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Comment by phh | Hacker News Reader

It doesn't sound like the improvement of cost is enough the justify using it only for few cycles a year as the title says rather than every other day. That said, I see nothing in this article saying why it would be limited to seasonal release, I'm guessing it just has a lower self-discharge.

The title made me thought of an idea my father had, for which I'm still totally ambivalent:

Freeze water in the cellar (speaking of like 30m^3) using thermal pomp during winter to heat house and when electricity costs little, and use that ice in summer to cool down the house. I didn't run the numbers, but I'd guess that if it was even remotely not a pure energy loss some other people would have already proposed such things.

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> Freeze water in the cellar (speaking of like 30m^3) using thermal pomp during winter to heat house and when electricity costs little, and use that ice in summer to cool down the house.

Unless I misunderstood, the Toronto Zoo has or had such a system setup for one or more of the food pavilions.

What's interesting about this is that the storage grows with the volume (n^3), but the heat/cold loss grows with the surface area (n^2). So you're ability to 'store cold' gets better as you get bigger.

Just the same, you could also use it backwards in the winter time. On hot, sunny days at the end of the summer, warm up the water stored.

The cube/square law also applies in the opposite direction, this is why it takes longer for lakes to freeze and why the Great Lakes never do.

I believe at least one university on the Great Lakes does heating and cooling with pipes deep under the lake.

The Great Lakes do occasionally freeze over significantly, though never completely. 2013-2014 was one such winter, when ice coverage reached 92% across all five lakes. That's quite unusual though.

And the city of Toronto uses lake water for cooling. Heat from a downtown cooling loop is dumped into the city's drinking water supply, bringing the temperature up to around 13° from 6° (if I remember correctly).

Not just drinking water. The cool water is pumped into buildings to work as the air conditioner for a lot of the big buildings.

> On hot, sunny days at the end of the summer, warm up the water stored.

Phase change stores/requires much more energy than simple temperature change. 0°C Ice to 0°C water transition is 334J/g, 0C water to 100C water is ~400J/g (ie 4J/g per degree C), 100C water to 100C steam is 2260J/g.

To store heat from the summer for winter warming (say best case 40C summer temp) you'd be looking at least 3x as much material for heat storage vs ice storage for summer cooling (at say -10C)

This is a useful thing: storing energy in a phase change makes it easier to keep the energy stored for a longer period of time compared to if there was no phase change. The difficult part is that steam is much farther from ambient temperatures than ice is (and also that it is far less compact). Newton's law of cooling means that the larger the temperature difference, the faster the heat loss, so steam would require much more insulation than ice would.

Besides insulation, there's no hope of storing thermal energy as steam because the density is 1000 times lower than ice or water while the specific heat is similar, so the heat capacity per unit volume is about 1000 times lower.

Storing heat as steam is actually very good and efficient - as long as you're storing the heat for location shifting, not temporal shifting. It's regularly used in combined heat + power plants

(Yeah, I know I'm being both pedantic and off topic, since the discussion here is specifically about seasonal storage)

Doesn't the word "storing" already mean temporal shifting?

How does this compare to hauling ice down from a local mountain lake?

Feels like 0-18th century tech. Doesn’t mean it’s bad though.

Don't forget that, until the invention of refrigeration, people used to harvest ice in northern climates. They would store it in hay, and then sell it throughout the year.

Ice was even shipped internationally.

(And, if you're a fan of Disney's Frozen, this is exactly what Sven did.)

Congratulations, you just invented geothermal heat pumps. :) They’ve been the preferred way of hearing single family houses in the Nordics since the 90s.

This exists and is actually used in Germany, it is called "Eisspeicher" (ice storage). It is utilizing the effect that it takes a huge amount of energy for the water to go from solid to fluid, about the equivalent of heating water from 1 to 81 degrees.

MGAThermal does this with a range of materials, allowing heat storage at very high temperatures. https://www.mgathermalstorage.com

Similar systems are actually being build, but with a bigger scale (like big office buildings). There is no freezing involved, just heating the office space with warm water in the winter (cooling the water to ~10°C) and cooling it in the summer (heating the water to about 40°C).

During the rebuild of Christchurch, NZ they used this technique for a number of buildings, basically pumping out water with one well, then re-injecting it with another as I understand.

Essentially exploits the ground water remaining a constant temperature year around, warmer than the surface in winter and colder in summer

Your father's idea is a good one. Here is a thermal heat pit which is being used to store heat for the winter:

https://stateofgreen.com/en/partners/ramboll/solutions/world...

> some other people would have already proposed such things.

Geothermal heat pumps. Been around for decades. Expensive to install due to drilling the well or laying the field, but very efficient.

Geothermal energy is risky AF though. Even with shallow drilling depths, you risk hitting anhydrite and, in combination with water, massive damage like in Staufen [1].

[1] https://de.wikipedia.org/wiki/Hebungsrisse_in_Staufen_im_Bre...

The large portion of single family homes in Sweden are heated (and cooled) using geothermal heat pumps. The drill holes are 100-150m deep.

Geothermal energy for power generation and heat pumps for heating homes are totally different systems. It's like comparing a fireplace in your house to a nuclear power plant.

I think there is terminological difference between ground source heat pumps and geothermal energy. First is in actuality naturally stored solar energy. Where later is from internal activity of earth.

There's a few large building air conditioning units that do exactly this. Ice Bear was one brand name I think.

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