pebble style rocket mass heater in the library

Plus, Mark Nye has been onto this for a while. It's been done before, and with mixed results.

http://www.gas-turbines.com/nt6/index.html

Another of his thingies.

http://www.gas-turbines.com/t98-nt-xx/index.html

I have told Mark about rockets. But he's got to make a living, and has other things in his head.

Satamax Antone wrote:Plus, Mark Nye has been onto this for a while. It's been done before, and with mixed results.

http://www.gas-turbines.com/nt6/index.html

Another of his thingies.

http://www.gas-turbines.com/t98-nt-xx/index.html

I have told Mark about rockets. But he's got to make a living, and has other things in his head.

I reviewed the article and the first two things that jumped out at me were...
This is a closed system and pressurized.
It has an electric oil pump.
In my prior article I laid out the differences between 2 systems fairly clearly.
the RMH is an open loop system and inherently safer.
the point of this project is to optimize the RMH without additional energy inputs (electric oil pump?)

I guess if you wanted to optimize a sealed wood stove with a turbine then go for it. But that isn't what's under discussion in this thread.
It will interesting to monitor progress but I don't know how us commoners could reproduce what is a huge piece of a equipment if it were sucessful. Cob is right below our feet!

Jim, i haven't said that the Nye NT6 was any better, or close in architecture to a rocket. What i understand, is that you sugested to use a turbocompressor type arangement to facilitate the exhaust. Tho, without presure differential, it wouldn't be easy. I might have read toofast. It could be possible that putting a turbine in the heat riser, and another one in the flue, which would have to pass directly above the heat riser, to ensure a way of direct mechanical link between the two, it could be possible. Tho, components would have to be able to wistand extreme heat.

Allen Herod wrote:... What about an exhaust recirculation back into the burn chamber, much like a turbo charger on a diesel engine? On a turbo diesel engine (I believe this is the concept) fresh air is pulled in but exaust is also forced back into the intake (via the turbo, driven by exhaust pressure) creating more fresh air draw (kind of like a siphon effect) but also recirculating heat that would otherwise be lost out the chimney...

I'm going to cut the Quote short there and not paste in the other incorrect posts on the way turbos work. Turbos use exhaust gas to turn a wheel that wheel turns a shaft connected to another wheel, that one pulls in fresh air only and forces it into the engine manifold at a speed faster than the engine can use that creates a pressure build up that boosts the power since more fuel can be dumped in without adding smoke. They do not bring in exhaust the systems that do that are EGRs (Exhaust Gas Recirculation).


I would not introduce exhause gas for several reasons.
1. Less dense air has less O2
2. Exhaust has less O2
3. It complicates the system
4. The intake would have to be closed off to keep smoke/exhaust out of the building

If there is not enough O2 the fire can go out if the fire goes out from lack of O2 there will be smoke if the piping is still hot convection will keep the siphon going and pull the smokey exhaust in to the building.


With that said if you were to heat the intake with exhaust and make sure that it does not get to cold (using a smaller pipe at the end can help) you could do it with one sleeved pipe (Concentric Venting pipe). Those are the pipes that are used for some of the newer hot water heaters. You would run the exhaust in the center pipe and pull the intake air from the outer pipe the trick would be creating a intake air chamber to get it to the feed tube. If you have the center pipe end above the outer pipe a few inches you will get mostly fresh air that will be warmed, if they end at the same height there will be a mix of exhaust and fresh air that might work.

With the above idea I would cap the feed pipe so air will only be pulled from the new warm air intake.

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To prevent the heat from escaping out the chimney after the fire has burned out I would just cap the feed tube and air intake tube if you have one. That could be done with a metal plate or some flat stone, or as my father in law has been doing for the last 7 or so winters using a metal snap collar to hold a lid on the small metal bucket/barrel used for the feed tube (sorry I could not find any pictures of this). By closing one end you have killed the siphon helping keep the heat in with that and blocking the exhaust partially should help.

I just listened to a recent podcast from Paul talking about the issues of the MANY TURNS in the exhaust heat exchanger causing drag and slowing down the rocketiness of the heater and even contributing to smoke back.

What if you eliminate the turns? What if there were three or four straight pipes going through the mass, with one input into them via a splitter and the same on the output. The area of these 3 or 4 pipes would be more than that of the main exhaust to the outside and thus it should not be a cause of a slowdown of the hot gasses.

The other solution is to lengthen the heat riser. This will create a greater force...yes that does entail a longer barrel, perhaps some welding or creative joining (not gluey tape!).

