Design help needed .... Mathmatical formula?

So I am in the process of building my own 'low profile' grow cab. I call it this and not a stealth cab because I'm realistic in knowing I won't be able to get it 100% light, heat, smell, and noise proof. As close to possible is all that I am looking for, put the cab in my closet where no one will look in the first place and as long as it isn't shining light out of the cracks, buzzing like a hornets nest and radiating heat like a furnace and I think I should be ok.

I took a 16.5" x 15.6" x 39.4" chest of drawers from walmart and gutted it, turning all of the five drawer faces into one cabinet door. Then using calk, foam, weather stripping, and 'blackout' fabric I made it 99% lightproof. After installing 3 'tot lock' magnetic 'invisible' locks, it now looks like a dresser, doesn't leak light (a few pin hole spots), and if you pull on the drawers the thing doesn't move. I installed two passive vents on the bottom to come out the back, moving at 90 degree angles to allow for free air flow with no light leaks. Also, as of right now I have a 6" Inline 449 CFM Vortex fan on it's way. I plan on using a dimmer to dial down the cfm a little to cut down on noise. Once flowering begins I'll get a carbon scrubber, but not a priority right now.

So now that you know the situation I'm in, we can get to the dillema: lighting and heat. I put in two 27 watt CFLs to check for light leaks, and once it passed threw a 70 watt HPS bulb in there to check heat with no moving air. It got up to 91 degrees F. I know that I need to get either 150 watt HPS or a 200 Watt HPS, or something lower and suppliment with CFLs if I want to make the 10,000 lumens per square foot goal, but I don't want to buy a 200 watt system and spend the capital on it only to find out that it's running too hot. Likewise, I don't want to spend the capital on a 100 watt hps only to find out that I could go higher, and then have to buy it later.

So, does anyone know some form of a mathmatical formula that I can use to figure out what I need to know? for instance, HPS bulbs put of x amount of heat per watt, or CFLs put off X amount of heat per watt? Or with 300 CFM and an outside temp of 73 F I need to keep the heat below Y? I'm generally a math and science oriented individual, so I figured if I knew the outside temp, the desired inside temp, the CFM, and the amount of heat that the different types of bulbs produce I could solve to find out the maximum amount of wattage I can use and of what type. I know that this is not exactly a science, and alot of it is done through experience, but any help would really work.

Oh, and I don't have an air cooled hood or anything, the Vortex would be exchanging the air for the entire cab. I don't even think it would be large enough of a dresser for one of those cooled hoods. Thanks guys, I appreciate the help.

First off i don't think a dimmer is a good idea with that fan. I believe dimmers lower voltage, speed controllers however [I Think Can anyone confirm] actually interrupt the power flow in cycles, kinda turns the steady flow of power into an adjustable flow of pulses. but all the pulses are still 120v current. However nearly as cheap as a dimmer is a "router speed controller" from harbor freight. And i believe it does the same as a fan speed controller, but for $10 instead of $40. Also you are right air cooled hoods tend to be quite large but a cool tube can be very small, diy would probably be best for your cab, get a bake a round off ebay there less then 4" in diameter.
Good luck

Cool tubes are still too big, as I only have 16" total length to deal with. I remember the DIY cool tube out of the pyrex bread tube on the old overgrow.com, so that's possible. But even with the cool tube, is there any way I can calculate the heat that it's going to put off in relation to the wattage that I'm going to use? I'm just looking for something a little more concrete than "get a light and put it in there and see". I don't mind spending the money on a 200 watt HPS or a 250 watt HPS/MH switchable, but I would hate to spend the money, find out it burns up more heat than I can deal with and have to buy something smaller.

You'd have to contact the manufacturer of the light in question and ask them for information on it's heat output. Then you'd have to get some kind of HVAC freak to help you calculate heat buildup vs. ventilation. You might be able to find those formulae on HVAC forums, I've seen them before, but they're rather confusing without someone to explain them to you. Of course, you need precise measurements for those calculations, both of ventilation and heat output.....ultimately, buying the light you want to use and throwing it in there is probably going to be cheaper than buying instruments to measure the air pressure in your cab, in the ducts, etc.

i agree with Maccabee, i understand the desire to be sure, to work everything out to numbers, black and white,yes or no. But for our work it's just not practical, the only hydro farmers with resources like that that i can think of would be nasa. I bet they go through a similar process but all we can do for the most part is envy them. Like i said i'm sure it can be done but that doesn't mean it's practical. Good luck, and if by some chance you do work it out please share with the group how you did it. Thanks and good luck

If you move the air a couple of times a minute(doable in that space) and ensure that the intake air is cool you should be able to keep heat under control i.e.85 or less. I just checked the temp on a 400 watt MH, 95 degrees 1" from bulb, if that's any help.

All of it helps. Thanks guys. I think I'm going to try and do a few measurements. Taking a cardboard box and measuring the regular temp, then the temp inside with one CFL with 23 watts, then with two of them, and so forth. Then graphing the temp change, then try doing the same thing with some air moving. Graphing the results. Then hopefully I can do this with the 70 w hps that I already have and be able to make rough assumptions based on the two previous graphs. Seems somewhat over simplified thinking, and I probably won't get the precise answers I was looking for, but hopefully it will help enough to get close to an answer.