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Post by gadget on Mar 11, 2018 20:37:32 GMT -8
I've been reading on this forum and on Permies researching for a long while now. I'm finally starting to buy parts for building a heater this summer. I am very familiar with secondary burn especially with wood stoves. I'm building a rocket/batch box masonry heater kinda hybrid. Looking at some of these number I'm seeing how clean you rocket guys are burning without secondary air and I don't see the need for it with a J tube with top fuel feeding. However, I'm building a batch box RMH and was thinking since the wood is not burning on the ends like a J tube there is going to be more pyrolysis for given amount of primary oxygen inlet. I'm wondering if anyone with a batch box rocket knows how much secondary air helps or if its necessary
I'm mulling over getting the secondary setup on my stove plans and would love to just not do it if it doesn't make much difference with the numbers. My current design is basically a firebrick lined batchbox that is back insulated with 1" ceramic wool. There will be a top plate over the firebox of 3" ceramic board and a port in the center top. The port will open to a 1" ceramic wool burn tube of unknown length/ 6"ish ID.
I appreciate and input.
Thanks, Gadget
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Post by pinhead on Mar 12, 2018 7:36:29 GMT -8
You might want to read the Small Scale Development thread. It's long but it covers the difference between burning with and without tertiary air.
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Post by josephcrawley on Mar 12, 2018 8:05:28 GMT -8
I'm a little confused the batch box design does include secondary air in the form of a ceiling mounted tube aka p channel or in the case of the sidewinder a floor mounted one. Look at batchrocket.eu/en/designs
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Post by drooster on Mar 12, 2018 10:47:33 GMT -8
... Looking at some of these number I'm seeing how clean you rocket guys are burning without secondary air and I don't see the need for it with a J tube with top fuel feeding. Most efficient J-tubes and especially batch boxes take secondary air supply very seriously indeed. P-channel, Floor-channel, S-thingy ...
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Post by peterberg on Mar 12, 2018 12:10:04 GMT -8
My current design is basically a firebrick lined batch box that is back insulated with 1" ceramic wool. There will be a top plate over the firebox of 3" ceramic board and a port in the center top. The port will open to a 1" ceramic wool burn tube of unknown length/ 6"ish ID. It looks like you take some aspects of existing designs, bolt those together and call it your design? I am quite sure this proposed combustion core won't burn clean at all. But please go ahead, build one like this and surprise us all. Oh, by the way, a batch box following my design is very much helped by a secondary air provision, otherwise it wouldn't be there. Those secondary air provisions are very specific, just a pipe leading to the port or worse, into the riser, could be diametrically in effect.
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Post by gadget on Mar 12, 2018 19:35:46 GMT -8
My current design is basically a firebrick lined batch box that is back insulated with 1" ceramic wool. There will be a top plate over the firebox of 3" ceramic board and a port in the center top. The port will open to a 1" ceramic wool burn tube of unknown length/ 6"ish ID. It looks like you take some aspects of existing designs, bolt those together and call it your design? I am quite sure this proposed combustion core won't burn clean at all. But please go ahead, build one like this and surprise us all. Oh, by the way, a batch box following my design is very much helped by a secondary air provision, otherwise it wouldn't be there. Those secondary air provisions are very specific, just a pipe leading to the port or worse, into the riser, could be diametrically in effect. Thanks everyone for the quick replies. Yes, I am going at my own design here. I'm working on some drawings and will post them when I get a chance. I decided that a top feed would not work. I can't ask my wife to tend a tube feed with 3 small kids taking up all her time so batch box is more desirable. Space is limited so the box may have to be turned 90 deg with the feed door on the wide side and the burn going strait up from there. I'm going to have a bell after the burn tube that will have forced air to move heat into the room and will be barried with cob and a skin. Then to a bench with another bell off to the side. But..........that is not where the design gets interesting.....I'm building a copper heat exchanger and a condensate tank to fully condense the exhaust. From here there is a blower that exits the remaining gases out 2" PVC on the side of the house. I do not want to run a chimney and I want a side exit exhaust. Reliable draft is a must so I decided and trying a condensing system. I already have the following pieces 75 firebrick splits 25 feet of fiber blanket 3" thick slab of fiber board for a burn chamber roof 4x8 sheet of 3/16" diamond plate steel for first bell(free from salvage) 300' of 1/2" copper tubing lots of perlite 50 CFM centrifugal blower from a furnace big pile of sub soil for cob Lots of 6" vent tubing and tees and bends I have built many unusual things in the past so going off known design does not bother me. I don't mind making changes and modifying down the road. Part of the reason to build this is because I find joy in inventing and trying new ways to solve new problems. Check out this freeze dryer I built using scrap; www.survivalistboards.com/showthread.php?t=234062&highlight=diy+freeze+dryerI don't mind being a guinne pig on this one and am planning on doing lots of documentation. The one thing I don't have is a gas analyzer though. I don't like the idea of steel in a burn chamber but I am going to do a secondary burn. The third burn sounds interesting. -Gadget
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Post by Vortex on Mar 13, 2018 3:01:42 GMT -8
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Post by smartliketruck on Mar 13, 2018 8:49:57 GMT -8
What happens to the exhaust when there's a loss of electricity?
