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portable rocket mass heater

paul wheaton
steward

Joined: Apr 01, 2005
Posts: 14191
Location: missoula, montana (zone 4)
    ∞
I'm thinking that tube is less likely to cave in from the mass of the thermal mass.

So - a six inch duct to an eight inch duct would probably be plenty?

I'm thinking that with the pic I posted earlier, doing this for the first 180 would probably be a big help.  Because after that, the gasses would have cooled a bit and the duct needs would be smaller anyway.  Does that sound reasonable?


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Abe Connally


Joined: Feb 20, 2010
Posts: 1317
Location: Chihuahua Desert
    
    6
yeah, a 6 going to 8 would barely make it.  If you could go a bit bigger, that would be better.

Try it out and see!


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divonbriesen Hatfield


Joined: Jan 26, 2011
Posts: 6
velacreations wrote:
don't know if this has been mentioned, but instead of lots of elbows (90 degree turn slow down the exhaust), you need to make some box ends for the pipes.  I can't remember what these are called, but instead of an elbow, it is a big box, so there is considerable volume right there, and you avoid the issues with gasses and lots of 90 degrees.

It is basically like this:
                   ______
--------------|          |
tube                       |
--------------|          |
                  |          |
--------------|          |
tube                       |
--------------|          |
                  |--------|

Does that make sense?


Vela- i believe this is called a plenum.

I was thinking along similar lines. I salvaged some big thick aluminum valves (basically boxes with bit vent doors inside) and was wondering if i could pipe the exhaust in one inlet and out the other since there should be little drag in that big open space, but it should provide a way to dissipate the heat (either to the air, or into bricks i'd put around the box).

icky
divonbriesen Hatfield


Joined: Jan 26, 2011
Posts: 6
Emerson White wrote:


The more heat you ditch from the top of the barrel the less you have to pay (with draft energy) to force to the bottom of the barrel. This makes it less efficient as a mass heater, but it ensures that it is an efficient combustion device.


Emerson-

So, if we didn't care as much about the mass heat, and wanted more efficient combustion, would it help to put something that could rapidly absorb heat on top of the barrel (i.e. a big pot of cold water, or an aluminum radiator or heat sink)?

I've been trying to use a triple wall stainless steel pipe to serve as both the riser and the outside barrel- for $99 you get the inner (6"?) tube, surrounded by about half an inch of insulation, surrounded by about 1.5" of hollow space. I put an inverted wok over the top, and in my initial experiments at home was able to get what smelled (and breathed) like pure steam out of the bottom. I had trouble replicating this a few days later with a different burn tube.

Some basic math ought to confirm that the outer donut is greater than the inner - if not, that's an obvious issue- but i'm wondering about the dynamics of getting the air up over and back down the outer tube.  Could i just take a cookie tin and use that over the top after bending or cutting the inner flange, which comes up about an inch? Will the supports that hold the outer part on interfere too much with the airflow?

I'm really trying to do this with a minimal amount of masonry - like paul, i want portability, and i'd rather not do anything that involves water or mixing- which means metal, pebbles, ashes, maybe some high-heat caulk.

Also curious about using the lightweight vent stuff for the exhaust- it seems like once we get to the bottom of the outer tube that the temperature will be below 500, so almost any material is safe.

Finally, as I understand it, what rocket stoves are doing is essentially gasification in the 2ndary burn in the torus- is this correct? Is there any way to make sure this is actually happening before going to the next step?

d.i.

ps- was looking at $4 computer fans (80mm size) which are nice and quiet and efficient and could be easily battery powered (12v I think...) - i've seen little gasification stoves that use a battery powered fan- has anyone used a fan to "assist" the rocket? I was thinking that if you had an appropriately sized horizontal inlet to the feed chamber, you could power up the fan for a little boost, to get the flow going (without have to stuff paper down in there, or light a candle, or whatever priming you'd normally do).  We're pretty much going to have some juice at all times in the battery bank, even though it's off grid. I'm still a little hazy on how cool air (in the latter portions of the vent) continues to draw air... it seems like i'd back it up, so you're really pushing it...

