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Post by amitos on Aug 2, 2013 20:06:15 GMT -8
Hello Peter and other moderators and users of this great forum. Myself and my partner have been building Rocket mass Heaters in Israel since last november. We have been building the J core so far, experimenting with different measurments and building materials. In the last two weeks we have discovered the wonder of the batch-box design and we are very interested in getting in to it and to be able to build this core in clients' houses. We have built an experimental 8" batch-box core using the P.B. Batch-box measurments and so far it appears to work quite well. The only thing we haven't done in this core is the P-channel because there are certain things we don't understand about that:
What is the distance between the back wall of the box and the P-channel vertical part? we see in the pictures that it is situated right before the entrance to the port, is it touching the back wall of the box and thus blocking some of the upper c.s.a of the port? I assume that not, but again what should be the distance there in this case?
What should be the length of the vertical channel from the ceiling of the box to the end of the P-channel?
Do you have any idea how we can add the P-channel without needing to replace it eventualy when the metal is starting to get extinguished?
Another question: What is the minimum distance between the top of the riser and the barrel? I know there are various opinions about this issue- I will be pleased to read as many.
Many thanks for all the generous help and info in this forum best regards Amit and Adiel
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Post by peterberg on Aug 3, 2013 1:32:14 GMT -8
What is the distance between the back wall of the box and the P-channel vertical part? we see in the pictures that it is situated right before the entrance to the port, is it touching the back wall of the box and thus blocking some of the upper c.s.a of the port? I assume that not, but again what should be the distance there in this case. Oh dear. A lot of people seem to have difficulties with the position and shape of the p-channel. The channel is resting with its backside against the back wall of the firebox. And as such, it is blocking a small part of the upper c.s.a. of the port, yes. What should be the length of the vertical channel from the ceiling of the box to the end of the P-channel? To answer this, you have to calculate the size of the channel first. It is a rectangle steel duct, the width the same as the port. The thickness can be calculated as follows: 5% of the riser c.s.a., divided by the width of the duct. The length of the vertical channel inside the firebox is the distance from the firebox ceiling to the upper edge of the port plus the depth of the channel. This may seem odd, but you have to shorten the backside of the channel in such a way that it is aligned with the upper edge, or ceiling, of the port. This way, a small under pressure is created just behind the front side of the channel. The net effect will be a sucking force inside the channel. I've tried about a dozen channels, this happened to be the best layout according to the Testo analizer. Do you have any idea how we can add the P-channel without needing to replace it eventualy when the metal is starting to get extinguished? Funny enough, it won't burn out for years to come. This channel happened to be air cooled, you know. When you want to be absolutely sure, use stainless steel instead. Another question: What is the minimum distance between the top of the riser and the barrel? I know there are various opinions about this issue- I will be pleased to read as many. I do think there shouldn't be any restriction above the riser of a batch box heater, or as small as one can achieve. But I know this: 10 cm seemed to yield sub-optimal results, from 30 cm and up the numbers didn't change. To resume: probably it will work with smaller top gaps, but the larger ones are definitely better. The lenth of the riser isn't that critical, however, so you could choose to make that 8 times the base dimension instead of 10. There's still room to play. Mind you, the above isn't a statement regarding rocket mass heaters Evans' style.
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Post by amitos on Aug 3, 2013 7:56:16 GMT -8
Hello again and thank you for the swift response. Everything is much much clearer now and I'm looking forward to making another experiment with the new understanding. I appreciate so much your sharing of information- great inspiration. warm regards from Israel
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Post by bernardbon on Aug 3, 2013 10:04:05 GMT -8
Amitos,
There are several 3D simulations (Sketchup) on this forum, it facilitates understanding.
