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Post by peterberg on Oct 8, 2023 6:16:53 GMT -8
1) In this photo, the flue intake (bottom of the ell) is only about 2 inches off the floor. I believe you said somewhere that you recommend at least 1/2 system size, or 4 inches above the floor? Try to view the space below the pipe's entrance as a ring. In order to facilitate a straight gas path, the ring's outside area should be as large as the system's cross section area. An 8" system is about 50 sq.inch, the ring with a height of 2" below the pipe is exactly the same. But... the gas path isn't straight, far from it. It comes primarily from above, goes through a 180º turn and up. In order to do that, the path should be much larger, at least twice. So, in short, the distance from the floor in this configuration should be 4", absolute minimum. 2) An easy alternative for the intake would be to bring the bottom horizontal pipe into the bell at floor level, and eliminate the ell. Letting exhaust gas flow directly into the horizontal pipe. Is this a bad idea, due to heat stratification, i.e. temperature differential from floor level vs. 8 inches above? Eliminating one 90º elbow is a good thing, that would be my 1st choice. Please don't bring the pipe in at floor level though, the bottom 1/4 circumference of the pipe wouldn't be functional to get the gases in. Also, fine dust will settle on the floor of the bell so it's best to provide for that as well. In general, keep the pipe's entrance at least half the diameter of the system size above the floor. More won't hurt, less would. This way, all of the pipe's circumference will be used for entrance of the gases. In case you want to do something extra to ensure almost frictionless flow: use a reducer from 10" to 8", seen in flow direction. This'll help tremendously, since the circumference of the pipe is 25% larger at its entrance. All gases will go through the 180º and partly 90º change of direction quite easily, converging everything into one direction. The lower part of the bell's wall will get warm enough anyway. Mostly by warming up indirectly through radiation and conduction from the higher parts. And last but not least: the calculation table of the bell, published on the batchrocket site, is presuming the exhaust opening is above the floor. |
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iau461
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Post by iau461 on Oct 8, 2023 6:34:32 GMT -8
1) In this photo, the flue intake (bottom of the ell) is only about 2 inches off the floor. I believe you said somewhere that you recommend at least 1/2 system size, or 4 inches above the floor? Try to view the space below the pipe's entrance as a ring. In order to facilitate a straight gas path, the ring's outside area should be as large as the system's cross section area. An 8" system is about 50 sq.inch, the ring with a height of 2" below the pipe is exactly the same. But... the gas path isn't straight, far from it. It comes primarily from above, goes through a 180º turn and up. In order to do that, the path should be much larger, at least twice. So, in short, the distance from the floor in this configuration should be 4", absolute minimum. 2) An easy alternative for the intake would be to bring the bottom horizontal pipe into the bell at floor level, and eliminate the ell. Letting exhaust gas flow directly into the horizontal pipe. Is this a bad idea, due to heat stratification, i.e. temperature differential from floor level vs. 8 inches above? Eliminating one 90º elbow is a good thing, that would be my 1st choice. Please don't bring the pipe in at floor level though, the bottom 1/4 circumference of the pipe wouldn't be functional to get the gases in. Also, fine dust will settle on the floor of the bell so it's best to provide for that as well. In general, keep the pipe's entrance at least half the diameter of the system size above the floor. More won't hurt, less would. This way, all of the pipe's circumference will be used for entrance of the gases. In case you want to do something extra to ensure almost frictionless flow: use a reducer from 10" to 8", seen in flow direction. This'll help tremendously, since the circumference of the pipe is 25% larger at its entrance. All gases will go through the 180º and partly 90º change of direction quite easily, converging everything into one direction. The lower part of the bell's wall will get warm enough anyway. Mostly by warming up indirectly through radiation and conduction from the higher parts. And last but not least: the calculation table of the bell, published on the batchrocket site, is presuming the exhaust opening is above the floor. Thank you Peter!!! |
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Post by peterberg on Oct 8, 2023 7:24:54 GMT -8
The first mockup of my flue and bypass.  Regarding 90º changes in direction: The 90º elbow above the bypass could be done with two 45º elbows. This will elimnate quite a substantial part of a possible friction point. |
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iau461
Junior Member
Posts: 60
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Post by iau461 on Oct 8, 2023 15:52:56 GMT -8
Regarding 90º changes in direction: The 90º elbow above the bypass could be done with two 45º elbows. This will elimnate quite a substantial part of a possible friction point. Brilliant! Will do, thanks. And on the bottom too. |
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iau461
Junior Member
Posts: 60
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Post by iau461 on Oct 31, 2023 19:55:50 GMT -8
Added a few pics to show progress. The two benches are fully functional, not yet aesthetically complete. Picked up our stand/frame/door for the core today, showing it in place in the partially finished red brick bell. Also, my solution for the 10' to 8" reducer that Peter recommended for the flue intake. I couldn't source one cheaply so I made a kluge. photos.app.goo.gl/VqjiHKNUafJUYqvXA |
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iau461
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Posts: 60
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Post by iau461 on Nov 8, 2023 20:20:19 GMT -8
We had our first DSR3 burn tonight, and we are over the moon. Basically went great.
