Why not consider putting copper coils around the rocket riser, then run "PEX" piping underground to the pond into another copper coil which would be your heat exchanger for the pond water. At this scale, I would imagine that 3/4" tubing would be the minimum size required. If idle-use freezing is an issue, your could use just enough propylene glycol (RV antifreeze) to fill the tubing, and a small, atmospheric feed reservoir. You would also need a small circulator pump for the system. It is possible to eliminate the need for a pump, by upsizing the tubing on the return side of the system, thereby achieving "gravity" flow. The pump would be much more efficient, though, in terms of speed of heat transfer. :
Andy -- looks very neat and well designed. Also, when you install your secondary chamber, it will not only increase your surface are for heat radiation, it will also provide you with a well-suited chamber between your riser and secondary wall that will lend itself nicely to the mounting of copper coils for water heating. My boiler has coils directly around the heat riser (insulated with perlite), and in the secondary chamber, as well. I have yet to see my exhaust gas temp exceed 90 degrees F. I believe that qualifies it as a "condensing boiler". Not a bad thing...
First reaction is that the horizontal burn tube is too long. Second, not enough rise in the stack to achieve barometric differential (chimney action), and third -- have no fear -- solution is simple: just add (6"?) by 2 ft. sections of stovepipe until you get that audible "rocket effect". Also, if new stack section(s) are insulated, depending on your application, it will be safer, and enable the chimney action to take effect much more quickly. My stove is also a boiler with 2 coils --ergo, high restriction, so I use a small draft inducer fan just to get things established. Further, we must remember the simplicity of the "rocket" concept. which is the shortness of the combustion area as it relates to the 90 degree upturn of the "stack", and the turbulence caused by the turn. I complicated the basic principle by using "on-hand" materials, and by preferring to use H2O as my mass heat storage medium. Forgive me for that, since I am an HVAC pro, enamored of water as a transferral method, since water lends itself to being heated by a great variety of means. Also, storage is easier, provided one has midrange plumbing skills. The draft problems in my system are mainly caused by the efficinecy of heat transferral to the water medium, thereby resulting in much lower "stack temperatures". The addition of a draft inducer creates much the same effect as it would in a "90% plus" efficiency furnace, in that it tends to create a vapor plume and condensate in the flue. These problems are not insurmountable -- all one has to do is anticipate the "low" spots, and provide passive drainage. Also, the draft inducer can be thermostaticallly controlled, so that it is not running 100% of the time. Actually, the higher your combustion temperature in the burn tube, the less likely you will have to handle condensate accumulation. My RMH boiler runs at temperatures where the flue temperature has yet to exceed 90 degrees Fahrenheit. I do get a little vapor plume at this temp, but not enough to have a condensate problem. This could probably change, depending on the moisture content of the fuel I am burning. In fact, most of the time after the combustion is established, the effluent is CLEAR. Oh, P.S.: Remember that controlling the burn is instrumental in the absolute maximum amount of heat obtainable from your chosen fuel, ergo, the maximum efficinecy. Therefore, the lower your final exhaust temperature. the greater the amount of heat you have "reclaimed".
: Thanks, John. If I can have your email address, I'll send you some I-phone pics. I am roy_emerson@hotmail.com. I am new to Permies, and I don't draw well. Sooner or later, I'll get out the mechanical drawing tools, and get this down in black and white.
I have built a "combo" RMH unit that will produce steam and hot water that runs 2 separate coils, 1 around the 4" (insulated)riser, and another looped through the secondary chamber. It works quite well, except it can be a little ticklish to get "kindled up". My stack temperature has yet to exceed 80 degrees F. I have overcome the initial draft problem by the addition of a draft inducer blower, installed in such a way that it can be shut down once the secondary temp is sufficient for sustained drafting. Basically, this works just like a modern 90+% efficiency gas furnace, except it is not necessary to leave the blower in operation during firing. The coils are valved in such a way that I can use them separately or in tandem for water & steam, steam, or just water.
Roy Emerson wrote: : Jeremiah, the extended heat capability of an RMH is obtained by using it in a mass heating mode, be it water or masonry. In addition to the cleanliness of burn and the expediency of available heat, the RMH is compact and lends itself readily to hydronic or convection apps. I am about 90% finished with a unit I built to produce both steam and hot water, either individually, separately, or simultaneously (2 coils). My fuel chamber measures 6" by 8" by 12", and I have gotten as much as a 3-hour productive burn out of it, depending on the fuel I use. It now will burn 5" X 10" firewood, wood pellets, or biomass briquettes. So far, I have been pleased and amazed at the results. I plan to extend the fuel chamber height to 16". The combustion air can enter either thru the bottom load, or through the fuel chamber lid, or both, as needed. With both coils in operation hydronically pumped by a small circulator, I have achieved a 120 degree rise in 5 g of water, in 20 minutes.
