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Post by Karl L on Jun 7, 2020 10:10:55 GMT -8
I am constructing a 125mm DSR2 heater with a steel inner bell and dry stacked firebricks for the thermal mass. The problems this heater is trying to address are these:
Heat up a room quickly from cold. Store heat in a thermal mass when the room is hot. Work with a non-ideal chimney (that probably can't be lined), with an unknown flue gas exit temperature requirement to generate sufficient draught. Overcome the risk of cracks in a single skin bell. Flexible/adjustable/experimental design to deal with the many unknowns.
The core will built inside a sheet steel box using Vermiculite board, split fire bricks and SuperWool board.
The primary air system has equivalent CSA to Peter's welded steel tube design, but is constructed differently.
The door is a sliding type, salvaged from a previous experimental stove.
The bell is constructed from welded sheet steel. It will be surrounded on 3 sides with bricks (thermal mass) and open at the front (for radiant heat).
The amount of heat extracted by the bell (and so the flue gas exit temperature) can be varied by adjusting the air gap between the bricks and the steel bell, and also by adjusting the area of the radiant surface. These are both 'build options' - but it should not take very long to do the rebuild because the bricks are dry stacked around the steel bell.
It may also work to close a 'door' over the radiant surface, to reduce the heat into an already-warm room. This might push some of that heat in the the thermal mass instead. This has to be tested.
I will try to load photographs...
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Post by Karl L on Jun 8, 2020 6:21:58 GMT -8
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Post by marcios on Jun 8, 2020 14:38:08 GMT -8
How about a variable blower making the air circulate in the gap? In speed to quickly warm the room, slow or off for heat storing.
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Post by Karl L on Jun 10, 2020 7:25:02 GMT -8
Thanks for the suggestion - but my experience says that warm air is not such a 'nice' form of heat, compared to radiant heat. So the design tries to maximise radiant heat and minimise convective heat.
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Post by coastalrocketeer on Jun 11, 2020 9:43:15 GMT -8
A top that is insulated with rock wool should work to force more heat to come out the sides and could be lifted to expose the radiant surface when fast heat is desired... I’m thinking made of thin sheet metal with rock wool sandwiched between... it could be light enough to be on hinges, or lifted by a cable or light chain?
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Post by coastalrocketeer on Jun 11, 2020 9:45:45 GMT -8
The other think to think about in a bell, is that the top half of the bell absorbs more of the heat energy than the bottom half, due to the thermal stratification.
A brick near the top will absorb more heat energy, reach a higher temp, and stay hot longer than low ones.
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Post by Karl L on Jun 11, 2020 22:47:04 GMT -8
A top that is insulated with rock wool should work to force more heat to come out the sides and could be lifted to expose the radiant surface when fast heat is desired... I’m thinking made of thin sheet metal with rock wool sandwiched between... it could be light enough to be on hinges, or lifted by a cable or light chain? Yes, thanks, I've also been thinking about similar ideas. The rig I've built should allow me to test things like that quite quickly. I've noticed that Aluminium foil is very effective at reflecting radiant heat, and so could be used over some heat resistant board to achieve a similar effect to your idea.
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Post by Karl L on Jun 11, 2020 22:50:12 GMT -8
The other think to think about in a bell, is that the top half of the bell absorbs more of the heat energy than the bottom half, due to the thermal stratification. A brick near the top will absorb more heat energy, reach a higher temp, and stay hot longer than low ones. Are you suggesting a particular distribution of bricks to make use of this?
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Post by ahansen on Jun 12, 2020 2:26:14 GMT -8
i'm not sure i understand but if the heatriser blows very hot air on top there could be some danger if metal is covered. maybe overheating but a 45 degree aluminium foil directing top heat right way out
the air can also circulate up the outsides of metal over top and down through hollow brick wall cool and back up fore distribution combined whit alumium on inside of bricks so all heat is forced more out when "doors" are open
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Post by Karl L on Jun 12, 2020 3:36:29 GMT -8
i'm not sure i understand but if the heatriser blows very hot air on top there could be some danger if metal is covered. maybe overheating but a 45 degree aluminium foil directing top heat right way out the air can also circulate up the outsides of metal over top and down through hollow brick wall cool and back up fore distribution combined whit alumium on inside of bricks so all heat is forced more out when "doors" are open (There isn't a heat rise in the DSR2, but still the hot gases will rise to the top.) Insulating the top isn't a problem, partly because the top surface will radiate heat inside the bell, thus cooling it and warming the other surfaces of the bell. (I've done this a number of times with no problems.) The 45 Deg. Al foil does work -- I've also tried that.
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Post by marcios on Jun 12, 2020 4:44:50 GMT -8
Thanks for the suggestion - but my experience says that warm air is not such a 'nice' form of heat, compared to radiant heat. So the design tries to maximise radiant heat and minimise convective heat. I also prefer radiant heat much more. Fortunately you may not need it, but in my similar project I don't know how to extract heat for silica gel dehumidification system without a blower.
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Post by Orange on Jun 15, 2020 10:04:43 GMT -8
how large is the space that needs heat, 125mm sounds weak?
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Post by Karl L on Jun 15, 2020 23:56:32 GMT -8
how large is the space that needs heat, 125mm sounds weak? 125mm is 5", which is the size Peter first used to develop the DSR2 concept. The space is a large room 6m x 4m x 2.5m (20' x 13' x 8'). I've already used a (very rough) experimental rig with 100mm (4") riser size, coupled to an oversized firebox, suitable for a 125mm system. There was no thermal mass, just a steel bell. It was easily powerful enough! I'm not going to use a lot of thermal mass -- all I need is enough to stop the heater overheating the room. I also found that the room itself stores a lot of heat when that heat is radiant, and the charcoal phase of the burn 'tops up' the heat over a long time.
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Post by Orange on Jun 21, 2020 0:59:33 GMT -8
that's interesting, since BB calculator says you'd need 165mm system. But I don't know what's your climate, inslation etc.
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Post by Karl L on Jun 21, 2020 10:21:41 GMT -8
Thanks, yes, I took a look at that calculator at some point.
There are several factors that mean I don't need so much heat on average: We don't get very cold winters here, usually. I sleep in this room, and like it not as warm at night (hence the low-ish themal mass) The room has several internal walls and a ceiling, to rooms which are heated by other sources. I don't mind lighting extra fires if necessary.
(Re. the calculator, I thought it odd that the heat requirement is calcuated from the volume of the house (or room), rather than it's area.)
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