Also get over the cost issue on these heaters! If you want cheap stick with the original design. If you want better it is going to cost. Except it and move on. First create a great working shippable design, then work on reducing the cost once you have a revenue from selling them.

Michael, it's way easier to make it a bell. Cheapest way, half barrel bell. The multiple tubes either indice drag or are not all in use at the same time. Well, you know, gases take the path of least resistance.

Michael Skowronski wrote:I just listened to a recent podcast from Paul talking about the issues of the MANY TURNS in the exhaust heat exchanger causing drag and slowing down the rocketiness of the heater and even contributing to smoke back.

What if you eliminate the turns? What if there were three or four straight pipes going through the mass, with one input into them via a splitter and the same on the output. The area of these 3 or 4 pipes would be more than that of the main exhaust to the outside and thus it should not be a cause of a slowdown of the hot gasses.

The other solution is to lengthen the heat riser. This will create a greater force...yes that does entail a longer barrel, perhaps some welding or creative joining (not gluey tape!).

Also get over the cost issue on these heaters! If you want cheap stick with the original design. If you want better it is going to cost. Except it and move on. First create a great working shippable design, then work on reducing the cost once you have a revenue from selling them.

Michael,
I would caution you in that there is a global audience here and while maybe a couple hundred bucks would be next to nothing to us, there are folks that couple hundred bucks is a month's salary and feeding your kids ranks over buying shiny objects. If we brainstorm enough with experimentation to get this thing super-efficient, by proper design and modifications thereto, maybe the super insulated manufactured stack wouldn't be even necessary. The first challenge ahead isn't what to buy to make the most of it, it's what tweaks can be done in the basic design to be a true ULTIMATE rocket stove. What would be truly awe inspiring is to be able to give this kind of technology to the peoples of the third world and improve their lives and health a hundred times over.

Michael Skowronski wrote:I just listened to a recent podcast from Paul talking about the issues of the MANY TURNS in the exhaust heat exchanger causing drag and slowing down the rocketiness of the heater and even contributing to smoke back.

That's what I suggested in this post.

Zach Weiss is here today. He is installing this gate on the back of the mass. The metal comes from Erica's designs. The two metal bumps are cleanouts. Lots of times, when the fire is going, the metal bumps are damn hot. This gate will make it so that there can be convective air flow over the bumps - thus cooling the bumps much faster (and heating the room much faster - and extracting more heat from the system).

Currently, the mass and the office are being used to thaw all sorts of stuff that has become frozen.

Paul, I have a question. Do the pebbles ever get warm? I have built a pebble style rmh and it is only a week old and I have only had fires in it for about 6 to 8 hours.

Yes, the pebbles get very warm.

Paul I'm curious how the clay and perlite core is holding up. I've settled on something along those lines for my own core and am wondering if I should be planning on any cracking or shrinkage.

Jesse, I am not sure how Paul's is doing but after running mine for 2 weeks I have notices a small amount of shrinkage. The clay and perlite mix around the burn chamber have a small gap now where they touch the wood of the box (originally the box was the form for the clay). I do not see any cracking and am not expecting to see any. Hope this helps.

Thanks Curt, that's great news.

Jesse Biggs wrote:Paul I'm curious how the clay and perlite core is holding up. I've settled on something along those lines for my own core and am wondering if I should be planning on any cracking or shrinkage.

On the first day, the cob-ish did crack and let some smoke through. I then smashed more cob-ish on that spot and haven't had a problem since.

So, overall, I think it is holding up exceptionally well.

Paul, I believe I'm hearing your need right, and suggesting your viewing of another YouTube video by ZeroFossillFuel video #326 his own rocket burner lab... And note his feed chamber addition. I think this might help with what it sounds like your wanting. It pulls directly from like a crawl space for extra rocket . You know... Hope I helped.

Back to baffles.

I think a feed tube that can be shut off completely is all that is really needed. But suppose that you really want a guilotine style closure immediately before the exhaust exits the home. Through use of cables or push rods, the exhaust shut off could be linked to a hinged feed door so that the exhaust shut off can only go into position when the feed door is closed. When the feed door is opened, the cable pulls the shut off open again. I don't know that this would be legal. It would ensure that fuel could not be fed into a system while the exhaust damper is closed.

Dale Hodgins wrote:Back to baffles.