Odds are extremely good that those who never make mistakes, never DO anything...engineering is 80% experimentation, 10% research,5% ability, and 5% effort.
: : Well, y'all, mainly what I need is various gears and brngs for the tailstock. Lil fingers, dontcha know. Shifting my lathe like it was a Ferrari...few years back...
: Jeremiah, the extended heat capability of an RMH is obtained by using it in a mass heating mode, be it water or masonry. In addition to the cleanliness of burn and the expediency of available heat, the RMH is compact and lends itself readily to hydronic or convection apps. I am about 90% finished with a unit I built to produce both steam and hot water, either individually, separately, or simultaneously (2 coils). My fuel chamber measures 6" by 8" by 12", and I have gotten as much as a 3-hour productive burn out of it, depending on the fuel I use. It now will burn 5" X 10" firewood, wood pellets, or biomass briquettes. So far, I have been pleased and amazed at the results. I plan to extend the fuel chamber height to 16". The combustion air can enter either thru the bottom load, or through the fuel chamber lid, or both, as needed. With both coils in operation hydronically pumped by a small circulator, I have achieved a 120 degree rise in 5 g of water, in 20 minutes.
Searching for "Atlas" 6 inch lathe parts for a table-top machine of about 35 years of age. Obtaining the needed parts is essential to my defeating the "Good Ole Boy", "Military-industrial complex", "Profit-Motivated" system. Currently, I have multiple projects, ideas going which require the use of this equipment to develop. Would appreciate any and all help y'all could render to get me in operation...
POSTSCRIPT: : Am thinking about stacking on a gasification chamber, and for now, channeling the possible wood gas produced back in to the combustion chamber. Think it might work? Also, copper coils around the gasification unit will serve to reclaim its heat, and serve as a "pre-heater" for the boiler make-up water. Am going to instrument all of this eventually, with pressure and temperature gages. For now, am using a "Sears" multimeter with "IR" function and "K" remote sensors.
Working now on a 2-stage Rocket boiler -- about 85% complete. It is multi-biomass fueled, and will gravity-feed operate on 20" X 5" logs, wood scrap, briquettes, or wood pellets (with a special gravity-feed sleeve). Results so far have been amazing. Will produce steam and hot water, simultaneously, from two separate coils within. On startup, initial convection water flow begins within 3 minutes. Hot water (from "secondary" coil) flow begins within 5 minutes. Secondary chamber gets no hotter than 200 degrees (working to lower that), and stack temperature ( 5") hovers around 75 degrees! The initial rocket stack is built from 4" stainless steel pipe, and the combustion chamber/feed hopper are built from a combination of 6" "U-channel" and 3/16" plate steel. All this stuff came from my junk pile. The secondary chamber is built from a discarded 40 gal. well pressure tank. My mass heat storage will be achieved using a discarded 75 gal. water pressure tank. I plan to hook these two units up to an air handler built from a Dodge van radiator, and possibly powered by a steam-driven fan. Hope I can get all this done before Winter is over! BTW, does anyone know where I can get parts for an older "Atlas" 6" metal lathe?
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Why not consider putting copper coils around the rocket riser, then run "PEX" piping underground to the pond into another copper coil which would be your heat exchanger for the pond water. At this scale, I would imagine that 3/4" tubing would be the minimum size required. If idle-use freezing is an issue, your could use just enough propylene glycol (RV antifreeze) to fill the tubing, and a small, atmospheric feed reservoir. You would also need a small circulator pump for the system. It is possible to eliminate the need for a pump, by upsizing the tubing on the return side of the system, thereby achieving "gravity" flow. The pump would be much more efficient, though, in terms of speed of heat transfer. :
I have built a "combo" RMH unit that will produce steam and hot water that runs 2 separate coils, 1 around the 4" (insulated)riser, and another looped through the secondary chamber. It works quite well, except it can be a little ticklish to get "kindled up". My stack temperature has yet to exceed 80 degrees F. I have overcome the initial draft problem by the addition of a draft inducer blower, installed in such a way that it can be shut down once the secondary temp is sufficient for sustained drafting. Basically, this works just like a modern 90+% efficiency gas furnace, except it is not necessary to leave the blower in operation during firing. The coils are valved in such a way that I can use them separately or in tandem for water & steam, steam, or just water.