We filled the firebox about 1/4 full of dry red oak (10-15% water), split into 1-2" pieces. From our experience with the old metal stove, we knew we would have to open a basement window to get the draft going, for the first fire of the year (until the chimney warms up). I also opened the bypass. Top-down light was easy. After 5 minutes it was clear we had a good draft, so I shut the bypass, and the fire didn't flinch. It did need the window to remain cracked open to prevent smoke in the firebox.
During the flame I was monitoring multiple temperatures. These three are measured with thermocouples connected to an Arduino:
- just above the exit port of the core, i.e. the gas exiting the core
- about halfway down the inside of the bell, 16" below the top of the core
- the flue gas, just at the point where it leaves the bell
All those temps peaked out at 45 minutes into the burn, at 571, 215, and 91F respectively. I expect them to get higher with future, larger fires as everything warms. At 2 hours past peak, those temps are 242, 151, and 84.
With the flue gas only peaking out at 91, the fan that will feed the very large "bed bench" never came on. It was set to come on once the flue temp reaches 200. I may adjust that, based on future data, I certainly expect the flue gas to eventually exceed 200 with repeated and larger fires.
The brick exterior is still climbing and is up to 100 in places now, 3 hours after start. Our plan is to build a 2nd bell of cob, 4" thick, around the brick bell, but I wanted to try it this way first, to see how responsive it is, and also to help the brick and clay mortar dry.
I've loaded more pics to photos.app.goo.gl/VqjiHKNUafJUYqvXA . Will try to get some to show here.
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iau461
Junior Member
Posts: 60
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Post by iau461 on Nov 8, 2023 20:52:53 GMT -8
Finished the brick bell, ready for first fire  First fire  |
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Post by skywalker on Nov 12, 2023 12:49:31 GMT -8
Nice build! Door frame looks nice! Maybe consider to weld a piece of metal in the top gap to prevent the air slot from bending when it gets too hot. If everything works right the airframe will be cooled by cold air, but you might forget to open the secondary air one time and then this piece can become quite hot. Just to be sure.
Also I notice the flames don't move straight in to the ceiling port. This could be a lack of draft and of course this stove is still wet, but from our experience we always see the flames moving straight away in the port and they are not dancing as much as your video shows. It could also be you should open your bypass for a longer time to get more temperature in your exhaust for a better draft.
Very interesting you installed some sensors to measure the temperatures. Could you provide us with some more numbers later on, when the stove is fully dried?
Good job and you are going to have lots of fun with this stove.
And also nice to see this DSR3 knowledge spreading again over the globe.
Greetings from the Netherlands
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iau461
Junior Member
Posts: 60
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Post by iau461 on Nov 12, 2023 16:24:20 GMT -8
Nice build! Door frame looks nice! Maybe consider to weld a piece of metal in the top gap to prevent the air slot from bending when it gets too hot. If everything works right the airframe will be cooled by cold air, but you might forget to open the secondary air one time and then this piece can become quite hot. Just to be sure. Also I notice the flames don't move straight in to the ceiling port. This could be a lack of draft and of course this stove is still wet, but from our experience we always see the flames moving straight away in the port and they are not dancing as much as your video shows. It could also be you should open your bypass for a longer time to get more temperature in your exhaust for a better draft. Very interesting you installed some sensors to measure the temperatures. Could you provide us with some more numbers later on, when the stove is fully dried? Hi Sieger, Thanks! My son knew of a local metal fab guy who we believe to be Amish, and who must be independently wealthy. He only charged us $400 for the door/frame/stand. Pretty sure the steel alone must have cost him over $200. I had another estimate for $1600. Are you talking about the air intake slot/port in the upper/horizontal frame member? Can't imagine that thing bending, but we'll keep an eye on it. Also not sure what you mean by "secondary" air? There's only 1 air supply here, through the bottom frame member. At this point we don't even have a way to shut that off, other than jamming a towel in it, but I think I have a good design for a future shutoff. I think you are right about the lack of draft in the video. But the weather has turned a bit colder, and yesterday we started having 2 fires a day, each one now filling about half the firebox. Probably as a result the data has continued to improve. This morning's fire was started with one basement window slightly cracked open, and with the bypass CLOSED, and there was no trouble with draft. The temperature above the core exit port peaked out at just over 900F. The only thing that surprises me a bit is that the peak flue temperature (at the bottom of the ductwork, just after it exits the bell) has only climbed to 140 so far. It's a lot better than the first fire, and still going up. And I'm sure that adding the 2nd bell (cob) will greatly improve all the temps. But I really want the flue temp to get close to 200 before we try heating the bed bench with the fan. I should also mention that the temperature in the stove room has been going up about 2 degrees F per day, starting at 68F, and held steady at about 75 today. Some heat is of course naturally escaping upstairs already. Once it gets above 80 in the stove room we'll start pushing heat to the rest of the house through the existing HVAC ducts, via the 6" fan that hangs from above. I'll provide updates on the temps, especially after we get bell #2 done and we establish a routine for winter burns. Best, Craig |
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iau461
Junior Member
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Post by iau461 on Nov 14, 2023 19:31:25 GMT -8
A brief update. We are now up to 2 full fires a day. Tonight's fire was started with the bypass and all windows closed, and had no trouble with draft. Burn proceeded well, and for the first time the temperature reported above the exit port exceeded 1000F.
