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Post by rakettimuurari on Dec 22, 2017 11:50:27 GMT -8
Very nice testing rakettimuurari ! Were the temperatures of the heater equal at the initial time, right before the two firings ? regards, You have excellent point there concerning the transparency of the test procedure Should have measured & reported those too. Nevertheless, both tests were conducted exactly 24hrs after previous full batch burn in very similar circumstances. Most telling part for damper open case for me is the 1) asymmetrical cooling of the heater and 2) some certain spots closer the fire bath, which give almost identical numbers with previous test; first resulting from the cooling air flow and second indicating that initial temps must have been somewhat the same. I am prone to think that asymmetrical cooling most likely also indicates that bell effect here might not be fully in operation due the cramped nature of the bell i made ('cause oven and its supports). On the other hand the stratification should be starting already in the oven, but the height is only 25cm. The exhaust slit is some 2,5 x CSA to help in the slowing the gases but then again the space between oven external ceiling and bell ceiling is some 17 cm. However, asymmetrical placement of the firebox and closing the damper seem to result in very uniform distribution of the heat in the end.
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Post by rakettimuurari on Dec 21, 2017 14:29:26 GMT -8
... For me it also seems that with a bell, the damper closing ASAP is not really so relevant (actually a no-brainer). I will do a temp difference comparison later between open and closed damper with my bell system to see how much difference there really is. Significance of the damper in my bell system Measured the temps outside the heater during 12hrs from highest burn of one full batch (6-7kg's of cord-wood spruce). Outside snowy and 0'C. Difference to first iteration is that chimney damper was left entirely open after the burn in purpose to find out about the usefulness of the damper in a bell system. Air inlets were closed of course. Temp comparison closed vs open damper
** all doors gasketed and quite gas tight, except the ash box door below firebox. That door is nevertheless quite tight too. I am closing my damper in future too.
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Post by rakettimuurari on Dec 21, 2017 14:18:27 GMT -8
can you compare effects of damper vs closing the air inlet? for the oven, you might need some metal or chamotte plate directly above the riser as the baking surface, should get higher temps. Here u go Orange:
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Post by rakettimuurari on Dec 21, 2017 14:14:30 GMT -8
Performance / temp analysis - second iteration - damper comparisonMeasured the temps outside the heater during 12hrs from highest burn of one full batch (6-7kg's of cord-wood spruce). Outside snowy and 0'C. Difference to first iteration is that chimney damper was left entirely open after the burn in purpose to find out about the usefulness of the damper in a bell system. Temp comparison closed vs open damper
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Post by rakettimuurari on Dec 20, 2017 12:55:40 GMT -8
It seems to me that in a properly functioning bell, where gases can thermally stratify, heat will always be retained in the upper bell, regardless the inlet/damper settings. Physics prevents heat escaping up the chimney. This is one of the big advantages of bells. The heat stays trapped in the living space. To put it another way, as soon as the gases coming from the firebox begin to cool (by dilution and/or diminished fuel), those cooler gases should pass through the bottom of the bell to the chimney, leaving the heat in the upper bell undisturbed. Of course this won't apply to a classic rocket with an oil drum and a piped bench, where all the gases are mixed and swept through the system together. There may be other reasons for closing the damper ASAP during coaling, such as retaining heat in the firebox and chimney, which might have some effect on overall efficiency. I find unburned charcoal annoying, so I prefer to let it burn completely, rather than deal with separating it from the ashes. I agree this train of thought with relation to bell theory. In actual use the effect of damper really seems to be almost marginal when compared to systems operating with forced gas movement principle such as contraflows. On the other hand however; chimney damper open and chimney warm + not fully 100% airtight doors etc. the draft is still going on surprisingly strong. In layman terms thinking +23'C air going in the heater and +60'C air escaping to chimney the equation is obvious. I still believe the damper is really helping to minimize the cooling airflow on its part. With contraflows and such the effect of damper is of course more obvious as no stratification has occurred -> gases are warmer 'cause colder and warmer ones are just mixed in one flow so we have much more to lose to chimney. Tomorrow morning I will starve the embers!
