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pebble style rocket mass heater in the library

 
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@Paul,

Would additional heat dispersed into the mass via fins also help? I'm assuming that anything after the burn being lower temps would help with that additional draw.

If and and when the mass is hot enough that the exposed fins and duct are too hot you're probably done burning then anyway right?

-Mike
 
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I suspect that the fins might work so well at heating the mass that it could end up being something that eliminates duct loops in the mass.
 
Mike Leonido
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Which would definitely improve the draw which might be enough of an assist to the side-flue to make that work.

I think I like the idea of fins in the mass and some fins and thermometer on the exposed flue in the room so that you can monitor lost heat.
 
paul wheaton
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Tony was working outside at -4F and his toes got cold, so he came into the office a buried his feet in the pebbles:

 
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It's been so cold recently! I was wondering how y'all are coping with the exceptionally cold weather. (I have Montana weather on my iPhone, along with some other cities where I know people, and I like to scroll through in the morning when I wake up.)
 
paul wheaton
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It got to 26 below a few nights back. The temp in the office before starting any fires was 50. And then we got it up to 83 for a while.

Jocelyn said something about when you go outside it "freezes your nose hairs".

It was CRISP!

The water to the washing machine froze. But I suspect that the plumbing in the house is pex, so no broken pipes.

We've been above freezing for a few days. It is 18 right now. Tim says it is supposed to rain in a few days.

 
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Get that man some snowboots!
 
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I see that riser section curing next to Tony's tootsies and badly want to know some deets!
 
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It's summer! no one cares about heaters in summer... A pair of quick questions.

I'm working through a plan for a high mass super insulated RMH for storing process heat (say for example heating sugar water to drive off the water). How much pea gravel is in the bench and what are the exhaust gas temperatures on this stove at the start and end of a burn?

Thank you for your time.
-g






 
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Tom Rutledge wrote:It's summer! no one cares about heaters in summer... A pair of quick questions.

I'm working through a plan for a high mass super insulated RMH for storing process heat (say for example heating sugar water to drive off the water). How much pea gravel is in the bench and what are the exhaust gas temperatures on this stove at the start and end of a burn?



A few comments...

Comparing the temperature of a non-insulated mass and an insulated mass will not help. In the non-insulated case the temperature of the surrounding air, the walls, the objects outside the windows, etc. all effect how fast the mass is loosing heat. Adding insulation changes that... but there are already too many unknowns and adding insulation doesn't change that.

The needed temperature for the insulated mass determines the exhaust temperature or, looking at things differently, the amount of wasted heat. The advantage of the RMH is removing the greatest amount of heat possible before exhaust. Part of this is the barrel itself where a large amount of heat is radiated into the room, the heat to the storage mass is already cooled a large amount by then.

So it seems that while the RMH is great for heating a room, it is not the best thing for making process heat. A well controlled Rocket Stove or a gasifier burner would make more sense for that application and probably use less fuel for the work. The exhaust heat could still be used for other purposes so it is not lost, such as preheating (if needed), home heating, providing domestic hot water or if all else fails heating the ground under the house for use when it is cold outside.

In the case you mentioned, evaporating water, the temperature required is relatively low, but the water itself soaks up a large amount of heat... that is it acts like a mass itself. The main thing is to keep from having hot spots that could over heat. I would suggest soapstone or cast iron for spreading the incoming heat. Well placed insulation could still be helpful... but probably more to keep the area cooler for people working there than saving heat. The evaporation process is generally a high heat loss deal... the surface of the liquid has to be open for it to work.
 
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paul wheaton wrote:

There is something called Physics and we can't fight that.



Is there a point in this somewhere that I am suggesting that we fight physics?

If you pull air out of a room there is something is that is going to replace it . In HVAC terms this is called makeup air. (cool air?) You will either depressurize the room if it were totally airtight or air will find it's own way in. Nature abhors a vacuum. (Permaculture principle )



Which is entirely the point. I prefer to have the stale, stinky air removed from the room and replaced with fresh air from outside. Yes, the air from outside will be cold - and it is coming in while my rocket mass heater is running.




I'm not sure if this has been addressed, but it seems to me that a good solution is SHCS, also called a Subterranean Heating and Cooling System.

Air entering the house is drawn through underground pipes which use geothermal energy to moderate the temperature of the air through the ambient temperatures underground.

This functions in the same way as a wofati stays warm in the winter, and also similar to the "deep wells" idea Paul mentioned in the WDG videos.

