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Comment by a9h74j | Hacker News Reader

Tangent, but in the seasonal storage context.

Apparently, according to a reported simulation, if you (1) take a ca 15m x 15m house thermally in contact with the ground, (2) insulate the ground outside to a radius of ca 40m, and (3) heat the interior to say 25C, then (4) evenually (50years?) the ground itself under the house will come up to a steady temperature consistent with that.

Even if the simulation was correct, I can only see this being sustainable with solar gain being used for heating, but it makes for an interesting long-term-oriented picture.

One imaginable scale of application could be for a cluster of houses in a larger agricultural setting.

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Gradual heating of the ground is definitely a thing; over the decades, certain London Tube lines have drifted from pleasantly cool to sweltering: https://www.wired.co.uk/article/central-line-temperature-lon...

Yes, people are literally dying in the heat from heart attacks because city planning won't allow TFL to knoxk down a house sp they cam build a ventillation shaft

Do the tubes never cross a road? Why knock down a building instead of taking a vent to a street?

I think you're underestimating the size of vent needed.

They'll turn the entire plot into a single giant chimney, and decorate the face to match the houses either side of it.

like this:

https://en.wikipedia.org/wiki/58_Joralemon_Street

Ah I was thinking of the subway vents you see along the street and sidewalks in New York. That is indeed a drastically different scale.

I'd love to read more about this simulation, have any links?

I am unable to find a link, and IIRC this was reported 10 years ago or so. I recall an attribution to German designers or architects. I cannot remember where exactly it was reported, but I remember it as moderately plausible reporting, although not in a journal.

A quick estimate with soil:

Take a specific gravity of 2.7 gm/cm^3, a specific heat of 0.2 cal/gm-K, and 1 cal ~ 4.2J ~ 4.2 W-sec. For a cube 25 m (2500cm) on a side, if I am not mistaken this suggests a thermal inertia of about 3.5E10 W-sec/K.

Now take a thermal conductivy of 1 W/m-K. For a slab of 25m x 25m, also with a thickness of 25m, we get a net conductivity of 25 W/K .

Then 3.5E10 W-sec/K divided by 25 W/K gives 1.4E9 sec . Given 3E7 sec/year, that suggests about 47 years.

Aka a 50 year time scale.

Of course this assumes a low water table.

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