grga
Junior Member
Posts: 76 
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Post by grga on Aug 25, 2017 0:51:54 GMT -8
After several test builds I would start to build a real heater in my living room, hopefully to use it this winter. It will be placed in the middle of the house where I have original chimney inlet at 1.8m height and I made additional inlet at 0.2m height.  my idea for the heater is to use 18 cm cast batchbox and a bell and bench witch together having 7.6m2 ISA.  Next step will be more detailed drawing and casting the 18cm batch box. I would appreciate a comment or your experiences: - do I need a bypass? The inlet at 1.8 height is a bit to high to us it for bypass and I do not like to mahe additional chimney in the bell. So I am thinking to simplify and to close this inlet and use only the lower one. House have good and straight 20 cm chimney with at least 7.5m height. With test builds in the past I did not have smoke back problems. Peter what is your experience with casted bell system you have, do you miss bypass? - any suggestion about the design |
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Post by Dan (Upstate NY, USA) on Aug 25, 2017 1:02:59 GMT -8
What is the wall made of, wood or masonry?
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Post by Jura on Aug 25, 2017 5:46:00 GMT -8
.... - do I need a bypass? The inlet at 1.8 height is a bit to high to us it for bypass and I do not like to mahe additional chimney in the bell. So I am thinking to simplify and to close this inlet and use only the lower one. House have good and straight 20 cm chimney with at least 7.5m height. With test builds in the past I did not have smoke back problems. Peter what is your experience with casted bell system you have, do you miss bypass? I questioned few ppl and the answer was "go for the bypass". Lastly I contacted josephcrawley as he had pretty similar build to the one we are to build and he confirmed a need of bypass. donkey32.proboards.com/post/19396/thread I'm also having a 20 cm chimney stack inlet @ 1,8 m high and I'm going to use it for mounting the bypass. Maybe it will be ready after this weekend so I'll be able to post some photos. - What's your bench width? - will it be blind? or channelled? |
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grga
Junior Member
Posts: 76
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Post by grga on Aug 25, 2017 11:56:55 GMT -8
What is the wall made of, wood or masonry? It is made from modular bricks. |
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grga
Junior Member
Posts: 76
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Post by grga on Aug 25, 2017 12:12:31 GMT -8
... I'm also having a 20 cm chimney stack inlet @ 1,8 m high and I'm going to use it for mounting the bypass. Maybe it will be ready after this weekend so I'll be able to post some photos. Thanks for this info. Images are very welcome. At what height will your bypass be, probably not at 1.8m - this is quite high I guess? Bench will be 75cm wide with 60 cm height and cca 1m long. It will be blind, with no channels. |
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Post by Jura on Aug 28, 2017 6:31:37 GMT -8
At what height will your bypass be, probably not at 1.8m - this is quite high I guess? well .. the inlet had been installed at that height (not by me, of course)as most of systemic chimneys assembled have it at this height as a standard fire box is the default heat source supposed to be connected to it. I did not want to drill another hole it the chimney so I decided to use the existing one. It adds some complexity to the construction as the short-way bypass damper valve must be shored up by some pillars. But I needed to add some extra surface to reach the desired ISA, so it was ok for me. |
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grga
Junior Member
Posts: 76
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Post by grga on Aug 30, 2017 2:24:26 GMT -8
I have made the casting. It looks fine however some more air bubbles appear on the surface of the cast. I filled them later with fine concrete mix. I did not manage to vibrate it good enough as in my previous test. I should have add a bit more water (more than recommended) or vibrate it longer. I hope that those bubbles are only on the surface, where is bigger friction with the mould. I guess that some air bubbles (if present) in the concrete would not harm (cracking due to thermal expansion) - probably they only lower compressive strength which is not so important for my case. Do you agree? What do you think is better: -Using mix with minimum water and run in the risk that there will be some air holes still left -or use a bit more water and get rid of most of air bubbles in the cast. In both cases the core is fully dried to enable not reacted water to evaporate from the concrete. Important is that the core is now fully dried before the first use. The mould (made from EPS) is still usable for another casting or two so I could make another one. And some images:    |
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Post by peterberg on Aug 30, 2017 7:26:18 GMT -8
Congrats, you are one of those people who aren't only talking about building one but you did! The core looks very good to me, what size is a large air bubble in your casting?
More water than the recommended amount could weaken the cast, I would accept holes provided those aren't huge. Compressive strength isn't important, uniformly heating up is. I am curious how your castings will behave, uptil now I have only mine at home as reference.
In case I forget later: try to fix the riser-to-be in place, otherwise it could wander off due to the repeated heating/cooling cycle.
