I have been reading/watching the RMH threads, the biggest advantage that I see is the capture of heat energy and the "clean" exhaust output
I would like to build a "large wood" stove using these principles. While I see the advantage of the small pieces of wood in a RMH it looks like a lot of work to keep one fed to produce heat on a larger scale.
My thoughts are to build a top wood fed fire box ,well insulated to support hot clean combustion , a secondary chamber like the "barrel" of a RMH and some type of storage mass, then the exhaust . the storage mass might be liquid to provide the function of a outdoor wood boiler without the smoke and incomplete combustion. the stove would be inside of a building to make use of the radiant heat.
I am not an engineer, so I cant comment on the forces involved that make the Rocket stove work so well. I can tell you that there is a wood stove avalible for purchase that used these same principals and claims about a 90% efficency. They do use a 300 gal water tank to store the heat to be given off later. Some of the larger units use 2 of these large tanks. I saw one in operation at a festival this year in Kompten Pa. They were very pricy, I think in the $8000 range. If you want to engineer and produce one yourself I would sugest that you make a mock up of your design and test it 1st. Since the Rockets I have seen use fire bricks for the fire box and the draft area, why hot lay one out with the size uoi want and use a barrel or something like that to make the up draft. You dont need to cement this prototye, just lay it out, maybe cover it with dirt to help seal it and do some test burns. If it draws well and burns like the smaller rockets then you know your unit will have the efficency that you want. Designing the water jacket you plan on using is another matter. You may need to play with that some to get the proper heat transfer that you want. The Rockets use the cobb mass to store the heat and provide that fly wheel effect. You may need alot of water to do the same thing. Maybe a combination of the 2 ideas would work best. Anyway, I have had the same thought about the Rocket stoves and their small fire box and no ask pit. Good luck with your plans.
Never doubt that a small group of dedicated people can change the world, Indeed it is the only thing that ever has. Formerly pa_friendly_guy_here
After reading Iano's book I beleive that the barrel is strictly for heat radiation and that the secondary combustion is in the verticle stack. I too am working along these lines. After our move and setting up a new shop this spring I hope to start working again on this. I want to experiment with burning waste wood from chipped tree trimmings and also burning larger split logs. I have two verticle water storage tanks, one 250 gal, the other 125 gal, plus I am making a fire tube boiler for heating the water and it will hold another 150 gal. I do like the simplicity of the traditional RMH design and think that it is is keeping things simple it makes for greater efficiency. kent
posted 8 years ago
There has been a lot of work done on masonry stoves/heaters and a lot of information is available in various sites around the internet. The most detailed one I have found so far is this one: http://stove.ru/index.php?lng=1&rs=15 There are a number of articles on there which get into the engineering of these things..his are designed so they can be adapted to heat multistory buildings and to heat water as well. The articles can get pretty technical.
Masonry stoves appear to be a sort of first cousin to rocket stoves in that they also are designed to use one or two very hot short burns a day. That they work like a damn is unarguable, my daughter has one in an old three (including a used attic space) story house in Nova Scotia and it has supplied satisfactory heat for the house for years now, using very little wood to do it. The thing with rocket stoves is that they would appear to be a lot easier to build but they also seem to end up looking a little funkier than I would like in my living room; masonry stoves are often (usually?) very attractive. They also tend to be VERY expensive. I believe there are a number of people now certified to build the things scattered about the country and there are also ( I think) "core " kits to buy for people who want to do their own but which make success somewhat more certain.
There are also plans here http://www.dnr.mo.gov/pubs/pub781.pdf which are very detailed and include the details for a stove with or without an oven, complete with material list and so forth. The plans don't include any way to heat water though.
If I remember the russian guy suggests keeping any water heating system out of the firebox itself. His stoves appear to have a slightly different design to them. At least one of his stoves has tested at 89% or better efficiency.
There seems to be a design decision split depending on how the heat is to be used. If you want slow release heat in a small house/ space, then a RMH or masonry stove is a good solution. But, If you want to heat water for hydronic heat distribution or DHW, then the designs to look at are for gasification boilers. These use refractory fire boxes and secondary burn chambers, most are downdraft types, and they are optimized for transfering the heat into the water. Check out www.greenwoodusa.com/resources.php I plan to build a boiler similar to the Tarm, http://www.woodboilers.com/wood-boilers.aspx, but using a fan induced draft for startup only. There are several great designs out there but I want passive draft and and low voltage controls. I know its possible, there just has to be more height between the burn chamber and the heat exchanger. Also, while these units are generically referred to as 'boilers', they don't make steam/ pressure, only HOT water.
posted 8 years ago
Thanks for the responses , got me thinking more .I read somewhere that temperature differential on the drum of a RMH is a big part of what drives the draft, and thought that jacketing the bottom 1/4 might help this along , still in the thinking stage, I may build a RMH first to learn that system so that I have something to compare to in enlarging the system. If a conventional ,pre epa wood heater of good design is run hot there is very little ash , it is the slow burn that causes ash in the first place. More head scratching and link reading