doerner67 McCoy


Joined: Feb 27, 2011
Posts: 1
Location: Missoula, Montana
Hello, and I am awed by this exchange. And odd, I seem to have found the right crowd. I'm Mike Doerner (and Paul, I also work at Home Resource, so we may have already met). I began recently on a RMH using various-sized water heater tanks, steel drums and pipes. Not far into it yet, and from the looks of it, I might be setting myself up for some return trips to the drawing board.
Oh well oh well. But as I progress, I am wondering if and how I can upload pictures and drawings to this forum, for further input, etc. And if you'd like sometime in the future to inspect the "finished" product.
It is being built (slowly) at FreeCycles on South First, so's ya know. Actually in our new "manufacturing" warehouse, which is virtually next door.
Like I said, it has presently presented some seemingly contentious issues, of course, but I am determined to see what my first conceptions might bring to bear, as I have not seen some of them implimented before. Yet.
Contact me thru email if you'd prefer, but I will be certainly returning to this forum, so either will do. Thanks. And again, this is awesome.


If at first you don't succeed, try not to look surprised.
paul wheaton
steward

Joined: Apr 01, 2005
Posts: 14191
Location: missoula, montana (zone 4)
    ∞
Pictures would be great.

I offered to build a portable rocket mass heater at home resource and at free cycles.  In fact, I thought we were going to be doing some actual building this last weekend, but I never heard back from anybody.  And now I'm headed out of town.

I actually have most of the materials from the rocket mass heater in this video:



After a long visit with ernie and erica, I came up with some big design improvements that I wanted to try at free cycles.

Max Tanner


Joined: Feb 26, 2011
Posts: 81
Location: Ontario North and South - right now, moving North Permanently soon. Timmins Cochrane areas
Hello I am new to the forum so forgive me if my protocols seem somewhat off here.

You are going to get mad at me for saying this, but please think about it first, ok. The title is Portable Rocket Mass Heater;
You are in fact trying to make two systems at the same time here, I think you need to break it down into;
A. Portable
B. Semi Permanent

My thoughts are that you are combining these ideas together as you have my OCD, or ADD (here I laugh at myself, it is getting worse with age not better) you mind is racing and your fingers and body can not make up fast enough for your brain.

I found this page through Rusty, who said go take, a look at the Rocket Heaters. As we will be going out for Winter Camping with Spring time, moving into a more permanent setup on the land every weekend in a progressive method, heating will be an issue.

system A. Portable - winter camping, lighter, easier to move, yes not as much mass to keep the system warm for long periods, but in a tent or Yurt of the Weekend, is it necessary? Create a truly portable system with a heating stove area, similar to the one in the pic that was posted that leads into the fireplace. Now instead of the pipe just going into the fireplace, this pipe could curve around similar to the Permanent and Semi Permanent though with lighter weight or replaceable mass. Perhaps simply putting the metal tubes into a clay pipe system would work not bad, put reflective material underneath and behind so the heat is radiated in a direction into the room/tent place a sitting platform or sleeping platform overtop of this and vent outside.

Another ideas was to use Water, sounds good especially if it is easy to get too! Fill 5 gal grease containers with water, they warm up/heat up and dissipate the heat into the tent/room slower than the pipe will, so a semi-permanent setup with a simple table top or plywood ontop to sleep/sit on. Why not use a system that is similar to a car Radiator and hot water reservoir as overheated water fill, connect it with metal tubes that go around the metal pipes and the metal Heat chamber as well. That way, you can use much less water, so it is much more portable, only a few gallons instead of 5+ gallons per pail.

Another idea would be to set the pipes ontop of bricks only a few as a spacer, wrap metal pipes or aluminium pipes around the exhaust piping, this will heat up drawing air into the tubes, especially if there is a cold end away from the heat source.

Another Place a pot of water on top of the fire chamber to give off ambient heat better, or a large flat metal plate, that is similar to a stovetop, to give ambient heat and to conduct heat into rocks, pots or kettles as an example.
Summary, the main heat chamber is the heavier Metal setup 1 piece
The pipe setup, with additional (optional) bio mass that is portable e.g.; water, metal tubes wrapped around the pipes, with some bricks to keep the pipes off the ground. Or metal fins to transfer the heat outwards.
All on a reflective sheeting to direct the heat into the tent/room instead of all directional like the Permanent Systems. Outside venting per the type of structure you are in, keep it safe no asphyxiations.
 
system B. Semi permanent – a large mass structure that can be disassembled into 3-4 components, to be re-assembled with rocks or bricks as mass. Great but heavy, great for longer term heat retention.
This is the system with the bricks for a base, heavier chimney for heat conduction, a system of bricks that can be placed around the piping for additional heat mass transfer into the structure. This closely resembles what you are building. This Semi-Portable system can be build off site, disassembled and then re-assembled fairly quickly compared to the full thermal mass of the cob structure that is a Permanent system.

