Project:RMH,horizontal feed Batchbox model 6",

[2tranceform]

Thank you this is most helpful

[dvawolk]

Oct 24, 2013 16:04:58 GMT -8 Donkey said:

Ok.. That's REALLY cool.. BUT!
I'd like to see some temperature measurements.
With and without the barrier and what it does to the temperatures below the barrier(s) and what it does above.

I did some tests now. Based on the temperatures i measured, it DOES WORK, but it is not the same as if one would put insulation all over the removed ISA... There is probably some turbulence between hot and cold air... The barrier is 11cm high now and i have measured at about 5cm height. One sensor in front of barrier and one sensor behind the barrier. The temperature (after loading a full batch) is always around 20°C lower behind the barrier. And this is usually less than 1°C of fluctuation..

It also comes to my mind that the actual temperature of gasses is lower, but the radiation from the ceiling of the bell warms the sensors a bit. On the other hand - both sensors are affected by that :-)

I will make some measures with/without barriers.. To compare more precisely... But it is a pain in the a.. because sometimes upper inlets are open and sometimes closed - and the draft is changing from burn to burn - hard to compare...

Donkey i will repeat a question for you from before, just to be sure:
"Donkey, so if i understand you, even if the concrete (or other surface) is dry, you don't wet it - you just paint it wit clay slip?"

[Donkey]

Oh, sorry.. Yes, I paint it with clay slip. Lots of water in slip, don't need to add more as long as the slip doesn't gel immediately. Sometimes the surface you paint it on will suck the moisture in so fast that it will go hard (gel) quickly. When that happens, either paint on more slip or splash it with water. I like to use a stiff scrub brush to put on water, it will rough up the surface as it wets.

[john44]

Peter,



Thank you for the great work that you have done and for sharing it.



You mentioned to Klemen the need for good chimney draft. Is it possible to build a batch box heater with a low exhaust temperature that only relies on heat riser draft? Some RMHs have been built with very low exhaust temperatures. Even as low as 90 degrees F. 


If it is possible to have low exhaust temperatures with the batch box what design changes would be necessary? Can a design rely only on draft from the heat riser?




I have two reasons for wanting to do this. Maximum heat extraction and a simplified exhaust at or near ground level.



Thanks,

John

[Donkey]

You CAN use just the heat riser.. Best if it's extra tall, and easier to do if you don't pump the heat down as far, like keeping bench runs above the level of the fire, using a short bench or bell system.. They work best when you live in a place with a consistent prevailing wind direction, where the exhaust port would be on the lee of the building.

It can leave your stove vulnerable to erratic weather patterns, more likely to smoke back on off days..
Also, it puts unbreathable and toxic fumes down at human height where they are easier to inhale. When the stove is running well this won't be a problem, it will be emitting mostly CO2, ballast gasses like nitrogen and water vapor. When the stove is first started, not burning up to temperature yet, it could be downright noxious.

[woodburner]

In the UK thereare regs for the position of the flue exit. If it goes up the wall, it will have to continue to (I think) 6' above the roof line. It may be 2', I'll edit later if necessary.

[dvawolk]

Without stack it would be a good option to have a batcbox in the lower floor and a bell in the upper. As far as I know J rocket stoves are better with shorter chimneys?

There comes to my mind another possibility. If you have a metal bell,the volume is much smaller to a masonry bell. I would say that the draft would stay better this way.. you can still build a masonry bell around metal,with large enough gap in between, to allow the same heat extraction? I would like to hear opinions for this solution...

[peterberg]

john44,
Yes, I know of J-tube rockets that exhaust at very low temperatures. But... in efficiency terms there is another, very important factor into play. That one is the excess air.

Efficiency calculation relies mainly on two parameters. Exhaust temperature and excess air, the last one, surprisingly, is the most important. A flow of 10 cubic feet of exhaust volume at 400 F is way better than 100 cubic feet at 200 F. The temperature of the latter one is halved but the volume is tenfold. All heated up and sent out the chimney to heat the birds.

The point here is, a J-tube rocket will run with a much larger excess air as compared to a batch box rocket. At the department of exhaust temperature and stack draft it's the other way around, the batch box has to have good draft, period. When you don't want to install a proper chimney, your best bet is a J-tube. I would estimate your chances to end with a proper working stove at fifty-fifty at best.

For me, this would be too much uncertainty.