In this way, cold air from outside is being warmed to comfortable temperatures before entering the house. "Stale" air from the house is being drawn into the RMH. Warm air from the RMH core is being drawn into the thermal mass. Exhaust air is being drawn out of the house by the secondary thermosiphon pump.

I think it's really important to consider that one of the factors that drive these systems and make them sing is the temperature differential.

Someone made mention of a system that uses the flue to heat the air, but this seems less ideal to me because it creates less of a difference between inside and outside air (within the system, obviously not referring to inside and outside the house).

Simply put, the RMH works because of the temperature differential. It is essential that the heat riser is insulated to create a temperature difference between the air inside the heat riser and the air outside the heat riser inside the barrel. Similarly, the air outside the barrel must be cooler than the air inside, which is why some people put fins on the barrel (though I also like the idea of putting fins on the ducting).

These factors are what create the torus. Hot air shoots out of the heat riser, heat is transferred to the barrel, and the cooler air gets sucked down toward the manifold. Hot air radiating off the outside of the barrel allows the barrel to give off the heat and become cooler. This is why designs which bury the barrel with decorative cob don't work as well.

For this reason, I think a good compromise is to warm the outside air to a comfortable temperature before entering the house, but not necessarily to heat the air using the flue. The house still gets a good exchange of fresh air, and in essence, the house is a layover for fresh air before feeding the RMH.
 
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Also the tube under the ground that have been warming the incoming air during the winter will be cooling the ground to supply cool air through those same tubes in the summer for cool fresh air in the house during the summer.
 
Tom Rutledge
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Len Ovens wrote:

A few comments...

Comparing the temperature of a non-insulated mass and an insulated mass will not help. In the non-insulated case the temperature of the surrounding air, the walls, the objects outside the windows, etc. all effect how fast the mass is loosing heat. Adding insulation changes that... but there are already too many unknowns and adding insulation doesn't change that.


The needed temperature for the insulated mass determines the exhaust temperature or, looking at things differently, the amount of wasted heat. The advantage of the RMH is removing the greatest amount of heat possible before exhaust. Part of this is the barrel itself where a large amount of heat is radiated into the room, the heat to the storage mass is already cooled a large amount by then.



I'm attempting to understand where the heat in a pebble bed RMH goes, and the approximate efficiency of transferring the heat between the exhaust pipe and the pebbles. I read somewhere on this forum that about 40% of the heat goes out the barrel and the rest goes out the bed / exhaust. I'm just gathering data points to understand the pebble bed version more. My hope was to burry most of the barrel in a pebble bed.


Len Ovens wrote:

So it seems that while the RMH is great for heating a room, it is not the best thing for making process heat. A well controlled Rocket Stove or a gasifier burner would make more sense for that application and probably use less fuel for the work. The exhaust heat could still be used for other purposes so it is not lost, such as preheating (if needed), home heating, providing domestic hot water or if all else fails heating the ground under the house for use when it is cold outside.

In the case you mentioned, evaporating water, the temperature required is relatively low, but the water itself soaks up a large amount of heat... that is it acts like a mass itself. The main thing is to keep from having hot spots that could over heat. I would suggest soapstone or cast iron for spreading the incoming heat. Well placed insulation could still be helpful... but probably more to keep the area cooler for people working there than saving heat. The evaporation process is generally a high heat loss deal... the surface of the liquid has to be open for it to work.



just one quibbly semantic point, heat lost through the boiling process is the goal not a loss... but yes it's a loss to the system... quibble done.

I am attempting to optimize somewhat for human time rather than strictly on fuel consumption. The load would be smaller batches of fluid a few times a day. It may be faster to have an already heated pan ready and waiting for service rather than having to start up a rocket stove and get it warm / burning clean and all that. There is also the further possibility that the process could be left unattended yet be fire safe, which would be totally awesome.

Getting a large mass up to say 300C then slowly drawing that down to maybe 150C might be the thing to do. I'm still noodling through the different tradeoffs. As you mentioned the lower grade heat at less than 100C could very well be used to preheat the fluid to boiling if done well. If done poorly it would just end up taking longer.






 
Len Ovens
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Tom Rutledge wrote:

I'm attempting to understand where the heat in a pebble bed RMH goes, and the approximate efficiency of transferring the heat between the exhaust pipe and the pebbles. I read somewhere on this forum that about 40% of the heat goes out the barrel and the rest goes out the bed / exhaust. I'm just gathering data points to understand the pebble bed version more. My hope was to burry most of the barrel in a pebble bed.



