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Post by ekwisner on Mar 25, 2012 1:36:58 GMT -8
Leaving the straw out of the areas around the heated ducting is for density of thermal mass, not fireproofing.
Straw coated in clay is surprisingly fire-resistant, but it is still insulative (doesn't store or conduct heat very well).
We often use straw or other natural fibers in the final plaster coatings, for crack-resistance, right up to the barrel. Occasionally the first 1/4 inch or so around the barrel may get hot enough to partially char the fiber or alter the color of the clay, but mostly, it doesn't even do that.
The top of the barrel will get hot enough for the first 1/4 to 1/2 inch, and we have made some 'cast-in-place', very rough terra-cotta chunks from earthen plasters left on top of the barrel for several months of firing.
-Erica
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Post by kemperextremegreen on Jul 9, 2012 8:05:52 GMT -8
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Hello all, This is my first post/question. I just dicovered rocket mass heaters 4 days ago. In this thread Donkey mentioned stainless as a riser. Wouldn't it last indefinately?
I was reading another thread this weekend in which Dakman was participating. I saw a lot of potential with the model shown in reply #19 dated Feb 2011. I am also of the opinion that he should focus on a continuous firing and use thermal storage.
I am building an off the grid - straw bale house and I see the beauty of the rocket mass heater for that application. And...
I have a current project that is much larger scale than anything I have seen in my short time researching rocket stoves. It is a 19,000 square foot slab inside a commercial building that was designed from the ground up to be super energy efficient. The entire slab is insulated and heated with hydronics. The ultimate plan is that Solar collectors on the roof will capture heat energy to store in a 1,200 gl. thermal bank. The back up for solar is to be wood fired heat and the secondary backup is what we are currently operating on which is a propane fired boiler "Munchkin".
So the subject here is wood fired heat. I have been expecting to use a wood gasification boiler such as Tarm. It's job is to recharge the delta T in the heat bank to aproximately 170*. The circulator system sends water to the zones at 130*.
The calculated maximum load in the building is 125,000 Btu. I need to get wood sourced heat installed before next winter.
Is there a rocket water heater in existance that is being used for an application similar to mine. Do any of you have opinions about feasibility of creating such a heater.
I am a fairly handy fabricator/builder/welder. I tend to think outside the box much like many of you. My intuition tells me that this is good stuff, and yes I know the devil is in the details. I also believe in keeping systems as simple as possible and I think the delta T of 40* in a 1,200 tank gives enough buffer to stay well clear of critical temperatures. I really don't want to play with bombs.
I am hoping to benefit from your experience with this technology and that you might speed my learning curve.
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trinkaaaaaa
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Post by trinkaaaaaa on Dec 2, 2012 6:23:22 GMT -8
Just got into rcket stove and building one myself....almost finished it but it's not rockety enogh compare to what it is without the barrel......
I'm working metrical here so.....building an approximately 6'' system one wich equals to 16cmx16cm burn system....but couldn't find a 25-30 gallon barrel so....i'm useing a 55 one.Does that make a difference....i mean a consistant one?!!Got the Ianto's book and it doesn't say anything on not using a 55 with a 6'' system....just says it work ''well'' with a 25-30 gallons...found this a bit approximate.
Got 4cm from top of the heat riser to top of the barrel, 3 cm on the side of the insulation to the walls of the barrel....
The vertical stack is not finished yet.Does that make a big difference?
The flue just flows in the room and i do smell like a pyromaniac for about a week or so now....please help!!!!!
Stefano Trinca
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Post by Donkey on Dec 2, 2012 21:31:47 GMT -8
Stefano,
As long as there is enough area for gas movement, it doesn't really matter what barrel you use.. The cross sectional area of your system needs to maintained as a MINIMUM, all the way through to the chimney exit.
Something you said is strange to me.. Please clarify, perhaps I'm not understanding.
A 6 inch pipe has an area of 28.26 square inches, or 71.78 sq. cm.
A 16X16 cm. burn system is 256 sq. cm. or 100.79 sq. inches.
Your burn system (if it is square) should be 8.47 cm on each side to match the 6 inch (15.24 cm.) diameter pipe, NOT 16x16 cm.
??
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Post by morticcio on Dec 3, 2012 4:19:51 GMT -8
Stefano, As long as there is enough area for gas movement, it doesn't really matter what barrel you use.. The cross sectional area of your system needs to maintained as a MINIMUM, all the way through to the chimney exit. Something you said is strange to me.. Please clarify, perhaps I'm not understanding. A 6 inch pipe has an area of 28.26 square inches, or 71.78 sq. cm. A 16X16 cm. burn system is 256 sq. cm. or 100.79 sq. inches. Your burn system (if it is square) should be 8.47 cm on each side to match the 6 inch (15.24 cm.) diameter pipe, NOT 16x16 cm. ?? You've miscalculated the metric conversion, using 1 sq in = 2.54 sq cm. That is the conversion for inches to centimetres. 1 sq inch = 6.45 sq cm 28.26 sq in = 176 sq cm Square tube would need to be approx 13 cm on each side |
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Post by permamax on Dec 3, 2012 4:27:30 GMT -8
Ok, so I know this is cheating, but I couldn't help noticing that here's a bit of activities by knowledgable folks, and I'd love if I'm able to divert some of you to head to last weeks comment posted here: donkey32.proboards.com/index.cgi?board=discuss&action=display&thread=625Thing is that on Wednesday I'll be shopping for whichever alteration I decide for, and I'd love more input before I decide... I'll re-make whichevet needs it on Thursday... Cheers, Mx |
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Post by trinkaaaaaa on Dec 3, 2012 4:41:30 GMT -8
Sorry for my clumsiness but it's my first time in a forum too so.....don't quite know how....well....let's cut the story short!
