Rear loaded heating boiler

[banung]

Hello,

I watch Batchrocket for about two years now. I read full thread of „Holtere“ heating boiler described on batchrocket.eu and www.ecologieforum.eu/viewtopic.php?f=3&t=2049
I want to create for myself Rear loaded heating boiler. Combination of „Holteres“ heating boiler and „see through mass heater“ www.youtube.com/watch?v=Q3ZBvrH8mjg&ab_channel=kaminmassa

I want to stick as much as possible to the original design of Batchrocket. So I have we few questions:
1) Regarding to effectivity and emmisions. Was there any testing of side placed riser made?
2) Regarding to effectivity and emmisions. Was there any testing of of „Holteres“ heating boiler made? (latest version)

3) I understand that for good performance the dimensions and shape of riser, box, port and air intakes must be stand by. The bell shape (heat exchanger in my case) is not so important. I`m I right?

Thanks very much and thanks to Petr and other inventors
Petr

[Forsythe]

Jul 12, 2022 0:43:53 GMT -8 banung said:

Hello,

I watch Batchrocket for about two years now. I read full thread of „Holtere“ heating boiler described on batchrocket.eu and www.ecologieforum.eu/viewtopic.php?f=3&t=2049
I want to create for myself Rear loaded heating boiler. Combination of „Holteres“ heating boiler and „see through mass heater“

www.stovemaster.com/files/masonry.pdf

"Although see-through options are possible in masonry heaters, additional glass pane increases amount of heat leaving firebox by direct radiation through the glass and therefore lowers combustion temperatures having adverse effect on emissions. See-through models will overall have somewhat higher emissions."

pyrofires.co.nz/knowledge-base/why-is-the-glass-small/

Why is the glass small?
"Big door glass = big waste of heat
Glass is a very poor insulator, which is not ideal when it comes to wood fires!
The original Pyroclassic fire did not even have a glass as the scientists wanted the fire to be as efficient as possible. Over time, consumers expressed their desire for a window into the fire which has resulted in the glass getting larger with each version."

insteading.com/blog/masonry-heater/

"Masonry heater with large see-through windows. A large firebox reduces combustion efficiency and generates higher emissions. See-through heaters also increase the amount of heat escaping the firebox and therefore lowers combustion temperature and generates higher emissions."

Glass windows emit an enormous amount of heat through the UV, red, and infrared spectra — and those high-energy light spectra account for the lion's share of heat created during efficient woodburning— so the larger the viewing window is, the lower the efficiency of the heater, and the greater the amount of pollutants it creates.

Consider, for example, how much heat is transmitted through a ceramic glass cooktop on an electric stove — and bear in mind that *that* type of ceramic glass is very similar in composition to the ceramic glass used for masonry heater doors and high-efficiency fireplaces.



The decrease in efficiency will depend on:
A) the type of glass (and its particular wavelength spectra transmittance vs. reflectance values) and
B) the windows' size in relation to the overall firebox size
...but... some rough estimates I've seen tossed around are that see-through masonry heaters can be 20-40% less efficient than their single-windowed counterparts. (A firebox with 2 light-transmitting exits at opposite ends allows for reflected heat to escape long before it can bounce around and accumulate in the firebox, simply because that energy wavelength has far more pathways to escape when bouncing off of the heat-retaining refractory sidewalls.)

...suffice it to say that: Putting see-through doors on a masonry stove/boiler/heater will lower the efficiency dramatically.— and that, in turn, increases particulate emissions of your woodburning unit.

[peterberg]

Jul 12, 2022 0:43:53 GMT -8 banung said:

I want to stick as much as possible to the original design of Batchrocket. So I have we few questions:
1) Regarding to effectivity and emmisions. Was there any testing of side placed riser made?

Yes, the sidewinder was tested quite extensively. I've been in Israel in 2015 or 2016 for exactly that goal. Later Adiel and Shilo bought their own gas analiser.

Jul 12, 2022 0:43:53 GMT -8 banung said:

2) Regarding to effectivity and emmisions. Was there any testing of of „Holteres“ heating boiler made? (latest version)

No, Holteres heater wasn't tested so I don't know how it performs.

