It has been tried here where hot water wells are plentiful and not too deep. The cost of the wells start at $20,000. The water is very high in boron and iron and after the heat has been extracted the water is required to be returned to the underground via another well. The minerals in the water build up in the pipeing and control valves and require a lot of maintenance. As a commercial venture it was not profitable and I think it too costly for the amount of savings for a hobby. Al

You don't need extract water from the well to transfer heat in geothermal systems. The wells are used to give a lot of earth surface area to move the heat to and from. We priced out geothermal for our future house, 2,300 ft2. 55,000 btu/hr heating load. Lowest bid so far is $22,000.

Is $20,000 a typical price for a well? What depth? I live in Chiacgo area.

Also, there are two ways of exchanging heat with the ground: vertical via multiple wells; or horizontal with hundreds of feet of copper (or other heat exchanging ) tubing buried about 6 feet below lawn. Does anybody know of a way to bury tubing 6 feet below lawn besides using heavy machinery that digs a 2-3 foot wide trench and ruins the surrounding lawn?

A friend sent me an e-mail telling me about the postings on this site concerning Geothermal heating for greenhouses. I read some and surprised at what was there. No seems to be aware of the Direct Exchange Geothermal systems and are only focused on water-base. The Direct Exchange system can be installed much cheaper and is much more efficient. Basically this technology uses cooper loops installed in drilled 3" holes in the ground filled with safe refrigerant (such as NU-22) that can deliver the capacity of heating and cooling of one's home. It can be used for greenhouses, commercial buildings, schools, etc.

If you are interested in information, do a search on Google for "direct exchange geothermal heating and cooling". You will find many sites that explain this better than I can in this short space. We are facing major environmental crises that will be costly to our pocket books  but more important costly to our environment, which we will be passing on to our children and our childrenÂs children.

JIM

Or we could avoid all of that and build efficient 'solar greenhouses', as designed in the 70s, which use only the sun's power. You can build a mighty fine greenhouse for $20k! (using triple glazing and R30 insulation round the south side, for example)

With cheap PEX tubing available, it should be relatively easy to build a simple geothermal system if you have enough space in your yard and don't mind trenching up part of it. Loops of tubing buried below the frost line (IL, about 40 inches) will remain relatively constant at about 55 deg. F. during the winter. Pumping a water/antifreeze solution through the tube and then through a heat exchanger in the GH with a fan on it should produce air at around the temperature of the liquid. In the winter it would provide basic heat and the summer, basic cooling. Of course, you can't exceed the capacity of the subsurface system to absorb or release the "free" heat or the frost line will be lowered. Most residential geothermal systems bury the pipe about 7-8 feet. The more pipe you can bury, the more BTU capacity you will have. Increasing the coupling between the tube and soil would increase transfer efficiency.

Absorbing heat during a winter day and transfering it to the subsurface coil could store it for later use during the night. A control system is needed to monitor the ground loop temperature and transfer the heating load to auxilary heaters if the ground loop temperature falls too low for useful heating.

Here is a study done by the NAHB Research Center on five residential geothermal systems in Ohio. These systems all use heat pumps, too, to raise the temperature to the normal 68 deg. range.

NAHB Geothermal Heating Study

Digging 8' deep trenches all over the yard is a lot of work! Perhaps a better solution would be two wells, several meters apart, and pump water up one, through the greenhouse and down the other.

I was thinking that you might use a trencher like the Ditch Witch RT36 that can dig a trench 4-6 ft. deep and 6-8" wide. These, or similar units, are available for rent.

Would that be deep enough?

Last year I had my 6" diameter well that I use for irrigation and to keep the pond topped off taken down to 100 ft from 42 ft the cost for this was 15.00 per ft plus 300.00 set-up as I already had a casing in for a grand total of $1200.00. New wells here cost 15 dollars a ft and that includes 20' of casing that gets it into the limestone. Might be a little more now cause of the cost of diesel fuel. The water comes out of the well at approx. 56 degrees year around. Hope that helps some.

Bob in North Alabama

There's an article in this month's Countryside about geothermal heat. Maybe this would provide more information/answers.