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Post by cletus on Feb 27, 2020 16:29:58 GMT -8
First of all, let me thank all of you who have and who continue to contribute here. I feel I've learned an incredible amount just reading through various threads. I hope that I can add value at some point as well.
I've been following, rather, trying to follow the development of the DSR2 and think that I have enough understanding now to risk a build. I'm an absolute novice with regards to masonry, stoves, RMHs, fluid dynamics...basically everything seemingly relevant. That said, I've worked a Sketch Up file of my intentions to build a hot, white oven with short bench around the DSR2 core. I can't figure out how to upload it, however. Maybe questions will suffice.
1) My understanding is that the distance between the top port and a radiant surface, say ceramic glass cook top or cast iron (is that a good idea?), should be about 4" and have plenty of horizontal surface area to disperse. Would that be optimal to heat a decent pile of sauna rocks if located directly above the top port of the core?
2) I am planning to have the heat then flow directly to a bell that would be sized just large enough to house about 1/2 of a steel barrel to act as a white oven and provide additional radiant heat for bringing the space up to sauna temps quicker. I've seen discussion about "internal surface area" and I'm wondering if there is such a thing as too little (such that it negatively impacts draft or something) or is it "just" a matter of trying to extract as much heat as possible with the mass?
3) I've planned a low extraction point in the bell of approximately the height and width of two full sized bricks, give or take about 1/2 a brick. I'm guessing I need to try and match this opening to an equivalent of the 6" stove pipe? Might I be missing anything here?
I have a couple of other questions but I think this is more than enough for now. I appreciate all thoughts and comments that might be offered here.
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Post by peterberg on Feb 28, 2020 9:12:28 GMT -8
HI Cletus, welcome to the boards. I might be in the right position to answer. 1) My understanding is that the distance between the top port and a radiant surface, say ceramic glass cook top or cast iron (is that a good idea?), should be about 4" and have plenty of horizontal surface area to disperse. Would that be optimal to heat a decent pile of sauna rocks if located directly above the top port of the core? Assuming you plan to build a 6" core, a safe distance between end port and cooking plate or whatever is on top would be 6" as well. Gas velocity is high there, the whole of the stream need to change direction. You could try to get away with less, there's actually no experience with this type of core regarding narrower top gaps. I would prefer a glass top, by the way. Not because it is prettier or something like that but for the limited heat dissipation compared to cast iron. 2) I am planning to have the heat then flow directly to a bell that would be sized just large enough to house about 1/2 of a steel barrel to act as a white oven and provide additional radiant heat for bringing the space up to sauna temps quicker. I've seen discussion about "internal surface area" and I'm wondering if there is such a thing as too little (such that it negatively impacts draft or something) or is it "just" a matter of trying to extract as much heat as possible with the mass? Internal surface area extracts heat. Too little means the chimney temperature would be higher, too much and there's no draft left to drive the combustion rate. It would be best to stick to the already established surface areas unless you are planning to install a very potent chimney stack. If this is the case, a somewhat larger ISA can be done although unlimited will lead to disappointment. 3) I've planned a low extraction point in the bell of approximately the height and width of two full sized bricks, give or take about 1/2 a brick. I'm guessing I need to try and match this opening to an equivalent of the 6" stove pipe? Might I be missing anything here? Yes, you might be missing something here. In a bell a large amount of the gases are coming from the top and need to change direction 90 degrees in order to stream into the exhaust opening. In order to avoid friction in the gas path it would best to have an opening that is at least 150% of the 6" stove pipe, 200% would be better. See it as a funnel to get water into a bottle, much easier than straight into the opening and quicker as well. Keep it low and wide so there's plenty of room for the gas to stream into it. Storage for uploaded pictures and files on this forum is filled up long ago, one has to store it somewhere else online and link to that from this forum.
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Post by wisc0james on Feb 29, 2020 11:31:55 GMT -8
Peterberg: you said "I would prefer a glass top, by the way. Not because it is prettier or something like that but for the limited heat dissipation compared to cast iron."
Why is the heat dissipation bad in this case? Are you saying that the glass is absorbing and radiating less than the cast iron is absorbing and radiating?
If I wanted to trap heat atop the thing with a small oven, I thought cast iron might be be better. What say you?
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Post by peterberg on Mar 1, 2020 12:00:36 GMT -8
Peterberg: you said "I would prefer a glass top, by the way. Not because it is prettier or something like that but for the limited heat dissipation compared to cast iron." Why is the heat dissipation bad in this case? Are you saying that the glass is absorbing and radiating less than the cast iron is absorbing and radiating? If I wanted to trap heat atop the thing with a small oven, I thought cast iron might be be better. What say you? Hmmm... Cast iron is dissipating a lot of heat, regardless being cooked on or not. Glass is different in that conduction through glass is a lot less as compared to iron. Under the pot the temperature is rising rapidly on glass so cooking isn't a problem and while not in use it won't radiate as much. See the double shoebox mark one, the afterburner area is right under the glass and it's still running remarkably clean. The above is an opinion based on the visable and measurable differences.
