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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)

#21

Post by onetimeuse92304 »

Sharlin wrote: post #5
Filligree wrote: post #4

Earlier quoted context omitted.

Seawater erodes everything it touches. It isn’t impossible to build hardware that touches it, but it’s more expensive and needs more maintenance. Fresh water makes the entire project much cheaper.

(Edit: this is wrong – see comments) And this water is supposed to be fed directly into the homes of hundreds of thousands of customers through the existing district heating network which obviously isn't built with seawater in mind. A seawater storage facility would at the very least require a heat exchanger which would decrease efficiency.

I don't think it is this water that is going to be fed directly to homes. More likely there is going to be systems of heat exchangers.

They mention they are recovering heat from waste water. Obviously, they aren't pumping waste water into the system but rather use heat exchange to extract energy.

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

#22

Post by onetimeuse92304 »

lazide wrote: post #14
michpoch wrote: post #9

Earlier quoted context omitted.

I don't think they'll be pumping that water directly into the heat distribution system. My understanding is that it'll be used as a heat reservoir and there will be some sort of heat exchanger to get the heat out of it.

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,

No, the only cost really is the cost of heat exchanger and maybe energy to pump water through the heat exchanger. Heat exchange approaches 100% thermal efficiency with large enough heat exchanger.

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

#23

Post by mschuster91 »

lazide wrote: post #14
michpoch wrote: post #9

Earlier quoted context omitted.

I don't think they'll be pumping that water directly into the heat distribution system. My understanding is that it'll be used as a heat reservoir and there will be some sort of heat exchanger to get the heat out of it.

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.

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

#25

Post by alright2565 »

onetimeuse92304 wrote: post #20
citrin_ru wrote: post #6

Earlier quoted context omitted.

Why they should use seawater? Fresh water is not in shortage in this region - yearly precipitation significantly exceeds evaporation.

Please, take a look at the map. Even cursory inspection of it will reveal to you that Finland is the land of lakes. Finland has vast stores of fresh water and annual precipitation has nothing to do with it.

They have a massive desalination and pipeline operation to create lakes throughout the country?

Or is it the the sun and rain that created the lakes?

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

#26

Post by Filligree »

lazide wrote: post #14
michpoch wrote: post #9

Earlier quoted context omitted.

I don't think they'll be pumping that water directly into the heat distribution system. My understanding is that it'll be used as a heat reservoir and there will be some sort of heat exchanger to get the heat out of it.

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.

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

#27

Post by kwhitefoot »

Torkel wrote: post #12
coffeebeqn wrote: post #3

I wonder why they used tap water instead of seawater

Sibling comments are on to this too, but I think an important detail here is that the water in lakes, river and ground in the nordics is so clean that the extra cleaning needed to make it "tap water" isn't really as big of a deal as it might be in other parts of the world.

The little town I live in (about 40 km south of Oslo) is supplied from a lake in the granite hills. They filter out the bugs and precipitate the solids with a little aluminium sulphate and that's it. It's above all the agriculture so no chlorine is needed and there is no chalk so no problems with deposits on the insides of kettles and water heaters.

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

#29

Post by toivotuo »

alright2565 wrote: post #25
onetimeuse92304 wrote: post #20

Earlier quoted context omitted.

Please, take a look at the map. Even cursory inspection of it will reveal to you that Finland is the land of lakes. Finland has vast stores of fresh water and annual precipitation has nothing to do with it.

They have a massive desalination and pipeline operation to create lakes throughout the country? Or is it the the sun and rain that created the lakes?

https://www.geographyrealm.com/finland-many-lakes/

Thanks to the last ice age and retreating glaciers...

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

#30

Post by kagakuninja »

sdflhasjd wrote: post #13
Torkel wrote: post #11

Earlier quoted context omitted.

If it isn't a story from the US, it will be Celsius.

That's what I would normally have assumed, but 100C seemed a little hot for water just sitting in a big cistern

I interpreted it as +100C compared to the temperature of the rock
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