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Wanted, suggestions for ways to produce domestic-scale geothermal microbores (water bores).
In most areas, temperatures rise as you go down from the local ground surface. Inexpensive methods are sought for inserting a 200-metre (say) length of 50 mm (say) plastic water pipe into the ground to reach warmer sub-ground water. As an indication, average temperature in Perth, Western Australia, just below the soil surface, is about 17 deg C and temperatures rise by about 3 deg C per 100 metres. At 200 m the temperature is around 23 deg C, and water at this temperature would be adequate for passing through a heat exchanger to warm a home. Boring speed may be slow, perhaps using a small electric motor to turn a 10 mm pipe with Archimedes-screw flanging to remove debris. Multiple suggestions, bids, and sketches are sought. (ZBL#117)
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The attached PDF report by Abdullah Khalid gives a summary of small-scale methods probably usable to produce a geothermal bore hole for domestic use. In general, it is difficult to find effective non-commercial methods for drilling to 200 metres or so.
One major consideration is that once the water table or an aquifer is reached, the base of the hole being drilled fills up with water, which prevents use of shallow-depth methods such as dropping percussive heads to break up rock or soil. This may possibly be avoidable by simultaneous hole-drilling and water-pumping, so the bottom of the hole remains mostly under air.
LATE ADDITION: The Chinese drilled boreholes manually up to 1500 metres deep, over 2000 years ago! They used heavy cast-iron percussion heads suspended from bamboo-skin cables, activated by men jumping off and off lever boards. The drill holes were lined with watertight bamboo tubes, with drill debris removed by suction, as in the previous paragraph. See Robert Temple's 2006 book "The Genius Of China".
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