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RMH autopsy and redesign modifications  RSS feed

 
Posts: 126
Location: Springfield, mo
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Well I had to get something together quick a few days ago for a very cold spell, but now it's time to try again to get it working optimally.
I had used the mortar in a tube initially but it didn't hold together so I'm going to re do the fire brick with refractory mortar I got at lowes.

Firstly I have 1 variable that cannot be changed namely 40ft of 6" duct under the gravel floor. 4 90deg L's 1 45, and 1 90deg L turning vertical at the end for the exterior stack. (which I had to use a booster fan on for the previous burning). I suppose this means I might have a problem if I have a 8" J tube trying to pump in to a 6" exhaust??

The pics show what I hope to use as a starting point with on the combustion core. It has a CSA of 26.56sq in (Just shy of a 6" pipe CSA) Original J dimensions were (not 100% sure where to make these measurements) measured at inside corners of the J- 9" feed, 17.25" burn, 34" riser.
I'm going to remove the first 90deg L and redo the barrel transition area with cob, and cover the combustion chamber as well.

Thoughts on whether to use perilite, vermiculite or sand to increase insulative properties of the cob. Any ideas how many 50# bags of fire clay mix I would need to use to cob the core and make a transition area? I would like to retain the barrel lid for the bottom so as to make for easy removal and inspection.
Another issue is the riser. Right now it's just the 1/2 thick fire brick stacked on it's side. I am going to further insulate it but how big (or small) of a diameter pipe/tube do I use around the riser? I guess the limit is to leave enough area between it and the inside of the 55gal barrel. bigger is better for more insulation?
Also need to make an ash pit in the feed tube.
I'm on a short time table as well as a very limited budget but any ideas would be helpful.
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all together
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combustion core
2013-11-15-15.16.13.jpg
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alt view
 
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John Adamz wrote:Well I had to get something together quick a few days ago for a very cold spell, but now it's time to try again to get it working optimally.
I had used the mortar in a tube initially but it didn't hold together so I'm going to re do the fire brick with refractory mortar I got at lowes.

Firstly I have 1 variable that cannot be changed namely 40ft of 6" duct under the gravel floor. 4 90deg L's 1 45, and 1 90deg L turning vertical at the end for the exterior stack. (which I had to use a booster fan on for the previous burning). I suppose this means I might have a problem if I have a 8" J tube trying to pump in to a 6" exhaust??


- That sounds like a very long, cold run for a 6" system. It would be on the long side even for an 8" system.
I'd seriously consider digging down and shortening the pipe. Either take out 2 of the 90's and about 10 feet of length, or about 20 feet of length with the same number of turns. Max. length on highly functional 6" systems is about 40 feet with no turns, or minus 10 feet for each 180 degree turn (or 5 feet per 90, 2-3 feet per 45, etc). With the turns you describe, your system has the drag equivalent to a 65-foot-long straight run. Most systems that long need a fan at least for startup, and some just don't work without a fan the entire time.

- Yes, you will have a problem hooking up an 8" heater core to a 6" exhaust. The cross-sectional areas should be consistent between firebox and exhaust, no big jumps up or down in size except that the barrel area can be larger.
The flow volume in the 6" pipe is almost half (28 sq inches compared to 50 for the 8").
However, you could potentially split the 8 inch exhaust into 2 6" runs, total length about 20-30 feet, and get some heat distribution into the various areas your long pipe is currently snaking through. It would take a little tweaking to get even flow in both/all runs, but might be another approach to the area coverage you want. Depending where the corners are it might also be easier than digging up the whole thing, and my gut says if it has two relatively straight paths it may be happier than with one long, windy one.
A shorter system will work better than the above. Either will likely require priming (put a candle under the heat riser, and warm the exit chimney somehow) to flush the cold, dense air or exhaust out of the floor pipes before you will have an easy start. Easier to start when the floor is warmer than outside air, which might be in the late evening after a sunny day, and then keeping the floor warm will make it easier the next time.


The pics show what I hope to use as a starting point with on the combustion core. It has a CSA of 26.56sq in (Just shy of a 6" pipe CSA) Original J dimensions were (not 100% sure where to make these measurements) measured at inside corners of the J- 9" feed, 17.25" burn, 34" riser.
I'm going to remove the first 90deg L and redo the barrel transition area with cob, and cover the combustion chamber as well.


The measurements we usually use are from the inside of the bricks, or outside corners of the void space - the widest dimensions of the "j".
We try to make the heat riser at least twice as tall as the overall length of the burn tunnel (e.g. 24" burn tunnel, 48" heat riser) and 3 times as long as the fuel feed (16" fuel feed, 48" heat riser).
It looks like you might be having some trouble keeping the CSA consistent between the feed, burn tunnel, and heat riser (and a low, slot-like tunnel gets choked with ash pretty easy, too). We like a more square opening if possible.
We have a bunch of pictures out that show how to stack bricks in courses so you can make any interior dimensions you want - we make the brick voids about 5.5x5.5 or 5x6 for a 6" system, and 7x7.5 or 6x8 for an 8" system.
I'd hit Paul's YouTube videos at www.richsoil.com/rocket-stove-mass-heaters.jsp first, and then buy one of our plans if you haven't got all these details from the video.


