My Setup - Heat issue questions (WIP)

[Strapped]

Here's a pic of my closet grow I'm in the process of building. I'll be using the whole thing to flower in.

I've got a 400w hps running in there, with a 270cfm fan/scrubber. Temps right now are sitting at about 83F with an ambient of 66F. Room dimensions are 66"x26"x26" with 40"x26"x26" for the grow space.

I'd like to get my temps down about 10 degrees. I already ordered an air tight hood (20.5x24x8) to get some air cooling on the light, but there's no way I can do a 2 stage cooling system in that small space. As it is, when my hood arrives I'll need to use a lot of 90 degree curves to get the thing to fit.

I'm planning to hook everything up like Scrubber = fan = hood = vent. Is 10 degrees cooler too much to hope for with this setup?

 

[Scrogerman]

It'll work, why not, as long as your fans big enough(should be). You might even wanna a fan speed controller?
G'Luck man!

 

[GanjaPharma]

you dont need an air cooled hood, you need to treat that entire lower chamber as one giant hood. you MUST bring cool air in (down low, passive intake)and have that fan sucking through your scrubber and out out the top of the chamber. also, a 4" hole in the top of the upper chamber with a little inline duct fan will pull that hot (shouldnt be stinky) air out of the ballast chamber. that alone should buy you 5 degrees.

i ran lots of (vert and flat) cabinet grows, about 15 years ago, and i learned it was more about a good airflow design than raw fan power. where is your cool outside air entering the lower chamber?

 

[Strapped]

thanks bro! I've got a temp controller, but it doesn't adjust speed, it just turns on if the temp gets higher than what you set it to (oversight on my part). I was a little disheartened because I thought I did good research into the setup, as you said the fan should be big enough. So I'm worried there may be an underlying issue... I'll post back when I test temps with the cooltube.

 

[intotheunknown]

a sealed hood is definitely going to help you out here.
and assuming you have the temp controller hooked up, i would ditch it and run the fan constantly.

 

[Strapped]

GanjaPharma, I've got a 8" square passive intake at the bottom, and the shelf that the ballast is resting on has about a 2 inch gap running all around the front and right sides of it, my exhaust is a 6 inch duct running out the back at the top. Do you think that the cool air might not be directed well enough? I was a little concerned that the cool air would just run from the intake at the front up the gap in the shelf, bypassing most of the grow area.

I did temp tests on the ballast area and it is 77 degrees up there. Would the vent in the top with the fan still make a big difference? It took me like 3 hours to seal the ceiling/ closet walls with foam board and duct tape lol But if it would give me 5 degrees I'd gladly cut a hole up there.

 

[Strapped]

lol, I have been checking my temps all day and have been pretty pissed because I went down there a few times and my thermometer was reading in the 90s. So I got another thermometer, hooked it up to the external probe and what do you know, the thermometer sitting directly under the light was reading 90, while the probe for the other thermometer sitting at the same level is reading 78...

Which one should I trust? Anybody have tips for getting an accurate temperature in there? It doesn't feel like 90 degrees in there... but I don't know how much I can trust that estimate.

 

[Crusader Rabbit]

The thermometers in your cab are absorbing heat by two different process. One way is from air molecules colliding with the surface of the thermometer/probe and exchanging heat. The other is by radiant energy (photons) from the light striking the surface of the thermometer/probe. The thermometer directly under the light is extra warm because it's absorbing a lot of radiant energy. To get the actual air temperature you can't have the thermometer/probe sitting in direct light.

 

[Strapped]

thanks dude, I remember seeing that a lot, but it didn't make sense until I tried it lol. I could never figure out how people got their thermometers in a grow space without being in direct light. any pointers? I have to wear sunglasses when I'm working down there or else when I close the door I'm blind for a few seconds.

 

[echo_chamber]

Every 90degree angled turn of your flexible ducting is reducing your output by 20% or so. Use sheet metal 90degree elbow's for any turns.

 

[Strapped]

thanks for the tip echo_chamber, I really hope I'll be able to fit them in there. I have about 26" square for my grow chamber and the reflector that I got is 20.5" x 24". About how big do the sheet metal elbows run typically?

