# "the correct Stoichiometric ratio"



## Monica in France (Feb 26, 2014)

I haven't found this document in English but in the French version of a Ravelli RDS manual I found this phrase :
<< Le système RDS permet à l’installation dans laquelle est assemblé, une fois programmées les valeurs calculées, de fournir toujours la correcte quantité d’air pour obtenir le parfait rapport stœchiométrique. 
Crudely translated this is claiming that once the system is set-up correctly it will *always supply air to the combustion in the correct Stoichiometric ratio*.

This obviously is a very good thing and on paper sounds impressive.

However I would like the views of this forum on the likelihood of ever attaining such an ideal.
I offer two evident problems :
A : different pellets will have different characteristics
B : varying pellet mass being dropped down the chute.

IS it possible ?

Does anyone know what the correct stoichiometric ratio is for pellets ?


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## JohnRXL (Feb 26, 2014)

Only thing I can tell you is that 14.7:1 is the correct stoichiometric for the air fuel mixture for an internal combustion motor. 
It may be a start.


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## DZL_Damon (Feb 26, 2014)

You need excess air beyond stochiometric combustion in real life.

It is usually measured in mass, and can vary on HOW the fuel is combusted.

My Kedel asks for 18% excess O2 ( different way to express excess air, and different reference) at idle, and 9% excess air at 100% fire. My work boiler only requires 4-5% excess O2 since we grind up the pellets and spray it in for combustion. Less air is required to combust all the fuel since its nearly atomized.

Out traditional way of burning it in our boilers/stoves require more air to do that though.


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## peakbagger (Feb 26, 2014)

_You need excess air beyond stochiometric combustion in real life_.

The ratio varies with the type of fuel, Gaseous fuels need lower amounts of excess air while solid fuel require more. About the only way to compensate for varying fuel characteristics is to install an O2 probe and vary the air flow to preset value. This is done on high end wood boilers but I am not aware of pellet stoves with this option. Generally a bit too much air does not hurt unless you have fan horsepower to deal with.


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## iceguy4 (Feb 26, 2014)

At  the risk of "iceing this thread, ....

Having my own equipment and knowledge to set up my oil boiler, I have wondered how pellet burners get their efficiency...while blasting VAST amounts of "air" into the combustion chamber.   Air consists of 21% oxygen, 79% nitrogen (generally accepted values)    Of that mix, ONLY the oxygen is used in the combustion process. .   The Nitrogen(inert= not used)is heated and sent on its way.    In the "old days"  , oil burner technicians would open up the air and get a good flame.  Setting up the burner "by eye"( Old timers will argue but it is IMPOSSABLE to do this)  This at the expense of the efficiency.  (a very GOOD reason why NOT to let your oil delivery people service your boiler)    
            At this point we measure exhaust gasses for  carbon dioxide, ....get that level as high as you can short of soot in exhaust (generally 13% +  -  any higher and insulating soot will form)        MY point,  too much air is good for flame...bad for efficiency....


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## Lake Girl (Feb 26, 2014)

Your stove is set up for your installation set-up?  Pelleting in NJ probably sent you both manuals...  From there, you can make minor adjustments to air and pellet drop - press buttons 6 & 7 together to get pellet and draught.  This would accommodate pellet change.

These stoves have multiple heat sensors but that really doesn't say much about the efficiency of the burn...  I have noticed the combustion blower will change slightly but not quite sure what triggers that as the temp remains fairly steady (state stove).


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## DZL_Damon (Feb 26, 2014)

When calculating efficiency by flue gas  analysis, I believe a ROUGH rule of thumb is 1% efficiency loss for every 1.5% increase in excess O2 above stochiometric combustion and that a 40*f increase in stack gas temp is roughly a percent as well.... this is for generating steam however. It changes with lower rejection temperatures and changes quick when you start condensing stack gasses.... but that's another massive conversation.


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## Lake Girl (Feb 26, 2014)

Checked both manuals I have for the word stoichiometric .. not to be found.  These manuals appear to be poorly set-up and hardly very informative on many of the technical details - no details on the board set-up, etc.  Wonder if there is a technicians manual....

Phil Do's Palazzetti appears to have a more advanced burn system but then it has the rotary or star feed and secondary combustion.  These are interesting.... http://en.rossatogroup.com/prodotti/generatori-biomassa/caldaie-a-pellet.html sound similar to the Palazzetti.