Thoughts on whether to use perilite, vermiculite or sand to increase insulative properties of the cob. Any ideas how many 50# bags of fire clay mix I would need to use to cob the core and make a transition area? I would like to retain the barrel lid for the bottom so as to make for easy removal and inspection.

Perlite gets you a lot further. Vermiculite loses some of its insulation value in cob, and sand just becomes thermal mass (it gets totally dense when stuck together with clay).
The clay is used for binder only - about 6% to 20% by weight, depending on the clay and the cob. I've used 1/2 bag (20-30 lbs) clay plus 5 gal water plus LOTS of sand - anywhere from 3 bags/buckets up to 10 bags/buckets of sand depending on the stickiness of the clay.
There are some good cob videos out there too for texture and so on.
I figured up the weight of the Annex core at one point, cob plus bricks came out just under 2000 lbs, so that's about a yard of masonry all together. Maybe 2/3 yard (20 cu ft) of cob. So if you did it with 2 cu ft bags of perlite you'd need 10, or about 15-20 bags of sand, or a combination. 5 bags of clay should be more than enough.


Another issue is the riser. Right now it's just the 1/2 thick fire brick stacked on it's side. I am going to further insulate it but how big (or small) of a diameter pipe/tube do I use around the riser? I guess the limit is to leave enough area between it and the inside of the 55gal barrel. bigger is better for more insulation?
Also need to make an ash pit in the feed tube.
I'm on a short time table as well as a very limited budget but any ideas would be helpful.


You definitely need insulation. Cheapest is a sheet metal cage (like 2 pieces of 8" or 10" ducting, snapped together to make one 16" to 20" cage that goes around your bricks) stuffed full of perlite-cob or clay-stabilized perlite. Slightly more expensive and way easier is 9-10 feet of rock wool or ceramic fiber refractory blanket. We usually get 1" Durablanket from our local fireplace shop, where it comes by the foot, cut from a 24" wide roll. Usually under $100 for the amount we use, cheapest I found it was a whole role (25 ft) from the mfrs for about $60 plus shipping. We protect and hold this in place with about the same amount of wire mesh, usually 1/4" hardware cloth, about $20 a roll.

Hope that helps!
Yours,
Erica W
 
Erica Wisner
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p.s. That's a new way to handle the manifold. Looks interesting. I might have to try it sometime.
You may want some gasket or refractory wool around the edges of the steel hole at the heat riser, so the thermal expansion doesn't wriggle things out of place over time. Definitely insulate this area between the bricks and the metal with something relatively flexible.

Yours,
EKR
 
John Adamz
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Erica Wisner wrote:p.s. That's a new way to handle the manifold. Looks interesting. I might have to try it sometime.
You may want some gasket or refractory wool around the edges of the steel hole at the heat riser, so the thermal expansion doesn't wriggle things out of place over time. Definitely insulate this area between the bricks and the metal with something relatively flexible.

Yours,
EKR



Since I wanted to get a higher riser than would fit inside the barrel I decided to try using the lid for the bottom and have the riser go thru it. The barrel I am using had the bottom swelled (Which gave me a 36.5" height) due to frozen water. It didn't rust because it had dried paint in it which I burned out prior to using.
I tried using the mortar caulk, but it cracked due to heat flexing of the lid. Even so with barely a 1/16 of an inch gap around the edges it had no noticeable leaking.
 
John Adamz
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Erica
Thanks so much for your detailed assessment.
The reason I said the 40' of pipe was a fixed point is that I have an aquaponics system over most of the duct in this 22' geodesic dome greenhouse. A 275gal IBC, top cut off flipped with floating bed, and 4 half barrel gravel grow beds times 2

The pipe is buried in a dirt trench and surrounded by 2-3"gravel on the sides and covered by ~4" of gravel on top. I might be able to shorten the underground tube by 10' and 1 90deg L (15') but that would still give me an effective straight run length of 50'. I had a booster fan on the last vertical turn 90deg elbow, and exhaust temps were at least 90degF there. I might just have to keep using the fan for now.

The CSA of the J is equal through out at 4.25Hx6.25W, but the burn tunnel is wider than high and it did get restricted with ash after several hours of burning. I hope to significantly reduce that issue by adding an ash pit/grate at the bottom of the feed tube.

Given your ratios for feed-burn-riser I might need to add height to feed tube. Would that simple addition help with draw any?