Bernard,
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adiel
Junior Member
Posts: 119
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Post by adiel on Aug 9, 2013 7:41:34 GMT -8
dear all these are three videos we took last night - www.youtube.com/watch?v=OaEKN5y3R5Iwww.youtube.com/watch?v=yeBkWt5MPO8www.youtube.com/watch?v=8GA5DQHOzSgthey all documenting our first exiting attempt to make a batch box. walls from fire bricks. ceiling from 4 cm vermiculight board. heat riser is clay perlight. it was smoky for about 40 minutes. once the box was hot it got much cleaner.even with little wood. but not 100%. of course we don't have peter berg's test equipment but we smell. we are trying to build systems that will heat a bench. wood is rare here so we we try to understand how efficient it is. we look for a system that can save 70% of the wood compering to a regular heater. we felt the j rmh can do that. also ash. we wonder what to expect with the batch box. people say that in the j system they get no ash. we didn't see that at all. here after 4 hours we got two handfuls of ash and half where coals. next time - a p channel. and walls from 4 cm vermiculight board with fire bricks cement as coating. amitos is going away for two weeks so till next attempt lots of time to think. thanks!!
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Post by peterberg on Aug 10, 2013 6:36:46 GMT -8
Adiel,
I've seen the videos. The only air intake is the one low in the door, probably there are some leaks around the door perimeter. This isn't adequate air supply, you need the p-channel, badly. For reference, main air intake should be something like 20% of the riser cross section area, p-channel 5%, totalling up to 25%. When you want to run it without p-channel, allow some air through the top of the door and don't load the firebox higher than the port.
The port seems to be there according to specification, but the sloped sides aren't there. They should be there, otherwise the glowing charcoal will form a too wide bed. Those sloped sides are calculated into the specification so your firebox is slightly too wide and high now.
What the videos won't show: what shape of the riser is, round, octagonal or square for example. Round is the best shape, octagonal is a close approximation to round. The height of the riser above the firebox isn't shown or mentioned as well. When up to temperature, the fuel shouldn't be arranged in a criss-cross fashion but lengthwise only. And, this is important, there shouldn't be any piece of wood sticking in the port, at all. When it does, the stove will smoke like mad.
At some point in the 2nd video the stove is making a rapid pulsating noise. This is to be regarded as a good sign although a little bit scaring at first. How much room is above the riser inside the barrel? Somewhere you say the stove is still not smokeless, that could be due to the barrel not being clean. When oil has been in there it has to burn off, the same goes for a coating inside the barrel.
The specifications of this design are tight: you can't leave something out or change it at will. Everything has to be there in the right proportions and shape, in that case only it will do what it says on the tin.
About the proposed bench: the pipes are there but completely bare at the moment. In this situation these pipes will dissect lots of heat, much more than when imbedded in cob. So for test purposes these ducts should be shorter, let's say half of the projected bench length.
Feel free to ask anything about this design, I will answer to the best of my abilities.
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Post by amitos on Sept 1, 2013 6:43:20 GMT -8
Hello to all. A question for peter: In your first replay here in this thread you suggested to reduce riser length to 8*B. Is this good only if I make riser/top of barrel gap 30+ cm or do you think this is an option in any case? Thanks for the help and regards amitos
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Post by peterberg on Sept 1, 2013 11:01:08 GMT -8
Yes, the riser height isn't that critical, so you could choose anything between 8*B and 10*B. The top gap between riser and barrel can be made too small, yes, but actually not too large. The final prototype do run very healthy using a top "gap" of over 3 foot.
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Post by amitos on Sept 23, 2013 20:34:12 GMT -8
A general question: In terms of efficiency\cleaness\wood consumption, can you make a clear distinction between J-core and batch-box? Is one of them segnificantly more efficient? I'm asking this in relation to peter's developments- the dragon heater J-design and the most up-to-date batch box design. Thanks and regards Amit
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Post by peterberg on Sept 24, 2013 1:39:30 GMT -8
In terms of efficiency\cleaness\wood consumption, can you make a clear distinction between J-core and batch-box? Is one of them segnificantly more efficient? I'm asking this in relation to peter's developments- the dragon heater J-design and the most up-to-date batch box design. In broader terms, the batch box is cleaner burning with a higher efficiency as compared to the J-tube by-the-book. The batch box do yield a higher power level but do consume more fuel accordingly. On the other hand, it do need a higher gas velocity and a higher chimney temperature. It's like a race horse, fast but nervous. The optimized dragon heater J-tube version is even better in efficiency/cleaness than the other two and also more reliable. All those differences aren't overly large, so if you ask me "is there a clear distinction?", I have to make several side notes to answer that. All the above is based on what I have found in my workshop, using my equipment. Other circumstances could yield different results I would say.
