Why dont we all want rocket mass heaters?

[georgepds]

Doesn't seem like it's enough to heat a double wide through a Montana winter.. and that little electric heater is 100% efficient.

Anyone care to do a manual j calculation... just where is that ASHRE expert?

 

[paul wheaton]

In my first post I said "I am not one of the top five brains in rocket mass heaters, but I think I might make the top ten list". And there were a lot of questions about numbers, efficiency, etc. So I present Peter van den Berg - definitely in top 3. Arguably, the top guy. Maybe the numbers he mentions here will quench some of the curiosity expressed here?

 

[georgepds]

Thanks

Couldn't help notice the wool cap,flannel shirt, and turtleneck... the stove must have been off


Do you know what device he used to measure co? Saw several lines on the graph but couldn't make out what they mean

 

[paul wheaton]

I think the stove was running (down to a few coals), but Peter was outside working in freezing temps when we asked him to come in for this bit of video. Plus, we are in the shop and a lot of that day the shop doors are wide open as a couple of dozen people were coming and going. This was in the middle of our "innovators event" and I think there were five builds happening simultaneously.

 

[bholler]

I think the stove was running (down to a few coals), but Peter was outside working in freezing temps when we asked him to come in for this bit of video. Plus, we are in the shop and a lot of that day the shop doors are wide open as a couple of dozen people were coming and going. This was in the middle of our "innovators event" and I think there were five builds happening simultaneously.

I would still like to know what stoves you are comparing to that you can save 10 times the wood. What type of burn technology are you comparing your stoves to?

 

[electrathon]

@paul wheaton Again, I really like the concept here. I would love to see some information that is not just anecdotal. People sitting in a room talking about the stove feels warm and fuzzy, but specific drawings and design layout would be very helpful. I still don't see how you can get the draft started when the stove is cold (or reverse drafting). A wood stove with a stack going up can be hard enough, your stove goes up, down, sideways and then up. Once it is pulling it makes since, I am curious about starting it without flooding the house with smoke. What keeps fly ash out of the main heating chambers? The turbo action should be drawing a lot of ash forwards and into areas that are not really accessible. Combustion chamber and orifice size will make or break this concept, even the angle could affect the burn. Details would help.

 

[Woodsplitter67]

To answer the op... i dont want a rocket mass heater because... i love the stove i have.. it looks prettier... my stove is very efficient to begin with.. and lastly i wouldn't one in my living room...

 

[bholler]

In my first post I said "I am not one of the top five brains in rocket mass heaters, but I think I might make the top ten list". And there were a lot of questions about numbers, efficiency, etc. So I present Peter van den Berg - definitely in top 3. Arguably, the top guy. Maybe the numbers he mentions here will quench some of the curiosity expressed here?

The only numbers he gave were for a 5 min period of a burn for co emissions. If you want to convince us of anything you are going to have to give us some real efficiency numbers compared to a modern woodstove using the same fuel and testing procedures.

He mentioned that there is no smoke. On any modern woodstove if it is being run correctly there will be no smoke either.

 

[georgepds]

To answer the op... i dont want a rocket mass heater because... i love the stove i have.. it looks prettier... my stove is very efficient to begin with.. and lastly i wouldn't one in my living room...

I used to want a masonry stove ( a rocket mass stove is close to a masonry one). Once I got a modern soap stone stove, I was content, and the desire to fill my life with extra large hot stone objects went away, except for the soapstone stove

I'm interested in low wood use, but I find the numbers for the rocket hard to believe. I do not doubt the enthusiast impression/ experience that it works well, but there is a big difference between works well and ten times better. I'm with @bholler I'd like to see less squishy numbers , and better description of what is being compared. Is it 10x better than an open fire? probably. Is it 10x better than a modern EPA stove? Until I see the test data, my guess is probably not.

 

[georgepds]

Wood stove

For those who like details I found a technical article describing wood stove emission measurements. The two stoves tested measured 77% and 79% efficient, comparable to EPA stoves

It is physically impossible to be 10 times better with any device that is not a heat pump To be 790% efficient you are no longer extracting heat from wood, but using the energy to run a heat pump, and that is not what a Rocket mass stove does

Anyway here us the link to stove testing article

http://www.sciencedirect.com/science/article/pii/S187661021403481X

 

[RobbieB]

I agree. It is easy to be 10X open fire efficiency 80% vs 8%, but not a modern stove which is already 70-80%

 

[electrathon]

I agree. It is easy to be 10X open fire efficiency 80% vs 8%, but not a modern stove which is already 70-80%

I think the squishy math works like this (from what I have been able to read and see online). Modern stove 80% efficient at full raging burn. A few hours later it is stepping back to 50% By six hours into the night it is at 20% By morning the fire is out, stove is cold and the draft is pulling, negative 5%.

