BBRMSH for Yurt

[jwal]

I'm finishing up a yurt on my Wisconsin homestead for the coming winter and looking to build a rocket heater to survive one season. I'm looking at batch box to maximize burn time overnight. I'll do a pebble box to be able to redo the design when I have more time and experience next year.

I had the good fortune to consult a bit with Donkey, Mud, and Rodney last month at an event on a bit of this. Unfortunately I had too little background with rockets to take full advantage of it. Donkey advised that a 6" BB would give the output of an 8" J-tube design, but I'm thinking maybe I would want to go with an 8" BB to get even more heat?

It is a 24' yurt with 12oz duck canvas and no other insulation (apart from whatever snow piles up around the sides). My first thought is to put the box/radiant chamber slightly off center, a series of 4' ducts with 60* corners to from a hexagon ring around the other side, returning to a straight chimney kissing the radiant barrel up through a hole in some glass in the central apex ring. I forget exactly the length this calculated to, but I think it was well within the guidelines from the Wisner book for a 6" system. My hope is to drop this down to just below grade, so that the pebble box is essentially part of the floor, or perhaps a slight step up. Donkey seemed to think that dropping the exhaust a foot or two down from the manifold wouldn't inhibit sufficient drafting of the system.

In discussing with some experienced homesteaders, there seems to be no consensus on what will happen with the pebble box in the ground like that. Most recommended digging around the perimeter of the yurt and installing some sort of insulation along the sides, but I'm limiting myself to 'natural' materials and there doesn't sound like there's a simple, quick solution for this outside of plastics, so I'm prepared to make do with what heat I can get for this year.

Any informed opinions on how the pebble boxes dug into the bare earth will do for storing heat?

Any suggestions on the simplest way to construct something in the ground to hold the pebbles that will function to draw out heat from the pipes and make extraction easiest next summer?

[fuegos]

"It is a 24' yurt with 12oz duck canvas and no other insulation"
we started out here in a bender - a traditional British gypsy structure made from hazel poles and canvas, a yurt more or less.At more than 2000ft up in the Spanish pyrenes the lowest T we saw was -15c.we had the structure on a floor made from pallets & finished with scrap timber we found & carpets.the bender had an inner layer made from blankets & cloths.we had a box stove on a stone slab.
In your case you could build a floor & have your stove on a plinth based on the ground.
"there seems to be no consensus on what will happen with the pebble box in the ground like that"
I would keep any mass off the floor otherwise you'll never get ahead of the mass of the ground.Also build a proper bed as high as is practical.In the UK you can buy very cheap synthetic blankets that are used for wrapping furniture during removals.We have a yurt now that we use as a guest house/summer bedroom & in mid septembre, even with a daytime T of 25c the nights can be chilly! a yurt with no insulation = basically sleeping outside without the wind chill!

[jwal]

For the bed, as this is a 24' yurt I will have a couple of support beams for the tono ring, and build off of those to place a loft for sleeping as high as practical.

Thinking of portable mass for the ducts, how would dry stacked concrete pavers around them in a tunnel 'box' compare to a wooden box full of pebbles?

[pigbuttons]

Much of your heat, rather most of your heat loss will be through radiation. Your friend in fending off radiant heat loss is barriers and distance. A barrier can be another layer of canvas, bed sheets, vinal, anything that will interrupt the direct transfer of heat, with an interveening layer of air if possible. Distance from the outside layer of the yurt is also key. By putting the piping around the outside of the yurt you are putting your main heat source at the worst possible location, and your bed loft idea as well. Radiation transfers heat at a rate of the difference of the two temperatures to the fourth power. The hotter your pipes get the faster and greater the transfer of heat to the outside. Move them to the center and store the heat there and live as far away from the yurt walls as possible. By placing your loft as close to the roof of the yurt you again radiate your body heat to the outside faster than if you are farther away. If you are expecting that the "warm air" from below will heat through convection you will be disappointed; Radiation always wins.

So my advice is to build yourself a platform to shield your device and piping from the ground, fill it with straw to insulate from the ground. Build a second platform above that one for the piping and fill it with rocks or pebbles. Sleep on the second platform. Hang whatever you can find to give you an inner boundary layer from walls and roof.

[jwal]

The floor is going to be what the floor is going to be at this point.

