Scottscoaled Boiler Sizing Method

I shouldn't weigh in on this but I have some experience with radiant in Maine. The complexity of the system you mention NoSmoke is part of the problem for many. Not many can hook it up and not many can run it. Unless the envelope of the building is ultra tight, which is unhealthy without a heat exchanger, it is difficult to modulate the temp well. I cannot remember how many homes I have seen that have toe kicks and other forms of heaters installed to supplement the radiant system. For instance, a cathedral living room, facing north up the lake, with plenty of glass, WILL not be heated with a radiant system no matter what the floor is made of. Add in a few drafts when the wind is blowing about 35 mph and it is downright cold. You get into things like the transfer rate of the medium being heated to the space being heated, it is very complex. School of hard knocks is a powerful thing.

Kevin

I agree this is an excellent thread and I'll make some contribution based on the design on my boiler. So far most of the postings have been about boilers that transfer heat from the burning coal gases to the vessel via a gas medium. The is coal burning on a inclined flat plate or underfeed rotary feed mechanism. Forced air provides the oxygen for combustion and the combustion gases make it's way to the boiler vessel walls. Conduction heat transfer through the wall heats the boiler water.

The Anthratube boilers (Axeman Anderson & AHS coalgun) are significantly different. They burn coal in a vertical pipe, the exterior of this pipe is part of the boiler vessel. Heat transfer from the coal bed is via conduction through the steel pipe directly to the boiler water. In an Anthratube boiler this is the dominate path to get heat from the coal to the water. The smaller the diameter of the pipe the larger percentage of heat transfer. Because all of the heat is not transferred by this method a two pass flue gas path, one before the combustion blower and one after the blower, also transfer heat to the boiler water. This transfer path is like the other boiler designs, a gas transfer path. These two different heat transfer methods make the Anthratube design inherently more efficient than other designs.

Clearly a heat transfer path that uses a good conductor solid will transfer heat more efficiency than any gas. This principle is also why the Anthrtube boilers are physically smaller. A more efficient way to get heat out of the coal. The fact that the pipe holding the burning coal is surrounded by boiler water results in very long, efficient idle times for the Anthratube designs. The warm or hot boiler water buffers cooling of the glowing coals. I have re-started my boiler with no problems ever after there was no electricity for 24-36 hours.

Unfortunately, the control system on an Anthratube boiler is not very good. It's response time is slow even by coal like time constants and is severely influenced by unwanted uncontrollable parameters. Think about what you would really like. You would like a control system that keeps the burning fire high in the tube and provides just the right amount of combustion air plus some excess. Where's the feedback sensor? A long way from where you want control. Why in Gods name would you put the sensor down in the ash area where it is influenced by heat radiating from the boiler vessel above it and the ash below it. Consider the long thermal path to what you want to control, the burning portion of the coal. It's got a lot of ash between it and the sensor. And you have no control over the thermal conductivity of that ash. It varies with the type (red or white ash) and/or quality of the coal. I believe this why some have such different results with the same AHS thermocouple settings.

The A-A uses a sensor based on bi-metallic expansion of different metals, the current AHS uses a electronic thermocouple controller. My boiler uses the older percentage cycle timer control method. No feedback at all. Once dialed in it works just fine. But it's not "the solution" because vary any of the parameters, like coal type/quality and you have to dial it in again.

A much better control system could be engineered, but it would be complicated and expensive. I doubt it would be worth it. For those of you with wondering minds, I would put a linear array of thermocouples in the Anthratube pipe. Then I would control the ashing motor to always have the hottest point near the top. Want an engineering and product development? Design it to be affordable. Or do it with software. Have two thermocouples one at the top of the pipe one at the bottom. Measure both temperatures and determine the burning coal's position with a software controlled algorithm. Yea right! Go Ravens.

