Here is an infrared of a short burn test of my Proto RMH.
The short burn tests:
Rocket stove: 1/2 pound oak log split into 8 parts burned in 25 minutes. Picture taken at 30 minutes. Little or no thermal mass stove exhaust designed to fit into picture to show exhaust heat
Barrel was tuned to a light rocket sound with no smoke in exhaust. exhaust temperature averaged 80 degrees F. Outside air temp 38 degrees F (stove is outisde)
Buck stove: 1/2 pound oak log split into 8 parts burned over 45 minutes. Picture taken at 30 minutes. After ignition, dampers tuned till the exhaust was around 80 degrees. very little smoke leaving exhaust. auto blower disabled to minimize heat leaving metal shell of stove. Outside air temp 38 degrees F (stove is inside 62 degrees F)
It is hard to compare the two images. It looks like the Buck stove got hotter in the flu and the rocket stove is really hot in the burn chamber and dissapates that heat to the large barrel fairly evenly in a short burn.
Anyone have any ideas? I can keep trying to get better images of longer burns if it could help.
allen lumley wrote:- i'm a little surprised that the Rocket stove did that well not having a chance to run on prewarmed room air, but you at least proved that some one could go away/come back to a cold house and the stove would still light, can you report on your lighting technique ?
This rocket stove is for a greenhouse. Because of efficiency reasons the rocket stove will burn outside air. Burning inside air and exhausting it causes cold outside air to come in to replace the exhausted air.
Lighting: I make a small pile of DRY wood varying in size from minute twigs to 1/2 inch splinters about the size of the fire box(kindling). I fill the bottom of the fire box with DRY crumpled paper and cardboard. Light the paper, wait till it really catches then blow hard toward the J tube. After the flames steadily head that direction, I drop a pile of mixed size kindling in the chamber and away it goes. The colder the outside air the faster the rocket drafts if it is built right. The draft is better because the difference between the barrel inside temp and outside temp is greater (rapid heat dissipation).
This is my lessons learned drawing:
If you are worried now about condensate (due to high humidity in outside air or wet soil) I leave to your imagination what will happen with the combination of water and the lye in your wood ashes making a LYE Slurry -brick mortar and stove pipe ! G'luck Allen L.
I would like to throw out there that a regular buck stove could give you similar if not better results if it were design right. although i chose the rocket stove because i could make it for free, others might have the money to spend on a better system.
Upon a cold start up, naturally the burn tunnel mass is cold, and I think your infrared pictures prove that, it would be interesting to see the burn tunnel mass infrared picture after the RMH has been run for 48 continuous hours (I would expect the mass temp. to rise, but I think most of your heat being consumed to the massive cooling effect of the earth the RMH is cut into & built upon).
If you could temporarily uncover the mass that is covering the burn tunnel roof, that might show you were most of the RMH heat is concentrated. The sides of the burn tunnel also absorb heat, but mostly I'm expecting in the roof bricks...if your simply looking for were the high temperatures are.
I think the heat riser is not even fully warmed up in a short 30 min. run & the burn tunnel mass is absorbing most of the heat, as it should, but cannot be seen because of the earth/ mass that covers it. But because your unit is outdoors, overcoming natural ground temperatures is an overwhelming task (nature provides more continuous freeze & moisture, than your fire can overcome). So it would be interesting to see thru the use of your infrared picture, just how far into the ground/mass does the heat penetrate, after a prolonged hard run?
Looking at your drawing, I think you're going to run into problems drawing all your air through the grate....it will get clogged with coals and ash...been there, done that. If your thermo image is based on this design, it may explain when it's running so cool.
I know your diagram isn't to scale, but IMHO, your burn tunnel looks too long.
Do you now have a way to close off your air supply through the grate and do you have one for the Feed Tube ?
I Know you said your picture was not to scale, but what I see looks like you should be having thermo-syphoning problems!
With air supply through your grate and Feed Tube , unless you have a way to shut them off I'm afraid that right after your burn is complete your cold outside air will continue to travel through the system picking up heat energy and blowing it outdoors !
