Positive pressure in tent to keep dust out, but Attracting pests?

[EDGarden]

Hey all,

So am setting up my tent and am in need of a little advice.

I have a 5x5 tent in a room between my house and the backyard.
I also have a dog that uses this area to stay warm and out of the weather.

I dont want to suck air in, because of dust, so i didnt want negative pressure.
I thought positive pressure would be best. I have a big filter on the intake so i am not worried abut dust or dog hair.

Now i know that means i will be pushing air out and eventually stink up the place.
But for now i am not worried about it.
In my mind, this helps with keeping dust, etc. out.

However will pests be able to smell the plants and be attracted to it?
More so than if the tent was set up for the negative pressure?

Thoughts?

I look forward to your advice.
Thanks all!

-E

 

[SolMJ]

Hey buddy, positive pressure is when there's more air coming in than out. Generally growers aim for negative pressure (which sounds like your plan) because positive pressure takes longer for hot air to be extracted which leads to heat buildup & other issues.

Pests are always a factor regardless, whats important is that you keep your grow area clean & always be ready to fight them off as soon as you spot them, for example with neem oil.

Good luck

 

[Stealthboat]

positive pressure = blowing out like a balloon, negative pressure = sucking in. By having positive pressure, some of the air will remain while most of it is pushed out, meaning the smell will protrude from the tent. Since some of the air doesn't escape the tent though your air flow isn't what it could be with negative pressure. Bugs will most likely smell the fragrance if positive pressure is used, not sure if it's better at preventing them from getting in though. My 4.5' x 4.5' tent uses 1 large extractor fan and 2 passive intakes. I taped some furnace filters over the intakes and made a light filter for the outtake, only way bugs can get in there is from the main door.

 

[Rodrigo]

Well, there's a small lapse in your design.
You said you didn't want negative pressure but you have a filter on your intake to keep dust and hair out, this is means that you're pushing air in, which is exactly what negative pressure does, so you might be a bit confused on this thing works, or didn't think it all the way through.

In order to have positive pressure you MUST push air in, otherwise you just have normal air pressure (one atmosphere) and there would be no air exchange, which is bad.
Also, you MUST have an extractor, stale air needs to be pushed out of he tent. This will inherently create negative pressure inside, so outside air will get into the tent one way or the other, either through passive or active intake.

I don't think you should worry too much about dust, unless you live in a place where dust is a real issue. Anyway, you should be able to solve this using a simple screen on the intake. But you must have an extractor to push the air out. I think you might catch a bit more dust on your intake filter if you keep it wet, but his will probably increase the RH inside.

To avoid stinking up the place, use a carbon filter, I use a $60 filter that was supposed to last about 8 months and I used it for over a year. So it's not a big expense.

Hope this helps.

Good luck and happy growing!

 

[EDGarden]

Thanks for all the replys.
@Sol: im picking up some neem tomorrow for sure, should have had it already. i do have general outdoor garden pest killer, organic if i remember. Ill check what in it.
@stealth: thanks for reaffirming my thoughts on the bugs, most likely will get switch back. I have a furnace filter on my main intake as well. Couldnt imagine not having one.
@Rodrigo: I do have a fan between the filter and the tent, for a positive pressure, but will be going back. I am intrigued by the idea of wetting the filter, i do need an increase in RH as i am between 35-40 on any given day or night. I have about a week logged so ill compare the RH some time soon.

And to add some more info:
it was late and i was quite medicated when i wrote up that post. Let me clarify a few things.
But first there is a lot of good information here, i have taken away a lot so far.

Anyways. I dont want to suck air in with negetive pressure in the same places that are leaking air with positive pressure(which is how its set now)
Which is really the heart of the question, blowing air out if the small leaks, or sucking in air from those same leaks.

Heat build up is not a problem. In fact its a bit welcome.
Nights here the tent gets to about 50F at its lowest. Then to about 70F ambient.
I have a data logger on the inside tent temp and the ambient outside.

At first with negetive pressure the ambient and tent temps were in lock step.
Now with posivite pressure I am seeing about 10F difference in temp from inside to ambient.
I think ill go back to negative for now and see how it does.
I did not have a speed controller at first and the 435 CFM fan was replacing the air roughly 2 times a minute(5x5x8 ft tent / 435 CFM)
Now i do so i am going to go back and turn the fan down.

Thoughts on that ramble?

Thanks all.

 

[Rodrigo]

My first thoughts are that you're worrying too much about the pressure in the tent. It is in fact better to have negative pressure inside, but other than that you shouldn't worry too much. You should focus on air exchange and temps rather than pressure.

It's good that you have a powerful extractor fan, there's nothing wrong with having a good air exchange, it will help keeping the temps down. You should take advantage of having a good extraction system and just go with passive intake. This leaks you speak of are probably too small to allow pests to get in. A nice filter on the intake opening should be sufficient. And although it is better no don't have them, pests don't become a problem overnight and in most cases they are easy to take care of if you're prepared beforehand.

A wet filter will definitely add humidity to the environment, but with all the air you're moving you'll need to keep it wet constantly, meaning that you're gonna have to create a recirculating system to keep water dripping on the filter.

Good luck and happy growing!

 

[EDGarden]

You are probably right about the pressure.
I have grown around dogs before but i was no where near as careful as i am now about it.

I havent grown in a bit and im trying to get the kinks out.
Thanks for advice @Rodrigo, im getting ready for any pests tomorrow and happy growing from there. I hope!

Take care,
-E

 

[Stealthboat]

Thanks for all the replys.
@sol: im picking up some neem tomorrow for sure, should have had it already. i do have general outdoor garden pest killer, organic if i remember. Ill check what in it.
@stealth: thanks for reaffirming my thoughts on the bugs, most likely will get switch back. I have a furnace filter on my main intake as well. Couldnt imagine not having one.
@Rodrigo: I do have a fan between the filter and the tent, for a positive pressure, but will be going back. I am intrigued by the idea of wetting the filter, i do need an increase in RH as i am between 35-40 on any given day or night. I have about a week logged so ill compare the RH some time soon.

And to add some more info:
it was late and i was quite medicated when i wrote up that post. Let me clarify a few things.
But first there is a lot of good information here, i have taken away a lot so far.

Anyways. I dont want to suck air in with negetive pressure in the same places that are leaking air with positive pressure(which is how its set now)
Which is really the heart of the question, blowing air out if the small leaks, or sucking in air from those same leaks.

Heat build up is not a problem. In fact its a bit welcome.
Nights here the tent gets to about 50F at its lowest. Then to about 70F ambient.
I have a data logger on the inside tent temp and the ambient outside.

At first with negetive pressure the ambient and tent temps were in lock step.
Now with posivite pressure I am seeing about 10F difference in temp from inside to ambient.
I think ill go back to negative for now and see how it does.
I did not have a speed controller at first and the 435 CFM fan was replacing the air roughly 2 times a minute(5x5x8 ft tent / 435 CFM)
Now i do so i am going to go back and turn the fan down.

Thoughts on that ramble?

Thanks all.

Good job with the Neem oil, I use it too! For some basic info, the ideal temp and humidity in veg are 73F-81F and 50-60%, the ideal temps and humidity for flower are 70-74F and 30-40% imo. Letting the temps reach anything under 65F will stress the plant and make them grow slower. If you want the best CO2 exchange for your plants then go with negative pressure over positive.
The area of your room is 200m^3 so with the 435CFM fan running full speed you will dump the air at least once every 2 minutes, good there. If you ever think about a carbon filter though, know that they work more efficiently with lower fan speeds and they also reduce your air flow/suction by 15% or so, maybe 20%.