I've added pic, the pipe in ground, and the dome layout (RMH is centered at end opposite of tanks)

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6" duct buried in the ground
AP_dome.jpg
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Aquaponics greenhouse dome interior
 
John Adamz
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Here's a pic of the J tube I couldn't attach to the last post. It's short 1 brick on the riser.
2013-11-10-14.43.24.jpg
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j tube
 
John Adamz
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After thinking of other possibilities for the exhaust duct I can cut the pipe length to 20' with 1 90, 1 45, and 1 90 going vertical.
I don't know if it's going to be enough length to get enough heat in to the dome. Since I'll have to dig new ditch 10"+ deep for 10' I thought about instead of covering that length with gravel maybe using cob.
Would it help radiate more heat? I suppose cob would do better at heat retention and radiation than the gravel.

Another observation to report is that when I was burning the heater it seemed like the barrel was getting pretty hot (no thermometer) the gravel floor only felt warm for about the first 15+ ft. another 15' downstream it was slightly warmer than the surrounding gravel. Unfortunately it was only keeping the dome about 25-30deg above the outside temp (it got down to 18 that night) after burning for 8 hours. Needless to say I used a lot of wood, way more than I was planning on. It was a 60/40 mix of pine and oak scraps from wood crafting projects.
Just to reiterate I had a 6" booster fan I made from an old desk fan (unknown CFM) on the pipe coming out of the ground. It worked really well and the exhaust temps were around 90deg most of the time. The exhaust was very clean, only steam and some times couldn't see anything. So burning must have been pretty efficient.

 
John Adamz
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OK I went ahead and dug a 10ft new 6" pipe trench which will make the total 21ft of pipe,+ 1 90, 1 45, 1 90 going vertical.
Quite the chore digging into the grave floor and cutting thru and into the existing pipe. I going to cob over the pipe and combustion core tonight.
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new pipe in ground
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old path to the left, new straight out
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digging the new 10ft trench
 
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John,

That is Amazing!!! I hope hope you're able to make it work!!! This gives me new ideas for our project!!! Good luck and keep us posted!!

Jennifer
 
John Adamz
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Anybody care to comment on the gravel as a covering for the exhaust tube.
Is it hurting the radiant heat factor? What if I mix gravel and cob to surround it and have just a thin gravel layer on the top for the floor surface?
 
Jennifer Charlton-Dennis
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Hey John,

Again great project and great photos!! Cant wait to hear more about it!! You should ask Erica Wisner about the gravel. Her and her husband pretty much know everything about RMH's and all the relevant materials. Good luck and keep us posted!!
 
John Adamz
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I would really appreciate some thoughts on the thermal mass aspects of my system.
I have the 6" pipe in a 10"+ wide trench in the dirt (very black former garden soil). I have covered the pipe with ~2" cob so far and filled in on either side with cob mixed ~15% small gravel well compacted to avoid air voids. I liken it to a sort of claycrete I estimate a total of 1050 lbs of cob for the entire project of the combustion core/barrel transition area and 12' of new pipe.

I'm now considering 2 alternatives to cover the duct up to surrounding floor level. 1) to just use the gravel that was there making it ~3" over the cob covered duct, or 2) go and buy solid concrete cap blocks (2x8x16 or 4x8x16) to go over the top of the cobbed duct (sort of "setting"the brick in a bed of cob over the duct). They would span the duct trench which is the path most traveled in the greenhouse. My concern is that with just 2-3" of gravel over the cobbed duct unless the cob is really set up it might tend to crush it from walking on it. The duct being crushed under the ~4"+ gravel floor wasn't a problem before.

So bottom line would I get more heat off the duct covered with gravel or with cap blocks?

pics of the progress so far.
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ready to cover the transition area 1/2 inch rabbit wire
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complete base layer of cob on the core and exit
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The transition area done with fine sand to get it smooth
 
Jennifer Charlton-Dennis
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John,

If you aren't able to get through to Erica and Ernie maybe you could try allen lumley. He's also very knowledgeable with RMH design, materials and construction. He's already helped me out a lot!
Again I love the design of your RMH!! It's so damn cool!!! Good luck

Jennifer
 
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John Adamz : W.O.W., great job, smooth walls, large C.S.A., what is not to like, you should have no problems with this, If you left those two cinder blocks in place, I would
tell the world they are sacrificial forms. If you still have some cob left that you can use to bed the pavers so that they Can Not rock, I would go with the most heat radiation
for the buck and go with the blocks Perhaps you could do a shoe print outline inside one of those circles with the Diagonal Bar Sinister thru it ! Irregardless, I see more RMHs
and happy Dragons in your future ! Big Al !
 
Jennifer Charlton-Dennis
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John,

Again such an amazing job on the beauty of this RMH!! We had to move ours tonight due to some...well less than supportive neighbors. Well it did give us a chance to try and duplicate your design and thus far we are unsuccessful. We'll try again tomorrow. Was there a certain technique that you used to get such a great finish on the transition tunnel? It's so beautiful!! I wish we were closer so we could look at your creation in person! Again keep up the great work and we look forward to more pictures of your progress!!

