Wow, sounds like quite the project! :)

For myself, I just use south facing windows to overwinter small citrus and herbs.

A really cool book for ideas (if you haven't come across it yet) is "Four-Season Harvest: Organic Vegetables from Your Home Garden All Year Long" by Eliot Coleman.

I love it up there and have hiked every inch of every trail in every Wilderness Area in that National Forest, so I'm envious of your paradise.

Currently geothermal is expensive, and generally the depth for effective heating/cooling (with heat pump) is on the order of tens of meters. If you have a geotherm pocket nearby then you are better off, but you are certainly on the right track. Plenty of info out on The Interwebs about these systems, you'll want to read up before you commit. You can also supplement with passive solar using water storage, but insulating the north wall and the extra glazing is the key - doubling twinwall might reduce your light too far down to be effective, so check that out too.

Dan

I have a greenhouse that is built with standard, 2 x 6 studs, siding, insulation, etc. on the west, north, and east wall, which joins the garage. On the west I have an 8' wide sliding glass door, and on the south, a row of 5' high windows going to the ceiling. The south roof is double walled plexiglass, the north roof is regular home construction with sheet rock, insulation, propanal roofing, etc, making an open to the roof interior.

The floor is a concrete slab. With decent insulation on all but the double-walled south facing roof, it rarely gets below 40º F at night, and thats only when the outside temperature is in the single digits. I use two small electric space heaters on a trip switch that will start them at 40º. Most years, they go off maybe 10 nights out of the year in January. This year, which was, it seems, 10º colder than average, they went off for a few hours just about every night in Jan/Feb.

All in all, its a great environment to to grow salad and some spices - eg cilantro, over the winter, and I over-winter a lot of large potted plants. In the spring, it shifts over to growing warm season seedlings for planting out in the garden.

The problem I've found is keeping it cool in the summer, not heating it in the winter. A couple of space heaters and a fan, I spent maybe $250 on the set up and no more than $50 a year in electricity.

Hi ogm,I have read of this in two places. An article on tubes below the surface circulating air into the beds, as opposed to the air. the other is a business that does just what you want to do,geodesic dome. tubes in ground and vents to let the hot air out in the summer. Their website is growing spaces.com and I have seen one in place and want one badly. Hope this helps. Not sure if I can find the article, I will try.

In many areas you can drill your own well. This is useful for both irrigation and as part of a geothermal heat pump system. There are instructions at http://www.drillyourownwell.com I did it and it works. You can use this technique for both a regular well and an injection well. It is absolutely the cheapest way to switch over to a geothermal heat pump system.

Here is a link that might be useful: Drill Your Own Well

Check online for low grade geothermal greenhouses in western Nebraska near Alliance. This is geo at the 8' depth.

Here is a link that might be useful: greenhouse