Peter van den Berg

[quote=Julian Adam]If I'm using the shorty core, I could keep the door in the middle, but there will be a 'slit' to the right of the core which I probably shouldn't count as clearance around the core. Plus the hot gas would directly be aimed at my chimney.[/quote]

If you shift the core a bit to the right to close that slit, you'll end up with a maximum space at the left.
A possible solution for the horizontal directed gas stream: just a little ski-ramp on top of the firebox so more heat is directed upwards. This ski-ramp as far away from the core exhaust as possible, not reaching higher than half the height of the exhaust opening.

I didn't try this construction myself, but it seems to be logical.

Matthias Hacker wrote: I‘m a bit confused, because I thought your batch box designs are supposed to run ether full throttle when burning or with the air supply completely closed at the end of the burn. I remember you did design an air flap on your commercial Dsr3 like this, ether fully closed or fully opened.

There are some differences between a standard batchrocket with long vertical riser and the other variants. The standard one has the habit of burning faster and faster until the point that the afterburner function isn't able to cope anymore with the woodgas production in the firebox. Resulting in a fuel overload and thick black smoke from the chimney.  In order to remedy that, the air inlet size is slightly restricted. Furthermore, air supply is a value that is a combination of opening and air velocity. In order to keep the supply on the same level, the opening should be smaller when the air velocity goes up. That's what I do with my heater, starting with a larger opening and successively making it smaller while the burn is under way. This could also be done electronically with the help of a stepper motor and a temperature sensor in the chimney pipe. OR with the maximum combustion rate function which is built-in the DSR3 and Shorty core designs.

Matthias Hacker wrote: Since I’m looking for starting a Dsr3 build soon, I wonder if I should go for a tuneable air flap design. With my traditional wood stove the several air intakes ask for a lot of tuning depending on outside temperatures, wind, chimney temps and so on. So I asked myself if this all is taken care of only by the internal self regulation of the special core design.

You don't need a tuneable flap design for the DSR3 core you are planning to build. The EU confirmation test on the DSR3 commercial heater was done in October, completely with the open-closed flap, nothing in between. Just build the heater to the specifications, preferably with a bypass, and you're good.
Hope this is clear, though.

Hi Christoph,

Yes, you can visit me in April, no problems there. I'll mail you for further details.

Julian Adam wrote:I must come back to my original question to you, Peter. That is, do you think the shorty sidewinder could be incorporated in my bell? My concern being that the flue gas flow coming from the riser may obstruct the downwards stratifying layers in the bell?

Hmmm... I've been reading through this whole topic, this question isn't asked earlier so it's a new question.
The answer is easy, I don't think a sideways exhausting Shorty core will interfere with the stratification in the bell. Or just as much as a now-standard-BBR with long riser, that one will disrupt the gases just as much but in a slightly different way.

As I see it, you should build your bell somewhat deeper and less wide so that the whole of the core is incorporated in the bell.
It's time now to stop asking questions and start building instead, don't you think?

Glenn Littman wrote:One of my good friends is doing a major remodel/expansion on an Earthship house and is going to build an 8" system in the main room. He was planning a basic (original) design but with your comments above I'm sure he will be rethinking that and going shorty. In this case my question would be whether there is no reasonable limit in the height inside the bell from the exit port of the Shorty core to the underside of the roof?

In case you mean the upper limit: no, there's no practical one. The now-standard BBR has once been done with with a "top gap" of 3.3 feet in a 6" system without any adverse effects as I could see.
The bottom limit is the height of the riser itself. The cook stove built last July didn't have any height above the riser, the cook top was resting directly on the riser which incidentally wasn't done with a refractory top slab. With a hefty fire in the riser/afterburner, one could see the spinning vortexes through the dark brown glass.
For a bell type heat exchanger, I'd prefer one system diameter's size above the riser. But it could be less if you want to, I presume.

Glenn Littman wrote:If you have no height or weight restriction don't discount the traditional core design. I'm actually curious to know Peter's thoughts on this. Specifically, given no restrictions on size, weight and materials cost/access what would be his order of preference for the combustion core: traditional tall riser, DSR2, DSR3, Shorty core?

The basic design is a very well-known one, there's lots of knowledge about it in the wider community. But there's a steel piece inside the firebox which could give up the ghost somewhere in time. And it's prone to overloads, I am very pleased that yours appears to be so stable, Glenn.

The DSR3 is a nice one, very spectacular to see it burn. Although complicated to build, some materials aren't available everywhere. But it is as self-regulating as a Shorty core which development followed logically after this one.

DSR2 is relatively easy to build, works real nice, low stature but features no self-regulating and has still the steel floor channel inside the firebox.

Shorty core is even lower, exhausting horizontally, clean burn, high overload resistence, good reloading characteristics. As a consequence, it is suitable for a cooking range and in a bell system the adagium "all above the riser should be refractory" doesn't count anymore. As easy to build as a DSR2, I might add.

All of the above core variants have their own merits. It depends greatly on one's need, budget and abilities what to choose. The whole of the above family is fully scalable as well, which can't be said about lots of other heaters and is unique in its own right. Furthermore, all of these family members works just as well as sidewinder variants, tested and all.

But, given no restrictions, the Shorty core would be my number one favourite. Secondly the DSR2 core, followed by the original BBR core and last but not least the DSR3.

Julian Adam wrote:1. If you say you tune down the air inlet, how often do you have to play with it? Is it just closing to x percent after x time once?