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Post by amitos on Nov 12, 2013 20:39:15 GMT -8
Here are a couple of essential questions that came up during our recent work with batch-box rocket mass heaters: 1. Our manifold seats well below the level of the floor of the firebox, so the heat and gases need to travel down below their initial level of production, also traveling the horizontal part of the flue at least partially below the level of the firebox floor. further down the system they exit the house through the roof well above, naturally. Do you think this can cause any problems regarding draft and correct functioning of the batch-box core? We ask this simply because we don't have enough experience with this core and we don't know what to expect so much. 2. So far we've been using pipes in the same diameter of the riser for the flue, but we're starting to get the strong impression (also from what we've heard rom your experience) that the batch-box needs a wider stream profile in the flue part, so we've used a bit bigger pipes in the last two systems we've built. Now the next thing we want to try is to stop using the metal pipes and try to build the flue rom bricks, creating a flue that has a square/rectangular profile. Do you have any experience with this? What would be the suggested CSA for such a duct in proportion to the riser? Do you have any coclusions and rules about the length and shape of such a duct? Thanks or the great help regards from Israel.... Amit
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Post by Rinchen on Nov 13, 2013 1:32:07 GMT -8
Hi,
I'll try to answer your questions from my own experience. 1) My system also has a pipe that is lower than the opening of the firebox (feedtube before), but this is not a problem as long as you have a proper chimney that provides enough draft. In my particular setup I know that 104F (40C) is the critical temperature level at the base of the chimney. When this temperature is reached there is no risk of stalling anymore and the systems starts to pick up speed quickly. I find that 176F (80C) is a good operating temperature at the minimum, but 212F (100C) is better in order to prevent condensation of flue gasses in the chimney. With a batchbox I can reach this 212F easily peaking at about 248F (120C) 2) I have had my pipe in the bench slightly larger than system size, but my new riser will be the same as the pipe in the bench. Either can work fine with the pipe being at least the same as the riser. My chimney is actually smaller (6" with 8" bench pipe) which does not seem to be a problem for me. Having a larger size of pipe/flue/channel in your bench is not a problem but you will have to realize that more heat will be extracted so you will have to reduce the length of your bench and perhaps take into account a thicker mass above the channel in order to get comfortable temperatures to sit on. Square or round doesn't matter too much when you are going larger than system size. With equal system size I would say round is preferable in order to reduce drag. My dimensions were: System size: 6.3" (16cm) X 7.1" (18cm) Bench pipe: 8" round Bench lenght: +- 26' (8m) with three 90deg bends before going straight up with a 90deg angle into the chimney. The chimney has a 30deg angle for the last 9' (3m) before exiting the roof.
These parameters worked well for me although it can be a bit finicky to start when outside temperatures are not so low yet.
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Post by pinhead on Nov 13, 2013 8:43:02 GMT -8
As Peter has said, the P-Channel makes a huge difference in both burn efficiency and the overall "personality" of the stove. It will start easier, burn cleaner, draft sooner, and operate more smoothly with a P-Channel of the proper dimensions and placement. The P-Channel is essential in the design. I was amazed how much of a difference it makes.
I like a large top gap. I've got about 30cm top gap, maybe a bit more, and it seems to work well. A smaller gap definitely hindered performance.
One of the important factors in favor of cobbing the bench is it's heat retention, both in terms of room comfort and draft; the warm bench will increase draft during the "coal" stage which will keep the entire system running at a higher temperature. I have a 15cm system with a low-mass bell/bench in my shop.
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Post by amitos on Nov 14, 2013 13:44:37 GMT -8
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Post by Rinchen on Nov 15, 2013 1:12:27 GMT -8
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