Apologies in advance for the wordiness of this next post. I'm keen to share this idea, as I'm still not sure if it will work.
Remember when I said that everything you do when setting up a tent for CO2 supplementation must be done with that in mind? Well heat control is an area which exemplifies this idea, and has left many people smarter than myself at a complete loss.
For the tent/closet grower, CO2 supplementation means that the environment inside my small space can't really interact much with the outside space, otherwise I'll vent all my CO2 and waste it. In other words, when the CO2 is running, I can't turn my tent vent fan on to drain the heat/bring in cool air. If I'm running anything more than a few CFLs for lighting, the temperature will rapidly rise under these circumstances. With my 250W MH/cool tube running, and the 180W LED turned on, my 22 cubic foot tent exceeds 100F in under 10 minutes. This happens when the ambient air in the closet is between 73-75 F. So as you can imagine, cooling the air inside the tent down is extremely important. Doing so without mixing it with the air outside the tent and thus losing the supplemental CO2, is tricky to say the least.
So this is my idea for getting around this problem. For most of you growing without CO2, this will be akin to attacking an ant hill with nuclear weapons. BOOOM! For gadget nerds like myself, and for those who have heat issues due to powerful HIDs in a small space, or who plan to use CO2 supplementation, maybe you can refine this idea and use it to cool your space. This isn't a guide per-se, so forgive me if it's not entirely clear to some people. Most of you should be able to figure out the concept from the description though, and then build something similar, but more tailored specifically for your needs. Feel free to ask for clarification on any of this stuff!
What this essentially is, is a tent sized air conditioner. It uses a 176W peltier chip, which is a ceramic 40mmX40mm "chip" that gets really cold on one side, and really hot on the other when electricity is passed through it. If I can effectively cool the hot side of the chip, then the cold side should be sufficient to cool the tent by 10-15 F. Easier said than done.
To cool the peltier, I have chosen to use a closed loop water cooling system. I'll make a reservoir out of a 1L stainless steel water bottle, and place it in the bottom of the DWC reservoir. Because the water in the DWC res is chilled to 67F by a 1/4Hp chiller, it will remove heat from the water cooling system reservoir while remaining at a constant temperature. This essentially amounts to transferring the heat removed from the the air in the tent to the chiller, so it will cause the chiller to run more often, however I am hoping it's not by much (as mentioned, my tent is 22 cubic feet). There is also an option to run the water cooling line through a stainless steel hose before it leaves the res, in order to shed more heat.
Remember the cooling system is closed loop, so I have to make sure it's properly sealed so that the cooling water doesn't leak out into the res.
This pic is the best I can do to show the three main components - heat sink, peltier, and water block. The peltier is only visible as a thin 'oreo filling' of the other two components. You can see the red and black wires emerging from it.
So the idea is to sandwich the peltier chip between a water block and a heat sink. The heat sink is an off the shelf model and is made by Thermaltake. The name of it is "Frio" and it's geared towards computer tweakers. I picked this one because it comes complete with two fans to blow air over the metal surface of the heat sink. The water block is visible at the top of the unit, where the two hose connectors are located. It allows me to pass cold water along the hot side of the chip, thus cooling it. The water block is the HF Supreme, by EK.
Because the heat sink and water block are designed for use with computer chips, they both have the same size attachment points, so they attach together easily. And, they just so happen to be perfectly sized for the peltier! I just used a little thermal paste on each side of the peltier, and then screwed the water block mounting points to the heat sink mounting points with the peltier sandwiched tightly in the middle. The trick is to make DOUBLE sure that the cold side of the peltier is being applied to the heat sink - this means I had to run some power through the peltier first.
Speaking of power, if you make one of these, you will need a power supply for the peltier. A computer power supply, plugged into the 12VDC line would work, as long as it provides at least 10A (for my 176W chip - consult the power requirements of your own chip before connecting it to a power supply). I opted for a dedicated laboratory-type variable power supply. This allows me to lower the power to the peltier, thus reducing the cooling effect. This model can run up to 10A, and up to 20V. I'm hoping to only use it at 50% power at most, so hopefully it will save some power. You definitely don't need one of these to make this work, but if you're interested, I picked mine up off eBay for $150.
Here's a picture of the almost complete setup required to run this thing
From left to right, there is the water pump for the closed loop water cooling system, a fan controller (intended for use in a computer) to run the two fans on the heat sink, the A/C unit itself, and its power supply. Missing is the 1L stainless steel water bottle.
The fans on the heat sink simply plug into the back of the fan controller. I took a 13V, 0.500mA power supply which I bought at a local hardware store, spliced the end off, and connected it to a 4 pin type computer power connector. It just plugs directly into the back of the fan controller, which then allows you to power and control the speed of the two heat sink fans separately.
So that's it. It's just a prototype, and won't get fired up until the 250W MH comes on well into the veg phase. The theory seems sound from what I can tell, but I cannot attest to its functionality. I'll keep you posted. In the mean time, I'd love to hear the thoughts as to whether or not this thing could work. Is there anything it's missing in order to make it better?
Bob