Tropicallvr

Found this googleing geothermal greenhouses. It's a zone 6 (Missouri)green house that grows figs without heat source, but it's not really geothermal. The owner says it never got below 48F last winter.
Missouri Vegetable Growers Association Newsletter - AgEBB

The basic idea is to have a network of large pipe 3ft down, covered in white rock(better for heat tranference), then covered by soil, but the ends of the pipe are vented into the greenhouse with quirrel fans inside the pipe which are set to a thermistat. He also insulated inside the trench around his greenhouse with 4" foam isulation.

A real geothermal greenhouse growing tomatoes in Utah without heating costs-
ksl.com - Iron County family grows tomatoes in the dead of winter

And a interesting travel perspective of Icelands geothermal baths, and tropical greenhouses, ect-
Strange Sensations in Iceland

Jack Daw

Interesting, I will read it through, thanks for the post!

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Scuba_Dave

Good info, my greenhouse is partially below ground
I'm digging down around the edges & putting insulation around the perimeter
I have one wall that is up against the house foundation
If I ever get ambitous maybe I will excavate it fully & do the rock trick
Of course thats further South then I am
Not sure how the winter compares...but I'm around a zone 6 too

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sunfish

Tropicallvr

Sunfish, that's a good take on the system with the solar, with the pea gravel. The only thing that seems like it would make it better is more of a underground pattern. Maybe inground water pipes with a solar water heater would be a good option for off the grid too- A Real 'Green' House: No Heating Bill for 25 Years | LiveScience
Just saw on one site that they insulate the ground with hard insulation before they put the floor down in the greenhouse, never would have thought of it.

Richard

Unless you live in the land of perma-frost or near-surface aquifers, 6 feet down in solid ground the temperature is 60 F or higher throughout the year. When I took an environmental engineering course some 35 years ago, building underground embedded heat exchangers was standard technology. I expect that if you looked in an undergraduate textbook today, you'd find all the details necessary to build an inexpensive system.

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Tropicallvr

A friend of mine in Montana has the inground temp heat exchange, but it's hooked up to her well water. It's supposed to cost alot more than a conventional, but pays for it self in 10+ years.
http://www.polarbearwshp.com/?w=PolarBearProducts
It seems like sunfish's, and the fig guy's are basically the same technology, but not the full 6 feet down.
Some pretty simple looking solar water heaters in israel- http://www.metaefficient.com/wp-cont...rs-on-roof.jpg
I wouldn't mind trying one of those with in floor heating in a greenhouse.

sunfish