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Post by cletus on Mar 3, 2020 14:01:10 GMT -8
Okay, I think I've figured out a way to share the .skp file. I've changed a couple of things in light of comments received so far and continued reflection. The file can be seen here: drive.google.com/open?id=1moe5HSVW0YZ7qTVeozJ4hSeyN0Q1kmJSIt's a rough draft, to be sure. Cast DSR2 core, open door version. Would like to encase in cob and build a white oven a la pizza oven style in the bell. I haven't figured out exactly what all that would look like (it seems the domed oven space would take up much of the bell space) but thought perhaps I should ask for feedback with it as it stands right now in case I'm going down a dubious path. Would greatly appreciate any and all thoughts. Also, on a slightly related note, I think the sand on my property is mostly decomposed granite. Would it be a bad idea to use that for the cob base? I think I was seeing somewhere that granite was suspect.
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Post by peterberg on Mar 5, 2020 0:54:37 GMT -8
I'm quite puzzled by the separation wall behind the white oven platform. Why is that? I'd start the chimney built out of bricks in the bell itself, in a corner. Saves a wall and the hassle of four separate openings. When the chimney starts in a corner one could leave the two sides facing the bell's inside nearly 90% open at floor level.
The floor of the white oven won't heat up as much, certainly not enough for pizza.
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Post by cletus on Mar 6, 2020 7:44:02 GMT -8
Hi Peter, Thanks for your continued support. I don't quite remember how that second wall made its way into the design. I think I was trying to increase dwell time around the oven. I've tried to come up with a better design than the previous upload. It can be seen here for anyone who is interested: drive.google.com/open?id=1vr1rRb7v_sN0C0lUcqcQ6dV4tVZpBX56 I realized that I let my imagination get carried away with the white oven idea. I really need to keep this simple. This latest attempt at a rough draft uses a stainless steel litterbox I came across on Amazon (https://www.amazon.com/Yangbaga-Stainless-Litter-Control-Surface/dp/B07CTJVKLJ/ref=sr_1_1?keywords=stainless%2Bsteel%2Bbox&qid=1583500038&sr=8-1&th=1) as a radiator, something I think is important for a stove that is primarily for a sauna. I was thinking that this box is wide enough to eliminate the need to incorporate steel angle iron headers and whatnot, but I'm not sure that it is appropriate for a radiator directly above the top port as shown, or even at all. In trying to avoid working with steel, I also just realized that I might need something around the flue (stove pipe?). Or, is that something that can just be packed with cob or masonry clay/sand mix? The reality is that I am quite a bit out of my element with regards to this whole rocket stove thing and possible in over my head! I ultimately just need this to heat up a pile of rocks in a hurry and store some heat as well. A black oven on the side, perhaps doubling as a clean out port, would be bonus.
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Post by Orange on Mar 6, 2020 13:43:12 GMT -8
Stainless Steel Litter Box for Cat and Rabbit - looks to small and shiney for radiatian surface. Better to make entire bell out of steel, you can use barrels too. And for 150mm dsr2 you can have around 5m2 of ISA.
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Post by cletus on Mar 7, 2020 10:21:51 GMT -8
Hi Orange,
Thanks for chiming in. Yeah, that shiny box isn't ideal. Honestly, I was trying to avoid the barrels out of a concern of off-gassing. One might say I'm paranoid...and they'd be right. The reality is, however, that I do need this build to be as simple as possible and if that means incorporating a barrel somehow than so be it. This barrel-as-a-bell that you suggest, does that look more or less what Peter's development build looked like (last I saw it)?
I do have easy access to food-grade 55gal drums. But, out of concern for off-gassing, would a 1/4" steel plate surface radiator, in lieu of a glass/ceramic top, be an acceptable compromise in terms of heat dissipation (vis a vis cast iron, masonry, cob, etc.)? I'm weary of stacking sauna rocks on a glass top.
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Post by Orange on Mar 7, 2020 12:44:47 GMT -8
sure the barrel would off-gas if there's paint on it. But you can burn a fire outside and burn the bareel until it's bare metal. As for materials - I've read that rough, non-polished materials radite the most.
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Post by cletus on Mar 9, 2020 11:12:53 GMT -8
Okay, Orange, I think I'm warming up to the steel barrel radiator idea. I've come up with another very rough draft: drive.google.com/open?id=1MmFHbKnucXC2DlNNrMJDYM4L5FkNeqq7 Obviously, there's not a lot of accuracy here. This drawing is just more to get an idea if it's possible. If anyone looks closely they'll see that I sketched in a masonry draft channel up the side of the bricks/steel drum. At first I was thinking maybe I'd just run a stove pipe straight up from there, but it would work better for me if I could funnel the exhaust across the back of the stove to where the stove pipe is shown. If this looks like a viable design I will get busy with a more respectable sketch up, maybe not quite respectable, but I'll try. Thanks again to anyone who feels like weighing in.
