Thoughts on this design for a ghetto air induction system ("natural A/C")?

[jd4083]

I know, I know...I'm quite the artiste.

So a combination of low ceilings and not enough circulation is causing some heat issues for me in my spare room where my tent currently is. Passively leaving the window cracked has not helped, so my thought is that by using an extra 4" inline fan and some ducting, I can actively pull cold, fresh air in from the outside and lower the ambient temperature in only that room and not my entire house.

Is there an easier way of doing this that I'm missing?

 

[bmp420gti]

Ideally, just like the tent you would like to passively pull in cold air from the outside and use the fan to blow the hot air somewhere else. There is no easy answer, every setup is different. If you pull cold air in with a fan, where is the current air going to go? You need to somehow exhaust the room too even its something like not covering the entire window hole so hot air can blow out once you start forcefully pulling cooler air in. Just keep thinking about airflow, the more flow you have the cooler your temps will be.

 

[jd4083]

Ideally, just like the tent you would like to passively pull in cold air from the outside and use the fan to blow the hot air somewhere else. There is no easy answer, every setup is different. If you pull cold air in with a fan, where is the current air going to go? You need to somehow exhaust the room too even its something like not covering the entire window hole so hot air can blow out once you start forcefully pulling cooler air in. Just keep thinking about airflow, the more flow you have the cooler your temps will be.

The major issue is that the tent is almost as tall as the ceiling itself and the room is very small, that's why the air exchange seems to be off. I suppose that I could use my other 4" fan (I have two of the same model laying around) as an active exhaust for the room as well and just put the two on timers to maximize air flow. Alternatively, I could probably get away with just the intake and then a passive exhaust in the form of another 4" hole (or two) in the same window. My 6" fan in the tent itself pushes 460CFM (I believe, maybe a bit less) and I would love to be able to just duct the exhaust out the same window I'm talking about putting this active intake on, but I don't think the fan could do it effectively. Or could I just put a passive intake or two in the window and then actively exhaust from the 6" fan out via additional ducting? I just question whether it could push enough air to make the air exchange work in that scenario. I unfortunately don't have easy attic access in that room or none of this would even be an issue to begin with.

However, I think that if I was pulling in the outside air often enough the air exchange would naturally work itself out just exhausting into the ambient air in the rest of the house. Thanks for the post, I've obviously still got some thinking to do here...

 

[Rolldaddy]

Use the 4" inline to pull the hot air out of tent (preferably through a scrubber unless smell doesn't matter) and exhaust that outside. And you can run a duct going into the tent from the outside if you want cooler air passively coming in from outside.

 

[DoubleTripleOG]

If you put a fan on the bottom of the tent pulling air into the tent, and have your window set up with the ductwork coming into the room.......It should work. As long as the room is sealed up good from the rest of the house that is.

Another option is to put the fan on the top of the tent and have the ductwork from the window hook into the bottom of the tent. Thus pulling cold air from outside thru the tent and into the room. The only thing with that option is the outside air directly from outside(no lung room) may be too cold for your plants liking (too much of too cool of air).

A solution to that is to firmly secure a piece of thick plastic over the end of the ductwork and cut a hole just big enough to allow a lesser amount of cold air to adjust your temps to your desired range.

 

[jd4083]

Use the 4" inline to pull the hot air out of tent (preferably through a scrubber unless smell doesn't matter) and exhaust that outside. And you can run a duct going into the tent from the outside if you want cooler air passively coming in from outside.

The tent itself has a ~460CFM 6" fan hooked up to it, currently pulling through the scrubber with about 8 feet of ducting total, exhausting out of the top of the tent with a 90* connector so it doesn't just blow straight up. At this point after doing some thinking I'm leaning towards just moving the tent closer to the window, putting in 2-3 4" holes for passive intake, and then actively exhausting the tent out the window instead of my original plan...just hate to add so much more ducting and further reduce the efficacy of the fan...

 

[jd4083]

If you put a fan on the bottom of the tent pulling air into the tent, and have your window set up with the ductwork coming into the room.......It should work. As long as the room is sealed up good from the rest of the house that is.

Another option is to put the fan on the top of the tent and have the ductwork from the window hook into the bottom of the tent. Thus pulling cold air from outside thru the tent and into the room. The only thing with that option is the outside air directly from outside(no lung room) may be too cold for your plants liking (too much of too cool of air).

A solution to that is to firmly secure a piece of thick plastic over the end of the ductwork and cut a hole just big enough to allow a lesser amount of cold air to adjust your temps to your desired range.

I can't really do active intakes on the tent itself and still maintain the negative pressure I need for my scrubber to be effective or I would consider that.

 

[rives]

I think that you might be better off exhausting your carbon filter from the top of the tent and then out the window. This would create a low pressure in the tent so that the cool air from the cracked window could fill the void, coming in the vents on the bottom of the tent. There might be some mixing of the air just outside the window so that the cooling is a little less effective, but it is still probably the most effective way to get cool air into the tent.

 

[Phychotron]

I have a piece of clear weather film over my window with two fans connected to it. The window is slightly open about 4". One fan blows directly out of the flower tent controlled by a temp/humidity sensor inside the garden. When either is too high it kicks on, so I set the speed of the fan so that it will stay on medium the whole time the lights are on basically. I do hear it shut off and start up from time to time, day or night.