By keeping the two systems in mind while you are designing, I think you can come up with two systems, both will assist in your teaching and both will be valuable to everyone in the future.
ideas are conceptual no drawings or test systems yet

http://wildernessreturn.wordpress.com/
my wilderness return story and adveture
Tarkus McCoy


Joined: Oct 21, 2010
Posts: 32
Wilderness: Build it and keep us informed of what you come up with.
I personally, for a truly portable unit think water as the heat sink would be the most versatile supplying hot water for cooking, showers and doing the dishes, especially in a camp environ. (subject to availability) I've used sand as my semi portable "Mass" and it works ok.

Good luck
David
Karl Teceno


Joined: Mar 16, 2010
Posts: 91
Location: Portland Maine
I am new to this type of heater. So I have a question, people use cobb because the clay is readily avaible and it won't crack going through the heat/cool cycle over and over, right?
I have zero access to clay. Using concrete or mortar would be a bad thing, right? How about a block wall with the cavities filled with sand and the piping for the RMH in a sand filled cavity?

Karl
dakman McCoy


Joined: Jan 29, 2011
Posts: 7
I am considering using flexible duct hose, such as the kind shown in this picture, to form the lower elbow and heat riser for an RMH.
I would cast an insulating refractory around the ductwork. Once the refractory was cured, the ductwork liner could be pulled out prior to firing. (Provided a release agent was applied liberally prior to casting.) I have read much about the need for turbulence in these areas, and it seems that the ribbed shape of the duct work would lend itself nicely. Comments? Thanks,
Dakman



[Thumbnail for SS_Flex_Hose.JPG]

Paul B


Joined: Dec 04, 2010
Posts: 79
Intresting idea, but I think you will find that the ribbing would lock the flexable form into place, or that you would need so much release agent that the ribs would no longer show up in the finished cast.  You may have to leave the ductwork in place permanently.
paul wheaton
steward

Joined: Apr 01, 2005
Posts: 14191
Location: missoula, montana (zone 4)
    ∞
here is the latest design.  Built in one hour and fifteen minutes:

Emerson White


Joined: May 02, 2010
Posts: 1206
Location: Alaska
Duck tape does not belong anywhere near a duct. You need some aluminum tape!
Max Kennedy


Joined: Feb 16, 2010
Posts: 453
Location: Kirkland Lake, Ontario, Canada
If you fire that baby long enough to heat the mass as you normally would in an indoor setting is there any charring on the wood frame?. Any temperature gradients on the thermal mass section??


It can be done!
paul wheaton
steward

Joined: Apr 01, 2005
Posts: 14191
Location: missoula, montana (zone 4)
    ∞
We had a point and shoot thermometer and were testing the temps of a lot of stuff. 

The duct was not getting very hot.  I think the highest we measured was around 140.
paul wheaton
steward

Joined: Apr 01, 2005
Posts: 14191
Location: missoula, montana (zone 4)
    ∞
The purpose of this video is to give folks an idea of how clean the
exhaust is while running a rocket mass heater in Missoula, Montana.

When we first start it, there will be smoke.  And there was smoke in
the middle of the burn sometimes, but I think that most of that has to
do with things that need more design improvements.  For most of the
time, the exhaust was a lot like what is shown in the video - there is
fire, but no smoke.  Marci Anderson gets her nose right in there.

Another important thing to note is that the temperature of the
exhaust:  see how we have a hot, clean fire burning and guido does not
burn his hand when he puts it in the exhaust.  It feels warm, but not
hot.  We measured it at about 90 degrees when the barrel was at about
850 degrees.

I show the materials being moved by the freecycles folks from the
freecycles HQ in Missoula to Caras Park (downtown Missoula).  Then a
bit of building it.

