Post by lella on Mar 5, 2020 4:46:24 GMT -8
Good day, Rocketeers.
Firstly, I want to acknowledge the generosity of all contributors and moderators engaged in this forum, especially that of Peter Van den Berg, and the fantastic fonte of information that he has made available via his Batchbox.eu site.
I live in Italy and having this particular resource, accessibile also in Italian, has made the construction of a RMH possible - well almost, after a few queries posed in this post are resolved.
The RMH project has great interest amongst friends and I will be sharing the information (greatly helped by the newly acquired Italian terminology) and the build experience with them when we hit go.
The design is based on Peter's BBR with Two Benches model - a 200mm/8" system (although this might be overkill. I'll come back to that later...).
I have a number of questions, but my principal concern is the circulation of the stove's gas stream.
My design deviates from Peter's in a number of details.
www.dropbox.com/s/rr0ekx7x3tp9zao/IMG_20200211_122948_191393981316082.jpg?dl=0
Firstly, it is using an existing structure as a bench, namely an old feeding trough/manger (pic) that will have the core and bell chamber built into it. There will be a 4m long heated bench to one side, with internal surface area 550x300 approx, and another 1m non-heated bench that houses the exiting exhaust pipe.
www.dropbox.com/s/zye9qrki02ex7pf/1582556523048.jpg?dl=0
Another is that the walls of the benches, and most likely the outer skin of the bell, will be in stone (not brick as in retouched visual). The rest of the build, that is: the fire-box, riser and the internal skin of bell, will be in refractory brick.
I also intend to build the core on masonry blocks to allow the exhaust stream to flow down, around and (ideally) through to the exit tube, which is currently housed at the end of the right bench, near to the floor (visual). The blocks will also elevate the core level with the floor of the left feed trough, soon-to-be bench, which is 800mm from ground.
www.dropbox.com/s/qtapnoyw9ftv95k/1582906258925.jpg?dl=0
As there is a significant difference in level between the entrance of the left bench and that of the exit tube, I am immagining that the hot exhaust, on leaving the riser, will enter and circulate around the left bench first, and as it cools, cascades downwards to be finally caught by the flue draft tube in the right bench, and taken out.
Or am I wrong?
(The exhaust tube will pass vertically through the bench top, 3m to ceiling, passing through cement floor, to room above, rising another 3m before exiting the roof. We dont anticipate problems due to a lack of draw).
So this brings me to my first concern. Could the scenario be that there is too much draw, causing the exhaust gasses to head to the flue first, bypassing the heating of the left bench completely?
If so, then how could this be rectified? How to direct to the gas stream to the bench first, by restricting flow into the exit tube?
Another feature I would like to include, if it has no negative impact on the stream circulation, is to have the additional function of a small oven above the batch box. OR a simple niche, no door, that will become suffiently hot as to keep a pot of soup on a simmer, hoping a 50mm refractory slab will both act as batch roof and oven (or niche) floor. Will this addition work? The secondary air channel will run along the batchbox floor.
Can anyone see any other flamingly obvious flaws with any aspect of the design?
Another query I have is in the system size.
Is a 200mm system build overkill for a draughty, stone room (5x8x3h) with 3 doors and a stairwell leading to another cold floor?
I am 500m above sea level in the Hyblean hills, SE of Sicily. With winter winds often bringing night time temps to well below zero. I have plenty of dead wood on property, mostly almond, but also olive, fig and carob prunings. Fuel costs arent going to be concern for the immediate future.
And I can always load the stove with less wood, right?
However, a smaller system would be obviously cheaper to build...
I have another set of questions concerning materials.
There's a certain amount of jargon in the description of materials in forums, and Im unsure of what's what, so I need guidance.
Since I cannot find anywhere that deals with any form of recuperated building material, I am having to purchase new. Refractory is expensive and I dont want to mess up.
Could I save money buying two types of differently rated bricks?
For instance, do the 700 or so bricks that make up the internal skin of the bell need to be of the same rating as the core and riser refractory bricks, 1300°C, which I sourced at €1.20 each (110x220x60)?
I have found a much cheaper brick @ .80c, same dimensions but rated for 1000°C, for example.
Might my shopping list look like this?
Refractory brick rated 1300°C, for firebox and riser build. Approx 70
Refractory brick rated 1000°C for bell internal walls. Approx 700
1 Refractory slab 50mm thick rated for core roof.
BB door & frame (plus oven door & frame?) and p-channel built by metalsmith.
Local stone slabs for capping benches.
Local stone for facing external bell walls.
9m of 200mm chimney pipe, approx
3-4 days work from a local builder - who knows alot about pizza ovens but zero rocket experience (and already burnt-out by a million simpleton's questions)
And finally to my last couple of queries.
On the material that will cap/cover the bell, and the material for the leg/blocks on which to build core structure:
I read somewhere that the highest temperature of gases leaving the riser were about 900°C.
Can someone recommend a commonly sourced material that would handle the job? I cannot find refractory material large enough to cap the bell.
Could a thick steel plate, with seal, be used as a cover? Old invection cooker top - if im lucky enough to find one at the right size.
As for lower in the bell, what commonly sourced materials could handle the type of temps found here. I have some AAC blocks leftover from a kitchen build. Are they appropriate for this enviroment?
Please keep any advice as idiot-proof as possible. I am way into alien terrain.
Many thanks in advance.