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Post by coastalrocketeer on Apr 26, 2019 9:43:02 GMT -8
In my outdoor “open tank topped bell” system I will deal with draft issues with a chimney bypass at the top of my bell that is variable by an exterior handle.
Cold starts would presumably be with full bypass, and as the bell warms, I expect to be able to turn it fully off, but want to be able to open it just a crack to orovide draft as needed it it turns out heat extraction exceeds the output of my core.. The tanks will only be in the top 1/4 of my bell, height wise, and below that will be filled with brake rotors and other scrap steel for additional thermal mass, so I may wind up making three exits, with one at the top of the bell, one a chimney diameter below the bottom of the tank, and one at the bottom for charging the full mass.
Since it’s all going to be outdoors, smoke-back is not the hazard or nuisance it could be indoors... and I expect it will take some time to figure out what the best way to operate it is, with the core I initially use.
I am making the core section a “doghouse” extension off of the metal shed that will house the bell and tank setup and it’s exterior insulation, and my initial core will be a cylindrical DSR (not a peterberg combustion analyzer tested design, so I do not advise following me in that unless you like experimenting)
I will be optimizing it based on observational evidence to hopefully perform similarly to Peter’s DSR II design currently being fleshed out. In any case, t will be easily replaceable with a cast DSR II once that design becomes finalized. And if I find my bell and tank setup just need a larger system CSA to match the bell that can be decided before casting my DSR.
I am hopeful that some Ideas that thread has given me about multiple zones of direction change and pressure change in the combustion path will allow me to optimize the cylindrical DSR concept to perform similarly.
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Post by coastalrocketeer on Apr 24, 2019 8:27:17 GMT -8
With water in it a 55 gallon drum will definitely be fine heat wise. You will likely have to replace it periodically due to it rusting from the water.
I am planning to use 55 gallon barrels as radiators in various locations in my house. Filled with 50 gallons of water, each one will represent 450lbs of thermal mass in the room it is in.
Since they will be easily replaceable I am not so worried about longetivity for these.
If you use one as your primary heated tank, you will want to make sure it can be replaced every 2-3 years, or when it starts to leak, without much trouble.
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Post by coastalrocketeer on Apr 23, 2019 10:08:59 GMT -8
These hazards of course, being significantly lower with an open system, like yours. :-)
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Post by coastalrocketeer on Apr 23, 2019 10:00:16 GMT -8
I am running 2 coils. One inside the barrel directly above the riser. The other is in a bell. The one in the bell does not add that much heat. Together, they both heat a 55 gallon barrel from 55F to 100F in about 3-4 hours. I have never gone much over 100F. The 55 gallon barrel can transfer the heat to 6 other 55 gallon barrels. I have never gotten them over 85F and that took many hours to get that high. I have accidentally ran both dry and boiled both coils in separate incidents. My system is "Open" on both ends of the coil. I would also worry about the damage to a dry coil that is mounted above the riser from over heating the copper. I don't think you will get fast heating action with a coil wrapped around the riser if that is what you are looking for. It will warm the water but not very quickly. Gadget... just to confirm, your system is using 2x3” gutter downspout as exhaust, correct? If that is the correct size, then the fact that you do not boil water in your coils at full fire is likely in large part due to very limited heat output of your core... a 6 or 8” system will run a MUCH higher heat output, and thus increase significantly, the risk of overheating the water inside coil heat exchangers in a hazardous way. Not saying this to criticize your system, or your testimony of your experience with it operating safely, just to point out that heat exchanger sizing and location as well as the amount of heat input to the exchanger are all interrelated, and the hazards of finding out one has erred in design can be catastrophic.
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Post by coastalrocketeer on Apr 23, 2019 9:51:20 GMT -8
Also, do you have photos or a drawing of your intended space and any fixed constraints such as chimney location that may exist? That may help with suggestions as to how to lay things out and how to design your heat extraction bench setup.
