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Post by stefanvh on Apr 18, 2019 7:24:31 GMT -8
The old (Flam) wood stove is going to retire so it is time for a new one. I've been loosely following the RMH developments for years, and lately the DSR2 experiments of Peter. I have zero experience building wood stoves, but I actually studied combustion technology so I should know a thing or two (for one, that combustion is extremely complicated and barely understood, especially combustion of solids that do not have a fixed composition).
I especially like the simplicity of the DSR2 design so I made a design which uses standard sized fire bricks. Unfortunately it's impossible to build a core without cutting any bricks, but I tried to keep it to a minimum. The bricks are 220x110x40 and 220x110x50 and the plates 400x200x28 and 300x200x28.
This stove is going to be the main one for heating the house, and the plan is to connect a Bell and some kind of water heating to supply the central heating. But first things first: building the core. I realize that there is only one way of making sure that it performs as I would like, and that is to actually build and test it. But before I am ordering a load of firebricks, some basic feedback on the design would be nice. The dimensions are based on a 180mm system. It's not possible to extrude solids in the free version of sketchup, so I just drew the port opening on the bricks. The end port is also still missing because I am not entirely sure where to place it yet. A side end port which will enter a Bell would be ideal (would leave the top free for cooking for example), but I don't know if this will work.
Forum has reached the attachment space limit.
So, my first question: How is the flue normally connected to the masonry? As the flue is circular (in my case 200mm) and the exit of the core is usually rectangular.
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Post by peterberg on Apr 18, 2019 8:15:36 GMT -8
But first things first: building the core. I realize that there is only one way of making sure that it performs as I would like, and that is to actually build and test it. But before I am ordering a load of firebricks, some basic feedback on the design would be nice. The dimensions are based on a 180mm system. Stefan, I spotted the first couple of mistakes: the top box should be as wide as the firebox and a square cross section. And since the top box is that wide, the location of the riser should be the same dimension as said box. Forming the riser can be done by cutting some splits and placing those inside, so the desired demensions can be obtained. It's not possible to extrude solids in the free version of sketchup, so I just drew the port opening on the bricks. The end port is also still missing because I am not entirely sure where to place it yet. A side end port which will enter a Bell would be ideal (would leave the top free for cooking for example), but I don't know if this will work. The free 2017 version of SketchUp is able to do extrusions, I've drawn all my designs using that same free version. As for the placement of the end port and other details, please download this principals drawing and study it carefully. So, my first question: How is the flue normally connected to the masonry? As the flue is circular (in my case 200mm) and the exit of the core is usually rectangular. Normally the core is placed inside the masonry bell, only the door is sticking out. The exhaust opening from the bell could be round, no problem there that I can see. Don't try to keep the core separate from the bell, this way you won't need a side end port also. Of course you could build anything you like but I'd suggest you would do best heading in the direction of one that is quaranteed to work.
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Post by stefanvh on Apr 18, 2019 13:12:08 GMT -8
Stefan, I spotted the first couple of mistakes: the top box should be as wide as the firebox and a square cross section. And since the top box is that wide, the location of the riser should be the same dimension as said box. Forming the riser can be done by cutting some splits and placing those inside, so the desired demensions can be obtained. Thanks Peter. I'm a little confused about the square cross section, as the reference design does not seem to have a square cross section: imgur.com/a/fmgl2kK ? I'll redesign the core and find a better way of using the bricks. Filling the extra space with some splits is probably indeed a better idea than shifting the location of the walls. The free 2017 version of SketchUp is able to do extrusions, I've drawn all my designs using that same free version. As for the placement of the end port and other details, please download this principals drawing and study it carefully. I think SketchUp 2017 only works on Windows, but I'll have to check again. Normally the core is placed inside the masonry bell, only the door is sticking out. The exhaust opening from the bell could be round, no problem there that I can see. Don't try to keep the core separate from the bell, this way you won't need a side end port also. Of course you could build anything you like but I'd suggest you would do best heading in the direction of one that is quaranteed to work. That makes sense. I'm just worried that if the core is placed inside the bell and it won't function properly, there is no way of reaching it without breaking the bell down with a hammer and chisel.
I'll redesign it and try to think of some clever way to minimize the amount of brick cutting that is necessary.