Jennifer
 
John Adamz
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Jennifer
Thanks for the praise of my work. I used a small piece of 6mil shrink wrap plastic from the dome cover wrapped around my hand and a bit of water to smooth the transition area. I used my bare wet hand at first and got it almost as smooth.
What part of my design did you try using?

If you made a large (Too large?) to small transition area you may be running into the same problems I'm having now. I did a test run tonight with rather poor results. Previously I had fair performance as far as actual burn, barrel heating and clear exhaust, but only with the booster fan. After eliminating 25ft of pipe ending up with an effective length of 33ft I still cannot get the thing to draw without a booster fan I suspect the current large area (~100sq in) at the top of the transition area is a problem. My best guess as of now. Also I double checked the distance from the top of the riser to the barrel and find it to be close to 2 1/2" also perhaps a bit too much.

I have yet to surround the fire brick riser with an insulating pipe. I plan on using a 14" duct pipe filled with either fiberglass insulation or maybe perlite/clay. That would obviously affect the area between the riser and the barrel and also reduce the size of the opening in to the transition area.
I hope to positively affect the general draw of the system and the flow of gasses out of the riser and down the barrel and out the exhaust duct in the floor with that addition.
 
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What is your chimney situation? Maybe that is your problem and not that transitional area.
 
John Adamz
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Cindy Mathieu wrote:What is your chimney situation? Maybe that is your problem and not that transitional area.


By chimney do you mean the riser or the final exhaust stack?
As far as the riser, I redid the whole J tube with liberal amounts of refractory mortar in a bucket. I had problems with the mortar in a tube probably because I didn't use enough.
As far as an exhaust stack I don't have one now. Just the final elbow out of the ground a few inches, which is where I have placed my little booster fan. Perhaps a serious omission? On the original design trial I had a 9ft stack but it didn't help any.

On the transitional area I wonder if when I add the 14" riser insulating pipe since it will cover part of the hole in the bottom going into the transition area. Do I need to cob in under there so that there is no air space under that pipe?? Also is the gap between the side of the barrel and the riser insulating pipe too large 14" riser, 22" barrel, =4" side gap (not even due to offset riser)
 
John Adamz
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I am rather frantic to get this thing done ASAP since it's going to get down into the teens for lows this weekend.
So any and all input would be appreciated.
 
John Adamz
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Another clue to my problems is that after the 30-40 minute test ran last night the inside and outside of the riser and the inside of the barrel are rather black and sooty. After the original run of a couple days the inside was pretty clean and the outside was only black in a few areas.
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sooty riser
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riser insulating pipe
2013-11-20-13.28.39.jpg
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Jennifer Charlton-Dennis
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John,

I reread the entire post again and noticed something that Erica mentioned. She said

The cross-sectional areas should be consistent between firebox and exhaust, no big jumps up or down in size except that the barrel area can be larger.

I'm just wondering if the opening in the transitional area may be to wide at the opening? Please keep in mind that I am so far from an expert it's not funny! It funnels down to a 6" pipe into the ground correct? Is there any way you could possibly temporarily reduce the opening a little just as an experiment to see if it makes any kind of difference?

Oh, as far as what we used from your design is the way you used the lid from the barrel as the manifold! Great thinking! I think ours wasn't sealed enough to properly get the draft going.

Hang in there John!! Don't give up! You'll figure it out! Its such a beautiful piece of functional art!

Jennifer
 
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John, you are a craftsman! Now I could be totally wrong, but I think the area in red should not be connected to the barrel exhaust The cooled air in yellow is getting mixed up with hot air going up the riser. The area in red should be solid so that the heated air goes up, gets cooled and drops down the sides of the barrel and "pumped" out.
2013-11-20-13.28.39.jpg
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allen lumley
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John Adamz : I had posted a P. M to you before I saw your outer shell for your insulation, I would like You to share how you are going to seal the part that is open at its bottom
and extends over the top of your Transitional Area ! More hardware cloth and cob? You would need to roughen up the area where the two patches should bond, perhaps all the
way back to the Transitional Area's hardware cloth ?

I am having a little trouble seeing how you are going to twist your body to see to work on it ! Good Luck, and for the good of the craft ! Big AL

Kevin Davis ; I am sure that this whole area will be sealed off and in fact, filled with ether perlite with a Clay slip and perlite Cap at the top of the Heat Riser, or perlite and cob, or
just rock wool stuffed in between the brick inner and outer metal shield, like the filling in a sandwich ! Big Al !
 
John Adamz
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allen lumley wrote:I would like You to share how you are going to seal the part that is open at its bottom
and extends over the top of your Transitional Area ! More hardware cloth and cob? You would need to roughen up the area where the two patches should bond, perhaps all the
way back to the Transitional Area's hardware cloth ?