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grga
Junior Member
Posts: 76
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Post by grga on Aug 30, 2017 11:46:02 GMT -8
Congrats, you are one of those people who aren't only talking about building one but you did! The core looks very good to me, what size is a large air bubble in your casting? More water than the recommended amount could weaken the cast, I would accept holes provided those aren't huge. Compressive strength isn't important, uniformly heating up is. I am curious how your castings will behave, uptil now I have only mine at home as reference. In case I forget later: try to fix the riser-to-be in place, otherwise it could wander off due to the repeated heating/cooling cycle. Thank you for comments. The largest holes were up to 3 mm. Otherwise I have also 12 cm cast (also from 3 parts) which is stable now, at the first two fires a few cracks appeared but now after more than 50 runs is the same. I will think something to fix the riser. I will probably use chimney tubes from schiedel with some isolation around, maybe CAC concrete with vermiculite. I would also like your opinion on bypass - you don't have it in your red casted heater. Do you experience any problems when starting the fire? |
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Post by peterberg on Aug 30, 2017 12:18:41 GMT -8
I would also like your opinion on bypass - you don't have it in your red casted heater. Do you experience any problems when starting the fire? Originally I had problems starting the thing from stone cold, yes. A moderate warm start won't pose problems anymore since in the very first month the bell is tuned down from 6 m² ISA to 5.4 m². I view a bypass as an unnecessary stop-gap to fix an untidy design. "Yes, we know the bell is too large or the exhaust isn't good enough but we'll compensate for that with a bypass." I prefer to do it in such a way the thing will work 99.9% of the time without cutting corners. A bypass is adding complexity, I can live with 1 time back smoking out of 1000 burns which would be once in 5.5 years if I recall correctly. |
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Post by satamax on Aug 30, 2017 21:56:56 GMT -8
Peter, i should say, i don't agree.
A bypass permits to have a bigger bell, at the cost of more complexity. But efficiency wise, a bigger bell also permits to extract more heat. I view it as a tool.
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Post by peterberg on Aug 31, 2017 0:51:59 GMT -8
At the risk of starting a discussion which is quite off-topic: it's an open question whether or not a bypass coupled to a bigger bell is better efficiency-wise. The first part (probably a third time-wise) of the burn is quite the opposite of efficient, most of the produced heat is going through the chimney and out the window so to speak. The crux in such a system is the point where one would close the bypass, be it gradually or not. My point is that people tend to get sloppy after some (maybe two?) burning seasons and there's the tendency to close the bypass too late, efficiency-wise, so the heater won't need any attention during the rest of the burn. There's a trade-off between ease of use, highest efficiency and quality of combustion. With a large bell the bypass need to be open until the exhaust temperature is high enough (200º C?) in order to compensate for the larger bell.
In contrast, my heater doesn't pose such a need for decisions, it works just by itself. When lit I close the door, open the inlet valve and let it go, and after some 45 minutes I'll have a look at it whether it is time to close the thing shut. In the mean time the exit temperature (when started warm) won't rise above 110º C even in the depth of winter. In the shoulder seasons it wouldn't rise above 80º C because of less accumulated heat before starting again.
It remains an open question whether or not a large bell/bypass combination would be more efficient than a simpler but better tuned system. What I have now is hard to beat on efficiency and it's on a par with the highest efficiency test runs the MHA have achieved in ten years or so. We have proof what such a system can achieve without the human factor and nothing about the one you are a firm proponent of.
Maybe it would be an idea to test your heater one day? It looks like I will be on Mallorca begin November for a week, for one of the (admittendly very few) workshops I agree to conduct. I could easily fly to Turin from there, don't you think?
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Post by satamax on Aug 31, 2017 12:01:43 GMT -8
Peter, i know what you mean. My situation, and i think the situation of people further north of you is quite different. As in, you need the very last joules you can gather. I bet with your passive house. Your heater is perfectly tuned. But in a sub optimal house. I feel the urge to have heat to spare. If you sense what i have in mind. I would be leaning towards a system with two separate bell, that you store heat in the second one, after the first one is charged. Yep, come over, i'll pick you up in turin no prob.
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grga
Junior Member
Posts: 76
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Post by grga on Sept 2, 2017 7:40:57 GMT -8
Stared with drawing 3d model and already hit several challenges that need to be solved. I have fresh air intake in the floor which I want to use, so the door and its valve need to designed to support it. After several versions I come with the following: drawing of the heater with fresh air intake from the floor, chimney  with batch box which has metal box with air intake and valve  and with the doors, main and for the box bellow the core. This box can also serve for ash drawer.  and a link to draft 3D model herethoughts: - Do you see any problems with the design - fresh air intake and control valve idea - door design is borrowed, I like as it seems simple to make. Even better would be if it has a channel to put sealing rope in it. Now the rope has to be glued to the door- is this a problem? - chimney inlet is near the floor. The one above could be used for bypass but since it is quite high and brings another complication I am thinking just to eliminate it. the chimney has good draft so it should work without it. Other possibility would be to make other bypass to close the bench from the main bell - this would also improve cold start problems? - I draw only one cleaning hole at the end of the heater (behind the bench, visible in the model). Should I put another one? |
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Post by Jura on Sept 3, 2017 1:47:29 GMT -8
...- Do you see any problems with the design - fresh air intake and control valve idea I dont know how much of guidance it will be but i'm posting images of the air entry valve throttle we used in my last project. (we added some silicone seal and strengthened the weld bonding between the throttle pivot and the "feathers" (couldn't find the proper tech eng name for it)) In fact I was against applying it in this particular place but a friend of mine insisted on having it installed so ..   |
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