I am surprised no one has NAKed that idea the general thought is that the barrel should in free air to work properly. My experience has been that it is ok to surround the barrel with mass. I have used clay brick on the outside of the barrel with no problems. It is true I have not then tried to push the exhaust through 25 feet of horizontal flu but I don't think you want to do that either.

Tom Rutledge wrote:
just one quibbly semantic point, heat lost through the boiling process is the goal not a loss... but yes it's a loss to the system... quibble done.



I think I understood that, and I was not calling it a loss as in something that needs to be retrieved, but rather as a comparison. With so much heat escaping in doing the work, I was wondering that the insulation would have any realistic effect. However:

Tom Rutledge wrote:
I am attempting to optimize somewhat for human time rather than strictly on fuel consumption. The load would be smaller batches of fluid a few times a day. It may be faster to have an already heated pan ready and waiting for service rather than having to start up a rocket stove and get it warm / burning clean and all that. There is also the further possibility that the process could be left unattended yet be fire safe, which would be totally awesome.



It would seem that the insulation is for retaining the heat while not using it. This makes a lot more sense. I think a traditional (if we can use that word for a technology that is less than 100 years old) RMH is not really what you want for this use. The rocket stove, as you said, is not the right animal either. The purpose of the barrel is to pump the exhaust through a long flu pipe. I really think a gasifier style burner would be best as they can run on one load of fuel for 8 or more hours (see the Kimberly heater). However, just the feed to riser top part of the RMH could do well too. Rather than force the flu gas back down, use as much as you can to heat your mass (I would still recommend some thing denser than gravel like iron or soapstone or even refractory concrete). If the mass was movable, it could have insulation around the sides and a removable insulator for a cover. Heat it up and slide it to one side on top of another insulator... now you have all 6 surfaces insulated. A second mass could be father along the flue path preheating up with what heat the first mass did not soak up... once the first mass was hot enough slide the second into place to finish it off. The preheat area may be still hot enough to maintain the heat of the first mass too (I don't know). In the end, a lot of heat is not going to be used, but compared to most of the syrup boilers I have seen (a bonfire under a boiler) it should be able to do much better.

My favorite idea for a small mass (as I have said before) would be a steel box filled with tin. Get it hot enough to melt the tin and the heat will last a long time.

Another "by the way" in parting. Soapstone slabs (small enough to be lifted and moved by the average "home maker" of 100 years ago or so) have been used for keeping an oven hot enough to cook in with no fire box, so your idea is certainly realistic.
 
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I swear I heard in a podcast weight related discussion of the pebble variant. Any leads to the weight of this build compared to traditional RMH with cob mass? A reference (even a best guess) would also be welcome as to which podcast this was discussed in. I have been listening to some to try and find it but have not come across it yet.

I'm thinking of building a smaller RMH for my partially covered deck, but of course I do not want to overload the load bearing capacity of my deck. It is ground level but still.
 
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Paul talking all about the pebble style rocket mass heater in his office!!

 
Lab Ant
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Is the loss in efficiency when using pebbles, compared to cob, due to the gaps between pebbles inhibiting the conduction of heat? If so, would it be possible to improve the efficiency of conduction by filling the empty space with sand or some other filler material? I think i have heard that sand makes a lousy thermal mass for some reason, but perhaps having a mix of sand and pebbles would be different.

If not sand, then how about just good old packed earth? It seems to me that if you have a container to hold the mass material, you could just fill it with dirt, pack it down a bit as you fill, and it would behave much like cob. It is basically the same material as cob, minus a bit of straw and the water which evaporates away anyway. You would still be able to remove the mass and move the whole rocket mass heater if you wanted to, but you wouldn't need to transport all that mass (pebbles) along with it, you could just dig up some new dirt from the new site.

Am I totally off on my understanding of the RMH physics here?
 
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Sand has so many tiny airspaces that they act as insulators. Pebbles have airspaces large enough and connected enough that air can flow through, taking heat from the core to outside. Sand would prevent this air movement.
Dirt without moist working would act similar to sand, maybe even more insulating. Organic content would decrease the mass per volume and probably add fluffy insulating patches. If it is dense enough to work well, it will turn somewhat hard and difficult to dig out later.
 
Mike Leonido
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I know this falls under Paul's "issues" with people poking at the innovators instead of trying it themselves (apologies in advance) but I am curious.

