4 ms·

> It also actively prevents heat from transferring into the sand So it's slower to charge. And the charge speed is presumably adjustable by circulating more ai

by sfink 4y ago

> It also actively prevents heat from transferring into the sand So it's slower to charge. And the charge speed is presumably adjustable by circulating more air (or moving it through faster). It's unclear whether this is a problem for its intended application. It may charge fast enough. > and stores far less heat than the sand itself. That would only be relevant if you were comparing an equal volume. The same mass of clay and sand should store roughly the same amount of energy, it's just that the sand one would be bigger to accommodate more air. And being bigger isn't even a drawback here, since bigger means proportionally less surface area to volume that you're losing heat through. > That's why in residential mass storage, ... "Residential" could imply that you don't want a giant sand silo in the middle of some housing units, so I agree there. You would need to put this somewhere that size doesn't matter much.

Someone 4y ago
> “Residential" could imply that you don't want a giant sand silo in the middle of some housing units, so I agree there. You would need to put this somewhere that size doesn't matter much. Can’t you build that silo underground? If so, size wouldn’t matter much. You could have a playground, communal garden or, if you must, parking spaces on top of it, so it wouldn’t really use any area.
- zdragnar 4y ago
  Digging out, building retaining walls and waterproofing (you really don't want ground water or rain water getting into your 600 degree C sand) and so forth make it much cheaper and more practical to build above ground.
zdragnar 4y ago
A few things: Clay weighs significantly more than sand. For the same volume of material, clay will store significantly more thermal energy. The big question is- is the hot air on a closed loop or an open loop? I don't know of too many fans comfortable cycling 600C air, which means that you need an open loop of air (fresh air > fan > heater > sand > exhaust). If the sand isn't drawing heat off of the hot air fast enough, the heat won't actually "sink" in through the sand. If we are talking a closed loop of air (fan > heater > sand > fan) then the sand will get fully heated. My reference to "residential" is the aformentioned rocket stove mass heater- see https://richsoil.com/rocket-stove-mass-heater.jsp https://richsoil.com/rocket-stove-mass-heater.jsp or https://www.youtube.com/watch?v=fwCz8Ris79g https://www.youtube.com/watch?v=fwCz8Ris79g and https://www.youtube.com/watch?v=8ptwncPImuo https://www.youtube.com/watch?v=8ptwncPImuo if you prefer videos. These types of things typically stay warm for about 24 hours, so they're burned once a day, maybe once every other day depending on how the house is insulated. Since these are all wood fired, they must be open loop, and sand is almost universally acknowledged as a terrible idea to use for thermal storage.

by sfink 4y ago

Someone 4y ago

> “Residential" could imply that you don't want a giant sand silo in the middle of some housing units, so I agree there. You would need to put this somewhere that size doesn't matter much. Can’t you build that silo underground? If so, size wouldn’t matter much. You could have a playground, communal garden or, if you must, parking spaces on top of it, so it wouldn’t really use any area.

zdragnar 4y ago
Digging out, building retaining walls and waterproofing (you really don't want ground water or rain water getting into your 600 degree C sand) and so forth make it much cheaper and more practical to build above ground.

zdragnar 4y ago

A few things: Clay weighs significantly more than sand. For the same volume of material, clay will store significantly more thermal energy. The big question is- is the hot air on a closed loop or an open loop? I don't know of too many fans comfortable cycling 600C air, which means that you need an open loop of air (fresh air > fan > heater > sand > exhaust). If the sand isn't drawing heat off of the hot air fast enough, the heat won't actually "sink" in through the sand. If we are talking a closed loop of air (fan > heater > sand > fan) then the sand will get fully heated. My reference to "residential" is the aformentioned rocket stove mass heater- see https://richsoil.com/rocket-stove-mass-heater.jsp https://richsoil.com/rocket-stove-mass-heater.jsp or https://www.youtube.com/watch?v=fwCz8Ris79g https://www.youtube.com/watch?v=fwCz8Ris79g and https://www.youtube.com/watch?v=8ptwncPImuo https://www.youtube.com/watch?v=8ptwncPImuo if you prefer videos. These types of things typically stay warm for about 24 hours, so they're burned once a day, maybe once every other day depending on how the house is insulated. Since these are all wood fired, they must be open loop, and sand is almost universally acknowledged as a terrible idea to use for thermal storage.