Sand battery

[loki]

Hi! As a new member,I am Interested in building a rocket heater inside a sand battery. My goal is simpel: heat up the sand and extract the generated heat by build in air pipes that blow the warmth into the house.
(260 m3)

The idea sounds simpel, but I am clueless how much sand storage I need and what's the best way to get the heat from the rocket heater into the sand. Little insulation on the rocket heater seems logical....

Any help or suggestions will be highly appreciated.

Thanks in advance

Robert

The Netherlands

[Dan (Upstate NY, USA)]

Much simpler to just put the mass in the house and heat that directly.

Then you don't need electricity to move the heat around.

[fiedia]

I would put a rocket inside a long bell. In order to reduce the bell height and increase length or depth, I would use a design without riser (vortex or DSR). Put your sand on top of the bell with your pipes in it.

Regarding power, what do you use presently to heat your house?

[gadget]

Mass thermal storage. You need to know your needed BTU's spread out over time between firing. You need to decide to build it big enough for the worst day or smaller for average winter days and just fire it more often.

Sand would require more surface area for your heat exchanger than say dirt or water. I don't know sands heat capacity vs volume but I believe it is much lower than dirt or water. Heat transfer will be slow through the sand, there is allot of air in there. You would be better off mixing the sand with clay and packing it.

Water has a very high heat capacity but has other issues to deal with. I calculated for my old house once I needed 3000(?) gallons of water to store BTU's for 12 hours. Thats a pretty big tank. You may need 2-3 times that volume for sand.

Are you planning on building it outside?

[fuegos]

Welcome to the forum Loki, its good to have new members.
Sand would require more surface area for your heat exchanger than say dirt or water. I don't know sands heat capacity vs volume but I believe it is much lower than dirt or water. Heat transfer will be slow through the sand, there is allot of air in there. You would be better off mixing the sand with clay and packing it.

Yes this has been discussed at some length before.Sand turned out to be not a good choice for filler in a piped bench.
I think the first step in any build is to calculate the M3 of your space - 263 M and then look up the spreadsheet in batchrocket.eu and using the data see what size of build you need.Rocket stoves tend to work best in fairly small, open spaces but there are some builds on here that heat quite large spaces. one in particular comes to mind from Canada with a bell that extended to the first floor of the building, using a 200mm system.Hopefully this rings a bell with someone (no pun intended) & a link could be posted ?

[fiedia]

May be instead of pipes in sand, you could build a brick structure on top of your bell. A sort of heat exchanger air/bricks.

[gadget]

I think OP wants to put the heater outside. That would be harsh going out and loading wood frequently.

[danpagan]

> "Yes this has been discussed at some length before.Sand turned out to be not a good choice for filler in a piped bench."

Sorry for necro-posting but I am interested in reading more about this. Was the conclusion that it was hard to get the heat into the sand, or from the sand? Please could you share a link.

As I understand it sand is overall the best storage medium for heat. It's cheap, easy to work with, and dense with great thermal properties. I also have one big advantage over water that it doesn't boil, so it's safer and capable of storing heat up to around 600 degrees celsius. Which is why it has been used in some innovative new start ups.

[foxtatic]

Oct 22, 2023 0:33:04 GMT -8 danpagan said:

"As I understand it sand is overall the best storage medium for heat."

I'm not sure how you came to this conclusion. Sand is widely regarded as a very low tier heat storage medium because it is not dense at all. All the air between the sand particles acts more as insulation. Best example is a sandy beach in the sun. The surface of the sand is hot, but if you wiggle your foot down a couple inches it is cool. This is because sand is not dense enough to conduct the heat from the surface even a few inches down. 


 

[satamax]

Well, dry sand is kind of insulating, with billionth of tiny air pockets. Monolithic mass is a smidge better. Stones embedded in mortar.

Check pebble style rockets at permies.