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Comment by elil17 | Hacker News Reader

Another type for thermal battery: ice thermal storage. Instead of running AC, it’s a freezer that makes ice during the night (using off-peak electricity and taking advantage of the cooler nighttime air) and then melts it during the day to cool large buildings. They’re a ridiculously good idea if you’re running a large enough HVAC system - they can even lower capital costs compared to traditional systems. Unfortunately, many building operators don’t use them because they’re unfamiliar with the technology or because they take up more building footprint. https://en.m.wikipedia.org/wiki/Ice_storage_air_conditioning

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There is a large building in Chicago that basically contains a giant ice cube.

https://www.enwave.com/locations/chicago.htm

From their website I gleaned that they have 5 facilities, and several miles of piping that carries ice-cold water to their customers, large buildings around.

It's the maximally outsourced air-conditioning solution I ever saw :)

The city of Munich in Germany actually has a cooling network to cool large buildings in the city centre. See here: https://www.swm.de/geschaeftskunden/fernkaelte

Helsinki too has district cooling in addition to district heating: https://www.helen.fi/en/news/2018/cooling-demand-in-helsinki...

District cooling (as opposed to district heating) is fairly common in Gulf countries.

I hadn't heard the term "district heating" before, but it makes sense.

The name puts me in mind of a chain called District Taco, but unfortunately that doesn't mean a supply of tacos piped directly into your house.

https://www.districttaco.com/

Not even slightly authentically Mexican, but nonetheless quite tasty.

They're around in the US as well. Worked on one in downtown Austin in a previous life.

There’s versions of this in NYC that use the bay as a first pass heat exchanger. Not sure how deep or cold the Chicago river is but I’d think they’d be able to do the same.

Don't forget that Chicago has Lake Michigan too.

Paris has a large cold water network:

https://www.climespace.fr/en

It's used by some datacenters IIRC.

FWIW they suck at their job. Every year there are some days where we don't have AC in the office during summer because they stop sending cold water to the building I work in.

The city of Austin has a chilled water loop and more. It's pretty neat how it all works. https://austinenergy.com/ae/commercial/commercial-services/d...

You'd like what we have in Toronto- we use Lake Ontario as a heat sink.

https://en.wikipedia.org/wiki/Enwave#Deep_Lake_Water_Cooling...

75% less energy than traditional air conditioning.

Doesn't that increase the lake's overall temp though?

Probably not, because there's a second interesting fact about the system (which I just learned): the water isn't returned to the lake directly.

Instead it's used as an input to the filtration plants, cleaned, and used as municipal water. I'm not sure what the overall effect of getting slightly warmer water in the municipal system is, but I bet it's a win overall since we spend so much energy heating up water (as per the article!).

Edit: also the lake is 1600 cubic km of water, so I dunno if we could ever noticeably change the lake temperature this way.

1600 km³ × .1 kcal/ℓ is 670 petajoules, so that's the energy input you'd need to heat the lake up by 0.1°. World marketed energy consumption is about 20 TW, so the entire world economy could heat the lake up at about 0.23° per day if you covered it in a blanket first. So it's not completely out of the question, but only 2.7 million people live in Toronto, so Toronto probably only uses about 20 GW.

By comparison, the lake's surface area is 19000 km², so when the sun is shining on it (at a slanting angle, as it always does that far north), it's receiving about 10 TW of solar energy, half the amount used by the entire human economy. It reflects about 10% of that into space and converts the rest into heat, then re-emits it as longwave infrared light, half at night.

For some places like Australia you would want to run it in the middle of the day when solar peaks and power prices go negative.

There's a local university that uses this method to cool their musical performance space, which causes it to be comfortably cold but without the noise of AC.

I'm curious of the mechanics of this, since the expansion of ice makes it a pain to manage.

Surprisingly simple design, actually. The water sits in a large tank with plenty of room to expand and contract. Pipes filled with refrigerant run inside the tank. Here’s a photo: https://images.app.goo.gl/Td6RdFbuVE8QJAmu6

This guy has ice storage:

https://youtu.be/N3Em64OBGqI

This seems like it could backfire if we start to get the majority of our electricity from solar, though, right? Nighttime may not always be considered off-peak.

Well you’d just make the ice whenever it’s cheapest, taking into account the effects of cold air and of electricity prices. In the future it might make sense to make the ice when it’s warm out because power is nearly free at those times. But a smart building automation system could know when cloud cover is predicted and make ice the night before.

If I recall correctly, these are not suitable for residential use, right?

One company tried to make a residential version (called Ice Bear, IIRC), but it was unsuccessful. There’s no reason it couldn’t be practical, though. Especially with something like some prototype concepts which propose putting all heating and cooling appliances (refrigerator, water heater, HVAC, and possibly even a drying machine) on a single heat pump loop, ice thermal storage could become economical for single family homes in the near future.

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