This rocket mass heater is a prototype for some variations.  A wood
box shows a different aesthetic, a much taller heat riser design,
using dry, loose fill (rocks and sand).  This should be a lighter
design than other rocket mass heaters - so it might be good for places
that have a wood floor.

This might also be the fastest time a rocket mass heater was ever
built:  an hour and fifteen minutes.



http://www.youtube.com/watch?v=kGaGtO8MkQk

Erica Wisner
volunteer

Joined: Feb 10, 2009
Posts: 692
Location: Okanogan Highlands, Washington
    
  80
dakman wrote:
I am considering using flexible duct hose, such as the kind shown in this picture, to form the lower elbow and heat riser for an RMH.
I would cast an insulating refractory around the ductwork. Once the refractory was cured, the ductwork liner could be pulled out prior to firing. (Provided a release agent was applied liberally prior to casting.) I have read much about the need for turbulence in these areas, and it seems that the ribbed shape of the duct work would lend itself nicely. Comments? Thanks,
Dakman




The main issue with that ribbed flexible ducting is that it slows down the airflow something fierce. You might be able to get away with it if you go one size larger, but we've had bad results when we've used it in the past.

If you're looking for castable tunnels, you might consider something smooth like those waxed-cardboard carpet rolls, or bread bags.


Play with nature, make nifty stuff:
www.ErnieAndErica.info
Erica Wisner
volunteer

Joined: Feb 10, 2009
Posts: 692
Location: Okanogan Highlands, Washington
    
  80
paul wheaton wrote:
The purpose of this video is to give folks an idea of how clean the
exhaust is while running a rocket mass heater in Missoula, Montana.

When we first start it, there will be smoke.  And there was smoke in
the middle of the burn sometimes, but I think that most of that has to
do with things that need more design improvements.   For most of the
time, the exhaust was a lot like what is shown in the video - there is
fire, but no smoke.   Marci Anderson gets her nose right in there.




http://www.youtube.com/watch?v=kGaGtO8MkQk




I wish the camera had caught more of the nose in the exhaust, instead of trying so hard to get video of flames.  The sideways flames are compelling in person, but not so much on camera.  Maybe I'm just jaded.

I think you're doing well with the overall performance.  The biggest thing I would look to is are you getting air leaks into the combustion area?  The firebrick may allow you to avoid running gaps if you stack it tighter, or you may need some kind of secondary seal. 

I couldn't entirely make out how you did the manifold, but it looked like sheet metal cutouts.  This might be the application to try a sheet metal box for the burn tunnel / feed tube area, that drops in place and holds the bricks where you want them.  I wouldn't eliminate the brick entirely because of the extreme temperatures and you want that little bit of surface turbulence from the hot masonry.

Another thing I've been wanting to try is kiln brick for its insulative value.  Might help if the floor and first course was kiln brick.  Lighter, too.

Neat project, and I'm excited to see you hanging out with a gang of neat folks.

-Erica W
paul wheaton
steward

Joined: Apr 01, 2005
Posts: 14191
Location: missoula, montana (zone 4)
    ∞
I think that there are probably leaks in the air intake.

I was thinking that a better approach might be to make a molded base with the burn tunnel and the transition form the barrel to the duct. 

What do you think of the tall riser approach?

What do you think of the rocks as the mass? 

What do you think of the sand as the seal around the barrel? 

What do you think of the wood box?
bill1111 McCoy


Joined: Apr 25, 2011
Posts: 6
I know you are calling this portable , but is there any way to add more mass [sand or something ,put on a outside wall , with wood covering so , SHE who must be obeyed , would not have a a large pile of cob in her living room?so longer brench
L shaped?
sand - fire bricks
wt for floor? can put load-bearing wall under
can you heat water with it - can it take the place of a radiator when hooked to a on-demand hot water heater some how?can I have a tempering tank which will run both ways
seems like you guys must spend a lot of time spliting wood


already heat with wood - 35 years . getting older and need a new way
6 cords /year aprox .
semi retired
northern Wi
Caleb Larson


Joined: Feb 02, 2011
Posts: 76
Location: Missoula,MT
    
    1
Erica & Ernie,

I am that guy with the funny contraption that was hanging around.  I tested several things with our companies Testo combustion analyzer.  If/When things work out I would be happy to test your RMH if I am in your area.