I think a feed tube that can be shut off completely is all that is really needed. But suppose that you really want a guilotine style closure immediately before the exhaust exits the home. Through use of cables or push rods, the exhaust shut off could be linked to a hinged feed door so that the exhaust shut off can only go into position when the feed door is closed. When the feed door is opened, the cable pulls the shut off open again. I don't know that this would be legal. It would ensure that fuel could not be fed into a system while the exhaust damper is closed.

So far as I know, in North America, 80% is the maximum flue/exhaust shutoff allowed. 100% intake shutoff is ok though. In this case, it is in a laboratory, not a home.

Len Ovens wrote:

Dale Hodgins wrote:Back to baffles.

I think a feed tube that can be shut off completely is all that is really needed. But suppose that you really want a guilotine style closure immediately before the exhaust exits the home. Through use of cables or push rods, the exhaust shut off could be linked to a hinged feed door so that the exhaust shut off can only go into position when the feed door is closed. When the feed door is opened, the cable pulls the shut off open again. I don't know that this would be legal. It would ensure that fuel could not be fed into a system while the exhaust damper is closed.

So far as I know, in North America, 80% is the maximum flue/exhaust shutoff allowed. 100% intake shutoff is ok though. In this case, it is in a laboratory, not a home.

This is where bells are intresting, no need for shutof valve. Since they act prety much like a siphon lock.

Satamax Antone wrote:

Len Ovens wrote:

Dale Hodgins wrote:Back to baffles.

I think a feed tube that can be shut off completely is all that is really needed. But suppose that you really want a guilotine style closure immediately before the exhaust exits the home. Through use of cables or push rods, the exhaust shut off could be linked to a hinged feed door so that the exhaust shut off can only go into position when the feed door is closed. When the feed door is opened, the cable pulls the shut off open again. I don't know that this would be legal. It would ensure that fuel could not be fed into a system while the exhaust damper is closed.

So far as I know, in North America, 80% is the maximum flue/exhaust shutoff allowed. 100% intake shutoff is ok though. In this case, it is in a laboratory, not a home.

This is where bells are intresting, no need for shutof valve. Since they act prety much like a siphon lock.

Yes a bell, or air supply valve will stop air from flowing through the system. However, at the beginning of the discussion, Paul indicated he was worried about the cold air outside the top of the flue, falling to the bottom, allowing warm air inside to rise and escape. Thermo-siphoning through one pipe because it is big enough at 8 inch to allow that. This could cool the mass from the inside out faster than if it was blocked. He wishes to be able to block that flow as close to the top of the flue as practical to see if it will make any difference over just blocking the intake.

A joint on the upper portion of the chimney that lets it bend over and point at the ground might help. Cold air is unlikely to fall up hill. I imagine it being cable operated. I imagine it would fail in an ice storm. The passage would always be open which should satisfy the legal dept.

The first two drawings show a flue that comes from a wall.
The last one comes from a flat roof.

When the opening points down, cold air can't fall and rising air meets a barrier. Snow and rain would run off. After a unit is warmed up and running well, the flap could be dropped as a partial damper.

When the flap is open, it will be easier to get a draft started. It can be left open until damping is required.

It might freeze shut sometimes. More priming would be needed to thaw the ice.

Well, i have something similar, and it doesn't stop the downdraft in the chimney. I have to fight with it everytime i light the stove. Mind you, if i had the chimney insulated, it might not be that bad.

Satamax Antone wrote:Well, i have something similar, and it doesn't stop the downdraft in the chimney. I have to fight with it everytime i light the stove. Mind you, if i had the chimney insulated, it might not be that bad.

It may be easier than you think. There are already commercially available dampers for chimney tops. http://www.finehomebuilding.com/item/4678/choosing-a-chimney-flue-top-damper About the only drawback for use with RMH's is that the SS pullwire dangles down the flue pipe.

Satamax, I think I would be ripping that secondary vent out ASAP. That will cause nothing but trouble.

Jim, which secondary vent?

This is the main vent. The chimney has been closed on top, and and the roof rebuilt above. My landlord doesn't want me to do anything to this. So, here's what i'm stuck with.

Satamax Antone wrote:Jim, which secondary vent?

This is the main vent. The chimney has been closed on top, and and the roof rebuilt above. My landlord doesn't want me to do anything to this. So, here's what i'm stuck with.

OH! That can't be good. Thought there was an additional flue vent above. Tough to tell from a pict. Good Luck with that.

paul wheaton wrote:If it is a really cold day outside, I wand to adjust things to be less rockety.

If it is a cool day outside (55 degrees) I want to adjust things to be more rockety.

There are things that can be controlled. I want to control them.