Jul 12, 2022 0:43:53 GMT -8 banung said:

3) I understand that for good performance the dimensions and shape of riser, box, port and air intakes must be stand by. The bell shape (heat exchanger in my case) is not so important. I`m I right?

Yes, the best road to a wel-performing batchrocket is to stick to the numbers. The shape of the bell isn't important, besides the total Internal Surface Area it need to be wide enough to slow down the hot gases.

Forsythe, you might be right regarding a normal firebox in a large masonry heater. However, the batchrocket core isn't like a "normal" firebox at all. The crux of this core is the afterburner function behind the narrow port. This afterburner doesn't have a glass window, most of it is an enclosed, very hot and turbulent environment. This is one of the reasons, or maybe even the single reason, why even an open system is way more efficient than a "normal" open fireplace. Rivalling in fact, some of the most efficient heaters on the market.

This was found out by yours truly, way back in 2012. Efficiency of an open system was a bit lower, in the range of 3% to 4%. Quality of the burn, if CO is anything to go by, at least as good as a system with a door and primary and secondary air inlets.

In my opinion the sidewinder type of batchrocket, see-through or not, can be as good as a straight one. Keeping your theory in mind, the sidewinder is possibly even marginally better. Because of the radiation from the port, which is hitting the opposite wall.

[Forsythe]

you might be right regarding a normal firebox in a large masonry heater. However, the batchrocket core isn't like a "normal" firebox at all. The crux of this core is the afterburner function behind the narrow port. This afterburner doesn't have a glass window, most of it is an enclosed, very hot and turbulent environment. This is one of the reasons, or maybe even the single reason, why even an open system is way more efficient than a "normal" open fireplace. Rivalling in fact, some of the most efficient heaters on the market.

This was found out by yours truly, way back in 2012. Efficiency of an open system was a bit lower, in the range of 3% to 4%. Quality of the burn, if CO is anything to go by, at least as good as a system with a door and primary and secondary air inlets.

In my opinion the sidewinder type of batchrocket, see-through or not, can be as good as a straight one. Keeping your theory in mind, the sidewinder is possibly even marginally better. Because of the radiation from the port, which is hitting the opposite wall.

Well, I'll be damned — that is an extremely salient point, peterberg . The figures I was referring to all relate to the designs of kachelöfen, grundöfen, and traditional contraflow-style masonry heaters where a great deal more of the combustion happens within the firebox itself — directly in front of those windows — with much less combustion happening downstream in a refractory-enclosed space. Of course you're right about this, and I'm embarrassed to say it didn't occur to me until you pointed it out. Indeed the afterburner/riser in a rocketstove core creates a totally different burn pattern than any of those aforementioned traditional masonry heater designs. I mean duh. That should have been obvious to me... the riser/ secondary burn chamber / afterburner is the heart of the rocketstove's functionality.

I stand corrected.

[banung]

Thanks for the replyies,

The heater will stand in the garage and will be loaded from garage through the rear isolated door. The front door will be just to watch the fire in the livingroom. Port will be on the side of rear door.
Between garage and living room is 20 cm thick wall. I want to have the front door aligned with the wall. So I have two more questions and after the answers I will be able to draw the heater, I think.

1) Because of the wall I need to lengthen (depth) the Box. (I want to watch the fire through the wall) What is the right way to do It, to not harm the perfonmance? Just do it longer and load the wood only in the „original defined“ space? Or put some glass between the door and the box? (how to clean it). Maybe it is possible to do it without lengthening the Box, but the construction will be more complicated.

2) Is there any way (formula, application, etc.) how to calculate the temperature drop after the fumes will exit the riser and expand in the bell? Due to the steel exchanger to survive the heat.

I will use simmliar sollution to Rémy Bakker, but I will use more, but shorter tubes -> fumes will expand on bigger „floor area“. I will also isolate this area with Vermuklite. (plate with holes)

Thanks wery much again.

[peterberg]

Jul 13, 2022 1:54:54 GMT -8 banung said:

The heater will stand in the garage and will be loaded from garage through the rear isolated door. The front door will be just to watch the fire in the livingroom. Port will be on the side of rear door.