Enter the rocket stove with LOTS of biomass. Starts out raging at 85% for 30 minutes. Fire goes out and you have mass storage heat for 6 house, 400% efficient factoring that part in. 8 times or so more efficient, depending on your exact numbers.

I think Paul Revere heard similar discussions when he welded together a bunch of plate steel and built a box in the middle of the room instead of a raging fire in the fireplace. Common since said if a stove worked better than a fireplace we would have been using them thousands of years earlier.

 

[bholler]

I think the squishy math works like this (from what I have been able to read and see online). Modern stove 80% efficient at full raging burn. A few hours later it is stepping back to 50% By six hours into the night it is at 20% By morning the fire is out, stove is cold and the draft is pulling, negative 5%.

Enter the rocket stove with LOTS of biomass. Starts out raging at 85% for 30 minutes. Fire goes out and you have mass storage heat for 6 house, 400% efficient factoring that part in. 8 times or so more efficient, depending on your exact numbers.

I think Paul Revere heard similar discussions when he welded together a bunch of plate steel and built a box in the middle of the room instead of a raging fire in the fireplace. Common since said if a stove worked better than a fireplace we would have been using them thousands of years earlier.

The problem is that those numbers are not the least bit accurate if you have a good modern stove that is run correctly. The lesson to be learned is that if you make up fake numbers for the other guy it is really easy to beat them.

I really think that it is a promising technology that could work for some people. But they need to be realistic with their numbers if they want to be taken seriously.

 

[georgepds]

Here is a good discussion on system efficiency. They distinguish between combustion efficiency (% of energy extracted from wood) and transfer efficiency (%of energy transferred to the room)

The basic idea is rocket mass heaters are better than wood stoves because the transfer efficiency is so high

https://permies.com/t/55938/rocket-mass-heater-works-efficiently

Sfaik, The claims about transfer efficiency are not based on measurements

 

[georgepds]

I think the squishy math works like this (from what I have been able ...

I think Paul Revere heard similar discussions when he welded together a bunch of plate steel and built a box in the middle of the room instead of a raging fire....

I think that was Ben Franklin

• 1728: Cast iron stoves begin to be made in quantity in the US. These first stoves of German design, are called Five-plate or Jamb stoves.
• 
  1744: Benjamin Franklin develops his own cast iron stove design. His Pennsylvania fireplace surpassed the efficiency of other inventions, and is still a popular heating stove today.
• 1763: Frederick the Great of Prussia stages a competition for a "room stove which would consume the least wood".
• 
  1772: David Rittenhouse added an 'L' shaped chimney to the Franklin Stove to prevent smoke from venting into the room. His design is what is known as a "Franklin Stove" today.

 

[bholler]

Here is a good discussion on system efficiency. They distinguish between combustion efficiency (% of energy extracted from wood) and transfer efficiency (%of energy transferred to the room)

The basic idea is rocket mass heaters are better than wood stoves because the transfer efficiency is so high

https://permies.com/t/55938/rocket-mass-heater-works-efficiently

Sfaik, The claims about transfer efficiency are not based on measurements

That is the problem they bash the woodstove numbers as being inaccurate. Yet they don't provide hard numbers of their own.

 

[electrathon]

Here is a good discussion on system efficiency. They distinguish between combustion efficiency (% of energy extracted from wood) and transfer efficiency (%of energy transferred to the room)

The basic idea is rocket mass heaters are better than wood stoves because the transfer efficiency is so high

https://permies.com/t/55938/rocket-mass-heater-works-efficiently

Sfaik, The claims about transfer efficiency are not based on measurements

That is a good explanation, sort of what I was thinking, only smarter.

I think that was Ben Franklin

Yea, him. But my answer was more funny.

