This is the same problem the smaller SuperClosets have: PC style fans just won't do the job unless you can keep your room temps super cold. Like, if you live in a chilly climate and have a garage that's routinely 50f, they work great.
Ultimately I think you may have little choice but to upgrade to a real exhaust fan. Unfortunately, I think you'd have to have the fan outside the box to prevent it from eating up an unacceptable amount of your box's headroom. Which also means reduced stealth.
For my own in-progress armoire design, I was originally inspired by the Superclosets but decided to design my own, mainly due to the SC's design flaws concerning heat.
There are some very nice 4" and 6" fans that are designed to be as quiet as it's possible for something blowing air to be. They're a bit spendy though. I was originally thinking about a 4" Soler & Palau TD-100x. Most fans require you to do your own electrical wiring, but this model is available in a pre-wired version for $127. But, it's only 140 cfm, and after seeing the issues you're still having with 110 cfm and what BID told me about his set up, I may go to a 6" Vortex S-Line ultra quiet 347 cfm instead.
These things are like the cadillac of inline fans! LOL SO much good design behind them. But super spendy at $188. But considering the amount of extra power and features you get for not all that much more expense, I'm realizing that the Vortex is really the way to go. Throw a speed controller on it, and it should handle anything you throw at it.
Good call on the humidifier, BTW. That's another problem with small spaces - you're pulling so much air through it to keep the temps down that you're drying out the space! I'm planning to add an RH monitor to turn the humidifier on and off and maintain total control over the environment.
Another thing I've been thinking about is I've designed my intake in a way that will allow me to put those reuseable blue freezer packs under it as a way to cool the incoming air. I thought that might make a good emergency fallback if everything else fails. LOL
The other conclusion I eventually came to with my design is that you need as much headroom as possible or you will eventually just regret it. I changed my design from a multi-chamber to one big open space and I feel much better about it. Especially using LEDs, you need to maintain at least 14-16 inches from your plants or the PAR will nuke them. I decided that I'd rather be able to grow bigger plants and keep the light at a safe distance than have painfully cramped grow/veg chambers that force me to grow tiny plants.
Plus I'm designing mine with a SCROG frame option to give me even more control to maximize the confined space. Though at this point I'm fascinated by Light Addict's Flux technique and may do that instead. Or maybe both? LOL
But that's just my own personal thinking for whatever it's worth. Just sharing because we're doing pretty much the same thing and I've already gone down a bunch of dead-end design paths.
I've been lurking on forums doing research for years, but the biggest source of info was seeing people's lamentations about the shortcomings of the smaller SuperClosets and figuring out how I could resolve them. In the end the key issues seemed to be 1. heat buildup/air flow 2. odor control 3. headroom. Design around those issues, and all the rest will fall into place. Or so it seems in my Google Sketchup model...
Sry about writing a novel! LOL And now back to your regularly scheduled thread, already in progress...