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Post by peterberg on Apr 19, 2019 0:37:04 GMT -8
Thanks Peter. I'm a little confused about the square cross section, as the reference design does not seem to have a square cross section: imgur.com/a/fmgl2kK? When I say the cross section of the top box is square, it is. You think in the reference design only the right wall is left out but this isn't the case. So you measured the riser and the step left of the riser, omitting the step at the right. It would be much clearer to measure from the centerline instead, which is in the middle of the port and riser, obviously. Creating a straight box that doesn't sport shifting of the walls where the riser is located means it's much simpler to build. Also, this way one could use insulative material of whatever kind to create the narrower riser. This fill in material is needed onlt at left, right and rear, i.e. not at the side of the port. Don't worry about the thing wouldn't work when the build is completed. Just do a mockup in the garden and run it. You'll need a length of (larger) stovepipe in order to create some draft, it won't start without it. If and when it works like that it should work in a bell system as well. Unless you made mistakes in the bell or exhaust of course.
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Post by stefanvh on Apr 19, 2019 3:47:08 GMT -8
Thanks Peter. I'm a little confused about the square cross section, as the reference design does not seem to have a square cross section: imgur.com/a/fmgl2kK? When I say the cross section of the top box is square, it is. You think in the reference design only the right wall is left out but this isn't the case. So you measured the riser and the step left of the riser, omitting the step at the right. It would be much clearer to measure from the centerline instead, which is in the middle of the port and riser, obviously. Creating a straight box that doesn't sport shifting of the walls where the riser is located means it's much simpler to build. Also, this way one could use insulative material of whatever kind to create the narrower riser. This fill in material is needed onlt at left, right and rear, i.e. not at the side of the port. You are the all-knowing authority in batch rocket world so I wouldn't dare to question what you say . So the design is actually symmetrical across the centerline? This would make a lot more sense, but it is not exactly square : Please enlighten me
I indeed that that just the right wall was missing and found it odd that the port and riser weren't centered, but it didn't occur to me that the view shown is basically just a 'random' section plane through the core, and not the core without a wall on the right hand side...
Don't worry about the thing wouldn't work when the build is completed. Just do a mockup in the garden and run it. You'll need a length of (larger) stovepipe in order to create some draft, it won't start without it. If and when it works like that it should work in a bell system as well. Unless you made mistakes in the bell or exhaust of course. This brings me back to my initial question: how do I connect the stovepipe to the core? Just put a piece of pipe on top of it and try to make the 'connection' air tight?
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Post by peterberg on Apr 19, 2019 5:40:58 GMT -8
So the design is actually symmetrical across the centerline? This would make a lot more sense, but it is not exactly square Please enlighten me
This brings me back to my initial question: how do I connect the stovepipe to the core? Just put a piece of pipe on top of it and try to make the 'connection' air tight? Hmmm... Let's see... You are right, width is 3.44828% or 6 mm larger than height. Well within allowable tolarances, I'd say. Exactly, a bigger piece a bit flattened at one end and made airtight with mud, papier mâché or whatever?
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Post by stefanvh on Apr 19, 2019 8:03:51 GMT -8
I'll create a new SketchUp design incorporating your feedback. I think I actually understand the design now . Happy Easter .
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Post by stefanvh on Apr 21, 2019 23:40:41 GMT -8
I made a new SketchUp drawing: www.dropbox.com/s/mz5fy0daglxmgmp/DSR2%20180-2.skpIs there also a way to close the 'roof' of the (shoe)box with two normal bricks instead of a long plate? Could I just connect them with some fire resistant mortar, or would that break easily? Edit: I am considering creating a 200mm system instead as it will be the main heater for the entire house (as it will be connected to the central heating). I've read that more than two fires a day will decrease the efficiency. I have no problem keeping it on the entire day, but would it still function properly?
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Post by stefanvh on Apr 23, 2019 4:55:19 GMT -8
I made a drawing for the 200mm system: imgur.com/a/BNen0JNwww.dropbox.com/s/3kfnc0jyv8po4ve/DSR%20200.skpAn extra layer of bricks around the riser would be possible, but I think the mass of the riser should be kept to a minimum so it will heat up faster?
For the 'roof', I noticed that in this video some steel angles (covered in superwool) are used to support the bricks in the roof. Seems like a simple but effective solution.
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Post by peterberg on Apr 23, 2019 7:50:30 GMT -8
I made a new SketchUp drawing: I spotted one blooper: at the rear of the riser there's a step into the riser instead of a step out. This is a real deal breaker, I tried to restrict the exit of the riser like that and it refused to work properly. Is there also a way to close the 'roof' of the (shoe)box with two normal bricks instead of a long plate? Could I just connect them with some fire resistant mortar, or would that break easily? Yes, you could use two bricks to span the firebox, let the bricks stick out of the sides. As long there's about as much of the brick sticking out at the sides as there is inside they would balance. By building the top box on top of these they'll stay in place. Closing the top box is another problem, you'll probably need something to keep that in place by placing some bricks above the walls. Edit: I am considering creating a 200mm system instead as it will be the main heater for the entire house (as it will be connected to the central heating). I've read that more than two fires a day will decrease the efficiency. I have no problem keeping it on the entire day, but would it still function properly? It would function properly all day as long as long as you don't load it full after first fire. Just adding two or three big logs at the time will keep it going. Tried that and it works.