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Post by rakettimuurari on Dec 20, 2017 2:52:55 GMT -8
How to shorten the red coal phase is easy: like the Austrians do, close the air inlet and keep the chimney damper open. The coals will die by themselves and there's a coal bed to start the next burn on. If I remember correctly, this will lower the CO production significantly. Good to know that this would be also optimal solution in relation to CO. I got interested in this as I have seen here many ways to handle the embers, which are considered "right". Of course the big difference around here is that Testo has seldom been used. Heat-wise I cannot observe remarkable difference when doing it either way... more air burns coals faster and more completely allowing quicker damper closing. With closed/ decreased inlets the cooling excess air is less but embers die slowly (but still quite soon) and the damper is longer open for safety reasons. When comparing these two ways I have found no difference in heat retention whatsoever... I should measure this too, especially by starving the majority of embers from air just after the flame dies. MHA firing instructions presented on the link's webpage interestingly kind of agree the same except the scenario of embers entirely starved from air is not actually discussed. (Scroll to section "Unwanted embers".) Peter: Would that Austrian coal bed method be also beneficial (or not detrimental at least) for burning in the sense it decreasing the ISA of firebox to be directly heated in the beginning of each burn as the floor is coal/ ash insulated? Maybe thus the firebox achieves hotter temps sooner? I remember you mentioned somewhere earlier that if system is burning well like yours, this method seems not to cause any remarkable ash accumulation as most of the excess coals are burned away during the following burn? For me it also seems that with a bell, the damper closing ASAP is not really so relevant (actually a no-brainer). I will do a temp difference comparison later between open and closed damper with my bell system to see how much difference there really is.
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Post by rakettimuurari on Dec 20, 2017 0:57:05 GMT -8
I have two conclusions about that : - It seems that the threshold of the floor channel is making the red coal phase longer, so the threshold is lowering the global efficiency of the heater. - Our way of measuring the efficiency of a heater is biaised and overestimates by approximately 15% the real global efficiencySo how can we shorten this red coals phase ?
Hello Yasintoda, It seems that optional under-air configuration with cast iron hearth-grid plate helps in that significantly. Cast iron grid will last remarkably long, even with the under-air being closed most of the burn. When flames die, you just close the door air inlet and open the under-air. Embers are done in 15 min. I have been using it for 1,5 months now and am really happy. Marcus Flynn/ Pyromasse seem to have also similar implementation option in his commercial builds. My cast iron cents...
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Post by rakettimuurari on Dec 8, 2017 0:23:57 GMT -8
Hello Antti, I had a thought drop in last night relating to the oven you have... I have been checking my chimney temps more during my burns the last few days and found that they go down rapidly at the end of the flaming part of the burn. I assume that the chimney still draws a similar volume of air through the fire box and oven at this point, compared with the height of the flames and also during the coaling phase. So if my assumption is right it seems that a lot of cooler air is pulled through the oven during the coaling phase which is transferring heat originally captured in the oven and move it into the bell. ... so if there was a by-pass/valve that could let the gasses go through the oven until the end of the flames, and then direct the gasses straight into the bell while the coals are burning out, the oven temps should stay up. Does this make sense? I have not tried it and am not sure how it would be possible to make it. A metal flap would die quite quickly at the end of the heat riser. A brick/split would be tricky to operate from the outside. So my thoughts go to a piece of ceramic glass, but again how to make the design to operate it? Holla Esbjorn, Your thought drop sounds reasonable to me too. I have my first thermometer in the middle of the oven exhaust and I can confirm the same. At climax phase of good full batch burn the thermometer goes all the way tho 400'C (usually 320-370), it will be some 225'C when flames disappear, 175'C when air inlets are closed and 150'C when I close the chimney damper. I think your idea would be of some remedy but lie u write, the implementation is really hard. I have been digging little more around traditional Russian/Finnish baking ovens and there could be something to utilize too. Normally the fire is burned directly in those and after suitable amount of burning wood the embers are swiped (in bread baking scenario) already in the beginning of the coaling phase through the "ember hatch" (located on oven floor) into the separate ember chamber below the oven while still in full glow. Ember Hatch is then immediately closed and so is the damper on the main gas channel/ chimney, effectively fully stopping the gas flow through the oven. Meanwhile the embers will coal all the way in their separate chamber below the oven, which has adjustable air inlet in its main door and a small 3-4 cm separate smoke duct directly to chimney, bypassing the damper. Thus the embers will still add on heat of the mass without the airflow cooling the oven itself. I think this implementation could be also tried in my kind of design with the actual firebox. All what is needed would be a couple of cm diameter hole from the ash box (below the actual firebox) to the lower bell + closable ash hatch in the bottom of the firebox. When the flames disappear, the embers are dropped into the ash box, the separate smoke duct is opened there and all air inlets except the ash box door inlet and ash hatch are closed. I will be probably trying this later. More immediate modification will be a specifically cut baking stone slap of 2-3 cm. I a case of bread baking it will be inserted vertically in the oven before the fire, effectively making a full wall between the back of the oven and the exhaust slot to eliminate the short cut of the gas stream. A system CSA sized slot is cut in it, in the floor level in order to bring the exhaust to meet the oven floor before its exit. When starting to bake, this standing and preheated stone slap is gently lowered on the oven floor to receive bread directly on it. This mod I expect to try in few weeks.
