Post by matthewwalker on Aug 15, 2012 9:11:36 GMT -8
Well, I've got something to share I'm kinda excited about. Since a few months ago when I built the final configuration of the outdoor cooking stove, I've been trying to think of a way to build that horizontal batch feed type firebox with the windows in a manner that was repeatable and cheap. I came up with a lot of ideas but they all involved a lot of expense and time. Suspending the insulating cob over the burn chamber once I incorporated the windows became a major challenge.
Then I struck on this idea, what about half barrels lengthwise? I'm very excited about it. You can use full size for a big firebox, although not so efficient, it makes a great batch loader. You can step down to the smallest 15 gallon barrels, where half of one has a CSA only slightly larger than an 8" flue. They can be insulated, and you can pack clay inside to change the tunnel shape or size. You can cut a hole and top feed or load from the front batch style.
Then I experimented with the same half barrels for the mass. Wow. The possibilities are endless. In this one I've stuck the exhaust way down in the barrel so the bench acts like a bell, but I played with the exhaust up high and it draws just like a flue. So again, free, strong, easy to work with, and a variety of options. I'm excited, it makes building a whole stove with the mass really quick and easy. It also opens up some interesting low-mass design options, as well it could be buried deep and power a large mass.
Hope you guys get some inspiration, thanks for all you've given me here.
Post by matthewwalker on Aug 16, 2012 10:35:24 GMT -8
Peterberg, your comment on Max's thread regarding the low resistance path a bell offers had me experimenting last night with this system. The exhaust flues are just suspended by friction, and I can adjust the depth pretty easily just by sliding them in and out. I stuffed the exhaust on the little stove wayyy down into the bench chamber, and while the burn slowed a bit, it didn't smoke back at all. That bench heated up FAST and got pretty dang warm. It's really fun to play with.
Post by matthewwalker on Sept 18, 2012 10:47:48 GMT -8
Thanks guys, yeah, you can do a lot of experimenting with these without much investment at all.
I thought I'd update this since the board has been so busy with the horizontal feed concept, and bells as well. These half barrel molds have been working out very well so far. For the mass, the bell bench I've made is quick to respond, and I have since helped on a build in a straw/cob cottage that used the half barrels as flue. That's working great as well. For a quick build of a horizontal burn chamber they are working great without needing exotic refractory. Just build 'em up strong with good insulative cob and for better efficiency the inside burn tunnel can be shaped by filling with the same. The barrels just make the process extremely easy since they can support the build and create that strong arch. The one in the cottage has a traditional top feed, square 50 sq. in. CSA tunnel, and a front window. It's a pretty versatile system.
Matthew, I've been ofline for some time and seeing this thread just made me smile. I think this is what you call the hundredth monkey. In August we built a bell at the end of a bench flue run using a barrel ripped in half lengthwise and also used the other half to form a bell/ash pit right up against the heat riser barrel. It is a brilliant idea that makes the job so much faster and more secure feeling than the expanded metal lath approach we've been using up till now. This really is a break through. I am glad you came up with the same thing and have already shared it! Keep up the good work! I will be interested to hear how long the half barrel in the combustion chamber lasts as my experience is any steel in that zone is burned up pretty quick.
Post by matthewwalker on Sept 25, 2012 12:25:12 GMT -8
Lasse, thanks so much for the encouragement. I was hoping folks here would see some value in this idea, and I'm not surprised you came across it yourself. I was just looking at your poster for one of your workshops and was struck by the similarities in shape of the burn chamber. I have since installed one in a friend's small cabin and just lined out another friend who will start on theirs tonight. It does simplify things, and cuts expense immensely.
I do expect the burn chamber to burn out quickly, but have begun to pack the inside with clay/perlite to refine the tunnel shape, and build up at least 6" of reinforced cob on the outside. My expectation is that the decaying of the barrel will not manifest as catastrophic failure given that the shape has enough cob to support itself. The barrel is hopefully acting as a mold/support for the shape rather than necessary structure. We will see. Nonetheless, it does make for a quick, cheap system that gives the builder a lot of options; batch load, top feed, large box, small insulated feed, etc.
