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Post by luke01 on Nov 29, 2017 7:12:09 GMT -8
today something funny happened. I light up the batch box while I was making breakfast and it was running well. All of a sudden the direction of flow changed and smoke started to pour out of the door. I had just started the batch so took everything outside and openend the windows. As soon as I opened the windows the the draft started going the right way again, so i made a small fire and then once I was happy that it was going well i loaded it up. It went fine. I first thought that the problem was maybe that the chimney was cold, but it wasnt as the heater was still warm from a batch I put on last night. Then I thought it might have something to do with the weather, low pressure high pressure or something... and then I realized that when I was cooking breakfast I had put the extractor fan on. So the chimney and the extractor wer competing for the air in the house and the extractor fan won. easy fix though, just open the window next to the extractor. a couple of questions Peter, How hot is too hot? Sometimes I get carried away and just keep on chucking logs in for a couple of hours. The bench has hit 60degrees at the most I have seen it. Certainly toasty. When starting the fire i get some smoke coming out the door, why might that be? And is there such a thing as burning the wood too fast? I can regulate it a little with the door, but what seems to happen when I close the door a bit is that the air speeds up so it actually seems to burn a little faster. I have also been getting some pulsing. In teh afternoon I sometimes do a second batch which normally starts on its own die to hot coals left from the previous batch, its in this case where I seem to get some pulsing, any ideas? thanks! Here is the link to the superwool for anyone else in Europe: www.ebay.es/itm/Superwool-Plus-Fibre-Blanket-13-mm-14-64-Metre-Roll-128-kg/132305457774?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649
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Post by rafael on Nov 29, 2017 22:15:02 GMT -8
Hi Luke, What bricks did you use? Watching the video they looked like R.A. (Refractarios de Andalucia). Then when i opened the sketch up file, the measures of the bricks do not much the R.A. bricks, that usually are 220 x 110 mm.
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Post by peterberg on Nov 30, 2017 2:03:17 GMT -8
How hot is too hot? Sometimes I get carried away and just keep on chucking logs in for a couple of hours. The bench has hit 60 degrees at the most I have seen it. Certainly toasty. Since it's in essence a single skin bell system it can get quite warm. I wouldn't be surprised it could hit 80º C some day in the future. When you see cracks appearing which won't go away when cooled down you probably are over doing it a bit. Most bricks are fired at a temperature of 1000º C, so the assumption those could take 500º C without trouble is a safe rule of thumb. Direct flame put to common bricks isn't a good idea, by the way. The top of the bench is in essence a sort of concrete consisting of sand and portland cement. The integrity of that material is at risk when nearing 500º C, so a 100º lower is what it could take it. The outside of the seat would be far too hot to sit on or touch when it's that hot inside, so 60º C is still considered moderate. When starting the fire i get some smoke coming out the door, why might that be? Depends how you fire the thing up. When making a small fire close to the port and fill it up when it's going fiercely, you can get some smoke out the door when it's open, yes. When you are using the top-down method, loading the firebox, biggest logs first, tinder last and lit on top, the door should be closed by the time the fire develops into a real fire. This can only been done when the heater doesn't contain hot coals, it's the preferred method to lit when there's a floor channel arrangement like yours. The other thing that's going on might be a crevice somewhere in the top of the roof, when lit the heater competes with that leak until the chimney stack warms up. Could be aliviated with a higher chimney but is it worth that? And is there such a thing as burning the wood too fast? I can regulate it a little with the door, but what seems to happen when I close the door a bit is that the air speeds up so it actually seems to burn a little faster. Normal behaviour, when the door is open a crack there's more air coming in which cools the fire somewhat. When closed the air coming through the air inlet is the only one, temperature goes up and the fire appears to burn brighter. Also, the front air is blowing directly into the fire so it burns faster again. One way to counter that effect is to install a steel L-profile as a threshold parallel to the door on top of the floor channel's start end. I have also been getting some pulsing. In teh afternoon I sometimes do a second batch which normally starts on its own die to hot coals left from the previous batch, its in this case where I seem to get some pulsing, any ideas? Off-gassing is going in a higher rate when fuel is placed on the hot coals. Use bigger pieces for the second batch, that slows down gasification.
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Post by luke01 on Nov 30, 2017 4:11:15 GMT -8
Hi Luke, What bricks did you use? Watching the video they looked like R.A. (Refractarios de Andalucia). Then when i opened the sketch up file, the measures of the bricks do not much the R.A. bricks, that usually are 220 x 110 mm. I dont know what factory the bricks came from as I got them from the local building supply store here. We actually had three different size bricks in the build the R.A ones I think were the bigger bricks that we used to close the top of the bell. Also the bricks were sold as being one size and then were really another. Peter modified the sketchup drawing to reflect the real size of the bricks. these are the supposed measurements of the bricks we got: Normal building brick 250x120x50 mm:348 Refractory bricks 200x100x50 mm:115 Refractory bricks 220x110x50 mm:18 Split refractory bricks 200x100x30 mm:35 the majority of the bricks arent refractory, they are just solid cooked bricks that we could get here locally.
