Here are my average temperatures for the outside of the system reading after about a 3 hour burn. takes more like an hour to reach these if the system warm. They do stay constant during the main burn, but very soon after I am left with mostly and only burning embers the whole system cools down about 20%+ in lets say about 20 minutes. Unless I fill the feed up again immediately. If I do not want to feed it I lets them burn out and then close my "damper" to the chimney I have fabricated. I feel I am loosing too much to my chimney.
My main concern is the orange rectangle on my picture. Where it seems like my inlet and outlets are "jumping" a bit. There is clear evidence that the bells are doing there jobs. I just figure my exhaust has to be as a high about 400ish in order to be keeping my exit to my chimney hotter than the rest of the system and except for above the riser top piece. So I wonder about my ISA? so this is what I did....
MY ISA MAX POSSIBLE
(14.75+14.75)x12x2 plus (15+13.5)x24x2 pluS (19+11.5)x36x2
plus 14.75x14.75 plus 15x13.5 plus 19x11.5
L x W x H [INCHES]
Riser Bell: 14.75 * 14.75 * 12 708+217
"Large" Bell 15 * 13.5 * 23 1344+202
"small" bell 19 * 11.5 * 36 2196+218
= 4885 square inches = 3.2 meters squared
These are numbers for taking my bell ISA calculation. This means that in order to see if my bells are not too big or small I measured the ISA above all inlets and outlets. So bear in mind there probably about another 1+ square meters of surface area possible. The reason I don't count the "falling" surface area at this point is because from what I understand "falling zones" mostly create draft because of gravity. And I will mention that my draft seems to be moving quite well. It sounds like a rocket!
Anyway my first idea was to add another section on top of the smaller bell raising it up to the height of the "big" bell. also adding in a vertical section of brick to direct the gasses up first in order to bypass the pulling outlet draft a bit hopefully encouraging it to go up into the bell first. My ISA calculation for the bell system with that add-on is about 4 meters squared possible a hair larger. According to Santamax advice.. 4 meters squared is a max size for a 6" system. So I would be in compliance with that ISA rule if it were set it stone, lol. Also i would be effectively raising the inlet/outlet height of that bell with that vertically placed brick so actually my ISA might be a bit lower than 4 meters squared. Possibly 3.9ish.
My question is for my direction of knowledge application. I am adjusting the ISA of the whole system as well as increase bell size to attempt a capture of more heat and eliminate the exhaust temp from being too high. Can I do that. Can I keep on making the ISA bigger? At least until my exit temps would get too low if went bigger, or if I figured I'd start to loose draft? Basically the concept in mind is that ISA is possibly a calculation that could be used to determine a MAX size, and that this "MAX" number can be figure also by how much heat the surfaces are actually "grabbing" So within reason I figure the hotter my exit temps are the more I can be encouraged to increase my ISA in order to keep more heat. So this is clearly for iffeciency purposes in mind of course. Please weigh in if you can/want.
..all from my first thread about this heater. at... http://www.permies.com/t/38963/rocket-stoves/Rocket-Mass-Heater-Basement .. if you want to refer to.
I'd really appreciate any great advice from any of you guys if you have the time. You guys were a great help in my other post"..
Erica Wisner wrote:Include the surface area of the bell or barrel directly over the heat riser, as well as the other bell(s) on the side.
Satamax Antone wrote:Matthew, to me there's plenty of details i'm not too keen on.
allen lumley wrote:..for the Craft ! Big AL
Peter van den Berg wrote:
Yes, my full name is Peter van den Berg or PvdB for short.
The top of your exhaust flue seems to be higher than the inlet into this bell! I bet that's bypassing. Furthermore, you're near the 4X CSA reccomendation by Peter. May be you have 5 or 6 times. I don't know, but that stays a small bell.
First thing i would do, is put a brick lip at the bottom of the inlet, so the gasses don't sweep the floor of the bell. And by butting into that lip, cooler gasses would kick the hotter ones a smidge further up, sending thoses in the right direction. After, if it keeps bypassing, build a little wall between inlet and exhaust flue. Accross the flue element, so you have equal csa on each side. May be the height of one flue element.
I think, if your chimney is drafty, build that bell up.
3.2m² seems all right, but myself, i wouldn't account the riser's radiator as a bell. Because the gases sweep and mix in there; they don't stratificate. So they don't exchange heat as well as in a real bell. Plus, your clay flue liners are a smidge more insulative than a barrel, so, they don't shed as much heat, leaving more to be gathered afterwards. So i'd say, don't worry about raising the height of your last bell. Even more when it's confirmed by your temps readings.
