|
Post by insight on Aug 28, 2015 11:20:35 GMT -8
I have a question about the duct work in the mass. I have plans for building a rocket mass heater with 6" pipe to heat a 900 sq ft space. Would there be an advantage of modifying the plans using 8" pipe vs 6" pipe to heat 1200 sq ft.
|
|
|
Post by wiscojames on Aug 28, 2015 11:39:58 GMT -8
It's my understanding that duct size in a flue style mass heater (as opposed to one that uses bells) will always correspond to your system size. If you change one, you must change the other so that the dimensions match.
|
|
|
Post by satamax on Aug 29, 2015 1:42:46 GMT -8
Wiscojames, not necessarily, tho, for 1200sqft, an eight incher would be better i think. Or a batch.
Having a 6 incher, with an 8 pipe behind slows down the gas circulation in the bench, giving more time to the gases to exchange their heat with the surounding mass. It works a bit more like a bell. Mind you, i would put a 6inch chimney after that 8 inch pipe to increase the upward speed of the gases in the chimney. And If one would like to use this type of architecture, he must be carefull not to cool his gases too much. Otherwise, the system will stall.
|
|
|
Post by insight on Aug 30, 2015 9:37:35 GMT -8
Thanks for the feedback. I need to research "the bell" is there a good thread on it? I think I saw it on one of Donkey's videos when he converted his indoor setup from J-tube to batch box and showed the end of the bench mass and there was a barrel placed there. What would I be looking at in being careful? Would that be too much length in the flue ,that is encased in the mass? Thus effecting the draft. Is there a specific ratio of length of flue related to the riser dimensions? Still reading and comprehending the separate aspects of this beast.
|
|
|
Post by satamax on Aug 30, 2015 11:08:05 GMT -8
|
|
|
Post by insight on Sept 8, 2015 9:26:38 GMT -8
thanks for the link ironically I was reading another article of his when I looked up your reply to this... so is the normal 55 gal drum (Heat Riser container) on a RMH, in essence a bell and also a bell can or is sometimes put in line with the flue that is going through the mass? Same principle, just one is experiencing extreme heat and the other the cooling flue gases.
|
|
|
Post by satamax on Sept 8, 2015 18:42:39 GMT -8
Insight, the barrel is, usualy, not a bell.
But a downdraft channel. Basicaly, it's intake is at the end of the heat riser, so on top. And it's volume isn't big enough for the hot gases to stagnate atop of the container, and slowly cool down, then drop down and exit through the flue.
A bell's footprint has to be at least 4 times system's cross sectional area to start to behave as one. Much bigger is preffered. Up to the point where you hit the dew point, because it's exchange surface is soo big that it cools down the hot gases more than few degrees above ambient, and the whole system stalls. Gases are not hot enough anymore to rise due to convection.
That point is verry tricky to reach, as it changes from summer to winter, with the gases moisture content. With the bell's temperature at a given, moment etc.
|
|
azor
New Member
,tweaking the build
Posts: 7
|
Post by azor on Sept 13, 2015 8:19:32 GMT -8
Thanks for the breakdown. details at every turn of these heaters. The more I learn, the more questions I have.
|
|