Yanche wrote:I agree this is an excellent thread and I'll make some contribution based on the design on my boiler. So far most of the postings have been about boilers that transfer heat from the burning coal gases to the vessel via a gas medium. The is coal burning on a inclined flat plate or underfeed rotary feed mechanism. Forced air provides the oxygen for combustion and the combustion gases make it's way to the boiler vessel walls. Conduction heat transfer through the wall heats the boiler water.

The Anthratube boilers (Axeman Anderson & AHS coalgun) are significantly different. They burn coal in a vertical pipe, the exterior of this pipe is part of the boiler vessel. Heat transfer from the coal bed is via conduction through the steel pipe directly to the boiler water. In an Anthratube boiler this is the dominate path to get heat from the coal to the water. The smaller the diameter of the pipe the larger percentage of heat transfer. Because all of the heat is not transferred by this method a two pass flue gas path, one before the combustion blower and one after the blower, also transfer heat to the boiler water. This transfer path is like the other boiler designs, a gas transfer path. These two different heat transfer methods make the Anthratube design inherently more efficient than other designs.

Clearly a heat transfer path that uses a good conductor solid will transfer heat more efficiency than any gas. This principle is also why the Anthrtube boilers are physically smaller. A more efficient way to get heat out of the coal. The fact that the pipe holding the burning coal is surrounded by boiler water results in very long, efficient idle times for the Anthratube designs.

I don't have personal experience with AA's or AHS's, but I'm having trouble grasping some of these generalizations about efficiency. Doesn't LL claim 85-90 percent efficiency from using their flat plate stoker with an AA flue gas heat exchanger? Even if the anthratube design conveys heat faster or more effectively, how is that an advantage at idle? On the sizing, I agree that the comparatively low water line on the AA may simplify piping in some steam applications, but beyond that I'm not sure I get the significance of the size issue. I'm a big fan of excess coal boiler capacity, but most of the time I'd agree that if a boiler is too big to get into your house you may not need one that big. With a little K-Y Jelly, an EFM 900 will fit through a 30.5" opening. And AFAIK the AA/AHS's aren't lightweight by any means.

I'm not trying to say anything bad about the AA/AHS's, but I'm not really seeing how the factors cited are meaningful advantages in practice.

Mike

Pacowy wrote:

Yanche wrote:I agree this is an excellent thread and I'll make some contribution based on the design on my boiler. So far most of the postings have been about boilers that transfer heat from the burning coal gases to the vessel via a gas medium. The is coal burning on a inclined flat plate or underfeed rotary feed mechanism. Forced air provides the oxygen for combustion and the combustion gases make it's way to the boiler vessel walls. Conduction heat transfer through the wall heats the boiler water.

The Anthratube boilers (Axeman Anderson & AHS coalgun) are significantly different. They burn coal in a vertical pipe, the exterior of this pipe is part of the boiler vessel. Heat transfer from the coal bed is via conduction through the steel pipe directly to the boiler water. In an Anthratube boiler this is the dominate path to get heat from the coal to the water. The smaller the diameter of the pipe the larger percentage of heat transfer. Because all of the heat is not transferred by this method a two pass flue gas path, one before the combustion blower and one after the blower, also transfer heat to the boiler water. This transfer path is like the other boiler designs, a gas transfer path. These two different heat transfer methods make the Anthratube design inherently more efficient than other designs.

Clearly a heat transfer path that uses a good conductor solid will transfer heat more efficiency than any gas. This principle is also why the Anthrtube boilers are physically smaller. A more efficient way to get heat out of the coal. The fact that the pipe holding the burning coal is surrounded by boiler water results in very long, efficient idle times for the Anthratube designs.

I don't have personal experience with AA's or AHS's, but I'm having trouble grasping some of these generalizations about efficiency. Doesn't LL claim 85-90 percent efficiency from using their flat plate stoker with an AA flue gas heat exchanger? Even if the anthratube design conveys heat faster or more effectively, how is that an advantage at idle? On the sizing, I agree that the comparatively low water line on the AA may simplify piping in some steam applications, but beyond that I'm not sure I get the significance of the size issue. I'm a big fan of excess coal boiler capacity, but most of the time I'd agree that if a boiler is too big to get into your house you may not need one that big. With a little K-Y Jelly, an EFM 900 will fit through a 30.5" opening. And AFAIK the AA/AHS's aren't lightweight by any means.