Also for the first time we got the bed bench fan running. After playing with it a bit we seemed to hit a stable configuration. We set it to turn on at about 180 degrees flue temp, but had to drop it to its lowest speed setting or else the cooler air getting pumped back from the bench would drop the flue below 180. Once we turned the fan to its lowest setting, it all stabilized. Almost 2 hours later, fire is mostly coals, temp above exit port is 784, the flue is still around 180, the bench fan is still running, and the temperature of the air at the fan (after winding its way through the bench ducts) is 97, about where I think it should be. The temperature in the room is 80, up from 75 at the start.
Like Peter's experience, our DSR3 runs best with the door cracked open. I guess it's OK, but some day I might try enlarging the supply vents on the vertical frame members.
Still some work to do but a success so far. Thanks again to all who got us this far.
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Post by skywalker on Nov 15, 2023 13:04:33 GMT -8
Thanks for the update, much appreciated. And happy for you to hear everything is working well.
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Post by aaron432 on Jan 22, 2024 15:38:15 GMT -8
Nice build! Door frame looks nice! Maybe consider to weld a piece of metal in the top gap to prevent the air slot from bending when it gets too hot. If everything works right the airframe will be cooled by cold air, but you might forget to open the secondary air one time and then this piece can become quite hot. Just to be sure. Also I notice the flames don't move straight in to the ceiling port. This could be a lack of draft and of course this stove is still wet, but from our experience we always see the flames moving straight away in the port and they are not dancing as much as your video shows. It could also be you should open your bypass for a longer time to get more temperature in your exhaust for a better draft. Very interesting you installed some sensors to measure the temperatures. Could you provide us with some more numbers later on, when the stove is fully dried? Hi Sieger, Thanks! My son knew of a local metal fab guy who we believe to be Amish, and who must be independently wealthy. He only charged us $400 for the door/frame/stand. Pretty sure the steel alone must have cost him over $200. I had another estimate for $1600. Are you talking about the air intake slot/port in the upper/horizontal frame member? Can't imagine that thing bending, but we'll keep an eye on it. Also not sure what you mean by "secondary" air? There's only 1 air supply here, through the bottom frame member. At this point we don't even have a way to shut that off, other than jamming a towel in it, but I think I have a good design for a future shutoff. I think you are right about the lack of draft in the video. But the weather has turned a bit colder, and yesterday we started having 2 fires a day, each one now filling about half the firebox. Probably as a result the data has continued to improve. This morning's fire was started with one basement window slightly cracked open, and with the bypass CLOSED, and there was no trouble with draft. The temperature above the core exit port peaked out at just over 900F. The only thing that surprises me a bit is that the peak flue temperature (at the bottom of the ductwork, just after it exits the bell) has only climbed to 140 so far. It's a lot better than the first fire, and still going up. And I'm sure that adding the 2nd bell (cob) will greatly improve all the temps. But I really want the flue temp to get close to 200 before we try heating the bed bench with the fan. Hi iau461, I like your build well done. I'm fairly new to some of this info and wondering why you are wanting the flue temp to get close to 200F. |
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iau461
Junior Member
Posts: 60
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Post by iau461 on Feb 23, 2024 15:10:50 GMT -8
Hi iau461, I like your build well done. I'm fairly new to some of this info and wondering why you are wanting the flue temp to get close to 200F. Hi Aaron432, sorry for slow reply, I've been dropped out here a bit since our stove continues to work well. If you read around this site a bit you can find recommendations for minimum flue temp. You don't want to send a lot of waste heat up the flue, but it has to get warm enough so that you never risk flue gas backing up into your living space. In my case, I was worried that once the fan turned on to start warming up the large bed bench thermal mass, the flue temp might drop so much that draft could become a concern. Seems my fears were unfounded. We've never been able to get the flue temp (measured inside the steel flue, about 12 inches above the floor) to read much over 140, but even with the fan pulling heat through the bench, there is no trouble with draft. |
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