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Post by freedomlives on Nov 2, 2016 0:34:50 GMT -8
Hi, Two years ago I put into operation a stove following the directions and dimension for the core from Matt Walker's youtube video. Actually, the core was made 3 years ago. Materials used for the core were simply perlite and our local clay subsoil-- quite pure clay from my jar tests, and probably the same thing that was used a few kilometers away at an old brick factory. On firing, that clay exposed to heat turns from a mud brown color to a brick red color. Early on some bits cracked off, but otherwise only pieces falling off have been due to mechanical contact of wood with the sides. On test firing outside, the cast core burned great. But inside I have a bench structure that has 7 90 degree turns so I think this has always caused a big hit on performance. It is an 8" core. Basically, we've mostly been burning it by sticking pieces of wood into the burn tunnel, because flame up happens often when loading it vertically in the feed tube, which despite having a cover, presents a problem for my wife that when she goes to pull off the cover to see if she should add wood or needs to shift it around then smoke will come out. We also had a problem a month ago when we started burning this year, which was that my oldest child (5yo) decided to throw some waste paper in, but as he feared the cover would be hot, he grabbed a throw rug to pick it up, using it light a highly flammable pot holder. The only damage was the complete loss of the throw rug, which I quickly put out with a fire extinguisher, and granted this is part my fault for not "refreshing" in my kids minds the "no messing with the fire rule" that they evidently forgot over the summer, but it also makes having a closable door in a horizontal feed where the flames aren't inclined to come out when opened an appealing feature! So what I'm thinking is remove one of the walls of the feed tube and install in its place a stove door (like this one: www.kerkotherm.sk/sk/ponuka-tovaru/dvierka/kachlove-dvierka/kachlove-dvierka-thorma-ohniskove-so-sklom-cierne) and build within the space of the feed tube and burn tunnel a 5" batch burner core. I'm still thinking about the "how" of this, but I suppose pieces could be cast with refractory concrete which is available here and then slid into place, possible scraping away as needed the relatively soft walls of the present cast core to fit it, then loose filling any gaps with perlite. But my main question is: how will performance of the 5" batch burner core be affected if the chimney/riser is a larger CSA? I have a square cross section heat riser (appx. 7"x7") made also from perlite-clay inside of a 32" tall barrel. Space at top of barrel from heat riser is appx. 2" (based on the knowledge I could find at that time, largely from the Ianto Evans RMH book). Given the 5" thickness of the top of cast core, my heat riser is probably 34" total height, thus in height practically the same as what the table of dimensions on batchrocket.eu calls for for a 5" system. Because it is already cold outside (night time temps around 0C) I don't want to make really drastic modifications to the structure or anything that would leave the stove out of commission for more than one night / two days. Also, while we were on vacation and my in-laws were here taking care of the animals they painted some of our rooms as well as the stove (because a year ago I had pulled the barrel off and then never repainted the clay that went on to reseal it), so I'd want to wait with changing the riser until next summer, as that would make quite a mess. Album with some photos of the stove is here: goo.gl/photos/yQuUHVtcRUVDhnCh9
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Post by freedomlives on Nov 2, 2016 1:03:03 GMT -8
btw, I guess this is the right subsection to post in-- I have some results from a rocket mass heater that aren't so great, so I want to experiment if the mass and ductwork can be fed more efficiently from a different core geometry for a smaller system size. :-)
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Post by peterberg on Nov 2, 2016 1:47:32 GMT -8
Hmmm... Matt Walker converted his own 8" Jube in his living room to a 6" batch rocket some time ago. Here it is: donkey32.proboards.com/thread/1361/converting-8-6-batch. Those 7 elbows in your bench could be a problem, too much friction isn't good for a rocket heater and the batch box in particular. Maybe even more digging in the system is in order. By the way, aim for a 6" system or even larger, a 5" firebox turns out to be quite cramped. Hello Freedomlives, welcome to the boards.
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Post by freedomlives on Nov 2, 2016 3:43:29 GMT -8
Matt's thread does indeed answer a lot! :-) Thanks!
In 2013 when I started researching the different options, I guess the ductwork in benches made more sense to me, at least because more had been written about it that I could find at the time than about bells. In retrospect building a large bell would have been better, given the space constraints of where I was building-- I could have taken more advantage of the vertical space available, given that having a seat (which that is all it is like-- chair for at most two persons to sit when really cold) was not a very important function. The duct work goes under the sitting part, turns 180 degrees to loop back behind it at the same vertical level, then another 180 degree turn up to loop back behind the backrest of the seat, before turning up 90 degrees and then another 90 degrees before the final part of the structure in front of the pre-existing chimney hole in the house. Somewhere I have a picture on my desktop, which is in my cold office (another problem area, separate small building, floor area of office 10m^2, so needs something quite small and just enough to heat up the room for 6 - 8 hours a day...)...