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## Pelleting In NJ (Feb 26, 2014)

The only way to properly regulate the air-fuel ratio in a pellet stove would be to use an exhaust gas sensor (chemical content), like an oxygen sensor used in cars. As far as I know, there is no pellet stove that uses an oxygen sensor.

The Ecoteck/Ravelli "RDS" stove models use a mass air-flow sensor in the intake air path, used to regulate the combustion fan speed to acheive a constant amount of combustion air, automatically compensating for the restriction of the particular flue pipe configuration installed with each stove, and the normal increase of combustion air restriction that occurs as the burn-pot holes and the exhaust passages get restricted as the stove is used, between cleanings. This type of system does help maintain a more consistent air-fuel ratio (compared to a stove which does not have a mass-airflow sensor), but it does not have the precise control that an oxygen sensor type of system can acheive. It is a stretch for the stove manufacturers to claim that the stove maintains the ideal stoichiometric air-fuel ratio with this mass-airflow system, a bit of marketing hype.

The same air-flow sensing/regulating system has been used by Rika-Austroflamm stoves for years, the Ravelli RDS feature is really nothing new, but it is certainly a desireable feature to have. I think the Pallazzetti stoves also use a mass-air-flow system.

I think Harman and Quad should update their products to use a mass-airflow system.....and at least catch-up to this early 1980s technology (electronic mass-airflow sensor).

http://www.wellsve.com/sft503/Counterpoint3_2.pdf


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## DZL_Damon (Feb 26, 2014)

Pelleting In NJ said:


> The only way to properly regulate the air-fuel ratio in a pellet stove would be to use an exhaust gas sensor (chemical content), like an oxygen sensor used in cars. As far as I know, there is no pellet stove that uses an oxygen sensor.
> 
> The Ecoteck/Ravelli "RDS" stove models use a mass air-flow sensor in the intake air path, used to regulate the combustion fan speed to acheive a constant amount of combustion air, automatically compensating for the restriction of the particular flue pipe configuration installed with each stove, and the normal increase of combustion air restriction that occurs as the burn-pot holes and the exhaust passages get restricted as the stove is used, between cleanings. This type of system does help maintain a more consistent air-fuel ratio (compared to a stove which does not have a mass-airflow sensor), but it does not have the precise control that an oxygen sensor type of system can acheive. It is a stretch for the stove manufacturers to claim that the stove maintains the ideal stoichiometric air-fuel ratio with this mass-airflow system, a bit of marketing hype.
> 
> ...



Some of the European pellet boilers are utilizing lambda probe oxygen sensors like you mentioned for oxygen monitoring in the exhaust stream. The Kedel has a curve set for low, mid, and high fire o2 targets and some variable fan speeds built in for each of those points that are all fully adjustable by the user. The fan will either speed up or slow down to match that target for best efficiency over the whole firing range. If the fan can not take care of a large difference (change in pellet brands for example) the auger will speed up or slow down to help out as well.

I figured some of the higher end stoves were doing this too already...?


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## Mt Bob (Feb 26, 2014)

T


DZL_Damon said:


> Some of the European pellet boilers are utilizing lambda probe oxygen sensors like you mentioned for oxygen monitoring in the exhaust stream. The Kedel has a curve set for low, mid, and high fire o2 targets and some variable fan speeds built in for each of those points that are all fully adjustable by the user. The fan will either speed up or slow down to match that target for best efficiency over the whole firing range. If the fan can not take care of a large difference (change in pellet brands for example) the auger will speed up or slow down to help out as well.
> 
> I figured some of the higher end stoves were doing this too already...?


The harmons and others use a temp sensor(range,not on/off)to keep burn rate what the programming wants to see.Some european stoves use a maf sensor and a exhaust temp probe together,along with programming(key here programming).Europeans still ahead of us in pellet technology.Original idea for austroflamm maf sensor was so stove could be used at any altitude,just happens it works well.Original design came from BMW.I think mfg. are using heat sensors because would be almost impossible to keep an 02 sensor clean.As far as advertising,look at china stove web sites,they advertise over 90% efficency!Some truth streaching there!I do not know how the boilers are keeping a o2 sensor clean.


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## Bioburner (Feb 26, 2014)

China with clean tech? Did you see the news tonight with the pollution in Bejing? I've seen cleaner air when cleaning the ash out of the shop vac. Worse visibility than here in the blizzard.


