Question on using a Peltier/TEC device for air temperature control - Help please. Answered
I want to have some control over the temperature inside the Orchidium I'm designing and I thought it might be cool :) to use a Peltier Device (device aka module) (Peltier aka TEC or Thermoelectric Cooler). I find I need a lot of help! (Please!) Alright, this isn't a completed Instructable, it's a plea for help, and maybe if the subjects lie in some of your fields of knowledge then we can all enjoy and learn from it. So, the Orchidium I'm designing is an acrylic case 24"W x 18"D x 30"High. It's to grow species orchids indoors in a microclimate, with LED grow lights, proper humidity, air movement and temperature control. (Of course, other critters would like the case, too: poison dart frogs, newts, carniverous plants, etc.. But I'm going to call it the Orchidium.) I've got it all pretty well planned out so that it can be built for a very reasonable price (yes, including the LEDs) and still be aesthetically pleasing and real purdy, too. All planned out EXCEPT FOR THE TEMPERATURE CONTROL. I was looking for some way to cool my case and I stumbled across Peltier devices in eBay. They are CHEAP, costing about $5 or more, depending on the Wattage, etc. The eBay sellers intimated that all you have to do is plug them in and the device gets ice cold. Later, with diligent web-study I learned that actually ONE SIDE of the peltier gets cold, while the other side gets hot. Also, you MUST attach a heat sink and fan to both (?) sides of the peltier. Also, that these devices are not ready to be plugged in; you must attach a DC power supply to them. Oh, another trick that these miraculous devices do is reverse their hot & cold sides when you reverse the polarity of their juice. Ideally, I would like a Peltier device with heatsinks, fans, a thermostat and a DC wall transformer attached... the Peltier/heatsinks/fans would measure about 2" x 2" x 6" and would be mounted in the sidewall of the Orchidium. When the temperature is 65-85F degrees the orchids are happy and the device is Off. But when the thermostat senses the internal temp going over 85F it turns on the Peltier, cold side inside, and so the inside of the case doesn't go up to 90-95F like mine does now; it cools the case a little. Conversely, for someone with chilly orchids or sneezing newts the thermostat would switch the Peltier to hot-side-in to heat the Orchidium a bit. The retail cost for us to buy a Peltier device, 2 heatsinks w/fans and a DC transformer is cheap... roughly $30. The thermostat might be cheap, but I don't know enough about what's needed. If it's too expensive then the Orchidium can do without it. I was hoping I could find an off-the-shelf Orchidium cooler/heater. No such luck. These miraculous Peltier devices are still practically undiscovered -- relatively speaking. People want to use them to cool their computer chips but are hampered by condensation; my orchids welcome condensation. Pathetically, it seems the most common use for Peltiers now is to cool/heat the little boxes on your car seat... they plug into your cigarette lighter and keep your 6-pack cold. Come on! You folks at Instructables can surely help me figure out how to best make an Orchidium cooler with this barely-discovered and poorly-utilized device. I started out a few weeks ago writing to many of the Peltier manufacturers around the world in hopes they might help me in choosing which of their modules I might purchase for my Orchidium. None of them was any help. They wanted to know how many million Orchidiums I planned per year. They told me my basic plan was hopeless or inefficient cost-wise. A Swedish company wanted $800. An American company wanted $500. Some other company wanted $5,000 to $8,000. I wrote back and said I could get a Peltier on eBay for five bucks. The Swedes snottily claimed that their Peltiers were very high quality. No. No way is any svensker Peltier $795 better than ANY other Peltier in the known universe. They both get cold and grow ice crystals on one side. I just need to cool the case A LITTLE BIT, like from 90 to 80 degrees Fahrenheit. I am not trying to make a refrigerator or freezer. The case (Orchidium) is large, at about 7.5 cubic feet, and there is practically no insulation. Acrylic provides a little insulation, that's all. The temp of the interior of the case is derived from the ambient room temperature of your house... and the lights... which is why I designed it with LEDs. There is a constantly-operating muffin fan inside the case to provide air movement for the plants, but it does not provide any evaporative cooling since it's a closed case. So, first off what size Peltier do you recommend... do you think a 40 Watt would be enough, or what? Next, the placement. I envision the Peltier device mounted vertically through a hole in the side of the case. It might be a plan to mount it in the ceiling, but remember that the LEDs take up most of the ceiling. Next, the heatsinks. I confess I'm not totally clear on this, but I "think" that 2 heatsinks-with-fans may be needed, with one sticking out the outside and the other inside the case. I went ahead and got 2 heatsink/fans from Newegg for supercheap ($1 after rebate), but they aren't really what I want. They're actually shaped to fit some AMD chip. What I think I need is a copper heatsink with a flat bottom a little bigger than the Peltier, and fins... and a heatsink fan attached... and some way to attach it to the Peltier, and through the case to the other heatsink. See? Simple... well it should be but I can find nothing. Next, the power supply. I know it has to be DC, but I don't know which brick to get. I did find a bunch of DC or AC Wall Transformers for sale at alltronics... around $10 or so. All that stuff would be enough... at least to test the cooling power. But if we want to go whole hog then the icing on the cake would be thermostatic control of the Peltier. Well, I throw that out in case one of you is sharp in that field.