JoeBlow5823
Well-Known Member
Fan pulls air through filter, pushes air through air cooled hood and out of the tent....
Apologies in advance
- Thread starter ThatGuy13
- Start date
ttystikk
Well-Known Member
NO.
Filter -> hood -> duct -> fan, mounted outside the tent.
If you don't believe me, conduct this experiment;
Fire up your lamp inside the hood with the fan pushing air through it. Wait 20 minutes, feel the hood- be careful, the fucker will be hot!
Then, take the fan off and turn it around and remount it so it's pulling air through the same hood. Wait 20 minutes and feel the hood again. It will be cool.
You'll never push air through a hood again.
JoeBlow5823
Well-Known Member
Ive been pushing air through my hood for multiple grows. It has never gotten hot. Ive measured every part of it with my laser thermometer- directly over the bulb it gets to a blistering 90 degrees. The rest of the hood stays under 85. I just ran it for 4 months like this.
Renfro
Well-Known Member
I dunno, I am confused on this one, to me it just seems like CFM is CFM, either way it's lined up. Now if something was happening to mess up air flow more in one arrangement then I could see there being a performance difference. Still it seems like the reflector is gonna add it's specific turbulence either way, @ttystikk are you saying that the push setup is more turbulent because the air is coming out of the blower already turbulent and then hits the awkward box before going into the duct? I am not disputing that you noticed a difference in your real world testing, I am just trying to figure out why, whats the physics behind it. It seems like CFM would be CFM either way.
.Smoke
Well-Known Member
Pushing air through adds heat from the fan motor to the air. The air particles getting churned, compressed and forced through the fan also raises the temperature of the "cool air" being blown into the reflector hood. In essence, reducing the cooling capability of the air resulting in (a minor) increase in hood temperature and overall tent temperatures.
Placing the fan outside negates these factors.
Pulling the air is easier on the motor due to the lack of back pressure, most likely resulting in a more efficient, higher CFM flow.
I've personally had lower tent temperatures just from pulling my air instead of pushing it like @ttystikk said.
Renfro
Well-Known Member
Hmm I'd like to see an IR gun reading on the blower output to prove that, I find it hard to believe that with the low wattage of the blower motor and the amount of air going through it that it wouldn't raise the air temperature more than a cunt hair. We aren't compressing the air enough to make it significantly hotter either. I just can't see it...
Renfro
Well-Known Member
lol haven't we all.
Forget about it until you get some experience, is what I'd say in regards to this question.
TLDR:
Fan: DC inline fan (power saving, very compact and light, very dimmable and designed for such use). "Oversize" it and dim for quieter an easier operation.
Lights: A reputable led brand, or I guess a well reputable knock off of one (I see you've ordered already, all good). DIY is a good way to save money; future reference.
Seems you have everything else sorted. Enjoy, dude.
In regards to inline fan selection, a "DC inline fan" is what I'd recommend. They're dimmable, and they're meant to be dimmable, and often - if not always - come with a dimmer. They don't just "pulse the electricity", which is what "speedster" type dimmers connected to a standard (vortex style) inline fan does, as best as I remember, which technically "isn't good" for the motor, and creates that hum/noise. DC fans also dim lower, and again, they're designed to do this. "Hyperfan" is just a brand example, check amazon for "DC inline fan" probably, for more. I'm almost 100% sure the AC infinity fans are DC fans, and they come in a temp regulated or humidity regulated version, I think. Another benefit is that they (DC) use much less power than a "standard" inline fan.
Edit: Removed shit that doesn't aid in OP's question.
Good luck on your first grow, guy.
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JoeBlow5823
Well-Known Member
My point exactly, the difference is minuscule. If your hood is getting to hot, there is a much bigger issue at hand.
ttystikk
Well-Known Member
I want measuring the remotest of the output air, I was measuring the temperature of the hood itself.
Anytime you blew air you compress it and one of the basic principles of compressing a gas is that in doing so, you heat it.
When blowing air through the hood, the hood got and stayed hot.
When drawing air through the hood- same hood, same lamp, same fan- the hood stayed cool.
It was not a subtle difference.
ttystikk
Well-Known Member
Your results mirror mine, even if I'm not sure I agree with your explanation for why it works that way.
ttystikk
Well-Known Member
Not minimal. When I did my back to back test, the difference was between a hood cool to the touch and one that was too hot to hold my hand on.
JoeBlow5823
Well-Known Member
Yeah I'm not buying it, something about your setup must have been different other than where the fan was positioned. Ive been blowing air through my hood for a long time and it stays cool to the touch.
Yeah something about his "test" is off.
Renfro
Well-Known Member
i have to agree.
ttystikk
Well-Known Member
It was an 8" fan on an 8"magnum XXXL hood with one SE 1000W HPS lamp in it. The only change was turning the fan around from blowing to sucking.
Try it yourself instead of doubting me with no evidence.
Renfro
Well-Known Member
Well I would test it just out of curiosity, if I had the gear to do it. I think I have an old air cooled 6" reflector in the garage but no spare blowers laying around. Maybe I can pick one up cheap on craigslist lol. I really am curious. I believe you when you say what you experienced, I am not calling you a liar, I am just trying to come to terms with why it happened.
A reasonably powerful ducted fan situation might be producing a pressure as high as 0.5" WC and thats about 0.018 PSI. Thats all the fan could actually compress the air in the duct system. I just don't see that small amount of compression heating the air by a measurable amount.
As to the motor dissipating heat, it's cooling itself constantly and yes that would warm the air stream but only a tiny amount due to the volume of air being moved.
I can only surmise that the airflow was somehow impeded with the push arrangement, but I really would love to test this. I will see what I can come up with.
A reasonably powerful ducted fan situation might be producing a pressure as high as 0.5" WC and thats about 0.018 PSI. Thats all the fan could actually compress the air in the duct system. I just don't see that small amount of compression heating the air by a measurable amount.
As to the motor dissipating heat, it's cooling itself constantly and yes that would warm the air stream but only a tiny amount due to the volume of air being moved.
I can only surmise that the airflow was somehow impeded with the push arrangement, but I really would love to test this. I will see what I can come up with.
NukaKola
Well-Known Member
Pulling is slightly more efficient than pushing but I don't believe it is because of the heat from the fan. I think it has to do with the fact that when pushing the air can swirl in the hood causing turbulence and disrupting the flow of air, whereas pulling the air is going to travel the path of least resistance in a more unidirectional fashion.
At least that is my assumption. Would be interesting to test with an infrared camera.
At least that is my assumption. Would be interesting to test with an infrared camera.
Renfro
Well-Known Member
Thats what I am thinking too, it's the only thing that makes sense. I mean if the air is moving like it should then the whole system would be cooled. So the air isn't moving like it should.