Increasing heat storage

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hobbyheater

hobbyheater

Minister of Fire
Nov 14, 2011
1,330
Port McNeill, Vancouver Island, BC Canada
I have used heat storage of 1000 gallons for thirty years but would really like another 250,000 btus of usable storage. In the 70s, before wood gasification, insulated bladder tanks and pressurized storage tanks, there was a movement to build concrete cisterns under the floor of a house, fill it with river rock and pump the water from boiler into this pit for heat storage. With advent of the Jetstream and the GARN, this form of storage disappeared.
Has any one ever tried adding grapefruit size river rock to a storage tank to increase the storage of the tank? Does anyone know what the btu storage capacity of 1 lb of rock?
My tank is constructed of 5/8" riveted boiler plate and is sitting on reinforced concrete saddles. It could accommodate the extra weight of about 4 yards of this rock which would be about 10,000 lbs. The rock would displace about 400-500 gallons of water.
I have left myself open on this one. Any ideas from anyone?

Allan
 
IIRC most common materials store .2btu/lb/degreeF (compared to water at 1) so only metals would be heavy enough to store more heat per unit of volume than water. Solid stone would be 40% of the capacity of the same volume of water (assuming 120 lb/cu ft stone and 60 lb/cu ft water)

edit: from the link below apparently even metals aren't more heat dense than water.
 
Interesting concept.

I would think that the water is actually going to be a better carrier of your heat than the river rock would be, depending on what the rock is made of. But looking at this link:

http://www.engineeringtoolbox.com/specific-heat-solids-d_154.html

it leads me to believe that the water is the better "battery" than the rock would be.

Using the river rock would reduce the volume of water that you need, and as a result it would remove the need for a bigger expansion tank in a pressurized system.

Also, just found this!

http://www.newton.dep.anl.gov/askasci/eng99/eng99597.htm
 
The rocks were good for storing energy if you planned on blowing air thru them, but water is by far a better heat storage and transfer medium. It takes a large pump to push rocks thru a piping system.

hr
 
Benjamin - Thank you for this very good info, and my wife just said thank you. She says that I have done 999 modifications to this system and only 333 have worked and she was not looking forward to collecting 5 tons of rock!!! :coolsmirk:

Allan
 
hobbyheater said:
Benjamin - Thank you for this very good info, and my wife just said thank you. She says that I have done 999 modifications to this system and only 333 have worked and she was not looking forward to collecting 5 tons of rock!!! :coolsmirk:

Allan
Click to expand...

LOL
 
There are some phase change materials that I saw at the solar decathlon in DC this year that can give you about 2x the BTU capacity per cubic foot compared to H2O. There were in a tank with an embedded HX (or window louver panels which was pretty neat). These were installed in net-zero home with limited space. I don't think they are economically viable for our boiler setups. Have you considered more aggressively address your heat load issues with sealing, caulking, insulation, etc?
 
My recollection from all the reading I did back in the seventies on solar heat is that water has a specific heat of 1 and all other materials' specific heat is something less than 1 except for phase change materials, i.e. eutectic salts. These materials freeze at temperatures of about 70 °F (I think. I'd have to research them again to be sure of temperatures) and melt above those temperatures. While re-freezing they give off their energy.

The best bang for your buck is water!
 
hobbyheater

How is your storage insulated? What do you figure you have for an R value for your storage tank? I insulated my tank with spray foam recently. I am amazed at how well it seals. The stuff seals every crack and crevace to give you zero air movement. It is expensive, but boy doys it do a nice job. When I gutted a floor of my house that had a crawl space under it and turned it into a garage I put in floor heating in the concrete floor and then I spray foamed the walls and ceiling with closed cell spray foam. Unbelievable. Almost all year round the garage hardly ever calls for heat. The sun warms it in the day time and the insulation holds that heat so well it is just awesome. In the dead of winter I heat the garage to 45-50 degrees. It does not take much to do that. My storage tank is 180 degrees and you can put your hand right on the foam and hardly tell it is hot on the other side. If your insulation on your tank is already good, no need to change obviously. But if it is not good, it would be something for you to consider in the future. My tank stays warm for quite a while, and I only have a little of the foam on it. Now I just need to put another layer on it to bring the whole R value up higher. I only have 1-2 inches on the bottom half and 3-5 on the top half. Hopefully next year I will have 5 inches over the whole thing with one more kit. That would give me an R35. Have a good one.
 
hobbyheater said:
... She says that I have done 999 modifications to this system and only 333 have worked ....
Click to expand...
Batting .333 I'd be happy to have you play on my team. And tell her with an average like that, 5 years after you stop making mods, you will be voted into the hall-of-fame :lol:
 
Gasifier said:
hobbyheater

How is your storage insulated? What do you figure you have for an R value for your storage tank? I insulated my tank with spray foam recently. I am amazed at how well it seals. The stuff seals every crack and crevace to give you zero air movement. It is expensive, but boy doys it do a nice job. When I gutted a floor of my house that had a crawl space under it and turned it into a garage I put in floor heating in the concrete floor and then I spray foamed the walls and ceiling with closed cell spray foam. Unbelievable. Almost all year round the garage hardly ever calls for heat. The sun warms it in the day time and the insulation holds that heat so well it is just awesome. In the dead of winter I heat the garage to 45-50 degrees. It does not take much to do that. My storage tank is 180 degrees and you can put your hand right on the foam and hardly tell it is hot on the other side. If your insulation on your tank is already good, no need to change obviously. But if it is not good, it would be something for you to consider in the future. My tank stays warm for quite a while, and I only have a little of the foam on it. Now I just need to put another layer on it to bring the whole R value up higher. I only have 1-2 inches on the bottom half and 3-5 on the top half. Hopefully next year I will have 5 inches over the whole thing with one more kit. That would give me an R35. Have a good one.
Click to expand...

Gasifier - For insulating the storage tank, we first wrapped in the tank in foil back insulation you can see on the Jetstream heat exchanger with the foil side in. Next we put one layer of 2 ft. X 4 ft. X 2 inches thick compressed insulation and used aluminum banding to pull it tight. We repeated this process two more times while staggering the joints of the three layers. Heat lost from this tank is 1%. Do not know the R value but in the summer I can go 10 - 14 days between firings. Your spray foam sure looks a lot easier to work with.
The only reason for wanting to increase my heat storage was to give our old Jetstream boiler a longer run as once it gets into 5 hour plus burn time, its thermal efficiency increases. Under a 5 hour burn, I get about 75% thermal efficiency while over 5 hours, it is 80% or better.
Your Wood Gun boiler looks interesting, the first unit that I have seen with a lower advertised stack temperature than the Jetstream .
Allan
 

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willworkforwood said:
hobbyheater said:
... She says that I have done 999 modifications to this system and only 333 have worked ....
Click to expand...
Batting .333 I'd be happy to have you play on my team. And tell her with an average like that, 5 years after you stop making mods, you will be voted into the hall-of-fame :lol:
Click to expand...

This is my maul and fitness club = one short finger.

Allan
 

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