Anyway, because the room the rocket stove is in is next to the bedroom, and our house doesn't have hallways, but you have to walk through every room, tearing up the massive structure of it and replacing it with a bell isn't an option until the summer. And of course I've grown attached to the look of it, so I'm hesitant to totally tear it up. :-) Actually, a better long term solution for our house (an long L-shape) would be in order and subject of a different thread, but I'm not tackling that anytime soon. The present RMH works pretty well at heating the room its in and the two adjacent rooms and then the kitchen and other room further away are presently heated by the kitchen cook stove, which is hardly efficient.
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Post by matthewwalker on Nov 2, 2016 5:21:10 GMT -8
Hey FL. I finally ended up building the cook stove and as you are speculating, two stoves was the right answer. It makes it real easy on both of them. Neither stove needs to be pushed too hard to keep the place really comfy.
I did run a 6" batch into my 8" chimney with good luck.
As for your issues, have you cleaned the system out in a while? That makes an enormous difference in draw. Also, a pot as a j tube cover works well to suck the smoke in but cover the fuel. My best advice is that whenever my J would start smoking, I could reduce the CSA of the feed either with a brick or two, or by re-forming it, and that would solve it.
Good luck.
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Post by freedomlives on Nov 2, 2016 14:29:05 GMT -8
Hey Matt,
Actually, cleaning it out did make a big difference a few weeks ago. I guess the performance had been declining last winter gradually so I didn't notice. But its still not the sort of draw that would allow the feed tube to be filled vertically. Reforming the feed tube and burn tunnel probably is worth trying, so see if I can get it working better this winter and put off major improvements / changes next summer.
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Post by freedomlives on Nov 21, 2016 13:58:56 GMT -8
I stuck in a brick in the feed tube to see if reducing its size would help, which it did. But today I finally mixed up some perlite with clay and a bit of water glass and reduced the CSA of the feed tube and the burn tunnel with that. Difference is like night and day. Before, burning without the cover partly on was impossible, now it does so just fine. See the linked video: goo.gl/photos/sxALF965uAskZiuN7
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Post by matthewwalker on Nov 21, 2016 14:28:02 GMT -8
That's it Andrew. It looks like it's running well.
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Post by freedomlives on Apr 22, 2017 4:47:56 GMT -8
Well, difference was like night and day for awhile, until the weak perlite clay mix started falling off. Although it was interesting using straight perlite clay in the stove, it is only good if the users of the stove will be gentle with the stove, and not e.g. shove wood in and chip off pieces of the stove. So this summer I've got to do a rebuild of the burn chamber.
But also a batch rocket system to heat water and set up radiators. We had a terrible time with the kids-- as adults, we put up with the changing temperatures in the house, or that we come home from being away for an entire day and the house is cooler, but the kids just started wanting to stay in the city with the in-laws in their flat, that has radiators and is constantly warm. So I have to compete in making a more comfortable house than my in-laws...
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Post by freedomlives on Nov 29, 2017 3:40:08 GMT -8
I still haven't gotten to doing the batch box. I perhaps did the wrong thing now-- which was lining the J-tube with castable refractory which required downsizing to approximately 10cm x 10 cm the feed tube and burn tunnel. It wasn't really effective this time, which seemed strange, given that I would expect a 4" feed and burn tunnel to not have flow issues, despite my twisting, turning bench structure.
We've had an electric radiator plugged in for a month in the front for that reason, while I've been finishing my garage/workshop so I can eventually make a batch burner core (and tons of other projects obviously), but last night I was lying awake thinking-- "I need to so something now, before we spend a fortune in electricity, which isn't even keeping the front rooms that warm-- temperature there is 18C max". And actually, right now our clay straw brick (adobe brick like) home is only insulated on the long north wall (it is an L shape, 20m on long part which has the windowless N wall, 8m on short part, bedroom makes the short part that sticks out), so I'm going to insulate finally those walls around the bedroom-- thanks to modern technology, there is the foam adhesive for polystyrene that allows the insulation to be put on walls down to -7C, just it will look ugly all winter without the plaster top coat, and I don't care now.