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Post by esbjornaneer on Mar 24, 2020 9:35:34 GMT -8
Hello Cletus, I have not looked at your earlier skp's but this last one is looking fairly straight forward. The gases will go where there is an opening so you can take them to where you have the chimney pipe rather than up the brick passage as long as there is a channel that does not impose significant restrictions (there would be no such problem if you keep it nice and wide).
Are you putting this into an already existing sauna? The reason for asking is that you would get to ~4.75m^2 of your 5m^2 ISA if you used 3 55-gallon drums stacked one on top of the other, like Peter has them stacked. If you wanted them to be located under the seating benches, i.e. lying down, you would get the heat closer to where you want it in a sauna. And if you chose to build a cage from metal wire (or wood if you think it is safe enough)to contain your rocks around the drums you don't need to think about putting them on a hob. Also it is a question of how much mass you want, the more mass the slower the heating up of the sauna, but the more stable the temp as the fire peaks and dies down, but I'm sure you already know about that.
If you don't mind me asking why would you want a hob and an oven in a sauna? Especially if you are not used to the materials nor experienced in stove building/designing it is a recipe for disappointment to expect too much from the one core... it may just have been me and my first build... but when I built my first batch rocket stove (after having build a more traditional mass heater previously) I wanted a hob, oven and space heating, but it was really only the space heating that worked. You can get it all but it will take experimenting and tweaking to get it all to work as intended. I am not trying to put you off but making you aware that it was said on this forum at one time that it is best to have one core for each use, that may have been referring to J-tubes, but my stoves are getting better at getting all 3 uses from the one core but I am not satisfied yet.
I wish success for you, Esbjorn
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Post by cletus on Mar 26, 2020 12:20:55 GMT -8
Hi Esbjorn, I really appreciate your comments. The barrel bench thing, along with some other videos/pics I've recently come across, have inspired what I think is a much improved, much simplified design. drive.google.com/open?id=120mckLStHuJtX7aDrtW4vnGmAf_vxQlLThis one incorporates a 1/2 barrel radiator on top of the DSR2 cast core. A cob-like bell(?) supports the radiator and encases the core. Two half barrels laid down form a second stratification chamber. My thinking is that I can make a wire cage around top radiator and bench radiator barrels to fill with some combination of cob, larger aggregate, and rocks for the main sauna function (on the top radiator). I located the chimney flue down low within the first stratification chamber/bell. It looks like I might be able to make some tabs or otherwise use the barrel to help hold the 6" flue pipe in place, thereby adding structural support and minimizing extra material costs. Finally, I drew in a black oven door opening. It seems to me that this feature could be used as the oven, on occasion, and as a clean out access. I still have some questions/concerns: 1) A close look at the DSR2 core in this draft will reveal that I thickened the sidewalls. For health (using the firebox as a cooking space)/peace of mind reasons I would like to keep this build as primitive as reasonably possible. I've seen Matt Walker use a 1:1 fire clay:perlite (if I recall correctly) mix for a j-tube with apparently decent results. I was hoping nice thick walls of that would be fine, and then I could add in some "furnace cement" for the top of the firebox and top of the top box so that they have more strength and to maintain the internal dimensions of the DSR2 core. Am I asking for trouble with this approach?! 2) Is the exhaust/gas flow design sufficiently "open", "free", what have you? I have the pipe down very low to help encourage the hot gasses to make their way into the lower barrels. Also, not sure if it's relevant, but that 17' chimney stack is indeed the correct anticipated height to clear the peak on the small structure. 3) Is cob alone sufficient to seal the joints at the barrels and chimney flue, or would I need to plan on some sort of conventional gaskets? 4) I had in mind an oven/clean out door not too unlike what I've seen used for pizza ovens. The change I was wondering about was sandwiching a 1" thick piece of cork board between a steel inner plate and a thick wood outer/visible face. I'm just not sure if cork would survive right there. 5) I was thinking that the system could be "tuned" a bit by adding perlite to the back space of the top barrel (to hopefully push the hotter heat forward). I could also add maybe another foot in length to the bench. And, I guess I could experiment with different combinations of larger/smaller stones and/or thicker layers of cob on the bench. In short, it seems like this system offers some flexibility to figure things out. Regarding the reasoning behind a combo heater like this, I am trying to get a foothold on a piece of remote mountain property in an area that I don't have much familiarity with (western Montana). Elevation is approximately 6600ft and it gets around 15 ft of snow over a long winter. I have limited funds and a limited build window. So, the sauna/changing-hanging out room would do double duty as a small cabin/base camp until I decide to build bigger or do something else. In the "oven" I wouldn't be baking, per se. Probably just doing things like making bone broths, soups, etc., possibly roasting some veg. It's not a deal breaker because I'm guessing I can manage with the hot rocks on top and my dutch oven---or an outside kitchen. To answer your other question, no the sauna hasn't been built yet...and again, thanks for the barrel bench encouragement! It absolutely makes sense to try and get that heat under the primary hot seating area and I think a thinner mass/barrel combo will add additional immediate radiant heat as I try to bring the temps up for sauna purposes. The space is planned to be 8x12' with about an 8' ceiling (3 bench heights). Heater is in the middle of the hot room, and in the middle of the entire structure (12x16 ft).
