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Is there such a thing as too much mass?  RSS feed

 
Posts: 5
Location: Mid Michigan
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I'm planning on building  an 8" BRMH this coming season in my shop. I have a daily burn time available of 4-6 hours. (Plenty of BTU's)   I will be following Peter van bergs batch system and applying the CSA dimensions and secondary air tubing. using a single 55gal bell for my sensible heat.  
My primary concern is to keep the mass warm for a long period. 
If 7500# mass  is good then why wouldn't  say 9-10,000# offer a longer radiant heat time?
I have read cover to cover the latest book by that couple ( sorry the book isn't in front of me to thank the writers. BTW its a great book chock full of info.)
I did not see anything in it about over building the mass,  pro or con. can anyone share their thoughts on this? 
Drafting or venting will not be a problem as I have designed in a non intrusive mechanical system located at the building outlet  for if or when its needed.

Dave
 
gardener
Posts: 2581
Location: Upstate NY, zone 5
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"Too much mass" is possible from a practical standpoint; if you have such thick mass that it takes a day for the heat to make its way out, you may not get space warming in time to overcome a cold night. Or the instant heat from a barrel radiator may be gone before the mass heat picks up the load. Of course if you have constant cold weather (cloudy, for example), you can maintain a steady state quite easily.

There is also a related factor in the internal surface area of the mass. There is an optimum ISA which gives full absorption of heat while leaving just enough heat for draft to function. Less, and you waste heat up the chimney (but have stronger draft); more, and you have cold exhaust and possibly weak draft and a non-functional system.
 
gardener
Posts: 2708
Location: Southern alps, on the French side of the french /italian border 5000ft high Southern alpine climate.
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Yep Dave, too much mass is possible.

And as Glenn explained, too thick a mass can be bad.

First question to ask, what volume you need to heat? And how well is it insulated?

On my workshop heater, i wish i could  modify the amount of direct heat to stored heat.

http://donkey32.proboards.com/post/19319/thread

I have 1.9m² of exposed metal approximately the same as a barrel. And after a while, it's too much quick heat. Mind you, with 635 m3 it takes a while to come up from the 9C° i've had lately, to 18C° Tho if it'm around 13/15C° i'm perfectly all right for working.

I think what i would do now, is to have the "barrel"  replaced by a big brick bell, tho, may be not 8 inches thick. It's simple, the bulk of the heat in this case, comes after a good six hours, through the bricks. Which is nice. Keeps the workshop warm during the night.

So i would have the brick bell first, and the metal "radiator"  or "barrel" after. Before the chimney. So your extracted heat is cooler.

I think it's hard to reach a good balance in a new build, without the experience.

Another idea i've had, is to use an horizontal metal radiator, onto which you could lay some more mass, in form of a big slab, held with pulleys and counterweights. So when your shop is hot enough, you store more heat. And don't overheat the place.
 
Posts: 217
Location: US, East Tennessee, north of Knoxville
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Dave, is you chosen system size due to the recommended 8" RMH in "the book by that couple"? As per Peter van den Berg, a 6" batch-box has about the same power as an 8" J-tube rocket. The larger 8" batch-box is much more powerful, and with just a single barrel will be way to hot to stand anywhere near it during the burn cycle.

As with Glenn and Satamax, how many sq. ft. of floor space are you planning on heating? Shop/building insulation values?

For an example, a 6" batch-box topped with a single 55 gallon steel barrel easily handles my 1350 sq. ft. cabin with power to spare. (R11 walls, R38 attic)
 
Dave Agar
Posts: 5
Location: Mid Michigan
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Thanks Guys,  I'm getting a better understanding of the density and size limitations.
I'm heating 1008ft2,  ten ft  ceiling half the insulation values as posted above.
Dave
 
Satamax Antone
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Location: Southern alps, on the French side of the french /italian border 5000ft high Southern alpine climate.
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So an eight incher batch is in order.
 
Glenn Herbert
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Location: Upstate NY, zone 5
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In your situation, in Michigan, I would agree that an 8" batch is called for.
 
Posts: 145
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I built a 6 inch RMH.

https://permies.com/t/40107/hot-barrel

When I installed my duct work in the mass, I aimed for 6" spacing . . . so front 6" mass . . . 6 inch exhaust . .  6 inch mass . .  6 inch exhaust . .  with the back of the mass at 6 inch  . . .

The Mass of the stove is roughly 10 feet long - 30 x 30 inches square  (roughly) . .

From an exhaust point of view, the exhaust is too cool - it exits the building at about 140 - 160 which is too cool for steam transportation (condenses in the pipe)  . . . So if I do this again, I would make the exhaust a bit shorter so I don't have moisture in the stove due to condensation . . .

From a heating point of view, heat moves thru the mass at about an inch an hour - so my 6 inch mass takes 6 hours too heat up . ..
I have burned my stove for 6 hours, and after that time, the top of the mass is nice warm 100 F . . . never have seen it hotter than that, but it takes that long too feel the heat as it works thru the mass.
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Byron Campbell
Posts: 217
Location: US, East Tennessee, north of Knoxville
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Dave Lot wrote:

When I installed my duct work in the mass, I aimed for 6" spacing . . . so front 6" mass . . . 6 inch exhaust . .  6 inch mass . .  6 inch exhaust . .  with the back of the mass at 6 inch  . . .



My bench run ducting is also in the same "hairpin" shape, but 8" ducting. To aid in a little more uniform bench temperature to the far end, and to keep the exhaust temperature up, I tapered the mass thickness via positioning the ducting as follows: Beginning of duct is 6" x 6" (front and top mass thickness), the end is 4" x 4", and the return loop is 4" x 4" (back and top mass thickness). Spacing between the two ducting pipes is 4". The ducting has a slight rise, as can be imagined with the mass thickness measurements. No condensate buildup problems, so I'm pleased with the result. After four to five hours of continuous firing the exhaust pipe is almost to hot to touch when you first grab it for the first few seconds, then one can hold it tightly for a full minute or more.

Dave, have you tried a larger 55 gallon barrel? The extra space around the heat riser, and greater riser top gap, together with less drag on the gases, will make for a little less barrel radiant heat but may raise your bench and exhaust temperature just over the point of generating condensate.
 
Dave Lot
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Byron Campbell wrote:

Dave Lot wrote:

When I installed my duct work in the mass, I aimed for 6" spacing . . . so front 6" mass . . . 6 inch exhaust . .  6 inch mass . .  6 inch exhaust . .  with the back of the mass at 6 inch  . . .



Dave, have you tried a larger 55 gallon barrel? The extra space around the heat riser, and greater riser top gap, together with less drag on the gases, will make for a little less barrel radiant heat but may raise your bench and exhaust temperature just over the point of generating condensate.



I followed the measurements in the videos that I downloaded and came across in my search for info when I built this stove . .  It rockets just great, and has gotten the top of the barrel glowing in the dark - a nice redish/pink  . . .  the stove runs just fine, so I don't really want too tamper with the size and  shape of any of the pieces, now that it's done - which is why I said "if I do this again . . "

Just putting in my two cents worth about having too much mass, and the effect of mass on heat transfer . . .

Thanks for the info though . . . maybe  . . . next time ?
 
If we don't do the shopping, we won't have anything for dinner. And I've invited this tiny ad:
five days of natural building (wofati and cob) and rocket cooktop oct 8-12, 2018
https://permies.com/t/92034/permaculture-projects/days-natural-building-wofati-cob
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