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Author Topic: Rocket mass stoves  (Read 1487 times)

Tom Sawyer

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Re: Rocket mass stoves
« Reply #15 on: July 20, 2012, 08:26 AM NHFT »

 8)

I thought of building a insulated concrete tank... more mass and last forever.
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MaineShark

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Re: Rocket mass stoves
« Reply #16 on: July 20, 2012, 11:08 AM NHFT »

The thermal mass of concrete is actually trivial, compared to the thermal mass of water.  If you go with a cheaper material and build a larger tank, you'll get more benefit.

A pound of water will store one btu for each degree of temperature change.

So, if you have a system which can operate on water as cool as 120F, and you have a tank which can withstand 170F as a normal maximum temperature, you have 50 degrees of temperature change (delta-T).  If you want to be able to last for 24 hours on that tank on the coldest day of the year, and your house draws 40,000 btu's per hour on that day, then you multiply 40,000 by 24 hours, to get 960,000 btus, then divide by the delta-T of 50 degrees, to get 19,200 pounds of water.

Divide that by 8.3 (pounds per gallon of water), and you get a total of about 2300 gallons.  If you want to be able to re-heat that with a four-hour burn, you'd divide the total storage capacity (960,000 btus) by four hours, to get a firing rate of 240,000 btus per hour.

If you're willing to do two fires per day on that coldest day of the year, then you can halve those numbers.  If you need to be able to last two days (eg, you might be away on a trip), you'll need to double them.  So, how you're willing to operate the system has a huge impact on how large it has to be.
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Tom Sawyer

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Re: Rocket mass stoves
« Reply #17 on: July 20, 2012, 11:17 AM NHFT »

Cool thanks for the info...

Although obviously the British Thermal Units calculation won't work here in the Colonies.  ;D

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MikeforLiberty

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Re: Rocket mass stoves
« Reply #18 on: July 20, 2012, 08:58 PM NHFT »

Thanks Joe, you've taken care of half of my homework ;)
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KBCraig

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Re: Rocket mass stoves
« Reply #19 on: July 21, 2012, 12:25 AM NHFT »

I would think that untreated water held at 120-170F would be a big bacteria party, so some sort of treatment would be necessary. Your liner, pipe, and fittings would all need to withstand it.
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Free libertarian

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Re: Rocket mass stoves
« Reply #20 on: July 21, 2012, 07:16 AM NHFT »

Cool idea.

Evan P.  here in Free Grafton has expressed alot of enthusiasm for making a rocket mass heating unit.  He has made a couple of small proto-types of stoves out of tin cans and cooked on them.  I'll let him know what you are up...besides you should come visit us in Free Grafton anyway and you guys can talk rocket mass stuff.  I've heard it's simple, not exactly rocket science.   :P
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MaineShark

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Re: Rocket mass stoves
« Reply #21 on: July 21, 2012, 09:18 AM NHFT »

I would think that untreated water held at 120-170F would be a big bacteria party, so some sort of treatment would be necessary. Your liner, pipe, and fittings would all need to withstand it.

Indeed, although the tank is covered, so the lack of free oxygen helps to reduce that effect.  There are bactericidal chemicals that can be added to the water.  The biggest issue, though, is to maintain the pH, so it doesn't become acidic and eat the copper.
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Russell Kanning

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Re: Rocket mass stoves
« Reply #22 on: July 21, 2012, 09:54 PM NHFT »

also Mike
your calculations could be wrong but the stove will still save money over heating oil or such
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MikeforLiberty

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Re: Rocket mass stoves
« Reply #23 on: July 22, 2012, 08:25 PM NHFT »

also Mike
your calculations could be wrong but the stove will still save money over heating oil or such
I calculated the heat loss for my tiny house to 8-9000 BTU/hr. It should get by on a cord of wood for the winter.

I had played with galvanised duct (I did not inhale) and found it burns out pretty quickly. I should put together the videos of my experiments.
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Russell Kanning

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Re: Rocket mass stoves
« Reply #24 on: July 22, 2012, 08:39 PM NHFT »

that would be great
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