What is the size of your system? The maximum ISA you could feed depends on that. Run the stove with the separation in place and do the measuring again, there should be a markedly difference.
Peter van den Berg wrote:What is the size of your system?
My cross sectional measure is a hair less than 30 inches squared. So a 6" J-tube is what i have basically. Also btw if you take those max temps i have listed and add 50 degrees to them is more like what i am getting after a 3-4 burn these days. We are getting better at feeding the beast. i plan to add another section to the top of the second bell as well as add that divider plate in order to stop the bypassing. My thought at this point along with what you and max are saying is i could almost go even bigger than my current plan possibly. I am getting a lot of heat. I really need to save it. It seems from the temps i am seeing that i could be extracting about 2x the heat into my house and effectively half my wood usage. Which isn't too much at this point already. I'm thinking i am halving what most conventional fire boxes use.
What do you guys think about my total mass. As it is right now i seem to get heat coming off this thing for about 8hours after a good burn. Id like to make that at least 12 or more if possible. I was thinking added plaster to the outside of the bells to add mass as well as my earlier plans for improving heat capture. I just think i am going to need something more to really achieve max efficiency. Let me know what ya think.
I guess what has really got me thinking is that my exhaust temp(450ish) are about double or more i presume than i really want in order to not be wasting heat out my chimney. I do plan to get a thermometer to stab into my exhaust flue to see where my gases are at for sure. so in theory if i can half that number i will effectively be doubling my total efficiency? So to do this will increasing my ISA even more than my plan as described earlier help be achieve this efficiency, or should i stick with the "plan" for now? I will for sure be doing those simple adjustments as described and confirmed by you and max. I just get the gut feeling i may need more adjusting again. although doing the simple additions first and then test maybe the best option for now. I just need to know how you guys are feeling about the situation. I trust you have a bit more experience in making modifications to builds on a similar level and what i would like to do. Please correct my logic if way off. Thanks a ton guys!!!
I'm pretty sure you can raise that second tower bell. I like thoses, because when you close the feed, when your burn is finished; they hold heat for a while by themself.
As for adding some mass, i would cast clay or whatever around the back bell, that's for sure. May be something like stove veneer like Cyndy and Sandy's "castle build
http://www.permies.com/forums/posts/list/28501#223088 and http://blog.dragonheaters.com/category/dragon-notes/6-dragon-burner-masonry-heater-with-flues/
Or building bricks on their edge. I quite like the looks of this one before being plastered. http://batchrocket.hostoi.com/html/foto.html
You can't do the system Peter used on the 8 batchbox thingy! http://www.permies.com/t/40007/rocket-stoves/Results-batch-box-thingy-Innovators picture #10
Nor Dragonheaters's derrick. http://www.permies.com/t/29772/rocket-stoves/Rocket-Masonry-Heater-Quick-Build
Hope this all gives you ideas. But your realy can't do the bricks inside, as it will reduce you 4xCSA required!
Peter van den Berg wrote: The second bell won't be as hot so this is not as good efficiency wise.
My 2nd bell is constructed of two 13x13 clay liners cut off on each end then the two are sandwiched together effectively making them about 20.5x13. They have thinner walls(about .625 inches max) than the 1st bells flues. Which are 20x24's and have about 1.5 inches thick walls, and then lined inside with about 18x15 clay liners which are about 1.325 inches thick(reference my ISA calculation above). The first bell seems to stay cooler than the second during the burn because there is a lot more mass. the 2nd bell's thinner walls seems to "gather and release" heat faster during and after the burn. the 2nd bell has quite a bit larger internal ISA than the first. so this also may contribute to the fact that the 2nd bells runs a bit hotter realtime(during burn time)... even though it is clearly having bypassing issues.
after the burn however in about an hour the outside of the first bell gets a bit hotter and then proceeds to stay a lot hotter as the 2nd bell cools. So i can see why adding mass to the first bell would be an obvious good idea because it does seems to gather a lot of raw heat and releases slowly. also the 1st bell is more of the heart(center) of the unit, and does come into contact with a hottest blast of heat coming off directly from the riser flue. however the 2nd bells hotter heat up and release during the burn tells me a bit more mass on that may be beneficial too. although i really do like the more instant heat it puts off and seems to have the capacity for a lot of heat(it has got to almost 270 degrees F!), so there may be a middle ground to find. also i would like to add that my wife yesterday while i was at work got the top of the riser flue to 570 degrees F!! Is a record so far, but we haven't done more than about 5-7 hours of constant burn yet. given this information how how do you think i should proceed?