> the temperature of the water in the heat cavern will vary between +45 and +100 degrees I'm not sure if I should be assuming Fahrenheit or Celsius? The article isn't clear on the units here.
If it isn't a story from the US, it will be Celsius.
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)
#12I 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.
Re: Gigantic heat caverns in Mustikkamaa have now been filled with water (2021)
#13> the temperature of the water in the heat cavern will vary between +45 and +100 degrees I'm not sure if I should be assuming Fahrenheit or Celsius? The article isn't clear on the units here.
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
Re: Gigantic heat caverns in Mustikkamaa have now been filled with water (2021)
#14Earlier quoted context omitted.
(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 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.
Re: Gigantic heat caverns in Mustikkamaa have now been filled with water (2021)
#15One application of this technology is to economically harnessing fusion power. Sadly there are considerable engineering and political difficulties. https://en.wikipedia.org/wiki/Project_PACER
Re: Gigantic heat caverns in Mustikkamaa have now been filled with water (2021)
#16There is also one of these in Västerås, Sweden, about 100 km from Stockholm. 3 caverns 30 m below the surface that used to store oil during the Cold War in case shit would hit the fan. 300,000 cubic meters, 13 GWh. Basically identical. Not as far along as the Finnish site though; it'll start backing up the district heating plant in 2024.
Re: Gigantic heat caverns in Mustikkamaa have now been filled with water (2021)
#17Earlier 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.
There is a heat exchanger.
https://www.slideshare.net/HelsinginEnergia/innovation-and-s... (slide 21)
Re: Gigantic heat caverns in Mustikkamaa have now been filled with water (2021)
#18Earlier quoted context omitted.
(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 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.
Ah, on second thought you're probably right.
Re: Gigantic heat caverns in Mustikkamaa have now been filled with water (2021)
#19Earlier 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'm no physicist but I assume that you'd need to put a lot more energy into the system before the water starts boiling, so you wouldn't have to worry about it?
If the energy would just be lost otherwise, you might as well go all the way to 100℃?
That's at 1 atm, perhaps the water is a bit pressurized as well?
A bit further down there's this confusing quote though:
> District heat is stored in two rock caverns in Mustikkamaa. The temperature of the water in the caverns varies between 50 and 90 °C.
Re: Gigantic heat caverns in Mustikkamaa have now been filled with water (2021)
#20I wonder why they used tap water instead of seawater
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.