Cooling and negative pressure advise needed

Discussion in 'Grow Room Design & Setup' started by HansBud, Jan 3, 2017.


    HansBud Well-Known Member

    how's it going RIU with spring time around the corner I just wanna make sure my new room will continue to be cooled and smell proof

    First off I built a room out of plywood and insulated it with pink insulation batts. The room I built is inside of a non insulated concrete barn/garage. Inside the room I built I set up my grow tent because I could not obtain negative pressure in the room alone and needed to contain the smell so my tent worked perfect in regards to negative pressure working with my carbon scrubbers

    Now for the details

    The room I built is 10 feet long by 7 feet wide and 8 feet tall everything is insulated the floors wall and ceiling the tent I have inside that room is 5x5x7
    The temperatures
    This is where it gets weird as I kind of have to go along with mother nature
    Inside the room I built the temps stays at 55f on by the floor and about 62f by the ceiling which is perfect as the tent stays at 80f at the top of the canopy and 73-75f by the floor.
    For my exhaust I have two 200cfm inline fans at the top of the tent each on opposite sides and each with a 200cfm phresh carbon filterand they exhaust into the room I built and also a medium sized fan just to push air around
    For the vents I have two holes open about half way up the tent on one wall (shown in picture) that pull in a good amount of air to cool the tent
    The lights I have are 4 Mars hydro 300s on 24/7 as I run autos

    Now my concerns are with spring right around the corner the temps will be rising right now it's around 20'sf but in summer it'll be 80-90f.

    This where my main questions are

    OK so right now everything works fine which means having the room.i built at 55f, this is a problem because there is no way I can keep it that cool during the summer I have a 5000 BTU AC unit I plan on putting in the room I built ( I have a piece cut out of the wall for the AC unit to mount into) but I know the AC alone won't cut it I can probably get it to 65 at the lowest.

    So I believe I have 2 options

    Option 1- instead of exhausting into the room I built I could exhaust into the barn that way the heat from the lights wont be heating up the room I built. My only concern with this way is that it still might not be enough to cool the tent and won't know until it's done

    Option 2- just say screw it and take the tent out if the room I built and purchase an 800cfm fan and a carbon filter to go with it and cut a hole in the room I built and exhaust that into the barn. With this option I don't know if that will be enough cfms to create negative pressure for the room and if it is if it will just suck all the cold air from the AC out and not cool it effectively

    Sorry for such a long post I just wanted to try and detail it as much as possible I also apologize for the absence of pictures as I am at work and will get some uploaded in a couple of hours

    I am open to any answers and gladly appreciate your input!!

    Samno Active Member

    As you know, the problem with the plywood and pink foam is that it insulates very well, I would personally exhaust it into the barn but like you said you won't know how well it works till its done

    The_Enthusiast Active Member

    Just interested, how can you have two little "CFM" to obtain negative pressure? Is your garage really like a train terminal?
    HansBud likes this.
    Budley Doright

    Budley Doright Well-Known Member

    The room you built should have had a plastic vapour barrier after the pink, this would have made the room air tight and then control would be easier. Also without the barrier there may be times when you'll create moisture in the wall cavity, then mould. Covering/sealing the interior of the room with a reflective barrier will help although not perfect. I have never used a tent but it seems to me that dealing with the single bigger room would be easier for climate control, and maybe use the tent as a veg room for photo's if you ever go there. I am able to shut down in the warm months and head outdoors or I would need a cooling unit and that's not feasible, also 400 CFM should be enough to creat a negative in the bigger room even if not sealed so that is kind of confusing. Just a thought but I used a reflective bubble wrap type material to cover the interior of my shed (8x8x8 ) and pretty cheap as well.
    Last edited: Jan 9, 2017
    HansBud, coreywebster and Moflow like this.

    Moflow Well-Known Member

    My mate uses a 5x5 ft tent in a bedroom with 4 x 600 watt 400v hps .
    He uses 2 x 200mm box fans for extraction , no cool tubes and gets good yeilds.
    He's hydro so chiller keeps his water at perfect temperature and helps with cooling
    30 - 31 oC in tent summer.
    Those mars lights run quite warm so I believe you are looking at cob options?
    You could also retrofit the Mars lights with Cobs as they eventually burn out or take a look at the quantum boards as well.
    The mars drivers should be around 600ma ish and 110 volts - ish so you only need to buy the cobs to fit.
    Citizen CLU48 1212 cobs are great value , around £9 .... 13$
    3 of 1212 x 36 volt nominal chips on chinee driver for 50% efficient light at 600ma
    Or 3 expensive 36v cree cxb3590s on same driver for a 64% efficient light at 600ma.
    Or less expensive 3070s for good efficiency too.
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    HansBud Well-Known Member

    Almost haha it's about 2500 sqft
    I can still go back plastic it off and might do that in a couple days for now I'll just have to go with mother nature, I've figured for now when it gets warm enough to not use the heater I have I'll throw the AC in and start monitoring temps and such and go from there, if starts getting to warm I'll start venting the hot air from the tent into the barn instead of into the room I built. If that still doesn't work I'll get the tent out and start from there and get it figured out. The cubic feet in the room I built is 560 so I figure I need a fan that will move that or more as when I didn't have the tent in the room.i built I had 2 200 cfm fans with carbon filters and they just didn't cut it and the whole neighborhood reeked!!!

    HansBud Well-Known Member

    That was my plan to start a cob build so I can have cooler lights cause you are right the Mars hydros run pretty warm almost as a warm as CFL, they work great for growing but the efficiency just isn't there, now my debate is should I wait until my lights burn out or just order some heatsinks and get started, my idea of my own cob build would be getting the typical 5.886 heatsink from heatsink USA and have it 36" long. But I also like the size of the Mars hydro as you can move them around more freely a bar 36" would be little bit more of a pain I could imagine. Also what color spectrum would you recommend as I run autos only and any links to where I can buy some citizens?

    coreywebster Well-Known Member

    I read your post when you first posted but got distracted and didn't reply.
    It seems to me that your going to be extracting your hot air from tent and into an outer room and were then hoping to cool that outer room with ac. But I would imagine you will soon have a room which has no co2 content and thus your plants will struggle to grow. That's if I have understood your set up. Recycling the same air from the outer room?

    I would extract straight out into the barn. Get yourself some oversized good quality filters if you have had a problem with smell.
    regarding the pressure, as long as your extracting you should have negative pressure. The main thing is you don't have positive pressure. Your outer room will still be a good insulator from the heat/cold. You will need a passive intake from the barn also.
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    coreywebster Well-Known Member

    Citizens from northern grow lights or cobkits who are both on RIU. 3500k a great all round spectrum.
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    HansBud Well-Known Member

    Awesome thank you for the help!! As far as the co2 goes I'm too too worried about that as I have had this setup like this for a couple grows and everything was fine. But yes you are right I vent the hot air out if the tent into the smaller room the tent is in, the air then gets cooled and goes back into the tent that's what i figure might happen if I install my AC ( the AC will cool the hot air coming out of the tent and then the air goes back into the tent eventually cooling it all down, I feel the AC will have to work harder if I vent the hot air into the barn as now more hotter air from the barn will try to seep back into the smaller room.)
    Here's some pics as they would prolly help

    Here's the smaller room I built

    Here's to the left when you open the door

    Here's to the right

    Here's in front of my tent
    coreywebster likes this.

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