[dvawolk]

It has been over a month now, with mainly very satisfying usage of my batchbox masonry heater... I will post my conclusions in the following days.
As for now, quick facts...
I can conclude that we will use less than half of a wood compared to previous two winters (we used fireplace insert Nordica ventilato 70). Moreower the room temperature is more comfortable and more even than before. Also the bench is an additionaly plus wich is used extensively! What a treat that is..
Temperatures in last month were around freezing (-10C to +5C) throughout the day and it was usually foggy. But we still didn't need to fire one full batch (with two exceptions). So for now i can say that one full batch a day keeps the cold away. Usually we fire in the morning, and cover the bench throughout the day. Over night we uncover the bench and in the morning we repeat the process.

The exhaust temperature reaches 115 C if i fire Chestnut wood (6,2kg). There were few occasions when i put in beech instead of chestnut and the difference was obvious: beech burns better and it has much more energy stored in the same volume (batch)... The exhaust temperature with beech went slightly over 130C and the sound was significantly more roaring...

More in the next posts...

[morticcio]

Klemen,
Great to hear it is a success. Look forward to the next posts.

[Robert]

Dear Klemen.

Can you please share some more of the experience on the temperature of your stove... how long you need to burn and how warm the stove gets, and how long it stays warm?

i am about to build a one bell batchbox to the client, so i would need some confirmation...
and do you have some photos from teh build that you could share with me (us) ?

oh... and where did you got your doors?

thank you so much.
robert

[dvawolk]

Hi, Robert.
It is funny that two days ago i started to thinking that now it is REALLY time to make another post... Just to quickly answer your posts:

it is hard to compare my temperatures and amount of fuel i use because the circumstances are not standardized at all.. I can only say that in previous winters i was using beech wood and nordica ventilato 70 fireplace insert and now i use 50 percent of firewood compared to previous years. This is wood per volume.. I should add that this year i use chestnut (castanea sp.) and previous year it was beech (fagus sp.).Chestnut has lower density, and consequetally storing less energy per volume. Also i would say that chestnut's tannin content is making hard for the wood to burn as great as beech - beech has a much louder roar etc. So if i would burn beech this year it would be probably 40% the amount of previous years...

I burn it once a day, usually morning, (with some occasions it is twice a day)and normally i cover the bench for the first 8 hours so that the heat is dissipated firstly from the vertical portion of the heater. After that i uncover the bench and it warms the area in the night-time... The thickness of bells is between 8cm (vertical walls) to 18cm (vertical ceiling and arch) and 13cm for the bench top. Neither part of the heater did pass over 100°C degree even with 2 full consequential firings of beech. The upper vertical wall part usualy goes to about 75-90°C in one firing (this depends of how much the heater cooled down from previous burning (1 or more days ago)...

I did doors myself, welded them...

Attached is the google sketch 3D file. Basically it is the same build. I just added sand/clay and sand/clay/straw plaster on the top...
Apart from that you can check some photos of the actual building here:
photobucket album

Klemen

[dvawolk]

In these months from previous posting now i have quite some experiences with this stove...
There have been temperatures here from -10°C to 10°C and the difference in draft can be seen..
As i have allready stated before my chimney really isn't that perfect... (two additional inserts upstairs). I would say that the following also adds to a lesser draft:
first two floors are connected... so the relative height difference from air intake to chimney exhaust is even lower... maybe, IMO...

Anyhow... when temperatures are around 10°C a small, simple gadget helps with draft (attached photo).
I noticed that when the batchbox was half full i never had any problem with draft.. But when i added it to full the problems draft problems may occur - i concluded that that is because of not too good chimney draft (ofcourse) and because the wood represents a barrier in CSA. There is not enough draft in the chimney to back up the heat riser to suck air with enough speed through the gaps in between the fuel pieces - this is obvious: if i put perfectly alligned fuel into the batchbox i can literally close the CSA.
Also i have seen that sometimes at the bottom of the batchbox arch is formed with burning coals and in this occurence it drafts propperly. so i added this short piece of 2" (5cm) diameter of iron pipe just behind the door - it serves as a "holder" for the rear part of the wood to stay slightly above the ground - and it provides a "cleaner" path for the air intake...

[dvawolk]

I was also thinking about this barrier thing (where you can lesser the ISA easily, or use it as some kind of bypass). This was mentioned and shortly discussed here: donkey32.proboards.com/post/8298/thread

I can say that it does work but my feeling is that there is some kind of lag in this system. I think that if i really close one part of my bench it would make a better draft compared to this barrier thing... It looks like it has something to do with this "dead air mass" that is still attached to the other moving air inside the bell...

[dvawolk]

Other than that: i am overly satisfied with this new part of our apartment.
I DO have some issues with it and it takes some time to use this heater properly, partly because it was built on edge of functionality - coupled with not so good chimney :-)

I will write about them and i will write down my conclusions as of what would i do/change if i was to build it again!