I'd like to through this idea out there in case it hasn't already been done/discussed.
How about using the thermal mass around an earth integrated home as the rocket mass heater's 'mass'?
This is assuming that the exhaust in not too long in relation to the size of the rocket stove being used of course, this is just a basic brainstorm.
Please comment, I think has great potential.
Location: Southern alps, on the French side of the french /italian border 5000ft high Southern alpine climate.
posted 2 years ago
Jason, too much exchange surface imho. Without insulation, i can't see it being feasible. Even if your "mass" is dry. Earth will always be a conductor, not insulation. So you will loose huge amounts of heat.
Better follow Peter's idea. And use an inside wall as your mass. Load bearing walls, in old european stone houses lend themselves rather well to this.
I hear what your saying about the earth being a conductor but, there is indeed insulation in the image. If you're familiar with John Hait's concept,
that dry earth under the insulation/umbrella a.k.a. 'Storage Zone' stores the heat without letting it go beyond the insulation & returns the heat back into the home during cool months.
It's an "Eb & Flow" of heat. Heat absorbs into the dry earth during Summer then, returns it into home during Winter.
It might take ~ 3 years for this phenomenon to occur as described in the book but, with the aid of the rocket heater's exhaust, I'm thinking this would speed that process up ?
I think it is going to be a wash either way. I am very familiar with John Haits work and I think your idea would work very well. However, RMHs are notorious for burning out. Do you want to have to open up an earthen wall to do maintenance over the years? I also think it would be very difficult to manage as far as what time a year you were firing off the RMH to heat load the walls so that the thermal flywheel is kicking in at the right time. You may end up with a steep learning curve trying to strike a balance between comfort, efficiency and convenience. Haits idea was to thermally load the earth by keeping it dry, but the heat came from people just living there along with some passive solar. I would be inclined to centrally locate the RMH in the house and run a PEX based heat exchanger in the periphery of the RMH to be able to control where you want your heat to go. That way if you have temp monitoring like Hait did, you can see if you are pumping too many BTUs directly into the outer walls. Otherwise, you can radiate and distribute heat via the floors which will not only make things more even, but also increase the area the heat is applied to. I am playing around with a lot of similar ideas to yours, so I'd love to bounce ideas back and forth. I think a hybrid system is what I am aiming for. I want to be able to combine geothermal groundloops, RMHs, "hot" and "cold" water reservoirs, and evacuated tube solar heat to make something similar to what you are after. I envision an underground home with a little more control over the hot and cold and zone heating/cooling.
You could use an RMH with the duct running in the outer earth mass, but I don't think it would be the most beneficial way to employ it. You would get a combination of lots of instant heating from the barrel when you are burning, and no heat when you stop burning, while the heat you sink into the mass would mostly not show up for days or longer depending on the exact layout. There would be no control at all of when you got the stored heat back.
Running the ducting through an internal mass wall would give the normal RMH heating effect, with a half day or more of comfort reliably after burning. Combined with the huge exterior mass for tempered heat, you would not have large swings in comfort. Some of the radiated heat would also sink into the exterior walls, contributing to the annual heat reservoir.
You could do lots of different things as suggested by John and others; I would carefully consider which combination would give the best return for the work invested.
Finally, RMHs are not notorious for burning out, if built according to directions, and the parts that will need maintenance would not be buried in the walls. The only thing you would need there is some method of access for cleanout purposes once a year.
The concept of earth sheltered homes is needing a lot less heating and cooling. If built right you shouldn't need a whole lot of RMH burning to keep warm. The whole energy umbrella concept is to maximize this earth shelter storage of heat or cold energy by isolating a large portion of earth mass with insulation and moisture barrier. So if your needing to charge up your umbrella with a RMH channeled into the umbrella, then you likely did something wrong in the building and design of the umbrella. It would mean it isn't operating as it is supposed to.
All that said, if you really want to explore this idea.
Something I think might be a good way to implement such an idea, would be a regular mass bench but including a bypass to an in ground section. You could then charge your regular mass, then switch to charge the ground.
This sort of set up with a bypass could in theory be installed and if found unnecessary or not working well, could be sealed up and forgotten.
"Where will you drive your own picket stake? Where will you choose to make your stand? Give me a threshold, a specific point at which you will finally stop running, at which you will finally fight back." (Derrick Jensen)
That's a great idea Devin, having a bypass so that there is a choice of sticking to the original rocket mass heater design in case the experiment proves fruitless.
In my mind it's hard to justify if my concept is worth the effort considering the Hait method is supposed to provide the answer anyways.
I suppose if one mostly followed the 'Hait' method but did not allow for adequate solar gain then, perhaps heating the walls via. my idea would be a way to compensate for lack of sun ?
Different climates and different site plans have different potentials for Hait's ideas to work without assistance. Sunny climates, or warmer average temperature areas, might work fine using only passive methods plus occupants, while colder, cloudier climates might need active heating to supplement the passive.
I kinda like the idea of having the chimney inside the wall.
If I were to build something like this idea, I would use a 6 or 8 inch layer of perelite/clay on the outside of the pipe, to channel the heat towards the house, as well as some mass (the wall) on the inside too absorb the heat from the chimney . . with the outside of the chimney inuslated, you would only loose 1/2 of the heat (absorbed into the wall) so - I am guessing at this - you could have a longer run of chimney while keeping the temps up for steam exhaust . .
The reason I like the perelite/clay outer insulation, is that I have the same thing in my rocket, and after a 6 hour burn the outer bricks (only 6 inches of P/C in between the 2,000 degree fire box) is still at room temperature. . . THE STUFF WORKS !
Here is my fire box construction . .
Edit : The riser inside the barrel with burn out and the fire brick will wear out, but I do not remember reading anything about the chimney burning out . . . since all the really hot gasses are already burned before they get that far . . .