Rocket mass heater mod?

OK,
I'm completely new to the idea of rocket stoves as mass heaters. It's a must in my next dwelling
What I keep seeing over and over again is how efficient they are, anywhere up to 98%.
So my question is has any one considered using the same basic design. With one modification, setting it up for propane or natural gas.

Yes, it would take a bit of engineering but ....

So you have all the advantages of the RMH with no ash, no baby sitting and maybe kicks on every other day?

Thoughts?

alergyfree wrote:
OK,
I'm completely new to the idea of rocket stoves as mass heaters. It's a must in my next dwelling
What I keep seeing over and over again is how efficient they are, anywhere up to 98%.
So my question is has any one considered using the same basic design. With one modification, setting it up for propane or natural gas.

Yes, it would take a bit of engineering but ....

So you have all the advantages of the RMH with no ash, no baby sitting and maybe kicks on every other day?

Thoughts?

Just one:

HERETIC!!!

j/k,

 

Thanks!
LOL
Any reply is better than none..

OK, now that I've gotten that out of my system...

I don't think it will work, at least not in the way you're thinking.  Propane and natural gas (PNG) are touted as high-efficiency technologies in an of themselves: the entire product gets burned, releasing all its energy, leaving no ash or other burn by-products.  The problem with trying to use PNG in an RMH is this lack of burn by-products.  Part of the efficiency of an RMH is that burning (releasing energy) continues inside the insulated chimney.  This won't be happening when using propane, etc. 

The exhaust gasses from a rocket stove can range from over 560*F to over 800*F (although the lower range is more frequent.)  It's totally possible for a PNG gas burner to reach these temperatures, depending on how much gas you're burning  (i.e., cubic feet per minute).  So yes, it would be possible.  The question is if it can be done to be as effective as using a RMH with wood.  I use the word "effective" rather than "efficient" since "effective" is a real-world situation.  Using PNG, you're paying by the cubic foot (or more exactly, by the hundred cubic foot, or CCF) that you're burning.  Gas furnaces DO need babysitting, it's just that the babysitting is done by the thermostat.  The PNG has to be collected and stored, it's just that this is handled by the gas company for you.  So a lot of what we'd term "efficiency" is simply stuff that has been passed off to something or someone else, and possibly aggregated among a large number of people.

One thing to keep in mind: A few years ago, we had a late-season ice storm.  I lost power for a day; others in the area lost power for a week.  I was feeling good for the first few hours because I had gas heat, until I realized that my gas furnace depended on the electricity to run the thermostat and light the furnace.  Luckily, I had a gas stove that I could turn to if things got really bad (they didn't).  But using PNG means you're STILL tied to a distribution grid, whether the gas is piped into your house or stored in a container on your land.  So, "efficient" vs. "effective"?

As far as actually using PNG in an RMG, what you're talking about is a re-engineered Bunsen burner.  You're going to want to mix the air with the gas before ignition.  Check out this Wikipedia article: http://en.wikipedia.org/wiki/Bunsen_burner .  Its' use in an RMH should be very easy to test, by getting your hands on some Bunsen burners and building an insulated chimney like you'd use in an RMH.  Build a  platform for the burners to sit on and for the chimney to sit over the burners and with air vents underneath, large enough to supply all the air needed.  Start with one burner and measure the heat of the exit gasses, then continue to add burners until the exit gasses reach almost 600*F.  Measure the amount of gas you're burning, and that should give you an idea if this would be worth exploring.

In a rocket stove wood gas is combusted, this makes it far more efficient than a fireplace or old woodstove.

Natural gas is pretty good at complete combustion.  So the chimney may not add anything.

In a rocket stove wood gas is combusted, this makes it far more efficient than a fireplace or old woodstove.

Natural gas is pretty good at complete combustion.  So the chimney may not add anything.


What it would add would be a way of storing and using the heat more effectively than just blowing it around as in conventional heating system.
Which I thought was one of the major points of a RMH in the first place.

Efficiency is more than just clean burning right?

alergyfree wrote:
What it would add would be a way of storing and using the heat more effectively than just blowing it around as in conventional heating system.
Which I thought was one of the major points of a RMH in the first place.

Efficiency is more than just clean burning right?

You're dealing with two different design philosophies.  A Propane/Natural Gas (PNG) furnace works by (and forgive me if this is an over-simplification) burning the PNG to generate heat, which is directed through a heat exchanger before the exhaust gasses are vented to the outside.  Blowers inside the furnace take the house air and blow it through the heat exchanger, where the air is (in theory, anyway) heated and returned to the house.  When the air in the house rises to a set temperature, the burner turns off and the air stops being heated.  The question is not "is natural gas more efficient" it is "how efficient is the heat exchanger?" 

In this instance efficiency is measured in both how quickly the heat is transferred from the burner side to the air side (i.e., how quickly is the air heated); and how much heat is extracted from the combustion exhaust.  My apartment's furnace is not particularly efficient, because I can hear the burner going on long before the blowers start moving air, and the air that comes out of the vent is still cold for the first few minutes.  A gas furnace gives no thought to storing any of the heat from the exhaust gasses; and in fact is NOT designed to store heat.  Doing so would interfere with the natural flow of exhaust out of the furnace and out of the building: extract too much heat and there is not enough lift for the gasses to leave through the chimney.  This would cause the gasses to leak back into the living area -- very not good.


In a RMH the purpose is to store heat from the combustion exhaust.  It extracts the heat not from the point of burning as the PNG furnace does, but from the exhaust gasses on their way to the vent to the outside.  It relies on the pressure produced by the "rocket" action to force the gasses through the tubes to the vent.  Efficiency for a RMH is usually defined in how much heat is extracted from the burning biomass, roughly measured in the mass of the ash remaining after the burn compared to the mass of the initial biomass fuel.  (less ash = more biomass converted to exhaust gas)

From what I understand, using PNG to fuel a RMH would require a redesign of a gas furnace so that the heat exchanger isn't heating air but heating a thermal mass.  This redesign would need to ensure that the resulting exhaust gasses would be safely vented outside after as much heat is extracted as possible.  IOW, the redesign would be a non-trivial task.

Yes. The net gain I believe would be in using fuel once a day to heat the mass as opposed to every couple hours.

"IOW, the redesign would be a non-trivial task. "

Sounds promising....