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## Monica in France (Feb 27, 2014)

I've been searching the web for information on the best way to burn pellets and I came across this thesis by a Polish guy who was experimenting with different control strategies for the combustion. Lots of formula and verbiage but the one thing stood out was that dynamic feedback control was not a great success. (It wasn't dynamic enough : the time lag screwed him )

So is the Lambda sensor the ultimate solution ? The cheap ones only tell you lambda  l : and now you tell me they can get blocked up with the soot as well.
The Ecoteck/Ravelli MAF sells for just €24 : two temperature sensors in series – the second heated. Simple and perhaps even reliable. 
But “stoichiometric” – you are right there <Pelleting in NJ> they are pushing it a bit : and worse it seems because for complete combustion of pellets convention wisdom states that you need a lambda of 1,2 – 1,3 ( I've even read of higher figures , and thank you <DZL_Damon> for your case study ( real ) figures ).
If Ecoteck are Hyping ( is this a word ? ) , I loved the page given to us by <Lake Girl> . I read it in the French translation as well – just as good. Are there any Italian readers on the forum to explain to us what the translators couldn't understand ? ( or swallow ?)


ChickenMan : I am disbelieving. 97% ???
Not because of the Chinese angle but because of those basic laws of physics.
You need to tell us more :
      What is your definition of efficiency.
      What sort of power levels are you talking about

For every Kg of fuel you burn you have to push out over (6,2 + 1) Kgs of hot air in the chimney.
How is the miracle performed ?


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## hyfire (Feb 27, 2014)

You can;t beat the European pellet  burning technology (Windhagger, froler, etc), no way the chinese will come up with a high efficiency number that is overstated!


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## iceguy4 (Feb 27, 2014)

chickenman said:


> The stove tested was from the US with our flue system.


   If you don't mind...what is your "flue system"?     PM me if your not comfortable posting it


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## Bioburner (Feb 27, 2014)

Chinese are burning US coal as well. US shut down several power plants as they cant meet new standards and the coal is going over seas and being burnt without any cleaning and then still floats over here contributing to 10% of west coast pollution. Was a major environmentalist on the tube last weekend being very disappointed with Obama administration as  it hits us three ways. Loss of jobs, loss of cheap power and still makes for pollution here What are the health issues the Chinese going to have with all that smog with unrestricted emissions? Hope we can get the stoves to burn better with some simple modifications. Studying simple rocket stove designs as now there is at least three designs for pellet burning without power.


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## iceguy4 (Feb 27, 2014)

Bioburner said:


> What are the health issues the Chinese going to have with all that smog with unrestricted emissions


   Let me tell you...I for one am glad they are only polluting their air!     and Japan is only altering their country with radioactivity ...  Are you aware China has build a dam that when it completely fills its weight will shift the earth on its axis


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## Bioburner (Feb 27, 2014)

iceguy4 said:


> Let me tell you...I for one am glad they are only polluting their air!     and Japan is only altering their country with radioactivity ...  Are you aware China has build a dam that when it completely fills its weight will shift the earth on its axis


They will have to have someplace to hide all those lung ailment victims Japan making glow in the dark tuna so its easier to catch em. Self cooking cows grazing the hot zones.


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## pen (Feb 27, 2014)

Time to steer things back to pellet stove operation, or this is going to make a move to the ash can.


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## DamienBricka (Feb 28, 2014)

Bioburner said:


> Loss of jobs, loss of cheap power and still makes for pollution here



Loss of job where: unemployment has decrease since he took office.

Cheap power does no longer exist. You have to realize that coal, oil and gas are only in a limited supply.

Pollution is here because some individual do not care about the environment.

JMHO


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## DZL_Damon (Feb 28, 2014)

chickenman said:


> Nothing special about our flue system and as I don't know how to PM so I will explain it here;  THe inner flue connects to the stove exhaust as normal.  The outer flue is sealed to the inner flue with a high temp flex hose going to the combustion air intake.  The outer flue draws the combustion air from outside and exchanges heat from the hot inner exhaust tube.
> You can see the flue adaptor on the back of our Nero stove on our website.  If I can make them so can you.
> THis makes a huge difference to the efficiency of the stove but, Like I have said you just need to be careful to not reduce the exit flue gas too much.