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Post by rakettimuurari on Dec 3, 2017 0:06:07 GMT -8
Definitely interesting! I try to get some translation back up soon for the first link (www.youtube.com/watch?v=vDYJrnulWA0). Youtube's speech-to-text and automatic translation had too much of challenge "Brother is tender at the bottom... why fit, it will change everything...."
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Post by rakettimuurari on Dec 2, 2017 1:57:55 GMT -8
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Post by rakettimuurari on Dec 2, 2017 0:53:07 GMT -8
Performance / temp analysis - first iterationGot my BP21 pyrometer finally. Measured the temps outside the heater during 25hrs from highest burn of one full batch (6-7kg's of cord-wood spruce). Outside snowy and -1'C. House is a wooden blockhouse of 65m 2 from 30's with some modernization of 15cm SPU foam insulation in the ceiling. Walls of the main room are not insulated expect the crevasses between the 30cm diameter wood blocks, wind stopper chipboarding of 1cm thickness, and modern windows. Apart from the BR heating is done with direct electric batteries and DC Converter/ air source heat pump (correct translation?). Room temps are measured in the living room where the BR stands. Original "battery" brick wall just behind the BR probably effects remarkably to the steadiness in room temps as it has gathered heat from weeks of daily heating. It is separated from heater by 1cm rock wool expansion joint. www.dropbox.com/s/4wplcmyx4r7qgzl/Heater%20temps.jpg?dl=0Firing sequence: Lighting from the dead middle of the batch, door open - under-air&secondary air closed 3 min: fire reaches port. Door closed - under-air fully open - window wash 3mm open 10 min: full blaze 61 min: last flames disappear. Window wash closed, under-air decreased. 75 min: couple of embers of fingertip size left on the grid. Under-air closed. 90 min: no glow anywhere - chimney damper closed.
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Post by rakettimuurari on Dec 2, 2017 0:09:44 GMT -8
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Post by rakettimuurari on Dec 2, 2017 0:07:28 GMT -8
titanium filter! ? ! ? Developing to promising direction... I'll be on watch
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Post by rakettimuurari on Nov 29, 2017 23:34:16 GMT -8
perhaps the problem has already been addressed. There may be the problem of ash being introduced by the riser in the oven. This is true, although it is more like a compulsory feature... This year I burn spruce, which produces even more ash so the issue is noticeable indeed. However, in cooking it does not matter as oven is only used after the fire (and airflow) has ceased. When baking bread however, I usually clean the oven with ash vacuum-cleaner before the fire in order to maximize oven's heat absorbing capability (ash acting as insulate). With other cooking I just sweep the floor with moist rag. Any ideas about how to catch the fly ash?
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Post by rakettimuurari on Nov 26, 2017 5:32:51 GMT -8
My heater's ISA is quite large, near 7m 2 because of the oven, which gives me relatively low stack temps; 60'C at hottest when bypass is not employed. I wonder if that combined to narrower than expected chimney stack will cause the need for bigger air inlet... maybe that would also explain why my fire is not too wild despite the below fed air and why the rocket works smoothly? The air inlet opening isn't the only parameter, when you take air velocity into consideration it all makes much more sense. Your end temps are quite low because of the oversized ISA and your chimney is restricted higher up in the stack. What you are looking at is actually air volume, which is fed through an opening with a variable velocity. The higher the stack temperature, the higher the velocity so the volume increases while the speed goes up. In your heater the velocity is restricted in two ways at least, so volume of incoming air isn't terribly high. Off-gassing of the fuel is limited this way, actually you are helping pyrolysis with adding under air. And you are right about the door, when you leave it open just a crack it allows more air in. My heater is at the edge of what's possible without bypass. So I always start the thing with the door ajar and the inlet fully open until the temperature of the stack is above 60º C. The warmer the heater, the quicker the temps are rising, logically. Actually your heater is operating in a too slow fashion,without under air it would probably stall the chimney through condensation. There is one modification which helps in this case: making a small intentional leak between the bell and the chimney stack. In Germany it's called a "raughschlitt", it's always open and warms the chimney in starting phase. In the middle of the burn it's still leaking but the bulk of the gases will take the wider and easier route through the heater's innards. OK. This neatly seems to put it all together. I consider myself lucky then with my design in relation to chimney setback. Performance is really steady currently and I am able to close the door entirely and simultaneously open the under-air hatch/ash-pit door in 2-3 minutes by the lighting, after which there is no need to open the door anymore. My thanks for analysis and for the modification tip. I will experiment that concept with the bypass valve. Tonight will be the raughschlitt night...
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