
Google-born startup thinks its time for a ground-source heat pump renaissance - shawndumas
https://arstechnica.com/information-technology/2017/08/google-born-startup-thinks-its-time-for-a-ground-source-heat-pump-renaissance/
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ddnb
So if I get this correctly, the 'renaissance' here is merely drilling smaller
holes for the pipes to go in, so the cost of hauling the dug up debris is
lowered. Anyone here know what the cost savings are as I can't image these are
big to begin with.

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jaclaz
Also it is not unusual to use a 4 inches (100 mm) down the hole hammer when
drilling vertical holes for geological prospection/sampling.

People which drill water wells use normally bigger diameters, such as 6 inches
(150 mm) or even bigger, their drilling rigs are huge truck mounted rigs, but
there are a number of much smaller machines suitable for the task of drilling
a 100 mm vertical hole up to 120-150 m or so.

The "resonance sonic drill heads to liquify the earth in the drill path" maybe
are the "new thing", but it actually dates back to the '80's:

[http://www.cpeo.org/techtree/ttdescript/soncdrl.htm](http://www.cpeo.org/techtree/ttdescript/soncdrl.htm)

Like more traditional temporary casing it is installed and removed afterwards
as actually the casing is made by the actual drilling pipes, of course it is
much faster (on the "right" terrains) than having to deal with two pipes (the
drilling one and the casing).

The difference in cost of hauling the debris is nothing.

Let's make a 100 m deep hole 10m mm in diamater:

0,05^2x355/113x100=0,78 cubic meters

the same hole but 150 mm in diameter:

0.075^2x355/113x100=1,77 cubic meters

Even if you multiply both by a factor of 2 (terrain "grows" when excavated and
the actual hole is bigger than the size of the drill) the difference is
between a half empty small truck and a filled up small truck.

If I have to give it a "universal" cost it cannot be more than 100 US$ per
cubic meter or 200 US$ for each drilled hole, whichever comes first.

I.e. 0.5 to 1% of the given estimated 20,000 US$ per installation.