I was wondering if you guys have done any combustion analysis with your stoves.  I got readings that were interesting.

My only major concern was the Carbon Monixide levels which were higher then I would have expected to see.  I think that after the exhaust was modified and the burn was done hotter that the CO will burn off.  I tested earlier in the day before the video was taken and the video shows a much cleaner exhaust.

I would be very interested to hear your results.


Rocket Mass Heater Workshop
October 26-28 with Erica & Ernie Wisner
http://www.permies.com/t/14828/missoula-eco-forum/Rocket-Mass-Heater-Workshop-just

For more info or to register
contact Caleb Larson @ ruggedtraditions@gmail.com
12much McCoy


Joined: Apr 21, 2011
Posts: 5
@Paul:

I love what you're doing! I built my wooden house by myself and it has cob innerwalls with heatingpipes , (fed by a downgraded heater at this moment) a RMH is the next thing to do. My one and only concern  is redoing things over and over again for the benefit of fun, changing forms and experimenting. So wouldn't be nice if that is possible with less effort as possible? I'll go for the sand and stone filling, but I've a question about the accumulation. Is it enough?  Is there a big difference in comparison with cob in terms of radiation?

Instead of a wooden case, I'll build a hollow bench from cob and want to make some connection with the walls in future, so it has to be changed easier than dried cob all around the duct will be. The second benefit will be the weight on my wooden floor. I already made some concrete poles for extra foundation last easter (forced to stay at home a couple of days in Holland

I also produced a few cubes 150x150x150mm from Curon 120S (famous Dutch refractory mortar, but very expensive) with vermiculite in different mixes to find out which ratio will be most efficient without degrading to fast. I want to produce the burntunnel and heatriser with drumstand and connections  for the duct, ash pit and cleanout in 3 molds, regarding to the dimensions mentioned in Ianto's (PDF)book. This way I hope I'll have less concerns when rebuilding.

Keep up the good work,

Regards, Boy - Holland.

paul wheaton
steward

Joined: Apr 01, 2005
Posts: 14191
Location: missoula, montana (zone 4)
    ∞
bill1111 wrote:

wt for floor? can put load-bearing wall under
can you heat water with it - can it take the place of a radiator when hooked to a on-demand hot water heater some how?can I have a tempering tank which will run both ways
seems like you guys must spend a lot of time spliting wood


Maybe my coffee hasn't kicked in yet.  I had a terrible time understanding the question.

This thread has talked at length about sand.

Hot water heater stuff is covered in another thread.

These tend to use about five to ten times less wood, not more wood.

paul wheaton
steward

Joined: Apr 01, 2005
Posts: 14191
Location: missoula, montana (zone 4)
    ∞
12much wrote:
I'll go for the sand and stone filling, but I've a question about the accumulation. Is it enough?  Is there a big difference in comparison with cob in terms of radiation?



If you are gonna do cob, I think you should go all cob.

As for which will do better, we would need to get one of these into a house and run it for a year.  Get some info about how it did.  If the information is that it was comparable, then we might give the cob stuff a run for their money!

Max Kennedy


Joined: Feb 16, 2010
Posts: 453
Location: Kirkland Lake, Ontario, Canada
Paul, I think he wants to do the cob wall so he can change the internals and experiment then when he feels he's got it right replace the sand with cob.  All cob won't allow him to rip out the innards and change things.  I would be concerned over the strength of the cob wall depending on how thick it was made.  If too thin the weight of the sand could exceed the strength + elasticity of the wall and crack it in the center of the bench.

paul wheaton wrote:
If you are gonna do cob, I think you should go all cob.

As for which will do better, we would need to get one of these into a house and run it for a year.  Get some info about how it did.  If the information is that it was comparable, then we might give the cob stuff a run for their money!


12much McCoy


Joined: Apr 21, 2011
Posts: 5
Tnxx for the answers,

I'm not a native speaker, so i'm so sorry if it isn't clear enough about what my question or explanation is.

