Figuring out length of tube / size of bell for a 6" system

[Bram]

Here is the album on building the bench. It incorporates the active hot air circulation system using bricks on the floor. The last few pictures show where this hot air will be taken to (kitchen and bedroom).

photos.google.com/share/AF1QipPbaDQ-elPPxT9PMxOl9CSU1PdHZH0dvoP7CazeggbwbF0Vj9zPeVrUI5VOIXIZcQ?key=cHQ4YVFvZHoyYkFBcnplbXMtamU5ZG1NaWVRQ2xn

[Jura]

Thanks for the link. What is the total length of the duct?

I can not find out where is the chimney supposed to be.

Do U have more albums of the built ? or the one I can see is the contemporary state of it?

[Dan (Upstate NY, USA)]

My built is very similar to yours. Make sure to insulate that metal clean out on the inside with some rock wool.
If you don't insulate it condensation will drip out of it when it is running.

[n8ivetxn]

Jan 24, 2017 13:34:29 GMT -8 peterberg said:

Some people here coupled a batch box to a piped bench. But: you need to realize every elbow will add friction. Even with a J-tube you need to distract 4' or about 1.22 m for every 90 degree elbow. Your planned bell also takes up heat so this ought to be included in the ISA calculation. In my view, I wouldn't use the combination of a piped bench and a batch box core of whatever construction. You'd do better with a bell bench, probably even a blind ended one in my opinion. Very low friction and no convoluted gas path. You could use Matt's half barrel system to build that bench, saves you on brickwork.

Donkey did a batch box rocket and two-sided blind benches last year... I've seen that one on facebook, a whole lot of pictures how he built it.
It's on the facebook page of the Sundog School for Natural Building.
www.facebook.com/pg/Sun-Dog-School-of-Natural-Building-184675818301910/photos/?tab=album&album_id=800693863366766

Please forgive my ignorance, but what is a "blind end bench?"
I'm leaning toward a bell style batch box, but since it will be in my greenhouse, I would like to incorporate a bench (for even warmth), if it will work efficiently.

Is there a link where I could see Matt's (Walker?) half barrel system?


The pics of Donkey's 2 sided batch box are great, that is a work of art!

Thank you so much for all the wonderful info!

~ Rita

[peterberg]

A heated bench is in essence a low and hollow stretch of mass. This could be formed with stove pipe and lots of cob, Ianto Evans' style. There's also the possibility to build it out of bricks, feeding it at one end and exhausting from the other. This bench is already a bell since the feed and exhaust opening are at the same low level at opposite ends.

A much more sophisticated model is the cul-de-sac or blind ended bench, which is built out of bricks but the feed opening and the exhaust opening are at the same end. And what I am very fond of is the bench where the feed and exhaust opening are combined into one, hot air streams in at the top and cooler air is streaming out at the bottom. The workings of that last one is entirely depending on the law of physics that predicts hot air is lighter than cold air so it will rise to the top of any confined space displacing colder air, driven by gravity in short.

An example of such a system can be seen here: batchrocket.eu/en/applications#culdesac

There are 111 pictures of Donkey's double bench heater build see here:
www.facebook.com/pg/sundogbuilders/photos/?tab=album&album_id=800693863366766

Not only it illustrates the principles of a blind ended bench but also Matt's half barrel system. The benches are build out of cob, the structure inside is a barrel cut up lengthwise. Of course a single bench could be built which would be twice as long in this case.

[n8ivetxn]

Thank you for explaining the differences - wow, it's really a mind-blowing concept (for somebody new to this)! But, I understand the principles involved.... The diagram on the batch rocket site make it look so simple compared to laying tubes and packing them in. It makes me wonder why more people aren't building the blind end benches?

Do you have any suggestions for the size of the flue and exhaust baffle for a 6" stove?

Is there a spreadsheet for the dimensions of the entire cul-de-sac model?

More good stuff to think about! Thanks again Peter, I'm really enjoying reading all this great material :-)

[n8ivetxn]

Peter,

I went through Donkey's pics again.... I see now how the barrels work, and I realize the flue size is still the same as the riser....

I'm not good at math, what size would I make the calcium silicate exhaust baffle for the 6" model? There's no mention of it, or pictures of it in Donkey's design...

Also, on the batchrocket site, there are some measurements for a floor channel, "The drawing shows a horizontal duct of 60x30x2 mm (2.36" x 1.18" x 0.08") , the vertical piece measures 35x35x2 mm (1.38"x 1.38" x 0.08")" but I don't know if these measurements are for a 6" or 8" model?
- I found a welder to fabricate the floor channel for me....

In a few hours I start the set up for a test in the yard!

Thanks so much

V/R,

~ Rita

[peterberg]

Donkey used that calcium silicate baffle as a stop gap, to correct a mistake. Baffles aren't required as such as I answered in another thread.

The measurements you've found are for a 6" system.
Happy testing, don't forget the thing won't work properly with leaks all around.

[pinhead]

If you're new to the bell concept, here's a visual explanation: energy.concord.org/energy2d/double-bell2.html

Note that you have to have a Java-capable web browser to view the demo. Internet Explorer is the only modern browser that works.

[matthewwalker]

[n8ivetxn]

Thanks Guys! I'm on it

I might try mixing up a little mud to fill some cracks for the test run....

Pinhead, I don't have IE (only Firefox & Safari), but thank you for the link....

The video is amazing - who would've thought?!

[Orange]

so berry how's the thing working? Did you put a bypass?

[esbjornaneer]

Hello Berry,
Here in Southern Spain (1200m above sea level) we are doing really with a 15cm batch box with prescribed bell size. We put a cast iron top on the fire box for rapid heat up. One fire per 24hrs keeps it plesant in out 50m^2 downstairs. The additional 50m^2 upstairs is cooler.

If you would put the whole system by the wall between the sitting room and the bedroom you will have them both heated without any need for fan or forced air. You also have some other rooms in your plan but are not talking about heating for them...

Depending on if you have already built the house I would potentially plan the house around the stove. A central stove heats all around it. If you put your stove by the outside wall you will heat the outside unless you add sufficient insulation. And then you only delay the time until the heat trickles out the wall.

Look forward to hearing how it has come together for you.
Esbjorn

[Orange]

Oct 30, 2017 7:50:20 GMT -8 esbjornaneer said:

We put a cast iron top on the fire box for rapid heat up. One fire per 24hrs keeps it plesant in out 50m^2 downstairs.

hey, how quickly does your BB iron top heat up the space?

i'd love to have the iron top instead of barrel for quick heat.

[esbjornaneer]

Hi Orange,
How quickly does the top heat up on a traditional cast iron fire box stove? As soon as the flames start licking it I would say. But the difference between the traditional cast iron fire box stove and a batch box RMH is that in the first case the flames lick the top more than in the RMH where the flames shoot out the port. Hence my top does not gat as warm.

As for how quickly it hets up the space, it depends on how draughty/insulated the space is... I am speaking off the top of my head (not measured and timed data) but I would say that I see the thermometer (at seiling level) in the room go up somewhere between 5 and 15 minutes after finishing filling the fire box. But then I also have one of the large walls of the fire box as a glass door, and a glass door in the primary bell/black oven. Both of which put out a significant amount of heat. The second of them being the hottest of the three surfaces.

Sorry I can't answer better than that.