The J-Bend Feed tube coupled to the Heat Riser alone, by itself is supposed to work like the water trap under your sink, stopping thermo-syphoning when the fire goes out !
That probably will work if the outside air to/through your grate is closed off.
Every knowledgeable person I talk to tells me that these two locations are the only where any kind off a damper to close off air flow should ever be used. I'm passing that on as a 'General Knowledge ' Pyro-AL
Based on this input I am going to take it apart and redesign with full thermal mass. After that I will burn for 5 hrs and retake a thermal image. I know I can get 500 degrees in 5hrs. We then can see how much heat is absorbed into the mass. Then I will take pictures every hour to show how slowly the heat dissipates into my WV clay earth.
Installing this into the 2000 dollar sollex greenhouse is nerve racking. Move over chickens here comes a rocket stove!
If anyone has a real science based article that discusses rocket mass vs other systems please let me know. From what I see and experience an old fashioned buck stove with a tall exhaust pipe inside the greenhouse seems to do much better that the RMH.
I have ultimately found that a wood fire hydronic system is the best for me. I like the simplicity of the wood fired boiler paired with the versatility of water heat storage and delivery. I state that solar water pump systems are not low tech, cheap, or easy. Water mass systems in greenhouse just work better. I also like having a way to use my well water for cooling and heat storage. A greenhouse that is 75 degrees during the day can store a lot in water to release on a 35 degree night and that is all I need.
Unfortunately I am in the process of a rebuild and I hope the new system cost will have an good return on investment. I am hoping to use DC solar pumps and aquaculture combined in my thermal mass. I should have some pictures of that by Spring meanwhile here is a simple diagram without the wood fired boiler and PV solar pumps.
Thanks much for the information. I understand your concern about the air infiltration and think it's wise to avoid that. Why was it not a value? Not enough heat given off because of the cold air intake? I posted that question in a another thread to see if people have had other experiences. I have seen many rocket mass heaters in greenhouses but don't know the specifics on their intake or performance.
On the solar hot water system, very intrigued. To clarify, your water barrels are housed in an insulated outbuilding? I've also been researching solar hot water, but like the idea of using the actual grow beds soil underground as the mass. Without an aquaponics set up that is a lot of storage space for water -- seems too space intensive. Complicated control system too (controls in the water tank, greenhouse and fish tanks). It seems you need a third heat exchanger coil to go to the aquaponics set up. Water can't be directly circulated with the sludgy fish waste water.
Would love to continue the conversation. I don't know if this thread is the best. I am doing my own research, I think I mentioned, on sustainable greenhouse heating systems for a book. Hope we can swap more ideas.
Everyone else spend the money on any of the better alternatives out there. I have always just asked for good testing with some science, We augmented the rocket stove to every internet guru's specs and found no real change except burn right or bad burn.
So here is the truth i didn't want to offend my fellow permies with until now:
If you are burning and it sounds like a low rocket sound you got it.
No smoke is coming out the exhaust you got it.
High heat in fire box low heat in exhaust you got it.
The thermal mass absorbs all you heat and you are happy with that you got it. No guru needed.
Take a look at the thermal images provided and decide for yourself. BTUs (heat) are going through my rocket stove system, Heat is going into the thermal mass, little heat is exiting the exhaust and i was impressed but not warm.
BTUs (heat) are going through my wood stove, Heat is going into the air, heat is exiting the exhaust i was not impressed but I was warm.
Which "internet gurus" did you follow? There are many theorists on the internet and youtube who are giving advice known by the major innovators (with hundreds of working examples to their credit) to have issues. Did you test a plain vanilla RMH built to specs published by Evans & Jackson, or ernie and erica Wisner?
I haven't seen where you describe the way your RMH thermal storage was set up, though from comments it sounded like it was under the greenhouse floor. What kind of isolation from the ground did you have? Trying to heat the whole earth is not going to work well.