In effect, this heater won't be a see-through construction since the rear door is heavily insulated. Keep in mind, the port should be away from the rear wall and centered in the riser.

Jul 13, 2022 1:54:54 GMT -8 banung said:

1) Because of the wall I need to lengthen (depth) the Box. (I want to watch the fire through the wall) What is the right way to do It, to not harm the perfonmance? Just do it longer and load the wood only in the „original defined“ space? Or put some glass between the door and the box? (how to clean it). Maybe it is possible to do it without lengthening the Box, but the construction will be more complicated.

I understand you want to make the hole in the wall just as large as the door, no more.
In my opinion you'd do better to make the hole bigger, so part of the firebox is inside the wall. This may sound tricky but that remains to be seen. With part of the firebox inside the wall but the original depth begind the wall, that part inside the wall will get as hot as the rest, please don't be mistaken about that. The hole in the wall need to be much larger because you'll need to insulate around it quite a bit in order to protect the brick wall.

Jul 13, 2022 1:54:54 GMT -8 banung said:

2) Is there any way (formula, application, etc.) how to calculate the temperature drop after the fumes will exit the riser and expand in the bell? Due to the steel exchanger to survive the heat. I will use simmliar sollution to Rémy Bakker, but I will use more, but shorter tubes -> fumes will expand on bigger „floor area“. I will also isolate this area with Vermuklite. (plate with holes)

I do think there's a formula for calculating the temperature drop. Personally, I've never had the necessity to use it, though. I keep myself away from heating water and the like, too dangerous for normal mortal people. Water tend to flash to steam in a not properly installed system. Expansion would be about 1500 times, every liter of water expands to 1.5 m³ in the wink of an eye. No hot water explosions for me, thank you.
Having said that, there are techniques, safety valves and whatnot to avoid such a dangerous event.

[banung]

The wall is 2x4 wood wall. So I can reduce the thickness of the wall to few cm.

I`m drawing the stove now. Box, Riser and Port will be as original design.
The only difference will be in the path of Air. Input and output areas will be he same as in the original design. Between input and output the air will expand (slow down) and preheat. And also cool the steel of stoves.
Primary air will go under the Box and exit near bottom of front door.
Secondary air will go under riser and exit in port as in the original design.

Because of better preheated air I expect good results. Or can there be some negatives?

[peterberg]

Jul 18, 2022 13:23:58 GMT -8 banung said:

Because of better preheated air I expect good results. Or can there be some negatives?

Yes, preheating the incoming air above a certain level can and will be negative.

Imagine air that preheats to, say, 600 ºC (1110 ºF). All of the components of this air will greatly expand. As the net result, one would need much more volume of that hot air through the primary and secondary air inlets. Even up to the point that there isn't enough oxygen available while there's a large volume streaming into the firebox at the same time.

This exact situation happened during development of the DSR3 combustion core. All air was coming in from under the heater, led through a vertical steel tube into a fairly large steel box under the firebox and from there through an air frame around the door. All the components were made of steel and situated in hot zones of the heater. The Testo measured very low oxygen and to the eye all flames were blown away big time from the air inlets.

This situation improved dramatically after I ditched the sophisticated air supply. Using a simple opening in the lower front of the air frame, in plain sight, the behaviour of this core was much, much better.

Having said that: are you planning to build a batchrocket heater with the core inside a combustible wall? Please, please, don't do that. This firebox will get awfully hot and insulation works only up to the point where the temperature difference is in the 10's of degrees. It will let the heat come through when the difference is several 100's degrees.

The thing about wood: its self-ignition temperature is about 540 ºC (+/- 1000 ºF) if I remember correctly. But at a lower temperature it will turn into charcoal very slowly, it could easily take 10 years or more. The self-ignition temperature of charcoal is much, much lower, about half compared to plain wood. So in 10 years or more, your house will be on fire. Probably also in the depth of winter because of the hotter firebox.

[banung]

Dear Peter,
thanks for reply. I have been on holiday, so therefore my late reply.

Don´t worry. I have constructed a lot of things and I know what could happen.
The heater will be cooled almost completely by water.

