6 ms·

Nearly have my own solar, I'm wondering if there's a way to do a home thermal battery like this (although for me might not be necessary, as I've also got a batt

Nearly have my own solar, I'm wondering if there's a way to do a home thermal battery like this (although for me might not be necessary, as I've also got a battery...) Like - if I put a water tank under the house, can I cool it (summers) / heat it (winters) as both a backup water supply, and thermal sink? And have that also work to help maintain house temperatures?

s1artibartfast 3y ago
You are talking about hydronic heating, which is old 1970s tech. Imo, it would make more sense to store the power in battery form, and cool or heat it on demand.
- jacquesm 3y ago
  That's true from an energy perspective but from an economics perspective it is very hard to beat a well insulated tank filled with water.
  - s1artibartfast 3y ago
    I get the physics, the question that economics when were talking about installing a well-insulated cistern under a house, and retrofitting it with hydronic Heating.
    - wolverine876 3y ago
      Disposing of the cistern capacitor chemical (H2O) is also better for the environment than the battery chemicals. Manufacturing is probably better too.
      - s1artibartfast 3y ago
        Sure. I have had hydronic heating in several houses. You don't even need storage. Soler thermal is common throughout the world. But on a price basis, you can get a 5kw battery for 2k. Good luck running water plumbing and radiators throughout your house for 20k
        wolverine876 3y ago
        > you can get a 5kw battery for 2k. Good luck running water plumbing and radiators throughout your house for 20k That's not quite apples-to-apples; the energy from the battery also needs distribution through the house. Of course, every house has wiring, not all already have radiators.
  - __MatrixMan__ 3y ago
    Especially if it's a large tank. You've got the square-cube law on your side here. Better still would be to use a truly huge cavern as a thermal battery for your whole city.
crote 3y ago
Using it for both heating and backup water supply is probably a really bad idea: you'd basically be storing water in the ideal temperature range for legionalla growth.
- __MatrixMan__ 3y ago
  The workaround is to use a heat exchanger so that you're not drinking the stored water, just transferring heat from it on-demand. They're doing similar things at larger scales in Sweden: https://www.bbvaopenmind.com/en/technology/innovation/underground-thermos-to-heat-a-city/ https://www.bbvaopenmind.com/en/technology/innovation/underg...
  - crote 3y ago
    Yes, but OP wanted to use it as both heat storage and emergency drinking water supply. If you're using a heat exchanger you'd still need separate tanks for hot water storage and for emergency drinking water - and that's the very thing they were trying to avoid.
toast0 3y ago
Water under your house is hard to use as a backup water supply. You would need a pump to use it in the house when your utility water had no (or low) pressure, and you'd want to bypass the pump in normal operations, etc: mechanically complex. It might be easier to have the water tank above the house, but only if your structure can manage the extra weight, and you need to be well prepped for leaks. And yeah, microorganisms.
petre 3y ago
It can be done but it's not that practical since you need a huge insulated tank and if you're also using the water you it's even less practical to store heat in it. One can use a pool as a heat sink during summer though. Water stores 1.16 kWh/m³K. The heat capacity could be increased with phase changing materials.

s1artibartfast 3y ago

You are talking about hydronic heating, which is old 1970s tech. Imo, it would make more sense to store the power in battery form, and cool or heat it on demand.

jacquesm 3y ago
That's true from an energy perspective but from an economics perspective it is very hard to beat a well insulated tank filled with water.
- s1artibartfast 3y ago
  I get the physics, the question that economics when were talking about installing a well-insulated cistern under a house, and retrofitting it with hydronic Heating.
  - wolverine876 3y ago
    Disposing of the cistern capacitor chemical (H2O) is also better for the environment than the battery chemicals. Manufacturing is probably better too.
    - s1artibartfast 3y ago
      Sure. I have had hydronic heating in several houses. You don't even need storage. Soler thermal is common throughout the world. But on a price basis, you can get a 5kw battery for 2k. Good luck running water plumbing and radiators throughout your house for 20k
      - wolverine876 3y ago
        > you can get a 5kw battery for 2k. Good luck running water plumbing and radiators throughout your house for 20k That's not quite apples-to-apples; the energy from the battery also needs distribution through the house. Of course, every house has wiring, not all already have radiators.
- __MatrixMan__ 3y ago
  Especially if it's a large tank. You've got the square-cube law on your side here. Better still would be to use a truly huge cavern as a thermal battery for your whole city.

crote 3y ago

Using it for both heating and backup water supply is probably a really bad idea: you'd basically be storing water in the ideal temperature range for legionalla growth.

__MatrixMan__ 3y ago
The workaround is to use a heat exchanger so that you're not drinking the stored water, just transferring heat from it on-demand. They're doing similar things at larger scales in Sweden: https://www.bbvaopenmind.com/en/technology/innovation/underground-thermos-to-heat-a-city/ https://www.bbvaopenmind.com/en/technology/innovation/underg...
- crote 3y ago
  Yes, but OP wanted to use it as both heat storage and emergency drinking water supply. If you're using a heat exchanger you'd still need separate tanks for hot water storage and for emergency drinking water - and that's the very thing they were trying to avoid.

toast0 3y ago

Water under your house is hard to use as a backup water supply. You would need a pump to use it in the house when your utility water had no (or low) pressure, and you'd want to bypass the pump in normal operations, etc: mechanically complex. It might be easier to have the water tank above the house, but only if your structure can manage the extra weight, and you need to be well prepped for leaks. And yeah, microorganisms.

petre 3y ago

It can be done but it's not that practical since you need a huge insulated tank and if you're also using the water you it's even less practical to store heat in it. One can use a pool as a heat sink during summer though. Water stores 1.16 kWh/m³K. The heat capacity could be increased with phase changing materials.