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Post by coastalrocketeer on Apr 23, 2019 9:44:52 GMT -8
Fasardi- you can use halved 55 gallon barrels to create a bell in a bench size area and build up the same cob and rubble over/around them as with ducts. The real requirement is a minimum of 4.5x system CSA so that gasses can slow and stratify inside the bench. At least I think this can work with the batch box rocket heaters... Certainly a “bell bench” has been done with J tubes after the metal barrel that provides immediate radiant heat. (That barrel could be covered with cob or masonry to make it thermal mass as well as far as I know) You would need SOME kind of chamber/passage from over the top box to carry the gasses down to your bench, and possibly a bypass of some sort to heat the chimney at startup... peterberg - do my thoughts above concur with your experiekce and what you have seen others do with batch box cores that worked?
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Post by coastalrocketeer on Apr 22, 2019 9:56:53 GMT -8
The best place to put your heat exchange coil would be in the bell, I would think... the riser needs to stay hot for clean combustion... and if low mass and well well insulated, a coil around the outside of it would not collect much of the heat from the gas stream passing inside of the riser, and really shouldn’t, if you want clean burning.
A bare coil also does not perform particularly well as an air/flue gas to water heat exchanger, and if one does, with the extreme heat of combustion it is exposed to, one runs into the “boom-squish” hazards of making water exceed 212F/100C in a closed system.
I am doing a directly heated open tank of “buffer water” in the top half of my bell, with water to water heat exchange coils, one of which will be a pressurized thermo-syphon loop to my domestic hot water heater.
Are you planning to have the coil set up to thermo-syphon to the storage tank? Larger diameter pipe (1”) would be advised in this case.
If actively pumped, provisions ought to be made to be able to deal with that pump failing, and cool water entry to the coil stopping, mid burn.
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Post by coastalrocketeer on Apr 22, 2019 9:43:38 GMT -8
For safety, I am always for protecting a closed heat exchanger like a coil, in an open twnk of water. This basically eliminates the hazard, and engineering requirement of sizing a heat exchanger such that it cannot be overheated by the maximum potential heat output of a burn cycle of the stove, or relying on T&P valves or other safeties that can fail...
The separate tank the fill valve will be in, is basically like a sight-glass on a boiler, except being open top, it can be connected just at the bottom. The connection between the two must be lower than the sight/fill tank’s bottom, and preferably of a diameter that keeps water in the connecting tube from boiling. I think 1/2” or 3/4 will be fine as long as it is down low in the bell.
The pipe could descend diagonally down from the main tank, until outside the bell, so that any water heated by exhaust gasses in the bell would percolate back into the heated tank and not the “sight/fill” tank.
The top of the sight/fill tank should be a little above the top fill height of the main tank, and could incorporate an overflow drain in case the fill valve ever sticks “on”
To incorporate a float that closes or opens a damper or changes the incoming exhaust gas stream to a “dump exhaust” that bypasses the bell would require a larger external sight/fill tank, and consideration of locating it in a place where any mechanical linkage is as simple as possible and provides easy access to adjust or work on it.
My own design will have the float that does that, in the main, heated tank, most likely, for space considerations, and because my tank and encompassing heat bell will be in an outdoor metal shed, with lots of insulation around it to maximize heat loss from the bell masonry, into the water mass in the upper half of the bell. The tanks will be salvaged stainless kitchen sinks, one single tub commercial one, and two dual tub kitchen sinks.
I don’t have an easy way to draw my ideas up, and post here, and have a lot going on today, but will try to draw up a sinple diagram of the design and post it as soon as I can.
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Post by coastalrocketeer on Apr 18, 2019 19:12:53 GMT -8
Also, if they are going inside a “heat bell” chamber, the closer to the top inside the chamber (but with some space for hot gases to pass over too) the more hot they will get and thus more heat they will store...
