I Hope I've Solved My Heat Problems. Please Help Me Determine if I Have Any Flaws

Greetings all. So I've been dealing with some major heat issues on my newly constructed room, and I'm hoping I have solved the problem. However, since I am a noob, I'm hoping you experienced growers can give me a critique to make sure my solution is good. Sorry it's so long-winded, but I want you to have a complete picture.

The setup: Small, insulated outdoor shed with a built-in 5' wide x 3' deep x 5' high insulated box. 400W MH, non-cooled, hanging 12 inches above canopy. Sufficient exhaust outside using modified blower fan sucking air out through 4" ducting, active intake with a modified blower fan sucking air in from outside, and a 14" oscillating fan blowing across canopy. Four plants 11 weeks into veg.

The problem: Despite having decent ventilation and active intake, my temps have been soaring to 100 degrees plus during lights-on and only dropping to a low of about 85 during lights-off. I think I underestimated how warm the shed would be, and I also realized the logic that pulling 95 degree heat during the day was obviously not going to keep the temps low regardless of how good exhaust I have. The plants are just now showing signs of heat stress with some leaf droop, but otherwise they look pretty good to my inexperienced eyes.

The solution: Today, I framed a 6500 btu window unit through the wall of the shed and set it to 78 degrees. I ran some 4" ducting from inside the shed into the box and plan to make that active intake as well. So I now have the box with conditioned air in one intake and outside air in another, with exhaust pulling from the top of the box to the outside. I don't think the AC pulls fresh air, so I plan to leave the outside intake running full time but I plan to cut the exhaust while lights are on and AC running. Then, I have set lights-out for midnight to 6:00 a.m. to take advantage of the cool evenings, so when lights go out, the AC timer will cut off and the exhaust timer will cut on. So in essence, I am only exhausting during lights out, but I'm drawing cool air from the AC and outside air (CO2) from the other intake, and I then exhaust and intake without AC running during lights out.

I really can't do any more big expenditures until the fall when I plan to add a cooltube to my light and probably upgrade my exhaust to an inline.

I think that's it. My main concern I guess is the lack of exhausting during the day. Is this a good plan, or should I exhaust periodically during the day? Any other holes you can see?

I'm not concerned at this point with smell or anything else. I'm just trying to solve this heat issue while not neglecting anything else. Thanks for any insight you can offer.

Dude

I would keep the air circulation going at all times. Fresh air pulled in, and exhausting air out. Just my opinion tho. Lights off, I set it up so lights are off during the hottest part of the day, easier to cool it at night with lights on. Stopping the air flow may give you problems with humidity.

One more detail I just thought of. The box takes up the majority of the space in the small shed and access is through a blind on the front of the box. I placed the AC outside the box only to keep any ambient light away, but if I exhaust full-time, I'm really just exhausting all my AC.

Put the A/C in the shed like you planned. Dump all ideas of running ducting and such. Have your box exhausting into the shed. The A/C will cool that air. Have passive intakes(created from the pull of your exhaust) pulling in cool air from the the shed. Like shown in diagram. As long as your box is sealed somewhat well and most of the air coming into it is coming from the passive intake, you will be good. The temps in the box will be whatever the temp is in the shed. As long as you have a good enough AC unit, this will work, guaranteed.

And dont exhaust out the shed at all, that way you dont exhaust all your cool AC air

TheDudeNextDoor said:

One more detail I just thought of. The box takes up the majority of the space in the small shed and access is through a blind on the front of the box. I placed the AC outside the box only to keep any ambient light away, but if I exhaust full-time, I'm really just exhausting all my AC.

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why not just turn the entire shed into the grow room? lol

hgkdehs said:

Put the A/C in the shed like you planned. Dump all ideas of running ducting and such. Have your box exhausting into the shed. The A/C will cool that air. Have passive intakes(created from the pull of your exhaust) pulling in cool air from the the shed. Like shown in diagram. As long as your box is sealed somewhat well and most of the air coming into it is coming from the passive intake, you will be good. The temps in the box will be whatever the temp is in the shed. As long as you have a good enough AC unit, this will work, guaranteed.

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Really interesting approach. One question, though. I don't have C02, and I'm pretty sure the AC recycles rather than drawing fresh air. Don't I need something bringing air into the shed or box?

Brian11543 said:

why not just turn the entire shed into the grow room? lol

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lol. That's actually a good question. It's not really a traditional squared shed like you're imagining. It's got a unique shape and has some cabinetry in it that limits how I can use the space and how I can make best use of the light. It does make sense, I promise. lol

co2 isn't really needed. it would help. but i doubt the shed is sealed completely everywhere. people grow in houses without co2 all the time with no probs, and it's basically the same thing

i think he means: doesnt he need fresh air for the plants. like if the only air they get is from the shed wont the C02 run out of the air eventually

Okay, I was under the impression that I needed regular air exchange for the health of the plant. Do I really need exhaust then? Imagine a three sided box with the dimensions above. On the fourth side, where I access the box, I have a room-darkening blind that I can lower and raise. The rest of the shed is light tight. It's hard to describe, but it also has some cabinets and small closets. At any rate, now that the shed has AC, I could raise the blind on the box half way or so to keep the light from spilling out too much and just allow the 3.5 sided box to become part of the room. Would I need exhaust at all in this plan?

Another idea if I do need exhaust: I have a row of top cabinets in the low ceiling. These cabinets are actually one long cabinet, about nine feet long by two feet tall running along the top of the wall. I could easily seal them. What if I exhausted on one end into those cabinets and allow the air to simply move down the row of cabinets to the other end where I could mount a length of carbon filter and have the exhaust enter the shed there. Would that work?

Or I could open a hole in the exterior wall there and have it filter outside. I wonder how much that would effect my ambient room temp.

Or I could seal the box with a better access door and do what hg suggests above. Anybody have any thoughts on this?

could u provide some pics so we can get a better idea of what your talking about. having a hard time picturing this mentally

Sorry, man. I started having all kinds of ideas while I was typing. I can try to get some pics tomorrow, but I guess the questions boil down to these:

1. Does having the lower half of one wall in a box dissipate the light too much for plants? My box is 5' x 3' x 5' high. I have one 400W MH/HPS and four plants.
2. With conditioned air, is it absolutely necessary to exhaust if I am not adding CO2?

I guess the idea of exhaust is confusing me. Is it only for heat exchange or is it also for plant health?

TheDudeNextDoor said:

Sorry, man. I started having all kinds of ideas while I was typing. I can try to get some pics tomorrow, but I guess the questions boil down to these:

1. Does having the lower half of one wall in a box dissipate the light too much for plants? My box is 5' x 3' x 5' high. I have one 400W MH/HPS and four plants.
2. With conditioned air, is it absolutely necessary to exhaust if I am not adding CO2?

I guess the idea of exhaust is confusing me. Is it only for heat exchange or is it also for plant health?

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Anybody know the answers to these questions?

you need pretty compleate darkness if thats what your askin. maybe hang a black out curtain loosely over the hole

Big P said:

you need pretty compleate darkness if thats what your askin. maybe hang a black out curtain loosely over the hole

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I have complete darkness in the shed; that's not the issue. What I'm trying to determine is if raising the curtain halfway on the box dissipates the light to a degree that it causes a deficiency to the plants. I have 400 watts for 75 cubic feet.