Rein Baarsma

Hi!

As experts I'd like to ask your opinion on a building technique. I saw plans for a very simple building using earth directly from a to-be pond with a mechanized digger and putting it in a half-circle (or square with one opening) by building the walls, compressing each layer with the machine.

Then on top simply build a roof with wood (or tree trunks) by simply laying them on top of the earth, building the rest of the roof from there, possibly covering the whole thing with earth again. My question to you is: do you think earthen walls build this way will hold the roof that way?

I'm sure cob would do so, but I'm talking (compacted) earth, which would obviously be much faster to build.

Sepp Holzer uses a similar technique for his 'stables', building a room into the mountain, but obviously that's not the same as building earthen walls on flat land and putting a roof on there. Also this idea came from Geoff Lawton who claims to have put this into practise, but I can't find any examples of how.

I guess the consistency of the earth matters, but even clay or loam would be prone to erode. But then again if the roof covers the earth walls, there shouldn't be too much danger. Also they can be very thick without much problem.

Thanks guys!
Rein

Heya all,

We've built ourselves a small rocket mass heater in our trailer.
You can see some pictures here:

bench (still needs toplayer of stone)
rocketmass heater above
rocketstove front
exhaust start and end
fire with helper plate
fire without helper plate == smoke
rocketstove behind
rocketstove side
close-up exhaust
full view with exhaust
inside barrel from above (note that heatriser insulation is vermiculite covered with ash)
inside barrel the connection to outside t-piece
ash outlet in t-piece directly after barrel

Now the problem is that even though the system works fairly well - and we do get enough warmth - it is not functioning really rockety.
It still gives smokeback often, which we mostly cancel out with a bar of pressed vermiculite which I use to control the air flow, which helps suck the smoke in.
It also still gives too much real smoke outside from the exhaust.
Therefore I think it is not burning hot enough.
Without the barrel it is actually burning much stronger.

The whole setup is small and the average pipe width throughout the system is 130mm (5.1 inch) The heat riser and wood feed are somewhat larger.
The barrels are 38cm diameter.
The bench is 2 meter long and the exhaust pipe goes through it on two sides (going 180 degrees at the end to come back)

It also seemed to be working slightly better when we hadn't finished the bench. The end of the exhaust pipe used to become 'warm' (still touchable), while now it's almost cold.
Also the bench itself is staying pretty cold - whilst before it did get warm.

I'd be happy with any ideas
Rein

Hi Peter.
Thanks for answering. I'm Dutch too, and unfortunately have a bit of trouble with your wording, so I'm just going to see if I understand you correctly.
I'll write in English so this post can maybe help others or get more feedback.

Peter Berg wrote:Not a single part should be smaller than the burn tunnel

Okay. The burn tunnel is about 13x12 square. That means a heat riser with 6 inches diameter would be bigger and therefore be better.

Peter Berg wrote:Stick to the rules and provide something of a vertical chimney stack

Not sure what a vertical chimney stack is exactly. But my exhaust pipe is going out at ground level, but afterwards going up pretty vertically about 2meters. Isn't that a vertical chimney?

Peter Berg wrote:the burn tunnel and riser should be insulated

Okay. For the new heat riser I'll use vermiculite (or perlite).
You say the burn tunnel needs to be insulated too. Also inside the barrel? For me the concept of insulating the whole burn tunnel is new. We did put extra stones around it, but I guess that's not insulation. It also begs the question if the vermiculite board that we used as a roof on the burn tunnel is allright? Or is it better to put fire bricks as a roof and insulate the whole thing with vermiculite?

Peter Berg wrote:when the stove is finally working like it should the metal pipes will burn out in no time.

I'll have to find a new solution for the heat riser anyway. I have the feeling fire bricks won't fit in the 55gallon barrel. What should I use as the inner core for the heat riser?

Thanks a lot for helping.

One more test I got from another thread:

I removed the barrel when there were only some hot coals burning, almost dying down.
Instantly the coals lit up and a draft was obviously going through much better. I added some wood and the whole thing was LOTS more rockety.

I tried putting the barrel back on and holding it at different heights. Putting it down decreases the rockety effect.




(I wrote this before your reply Peter. I'm going to look into what you say)

Ok so I did a few things:

- I checked the barrel top to the heat riser. It was only 2 cm, so I changed that to the intended 4 cm.
- I made the wood feed a bit higher and smaller

It seems to function only marginally better than before. After some hours of moderate success the fire is pretty hot and I put more sticks in vertically. Somehow the fire doesn't burn enough sideways. The sticks start catching fire too high and eventually the fire comes back out of the wood feed, killing itself quickly afterwards with lots of smoke. From this point onward I tried everything, with only little succes. Many times the flames go in the wrong direction. Sometimes only partly - but with lots of smoke as a result.

My next idea what's wrong is the heat riser. It's inner pipe is only 10cm, while on the design it is 6 inch (15 cm). That's 1 1/2 times my core. Can this be the problem? It's seems a pain to start again with a new heat riser, but if you guys think this helps I will.

Heya,

Our intention: We want a rocket mass heater that can keep our small house warm during winter, preferably without lots of wood.

Our design:
We used 2 barrels of the same diameter (38cm). The bottom one we halved and cut a square hole where the fire chamber will be. We build a fire chamber of fire bricks. the inner chamber is 2 bricks (40cm) long and 1/2 brick width (10cm). As a roof for the firechamber inside the barrel we used a vermiculite board, where we cut in a circle for the heat riser. The heatriser's inner pipe has a diameter of 10cm. It has an outer pipe of 16cm diameter. The space in between is filled with clay mixed with a lot of sand (we didn't have much clay left). There is approximately 4cm between the heatriser top and the barrel top. On the other side of the bottom-half barrel we made a smaller hole for a 130mm T-shaped steel pipe. One end we put in an loosely fitting steel lid and taped it over with aluminium tape to make it air-tight. The other end we put almost 10 meters of aliminium bendable pipe, which we put in several S shapes to give as much heat as possible to the bench. We put the whole thing on a layer of stone, with underneath old carpet and the original wooden floor. The exhaust comes out low in the wall and goes inside, where it goes 2 meters up to exhaust above the roof. The wood feed starts where the barrel ends (there's no fire brick 'bridge'). The feed itself is therefore pretty long (16cm), 10cm width and 12cm deep.

The Problem:
It's only burned for 2 days. But even now I think it's not getting hot enough. There's a lot of residue ash, both in the fire chamber and inside the barrel. When I've burned it a few hours the ash and hot coals start taking up a lot of space and eventually I start getting a lot of smokeback. I think it's not rockety enough. There's just too much charcoal left too quickly. Even if it seems to work the exhaust is defnitely also real smoke.

How can I change my rocket mass heater so it will function better?

I thought the wood feed might be wrong and had several attempts with adding 1-4 bricks to make the wood feed a bit deeper and less long. Doesn't seem to help a lot.
At this point I have the most success with no smokeback when I make the fire deep inside the fire chamber (inside the barrel).
Is the heat riser too small?


thanks,
Rein