Intake, exhaust through one window?

jarlak · Oct 9, 2011

Hey farmers. I am having trouble keeping my 4ft.x8ft. tent cool, getting into high 80's running at night. 2x 1000w and 455 cfm exhaust fan doesn't seem to be enough pulling through carbon filter>both hoods>fan>exhaust ducting. Temps inside room with tent are low 70s, tent just gets very hot. I think I need to install an active input...

Can I take the cool air from outside into the tent via intake fan, and then exhaust the hot air from the tent outside of the same window? I figure I might be able to have the intake as low as possible and the exhaust as high as possible so the heat will rise away from the intake. Will this work or will the hot exhaust air mix with the cool air i am trying to bring in?

Thanks guys

Graywolf · Oct 9, 2011

ttystikk · Oct 10, 2011

The short answer is 'yes'. The long answer is more interesting... First, is the window you're trying to use going to be seen by a lot of people, or is it more or less hidden? If so, then you can use semi- or rigid ducting to pull in cool air from a duct placed out the window, with the tip pointing down. Then, the exhaust air can be sent out another duct with the tip pointing up. If you can keep the two ends as far apart as possible, you'll be able to exchange enough air to make the thing work well enough.

No matter what though, you're going to want more than that little fan to deal with all those airflow restrictions you listed.

Can you afford AC? That might solve more problems than it creates, including cost, smell, strange things poking out of windows, etc... Plus, you'll end up with a sealed room which you can then crank up the CO2 inside.

Emithsuk · Oct 10, 2011

It is possible but a portable ac may be a better option as you could get one cheap from craigslist.

blue-dreamer · Nov 17, 2011

so just use a AC pulling air in? what about an exhaust? is one still needed?

ttystikk · Nov 18, 2011

blue-dreamer said:
so just use a AC pulling air in? what about an exhaust? is one still needed?

An AC unit doesn't pull air from anywhere, it cools the air already there. More to the point, it MOVES the heat from the air inside- or the front of the unit- to outside, or the back of a window mounted style unit. A mini split moves heat from the unit that goes inside to the unit that stays outside.

Most window mounted AC units have an air intake adjustment. Try to close it completely.

That's why I suggested an AC unit; if you can set one up to work effectively, you've eliminated the need to change the air itself to cool the room, and then you can enrich it with CO2, and gain the benefits of sealed room agriculture.

Lots of threads here on the farm about these ideas, I'd suggest looking around here a bit and reading up.

paperplane · Nov 18, 2011

I exhausted and brang in fresh air from a window before. It does work, but make sure that window is not in plae where there is alot of traffic. There will be noise SWOOSHING from the air being pushed and pulled. Best thing to do is build a window box and cut your exhaust and intake holes out.

Farmer Hook · Jul 24, 2012

any1 know wherre to get a cheap ac unit for a 10x5x6.5 tent? plz i need the help i didnt find anything within my price range @ the expo!

im a farmer on a Budget!

Growops · Jul 24, 2012

portable ac suck for growing in my opinon . i just put in a 12000btu window ac with C02 Gen. ill never go back to exhausting . next is a spilt system . good luck on your choice. i would not want anything involving exhaust hanging from ANY window . my 2cents

Farmer Hook · Jul 24, 2012

how much did it cost u?

Farmer Hook · Jul 24, 2012

iv been looking at a portable ac unit.
Hydrofarm ACAN13 Active Air 12,000 BTU Portable Air Conditioner For Growing Areas
any opinions?

sedate · Jul 28, 2012

Farmer Hook said:
carbon filter>both hoods>fan>exhaust ducting.

I think your solution is probably much simpler than you are making it.

Are your reflectors daisy-chained?

Split the duct off the air filter so both hoods get 200ish CFM of ambient air, instead of the second hood getting the exhaust from the first hood.

A pair of 6x6x6 y-ducts should run you $40 - maybe $20 more for clamps.

When you actually do the math, hotter air can hold exponentially less heat, mole for mole, than cooler air.

Farmer Hook said:
im a farmer on a Budget!

We all are. ;)

Farmer Hook · Jul 28, 2012

Thanx sedate, I have a 450 cfm fan directly to the filter and to the first hood and another 450 cfm fan pulling on the second hood and right now I'm at 75 degrees. I'll put photos up as soon as I can, can't seem to upload pics on my iPad

sedate · Jul 29, 2012

If you have two fans in-line with each other you are moving much less air than you otherwise could be.