My plan was to cool bottom of heater by air.
Are there any optimal temperatures for primary and secondary air?

[peterberg]

Aug 15, 2022 7:58:45 GMT -8 banung said:

Are there any optimal temperatures for primary and secondary air?

Primary air doesn't need to be hot, room temperature would be fine. Too hot and there's not enough oxygen in the volume of air. Resulting in similar problems I experienced with my DSR3 prototype.
Secondary air is another matter, although it's easily overdone. A temperature of between 200 and 300 ºC might be OK. I hasten to add this is mostly speculation from my point of view.

[Vortex]

Aug 16, 2022 0:28:55 GMT -8 peterberg said:

Primary air doesn't need to be hot, room temperature would be fine. Too hot and there's not enough oxygen in the volume of air. Resulting in similar problems I experienced with my DSR3 prototype.

That's a real gem of info, Peter. It seems so obvious now, but it never crossed my mind before.

Searching online I see that air raised from 22C to 49C increases in volume by 10%, I couldn't find info for higher temps, but if it carries on at that kind of expansion rate then that is a significant difference. Also room temperature air would expand more upon combustion in the stove creating more draft.

[peterberg]

Here's some good info about volume of air in relation to temperature.
It's on this forum, donkey32.proboards.com/post/1021/thread

Raising the air temperature from 20 ºC to +/-320 ºC will result in twice the volume. I wouldn't be surprised when the DSR3 prototype did something in that range. Which means it will require twice the volume in order to get enough oxygen inside. It would be interesting to tune such a device. The character of such a stove would be very, very different from what we are used to, if the DSR3 prototype's peculiar behaviour is anything to go by.

[Karl L]

Aug 17, 2022 2:09:52 GMT -8 Vortex said:

Aug 16, 2022 0:28:55 GMT -8 peterberg said:

Primary air doesn't need to be hot, room temperature would be fine. Too hot and there's not enough oxygen in the volume of air. Resulting in similar problems I experienced with my DSR3 prototype.

That's a real gem of info, Peter. It seems so obvious now, but it never crossed my mind before.

Searching online I see that air raised from 22C to 49C increases in volume by 10%, I couldn't find info for higher temps, but if it carries on at that kind of expansion rate then that is a significant difference. Also room temperature air would expand more upon combustion in the stove creating more draft.

The calculation is quite simple: The volume of any gas is almost exactly proportional to its absolute temperature -- i.e. it's temperature measured in degrees Kelvin (K).

To calculate the temperature in K, just add 273 to the temperature in Celcius (C). So room temperature in K is 22 + 273 = 295K.

So if the temperature of a gas rises from 20C to 320C, then it rises from 293K to 593K.

So the proportional increase is 593/293 = 2.02. So the volume will double.

[banung]

Dear Peter,
I will be builing 150 mm version. When i look at your building site, I see:

Depth of firebox is 4 to 5.5 times base and
Height of the riser is 8 to 10 times base

In the table above is:

Height of the riser is 108 cm (10x base, higher limit) and
Depth of firebox is 43,2 cm (4x base, lower limit)

How should I understand this? The higher riser, the better. The less depth of firebox, the better?
Longer depth of firebox will help me to install the heater in to the wall.


To the air imput. There will be possible modifications if there will be not expected results.
Petr

[peterberg]

Aug 18, 2022 3:49:40 GMT -8 banung said:

How should I understand this? The higher riser, the better.

Not correct, sorry. There's also mass in most risers which need to warm up. Above 10xB there's nothing to gain, below 8xB stability of the burn is getting less.

Aug 18, 2022 3:49:40 GMT -8 banung said:

The less depth of firebox, the better?

Hihihi, this sounds like no depth at all is the best.
The reference design worked very well with the 4xB firebox depth. Due to questions on this forum I also tested a deeper firebox which also worked well.

Aug 18, 2022 3:49:40 GMT -8 banung said:

Longer depth of firebox will help me to install the heater in to the wall.

Can be done. Please be aware that this deeper firebox, filled to the very top with high-energy fuel like beech, could result in smoke from the chimney. Remedy: keep 10 cm space above the fuel and/or use shorter fuel.