I have the walls up, trying to figure out how to get the massive 2x6 kludge of a ring up on the tiny <1" uni. I've secured an old sewing machine, cutting the canvas tomorrow and will hopefully have it sewn up in the next week. I bought 32 new dedicated firebricks and should be securing a large number of regular clay bricks. I've found a bunch of used 6" and 8" duct work. The insulated chimney I could buy used is 6". Looks like I will just have to buy elbows and Ts for the rocket.

I'm going to run the ducts just below grade with bricks/dirt and/or maybe some pebbles around it. Still working out those details, but need to decide on size to draw up plans for. I'm thinking the more heat the better given the situation, so leaning toward an 8" batch box. Is there any concern going too large that way other than not having enough mass extraction and sweating myself out of the space, having to let it cool down and rerun it too rather than enjoying a more smooth continuous run cycle?

[jwal]

Dec 5, 2021 16:59:38 GMT -8 pigbuttons said:

Much of your heat, rather most of your heat loss will be through radiation. Your friend in fending off radiant heat loss is barriers and distance. A barrier can be another layer of canvas, bed sheets, vinal, anything that will interrupt the direct transfer of heat, with an interveening layer of air if possible. Distance from the outside layer of the yurt is also key. By putting the piping around the outside of the yurt you are putting your main heat source at the worst possible location, and your bed loft idea as well. Radiation transfers heat at a rate of the difference of the two temperatures to the fourth power. The hotter your pipes get the faster and greater the transfer of heat to the outside. Move them to the center and store the heat there and live as far away from the yurt walls as possible. By placing your loft as close to the roof of the yurt you again radiate your body heat to the outside faster than if you are farther away. If you are expecting that the "warm air" from below will heat through convection you will be disappointed; Radiation always wins.

So my advice is to build yourself a platform to shield your device and piping from the ground, fill it with straw to insulate from the ground. Build a second platform above that one for the piping and fill it with rocks or pebbles. Sleep on the second platform. Hang whatever you can find to give you an inner boundary layer from walls and roof.

Didn't mean to ignore your post in my last one, I have limited net access and can't figure out how to have this site notify me of updates to this thread so I didn't see yours immediately. Thanks for the perspective on radiant heat, I can see where the loft idea would not work well for sleeping. I will also see about suspending extra sheets around the roof section for a bit of insulation. The idea of the piping is not to put it outside of the yurt though. I intend to make a ring in the ground inside the yurt, well away from the walls. Maybe a 10' circle inside the 24' yurt? Slightly off center to accommodate the burner/chimney position going through the ring. I'm thinking immediately below foot level is the best location to store a mass of heat, it would radiate immediately to where it is most useful no? I could arrange some sort of bedding right over a section of the pipe.

My question is what combination of material would make the best mass extraction around the pipe ducts? The soil is pretty sandy so sorta good to insulate against cold once an envelope of warmth is generated, but not good around the actual duct. I'm thinking a 'v' channel of pavers with small stones directly on top and some sort of larger paver or tile at the top of the V. I'd place openings every foot or two along the pavers such that air could be drawn down the sides to flow up through the pebbles for some convective heat also.

[pigbuttons]

Thank you for listening to my comments. One last attempt to try and convince you to reconsider the "in ground" placement of the pipes; The soil in Wisconsin freezes down at least one foot maybe two. What portion of the Earth's crust do you think you will be able to "heat" with a 8" rocket stove. My guess is that you won't have enough residual heat to make the flue draw if you do a 10' dia circle in the ground (circumfrence is 2x3.14x5 = 31.4 feet of pipe in the floor). With excellent insulation between the pipes and the ground you may be able to get it to draw but three sides of the "box" are heat sinks and once the heat has reached the exterior surface of the insulation, heat will transfered at a constant rate. R values only reflect the time it takes for the heat to radiate across the insulation, it has nothing to do with what happens after it is bridged. In my opinion you'd be better off with two barrels as bells and covering/surrounding them with stones to retain heat. You could use a couple of layers of plywood/OSB as flooring with maybe 1" of rigid foam insulation sandwiched in between to set the barrels on.

Best of luck with your build. I've lived in AK and it is amazing what people can endure and survive. Stay hydrated and eat lots of fatty foods and stay dry, shivering makes you sweat more than you would expect.