I know sand was found to be unsatisfactory and pebbles worked better, especially the smallish ones. Was rock or stone dust tried? If it's a heat conductivity issue the dust should behave more like rock than sand and if it's an airflow issue a bucket or two on top to slow/stop the airflow should help the pebbles also.
 
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Very interesting. I would like to know more!

Questions:

1. The guillotine: I am curious about the construction details. Specifically, how is it made air-tight? Perhaps a rockwool gasket on the bottom, upon which the plate floats/rides?

2. The Bubble: Is that just an extension of the feed tube, with a closed lid on top? If so, is it a good idea to add an air port that may be opened (much like the air input ports on a traditional wood stove, used to control intake air flow) for 10 or 20 seconds before swinging the door open (to discourage a potential flare up of gases, suddenly exposed to a rush of fresh air)? And if so, how is the air intake flow managed (if the bubble encloses the feed tube opening, one cannot just keep the covering bricks snug against the wood)?

3. Gas venting. Some persons are interested in making code-buildable RMHs. I've read some code prohibits 100% closing the flue, and I have also read that some of the masonry heater designs take gas venting/escape into account, by placing 3/8" gaps allowing light gases to rise to the chimney. Has this been a subject of much discussion and/or trial?
 
Erik Weaver
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Erik Weaver wrote:Very interesting. I would like to know more!

Questions:

1. The guillotine: I am curious about the construction details. Specifically, how is it made air-tight? Perhaps a rockwool gasket on the bottom, upon which the plate floats/rides?

2. The Bubble: Is that just an extension of the feed tube, with a closed lid on top? If so, is it a good idea to add an air port that may be opened (much like the air input ports on a traditional wood stove, used to control intake air flow) for 10 or 20 seconds before swinging the door open (to discourage a potential flare up of gases, suddenly exposed to a rush of fresh air)? And if so, how is the air intake flow managed (if the bubble encloses the feed tube opening, one cannot just keep the covering bricks snug against the wood)?

3. Gas venting. Some persons are interested in making code-buildable RMHs. I've read some code prohibits 100% closing the flue, and I have also read that some of the masonry heater designs take gas venting/escape into account, by placing 3/8" gaps allowing light gases to rise to the chimney. Has this been a subject of much discussion and/or trial?



I just saw that Paul has already started a new thread to address questions to this build. I'll redirect my questions there.
 
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Hi everybody!

I don't know if i have said this here before. But with Peter, we've talked about rocks, pebles etc.

And i think the best way to make a dismantleable, portable and real efficient mass is to use a rock filled bell.

I mean, imagine Army trunks (well we have a different type over here)

https://www.google.fr/images?q=cantine+m%C3%A9tallique&safe=off&rlz=1T4SAVJ_enFR550FR551&hl=fr&tbm=isch&oq=&gs_l=

Filled with rocks, a good head sized, to handball ball. Two tubes down low, one intake, one exit, linking to the next trunk. The rocks would be directly in the flue path. So that's the best for heat exchange. Then, when the fire is out, you close the guillotine. And if more radiating heat is needed, you can open the trunks's lids. You could even put a fan into the equation, to warm the place even more. At the expense of duration of the heating. The rocks need to be on the big side, to let the flue path be free'ish!
 
Chad Sentman
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I found this video extremely helpful to see the various parts, especially in relation to each other, being talked about individually.

Video is SUCH an important medium. Podcasts just leave me to my imagination, and the photo threads also didn't clarify how it all fit together. (In my head, the guillotine was located where the bypass is, for some reason.) As much as I've heard, read and seen in photos, this video brought it all together for me. More please.

Satamax, for the sake of clarity, I'd like to point out that Americans have a different understanding of handball than Europeans. European handball is a team sport, more like rugby. What should be self-explanatory, European handball is like European football (which Americans call soccer) except you use your hands instead of your feet, which makes good logical sense to Europeans. American handball is like racquetball, only with hands instead of a racquet: Two players in a room taking turns hitting a golfball-sized ball against a wall with their hands. European handball is largely unknown to Americans, as far as I know.

That said, could you explain in a different way what your mean with a rock-filled bell? I still don't follow.
 
Satamax Antone
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Chad Sentman wrote:.

That said, could you explain in a different way what your mean with a rock-filled bell? I still don't follow.




Hi Chad. I mean exactly that. A fireproof container, with low entry and exit, where the hot gases would stratify towards the top, untill cooled, filled with rocks, big enough so the there's "flue" paths in between thoses, so they heat up in direct contact with the hot gases. When the fire is completely dead, you bypass the bell and mass from the main flue Stream, and open the container to the surounding room, for better thermal exchange.
 