As for using it for the bench, it's wonderful in my opinion. Especially for applications that can't take the load of a full cob bench. The large barrels halved do a good job of spreading out the load and can be covered lightly to provide quick response in a much lighter system. Compromise for sure, but for some applications it could be just the thing. If more mass is appropriate they can be covered more deeply, corbelled for a wider surface, or even quarter barrels can be used to allow for more cob mass. Not to mention not needing to buy the expensive Ts and 90s and such. Setting the exhaust up to draw from about halfway down in the half barrel provides quite a bit of hot surface area to transfer heat to the mass efficiently.
Well, chalenge is, to transform my old leather sofa into mass. I've found a way to implement the whole thing in. I just will have to move my guitar rack elsewhere.
Well i thought about two half barrels bell lenghwise, i can weld the two edges, i think with my new inverter, i'll be able to do this. But i can't weld a piece of steel at the bottom without a mig, i think. The metal is too thin for my skills. But i'd like the thing to be air tight, before i put any mass above. As it has to be movable in the future. No monolithic conception. So there will be gaps in the mass.
Waht would you do guys? If only i could find a two metre long box, by one metre wide and ten or so cm thick, that would be lovely.
I used the half-barrel system for my mass, in a dual-bell configuration (the first half-barrel feeding into the second at the bottom of the two, and the exhaust exiting at the bottom of the second). The first barrel gets a lot hotter than the second and the exhaust is barely above room temperature.
I definitely consider the barrel configuration a success, as the natural convection within the bell makes for a very efficient heat exchange system.
Last Edit: Nov 27, 2012 11:14:36 GMT -8 by pinhead
Post by matthewwalker on Nov 27, 2012 13:27:06 GMT -8
Man, cool Pinhead. I hadn't thought to do it like that, with the halves set up like two independent bells. I'm not surprised at the temp difference between the two halves. Sounds cool. Really glad to hear it's working for you. I've done quite a few set ups since I posted this and it has been a lot of fun to experiment with. Once you have some half barrel "modules" cut up, you can whip up new configurations really quickly. I'll try to get a pic of the latest one in my shop, running off of a Peterberg horizontal firebox. It's a beast.
Max, sorry I missed your last post on this thread. One thing I've learned, if you don't seal the bottoms they WILL leak out that acrid black exhaust that I assume is from condensing inside the bell. It's heavy, so it sinks, and will creep out of gaps at the bottom when the stove is starting up. Once it's all warm it doesn't do it, but when drying out mass it can be pretty significant. I haven't had any problems when setting them in cob, but when I just drop the barrels on the ground for a quick and dirty system it's obvious that if it was gonna be indoors you'd want to make sure you had a good seal there. I know you are gonna protest, but I'm gonna say it again. Go dig up some of that grass and pour some water in the hole. That's mud you have there. It's good enough for a seal, I promise. Shovel that into a wheelbarrow and make a mud base for your barrels, maybe mix in some grass or straw or sheep's wool or your girlfriend's poncho's fringe. You can do it man.
Thanks a lot Matthew. Well, i was thinking of pouring concrete in the bottom of the boxes.
And actualy thinking exactly the same as pinhead, two benches, the lengh of a barrel and a smidge more. I have calculated, if i pour concrete on top, each bell would be about 600kg. That's heavy to move around in my flat.
You have probably already gathered this, but I think it won't hurt to repeat.
If you connect them at the top the temperature will be pretty even between the two.
If you connect them at the bottom the first one will be much warmer than the second one.
I set it up as two bells (second configuration) because my second bell is in the corner of the shop close to the chimney where I don't need a whole lot of heat. The first bell, being closer to the middle of my tiny shop, puts out more usable heat.
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