Use lighter weight pieces down low, to support heavier/denser stuff up higher and that should give you more bang for your scrap metal “buck”
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Post by coastalrocketeer on Apr 18, 2019 18:57:18 GMT -8
My system of stopping/preventing the combustion is tied to an open tank system... no use for a T&P valve there as my pressurized pipes will be in that open top tank of heated water and thus never be exposed to more ham 212F/100C
A T&P valve will be placed near the top end of that coil but would never actually blow in any foreseeable situation of use, but will be there to keep any inspectors or insurance adjusters who see my system.
The valve that keeps the tank filled is in a separate small tank outside my heated tank through the outside wall by a larger diameter pipe possibly with a P-trap type of arrangement below it, such that hot water will not be induced into the outside tank, but I will be able to see the level of the main tank inside the structure, and use a normal toilet fill valve.
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Post by coastalrocketeer on Mar 31, 2019 17:27:17 GMT -8
What a cool looking rocket! Was there ever a video? I think eric is still working on it... i am excited to see his next update!
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Post by coastalrocketeer on Mar 22, 2019 11:58:45 GMT -8
The water does not have to absorb all of the heat from the fire... the masonry will go to higher temperatures, and then release them back into the air space of the bell.
My design is about switching things from a short duration, high temperature, high velocity gas stream, directly heating the heat exchanger, to slower velocity, longer duration, at lower temperature differentials, by strategic placement of the exchanger, and having higher temperature materials absorb heat during periods of the burn where gasses are not cooled to less than 100C and lower areas of the bell heat up past that temp.
By heating other mass to higher temps during periods when the heat input exceeds the extraction ability of my open tank’s heat-exchange surfaces, the other mass will rise to a higher temperature than water boils at, and being well insulated outside, give most of that heat back to the heating coils inside my open tank, with the air in the bell as a buffer to the temperature differences between the masonry and the water in the coil. If closing my inlet and exhausts with dampers after firing is through, I hope to be able to get most of the heat captured into my other storage tanks over a number of hours after the fire has burned, without losing too much of it up the chimney.
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Post by coastalrocketeer on Mar 22, 2019 11:31:11 GMT -8
If your heat collection area is at/near the top of your insulated bell, then all heat deposited into mass below will eventually rise to the collector area, be cooled, and fall back down (minus losses through the insulation and whatever goes up the chimney to maintain stack effect)...
Circulation of warmer gasses over the heat exchanger being created by convection, which will happen for as long as the water entering the heat exchanger is cooler than the inside of the bell. Even after the fire has gone out and is no longer driving a flow of gasses at all.
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Post by coastalrocketeer on Mar 22, 2019 10:13:47 GMT -8
Underwater basket weaving... lol! True tho!
Sounds like that could work... tho my system will feed gasses directly from core, into a masonry bell... No barrel/radiative section. A flat, spiraled coil at the top of the bell would be a very good heat collector, always in the maximum Delta-T zone, and could be easier to “basket weave.”
You do, however, need a BIG barrel (in proportion to your riser CSA) for “trapping heat” as a bell. The standard 55 gallon barrel won’t even stratify effectively with a tiny 4“ batch box feeding it. Too much gas volume at too high a velocity keeps things mixed. It is normally a turbulent zone.
One could conceivably change this by stacking two barrels and providing some kind of interior baffle system to “randomize” the direction of the incoming gasses, diffusing their directional kinetic energy, and providing entry and exit to the top half of the chamber for high and low temperature gasses, with minimal turbulent mixing of the gasses in the top “stratification chamber” zone.
I plan to put ALL of my heat into that much larger, insulated masonry bell, with strategically placed ceramic fiber blanket baffles, and this should keep any of it from being exposed to “riser-top” temperatures, maximizing my water heating capability.
Too much
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Post by coastalrocketeer on Mar 16, 2019 9:34:07 GMT -8
Anticipation is killing me... Can’t wait for a finalized design and drawings of this core... Thank you for your dedication and hard work Peter!
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