Hi,

I recently ran across info about the GeoColumn
( http://www.geoenergyusa.com/column.htm ).  The idea is
intruiging but their design seems overly complicated.  

The basic idea seems to be to reduce cost of a DX install by
drilling a 2 foot hole 25 feed deep rather than a 3 inch hole
100 feet deep for each ton of heating/cooling.

I don't know *anything* about the drilling business. Or much
about the mechanics of heat transfer through the ground.  That
should probably stop me right there, but I'll happily
compensate by making several completely unjustified
assumptions.

I'm assuming that with a thermally conductive grout, most of
the resistance to thermal transfer in the standard 100 foot by
3 inch setup comes from the surface where the grout meets the
surounding rock/ground.  And that, at least for a rough
approximation. the resistance is proportional to that area of
contact (basically a cylinder 100 feet long with a 3 inch diameter)

It seems to me that you could get the same effect of the
GeoColumn by drilling a 25 to 30 foot deep hole about 1 foot
in diameter and installing a steel casing using totally
standard water well drilling techniques.  But then, dump
enough grout inside the casing to form an 8 inch plug at the
bottom.  Then fill the casing with water.

Now, you've got just as much surface area in contact with the
rock/ground as the standard 100 foot well.  If the steel
casing makes good enough thermal contact with the ground, no
grout the casing may be necessary.  Or, maybe the grout
outside the casing is necessary.  I don't know.

Next, you bend the standard 100 ft loop of copper tubing into 4
25 foot loops that pass the refrigerant up and down the 25 foot
well 4 times, or maybe into a spiral shape down 25 feet with a
straight return back up.  Doesn't matter, there are a couple of
ways to shape the 100 foot loop into a 25 foot length.

Put a cap (maybe HDPE) on it, run the copper tubing loop out the
top, and connect it to your manifold.

I *think* that would give approximately the same thermal
transfer to and from the ground as the stanard 100 ft well.  And,
it might be significantly better if the steel to ground thermal
coupling is better than grout to ground.  (More assumptions:  
steel to water and water to copper thermal couplings are way
better than grout to ground).

So, given all of my unjusified assumptions above we get down
(as always) to cost.

Would it be signficantly cheaper to drill a 30 foot deep 1 foot
diamter well and add steel casing than to do the usual 100 foot
deep by 3 inch well and fill it with grout?

Hopefully some of the professional drillers in the group can
comment.

For the record, my interest at this point is just theoretical.  
I'm just facinated by this technology and hope it continues
expanding into the mainstream.

Thoughts anyone?

Thanks for reading my ramblings.

Some good thinking there, but I would have a couple of concerns:  The steel casing might become the anode for the copper (galvanic corrosion) but it should last several years since the two metals are not that dis-similar  (refer to galvanic series chart).  However, the water in contact with both metals might increase the speed of corrosion.  Using high-conductive grout might be better than water by isolating the two metals. 

The non-moving water in the column might have a tendency to insulate the copper instead of allowing conduction (similar to insulation of an air film).

I don't know if this type of drilling reduces the cost or not, but instead of having vertical wells, six wells are drilled at 30 degree angles from a central manifold. Here is a link with a brief presentation of an install with this type of drilling:

http://www.sundialgeo.com/ei2007/drilling.htm

For a 12" well, you'd be looking at around $50-$120 per foot. Steel casing would add about $5-$20 per foot, installed. At least it is in my area.

Interesting idea.

does anyone know how many kw a 6 inch well 200 feet with a average water temp of 50 degrees will allow without lowering the well temp more than 15 degrees

Nope, no one knows.

Need site specific info such as soil composition and dampness.

If you are hinting at a standing column well, that's a different kettle of fish - I think you'd  need height of water table, length of well uncased, and some idea of potential lateral flow within the aquifer.

Surf "Standing Column Well" to learn more.

yep standing column 20 foot water table 200 feet cased 300 feet uncased unsure lateral flow any way to take a guess on flow or come up with a range

I came across (and thought I'd saved, but evidently not) a study indicating that SCWs could work with well under 100' per ton. Part of their benefit comes from lateral flow of the aquifer, so cased length is less effective.

Try a search on Carl Orio, a long time proponent of SCW

I have been trying to get info from the geocolumn group for over a year. Always very vague about when it would be ready. The concept has been in R/D for quite some time. Have tried contacting via email some projects for information but no one has answered. Some part of DOE rated it highly last year. It is NEW and with NEW there may be glitches. If they go out of business, you may get stuck.

I recently gave up and am having a DX system installed. It is tried and will work.

alice

Thanks all for commenting, especially to tuffluckdriller for giving some real dollar figures.

From those numbers, I don't see how the GeoColumn concept (either the one from GEE or my hack) could ever be economically feasable.   At even at the low end of the range suggested, drilling the larger ( 1 foot diam) 30' well (per ton) costs 50% more than the numbers I've seen on this board for a 3 inch diam 100 ft well for regular DX.  I'd have to guess that a 2 foot diam well would be significantly more.

But, I guess an idea doesn't have to make economic sense to pull in nice big goverment grants.

I tried for 2 years to get info. Even asked about inestment info. What you see on the website is what you get. Found that odd.

The geo column was to be about 2 ft across and maybe 20 ft deep--one column per ton depending on soil types. The column was to augered not drilled and and rigid column made out of landfill fabric was to be into the hole.

The sales person responded vaguely to emails and could not get calls answered.

on the 200 foot well what if there is no lateral flow

A cased section won't contribute as much heat transfer as an uncased section of well