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Post by gadget on Mar 13, 2018 10:04:31 GMT -8
What happens to the exhaust when there's a loss of electricity? I have about 2700w of solar. 1200w 24v system and a 1500w 12v system. I'm glad you brought it up because it is a negative aspect of having an induction blower
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Post by drooster on Mar 13, 2018 13:32:43 GMT -8
You are building a firebox with a hole in the top going into a vertical riser? Please stop calling it a Batch box.
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Post by gadget on Mar 13, 2018 13:43:39 GMT -8
You are building a firebox with a hole in the top going into a vertical riser? Please stop calling it a Batch box. I don't know yet what I'm building. Still working out details. Please forgive me for abusing the term.
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Post by gadget on Mar 13, 2018 14:28:35 GMT -8
Thanks, I just read through all that. I am not surprised the flue pipe with wet towels did not work, especially without a blower in the system. I built a 2 stage swamp cooler last year and learned allot about heat exchangers. It has a heat exchanger made out of 3200 aluminum cans. It is 8'x8'x18". A large monster of an heat exchanger. There are things that make heat exchangers work well and 3 come to my mind; 1 high temperature gradient 2 large surface area of the heat exchanger medium 3 slow face velocity of gases passing over surfaces of heat exchanger. My thought is this; The last bit of heat coming out of the stove is not going to be hot enough to work in a small heat exchanger. There needs to be lots of surface to make up for the small difference in temps. A single large exhaust pipe is probably not going to be affective. I imaging there will be some condensing but over all maybe still lots of heat left behind. The other thing is an effective heat exchanger is going to kill the draft and there must be a blower. I don't see a way around this. I know this is a big turn off having to have an electric motor in the system. Who wants to complicate the heater with a blower, right? I have searched all over the web for projects on condensing wood heaters. There is very little info out there.
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Post by gadget on Mar 15, 2018 12:36:59 GMT -8
I was looking at some Contraflow Masonry heater designs last night. Secondary air with no metal pipes to corrode. I love the idea of no metal tubes in the flame path. www.pyromasse.ca/en/firing.htmlSecondary air is introduced just above the wood. Looks like a great setup. -Gadget
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Post by peterberg on Mar 15, 2018 12:49:56 GMT -8
PLease take note that the fuel is away from side and rear walls plus as far away from the door as possible. The fuel is stacked log cabin style so lots of air can go through. You need a large, wide firebox for this setup to work. In my experience, it matters where the secondary air is introduced exactly and at what temperature.
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Post by gadget on Mar 15, 2018 13:06:58 GMT -8
PLease take note that the fuel is away from side and rear walls plus as far away from the door as possible. The fuel is stacked log cabin style so lots of air can go through. You need a large, wide firebox for this setup to work. In my experience, it matters where the secondary air is introduced exactly and at what temperature. Yes, I was reading on the top down burn method and importance of wood layout. Also, occasional loss of burn if not just right. Sounds temperamental. The secondary air is not heated at all. How does that work out?
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