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Comment by leoedin | Hacker News Reader

This could also have good use for ground source heat pumps - they're the most efficient, robust and consistent source of domestic heating we have, but require fairly deep (60m ish) boreholes. If digging could be quicker, easier or faster these heat pumps could be installed everywhere.

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I have one of those. The well is 170m deep. Took 2 guys about half a day to drill it, so that actually doesn’t seem excessive in terms of time required (mostly sand, no rock below my house).

I assume you mean “2 guys and some heavy equipment”? As a kid it took me a whole summer of on-and-off digging to make a 1 meter deep hole for fun.

That’s what they mean. My neighbor had one drilled and the contractors showed up with a huge well-drilling truck.

It’s just a huge vertical drill with segments you add on as it goes deeper, like an oil well drill.

Correct, it's big but I wouldn't say huge (maybe 4.5x2.5m). This is the machine they used: https://conrad-stanen.nl/nl/producten/boxer-200

Most drills I’ve used fit in your hand. Compared to that, it’s huge :)

(although on rereading I didn’t mean to say ‘huge’ twice in my previous post)

Out of curiosity, what were you digging with? Unless you were digging with a toy sand shovel or making a very large hole, that seems like a very long time.

As a kid, my cousin, my sister, and myself were able to dig a hole deep enough for me to be completely inside in an hour or two using a post hole digger. (Yes, this is a very stupid idea.)

You have to make sure it's straight, drop sheathing in to the hole, and then cap it if it isn't going to be used right away.

More importantly, geothermal/ground source is rarely 1 well either, in our case it was 8.

A shovel. I couldn't get past 1m because of the rocks were too difficult to shatter.

That’s fair. We were not digging through rocks.

Awesome! Do you sink heat into it during the summer, or do you also use it for airco?

Sink directly into it for the summer. Heat exchanger between the source (approx 10-15C) and the water from the floor heating/cooling system. Because the heat pump is not involved it's very efficient (only the power of the well pump)

I'm actually considering if it makes sense to push a lot more heat into it in the summer (Deliberately leaving curtains open, then moving this heat into the well; or even PVT panels), but I'm not sure if the well would retain heat long enough to make a difference towards the winter.

It definitely should, I'm not sure making your A/C work harder deliberately makes sense economically, I guess you'd have to do the math. PVT or even just thermal panels (i.e. rolls of garden hose painted black in a glass covered box) would make a lot of sense if you're in a colder climate though.

Your system should give a an overview of your yearly input/output and any drift of the well temperature right?

Except this technology is for after you get to the plate of rock at the bottom of topsoil unfortunately. They mentioned it in the article. You use conventional drilling to get to depth first.

They can also be horizontal, covering a larger area at a much shallower depth.

Indeed horizontal (pipe network, like underfloor heating in reverse) is the most efficient solution, digging deep is for when the plot is too small or otherwise encumbered (or if one sits on top of a volcano).

A 60m borehole is not a source of energy, it is a store of energy. It only makes sense if you can sink enough heat into it in the summer, to use that energy in the winter. Or vice versa in warmer climates.

We have a ground source heat pump and one summer we were away and did not use out air conditioning that year much at all. Mid winter our return loop temperatures (the glycol being brought in to our heat pump after circulating in the ground) was at one point 3 degrees C cooler than it had been any other year. Quite a noticeable difference. For reference, our loops are 8 vertical at 250ft.

Wait, do you need eight 250ft wells?

Yeah for a family home that seems about right. 250ft is not very deep at all, and you need to store a lot of energy to past a whole winter/summer.

For a closed loop system, yes. I think that would be the minimum (6000 sq ft house) at 250ft depths.

Couldn't we have one big plant with a large hole that distributes heat to surrounding homes?

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