Pushing and pulling together isn't going to be any more effective than just pulling it -

http://en.wikipedia.org/wiki/Bernoulli's_principle

If your hoods are daisy chained together, you really should try to run fresh air to them separately before you run off buying an a/c.

Farmer Hook · Jul 29, 2012

send me pic of your set up plz!!!! here is minethe First Fan @ the Highest Point! Second Fan!
What the problem iz?

ttystikk · Jul 29, 2012

One big problem is that you're trying to push air through hoods to cool them, and that just doesn't work. Get that muffin fan off the intake side and I'll bet temps will fall by 5-10 degrees without any other changes.

sedate · Jul 29, 2012

Yea I really don't understand the need for pics ...

I don't see the carbon filter he mentioned anywhere either . .

You need split the duct-work between a SINGLE EXHAUST fan. With your fans daisy chained like that I'm sure it makes sense in your head but you are wasting a fan.

The technical explanation can be found here:

http://en.wikipedia.org/wiki/Bernoulli's_principle

But all that aside, do exactly these things:

1) Get one of these:

http://www.rewci.com/6x6x6yduad.html?gclid=CMCmmqeHwLECFRGEhwodEFkAJQ

2) And then plumb each hood INDIVIDUALLY to one of the two receptacles, (as in they are NOT to be strewn together like in pic 2) with the thing plugged into the INTAKE side of your fan, which then should be plumbed IMMEDIATELY OUT OF THE TENT, preferably to OUTSIDE airspace.

3) Take your newly spare fan and use that as an INTAKE fan from one of the holes on the other end of the tent

4) Attach one of these to your new intake:

You're welcome.

sedate · Jul 29, 2012

Huh. It turns out I do have a visual aid.

Here is what I am talking about:

See how the duct work is split directly off the carbon filter? That is so BOTH hoods get 200ish CFM of nicely temperatured, carbon-scrubbed ambient air.

Here is how amazing it works in practice - note the amazing deep blue/purple colors at the far end of the next photo - telling us our canopy space is nicely cool across the entire area:

And then the ducting is y'd together back at the fan, and our hot exhaust air is now shot out of the grow space completely.

Irrespective of often you see it, daisy-chaining hoods together is, generally speaking, what you might call "doing it wrong" . . .

Mississip Hip · Aug 1, 2012

Is daisy chaining a bad idea if you are pulling fresh outside air thru them?

Like 3 fans for 12 lights. 3 seperate runs of 4 each?

I was reading thru this and I think I am missing something. I need another cup of coffee.

ttystikk · Aug 1, 2012

Mississip Hip said:
Is daisy chaining a bad idea if you are pulling fresh outside air thru them?

Like 3 fans for 12 lights. 3 seperate runs of 4 each?

I was reading thru this and I think I am missing something. I need another cup of coffee.

Sedate is doing justice to a valid point by showing how to get the coolest air possible delivered to the hoods. The basic principle is sound, but many factors can affect the actual outcome significantly; 8" diameter vents in hoods and duct have 60% more surface area and thus less airflow restriction than 6" ducting. Short and straight air duct runs also maximize airflow and heat removal.

I run 8 x 1kW Magnum 'ocho' hoods double barrel style in two rows of four, with one 8" maxfan pulling air from an 8" Y collector just like the link to the website he provided. With all 8kW running, air entering from the house at 70 gains less than 5 degrees as it passes through each successive reflector. The air immediately downstream of the fan is over 100 degrees and passes through insulated ductwork and directly outside. This only works so well because of the attention paid to reducing as much airflow restriction as possible throughout the entire system.

Since the air is drawn in through ducting from outside the room, it exchanges no air with the sealed environment inside, and effectively carries off some 2/3 of all the heat generated by all those bulbs... which directly translates into reduced cooling costs and better temperature stability in the room.

Intake, exhaust through one window?

Intake, exhaust through one window?

jarlak

Graywolf

ttystikk

Emithsuk

blue-dreamer

ttystikk

paperplane

Farmer Hook

Growops

Farmer Hook

Farmer Hook

sedate

Farmer Hook

sedate

Farmer Hook

ttystikk

sedate

sedate

Mississip Hip

ttystikk

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