I prefer to have air pulled out of the room instead of having air pulled from outside. Most of the time. For that 10% of the time I want air to be pulled from outside, I want the option.

When the fire is out - i want to make sure that the air moving through the system is at a FULL STOP.

If the exhaust is leaving at 140 degrees, I want to fix that.

I do not need perfect. But I do want better.

I like control.

I remember in one of the videos with E&E Ernie takes the top off of the barrel to show the top of the riser and inside the system. If that feature was included in most designs it adds the opportunity to provide your 100% shutoff I think. When the burn stops the top could be opened and a nearly snug fit baffle plate could be dropped in.

Now this could be stone, wood, metal, insulated combinations of all of the above or whatever you like that wouldn't melt when in contact with the warm riser. You place your baffle plate on top of the heat riser and this blocks 100% air coming through the burn tunnel and woodfeed and because the baffle plate blocks almost the whole diameter of the downdraft barrel it would also stop air flow being tugged out of the system from the flue.

I'm pretty sure this would work without any additional blockage at the beginning or end of the system, would allow for this to be implemented without going outside and would eliminate the need for a separate intake-block for an alternate intake if you had one.

I got home yesterday to find that the rocket mass heater in the office was put back together and it was 85 degrees! Jocelyn immediately opened a window to bring things back down to 75. The pebble mass was too hot to touch near the barrel.

I was told that the fire was started using the new bypass and it was a very easy start.

Mostly, I have to express how cool it is that I was gone for a stressful three days and then come home to all sorts of projects having been completed or with lots of progress. I should leave more often!

The office rocket mass heater is where we do most of our experiments. And there were a lot of things that we need to try/prove.

Probably the one that is most important is: can we make the heater more efficient by shutting down everything to the outside once the fire is out. My brother, Tim, welded up some guillotines to 99.99% shut off the exhaust through the roof or through the wall. At the same time, he moved the wall exit so that it is a more "fair" test between going out the roof vs. out the wall.



So in this picture you can see the old hole through the wall (stuffed with insulation) and you get a clear idea where the new hole is complete with insulation.

You can also get an idea of the cutoff. So when we are starting the fire, or if there is any sort of smokeback sadness, we can open the cutoff to bypass the mass and go straight outside.



Here you can see the guillotine for the roof (it is currently very sticky):



The red stuff is some of that silicone "tape" we are experimenting with. Handles high temps and has not adhesive goo.



Last night the fire went out at about 5. I closed the guillotine at about 7 (I used a hammer). It was 71 degrees. This morning it was 61 degrees inside and 20 degrees outside. So I think this is progress.

More news as events warrant.

The external air intake is currently shut off. But here is an interesting advantage to the contraption even when it is shut off.

Suppose that once every 45 minutes something happens and a puff of smoke escapes the wood feed. Usually it is instantly sucked back in, but sometimes a bit of the smoke doesn't get sucked back in.

But with the bubble over the wood feed, that puff of smoke is about 20 times more likely to get sucked back in.

Paul, would you mind further explaining this "bubble" you speak of? Maybe just a photo.

paul wheaton wrote:The external air intake is currently shut off. But here is an interesting advantage to the contraption even when it is shut off.

Suppose that once every 45 minutes something happens and a puff of smoke escapes the wood feed. Usually it is instantly sucked back in, but sometimes a bit of the smoke doesn't get sucked back in.

But with the bubble over the wood feed, that puff of smoke is about 20 times more likely to get sucked back in.

Does this extra bubble add to the effective height of the feed... That is does it need a higher riser? Or was this included in the original build? Or is there a hole in the bubble at feed level that lets air in?

Paul W. : O. K. is it a throw back to Ianto Evans' old way of making up the feed tube with the top part of a grease barrel ?!! Big AL !

Bubble pics coming soon. This is actually part of the external air intake.

I needed a way to move the bricks over the wood feed. And I needed the air intake to come in over the wood feed.

This is an Ernie and Erica design.

the bubble

the bubble

Another improvement that has recently been put in: the riser was too short. So the riser was modified to be the right height. That means the barrel had to be raised also.

We do have a rocketier burn (stronger draw). BUT we now seem to have a less clean burn (more smoke coming out). I have an email out to E&E for ideas. My best guess is that the gap at the top might be too big. I think we need to the cob-ball-squish-test.

We also have not been able to get the exhaust-out-the-wall to work just yet. I have some more experiments to try in that space.

I am also thinking of a test to add heat sink "fins" to the last run of the duct.