3 ms·

> The borehole thermal energy system (BTES) is located underground to store large quantities of heat collected in the summer to be used in the winter. Basicall

by rcv 4y ago

> The borehole thermal energy system (BTES) is located underground to store large quantities of heat collected in the summer to be used in the winter. Basically they heat up the soil and rock beneath their park during the summer using hot water/glycol from their solar arrays, and then during the winter they pump cold water through it which soaks that heat back up. What's amazing is that it apparently took 4 years to fully saturate the area with heat energy.

tsol 4y ago
And there isn't a massive amount of heat loss with that? It's a cool idea, what surprises me is that it actually works
- ggm 4y ago
  London Underground originally was kept cool because of its thermal mass. Over the last 100 years, it has now turned into a giant heat store, and there is an emerging airconditioning problem. I believe its the resistive heating from the trains passing through, over time, plus the sweaty exhalation of millions of people. TL;DR ground heat is remarkably persisting and takes years to dissipate, if deep enough. Coolth, the absence of heat, is really the same in this regard, because the heat transport through the ground is not rapid. This is also why deep hot rocks need fracking to get thermal energy working unless its happening naturally. Rocks all around the place "down there" are hot. Very hot. A lot of ground water comes out hot. Bath (uk) for instance. its hot. So how come the rest of bath is cold and wet? Because ground heat doesn't move fast.
  - O__________O 4y ago
    From Wikipedia, “When the tunnels were built the clay temperature was around 14 °C; this has now risen to 19–26 °C” According to the same page though, the tunnels only add 4% to the heat and humans add 7% — remaining 89% comes from the trains; unless I misunderstood something. https://en.m.wikipedia.org/wiki/London_Underground_cooling https://en.m.wikipedia.org/wiki/London_Underground_cooling
- O__________O 4y ago
  Yes, appears so; after looking around, found three additional documents. (1) 10 year report on the project, which has detailed charts on the performance of the system: https://www.dlsc.ca/reports/swc2017-0033-Mesquita.pdf https://www.dlsc.ca/reports/swc2017-0033-Mesquita.pdf (2) More mathematical explanation of the dynamics of the system, specifically: “Because of their construction principle, BTES are not thermally insulated to the bottom and the side; only a top insulation layer reduces the losses to the environment. As the thermal conductivity of underground material is rather moderate, in a range of 1–5 W/m·K, heat losses can be kept low if the total volume is large enough to achieve a good surface-to-volume ratio. Size is important because heat losses are proportional to the storage surface while the storage capacity is proportional to the volume.“ https://www.sciencedirect.com/topics/engineering/borehole-thermal-energy-storage https://www.sciencedirect.com/topics/engineering/borehole-th... (3) What is the specification W/mK https://forum.digikey.com/t/what-is-the-specification-w-mk/370 https://forum.digikey.com/t/what-is-the-specification-w-mk/3...

by rcv 4y ago

tsol 4y ago

And there isn't a massive amount of heat loss with that? It's a cool idea, what surprises me is that it actually works

ggm 4y ago
London Underground originally was kept cool because of its thermal mass. Over the last 100 years, it has now turned into a giant heat store, and there is an emerging airconditioning problem. I believe its the resistive heating from the trains passing through, over time, plus the sweaty exhalation of millions of people. TL;DR ground heat is remarkably persisting and takes years to dissipate, if deep enough. Coolth, the absence of heat, is really the same in this regard, because the heat transport through the ground is not rapid. This is also why deep hot rocks need fracking to get thermal energy working unless its happening naturally. Rocks all around the place "down there" are hot. Very hot. A lot of ground water comes out hot. Bath (uk) for instance. its hot. So how come the rest of bath is cold and wet? Because ground heat doesn't move fast.
- O__________O 4y ago
  From Wikipedia, “When the tunnels were built the clay temperature was around 14 °C; this has now risen to 19–26 °C” According to the same page though, the tunnels only add 4% to the heat and humans add 7% — remaining 89% comes from the trains; unless I misunderstood something. https://en.m.wikipedia.org/wiki/London_Underground_cooling https://en.m.wikipedia.org/wiki/London_Underground_cooling
O__________O 4y ago
Yes, appears so; after looking around, found three additional documents. (1) 10 year report on the project, which has detailed charts on the performance of the system: https://www.dlsc.ca/reports/swc2017-0033-Mesquita.pdf https://www.dlsc.ca/reports/swc2017-0033-Mesquita.pdf (2) More mathematical explanation of the dynamics of the system, specifically: “Because of their construction principle, BTES are not thermally insulated to the bottom and the side; only a top insulation layer reduces the losses to the environment. As the thermal conductivity of underground material is rather moderate, in a range of 1–5 W/m·K, heat losses can be kept low if the total volume is large enough to achieve a good surface-to-volume ratio. Size is important because heat losses are proportional to the storage surface while the storage capacity is proportional to the volume.“ https://www.sciencedirect.com/topics/engineering/borehole-thermal-energy-storage https://www.sciencedirect.com/topics/engineering/borehole-th... (3) What is the specification W/mK https://forum.digikey.com/t/what-is-the-specification-w-mk/370 https://forum.digikey.com/t/what-is-the-specification-w-mk/3...