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Hmmm... Max, allow me to disagree. When a container is filled with rocks, for the sake of simplicity say it's a barrel, it stops acting like a bell. When the spaces between the rocks won't add up to at least 4 times the cross section area of the inlet pipe stratification won't occur anymore. In this case the bulk of the gases is shortcutting to the exhaust. There's a way around it, for instance feeding in at the top and exhausting at the bottom. This way it is a distributed contraflow system, provided the sum of all the openings between the rocks at any given height is at least twice the inlet opening. To make sure the inlet and exhaust openings are never blocked I would opt for a larger open space at the top and the bottom.

All the above doesn't apply when the container isn't upright but laid flat instead. With both openings at the same height and opposite each other is is a simple stream-through system like a bench. Just my two cents.
 
Satamax Antone
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Hi Peter. Yes, i agree if it's like a barrel. Tho, since the stones are deflecting the flow; there could be some stratification , if the gases "Stream through" the rocks, in the case of a long box. There will also be mixing, because of the chaotic nature of the flow through randomly piled up rocks. All in all; it's just my opinion; we would see something different from the usual direct Stream through of a pipe through mass. I'm Under the impression that it would be better at heat exctraction than a plain pipe in a cob bench. Due to the greater surface.


Just an idea; would you agree that a rock, heated solely on the bottom by the Stream, when it gets hotter than the gases surounding it, would heat thoses , and induce a movement of convection in the gaps which were stalled before?

What do you think? Wouldn't that induce some sort of stratification in the end?
 
Peter van den Berg
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Good question. I wouldn't call it stratification but convection instead. This is very much depending on the gaps between the rocks. So whether or not it will work as intended is unsure unless you could give a recipe of how large and how irregular the rocks should be. Doesn't sound like a transferable and repeatable experiment to me, more like a random shot in the dark. Sorry.
 
Hans Quistorff
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I recall an earlier discussion of using bricks in the flue path to absorb heat. these could be distributed in an organized way to maintain the flow volume. This is interesting to me because I have an oil burner heat exchanger to use as my barral. It is 4'x4'x4' for the fire box with an integrated heat exchanger which will be to one side As it is configured I could stack bricks around the riser to reduce the extra volume and keep the down flow along the sides of the fire box. This will be a replacement for a mass heater in a 100 year old chicken barn. Part of the cement floor has collapsed so I can build the batch box in the dirt the t has been dry all that time and put the heat exchanger on top and then route the exhaust into the old cement mass. I hope to use the door of the old mass heater on the batch box. I will have to start a project page and post pictures of that old mass heater use to keep baby chicks warm.
 
Satamax Antone
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Peter van den Berg wrote:Good question. I wouldn't call it stratification but convection instead. This is very much depending on the gaps between the rocks. So whether or not it will work as intended is unsure unless you could give a recipe of how large and how irregular the rocks should be. Doesn't sound like a transferable and repeatable experiment to me, more like a random shot in the dark. Sorry.



Peter, i think the rocks shouldn't be too iregular. We don't want to block the path, so river or beach pebles would do the trick may be.

At first, i envisioned fist sized, few months back. But soon realized that the gap would be too small. So, for a size everybody can understand, i'd say from a baby's head to an adult's head. You remember how grocery stores used to pile up oranges? That would be rather even.


I've never said i wasn't shooting in the dark. With the tiny bit of theoretical background i have, i get thoses ideas poping in my head. Often initiated by previous ideas from another field, or ideas from others And not having time to test thoses myself, i throw them in the air, to see if someone is keen, and would try it for himself.

If we want more of a bell's behavior, we could pile more iregular, interlocking rocks on the perimeter of the container, with two pipe stubs entering end leaving it, so rocks could be piled onto the pipe stubs. Let say, six to eight inches of rock each side of the central channel and on the ends; and the central channel about 8 inches wide. But just thinking this, that's not 4X CSA! Could it work if the central channel was 32 inches high? A bit like the Lopez lab experiment.

Hans, it could be done with bricks. But that getting nearer and nearer to an old proven design, the multiple path flues of massonry heaters.
 
Peter van den Berg
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Satamax Antone wrote:I've never said i wasn't shooting in the dark. With the tiny bit of theoretical background i have, i get thoses ideas poping in my head. Often initiated by previous ideas from another field, or ideas from others And not having time to test thoses myself, i throw them in the air, to see if someone is keen, and would try it for himself.