The other fan is an intake fan to my bedroom with the tent. That is controlled by a temp sensor that will turn it on when the bedroom gets above 85. Its winter right now so it doesnt turn on. I just set this up so I'm not sure how it will operate in the summer, when I might have to have a separate intake, as right now the exhaust can also get pushed through the input fan while its off, or when both are on it will take a mix of outside and exhaust through the input. Exhaust in the top, intake in the bottom of the window and on opposite sides, so that the intake will suck from the open window side.

The best way to cut a hole in the plastic is to trace the vent with a sharpie then cut about half inch inside the circle to let the plastic hug the vent. Also I used a large binder clip screwed into the window sill with a washer to hold one handle for quick release. They hold really well. I suggest you use the heavy duty window plastic as it will hold up better to working with the vents.

Also covered the window with aluminum foil to stop the nosy neighbors from seeing ventilation equipment in the window.

 

[Phychotron]

Let me also say that if I don't exhaust the air to the outside of the house the humidity in my apartment goes through the roof. If you only have one fan, blow the hot air out and let the cold in passively.

 

[Phychotron]

Even have a photo, doing exactly what you planned. It doesn't work because your just blowing air into the room and the hot humid air has no place to go. Notice all the humidity on the plastic.

That hole was the first one I cut without tracing the duct, you can tell its all ghetto taped together because of it. I had it like that for one night before I woke up in a sweat and the house like a sauna. Changed it to active output and its much better.

My veg tent has passive input with an 8" booster fan between the 4x4 veg and 4x8 flower. The exhaust from the flower tent goes through a carbon filter and out the window.

 

[jd4083]

I think that you might be better off exhausting your carbon filter from the top of the tent and then out the window. This would create a low pressure in the tent so that the cool air from the cracked window could fill the void, coming in the vents on the bottom of the tent. There might be some mixing of the air just outside the window so that the cooling is a little less effective, but it is still probably the most effective way to get cool air into the tent.

I think you're absolutely right and I've been overthinking and overcomplicating a simple concept that we're all familiar with...passive intake and active exhaust. I'm going to just do this I think. So I'll have a 6" hole in the wood/polyboard/whatever I end up using for the exhaust -- do I need to use the standard 1:2 rule for a passive intake for this, or does it not matter since I'm not aiming for neg pressure in the room itself?

Thanks for your help man!

 

[jd4083]

I have a piece of clear weather film over my window with two fans connected to it. The window is slightly open about 4". One fan blows directly out of the flower tent controlled by a temp/humidity sensor inside the garden. When either is too high it kicks on, so I set the speed of the fan so that it will stay on medium the whole time the lights are on basically. I do hear it shut off and start up from time to time, day or night.

The other fan is an intake fan to my bedroom with the tent. That is controlled by a temp sensor that will turn it on when the bedroom gets above 85. Its winter right now so it doesnt turn on. I just set this up so I'm not sure how it will operate in the summer, when I might have to have a separate intake, as right now the exhaust can also get pushed through the input fan while its off, or when both are on it will take a mix of outside and exhaust through the input. Exhaust in the top, intake in the bottom of the window and on opposite sides, so that the intake will suck from the open window side.

The best way to cut a hole in the plastic is to trace the vent with a sharpie then cut about half inch inside the circle to let the plastic hug the vent. Also I used a large binder clip screwed into the window sill with a washer to hold one handle for quick release. They hold really well. I suggest you use the heavy duty window plastic as it will hold up better to working with the vents.

Also covered the window with aluminum foil to stop the nosy neighbors from seeing ventilation equipment in the window.

Let me also say that if I don't exhaust the air to the outside of the house the humidity in my apartment goes through the roof. If you only have one fan, blow the hot air out and let the cold in passively.

View Image

Even have a photo, doing exactly what you planned. It doesn't work because your just blowing air into the room and the hot humid air has no place to go. Notice all the humidity on the plastic.

That hole was the first one I cut without tracing the duct, you can tell its all ghetto taped together because of it. I had it like that for one night before I woke up in a sweat and the house like a sauna. Changed it to active output and its much better.

My veg tent has passive input with an 8" booster fan between the 4x4 veg and 4x8 flower. The exhaust from the flower tent goes through a carbon filter and out the window.

Yup. Awesome info, thanks to you and rives and everybody else. Looks like I will be doing this exact same thing. I feel silly for even thinking about actively pulling in and not just exhausting, that's like grow room ventilation 101.

As I asked above, how much surface area for passive intake vs. the 6" exhaust for the window? Do I treat it like a cab and 1:2 it or not really worry about that?

 

[Granger2]

2 x passive intake as exhaust would be best. Good luck. -granger

 

[jd4083]

2 x passive intake as exhaust would be best. Good luck. -granger

That was my question, so the standard formula works here? Would you say 3x 4" or 2x 6" or does it even matter?

This is awesome, I'm going to snag some more ducting and the thickest poly I can find at Lowe's and get to work tonight...I think I might be able to get away without having to use a hole saw after all if I go the route Phycotron detailed thanks again everybody

 

[rives]

Yep, I'd go with 2:1 or even more. How you get there is irrelevant, but if you use a number of small holes, I'd add a few to compensate for the higher levels of drag.

 

[jd4083]

10-4, makes sense. Thanks again rives & everybody, you guys rock.

 

[Granger2]

2-6" or a rectangular intake that is about 7x8." Good luck. -granger

Re: pi x r squared. 6" D = radius of 3, squared = 9 x pi= 9 x 3.142 = 28 sq in, x 2 =56 sq in intake. 56 sq in is 2 6" round, or any number of rectangular sizes, such as 8x7, or a 30" window raised open 2", ect.