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Gigantic heat caverns in Mustikkamaa have now been filled with water (2021)

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Re: Gigantic heat caverns in Mustikkamaa have now been filled with water (2021)

#51

Post by lazide »

Filligree wrote: post #26
lazide wrote: post #14

Earlier quoted context omitted.

It would be more efficient without the heat exchanger, but you’re almost certainly right - the reservoir water would probably be too oxygenated/mineralized for direct use if being stored in contact with the rock, at least without a lot of additional treatment. Don’t want to kill all those underground pipes with mineral buildup as things precipitate out as it cools.

Counterflow heat exchangers easily approach 100% efficiency. It needs to be large enough, and needs sensors to control the flow, but both of those are trivial at this scale.

They’ll need to move 2x the volume of water, and have more infrastructure to maintain - even if it was actually 100% thermally efficient. Not counting capital costs. Which I’d count as efficiency issues.

The water pumping and maintenance costs are likely going to be their largest ongoing costs, no?

Re: Gigantic heat caverns in Mustikkamaa have now been filled with water (2021)

#52

Post by notforviewingit »

andrelaszlo wrote: post #43
SAI_Peregrinus wrote: post #35

Earlier quoted context omitted.

+100°C (relative to some other temperature not clearly explained, probably the rock) vs 90°C absolute temperature.

That would mean that the rock baseline would be 10 degrees below freezing, which seems improbable. I think it would be close to the yearly average temperature for Helsinki (6.5°C) that close to the surface. Maybe I'm missing your point?

The heat store is used in the winter when it is cold.

Re: Gigantic heat caverns in Mustikkamaa have now been filled with water (2021)

#53

Post by lazide »

mschuster91 wrote: post #23
lazide wrote: post #14

Earlier quoted context omitted.

It would be more efficient without the heat exchanger, but you’re almost certainly right - the reservoir water would probably be too oxygenated/mineralized for direct use if being stored in contact with the rock, at least without a lot of additional treatment. Don’t want to kill all those underground pipes with mineral buildup as things precipitate out as it cools.

> It would be more efficient without the heat exchanger Not really, heat pumps as a transfer method can achieve better total efficiency and make distribution of the heat easier.

That is an interesting thought, but seems like the capex and ongoing electrical costs of the heat pump would be too high?

They’re looking to make cheap use of the existing waste heat, after all, which while ‘low quality’ is high enough quality for district heating already.

Re: Gigantic heat caverns in Mustikkamaa have now been filled with water (2021)

#54

Post by yason »

cmrdporcupine wrote: post #45

Got to wonder if this kind of thing wouldn't be possible here in Canada on the Canadian Shield (half-a-continent-sized slab o' granite), especially in places in Northern Ontario where there's old nickel mines, etc. Bonus points if one uses the waste heat from e.g. industrial plants to help heat up the water.

The municipal heating network consists of both cooling and warming networks. Excess heat from, for example, data centers will be used to heat the water. Newer apartments are cooled using cold water from the network in the summer and heated using hot water in the winter. There are also joint power-and-heat plants connected to the heating network which are quite efficient: first the generated heat is used to drive a generator turbine and the remaining waste heat is piped into the municipal heating network. Combined efficiency is way higher than with generator-only plants or heating-only plants.

Re: Gigantic heat caverns in Mustikkamaa have now been filled with water (2021)

#55

Post by nikanj »

Reason077 wrote: post #37
iljah wrote: post #2

This energy storage system near Helsinki, Finland operated by Helen ( https://en.wikipedia.org/wiki/Helen_Oy ) might be interesting for HN readers. Some facts from previous article ( https://www.helen.fi/en/news/2020/mustikkamaa ), not sure which one would've been better in url field: District heat is stored in two rock caverns in Mustikkamaa. The temperature of the water in the caverns varies between 50 and 90 °C. T…

This is a cool project, and I'm sure it has many benefits beyond just carbon savings. But 21,000 tonnes per year is surprisingly little in the scheme of things. Equivalent of about 150 or so long-haul 777 flights?

That tells you how pointless all the at-home energy savings are when everyone and their dog flies to a weekend getaway every month

Re: Gigantic heat caverns in Mustikkamaa have now been filled with water (2021)

#56

Post by euroderf »

iljah wrote: post #2

This energy storage system near Helsinki, Finland operated by Helen ( https://en.wikipedia.org/wiki/Helen_Oy ) might be interesting for HN readers. Some facts from previous article ( https://www.helen.fi/en/news/2020/mustikkamaa ), not sure which one would've been better in url field: District heat is stored in two rock caverns in Mustikkamaa. The temperature of the water in the caverns varies between 50 and 90 °C. T…

> The temperature of the water in the caverns varies between 50 and 90 °C.

Presumably 50 is in April or May and 90 is in August or September. Or are these swings shorter-term ?

Re: Gigantic heat caverns in Mustikkamaa have now been filled with water (2021)

#57

Post by euroderf »

anttiharju wrote: post #38
askonomm wrote: post #24

Earlier quoted context omitted.

Mustikamaa in Estonian :)

I've heard people joke that if a Finnish person just spends enough time in Estonia they start to understand it :)

Finns will say that Estonian sounds like some kind of really odd super-rural accent.

Estonians will say they wonder why the heck it takes a Finn twice as long as an Estonian to say the same thing.

Re: Gigantic heat caverns in Mustikkamaa have now been filled with water (2021)

#58

Post by euroderf »

cromulent wrote: post #39

Mustikkamaa is a recreational island about 3 kilometres from Helsinki’s center. It’s really nice. It’s a gateway island to Korkeasaari, the city zoo island.

So there must be a maze of underground pipes westward to Helsinki peninsula and to points north of Mustikkamaa. In any case the ground under Helsinki must look like Swiss cheese - Finns are tunnelers. Thru granite.

Re: Gigantic heat caverns in Mustikkamaa have now been filled with water (2021)

#59

Post by euroderf »

andrelaszlo wrote: post #43
SAI_Peregrinus wrote: post #35

Earlier quoted context omitted.

+100°C (relative to some other temperature not clearly explained, probably the rock) vs 90°C absolute temperature.

That would mean that the rock baseline would be 10 degrees below freezing, which seems improbable. I think it would be close to the yearly average temperature for Helsinki (6.5°C) that close to the surface. Maybe I'm missing your point?

6.5 sounds right. Average ground temperatures down where they are stable are under ten degrees C. So this project will definitely warm up the surrounding rock, which (I guess) will increase its effective heat capacity.

Re: Gigantic heat caverns in Mustikkamaa have now been filled with water (2021)

#60

Post by quacked »

nikanj wrote: post #55
Reason077 wrote: post #37

Earlier quoted context omitted.

This is a cool project, and I'm sure it has many benefits beyond just carbon savings. But 21,000 tonnes per year is surprisingly little in the scheme of things. Equivalent of about 150 or so long-haul 777 flights?

That tells you how pointless all the at-home energy savings are when everyone and their dog flies to a weekend getaway every month

I know people who attend sit-in protests at Chase Bank locations over fossil fuel divestment who also fly internationally 3-4 times per year for pleasure. The cognitive dissonance and lack of engineering intuition among the general populace is staggering.
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