> Heat loss inside of dirt is so incredibly slow it's hard to wrap your head around. One fact that I find helps is the fact that after an entire winter of extremely cold temperatures, you only need to go down 10 ft or so before you hit the average annual temperature. 4 months of winter buffered by 10 ft of ground!

That’s not entirely insulation. Some of the heat flows upward toward the surface during winter and some warmth flows downward during summer.

> If we could just create hot and cold piles or underground wells or something that we could tap into 4 months later when the temperature has changed, you would have completely solved heating and cooling.

Geothermal heating and cooling already exists. It’s semi-popular in some areas. It can be expensive to install depending on your geology and the energy savings might not compensate for that cost for many years. Modern heat pumps are very efficient even if the other side is exposed to normal outdoor air, so digging deep into the earth and risking leaks in the underground system isn’t an easy win.

▲

2 days ago | parent | next [-]

[deleted]

▲

afiori 2 days ago | parent | prev [-]

the parent was not talking about geothermal, but storage which would come as interesting to store winter cold for the summer, I have no idea whether it would work.

Based on some guesses and uninformed searches if a house spends 200MJ on cooling and there is a 20 C delta between winter temperatures and desired cooling temperature and assuming a specific heat capacity of ~800 J/(kg*K) you would need 12.5 tons of rock as battery which would be around 6~8 m³ which sound very small.

I am sure that there are hundreds of complex factors at plays (eg rain water and aquifers reheating the battery during spring) but it came out to be a far smaller number than I would have guessed.

▲

IAmBroom a day ago | parent | next [-]

Again, dirt isn't very insulative. It has a high thermal storage capacity, but if you pumped heat into it, it would dissipate to all compass directions and downwards, and you couldn't retrieve it later.

If that wasn't true, you'd need to keep moving the underground passageways of buried passive cooling systems.

▲

lazide 2 days ago | parent | prev [-]

That’s because 200 MJ is a small amount of cooling. It’s only about 55 kWh.

▲

afiori 2 days ago | parent [-]

I considered 400W 6 hours a day for 20 days because it is about what we I use.

	▲	dbeardsl a day ago \| parent \| next [-]
		I think you missed a 0. I've never heard of an AC unit for a house that's 400W. 4000W and above is more common. Google: > An AC unit's electricity usage varies by type, with window units using around 500–1,500 watts and central air systems using 3,000–5,000 watts, though usage can range from 2,000 to over 6,000 kWh annually for central units Also, how much you use it during the year can vary hugely from 0 (when I lived near the coast) to like 10 hours a day for months in hot or cold places. There's not a standard, but 55kwh for a year means you live someplace that doesn't really need AC / heating.
	▲	lazide 2 days ago \| parent \| prev [-]
		Which climate zone? In this example it would be for the whole year, yes? Anywhere in the South, Southwest, West, or many places in the Midwest will be doing that each month for 6 months out of the year at least.