O/T Really neat new technology

Some of you may have heard about this, as there is a video on YT called "Citrus in the Snow". Check it out. But as well as his system works, it has been greatly improved upon by others.

It's a very inexpensive way to heat a greenhouse. It's Solar-Geo.

Dig a hole, the deeper the better. Most parts of the world at 8 feet deep are around 52 degrees. Dig it square, or rectangular, then cover with 4 or 6 mil plastic, across bottom and up the sides. Then install 6 inches of just regular old white Styrofoam, actually called expanded polystyrene I believe. Now you run pipe down one side, across the bottom, and back up the other side. They should be a foot apart and at least 2 layers, 3 or 4 is better. You terminate that pipe in boxes, (pipe can be schedule 40 or even drainage tile, if your water table isn't too high), at either end, then stick a duct fan on top of the box on one side, on the other side you run 6 or 8 inch pipe from the box up to the ceiling to make a plenum box. Turn on the fan and it pulls warmest air from the top of the greenhouse down through the ground, warming it, and out the fan into the greenhouse. By lining the box with Styrofoam you can actually warm the box way above 52 degrees. The fan I'm using are 24volt low draw, less than a dollar a day to run. I can keep the greenhouse at least 25 degrees warmer than outside temps. It's perfect for citrus as those trees don't mind going down near freezing, unlike some fruits and veggies. My greenhouse is just 20 x 20, but I have detailed plans for a 30 x 100 greenhouse. Could put a lot f dwarf orange, lemon, lime, clementine, avocado, etc. in there, and heat it for almost nothing, Compared to the big commercial greenhouses that spend 20K a month pumping heat into their's. The fans need to be able to turn the air over within a few minutes. Also, you line the back of the greenhouse with 6 inches of foam too. Mine is a just a pvc hoophouse situated so the ends are east and west, and what you would normally think of as sides are facing N and S. The north side gets covered in Styrofoam, as no growing rays come from that direction, and heat slides up the back wall and into the plenum. I'm using 2 ply plastic cover and they make fans now to pump air in between, that helps a lot too. So basically you keep it close to air tight and just recirculate the air. During the day the sun heats it up inside, and you pump that heat down into the ground. At night it pulls it out and warms. At 90 degrees in the greenhouse on a sunny day the air coming out of the fans is 50 something that's how much heat is staying in the ground. I'm not a big green guy at all. But this is really neat technology. The earth in my box is at 60 degrees. With outside temps at 20 degrees I can keep it at 50+ inside. Just moving air. I'll post some pics if anyone's interested.

Earth heat is really good to capitalize on. Digging a rectangular hole 8' deep is Ok but requires structural reinforcement to keep it from collapsing in is Dangerous. Your idea would work better if the insulation was placed uust under the surface of the ground below the green house floor, and to 10 feet to the outside of the green house. Putting the pipes in direct contact with the ground, Deep in trenches made with a narrow back hoe, then covering them with the material removed, conducts much more heat into the soil, and back out of it. This is not a flame, I teach this material in my alternate energy classes and Leed certification instruction. You never indicated weather the resulting hole was filled back up. Jim

I've seen systems where houses are helped with heating and cooling by pulling water out of the bottom of a deep pond with pretty much the same principle as what you describe.

That's what we're doing Jim, I think. Yes, the hole is filled back in. So essentially it is an 18 foot tall styrofoam box buried in the ground to 8 feet with 10 feet above ground and just one side, (south facing) open to receive sunlight. Both end walls are insulated as well. The key is not letting any heat out once it gets in, but you know that.

That little factoid I sent you the other day about lack of sun here made me nervous, as sun is the only heat source and we get so little. So I built a little one as a prototype to see if it would work. It woks. Although we'll see how well next winter. I finished it about 6 weeks ago, so days are longer and it's warmer than Jan and Feb. Will be interesting to see how well it works in the short days with a week of no sun. If you watch that Citrus in the snow video, he just trenched outside his greenhouse and threw about 8 pipes down in there and covered them up, not very efficient. Plus he was drawing air from outside, and it still worked pretty well. A group called Greencube Research picked up on the idea and brought in thermal engineers to make a new design, and it is much more efficient. The earth in my box is up to 60 degrees. Run the fans all night and it is still blowing 60 degrees in the morning. It's pretty darned amazing.

So when you consider all the problems they're having in Florida with the green rot or whatever it's called, then the crop they do get sits in warehouses and finally gets shiped 1500 miles up north, that's some old fruit that cost a ton to ship and has been sprayed about 8 times with all kinds of gunk. This is naturally organic, don't have bug problems as it's mostly sealed all year. Local citrus up north, and it costs so very little produce. The excavation was by far the most expensive part, as I had to rent equipment. Spent about 3k on that, the rest was only about $2500 for pipe and a ton of polystyrene. To build a 30x100 woul dprobably cost about 60k, but almost no maintenance and very low heating costs. Like I say, this small one costs less that a dollar a day in electricity. Could easily be powered by solar panels in most places, just not here.

They call it a Thermal Battery. Filling in is the hard part. Important to pack dirt tightly around pipes.

Wouldn't you want at some point air exchange as plants would need carbon dioxide?

The video, https://www.youtube.com/watch?v=ZD_3_gsgsnk

A geothermal heat exchanger is not really new technology. But, one thing that you forget to mention is the hours of daylight.

Most fruit trees as well as vegetables need a minimum of hours of daylight to bear fruit. During the winter and colder weather, that becomes an issue. Not only must artificial light be provided, but it must also be of sufficient intensity to satisfy the plants or trees.