 

[Heftiger]

I think the squishy math works like this (from what I have been able to read and see online). Modern stove 80% efficient at full raging burn. A few hours later it is stepping back to 50% By six hours into the night it is at 20% By morning the fire is out, stove is cold and the draft is pulling, negative 5%.

Enter the rocket stove with LOTS of biomass. Starts out raging at 85% for 30 minutes. Fire goes out and you have mass storage heat for 6 house, 400% efficient factoring that part in. 8 times or so more efficient, depending on your exact numbers.

I think Paul Revere heard similar discussions when he welded together a bunch of plate steel and built a box in the middle of the room instead of a raging fire in the fireplace. Common since said if a stove worked better than a fireplace we would have been using them thousands of years earlier.

You’re giving 400% credit for the heat storage in the biomass, but not giving any credit to the biomass heat storage of the wood stove. My cast iron jacketed stove continues to be warm after the fire is out.

 

[electrathon]

You’re giving 400% credit for the heat storage in the biomass, but not giving any credit to the biomass heat storage of the wood stove. My cast iron jacketed stove continues to be warm after the fire is out.

I just guessed at numbers that I think is how they come up with the huge efficiency variations.

 

[RobbieB]

My nat gas furnace is 95% efficient. It's a modern condensing unit that needs a draft inducer, a condensate collection trough and extracts so much heat that the flue is 2 inch PVC pipe. Now that's pretty good extraction, but not the best. The modulating units will hit 98%.

But the old (non condensing) units ran at 80%. I am amazed that modern wood stoves can hit this.

And you are comparing blower driven transfer to "hot rock" storage and I imagine that few people really want a big stack of hot rocks in the middle of their house.

Maybe good for cavemen.

 

[georgepds]

Here is an example of rocket mass heater math.... explains a bit how they get their numbers... they assume woodstove efficiency is really 3% to 15%

https://www.richsoil.com/wood-heat.jsp#efficient-heat

"First, "75% efficient" isn't really 75% efficient. 16% is allowed for heat going up the chimney, so it is actually 59% efficient. And that was from the best burn in a lab under optimal conditions. An excellent operator might be able to get about 35% efficiency. Most people run their "75% efficient wood stove" at 3% to 15% efficiency."



To me this is gobbledygook.. how do they know most people operate at so low efficiencies?

 

[bholler]

I also have to question the wood around their thermal masses. I heard several times that the thermal mass is uncomfortable to touch. That could easily mean it is into pyrolysis teritory. Wood is also pretty close to the burn chamber on both example we see in the videos.

 

[peakbagger]

Funny thing is the world most efficient "wood stove" (most folks would call it a boiler)was designed and sold 35 years ago. It was a short burn very high temperature combustion that put out little or no emissions mostly water vapor. The major difference was that the designer developed it for space heating a conventional home so it used water for thermal storage instead of masonry. http://people.umass.edu/dac/projects/Hills_Furnace/Hills_Furnace.html. There are a few Jetstream owners on Hearth. Tom In Maine a member of hearth has designed and built a similar unit that uses pellets for fuel but due to the cost of certification and production he is unable to sell it commercially. (he worked with Dick Hill for years).

FYI few folks like to talk about NOx emissions, burn hot and fast like a rocket stove and NOx goes way up but CO goes down. The only way to keep NOx down is staged combustion or put in ammonia injection and NOx catalysts.

 

[maple1]

Too bad they have to make up smoke & mirrors numbers to try to make 'the others' look bad, in order to try to make 'their own' look better. As I said before I am sure it is a very efficient unit but the comparison claims being put forward are just silly stupid wrong. I am willing to bet that if this heater can heat this double wide on 0.6 cord, a properly sized and installed wood stove would burn no more than 2 cord, at the very most, all else being equal, and being generously estimated in favor of the rocket. And the home would likely be warmer.

One simple thing I would be curious to see is flu pipe or chimney temp readings on one of these units both through an entire burn and also through an entire 'coasting' session when the fire is out. Should be an elementary exercise but I haven't seen any flue temp data at all yet - but I have not searched for it. I would think it would be readily available and posted already in this thread if it was there. I am sure there is some heat leaking up the chimney after the fire goes out - which is kind of an efficiency hit. My storage tanks only leak heat within the building envelope after my fire is out - they don't have a pipe to the outdoors.

 

[NateB]

What is the cleaning schedule for a rocket thermal mass stove? And how often do you have to replace the exhaust pipe?