Big AL



I'm a master metal fabricator I made metal pieces to cover the top and bottom of the insulating pipe. I'm not sure whether I need to fill in under that area with cob so that it is a straight drop into the transition.

Kevin Davis ; I am sure that this whole area will be sealed off and in fact, filled with ether perlite with a Clay slip and perlite Cap at the top of the Heat Riser, or perlite and cob, or
just rock wool stuffed in between the brick inner and outer metal shield, like the filling in a sandwich ! Big Al !



Wish I had any more money for perlite, but I used some old fiberglass insulation lightly packed in around the riser. and sealed in metal top and bottom.

Now for the latest. I put it all together as shown, and at least temporarily sealed the barrel to the lid with some clay slip in the lip of the lid and screwed it together. I spent my last $10 for 10ft of 6" duct for the chimney stack on the outside pipe.

And the verdict is..... It works pretty well. Draw is passable not as rockety as I have seen but no smoke back or fire creep up with NO booster fan Barrel got fairly hot (still no thermometer) cob on duct to the end of the 12ft that's exposed is pretty warm, and exhaust from stack is pretty clean and doesn't smell like smoke. Now to decide how long to run it to get the cob to cure. Although I still need to put the rest of the cob I have on the duct, and cover that with some 2" pavers.
Any thought on how long it would take to get the cob dried, and should it radiate more heat after it cures?
2013-11-20-15.13.06.jpg
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bottom of riser insulating pipe sealed with metal
2013-11-20-15.13.00.jpg
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insulaed riser sealed with metal on top
 
allen lumley
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John Adamz ; A good looking job ! Yes, you are a pretty good tin knocker ! If it is drawing well I think you have a winner ! your upside down barrel deserves lots more trial
and experimentation, or just a similar configuration of holes cut in the other end, I think you will have very few problems with sealing the barrel as you have such a
large contact area ! I hope you saved the pattern, others may want to try your build,

It always seems to take a large amount of wood and a large amount of time to dry the cob, during this part of your build, you have the water that is in the Cob, the ~20%~
water vapor trapped in the wood and the water 'made' by the fire as 2 atoms of Elemental hydrogen join with a molecule of Oxygen (O2) to create, more water, only the later
can be considered to be free of an energy debt, the latent heat of evaporation is heat energy that we have spent to vaporize the water, later when your RMH is working as it
should, with exhaust Temps in the 150*F range and the water vapor recombines into visible vapor and water puddles we will get all of that 'Latent heat of Evaporation' back
again, so do not worry over how much wood you are using now, later it will be much less, though in fareness you can only measure it next year when you should have similar
weather !For all of these H2O reasons it should get hotter ! just not out the final vertical chimney !

Oh, and the Cob bench will constantly try to balance the H2O in the air, absorbing when the humidity is high, and letting it back out during low humidity!

You will have a hotter and cooler side to your barrel, I Think that is where you should place your thermometer,as when it shows a cooling trend there it will happen
faster, and tell you its time to add wood sooner !

Dont forget to fasten your pipe sections ('male goes into's facing down!) together with screws, and brace that pipe what kind of a hat to put on it is anyones best guess,Big AL
 
John Adamz
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Location: Springfield, mo
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I thought about adding another thread for this question, but as an ongoing process to finish this to a functioning RMH I'll do it here.
I continue to have excessive ash/hot coal buildup with a 6.25x4.25x2.25 deep ash pit. It requires constant attention to keep burn tube from choking up with coals. I might not have this big a problem when the cob is cured and I don't have to have such a prolonged intense fire, but the problem exists now.

Feed tube ash pit modifications
Here's idea 1- expand bottom portion of feed tube back, retain same feed tube opening (see pic) I used some partial bricks for mock up
idea 2- expand all of feed tube back the width of a brick, same feed tube opening (see pic) A basic doubling of the volume of the feed tube, but keeping same feed location.

Thoughts please
original_ash_pit_feedtube.jpg
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Ash_pit_alt1.jpg
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ash_pit_alt2.jpg
[Thumbnail for ash_pit_alt2.jpg]
 
Jennifer Charlton-Dennis
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Location: North East Ohio
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Hey John,

1st I've got to say I'm learning more about the in's and out's of RMH from your thread than all the reading I've done thus far!! I really admire your drive and ambition in this project!! It's very refreshing!

In our little practice RMH we had the same problem with ash build up. And that was just after two burns. I keep reading about the dryer the wood the better. The wood we used was not cured and you could see water boiling out of the tops when we burned them. You know, that hiss of steam, bubbles and such coming from the top of the cut up logs.

Our 4th burn (I believe) I went to my father's and (borrowed ) some of his cured wood for his wood burning stove and the ash problem was drastically reduced. Again, this is just an idea. I'm still learning about these too!! Good luck and let us know what you decide to do, and how it turns out.

Jennifer
 
allen lumley
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John : Out of the mouths of 'der kinder', It is possible with the weather cooperating, to greatly improve the dryness of of your wood by toasting it, it is also possible to get in trouble
that way!