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Post by peterberg on Apr 23, 2019 7:59:10 GMT -8
I made a drawing for the 200mm system: Still, I am missing the step out at the back of the riser, similar to the sides. An extra layer of bricks around the riser would be possible, but I think the mass of the riser should be kept to a minimum so it will heat up faster? Yes, the riser would heat up faster when there's less mass there. You could use the solution of Pinhead's 5-minutes riser. For the 'roof', I noticed that in this video some steel angles (covered in superwool) are used to support the bricks in the roof. Seems like a simple but effective solution. This'll work in the top of a bell, personally I didn't use it in a firebox as yet. The video isn't visable, by the way.
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Post by stefanvh on Apr 23, 2019 23:55:19 GMT -8
Thanks Peter. You are right about the step out at the back of the riser. Too busy trying to stack the bricks in the easiest way, I forgot about it. The brick that steps into the riser at the top is just laziness to extrude a piece out of the brick, but I also thought it might help the combustion. But as you've already tried it there is no point in testing it like that. I updated the drawing again (I just drew a black rectangle on the 'step in' brick as I still use SketchUp web ):
But you're right, that is indeed a bell and not a firebox. I'll try to think of a way to close it with bricks, as I doubt a vermiculite plate will hold for a very long time. In our regular woodstove they regularly break, so I doubt a 28mm plate will be able to withstand rocket power.
Edit: With regards to the Bell: my idea was to place an uninsulated stove pipe inside the bell which would draw at the bottom of the bell (i.e. it floats above the floor of the bell) instead of having the flue pipe outside of the bell. I'd imagine that this will create a better draw through the system as the stove pipe will start heating up immediately after starting the fire. Am I right about this?
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Post by peterberg on Apr 24, 2019 4:46:59 GMT -8
I'll try to think of a way to close it with bricks, as I doubt a vermiculite plate will hold for a very long time. In our regular woodstove they regularly break, so I doubt a 28mm plate will be able to withstand rocket power. Vermiculite board won't hold, temperatures are simply too high for that. With regards to the Bell: my idea was to place an uninsulated stove pipe inside the bell which would draw at the bottom of the bell (i.e. it floats above the floor of the bell) instead of having the flue pipe outside of the bell. I'd imagine that this will create a better draw through the system as the stove pipe will start heating up immediately after starting the fire. Am I right about this? In a way you are right, in that the draw is initiated immediatly. On the other hand though, a lot of efficiency is lost this way. Simply because all the heat that is getting into the pipe is exhausted through the chimney stack, even after the fire is gone. A pipe inside the bell is in fact an upstream channel (sometimes called a plunger tube) and need to be insulated from the main bell structure. I did this a number of times, one of those is the Münster build, another the Brussels build. Both chimneys were inside the bell and worked admirably. The upstream channel/pipe outside the bell has the advantage of easy cleaning without using a soot door.
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Post by stefanvh on Apr 26, 2019 7:41:29 GMT -8
I made a drawing of the complete system: imgur.com/a/auf9yvAwww.dropbox.com/s/bcwc42pymq505mo/Bell.skpThe ISA of the Bell is approx 7 m² and the distance between exhaust and top of the bell 30 cm. I am planning to use a metal plate as top of the Bell. This would make it a lot easier to close it at the top and the idea is that it will be warm enough to keep a pan of soup warm for example. I can't really find any other builds that do this, but people also build cook stoves with metal plates as top so I'd think it should be possible (as in, the stove would function properly). I'm not entirely sure yet where the exhaust is in the ceiling compared to the location of the bell so that might change. If possible I'll keep the pipe outside of the bell, if not I'll make sure to insulate it properly.
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Post by peterberg on Apr 27, 2019 0:39:04 GMT -8
Looks much better now. Remarks: shortest distance from the port's corner to the side of the channel stub is 49 mm in your drawing. This distance should be half of the port's width, in this case 35 mm. I moved around a bit with parts: the forward corner of the channel stub should be 14 mm away from the rear wall's face as a consequence. I'll do a picture to clarify. Another remark: beneath the firebox there's a massive block of bricks, not very useful there. This could be a steel pedestal or brick pillars, say three or four with some sidewalk pavers on top. A steel plate on top isn't a good idea, it'll warp like mad. A steel frame and the glass top plate of an induction cooker is a much better option. Or dividing the frame in squares, each square holding a 6 mm steel plate on a superwool gasket so all squares are able to expand freely.
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