So today I took off the barrel, and at the top of heat riser there was about 3cm of ash, and the gap between barrel and riser is about 5cm. So I think that is a big part of the problem! I'm going to at least put the barrel back, and build up around the base so that the gap will be much larger. But the heat riser itself is 18x18cm square profile inside, outside a 49cm diameter cylinder, made from perlite-clay, its top 105cm from the floor of the burn tunnel. This means that there isn't much space between the sides of the barrel (ID 56cm) and the outside of the riser-- gosh, it is only 3.5cm gap. So I think the way I made this heat riser, which for some reason seemed like a good idea back in 2014, was a big mistake. In the interim I've read about bells and such and Peter's batchrocket site, and obviously this idea that the gap shouldn't be too large to encourage high velocity exhaust flow-- I guess its a problem.
A quick solution I have in mind is that here there was used in the past asbestos-cement pipe, internal diameter ~10cm. I see it was used for chimneys as well. I am thinking this would make my barrel into more of a proper bell by removing my faulty design heat riser. It just wouldn't be insulated, only 1cm thick cement-asbestos.
What do you all think?
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Post by peterberg on Nov 29, 2017 5:08:57 GMT -8
PLease, don't use asbestos-cement, it isn't heat resistant. The cement in there is just ordinairy portland type which could explode when the temperature of the material rise above 540º C if I remember correctly. Above this temp the christal structure of the silicon in the cement changes, accompanied by rapid expansion. So you could end up with a barrel full of fine asbestos fibers, only to be removed by a specialised firm.
Your rocket mass heater has a riser of 8" equivalent now, and a 4" by 4" feed and tunnel. No wonder why it won't work satisfactorily that small, a rocket core is very difficult to get right. The riser is more than 3 times as wide as compared to the rest of the system.
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Post by freedomlives on Nov 29, 2017 6:01:02 GMT -8
I won't say how asbestos tile roofs get removed here mostly. Thankfully our old roof was clay tile. So second options-- I have sheet metal gutter downspout -- 11cm diameter, or I could make a square cross section form from wood. Then make more perlite-clay mix, add in the 3kg of castable refractory I have left for a bit more strength, and laminate with fiberglass plastering reinforcement mesh -- I read various sources about fiberglass, some state 900C it starts to soften, others 1200C. Suffice it to say that the technical data sheet for the reinforcement cloth doesn't mention melting point! Like I said, I need to just make it work for a month or two while I finish my workshop. Probably biggest mistake I've made is that 5 years ago when my wife was given the house by her mother and aunt (first two years, we were renting, so not inclined to invest money in to it) I did not immediately make the garage/workshop area I'm not finishing. Instead it was replacing old floors with radon emitting cinders underneath, redoing kitchen, plastering cracked walls, changing windows, etc. and somehow it never clicked to me that an enclosed garage is not just a nice thing to have, but basically essential, since it is cold months when there is most time to be repairing broken equipment, doing woodworking, etc. Oh well, I could write a book on "Things I learned the hard way"
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Post by drooster on Nov 29, 2017 10:35:46 GMT -8
So today I took off the barrel, and at the top of heat riser there was about 3cm of ash, and the gap between barrel and riser is about 5cm. So I think that is a big part of the problem! I'm going to at least put the barrel back, and build up around the base so that the gap will be much larger. What do you all think? Do that, you might have a decent system, but the bit that disturbed me was all the turns inside the bench, and not once was a bypass mentioned ; When lighting, and when the wife wants to check to add wood, surely a bypass straight to chimney would make smokeback a thing of the past ... she can turn the lever, open for as long as she wants, add wood, when roaring she can turn the bypass closed again. (If Matt wants to critically interject, feel free ... rollseyes smiley) [Asbestos cement pipe does indeed explode under direct heat]
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Post by freedomlives on Nov 29, 2017 10:57:42 GMT -8
The problem is more that the smokeback wasn't just at lighting. Actually we have in the kitchen an ordinary wood cookstove, which is also always having a fire. So typically, I take hot coals from it, drop those down the J-tube and then insert wood. The problem was always that basically there is too much constriction in the system for it to really burn well full throttle. And while all the turns are a factor, now that I took off the barrel and saw how choked the top of the heat riser with ashes was, as well as the narrow path. I could easily bypass part of the system though. That is a good idea to have the option.
So the old heat riser is out now. But it is also dark and cold (below freezing) already. So probably the end of today.
Thinking about it, I should be able to make an octagonal riser from OSB strips glued together.
Now that the whole thing is exposed, I wish I could just do the conversion to BB right away. But I'd feel safer casting the BB and testing it well -- perhaps by making a heater for my workshop first.
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Post by freedomlives on Nov 29, 2017 12:25:30 GMT -8
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