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Post by rafael on Dec 1, 2017 3:43:57 GMT -8
Thanks Luke!
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Post by dougduplessis on Jan 15, 2018 12:03:17 GMT -8
Hello and thank you all for posting this video and for the wonderful discussion surrounding this build. I'm considering building a similar system and wonder if there's a way to calculate the size of the bench system so that it will not cool the exhaust gas too far. Are there any rules of thumb to use when sizing the bench opening and mass for these applications? The bench seemed a bit small in this build and I see that Luke was wondering about the 60 deg temperature at the surface. Any guidance on this aspect would be greatly appreciated.
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Post by peterberg on Jan 15, 2018 13:06:30 GMT -8
Hello and thank you all for posting this video and for the wonderful discussion surrounding this build. I'm considering building a similar system and wonder if there's a way to calculate the size of the bench system so that it will not cool the exhaust gas too far. Are there any rules of thumb to use when sizing the bench opening and mass for these applications? The bench seemed a bit small in this build and I see that Luke was wondering about the 60 deg temperature at the surface. Any guidance on this aspect would be greatly appreciated. Hi Doug, welcome to the boards. Yes, there's a way to calculate the size of the system. This one is calculated to 5.2 m² internal surface area, excluding the floor and the firebox itself. The method is described on the batchrocket site, where most of the information about this type of combustion system is concentrated. There's no mass calculator, by the way, Luke's heater weigh in at about 2000 kg and is able to stay warm for something between 15 and 20 hours depending on circumstances. Please read the information on the batchrocket site, in particular the Building section.
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Deleted
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Post by Deleted on Mar 12, 2018 9:17:43 GMT -8
Hi all, peterberg, on this build the port is not as high as recommended specification : 220mm instead of 238 mm. Is that an error of the sketchup drawing or a was is intended ? Regards,
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Post by peterberg on Mar 12, 2018 12:24:42 GMT -8
Hey, you actually studied the drawing! The deviant size of the port is intentionally, That 238 mm is originally made smaller by the overhang of the p-channel, the resulting port is down to 70% of the riser's cross section area.
Since this heater sports a floor channel with no overhang or something, I calculated the port directly to that 70%. It's just a small difference, an even smaller port down to 60% would be working as well but isn't often as stable as the 70% proportion.
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Post by Deleted on Mar 12, 2018 22:48:26 GMT -8
OK, thanks ! I was looking for something else and it caught my eyes ! It simplifies the design I'm working on, so that's always good to take ! Regards,
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Ralf
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Post by Ralf on Mar 25, 2018 13:39:03 GMT -8
Hey Luke, How big is the room you are heating with the stove ? Thanks to all for the shared information!
Ralf
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Post by breckwoldt on Aug 25, 2019 4:23:52 GMT -8
Looking at the SketchUp for this build, it seems that the riser height is well under BatchBox dimension Spec for this CSA. Am I mistaken? What were the factors/trade-offs that went into the decision to shorten the riser? Thanks!
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Post by peterberg on Aug 25, 2019 11:27:11 GMT -8
Looking at the SketchUp for this build, it seems that the riser height is well under BatchBox dimension Spec for this CSA. Am I mistaken? What were the factors/trade-offs that went into the decision to shorten the riser? OK, I checked the drawing and the riser is 900 mm high, measured from riser floor. According to the formula, this is 8.29 times the base figure which is well within the 8 to 10 times I use to recommend. So you are not mistaken, it's at the short end although not too short. I wanted to do this build with as little internal friction as possible since the chimney was a very unfavourable one. So all the internal spaces where the gases needed to make a change in direction were really spacious. Plus the house itself was far from airtight in the top so the chimney draft needed to be strongest in most if not all cases. And it worked, the heater ran right out of the box wet and all without even priming the chimney. This is what a well-tailored design can do.
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Post by breckwoldt on Aug 25, 2019 16:23:50 GMT -8
Ok very good. I was going by "B*10" -no range given. What was unfavorable about the chimney? not being insulated well? This brings up the question of steel stove pipe. If one uses single wall stove pipe for the indoors part of the chimney (which I assume would be a quite common installation) this being an uninsulated "radiator", may, be better included as part of the bell surface area spec? Then again one could always insulate or prime the cold chimney. Experience likely necessary in hitting that balance.
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Post by peterberg on Aug 26, 2019 0:06:07 GMT -8
Chimney single wall up to two meters, two turns of 45 degrees, another meter up, 90 degrees through wall, at the outside 90 degrees up and ending barely above the highest roof line. Outside double-walled insulated though.
I've done single walled stove pipe inside a bell. Starting a fire is ridicully easy but temperature of the exit pipe kept rising, the highest temps in the bell are at the top after all. After the fire was gone the stove pipe kept quite hot, dissipating heat away into the higher parts of the chimney. I also built a couple with an insulated pipe inside the bell, this worked much better.
When calculating the bell the chimney isn't one of the parameters and thus is largely ignored.
All of my tailored designs didn't sport a bypass or means to prime the chimney, not even the open systems.
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