Please help: Rocket Stove in greenhouse does not work

Burra Maluca wrote:On your picture, it says 5000 and 3500.

Does that mean 5 metres and 3.5 metres?

Burra Maluca wrote:For video you'll need to upload it to youtube or vimeo and then post a link.

Satamax Antone wrote:Michael, on jour vidéo. I can see an all metal core, non insulated, with a very long burn tunnel and an angled feed. Plus a cyclonic heat riser.  Not a good start for a first build.

And, i wanted to ask, what's your rend pipe?

Rick Hannaman wrote:
  Guten tag Michael, is that dutch for good evening? Hope so. Look's like a loooooooooong draw for your exhaust. Any feasible way to pre heat the last few feet of the chimney/flue so as to initiate the flow of hot gas'es? Just a thought.

        Rick in Pantano, Arizona.
        yes the ghost town.

Sam Fel wrote:Perhaps a downdraft fan will help to actively push the heated gases thru the pipe?

Glenn Herbert wrote:An excellent source for information about batch box rocket mass heaters is batchrocket.eu - it is translated into several languages, unfortunately not yet including German, but originally in Dutch - I don't know if that is any better than English for you. Even though you have built something like a J-tube or L-tube, there is information there that could help you.

In general, a standard 6"/150mm J-tube is said to be good for about 30-40 feet (9-13m more or less) of horizontal duct, minus 5' for every elbow. You show about 7 elbows, which kills your safe length. Your combustion chamber is also smaller than 6", so it would not have that much power. I don't think it will ever work well as is. A fan at the chimney end could pull enough air for good combustion, but you would use up all the heat halfway through the ducts and the end would be cold, doing nothing for you.

I think you need to shorten your duct run, and have fewer elbows, and change your combustion core. What you have built breaks a lot of best practices that have been found to work, and has a lot of experiments like the fresh air in the heat riser that have been found to not actually help as much as fresh air right in the burn tunnel.

Replacing all of the duct in the ground if you already have it is a big job, so if you can't do that, I recommend you scrap the steel combustion core and build a firebrick (or even old soft red brick) 6"/150mm batch box according to the dimensions in the batchrocket site. You can still use the heat riser and barrel you have, with the new batch box connected to it.

I do note the pellet feed you show, and if you can only get pellets to burn, you may not be able to use a batch box. If you can get firewood, even small sticks, a batch box burns for an hour without tending, and one or two loads can put a lot of heat into your ducts. A batch box is said to have about twice the heating power of a standard J-tube the same size, and would have much more power than your experimental core.

Peter van den Berg wrote:Hi Michael,
The color of the buried pipe I find a bit suspicious. To my eye, it is the same as the PVC pipe for sewers here in Western Europe. So, just to be sure, that pipe should be metal otherwise you can't expect heat transfer from the pipe to the surrounding soil. Let alone the risk of melting or burning of that pipe.

Another possible snag: in the third picture the vertical exhaust diameter seems to be quite a bit smaller than the rest of the pipes and heater core. You definitely need a proper vertical exhaust pipe, reaching at least above the greenhouse roof and any higher objects in the direct vicinity.

I'll second Glenn's remarks, nearly every aspect of your design is out of the known configurations. When you want to build something that is quanteed to work, stick to the documented and tried solutions. Please note Glenn is talking about 30 to 40 feet, as opposed to 30 to 40 meter, which is 3.3 times as long as feet.

Satamax Antone wrote:Michael, don't use those pipes. 65c° nowhere near good.

Michael Baer wrote:

Satamax Antone wrote:Michael, don't use those pipes. 65c° nowhere near good.

Well, I've understood.
But what are the alternatives?

Peter van den Berg wrote:Hi Michael,
The color of the buried pipe I find a bit suspicious. To my eye, it is the same as the PVC pipe for sewers here in Western Europe. So, just to be sure, that pipe should be metal otherwise you can't expect heat transfer from the pipe to the surrounding soil. Let alone the risk of melting or burning of that pipe.

Another possible snag: in the third picture the vertical exhaust diameter seems to be quite a bit smaller than the rest of the pipes and heater core. You definitely need a proper vertical exhaust pipe, reaching at least above the greenhouse roof and any higher objects in the direct vicinity.

I'll second Glenn's remarks, nearly every aspect of your design is out of the known configurations. When you want to build something that is quanteed to work, stick to the documented and tried solutions. Please note Glenn is talking about 30 to 40 feet, as opposed to 30 to 40 meter, which is 3.3 times as long as feet.

Hans Quistorff wrote:2 suggestions: There is a limit as to how much heat can be extracted from the the flue gasses.  They tried heating the ground in the underground house and it did not work the same as yours. possibly if you make several short runs and with dampers heat one at a time it could be managed.

The better way to heat the ground which also works in the summer is to use the pipe in the ground and bring the chimney back inside the greenhouse to draw the hot air from the peak of the greenhouse  with a fan pulling the air up from the underground pipe.  This will heat he ground from your rocket stove in the winter and store heat from the sun all summer so the ground is warm in the winter  The plastic pipe will work for this but you may want to drill  some drain holes because water will condense in the pipes.  This will also happen trying to heat the ground with fire exhaust which has even more water in it.