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Post by esbjornaneer on Apr 2, 2020 6:50:55 GMT -8
Looking at this updated version my comments are a)that you are not extracting a lot of heat, and b)the 'oven' door to the right of the firebox is a very cool place. a) The reason a rocket mass heater is very efficient is because of two aspects: first, the combustion of the carbon in the wood is about as close to complete as possible; second, as much as possible of the heat generated in the combustion is extracted for use. The first part is achieved by Peter's design of the DSR2. The second part is achieved if your ISA is following the recommendation for your size of stove. Your size (6"=150mm chimney diameter) you should have 5 square meters of internal surface area if you want the stove to be in the region of 90% efficient. If you choose the only have half the ISA you will halve the heat extraction and only be in the region of 45% efficient even if the combustion is 100%complete. It is not really up to be to be frustrated by the choices that you make, but having 3 half-barrels is halving the ISA, it means that you are letting 50% of the potentially recoverable heat go out the chimney. b) The way a 'bell' heat extraction unit works is that the hot gasses stay at the highest part of the cavity, and only the coolest gasses in the cavity, close to floor level, is allowed to fly out the chimney. You would be reaching a much higher temp at that location by not using the full potential ISA in your build, but you could alternatively locate the oven in the half drum at the top and extend the bench at with another 2-3 half-barrels, potentially with a 90-deg bend and still get a higher oven temp but with a greater total efficiency. But you will also have to tell me if that oven location will be more useful that the firebox as an oven Now to your questions: 1 You may be on to something here, but it is usually safer to stick with things tried by other builders if you are lacking in experience. I use hard fire bricks as the inner layer of the firebox as they are very abrasion resistant, and when I have used "furnace cement" to lay them with that is what has been lacking in strength to the same degree as a sand/clay/ash mix. If you are building the walls with thick clay/perlite there will be parts of that mix that don't get heated to a temp that it is burned. The burned parts may be sufficiently abrasion resistant for your method of loading wood and it can be patched if you get them too gouged out. 2 The length sounds about the same as I have on my 150mm stove. At the bottom of the pipe you might get away with that low a pipe (Peter recommends 150-200% of 6" in his post above 28th Feb), but only if you make sure it is open all the way around it, that means remove the flanges of the half-barrel. Yes you can prop it up on something but make that as small as possible and in the direction that least gasses will be flowing from (usually nearest the wall or in opposite direction from the horizontal furtheres distance). 3 I have done it with cob alone but it needed going over several times with more cob to seal gaps. The chimney in my build was not very good so it was easier for the smoke to escape at the bottom than up the chimney. 4 It depends on the temperature for spontaneous combustion for cork and what temp it will be inside the door. I just use a 2mm steel plate held in place by bolts with wing-nuts for my clean-outs. They allow heat to go out but can not burn. A wood exterior would look better but only of you place it where you will be safe. Wood combusts at 250C if I remember correctly. 5 No comment. I have no idea about the number of sun-days in western Montana, but my two favourite oven options are a solar oven for sunny days (I bake bread even at 120C, it takes longer than at 200, but any soup/stew/pot roast is possible there too) and the firebox of the rocket stove when most embers have gone out. My firebox is 4cm thick fire brick walls inside the bell, and the temp starts really high but goes down in 1.5-2hrs. Either a thicker wall or a layer of insulation on the outside of the bricks (or both) would make the cooking temp more stable for longer, but that is an improvement for my next build. I hope the comments are useful and that you will get a satisfactory heater in your sauna/cabin, Esbjorn
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Post by cletus on Apr 3, 2020 10:19:49 GMT -8
Thanks, Esbjorn,
Your comments have been very useful. I think it might be best to use hard fire bricks and not risk fragility and anything else that could go wrong with my inexperience. I will consider relocating the oven to the top barrel. And will definitely look at adding ISA to the bell, either by raising it a bit or extending it as you suggested.
Again, thanks for taking the time to look at my drafts and answer my questions!
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