I am in the process of building my first box. It will consist of two 4'x4'x4' chambers one for veg the other for flowering. I plan to run cfl's, 6 of the 55 watters like in the Dank Tank barrel around the side with 42w spirals up top in each box. My problem and ideas come due to this being in an outbuilding that will run 90-100 degrees in the summer and down to the 30's in the winter. I need some way to maintain constant temps. So I came up with a geothermal idea and want opinions before undertaking it. My idea is to dig a 6ft hole and put about 50ft of polyethlyne pipe in the bottom 2-3 foot, cover it up. Each end would be ran into the outbuilding, one end would be return to the coil in the ground and one end would go to the box where it would run to transmission coolers like this, Al Transmission Engine Oil Cooler 25 row Hi Performance : eBay Motors (item 350332720676 end time Mar-31-10 18:39:04 PDT) that will be in the bottom of the box and air will be drawn in through them by a fan like this, PROCOMP 8 INCH ELECTRIC TRANSMISSION OIL COOLER FAN 8" : eBay Motors (item 330413010371 end time Apr-10-10 10:19:36 PDT) at the top of the box. The system will be filled with engine coolant and circulated by a small pump. The ground is a constant 72 degrees. I have thought about a air recirculation system also that allows fresh air to enter in small amounts as another way to maintain temps. Yes I know I could get an a/c but this way saves money and electricity and should achieve the same result. Ideas, opinions?
a 6ft hole... like 6ft deep? i think you'll need to go a lot deeper than that to reach a temp that's unaffected by the surface temp... but that's a really novel idea, i think it might actually work if done right
6ft deep is all it takes to reach a stable temp year round where I live. In fact it is in most places. Have also thought of doing the same type thing except using a mini fridge with a cooling coil inside that circulates the coolant through it. Would work for the summer but still have to figure something out for the winter.
6' deep is plenty, you will get some cooling effect after 6 inches. You need to be aware of your water table though, and if you are on a septic system make sure you aren't near your leach field.
Also, if you are going to be entering the hole, make sure it is properly sloped on the sides 1:1, or shored up with wood. You can die quickly in a hole like that, happens all the time.
Thanks for the concern Doc. I live on a fairly large farm so a tractor with a front end loader will be doing the digging, be a nice smooth ramp down into the whole. I was in the shop today making room for the box and noticed a 15.5 gal aluminum beer keg. I got to thinking that that this may make an in-ground tank and be better than the coil of pipe/tubing. Aluminum dissipates heat great, plus it would allow more cooling time before having to return to the box. Return line in the top with a pickup line about 4 inches off the bottom. Thoughts?
The best results you will get is from copper tubing coiled at the bottom. The "tank" wont allow the water constant contact with the cooling metal like a coil will. Copper is expensive, so aluminum or some other good conductor would work well also.
For home geothermal in homes they use pipe like this, Shop Aqua-Jet 1-1/2" x 100' 100 PSI Polyethylene Pipe at Lowes.com, I agree that copper or aluminum would work best as far as heat transfer but there is also the problem from corrosion which would cause eventual pin holes and leaks in tubing.