4 ms·

Stupid question: can we harness this 100 year old heat to power something today?

thescriptkiddie 5y ago
Yes https://www.newcivilengineer.com/innovative-thinking/harnessing-heat-from-the-tube-11-05-2020/ https://www.newcivilengineer.com/innovative-thinking/harness...
vikingerik 5y ago
You can't exactly harness heat; what can be harnessed is a temperature differential, to convert into some form of mechanical motion or electrical potential. You'd need some apparatus that connects the hot mass and some cold sink with thermocouples. Whether that's possible or feasible on the scale of the London Tube, I don't know. https://en.wikipedia.org/wiki/Thermoelectric_effect https://en.wikipedia.org/wiki/Thermoelectric_effect Instead of that, probably a more feasible way to make use of heat is just as heat, by some way of circulating it into buildings in the winter. One interesting angle of looking at this would be that it's really an artificially created geothermal source.
- simulate-me 5y ago
  Heat is energy, so I find it surprising that it can't be harnessed. Is it really not possible to take some of the energy out of a system and use it for something?
  - willcipriano 5y ago
    Air conditioning is really silly when you think about it. It takes a ton of energy to move some energy outside. It feels like it could be self powered.
    - BenjiWiebe 5y ago
      It's actually forcing the energy apart. The energy wants make this one big mess where every bit is the same temperature as every other bit. Your AC is working hard at pushing all the heat outdoors and making a pocket of cool inside.
    - ouchjars 5y ago
      Self-powered evaporative air conditioning is an ancient technology. Air conditioning as we understand and use it today is a gold-plated band-aid over bad design. It's so entrenched you almost can't get a house built any other way.
  - ac29 5y ago
    Not all heat is useful. If there was a magic device that could take any heat and convert it into electricity, global warming could be trivially reversed.
    - arcticbull 5y ago
      There is the Seebeck effect, where you run a Peltier junction in reverse. Efficiency is, to put it mildly, low. [1] [1] https://en.wikipedia.org/wiki/Thermoelectric_generator https://en.wikipedia.org/wiki/Thermoelectric_generator
      - vikingerik 5y ago
        This still works from a temperature differential, not just a quantity of heat.
    - nixonpjoshua1 5y ago
      furthermore you could prevent the heat death of the universe :)
  - RugnirViking 5y ago
    If it got hot enough you could use a geothermal-type generator for reasonable efficiency, but that is (of course) still exploiting a temprature differential (a place where water remains liquid, and a hot place where it becomes high pressure steam to drive a turbine). However sadly that is unlikely to happen before the tunnels become unlivable :)
- naravara 5y ago
  An additional dumb question. If all the expense was undertaken to build all the piping to functionally turn the tube into a heat source for buildings, how long would it take to sap the stored heat from the soil to the point where the temperature differential doesn't work anymore? At some point would they have to switch from having it be a heat source in winter to making it a heat dump in summer?
stubish 5y ago
Pump cold air down, suck warmer air up, heat buildings in winter. Same idea lots of passive houses use to regulate temperature.

Yes https://www.newcivilengineer.com/innovative-thinking/harnessing-heat-from-the-tube-11-05-2020/ https://www.newcivilengineer.com/innovative-thinking/harness...

vikingerik 5y ago

You can't exactly harness heat; what can be harnessed is a temperature differential, to convert into some form of mechanical motion or electrical potential. You'd need some apparatus that connects the hot mass and some cold sink with thermocouples. Whether that's possible or feasible on the scale of the London Tube, I don't know. https://en.wikipedia.org/wiki/Thermoelectric_effect https://en.wikipedia.org/wiki/Thermoelectric_effect Instead of that, probably a more feasible way to make use of heat is just as heat, by some way of circulating it into buildings in the winter. One interesting angle of looking at this would be that it's really an artificially created geothermal source.

simulate-me 5y ago
Heat is energy, so I find it surprising that it can't be harnessed. Is it really not possible to take some of the energy out of a system and use it for something?
- willcipriano 5y ago
  Air conditioning is really silly when you think about it. It takes a ton of energy to move some energy outside. It feels like it could be self powered.
  - BenjiWiebe 5y ago
    It's actually forcing the energy apart. The energy wants make this one big mess where every bit is the same temperature as every other bit. Your AC is working hard at pushing all the heat outdoors and making a pocket of cool inside.
  - ouchjars 5y ago
    Self-powered evaporative air conditioning is an ancient technology. Air conditioning as we understand and use it today is a gold-plated band-aid over bad design. It's so entrenched you almost can't get a house built any other way.
- ac29 5y ago
  Not all heat is useful. If there was a magic device that could take any heat and convert it into electricity, global warming could be trivially reversed.
  - arcticbull 5y ago
    There is the Seebeck effect, where you run a Peltier junction in reverse. Efficiency is, to put it mildly, low. [1] [1] https://en.wikipedia.org/wiki/Thermoelectric_generator https://en.wikipedia.org/wiki/Thermoelectric_generator
    - vikingerik 5y ago
      This still works from a temperature differential, not just a quantity of heat.
  - nixonpjoshua1 5y ago
    furthermore you could prevent the heat death of the universe :)
- RugnirViking 5y ago
  If it got hot enough you could use a geothermal-type generator for reasonable efficiency, but that is (of course) still exploiting a temprature differential (a place where water remains liquid, and a hot place where it becomes high pressure steam to drive a turbine). However sadly that is unlikely to happen before the tunnels become unlivable :)
naravara 5y ago
An additional dumb question. If all the expense was undertaken to build all the piping to functionally turn the tube into a heat source for buildings, how long would it take to sap the stored heat from the soil to the point where the temperature differential doesn't work anymore? At some point would they have to switch from having it be a heat source in winter to making it a heat dump in summer?

stubish 5y ago

Pump cold air down, suck warmer air up, heat buildings in winter. Same idea lots of passive houses use to regulate temperature.