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Comment by tyfon | Hacker News Reader

There is a school close to where I live that does something like this.

During the summer they heat the bedrock using solar panels (thermal and electric via a heapump) to heat the bedrock far down using water pipes. In winter they extract this energy for heating, electricity and hot water making the school self sufficient for energy.

Here is a write-up from the municipality about it, but it's in Norwegian

https://www.drammen.kommune.no/om-kommunen/aktuelt/unikt-pro...

Edit: translated version

https://www-drammen-kommune-no.translate.goog/om-kommunen/ak...

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In a smaller scale, this is also what the French solar panel manufacturer Dual Sun [^1] sell with their geothermal+hybrid panels solution for individual houses.

- In winter, heat is generated with a geothermal heat pump and an horizontal underground network of pipe.

- In summer, the thermal solar excess energy is used to warm up the soil that has been cool down during winter and also to avoid permafrost.

[1]: https://dualsun.com/applications/pompe-a-chaleur-solaire/

How effectively does the ground maintain this heat, and how much of it dissipates up and out?

As a side effect: using a heat pump to heat the ground during summer also cools the building on top! (When its at the other side of the heat pump loop)

Same idea in Alberta: http://dlsc.ca/borehole.htm

And at the Blavatnik School of Government building in Oxford: https://www.bsg.ox.ac.uk/about/our-building

That's just a ground heat pump no? I have the same on my house. It's pretty great. I get cooling in summer and heat in the winter.

If you're in an area that gets hot enough in summer for you to want cooling, then yes you'll be pumping heat into the ground during summer and extracting it in the winter. For those of us who don't get hot enough in summer to want cooling, we're always extracting heat from the ground, and so the ground we're extracting heat from gets cold, which reduces the efficiency of the system. Having a solar powered mechanism for putting some heat back into the ground in summer would help alleviate this problem.

> the ground we're extracting heat from gets cold

Not if you’re using deep drilled holes (100m+). You can run a heat pump of the differential indefinitely

Apartment buildings in Finland have these 100m to 200m drill holes for the heat loops since you can't run those horizontally to the neighbor's yard. A bonus benefit is that the core of Earth has to basically cool down before they run out of heat to extract.

Another approach would be to have a longer length of piping. The rate at which the soil temperature drops when you extract heat, and then 'recharges' naturally, will vary greatly if you have 100m vs 1000m of piping. This is why ground source heat pumps use pipes laid out in coils, as it greatly increases the surface area.

Wait how long does that heat last. I wouldn’t imagine more than a week since it’s not insulated?

You don't have to dig very deep for the soil on top to be decent insulation.

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