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Piwoslaw,
> On top of drilling costs, local laws require permits and fees for drilling,
> while the soil under us is dry (wet is better for GSHP).
The local laws and permits issue is why I built an ELECTRIC earth auger. It's very quite.
Around here, a finished borehole (drilling + pipe +grouting) that will yield 12,000 BTU per hour, costs $7000 (3.5 KW per 24,660 PLN) and would be 200 feet deep (61 meters). It could also be two 100 foot holes, or four 50 foot holes, or eight 25 foot holes, etc.
$7000 is a lot of money for me, that is why I built an electric earth auger (see photo below). I think I can actually do 25 foot holes. The auger shown on the photo uses a quarter-horse drill motor (187 watts) and a 25:1 gear reduction. I didn't get very far drilling dry, then I discovered using drilling mud which required using a pump to send drilling fluid down the hollow drillling pipe. This of course required making a drilling fliid swivel arrrangement, and a drilling fluid recirculation system. I discovered the drilling mud secret late in the summer, and it greatly improved my success, but then cold weather overtook me and I had to stop.
My gearmotor auger, at a quarter horse (187 watts) is really absurdly small. Most homemade augers are in the range of five horsepower (3730 watts) or bigger. Here in Portland, Oregon the ground is very difficult to drill. Lots of big rocks deposited by glacial deposits during the last ice age. However, even though it's slow, hard work, I have gotten down to 17 feet. If worse comes to worse, I can succeed with a loop filed that consists of 18 holes that are 17 feet deep each. In the mean time, I'm scouting around for a larger gearmotor for my drilling setup.
Earth structure really has a lot to do with it. Even my tiny 187 watt gearmotor auger would do a great job if the earth conditions were favorable. About 30 miles from here, there is sand that goes down about 85 feet. If that were my case, I'd have been done last summer.
Oh, and I should mention that I made a T-handle hand-powered test drill, which used domestic water pressure to flush out the drill cuttings. I was actually able to get down nearly 12 feet. With favorable conditions, it would be possible to do the loop field by hand!
The photos:
Gearmotor-Auger-2(small).jpg - This is a close-up of the gearmotor auger showing the first swivel which didn't work very well. It had O-ring seals and so much friction that I lost almost 1/3 of my drilling power (which wasn't much to begin with). Also seen is a garden hose feeding the auger. With the soil conditions here, sand and not much clay, cave-ins were a problem after maybe 5 or 6 foot depth.
Swivel(small).jpg - Here's the second generation swivel which worked much better. Once I realized that I was going to need to use drilling mud, I started taking my swivel more seriously.Hhere I'm using 3/4 pipe skimmed down to fit 1" ID sealed ball bearings. A happy fit was that the OD of the bearings just worked inside the plastic T-fitting. The whole swivel cost was about $23. Commercial ones are $300 or so. The friction is almost non-existant. Works great.
transfer-test(small).JPG - Here I'm making a test hole to see what the rate of thermal transfer is from the earth to the water.
Best Regards,
-AC_Hacker
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