 

[Crusader Rabbit]

thanks dude, I remember seeing that a lot, but it didn't make sense until I tried it lol. I could never figure out how people got their thermometers in a grow space without being in direct light. any pointers? I have to wear sunglasses when I'm working down there or else when I close the door I'm blind for a few seconds.

My thermometer is an indoor/outdoor remote transmitter with the receiver sitting next to my desk so that I can keep an eye on temps in the grow room. I have it right now leaning against the shady side of a plant container. Right now I'm more worried about soil temps.

Meteorological weather stations sit out in the sun and are typically painted white to minimize the absorption of radiant energy. The thermometer is contained inside this ventilated white box. You could make a ventilated white container for the thermometer to contain the thermometer/probe. Even finding a way to shade it with a piece of white cardboard should do the trick. Just make sure the thermometer/probe is measuring air temp, and not the temperature of a surface which is absorbing light. As an example, the black plastic tubs my plants sit in get pretty warm where the light shines. Placing my thermometer transmitter on this warm plastic surface would give me the plastic tub's temperature instead of the air temp. Good luck with your grow!

 

[Strapped]

thanks crusader rabbit. I can't wait to get growing. I'm beginning to think the temps I'm getting right now will be decent, but I'm still going to try to cool things down. It is a good thing that I tried to go overkill with the ventilation in the first place, or I'd be very unhappy.

 

[Strapped]

My ac hood came and I hooked it up. My temps are now a pretty steady 77 degrees after running it for about an hour with the door closed (ambient 68). When I open the door temps drop almost immediately to about 75 so I'm pretty sure I've got some accurate readings and adequate ventilation.

As I mentioned before, I had to put roughly 1 180 degree turn, and 2 90 degree turns in my vents, so I'm sure temps would be better if I had the space... but from what I've been reading on here, I'm lucky to get 77 with a 400 in a space that small anyway, so I'm pretty pleased with the results. Luckily the pressure I've got is enough to push it around. I have a backdraft damper installed, and I'm hearing it open every time I turn the fan on.

An unintended bonus: The exhaust for my grow goes directly into my house's central air. Before, when the fan was running you could hear air moving if you were sitting sitting in a very well traveled area of the house, now you can't.

 

[Scrogerman]

I usually double the size of my passive intake if not tripple it. you got a 6" exhaust & only 8" passive intake, you need at least 12" of passive intake area imo, id go a little more. theres prolly too much negative pressure, id also consider boreing out some 4" holes in the board that the fan/ballast etc is sitting on, that help equalise flow a bit, i wouldnt be happy with that 2" myself. just a couple of things i think may help!

 

[Strapped]

I usually double the size of my passive intake if not tripple it. you got a 6" exhaust & only 8" passive intake, you need at least 12" of passive intake area imo, id go a little more. theres prolly too much negative pressure, id also consider boreing out some 4" holes in the board that the fan/ballast etc is sitting on, that help equalise flow a bit, i wouldnt be happy with that 2" myself. just a couple of things i think may help!

Scrogerman, I'm not totally sure on this, but I was hoping I would be good since my intake is 8" square (64" area), and a 6" circular vent is a little more than 28" of area.

When I put in the ac hood I had to cut 2 huge holes in the shelf, so I am sure that helped too! Thank you for the tips, I am glad we are thinking along the same lines

This is what everything looks like now... without the light being on even!

 

[Scrogerman]

ahh, well thats different, sounds like you got plenty of intake then. Ive been considering Co2 & going sealed completely. rule of thumb is double/triple up intake area to whatever your output is, ie- 6" output, 12" intake(minimum), i'd go 3 x's myself, so 3 x 6" intake duct holes. looks like your ready for some plants then?

G'Luck man!

 

[Strapped]

Dude, I'm chomping at the bit wanting to get some plants in there I have to go out of town for almost a month in May though so I will be waiting until I get back from that trip most likely. This is my 1st grow so I want to be able to do it right, with plenty of pics and (hopefully) feedback from our awesome members.

Should give me just enough time to make sure I can procure some badass genetics in the mean time.

Thanks man, I really appreciate all your input.