[jwal]

Dec 7, 2021 21:28:44 GMT -8 pigbuttons said:

Thank you for listening to my comments. One last attempt to try and convince you to reconsider the "in ground" placement of the pipes; The soil in Wisconsin freezes down at least one foot maybe two. What portion of the Earth's crust do you think you will be able to "heat" with a 8" rocket stove. My guess is that you won't have enough residual heat to make the flue draw if you do a 10' dia circle in the ground (circumfrence is 2x3.14x5 = 31.4 feet of pipe in the floor). With excellent insulation between the pipes and the ground you may be able to get it to draw but three sides of the "box" are heat sinks and once the heat has reached the exterior surface of the insulation, heat will transfered at a constant rate. R values only reflect the time it takes for the heat to radiate across the insulation, it has nothing to do with what happens after it is bridged. In my opinion you'd be better off with two barrels as bells and covering/surrounding them with stones to retain heat. You could use a couple of layers of plywood/OSB as flooring with maybe 1" of rigid foam insulation sandwiched in between to set the barrels on.

Best of luck with your build. I've lived in AK and it is amazing what people can endure and survive. Stay hydrated and eat lots of fatty foods and stay dry, shivering makes you sweat more than you would expect.

You raise an important point I've been trying to find information on but coming up empty. How does the draw around the ducts affect system performance? What I've read seems to imply escaping air travels along the path based on flow resistence, no consideration is given to extraction around the run as affecting the draw. It seems to make sense that insulative/conducting parts of the ducts will impact the temp of the final exit gasses. If my ducts were simply stuck in the soil direct, it seems you are saying the extraction of heat from the system would be extreme and I wouldn't be able to have much of a run of ducts?

I'm not trying to heat the earth's crust. Since I will be dealing with a bare earth floor for this first year, seems to me any heat I put into it will make the overall effect of the floor on the tent environment warmer to some extent. My current plan is to line a trench with red clay bricks spaced to absorb some heat through conduction, but sparsely place to allow air flow and convective heating through the loop. Seems to me any block of ground I'm able to enclose in the circle will be in effect insulated from the surrounding frosted ground by the duct trench, hoping to get some sort of heated mass retention there. Not looking for cozy, but not being an ice block would be a win to me.

I'm currently staying in a largish PVC camping tent with screen walls under a rainfly, so negligible heat retention. It has been livable down to single digits so far. Something bigger with no direct convection to the outside will be like heaven. Any heat source would be amazing. But for this experiment I should know the amount of ducting I can expect an 8' batch box to push through a bricked trench in the cold ground. If an 8" J-tube system can deal with close to 50' runs, will a batch box be more or less than that? The apex ring of the yurt is 15' up, so the (directly vertical) chimney will be about that...

[fuegos]

"One last attempt to try and convince you to reconsider the "in ground" placement of the pipes" good advice from Pigbuttons
"I'm not trying to heat the earth's crust. Since I will be dealing with a bare earth floor for this first year, seems to me any heat I put into it will make the overall effect of the floor on the tent environment warmer to some extent"no, never happen.

"Seems to me any block of ground I'm able to enclose in the circle will be in effect insulated from the surrounding frosted ground by the duct trench" the only way to insulate any duct or trench from the ground is to have actual insulation between it & the ground.We built our cabin in 2 phases & the 2nd part has 6cm of insulation in the floor -in bare feet the difference is striking , this despite both floors being 40cm minimum above the earth.The other consideration is firewood.Do you have a good stock of seasoned wood ? Without this any stove will be pretty useless.I assume you have some sort of car/truck to transport materiales to site so my advice is to get some pallets - should be free - & make an improvised floor.Then a simple box stove may be a better bet short term rather than traying what is quite an ambitious build for a first attempt.Put the stove on a stone or concrete slab & stack bricks around it or cover it in cob.It will heat up a small space a lot quicker than a RMH & will be easier to light.With a bed off the ground if you go to sleep warm & are wrapped up in this sort of setup you should be good down to about -15c - i know from experience.

[jules]

Storing heat in the ground under the house is also a bad idea. what condition is the soil in now? I mean humidity, hardness, temperature, frozen and the like. depending on the condition, I would consider how to store heat or what could be done to improve the condition.