DIY Primitive Batch Rocket Mass Heater design: Cyclone RMH batch design got dismantled?!

 I probably blogged on this already but time for a second look.

So he has normal bricks along with a home made cob to create the burn chamber.

https://permies.com/t/71576/tiny-house-rocket-mass-heater

 

The Bell for the mass to store the heat is also more normal bricks. so 4 x 2 x 2 x 6= about 100 bricks just for the Bell.

a 4 inch Batch Box RMH, as described by Peter Van den Berg here: http://batchrocket.eu/en/

OK so that's what he meant when he says there's no "double vortex" at the top of the heat riser since the heat riser is off to one side.

Cool use of bricks for the bell also.

So probably 200 bricks in all. And the cob mixture:

point out that the firebox of this stove is a homemade mixture that consists of crushed red brick (grog), wood ash, cow manure and locally sourced clay soil.... clay slip with ash until a sticky dough was getting less sticky, then mixed in crushed brick or unglazed pottery grog until it felt like cob, then added water to get it moist and sticky enough to mix in powdered cow poo...Start with presoaked clay slip and slowly add equal parts sifted ash and sifted or well soaked manure until it feels like brownie mix then make some test patches and let those dry so you can see how they crack (or don't crack). Write down how much of each thing you use including how much water and clay were used to make the slip. I would also test mixes with half as much and twice as much of the ash and manure to help you zero in on which mix will crack the least.

 vid description of the rocket mass heater

The mortar is clay/sand, again using locally sourced clay soil for the clay and locally sourced sand too. Cement based mixes can't handle the heat and should NEVER be used in stoves.

 Both primary and secondary enter in that same opening. There is a metal channel that moves secondary air to the throat at the back and an air slot below the door that feeds primary to the front.

That metal secondary air channel is the only part of the stove that can not be easily replaced with some kind of neo-lithic mud mixture.. I'm working on an idea, but am not there yet.

 The firebox is 18 inches deep.

 I'd make a longer bell. It was too short and didn't leave room for the riser to go in straight and allow flow to the chimney. It forced us to offset the riser to one side, which made the double rams horn pattern impossible. I think we made up for it pretty well with the single sided cyclone, but I wanted to look down and see those horns!!

 my mix is really light (wood ash and all) it insulates well, which helps get the temps up. The other important detail is undersized bell leading to a hot chimney (not too hot, you'd have to work hard to get burned on it).

 Total of the inside bell surface areas: 2796 square inches, or 19.4 square feet, or 1.83 square meters.


Lesser Extraction Surfaces:
Not sure whether to count the firebox top; that would be an additional 12x24=288 sq. inches.

The heat riser is in there (8" cylinder, extending from the floor up to the rim below the arch); exposed SA about pi*8*24=602 sq. in.  
Not sure whether it counts for surface area; the mix of that and the firebox looked dense enough to store some heat, but they also function as insulation.

Beside the heat riser, the path going down to the chimney is also about 8" long by 4 or 5" wide by about 12" or 13" tall. If we count it, it's roughly 12" by 24" total, another 288 sq. inches
I think Peter sometimes doesn't count the bottom surfaces due to lower temperatures, so we may be able to omit this too.

If we did count all those surfaces too, then we'd have another 1178 square inches, or 8 square feet, or 0.77 square meters.
Total would then be 2.6 square meters / 27.5 square feet / 3974 sq. in.

Plus a bit for the firebox itself, if we like.  That was 18" deep by about 8" tall by 5" wide, so 380 sq. inches or so.
I believe this is usually not counted - however in this build, I think that block of refractory at the bottom was a significant factor in holding heat through the night.

 A cubic foot of this dense building brick weighs about 125-150 lbs.  A cubic foot of brick would be about 20 bricks. I'll go with 135 lbs/cu ft for estimating.

13 courses x 13 bricks per course + 6 bands x 8 bricks per band = 10 or 11 cu ft of brick.
+ 1 cu ft arch ends and wedges
+ 2 cu ft firebox and heat riser (I'm counting a 5-gal bucket of mix as 1 cu ft. for estimation purposes)
= total of about 14 cu ft. of masonry in this project.  
Thermal Mass (without footing)= 1850 lbs = 0.9 Imperial tons or 0.8 metric tons / 840 kilograms)

 I have a new batch box masonry bell similar to this one, and about the same age, too!  I finished it last month, and now that it has dried out, we're burning it usually twice a day for 1-2 hours at a time (around 2-4 loads of wood).  It puts out heat like a radiator once hot, and that lasts for around 6-8 hours.  It heats up the two downstairs rooms with that radiant heat, and if we are really cold, we can sit up against it on our piano stool to warm up.  

Bear in mind we live in a cool, not cold climate--we don't often go below freezing during the day, and usually not at night either.  I can't say what it'll be like for us for the rest of the winter, but for the past month, using this heater has been comfortable enough for us to go without turning on our central heating. 

https://donkey32.proboards.com/thread/3830/more-info-lightweight-cyclone-heater 

At some point, Paul seemed to think there's no room for two similar systems. So J-tube rocket mass heaters are promoted and batch box rockets are discredited as the net result.

A pure mass heater requires some forward thinking: in fact the burn at this evening is providing heat for the following night and day. The story is about the Red Cabin, a guest hut that's largely uninsulated. The only thing that needed to be done is burning one single batch the evening before the guests arrive.
So the above criticisms are largely due to not being familiar with the ins and outs a of a true mass heater.

Moreover, since a batchrocket is a combustion core being the front end, the back end or heat extraction part could be anything. Including a barrel, cob bench and whatnot.

 the original riser of the cyclone rocket tended to crumble, at some point it was replaced. This was done using insulating firebricks. Since there wasn't space enough, a rectangular riser was installed. ... during years of development is became clear such a riser shape is murderous for the proper afterburner function of a batchrocket.

1: for a batch box rocket mass heater, make sure that the riser slot is taller than the wood feed. Or else smoke will come out the front. And smoke out the front is utterly unacceptable.

 I tested a version with the port up to the firebox ceiling. The net result was a lot more CO, and I mean a lot, indicating the mixing of the combustibles with fresh air wasn't as good. Mind you, no smoke out of the chimney since CO isn't visible to the human eye. The space above the port is important in this, see an explanation of the gas streams in the port

 https://batchrocket.eu/en/workings#stream

Thus the port should always have two right angles and should open up in the center of the riser.

For example, it is tempting to build a sidewinder in such a way that the back wall of the firebox is flush with the wall of the port. This situation does not meet the conditions outlined above and the properties of the batch rocket may be worse as a result. If the port is not built in the center of the riser but on one side, a single vortex is created. The residence time in the hot environment of the riser then becomes shorter, which in turn affects the quality of combustion.