Also Jennifer C.-D. meant to say she went shopping at mom and dads, somehow THIS Tradition remans unbroken ! For the Craft ! Big AL

Late note, I like the second one best but try them both and come back here to report on your results! Also the finer you can split them, the more of them you can have in your Feed
Tube -the space between them acts like upside down and sideways chimneys and they feed off of each other ! A. L.
 
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John Adamz wrote:I would really appreciate some thoughts on the thermal mass aspects of my system.
I have the 6" pipe in a 10"+ wide trench in the dirt (very black former garden soil). I have covered the pipe with ~2" cob so far and filled in on either side with cob mixed ~15% small gravel well compacted to avoid air voids. I liken it to a sort of claycrete I estimate a total of 1050 lbs of cob for the entire project of the combustion core/barrel transition area and 12' of new pipe.

I'm now considering 2 alternatives to cover the duct up to surrounding floor level. 1) to just use the gravel that was there making it ~3" over the cob covered duct, or 2) go and buy solid concrete cap blocks (2x8x16 or 4x8x16) to go over the top of the cobbed duct (sort of "setting"the brick in a bed of cob over the duct). They would span the duct trench which is the path most traveled in the greenhouse. My concern is that with just 2-3" of gravel over the cobbed duct unless the cob is really set up it might tend to crush it from walking on it. The duct being crushed under the ~4"+ gravel floor wasn't a problem before.

So bottom line would I get more heat off the duct covered with gravel or with cap blocks?

pics of the progress so far.



John,
I really appreciate all the detailed picts of your ongoing build. My comments are addressed to you ducts and mass. The changes I'm suggesting are probably something that you would want to consider next spring.There are some things you need to think about with your ducts. First off, what you are trying to do at the moment is the equivalent of trying to cause "Global Warming". (not going to happen by your individual efforts.)The earth is an infinite heat sink and no matter how big a RMH you make it will not be big enough to make any significant rise of temperature of the surrounding earth. If you have noticed most RMH's incorporate some kind of bench or hearth that is above ground/floor level. You need to consider insulating with EPS foam board on the sub layer of your setup. A minimum 6" to isolate the areas you want to try to effect. On top of that warm air through a duct is not the optimal solution because the ducts would have to be too close together to have any kind of impact. You might want to look at liquids in pipes (hydronics) to serve your purpose. I would design the ducting into a bench style and then think about adding a hydronic component. (Don't forget the BOOM SQUISH Factor) Bigelow Brooks Farm (on Youttube) has some excellent videos on how he did his green house. The other problem is that your wall thickness is measured in mils because you are using plastic sheeting for walls which has zero insulation factor. What ever heat you do generate will be leaving immediately. It is very hard to keep a plastic sheeting green house warm enough overnight without huge inputs of energy. About the only way I could see you do this is to be located in San Diego or Southern parts of Florida. Just don't want to see you expecting to get results by these minor changes. About the only greenhouses that I've seen be successful at overwintering have hard sides to them and some sort of insulation factor above zero. Just one man's opinion. Good Luck
Jim
 
John Adamz
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Jim LaFrom- Thanks for the thoughts to ponder. It might just turn into action.

About a year ago my original inspiration for my whole aquaponics setup was a friend who has a 15x20 greenhouse made from steel frame and covered entirely with clear plastic panels (like my covering, also near 0 R factor). His was the first RMH I had ever seen. It is a 55gal 6" system with the exhaust duct buried in a 10" bed of gravel on top of his back yard with a wood formed border (the building base) . So the ~25ft of 6" duct he has in the ground was keeping his green house at 80deg (a few hours after the fire went out) when I went over on a day of 35deg. I thought he told me he has used 40ft of pipe hence my original design plan.

The additional mass of the 500gal of aquaponics water and nearly a 1.5 tons of growbed media will I hope help to maintain temps. That would obviously take a lot of heat energy to transfer from the air in that. I'm still thinking of a way to incorporate the RMH to heat the aquaponics water.. That alone might be enough to keep the dome warm since all I really need to keep warm is the water. The fish and the plants would do just great at 70-75deg.
I probably should go over to the aquaponics forum here and check it out.
 
Jennifer Charlton-Dennis
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Hey John,

Just wondering if you had the chance to try out any drier wood to see if it reduced the ash problem as it did for ours. Keep us the great work and keep up posted!!

Jennifer
 
John Adamz
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Jennifer Charlton-Dennis wrote:Hey John,

Just wondering if you had the chance to try out any drier wood to see if it reduced the ash problem as it did for ours. Keep us the great work and keep up posted!!