I'm not trying to say anything bad about the AA/AHS's, but I'm not really seeing how the factors cited are meaningful advantages in practice.

Mike

I'll try to elaborate about the idle, at idle or when the fan cycles off, the fire view port flapper swings back open. This then breaks the air path from the below grate area and air is now drafted across the top of the hot coal column, so the coals are now oxygen deprived until the next call for heat and meanwhile any residual heat remaining is absorbed by the water surrounding the column of hot coals. At next call for heat, this then repeats, fan starts, flapper is sucked closed and air is drawn from below grate area and coal bed is raging in a short time delivering heat to boiler water throughout.

Guys,

Let me first say I don't have any formal training in all this but..... From practical experience Im gonna say that the loss in efficiency due to an oversize boiler is insignificant compared to the inconvenience of an undersized boiler. Especially when your talking about the cost per BTU of coal. Also the heat gain from exhaust gasses is miniscule compared to the radiant energy of the fire. Again Im not claiming any formal scientific training , But Im saying that the battle for efficiency is won or lost in the combustion chamber, ie. direct line of sight of the fire. Any engineers that could weigh in here? And Sting if your gonna post, please no riddles.... Im a little foggy this am.

Waldo

McGiever wrote:I'll try to elaborate about the idle, at idle or when the fan cycles off, the fire view port flapper swings back open. This then breaks the air path from the below grate area and air is now drafted across the top of the hot coal column, so the coals are now oxygen deprived until the next call for heat and meanwhile any residual heat remaining is absorbed by the water surrounding the column of hot coals. At next call for heat, this then repeats, fan starts, flapper is sucked closed and air is drawn from below grate area and coal bed is raging in a short time delivering heat to boiler water throughout.

I'm curious - How much coal does it take to maintain a fire in your AA130 for 24 hrs? I seem to remember Steamup doing an experiment and coming up with 25 lbs, but I can't find the thread.

McGiever wrote: I'll try to elaborate about the idle, at idle or when the fan cycles off, the fire view port flapper swings back open. This then breaks the air path from the below grate area and air is now drafted across the top of the hot coal column, so the coals are now oxygen deprived until the next call for heat and meanwhile any residual heat remaining is absorbed by the water surrounding the column of hot coals. At next call for heat, this then repeats, fan starts, flapper is sucked closed and air is drawn from below grate area and coal bed is raging in a short time delivering heat to boiler water throughout.

Thanks for the description of how it works. In part, I was having trouble with the prior statement that "The fact that the pipe holding the burning coal is surrounded by boiler water results in very long, efficient idle times for the Anthratube designs." It sounds like it is the action of the port flapper that extends the idle times.

Mike

Lets not forget one of the basic fundamentals of physics. Heat is never lost, as in it doesn't vanish or go missing. Considering all the coal is burnt, the total BTUs are divided into several parts. Heat to the home, heat up the chimney, and radiant heat absorbed by the surrounding environment or in piping or duct work depending on the appliance. By minimizing heat transfer to the undesirable locations, you will get more heat where it counts...

So, based on heat output this is what I consider the efficiency of the whole system. In my case, with the furnace in the basement, the only undesirable place for the heat to go would be up the chimney. And since I can comfortably lay my hand on the flue pipe, I'm willing to say my barbaric appliance is pretty dam efficient hahaha

So long story short, whatever mechanism is burning the coal, its the outside variables that are most important. Thats just my own take on the whole thing. Add salt, stir gently lol

Heat transfer from the coal bed is via conduction through the steel pipe directly to the boiler water.[/quote]
If I were to set out to design the most inefficient worst combustion chamber I could think of, this is the method I would choose. It guarantees uneven burn with with large co generation.