@mekennedy1313:

you're allright, that was what I ment. I've some clay bricks and will make some "bridges" to achieve enough strength.  I was curious about the accumulation because off the next thought: If you walk on a beach, the top layers for about 3-6 inch will be warm after a day sunshine. If the kids dig a hole, it is rather cool down under

So if there is a big difference, i'll have to look for another solution in between.

The big issue is: It will be changed within the next months/years, I'm sure of that. Sand and stones will make the job much easier. And then it sounds appealing how fast your portable is build when all the stuff is laying around (and hands.......

@Paul:

maybe I'll steal your idea of the wooden box and replace one long side for clay bricks, for my wife likes to sit on the floor with her back against the sofa...
MMC11 McCoy


Joined: Apr 27, 2011
Posts: 56
Location: MONTANA, Bozeman area; ZONE 4
How about putting some type of handles on it so 4 guys could just pick it up and move it?

Or build it on a board that would just fit through the door, which platform could be put on wheels, perhaps by two guys.
MMC11 McCoy


Joined: Apr 27, 2011
Posts: 56
Location: MONTANA, Bozeman area; ZONE 4
Is there a much greater heat absorbing effect of hardened, dried cob over just dry dirt?

You could do earth bags of dry dirt, or of rocks, or earth bags of cob.  Then fill in the area around it with something appropriate.
Max Kennedy


Joined: Feb 16, 2010
Posts: 453
Location: Kirkland Lake, Ontario, Canada
12much wrote:
If you walk on a beach, the top layers for about 3-6 inch will be warm after a day sunshine. If the kids dig a hole, it is rather cool down under


Your sand down under is moist and has constant access to water, as the sun drives it off more seeps in from the lake or sea.  If the sand is dry you will find the heat penetrating deeper as the summer season wears on.  Also the heat re-radiates from the sand at night which you can feel if you walk on the beach.  In this kind of bench the heat is coming from inside and moves outwards.  Heat is never lost, it is stored and released slowly.  
Max Kennedy


Joined: Feb 16, 2010
Posts: 453
Location: Kirkland Lake, Ontario, Canada
MMC11 wrote:
Is there a much greater heat absorbing effect of hardened, dried cob over just dry dirt?


Yes, the clay component of cob fills much of the air gaps in dirt and the hardened material has a much higher heat retention capacity than dry dirt.  If the dirt we compacted, similar to rammed earth walls, then heat capacity would be similar but I can't see how to ram the dirt without crushing the heat pipes.
MMC11 McCoy


Joined: Apr 27, 2011
Posts: 56
Location: MONTANA, Bozeman area; ZONE 4
Thanks for that explanation.

So then, making really big cob bricks that could be quickly taken apart adn put together again might be a way. Then fill in the space around the circular pipe with dirt, or perhaps sand.
Emerson White


Joined: May 02, 2010
Posts: 1206
Location: Alaska
mekennedy1313 wrote:
Your sand down under is moist and has constant access to water, as the sun drives it off more seeps in from the lake or sea.  If the sand is dry you will find the heat penetrating deeper as the summer season wears on.  Also the heat re-radiates from the sand at night which you can feel if you walk on the beach.  In this kind of bench the heat is coming from inside and moves outwards.  Heat is never lost, it is stored and released slowly.  


My experience with summer heat and dry sand (several dozen feet above the waterline, dry to touch down at least 4 feet) incidate that it is a good insulative material, with a whole days worth of sun penetrating to heat only the top inch or so.
Max Kennedy


Joined: Feb 16, 2010
Posts: 453
Location: Kirkland Lake, Ontario, Canada
True, however heat rises and the heat source is above on the beach.  Then a huge amount of the heat is lost radiatively each evening but if you actually monitor the temperature about 1' down over a week of sunshine you will see the temperature rise steadily.  Any extended period of cloud or precipitation wipes this out.  Remember the sand in an RMH is above the heat source and thus the rising heat moves slowly to the outer surfaces rather than being trapped on the interior.
Emerson White


Joined: May 02, 2010
Posts: 1206
Location: Alaska
only convective heat rises, conductive and radiative heat don't care which direction gravity pulls. But yes I could see that mattering.
paul wheaton
steward

Joined: Apr 01, 2005
Posts: 14191
Location: missoula, montana (zone 4)
    ∞
I am moments away from uploading the very long video of the portable rocket mass heater.  This was a lot of footage, plus a lot of editing. 