Jennifer



Yes I did. It seemed to work out pretty well. I used some of my firewood for the house fireplace insert. It's untreated railroad tie end cutoffs I get from a guy who works where they make railroad ties. 1 6" long piece will split up in to enough of a pile to last over an hour. It's the best wood I've ever seen. I can burn for a week in the house and get maybe 2 gal of ash.
Unfortunately for some reason I had to go back to using the booster fan tonight to get a decent draw. more to ponder.

I also tried out the alternative feed options tonight. Didn't try Alt 1 as I would have to have cut a brick or 2, So I tried Alt 2, the bigger one didn't really work at all. I tried moving the bricks around to sort of a modified small batch feed style, but no luck. The problem is that in order for the fire to burn correctly it needs the intake air to pass over the wood and directly in to the burn chamber. The dead space behind the feed tube opening does not let that happen. I should have foreseen that. Alt 1 might work, but a deeper ash pit at the bottom of the feed tube and possibly a grate in there somewhere is most likely the correct configuration. So I'm back to my original configuration since burning the good wood has made the ash build up manageable I'll keep on with that for now.
I'm not sure how to incorporate this concept into a RMH, but the best wood box I have ever used has the air intake draw from UNDER the grate up through the burning wood. Sadly that wood box loses WAY too much heat up the flue. I'm going to add a heat exchanger barrel on top or something to reclaim all that heat BEFORE it goes up the flue. Sort of a modified double barrel stove type system. I only rarely use it in one of my shop buildings so it's a plan on the back burner (ha ha) for now.
 
Jennifer Charlton-Dennis
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Hey John,

I'm just wondering with all the ash build up you had in the burn chamber maybe some made it to the stove pipe running through the cob? I know I've read that it's good to have a little bit, but maybe it built up from the 1st couple of burns since you redesigned it? I only mention this since you said you had to use the booster fan again. Just my thoughts.

Oh the other stove you mentioned. I think a company called Vogelzang makes a Double barrel kit. http://www.northlineexpress.com/vogelzang-double-barrel-stove-adapter-kit-bk50e-bk50e.html?utm_source=googleproducts&utm_medium=feed&utm_content=cse&utm_term=5VZ-BK50E&CAWELAID=974975368&gclid=CM-c9u-f-boCFVFgMgod5yoAsg

I know your burner isn't a barrel but thought the top part mite help for capturing some of the heat loss. Ok, good luck hope it works!!


Jennifer
 
allen lumley
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John Adamz : Have you had a chance to go to 'Rockets in Greenhouses. . . . 'in this Forum to check on Amos Valenti's modified feed tube ?

He must be having some of the same problems you are as he likes to throw whole chunks down into the bottom of the Feed Tube, YOU are just feeding
the wood in so that only the lower tips of the wood is burning right, not dumping in chunks like you were throwing your dirty socks on the floor next to
your shoes ?! for the good of the Craft ! Big AL
 
John Adamz
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allen lumley wrote: YOU are just feeding the wood in so that only the lower tips of the wood is burning right, not dumping in chunks like you were throwing your dirty socks on the floor next to
your shoes ?! for the good of the Craft ! Big AL



Reeboks, no socks
Correct about the feeding in of the wood. I have pieces about 6" long, 1-1.5" diameter. I also have a bunch of little chunks of the tie wood. I tried before but the chunks were hard to keep out of the burn tube (before the added ash pit), so the sticks seem to work better. I might try again since I'm getting a little tired of splitting up big chunks.
 
Jennifer Charlton-Dennis
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John,

Hey just wondering if you had any success with the rest of your modifications. The low tonight is 18 where we are in Ohio so I know it's cold there too!! Hope it's working out!

Jennifer
 
John Adamz
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Jennifer Charlton-Dennis wrote:John,

Hey just wondering if you had any success with the rest of your modifications. The low tonight is 18 where we are in Ohio so I know it's cold there too!! Hope it's working out!

Jennifer


Jennifer, thanks for prompting my continued updating of my project. The burn system is unchanged as of today. Still having to use booster fan to get consistent good flow and maximum heating. 10ft vertical final stack out of the ground is not enough although it works moderately well if the system is up to peak operating temp.
Yes it was a bit cold last night. Got down to 14 this morning after a high yesterday of 36. Today's high was 28. Burned til midnight last night, today at 10am it was 17, it was 40 in the dome. I got it to the low 60's for a few hours then let it go til 6p, back to 40. 40 seems to be the low point so far. The aquaponics water stays in the upper 50's, so that's helping keep things warm. Expected to get down to the mid to upper teens a couple more nights mid week.

The cob on the floor duct finally dried out last night. It seems to be getting up to ~120-130deg to the end of that 12ft section. I've got a really good feel for temps, but I'm still in desperate need of a non contact laser thermometer to accurately evaluate the system operation. Still have more cob to put there, and also set the 2in cap blocks over the pipe. I still wonder if the blocks set in/on fresh cob will give me more or less radiant heating than just cob with a thin layer of gravel on top. I think I read about this, but just can't remember.