Most of the time there are three steps:  door open a crack to start with, door open half a crack (step1), door closed (step2), partially close the air inlet (step 3). With half a load step 3 is left out, the exhaust temperature will be stable by itself in that case. Time isn't the factor to go by, always the exhaust temperature. This a result of testing this heater endlessly, there seemed to be a direct correlation between chimney temp on the one hand and performance in terms of highest efficiency and lowest CO level on the other.

Julian Adam wrote:2. I can see the advantages of the shorty core. My bell will be high but the shortness appeals to me because if the regular sidewinder core would ever need replacing I would be up for a (huge) rebuild, because of the tall riser. Only recently I discovered that you had mentioned the build of a sidewinder shorty version as well. I was wondering if you tested this version with your Testo? I would assume the lack of floor channel may make the sidewinder less ideal?

No problems with the sidewinder Shorty core, it runs beautifully. I tested it last July during a workshop and it performed just the same as a straight one. A couple of guys tried to overload the thing for hours on end and they didn't succeed, not even with a reload right in front of the port. It was a strange sight while I walked to the workshop site, saw nothing leaving the bare chimney pipe only to be met with a heater that housed a huge, roaring fire. Such moments, I became unresistable giggly and felt very, very satisfied. No wonder, its development took the best part of a year, after all.

Julian Adam wrote:Out of interest, could you elaborate on this insulating effect Peter, e.g. what kind of rise in the flue gas temperature are we speaking of, clean compared to fouled (= e.g. after 2 years).

Hard to say, it depends greatly on the gas temperature versus the temperature of the bell walls, expressed as deltaT. As a guess: maybe 2 to 5 degrees C, nothing much to speak of. With a little insulation, the exhaust temperature goes up rather quick, due to the walls aren't as absorbing with a low gas temperature. The higher the gas temperature and thus the deltaT, the more heat is reaching the walls. A complicating factor is the fact that I am used to tuning the heater down with the air inlet during the burn, in order to keep the exhaust temperature below 120 ºC (248 ºF). Between 100 and 110 ºC (212 and 230 ºF), while the roar is unaffected is very close to ideal. This is one of the things I tried very hard to have it built-in with the Shorty core, it is meant to regulate itself, independent of the air supply. That's why the Shorty is a casual burner, burning clean with a high overload resistance and good hot refueling characteristics.

Julian Adam wrote:Also out of curiosity, did you build the extension to get your ISA up and flue gas temperature down slightly, I seem to recall you had around 120 °C exit T?

The ISA has been 5 m2 (53.8 sq. ft) for the last nine years, at the time there wasn't a clear figure how large it could be. After the alteration it's now 5.25 m2 (56.5 sq, ft), pretty close to the current recommended value and the weight has been risen to 2.2 metric tons (2.43 US tons). It still reaches the critical exit temperature of 60 ºC (140 ºF) rather quick, after that the temp is going up more slowly than before. And the bell is now capable of holding more heat due to the higher mass.

Good question, I try to answer it to the best of my abilities.
First and foremost: in the early stage of the burn there will be some soot that condensates on the walls (and ceiling) of a bell. This layer is very, very thin, nothing to be worried about. It will build up in months, up to the stage that it is quite flammable. So most of it will be turned into ash when the bell is getting hot enough, in a frost period for example.

Nothing to be worried about again, in no circumstance it will be something like a chimney fire, actually far from that. You won't notice it, the layer is glowing a bit and that's it. This process is repeated over and over again, the layer of ash will grow until it will get unstable on vertical surfaces, just falls down and accumulates on the floor of the bell.

So most ash falls down, some will stay and forms the base for a new layer of soot that'll turn into ash, and so on. This layer will be insulative but is quite thin. The higher the temperature difference between combustion gases and the bell walls, the less insulative it is. Insulation isn't blocking the heat, it slows it down.

Now my own situation: last winter I could tell my heater wasn't really happy, the burns were quite lazy. So during a warm spell, I took out the stove pipe and with the help of a flashlight I inspected the floor under and around the combustion core, which is raised above the floor by two feet. There happened to be a very generous layer of ash that wasn't smooth and level as I expected but rough and bumpy instead. It even did rise up to the level of the exhaust opening, blocking it partly.

Easy enough to scoop most of it out, the vacuum cleaner did most of the rest. Not all the ash was removed though, some was left but I couldn't care less. After that cleaning action the heater was its normal self again. Last fall I modified the top of the bell, a small extension and another way to close the top. The closing method was very similar to the Mallorca build, back in 2017.

While the bell was open at the top I noticed there was a thin layer of ash along the walls, nothing dramatic. The top of that layer was black and underneath it was just light grey ash. I left it there, I wasn't motivated to stir up lots of ash in the living room. Now, how quick would that layer grow?

This winter it's ten years ago that my red bell heater was built. Year after year, our fuel consumption was around 1.5 m3 of soft coniferous species, which equals 0.4 cords in imperial terms. In ten years, that would mean 4 cords or 6 m3, so I could expect to clean the floor of my bell when that amount is reached again. For other heaters: of course depending on the heater's size, it's construction, how high the exhaust opening is above the floor and whether or not the core is elevated. When you have lots of space down there, the interval could be anything between 2 and 10 years.

To answer the question directly: no need to clean the walls of a bell. That ash layer will fall down automatically, gravity will take care of that.

kees ijpelaar wrote:I have now done some more drawing, looks like it go look good and also compact.

It may look compact, but the core is too large for the bell. Or the bell is too cramped for the core. In order to build a bell like that for the core, the heater will be very high.
Building a wider bell so the gases will flow freely down the sides would help already. It would be even better to lift the core from the floor to such an extend that it's above the exhaust opening.
For a well-proportioned bell: see https://permies.com/t/238503/Batch-Rocket-Build

What you could do is scaling the core down and leave the bell size as it is.