At the end of all of this, I had an idea. 

It would be great to have a ....  PRMH core.  A single piece that would have the wood feed, the burn tunnel and a few other bits and bobs.  You would set a heat riser on it (or in it).  Then you would set a barrel on it.  And then you would connect your exhaust to it. 

It could be made from a mold.  So it might even be possible to make many from this one mold. 

The design would not only make building your first RMH easier, but it would also make for a higher quality RMH.  better seals would make for less drafts. 

I suppose somebody could even do this as a sort of business.  They could sell RMH cores. 

Just a thought I wanted to jot down before I forgot.


Len Ovens


Joined: Aug 26, 2010
Posts: 1238
Location: Vancouver Island
    
  14
paul wheaton wrote:
It would be great to have a ....  PRMH core.  A single piece that would have the wood feed, the burn tunnel and a few other bits and bobs.  You would set a heat riser on it (or in it).  Then you would set a barrel on it.  And then you would connect your exhaust to it. 


I had a similar thought, but all steel. The feed, tunnel, riser and barrel would be one piece with a 6 or 8 inch fitting for output. The whole thing could then be set in the wood box... the long pipe attached and the box filled with gravel or dirt or whatever. I would then put patio slabs over top to finish it off, making sure the fill was touching it. The cap would not only make it look finished but trap heated air from around the gravel from escaping so it could heat the cap.

My thought was to start with something like this:

http://www.iwilltry.org/b/build-a-rocket-stove-for-home-heating/

or this:

http://streetjesus.blogspot.com/2010/12/rocket-mass-heater-project.html

as an air tight starter unit and add whatever mass bench to that. Now both of these examples work, But they use a 3 and 4 inch riser, so I do not know how long a bench pipe would still work. My thought though, was to take the same idea but make it 6 or 8 inch. This may need two 55 gal barrels to get enough height (though I think there would be enough room in a water heater to do 6 inch). I was thinking that for portable use Roxul may be a better insulator less likely to fall apart in transport, though more costly up front.

I know this tends away from the "use junk" ideas of the original RMH, but....

1) for a lot of people bits of steel and welding supplies is what happens to be sitting around and is therefore free.

2) this can obviously be a standardised RMH core that could be (at some cost) certified making it's use "permit-able".

3) for a portable use, it is robust, compact and of unit construction making setup quick and easy.

I happen to find water heaters easier and happen to have a welder sitting here, so that is what I will use. I will try a (Oh no!) 4inch system first just to see how long the mass heat pipe can be. I think I heard that on an 8 inch system it can be as much as 40 feet and a 6 inch system can handle 28 or 32? So maybe a 4inch system will only be 12 to 16 feet... but that may still be useful. I want to measure temperature in the middle of the flue stream instead of the pipes surface at different points along the pipe... maybe even a few points in the barrel where the water heater already has plugs.

My feeling (yet to be proved right or wrong) is that the top surface of the barrel shows more the true flue temp. because the flue gas is pushed against it. I think that even though the barrel is cooler towards the bottom, that the flue gas is still very hot and the cooling effect as the gas drops is fewer degrees than thought. What happens, is that the gasses close to the sides do not move as fast as the gas in the centre and so cool down faster around the edges close to the pipe. So measuring the pipe temp would give false idea of the gas temp. in the flue. (this from professional people who have already measured these kinds of things.)

Unfortunately, I have a family and not as much time as I would like to devote to this as I would like. I have played around with some bricks making burn tunnel/heat riser kinds of things.... and have stripped the water tank but not cut it yet. I still need to find some square steel tube to make the innards. I also have some solar panels that need to go on my roof.... and maybe a 25year old roof that needs to be redone first. You may finish before I even start. Though our power is going up 20% over the next few years so this project may get some extra push.
Max Kennedy


Joined: Feb 16, 2010
Posts: 453
Location: Kirkland Lake, Ontario, Canada
paul wheaton wrote:
I am moments away from uploading the very long video of the portable rocket mass heater.  This was a lot of footage, plus a lot of editing. 

At the end of all of this, I had an idea. 