I'm really beginning to wonder if I can keep temps up in my dome with just radiant heat from the barrel and cobbed over floor duct even with that mass ~1000lbs. I understand a significant amount of heat energy will be required but since I have WAY more mass in water and growbed gravel (500+gal water, 2500lbs of growbed gravel) I have rigged up an experimental water heating apparatus using an aluminum car radiator (I have a stock pile of them, 10+). I temporarily connected with garden hose out of the floating bed water feed line, to the radiator suspended ~3in over the top of the barrel, and back in to the floating bed on top of the IBC fish tank.

Since my AP pump is on a timer (15on/15off) and somewhat difficult to regulate flow it is only moderately effective. To really get it to work I'm going top have to try a couple other ideas. 1-use a separate low flow pump to circulate the water thru the radiator over the barrel. The flow rate needs to be constant and fine tuned to get any really effective heating of the water.
or 2-maybe try running pex pipe (more stuff from the pile) back and forth along the sides of the duct imbedded in the additional cob I plan on putting over the duct. (also using a low flow pump)

I guess I should read/post over on the AP forum for input on this idea.
 
Jennifer Charlton-Dennis
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John,

Have you checked ebay for the thermometers? We buy and sell stuff on ebay All the time!! You can usually find great deals and if your unhappy you'll always get your money back!!

Oh, have you seen any of the set ups where people ran copper tubing through the barrel on their RMH for heating water? Not just for hot water but for radiant heating. I know it would probably be to hot to go right into your AP tanks but maybe you could run some through the floor for radient heat then to the tank once its cooled enough to not damage the plants. I just hate to see that awesome set up not make it! Well hope its working out!

Jennifer

 
allen lumley
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J.C.-D. : Here I am, up early to tend fires and find a non-panfull way to stretch out the mornings kinks, and Then I read this ! O. K. Smile on ! Full steam ahead !

The entire land of You-tube is filled with Mines and Booby traps, You see a posted video where someone is stating look what I have Done ! and there assembled before
your eyes is a Franken-clone of a Unit of flaming Death! Care full research will show that after a few negative comments the builder has blocked all comments and the
fact that he has stopped posting to his own video with any up-dates, shows that he has lost interest in his toy and has moved onto chasing the next, shiny Bauble .

This does not stop people reposting nor is there any way to challenge these builds for safety, and 6 months from now a new crop of flaming units of death are out there.

It is my opinion that -

Anyone proposing the take hot water off of The Entire Rocket burner, Barrel and Base should be immediately sat down to watch the Myth Busters Episode The explod-
-ing hot water heater !( See, the contagion provides it's own antidote !) Think the Boston Marathon Bombing, with more full body, full thickness burns , Or just go to our
Permies tool box and Google Boom-Squish ! For the record ! Big Al !
 
John Adamz
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Allen- I agree that trying to heat the water by placing the pipe to be heated anywhere inside the barrel is insane. That being said I wonder if would be possible to employ a properly designed heat exchanger on the bottom outside of the barrel. Even though that area is well over the boiling point if the water system was not closed, and the operation was closely monitored and only run long enough to maintain a heated water mass it might be one option. Obviously not a system for the masses which is something we should try to develop.
I've been reading a lot on the idea of heating the water either for actual consumption (shower etc.) or heating a thermal mass of water for radiant heat. The later is what I'm interested in doing.
A more practical idea is to heat the water by routing some pipe thru a solid mass like the cob bench. Or in my case the cob covering the exhaust duct in the floor/ground. Either would require a small pump, but it's failure would not cause any catastrophic consequence.
For my situation I wonder if the heat transfer to the water would be sufficient to raise the temp of the fish tank water (~500gal system total) an appreciable amount with out taking away from the heat of the limited mass (Not a bench of 1000's of lbs) of cob. I suppose the point is to heat a mass with the RMH, whether it's water or cob is a matter of preference. However It's my understanding that water might be better at holding the heat and warming the space. Ultimately it's only the water I need to have warm in my aquaponics dome.

My current thought is to use somewhere around 50ft of pex pipe encased in the yet to be applied cob on the duct, and slow pump it out of and back into the tanks. Should I try more or less pipe to get the water warm? Flow rate of the water would be a factor as well on how much heat is transferred as opposed to cooling the cob by pumping 55-60deg water thru it.

I finally got a non contact laser thermometer and took some readings. Top of barrel is ~500+deg, bottom is ~250, cob on duct a foot or two out of the barrel is 145, 115 at the end of the 12ft cob covered run, and 90 at the bottom of the outside exhaust stack.
I also got the RMH to get decent flow by slightly altering the feed tube configuration and using the 10ft vertical pipe outside without a booster fan. Allowing some air to enter the feed tube at the level of the ash pit and partially covering the top with a brick or 3" angle iron piece a has done the trick for now.
2013-11-26-12.34.13.jpg
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Modified feed tube intake
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another view of the altered feed tube intake
 
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