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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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lsch
New Member
Posts: 18
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Post by lsch on Mar 22, 2019 10:47:32 GMT -8
greeting the heat transfer depends on the gas velocity as well (see gas heating).so not sure that stratification is a plus
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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 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 DCish on Mar 22, 2019 17:22:54 GMT -8
Interesting theory, I'll be curious to hear how it works in practice. I hope the air buffer is a good enough heat exchange medium between the mass and the coils.
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Post by gadget on Mar 22, 2019 19:41:21 GMT -8
I don't know if you have seen my thread on my little rocket heater but I had a 55 gallon barrel bell with coils inside the top. It wasn't insulated but it was full of old brake rotors. It was after the barrel/riser so it saw between 300F-400F. It works pretty good. last burn I did it was seeing 300F in and 100F out the exit. I agree, higher gas flows = lower efficiency in the barrel/bell
On a side note, I took 5 gallons of water out of it the other day that had collected(along with a ton of ash)
The 2 barrels stacked together is not a bad idea, assuming there is space for it. Just need to deal with condensation
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Post by Sidney on Mar 23, 2019 3:46:06 GMT -8
I'm looking to do something similar. When you look at water's specific heat, it is pound for pound the most effective matter to store heat energy in by cost of material. There are some serious dangers in using water that is mentioned in this forum many times over, so you need to design this properly or it becomes a bomb. Literally.
Since water absorbs heat relatively slowly (also releases it slowly) you need to increase the temperature difference as much as possible to maximize the heat transfer. f you can design the system to absorb the heat as much as possible during the burn, you can release it slowly later. The drawback is you need a large water reserve to ensure the water max's out at around 80C.
Fortunately, there are solutions out there that work great for this designed for solar evacuated tube heaters. I intend to combine the 2 technologies since the solar heat is greater during the summer but lacks in winter. The Rocket mass heater will supplement the solar system. If one would choose to design a closed system, you can use existing technologies from the automotive industry and hot water tanks to implement safeguards so there are no disasters waiting to happen.
If you have a large house, you can use an open thermos siphon steam system to distribute the heat to different water reserves throughout the house. The systems are well documented and designs are easy to get to.
On the other hand, I'm a strong believer in the KISS approach so I'm looking at an open system. The more the complexity, the greater the risk of failure.
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Post by gadget on Mar 23, 2019 8:41:25 GMT -8
If you have a large house, you can use an open thermos siphon steam system to distribute the heat to different water reserves throughout the house. The systems are well documented and designs are easy to get to.
I have heard that steam return boilers work great for moving heat and are good for tall buildings where there is a good return with gravity. Apparently the problem with them is they require tuning and lots of experience to get them to work good. But when they are setup right, they are very efficient. Boiler needs to be below all the heat exchangers. There are strict laws installing and building them to apparently. Licensing, certifying and such due to the dangers involved. Its essentially like a complex gravity return heat pipe. I don't think it would be possible to do a steam return in an open system
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Post by Sidney on Mar 23, 2019 15:15:41 GMT -8
I have heard that steam return boilers work great for moving heat and are good for tall buildings where there is a good return with gravity. Apparently the problem with them is they require tuning and lots of experience to get them to work good. But when they are setup right, they are very efficient. Boiler needs to be below all the heat exchangers. There are strict laws installing and building them to apparently. Licensing, certifying and such due to the dangers involved. Its essentially like a complex gravity return heat pipe. I don't think it would be possible to do a steam return in an open system You are right. This means it might be worth the investment in a new construction, but I'm not convinced it is worth in an existing building generally speaking.
It is possible to do a steam return in an open system, I've seen some older designs. They are tricky so a closed system is preferred as it requires less maintenance and less risk of something going wrong. They are particularly hazardous where the weather drop is very cold as the vents ice up and clogs.
I had found a site with a lot of information and many designs. I thought I had saved the link but since it was to complex and decided it was not an option I think I discarded it. The regulations surrounding these systems is to heavy and increases the expenses way above the limit of reason. None the less some of its concepts could be applied to a system to improve its efficiency I think.
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Post by fasardi on Apr 16, 2019 6:16:50 GMT -8
If you have the faucet closed at some point the copper heat exchanger will have the same temperature as the water tank. That means, if the water tank is at boiling temperature then the heat exchanger will also be at boiling temperature. So, the water pipes can still explode, right? Correct me if I'm wrong. You're wrong, the copper pipe is at the mains pressure. Which means boiling temperature in the pipe is higher as compared to atmospheric pressure. The water in the tank won't get hotter than 100º C while boiling point in the pipe is 110 or 120º C. So it'll never go boom this way. See the explanation by the inventor permaculturenews.org/2012/11/23/rocket-stove-hot-water/Hi, i`m new to the forum, came here from permies.com looking for ideas like this. I`m planning on building a BBR8 or 10, or maybe a DSB MarkII of the same size, to heat a water thermal battery, and with a copper heat exchanger heat a circuit of radiant wall (i don`t know if that is the best words to describe it). Someone in this thread said than could use the steam outlet of the thermal battery to put out the fire, in case of overheating, by letting the steam go in the batch box. How could this be achieved? wouldn`t be bad to the fire bricks? and difficult to fire up later when needed? coastalrocketeer also talked about a sistem to close the door if not enogh water is in the tank, would it be better that way? will the usual float system used in common water tanks fail in a heated water tank? Thanks to all in advance.
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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 fasardi on Apr 22, 2019 4:49:59 GMT -8
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. Thanks for the reply! That small tank will have to be at the same level or higher? I`m sorry to bother, but if you can make a sketch of the system guess i`ll be able to figure it out with it (i`m not in a rush, when you have the time!) I will have to push back the start of my construction a little more, because right now i don´t have the space to have the water tank near the stove. I was thinking, maybe for the next winter (i`m in the patagonia, so July 2020) i will have some more room, and can have a bell with a water tank inside it on the side of the box and the flue derived to it. Other posibility is to make a copper coil and add it to the existing stove, i don´t know wich option will be better/safer
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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 fasardi on Apr 25, 2019 9:14:09 GMT -8
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. It won´t be necessary for me, your explanation make it very clearly! Thanks for your help!
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Post by dirtdevil on Jul 3, 2019 10:46:45 GMT -8
I have been heating my house with in-floor pex for twenty years. I have a built in wood heater with a somewhat convoluted smoke path and I use two three quarter inch black iron pipe grids in the back of the stove. Each one feeds a storage tank above the stove. One is a full sized oxygen tank and the other a hundred pound propane tank. These are both open to the atmosphere by slightly cracking the valves so no pressure builds. The tanks rely on pumps to move the water though the pex in the floors and it keeps the temps in the tanks within limits while they are running but even if they are not and the water in the tanks hits the boiling point there is no danger and they just vent off the steam. The water feeds from the bottom of the tanks to the bottom of the pipe grids and then thermosyphons back to the top of the tanks. I'm just mentioning all this to show that a hot water heating system can be operated perfectly safely over a long period of time.
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