geo thermal heating

ongodsmountainApril 29, 2010

I live in Nor Cal (Next to Mt Lassen Natl Park), and I thought I'd try this question here as a lot of you live in snow country... elevation is about 4200'

I want to build a green house for veggies, dwarf fruit trees, herbs, and the like, for personal consumption and trading/sharing with neighbors... but heating the thing in the winter is a concern (trying to reduce my expenses not increase them)..

So I've been thinking about the idea of using geo thermal heat to heat the greenhouse in the winter... The greenhouse will likely be a geodesic dome built on top of 8 foot high perimeter walls.. one or more greenhouses approximately 12' in diameter... most likely caulked solexx panels will be used on a wooden frame... was even kicking around the idea of using dual layers of solexx with an air space between them to increase insulating ability...

Was thinking about having a buddy of mine dig a hole 9 or ten feet deep, probably slightly larger footprint than the greenhouse, and then looping a couple hundred feet of 1/2" pex in the bottom of the hole (back and forth 'radiator style'), throwing a foot or two of dirt on top, looping another couple hundred feet of pex back and forth, then insulating the pex risers into the greenhouse with neoprene sleeves, and refilling the hole with dirt..

The idea is to use a low wattage pump to circulate water through the pex system into a small radiator (perhaps like that of a cars heater core) and/or through a 55g drum (thermal mass).. A low wattage fan (ie computer fan could then be used to circulate air through the heater core....

I'm also thinking of doing composting 'inside' the greenhouse to provide additional heat....

I understand that the earth stays pretty constant in temperature through out all four seasons (I've heard in the mid fifties) at a level of 8 feet or more down...

Have any of you tried or heard of anyone that's tried such a method and what the results were?

Any other idea of how to heat a greenhouse in the winter in snow country without breaking the bank?

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laura_42(4b-5a Colorado)

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.

    Bookmark   April 29, 2010 at 3:23PM
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Dan Staley

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

    Bookmark   April 29, 2010 at 3:48PM
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david52 Zone 6

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.

    Bookmark   April 29, 2010 at 6:37PM
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mcfaroff(z5/6 NM)

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.

    Bookmark   May 2, 2010 at 9:02AM
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mike3325

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

    Bookmark   May 29, 2010 at 11:44AM
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darnrus

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

    Bookmark   May 12, 2014 at 6:36PM
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