3 ms·

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

by Torkel 3y ago

sdflhasjd 3y ago
That's what I would normally have assumed, but 100C seemed a little hot for water just sitting in a big cistern
- andrelaszlo 3y ago
  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.
  - SAI_Peregrinus 3y ago
    +100°C (relative to some other temperature not clearly explained, probably the rock) vs 90°C absolute temperature.
    - andrelaszlo 3y ago
      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?
      - notforviewingit 3y ago
        The heat store is used in the winter when it is cold.
      - euroderf 3y ago
        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.
  - Reason077 3y ago
    > "perhaps the water is a bit pressurized as well?" I suppose in such a large storage vessel, most of the water is naturally pressurised by its own weight. So most of it won't boil, even at 100°C, except right at the surface?
    - pixl97 3y ago
      If the water is not being heated from the bottom then I'd expect all the hottest water at the top/and or at the point of entry to the system. Heat loss into the holding substrate will cause rather rapid convection and surface boiling.
- kagakuninja 3y ago
  I interpreted it as +100C compared to the temperature of the rock
  - ceejayoz 3y ago
    That would be well above boiling.
    - kagakuninja 3y ago
      Lol, you are right...

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

by Torkel 3y ago

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

sdflhasjd 3y ago

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

andrelaszlo 3y ago
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.
- SAI_Peregrinus 3y ago
  +100°C (relative to some other temperature not clearly explained, probably the rock) vs 90°C absolute temperature.
  - andrelaszlo 3y ago
    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?
    - notforviewingit 3y ago
      The heat store is used in the winter when it is cold.
    - euroderf 3y ago
      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.
- Reason077 3y ago
  > "perhaps the water is a bit pressurized as well?" I suppose in such a large storage vessel, most of the water is naturally pressurised by its own weight. So most of it won't boil, even at 100°C, except right at the surface?
  - pixl97 3y ago
    If the water is not being heated from the bottom then I'd expect all the hottest water at the top/and or at the point of entry to the system. Heat loss into the holding substrate will cause rather rapid convection and surface boiling.
kagakuninja 3y ago
I interpreted it as +100C compared to the temperature of the rock
- ceejayoz 3y ago
  That would be well above boiling.
  - kagakuninja 3y ago
    Lol, you are right...