<grin mode>So your assignment is to launch the idea and mine is to shoot at it.</grin mode> I would love to try some of these ideas but I don't have access to river rocks the size of a human head. I have to think it over, maybe I could cast those out of concrete. But I don't want to take on new experiments at the mo, since I have the MHA annual meeting in the pipeline.
 
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I would be wary about exposing freshly heated rocks to an inhabited room. These are potentially harmful gases that are heating the rocks and even if the stove was out there could be either gases or toxins present and available to mix with the room air. Having a sealed unit at all times seems the only safe route to me. I am not too worried about clouds of smoke because people get out of the way, I would be more concerned with smaller amounts of carbon monoxide nibbling away at someones health.
 
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Peter van den Berg wrote:

Satamax Antone wrote:I've never said i wasn't shooting in the dark. With the tiny bit of theoretical background i have, i get thoses ideas poping in my head. Often initiated by previous ideas from another field, or ideas from others And not having time to test thoses myself, i throw them in the air, to see if someone is keen, and would try it for himself.


<grin mode>So your assignment is to launch the idea and mine is to shoot at it.</grin mode> I would love to try some of these ideas but I don't have access to river rocks the size of a human head. I have to think it over, maybe I could cast those out of concrete. But I don't want to take on new experiments at the mo, since I have the MHA annual meeting in the pipeline.




Let's use human skulls, freshly skinned, filled with concrete
 
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The guillotine: I am curious about the construction details. Specifically, how is it made air-tight? Perhaps a rockwool gasket on the bottom, upon which the plate floats/rides?
 
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A nifty lil image that we used during our kickstarter. Thought it should go here.

 
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Regarding the pebble bed, have you experimented with different sizes of pebbles to see how well they breathe?
I have a sand pit near me that routinely has piles of larger rocks (egg sized) that get screened out& eventually dumped back into the pit for lack of demand, these are rounded stones as this part of the sate was under sea once, but i wondered if these were used in the mass bed, if some sort of screen was used under the bed, or slots were cut if air would circulate through the bed via convection.
 
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russell smith wrote:Regarding the pebble bed, have you experimented with different sizes of pebbles to see how well they breathe?
I have a sand pit near me that routinely has piles of larger rocks (egg sized) that get screened out& eventually dumped back into the pit for lack of demand, these are rounded stones as this part of the sate was under sea once, but i wondered if these were used in the mass bed, if some sort of screen was used under the bed, or slots were cut if air would circulate through the bed via convection.



I think you could do half egg size and half pea size.

If you did all egg size, I think the rocks would barely get warm before the fire is out and then there would be too little residual heat.
 
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Len Ovens wrote:

paul wheaton wrote:
So maybe just mount some sort of manual plug outside?



Maybe some pictures will help. All of these are from this page:
A story about an abandoned village. (Quite interesting in it's own right)

This first one is open but shows the inside quite well:

You can see the flue sticking up from the bottom. The chimney continues overhead. (brick)

The next one shows the cap and the outside door (not from the same heater though)


While all of this seems to be brick work, I see no reason this could not be done with cob or insulated tin.



At a late date, I finally visited Len's original site, found a quote by the picture of the hand holding the cap (wad49.jpg):

"The shut off cap. The tin cap is placed over the opening from the avaloire to the chimney by hand once the fire has gone out, and stops the chimney drawing warm air from the house. "

The process of putting your hand into what amounts to a chimney-bubble to put the shutoff cap in place may be a KISS solution to some of the problems of operator error with top closing heat traps, like Paul's guillotine or chimney-shutoff dampers on fireplaces. At the end of the fire, if you close the top-closing mechanism too early, you get positive pressure in the system and the toxic gases that are released into your home are invisible, making it a deadly and non-intuitive learning process.

if the fire is still going, you are definitely going to notice when you stick your hand in there to put the cap on the chimney too early.

It doesn't stop people from lighting the fire with the cap in place, but lighting the fire it's usually easier to notice the problem, and to get things under control.

One more lesson the Old World figured out - don't fuss over making it clean, tidy, and convenient - and you also make it less easy to use it wrong by accident.
 
paul wheaton
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Priscilla's pic. I had no idea that such a rough contraption like this could be made to look so cool.
rocket-mass-heater-wood.jpg
[Thumbnail for rocket-mass-heater-wood.jpg]
 
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Thumbs up this post if you arrived at this thread from the dailyish email and were hoping for another photograph of Katelin.
 
paul wheaton
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Julianne has a brand new video of me talking about this rocket mass heater.

 
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