It would be great to have a ....  PRMH core.  A single piece that would have the wood feed, the burn tunnel and a few other bits and bobs.  You would set a heat riser on it (or in it).  Then you would set a barrel on it.  And then you would connect your exhaust to it. 

It could be made from a mold.  So it might even be possible to make many from this one mold. 

The design would not only make building your first RMH easier, but it would also make for a higher quality RMH.  better seals would make for less drafts. 

I suppose somebody could even do this as a sort of business.  They could sell RMH cores. 

Just a thought I wanted to jot down before I forgot.





Am actually working on something like this.  A modular RMH with a standard core, including the barrel, several run sections and a standard exhaust section.  The sections would slide together and seal, working on the seals (several possibilities but figuring out which works best), the joints would be mudded with cob.  The sections are a standard width to bet in doors using a hand trolly.
paul wheaton
steward

Joined: Apr 01, 2005
Posts: 14191
Location: missoula, montana (zone 4)
    ∞
This design starts off with three big missions:

1) rocket mass heaters for apartment dwellers.  the idea is that this can be taken apart, put on a truck, moved, and put back together.  I was hoping that the time it would take to get it loaded onto a truck would be less than an hour.  We did demonstrate that.  I was hoping that the time it would take to rebuild it would be less than an hour - in the end we missed that by ten minutes.  I think under an hour can be done.

2) A different aesthetic.  This rocket mass heater has a wood frame.  To my knowledge, this is the first time this has been done.

3) A lighter design for places that have wood floors that don't hold a lot of weight.  The fact that there is a LOT of duct in this design does make it much lighter.

I think we had success in all three of these. 

Along the way, we also came up with some other improvements. 

A)  Rather than a brick core with a heat riser that sits on top, we have the heat riser go all the way to the ground.  This eliminates a bottleneck when the burn tunnel (square) and the heat riser (round) meet. 

B)  Must use a square burn tunnel.  So the walls of the burn tunnel are defined by bricks, and a brick bottom is defined by a single brick who's height can be changed based on the amount of sand under the brick.

C)  Sand as the mass turned out to be a bad idea.  Better to have pea gravel and rocks.  Air is allowed to move through the mass - so there is better transfer of heat before the exhaust exits.  This is also lighter.

Geoff Badenoch talks about brick quality and has a good idea on where the brick came from which reflects on the quality.  The Brickyard hill Brick works in Missoula.

Version 1.0 was okay.  We then did A and B to get a better burn.  Which worked.  Thanks to Anne Binninger for helping with the construction of 1.0. 

Oh - and we learned that when you store sand in buckets, you should always keep your sand sealed, or cats will find it and ... uh ... enhance the sand.

Version 1.1 was a better burn.  When we started making version 1.2 the heat riser where we extended looked pretty bad.  Like it might restrict flow.  So I got the idea that it would be good to make one solid heat riser that was a little taller.  Thanks to Geoff badenoch and Greg Guscio for helping with version 1.1.

version 1.2 gave us the best burn.  Thanks to Caleb Larson for bringing in rocks and helping with the build.  Thanks to Joel, Mike Doerner, Guido and Suzy Bean for helping with construction.  Thanks to Tim Skufca for providing some of the materials, helping with the build and arranging a spot for us at the Missoula earth day event.

Five guys from free cycles of missoula loaded up the rocket mass heater on bicycles with nutty home made bicycle trailers.  Success!  The rocket mass heater was successfully moved about two miles on bicycle trailers!  I would like to thank Bob Giordano of Missoula Free Cycles for arranging the transportation and jumping in on the build! 

We then built the portable rocket mass heater at the missoula earth day festival in caras park.

Version 1.3 didn't have as good of a burn.  I think it was because of leaks and because the heat riser wasn't warmed up at first.




http://www.youtube.com/watch?v=GkHOwmKyL7A

Luke Miller Callahan


Joined: Jan 24, 2011
Posts: 19
Location: Edinburgh, UK
Amazing Paul!

I can't wait to try my hand at one of these. Keep up the great work!


-Luke

http://GroAction.com - Showcasing Real Change Throughout the World
Jim Argeropoulos


Joined: Jan 11, 2010
Posts: 96
Paul
I like your idea of a cast core. If I didn't have a mostly clay free soil area, I'd be looking into that.
 
 
subject: portable rocket mass heater
 
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