If you want to burn any fuel it makes sense to design a combustion chamber that least hinders combustion. Drawing heat from that chamber is not the way to do it. Heat exchange needs to be addressed only after best possible combustion is satisfied. The two are completely separate problems. Failure to recognize this is why there are so many bad designs both in the past and in the present.

Rob R. wrote:

McGiever wrote:I'll try to elaborate about the idle, at idle or when the fan cycles off, the fire view port flapper swings back open. This then breaks the air path from the below grate area and air is now drafted across the top of the hot coal column, so the coals are now oxygen deprived until the next call for heat and meanwhile any residual heat remaining is absorbed by the water surrounding the column of hot coals. At next call for heat, this then repeats, fan starts, flapper is sucked closed and air is drawn from below grate area and coal bed is raging in a short time delivering heat to boiler water throughout.

I'm curious - How much coal does it take to maintain a fire in your AA130 for 24 hrs? I seem to remember Steamup doing an experiment and coming up with 25 lbs, but I can't find the thread.

Sorry, I really do not know.
Not even sure if it has ever idled for 24 hrs straight.

I am not trying to make any claims here as to the efficiency, just trying to described the operation, as it is some what different than most.

My similar AHS S130 runs on an average of about 14.5 lbs. per day during the summer. Some portion of that is heating the homes water, so how much it needs simply to idle for 24 hours is unknown, but it is certainly well below 25 lbs.

Well,,,,,,,,,,,,,,,,,,,,,,,,,,,, You guys going to refute my sizing method or are you going to forth those same lame arguements

Scottscoaled wrote:Well,,,,,,,,,,,,,,,,,,,,,,,,,,,, You guys going to refute my sizing method or are you going to forth those same lame arguements

No I will not refute , it will work for most homes in most of the country. It will however not an optimum solution. What's optimum is up to the buyers eyes and wallet. I don't consider a discussion lame arguments, it's using ones intellect to make a proper choice. Just like money, some don't have much. Both limit getting an optimum solution.

Scottscoaled wrote:In response to all the threads about boiler sizing and not keeping warm.

Scott's two step boiler sizing method;

Step 1. Determine if the building is less than 5000 square feet, has four walls and a roof.
Step 2. Install EFM 520.

Can you give me a rough idea of how much one of these brand new would cost. I don't have any radiators so I would need to go the heat exchanger route in to my forced air oil furnace ducts. Can they be power vented?

Thanks

Lightning wrote:Lets not forget one of the basic fundamentals of physics. Heat is never lost, as in it doesn't vanish or go missing. Considering all the coal is burnt, the total BTUs are divided into several parts. Heat to the home, heat up the chimney, and radiant heat absorbed by the surrounding environment or in piping or duct work depending on the appliance. By minimizing heat transfer to the undesirable locations, you will get more heat where it counts...

So, based on heat output this is what I consider the efficiency of the whole system. In my case, with the furnace in the basement, the only undesirable place for the heat to go would be up the chimney. And since I can comfortably lay my hand on the flue pipe, I'm willing to say my barbaric appliance is pretty dam efficient hahaha

So long story short, whatever mechanism is burning the coal, its the outside variables that are most important. Thats just my own take on the whole thing. Add salt, stir gently lol

That's how I look at it
Lightning . I'm not trying to heat my basement with my Kaa-2, yet it is 68* all the time. My basement is 65 feet long. The bare pipes give up heat while water is traveling that distance. I've thought about insulating the pipes, which would put most all the heat exactly where I want it, and save fuel. But, I also enjoy the warm floors. Magnetic thermometer on stove pipe reads 50* stack temp most all the time. That's BEFORE the barometric damper. I would say that's quite efficient compared to a coal stove, which reads 175* - 200* with all conditions the same. In bitter cold, windy wheather, my Kaa-2 stack temp has NEVER gone above 100*; And that's cranking along steady. Like you say, not much heat going up the chimney.