Stevan Covic

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since Jan 01, 2015
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Recent posts by Stevan Covic

Hey there, thank you all for the constructive criticism. I did read the book a while ago, however this build came suddenly and I am in the middle of a bunch of other projects, so that is why we kind of just slapped it all together.
Just got back from the farm and although I didn't get to take any pics, I did get the measurements- feed tube (will be) 40cm, burn tunnel 90cm, heat riser 120cm

We will also discard the L tube that connects the barrel with the thermal mass, and build a wider chamber (manifold) as you've suggested.

I will also try to source a smaller barrel that I can place over the heat riser and then fill the gap with some kind of insulation(clay+perlite probably).

Thomas I can get perlite, and I'll ask around about the fireclay. What we use here for all types of furnaces is called "yellow earth". Essentially it's a kind of clay used for cob, for building or plastering houses.
4 years ago
Ok, thanks for the replies. I seems I misunderstood a couple of things..

First, the burn chamber. I just realised that in hurry yesterday I posted another "mockup" pic. The burn chamber was later shortened and is about 3-4 bricks now.
I also thought that if we built the heat riser out of bricks there would be no need for additional insulation.

All the ducts are the same diameter. What I could do, is reduce the diameter of the burn chamber.

There is no special connection from the barrel to the exit flue. There is just a hole in the bottom of the barrel that fits on top of an L shaped pipe connector and then goes into the thermal mass. I could possibly dismiss the L connector, and build a wider one out of bricks, to prevent a bottleneck.

Another big mistake, but fixable, is that, in all the hurry to get it finished, we did not notice that we don't have the J shape. I just realised that we don't have a feed tube! We just left an opening on top of the burn chamber (similar to pic no2). We'll try to fix that today and I'll get back to you with new pics, measurements and the results.

Some rookie mistakes there, cause this was not really well planned but done in a hurry. We'll probably dismantle it after spring, and build a new one before next winter..
4 years ago
Ho guys. I decided to build a test RMH in my brothers little walipini. Everything worked out fine, however, as I've heard someone say this, my RMH is not "rockety" enough and there is still smoke coming out of the chimney which leads me to believe the RMH is not generating enough temperature.

Now, we dont have 8 or 6 inch pipes, we only have 5" pipes here. I calculated that we can have about 5-6m of thermal mass. Here are some pics from the build>


testing


the heat riser was tilted so later we rebuilt it


laying down the pipes


thermal mass


So the RMH is functioning. There are no leaks. At times it starts pulling air much faster, other times not. The barrel is hot, but not as hot as I'd expect.

I suspect the problem might be in the gap between the top of the heat riser and the top of the barrel. I think it turned out about 8cm, and I think it should have been 4-5.
Any suggestions?
4 years ago
I just stumbled upon this.. it seems there is a guy in my country building RMHs for greenhouses commercially. Here is the add. You probably won't understand it but you can see the pics.

http://www.kupujemprodajem.com/Raketna-pec-17785245-oglas.htm

The guy claims that for 4 hours of burning it will radiate heat for the next 12h, and keep a 175 square meter greenhouse at 18 C. (that's about 1800 square feet, at 64 F)
4 years ago
Hi! Have you seen the RMH water heater they constructed at Zaytuna farm? There are videos on youtube that explain it in detail. Pretty simple but effective..
4 years ago
No. I have never built one before. I watched guys assemble a ceramic heating stove (typical for these parts) that is reinforced with cob.
I am not even sure when I will be able to start. I am hoping to get some testing done this spring, but it all depends on whether I finish my greenhouse in time.

Glenn, I am hoping to use a metal tube, or pipe, as a batch feeder. I think, if I can find a pipe that is a little wider then the bricketes, I can stack them inside and provide a stable source of fuel. As the one in the burn chamber burns away, the next one falls out. I am hoping that the draft will be so good as not to allow flames going up the feed tube.
4 years ago
Interesting concept Glenn, Thanks for sharing. I will definitely have to try different variations before I cob everything up, and this concept might be useful. I will definitely give it a try.

Allen, those are exactly the ones I had in mind. As I've said, my NGO did a project and got a brickete making machine, and it's fully operational. It's just a press. You feed the sawdust trough a huge funnel and it compresses it into brickets. I am hoping that if I place those bricketes one on top of the other in a long pipe, they will not clog up. I've held the bricketes in my hand and they tend to chip off easily. I am worried that if they chip while I'm putting them in the tube, they will clog up.
Remains to be seen..
4 years ago
You may be right and I am not excluding thermal mass. I thought of running the exhaust just bellow the worm bins, giving them "floor heating". But again, I fear that by the time the gases reach half of the greenhouse they will cool down, so half of the worm bins will be heated, and half would remain cold. But I will test multiple options. I guess it remains to be seen which approach will work best.

However, I am sure it will not be "a trickle". I expect that the RMH will have to work full power all the time. I just want to have an automatic feed so I don't have to sit there all the time adding "fuel" to the fire.
4 years ago
I understand how the RMH was conceived. I just want to apply the principles in a different way.
Yes, the advantage is thermal mass, and it's good when you heat a bench or smaller area. If I make a standard RMH and place 160 foot exhaust trough a thermal mass, I doubt I could get it warm enough with just one batch of wood or pellets.
Or, if we go with the second option (which I think will eventually be the solution), I would discard the thermal mass portion of it, and use the RMH to heat water (like they did on Zaytuna farm). Even then, by the time my heated water circulates trough a number of pipes going up and down the greenhouse, by the time it comes back it will be cold. I believe this "loss" of heat from the RMH itself, would cool it down very fast if the fire was out. That is why I believe I would need a constant feed, because the area to be heated is just huge.

The main reason why I am going with an RMH is because standard furnaces loose a lot of the heat trough smoke. RMH has much better way of using all the generated heat from the fumes. Big Al believes I will probably need more than one RMH. Only testing will show the way to go..
4 years ago
Ok, I understand. Figure 4 seems doable, but it will demand additional space, so let me explore some alternatives here..

During the last months we went trough a lot of variations. One option was to reinforce the earth bag wall with wooden posts, connected by horizontal beams. If done so, what would have to be the max spacing between the posts? The arches are 1.5m appart.

One addition was to spread a wire mesh (like for making fences) between the posts and the wall. It would be nailed to the posts to provide tension.
Are the posts even necessary then, or is it enough to put chicken wire mesh, tie it to sections of the wall with wire and plaster it to the wall. Would that serve our purpose?

Another option is vertical rebar pins.
I forgot to mention that we will dig out a lot of clay, so the bags will be filled with a clay/sand mix.

And sorry about the trench/drench thing... don't know what that was about.. :/
4 years ago