe the fan just doesnt have the pull power to cool the 400.

you can get an hydrofarm blower for like $90 where Im at. I think you may have to look at those of a true "vortex" style fan.

good luck.

 

[Batboy]

I stupidly never considered the location of the sensor.
It was 1/2 of the way up one side of the cab, in direct light.

I just ran it again for 30 minutes with the sensor shaded in the middle of the floor of the cab. Temps only went up 5 degrees. And the fan was not turned all the way up.

qbert - the fan does not get funky at either end of the speed spectrum.

Blunt - what do you mean, 2 4" fans and 1 6" fan? Are you talking about intake, exhaust, cooling? If you are talking about internal circulation, I will have a fan for the plants, but it isn't yet running.

I'm still hoping that I can make this fan work. . .

 

[BLUNToPOTomuss]

Hey Bat!

Sorry for the delay, been on vaca for the last week! yeah those fans are for internal circulation only.

Its better to have an extra fan blowing on the tops, with the girls dancing the rumba spidermites have a harder time getting on he top of leaves to mate.