My friend has a regular rocket mass bench above ground to warm the flats of seed starts. Our weather here is much like in Germany so we can start seeds of some plants under cover in January if the soil is warm.

Peter van den Berg wrote:Yes and yes. Just like it's described at the http://batchrocket.eu/en/ site.
The next most common mistake is making the transition from the barrel to the rest of the heat extractor too narrow. Please, build this as wide and spaciously as you possible can, it will spare you a lot of headaches.

Burra Maluca wrote:On your picture, it says 5000 and 3500.

Does that mean 5 metres and 3.5 metres?

If so, I think there is too much pipe.  The stove won't be able to push the hot gas all the way through that much pipe, especially with all those corners.

What is the diameter of the feed tube and heat riser on the stove?  The greater the diameter, the further it can push, but I think you will still need to reduce the length of the pipes.

Peter van den Berg wrote:The reason why secundary air is added just before or even in the port is because pressure is lowest, and gas velocity is highest. Air will be sucked in at that spot most efficiently, violent turbulence just behind will cause adequate mixing of the combustible gases and fresh air. When you feed air in at a later stage this isn't mixed that well. To find out all this costs me the best part of a year, and I tried literally every configuration I could think of, including something similar to yours.

So the answer to your interpretation is, broadly speaking, yes. Feeding in air at high temperature (commonly 350º C or there about, being the self-combustion level of woodgas) is also very important, nicely done by p-channel or floor channel alike.

gelu lacusta wrote:

Burra Maluca wrote:On your picture, it says 5000 and 3500.

Does that mean 5 metres and 3.5 metres?

If so, I think there is too much pipe.  The stove won't be able to push the hot gas all the way through that much pipe, especially with all those corners.

What is the diameter of the feed tube and heat riser on the stove?  The greater the diameter, the further it can push, but I think you will still need to reduce the length of the pipes.

Satamax Antone wrote:

Michael Baer wrote:

Satamax Antone wrote:Michael, don't use those pipes. 65c° nowhere near good.

Well, I've understood.
But what are the alternatives?

Cheapest usually, hvac pipes (air conditioning or ventilation pipes)

Michael Baer wrote:As intended in the drawing, I intend to direct the combustion air through a DN 160 mm pipe into the walled wreath.
Is this ok or should the greenhouse be used for combustion.

Peter van den Berg wrote:

Michael Baer wrote:As intended in the drawing, I intend to direct the combustion air through a DN 160 mm pipe into the walled wreath.
Is this ok or should the greenhouse be used for combustion.

Please don't connect an outside air feed directly to the combustion core, you'll run into problems with the air distribution between primary and secundary air like that. I would prefer to use the air inside the greenhouse. That greenhouse is leaky as it is, it isn't a passive house, isn't it?

Pascal Paoli wrote:Hi Michael,
falls du etwas übersetzt brauchst, schreib es hier rein. Der Luftzug wird z. B. nicht mit "train" (wie zug) sondern mit "draft" übersetzt. Das sollte dir vielleicht weiterhelfen. Updraft ist z.B Luftzug nach oben.

martyn parish wrote:Hi Micheal
I would like to add something to all the good advice on this this thread. I have built three rocket stoves and hope I can help a little.

The volume of each part of the stove is the critical factor. Each section of the construction should hold more volume of air than the last, if not you get poor air flow. It looks like the space above your internal chimeney riser between the enclosing drum/lid/barrel is too small. I would suggest either raising the drum, or shortening the riser. I had exactly this problem with my first rocket. The next ratio is the side space between the drum and the internal chimney riser. I use an 18 cm riser and 68 cm old oil barrels. This gives lots of space for the air at the top to fall to the exit pipe.
I agree with other comments about the exit pipe, it is too small in diameter. I estimate that with your current rocket dimensions your exit pipe must be at least 30 cm, but also the length of the pipe is too much and has too many angle bends. For best effect have a maximum of two angle bends. After each angle increase pipe diameter by about 20%. The pipe should be metal or ceramic. Not plastic or anything with a heat compustion temperature less than 200 degrees celcius!! Otherwise it can be very dangerous.
You could have the exit pipe not fully horizontal but at a few degrees angled up to encourage air flow in the right direction. Consider a 12 volt fan at the final outlet of the pipe. With these considerations you should be able to maximise the length of pipe in the ground, but it will require experimentation to see how much length you can have in this setup. I suggest buildling the rocket itself first without the exit chimney, test and get it burning well before adding the chimney pipes piece by piece to find the limits of your system. The performance will depend on some critical factors: ambient temperature and humidity, internal temperature and humidity (a rocket already warm inside will light much faster than a cold one, so the first time you light it is normally the most difficult), also the airflow into the greenhouse must be sufficient to keep the fire alight. An external cold air inlet tube is a good idea I think.
It takes some time to understand these little miracles and it it working, but it's well worth it! So have fun my friend!
If you have any further questions I am happy to help

Peter van den Berg wrote:

Michael Baer wrote:As intended in the drawing, I intend to direct the combustion air through a DN 160 mm pipe into the walled wreath.
Is this ok or should the greenhouse be used for combustion.

Please don't connect an outside air feed directly to the combustion core, you'll run into problems with the air distribution between primary and secundary air like that. I would prefer to use the air inside the greenhouse. That greenhouse is leaky as it is, it isn't a passive house, isn't it?