My combustion chamber is 16cmx16cm.My fuel feed is 16cmx16cm.Useing a 55 gallon barrel ,left 4cm of air between the insulation of the riser and the barrel.Left about 5cm from top of the riser to top of the barrel.My flue system is 17cmx17cm all the way...have no chimney yet(vertical stack).
The Rocket rocks ASS when without the barrel and as i put it on backfires sometimes and have a lot less pull.Yesterday i've tried to put additional air flow with a air compressor in the last part of the flue and seems to work well with it.Basically i have created an artificial pull wich makes me think that all this is 'cause of the lack of the vartical stack(outside vertical chimney).But again....shouldn't it work anyway?
I tried the Barrel without attaching it to the flue so to exclude the flue as a problem and still have backfiring and weak pull.Tried to rise the barrel more but no change.I try to put pictures in as soon as i have them......meanwhile thanks for your help......
Oh!!!....by the way....my flue is made out of bricks and not pipe.....we found pipes really expensive and had a stack of old brick available for free so we used them....does that make the difference?
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Post by Donkey on Dec 3, 2012 9:02:16 GMT -8
Rocket stoves without the barrel almost ALWAYS run great. It's when you put on the barrel that things get complicated. Here we go again.. (sorry about the mix up above, I'm American and over 40, so I've practically zero competence with metric conversions..  16x16 cm = 256 sq. cm. This is your MINIMUM system size. Nothing in the system can be less than this cross sectional area. The heat riser transition to barrel can be visualized as an imaginary cube, between the top of the riser and the top of the barrel.. 16 cm on a side, 16+16+16+16= 64 cm times 5 cm = 320 sq cm. The gap above your heat riser seems ok. A 55 gallon barrel is 22.5 inches across. According to metricconversions.com, that's 57.15 cm across. The CSA of your barrel should be (pi R squared) 28.575 x 28.575 x 3.14= 2563.9 square cm. Assuming 4 cm gap all the way around the barrel (8 cm shorter in diameter than the barrel), your insulation jacket should have a diameter of 49.15 cm, a radius of 24.575 cm. It's CSA then is 24.575 x 24.575 x 3.14 = 1896.3 sq. cm. Subtracting the insulation CSA from the barrel CSA gives the gas path CSA of 667.6 square cm.. Your barrel gap should be fine. What is left is that join at the bottom of the barrel. which is what this thread was originally about. Go to the beginning of this thread and read through again. Make SURE that your manifold is large enough. Also, why is your flue system so much larger that your burn works?? This could cause problems, though you've said that your system has issues without connecting to it.. Also, check that he burn works have a consistent CSA all the way through and that it is all well sealed and well insulated. If everything checks out, in the final analysis, a good chimney with enough heat to drive it will improve your system greatly. |
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Post by trinkaaaaaa on Dec 3, 2012 15:25:40 GMT -8
Experienced an improvement today with the chimney attached but after few hours started to back draft again......
You've said that the bench system is too big but tha manual says it should be NO LESS then bla, bla, bla and possibly slightly bigger.
Sorry but i'm just getting confused here......i appreciate your time though and am really thankfull.....gonna ''sleep'' over it tonight and see if something comes out of it.....
Is the RMH supposed to draw like it is without the barrel, once finished?...or is it just a dream seen on youtube?
Does it all depend on dump in the fumes 'cause is drying?
Just out of curiosity,how big is your flue(width & high)?..and with what burn system(8'' ,6'')?....is your combusuion unit all the same?from feed tube to heat riser?
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Post by matthewwalker on Dec 3, 2012 18:56:10 GMT -8
Trinka, I'm just gonna throw this out there, but I'd suspect that your spacing between inner insulation and outer barrel is too tight. The math works, but 4cm is awfully tight, and there's a whole lot of surface area for boundary layer friction to work on. I'm pretty bad at all the math, but my gut tells me 4cm is not enough space here.
What size is your outer barrel? Can you put a bigger one on there and see how it goes? My tightest insulation/outer barrel gap ever was almost double what you have there.
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Post by trinkaaaaaa on Dec 4, 2012 5:29:55 GMT -8
Woa!!!!If that's too tight.....then the manual really doesn't nail a thing!Jee!!!.......even more confused now....but do you know what?...i've actually tried it without insulation just to see what happens and no big change.Pffffff....don't know anyway... thank you....
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Post by trinkaaaaaa on Dec 5, 2012 13:14:29 GMT -8
Not as rockety as it could be but not bad at all!!!I guess that the whole thing has to do with it being dry......and the chimney made a big difference.....pretty happy now and can sleep sweet dreams again....thank's everyone!!!!!!
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Post by Donkey on Jan 22, 2013 11:01:26 GMT -8
The manifold can be lower, doesn't matter... What DOES matter is volume. The helpful hints thread does a pretty good job of describing it. 30 feet of horizontal run should be no problem with an 8 inch system if you get the internals right. A nice vertical chimney at the end helps too. |
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