This does work but its an uncontrolled route to condensation of flue gasses in your exhaust. I wouldn't advise this unless the homeowner understands the risk of creosote and checks for it often.


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## Lake Girl (Feb 28, 2014)

chickenman, sounds like the Selkirk DT that can be purchased in the US http://www.selkirkcorp.com/Selkirk/Product.aspx?id=7428

To PM, click on the poster's name and you will see "start a conversation" among other things.


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## iceguy4 (Feb 28, 2014)

chickenman said:


> The outer flue draws the combustion air from outside and exchanges heat from the hot inner exhaust tube.


 AAaahh. I have been doing just that for over a year ("in spite of neigh Sayers")  I chose to make my own because my vent pipe was just onths old.  when I replace my vent , I plan to use the "Selkirk" system Lake girl  mentions.  Common sense tells me I have improved its efficiency  I have attached pictures....What your are looking at is a 6" regular pipe OVER the exhaust vent...
	

		
			
		

		
	










DZL_Damon said:


> This does work but its an uncontrolled route to condensation of flue gasses in your exhaust. I wouldn't advise this unless the homeowner understands the risk of creosote and checks for it often.



    As for creosote....Not even close (on my application)   Nothing but ash in my vent. I agree ...you should keep an eye out for it....on ANY device that has the potential to produce it....Just saying


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## DZL_Damon (Feb 28, 2014)

iceguy4 said:


> AAaahh. I have been doing just that for over a year ("in spite of neigh Sayers")  I chose to make my own because my vent pipe was just onths old.  when I replace my vent , I plan to use the "Selkirk" system Lake girl  mentions.  Common sense tells me I have improved its efficiency  I have attached pictures....What your are looking at is a 6" regular pipe OVER the exhaust vent...
> 
> 
> 
> ...


 
Is the PB105 direct vent? That's one of the things I really wish the Kedel was....

Have you measured your Exhaust temps before and after? My flue temps are quite low already so I don't want to reduce the further... usually below 200*F at lower firing rates while making 170*F output water. If I had radiant floors or radiators I would run lower temps and get closer to condensation range which I suppose would not be the end of the world if you check your flue often and don't allow it to build up.

I lived with a wood stove my whole life and always took care of my chimney (dad owned a chimney sweep business and tought me well, young). However, I had the opportunity with a woodstove to heat it up well every morning and clean it up well. Not an option with a boiler.


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## DZL_Damon (Feb 28, 2014)

Back on target about stoichiometric air.... this is a decent short read with a nice correlation between Excess Air, lambda, Excess O2, and CO2: http://www.videncenter.dk/Groenne trae haefte/Groen_Engelsk/Kap_06.pdf


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## iceguy4 (Feb 28, 2014)

DZL_Damon said:


> Have you measured your Exhaust temps before and after? My flue temps are quite low already so I don't want to reduce the further...



 No I haven't   BUT I will say my temp's are VERY  low too.    Not even a "hint " of creosote



DZL_Damon said:


> Is the PB105 direct vent?


   Yes...Direct vent   (one of the main  reasons I chose a pellet boiler over a "gasified wood boiler"    I too have burned wood for a good portion of my life. I have ALL the equipment for wood harvesting "and then some"    sssoooo  my choice to burn pellets was not an easy choice.      I  also had my concerns about pellet prices .....What sets my mind "at ease" is the fact that I will buy a "pellet mill" in a heart beat ....just seconds after pellets start to  get "ridiculous"  (at current prices its not feasible)


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## Monica in France (Feb 28, 2014)

These concentric tubes are standard fittings around here. (Except for me ! )
Logically they produce a more controlled environment.
No pressure differences across the fresh air / smoke tubes from the wind etc.
Fresh air  probably at nearly the same temperature all the time.
But otherwise I can't see why they are they should perform better .


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## iceguy4 (Feb 28, 2014)

Monica in France said:


> I can't see why they are they should perform better


     Some cant "see"   .  Some cant cook either...lol


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## iceguy4 (Feb 28, 2014)

One thing  we can all can agree with....most pellet burners supplie  too  much air for combustion.    Lowering the amount of air...a good thing. so taking the more dense air (denser because of its lower temp) from outside  and lowering its density(by raising its temp)  will actually lower the amount of air delivered to the combustion chamber.  (a good thing...remember aprox 79% of combustion air is inert)   This combined with the fact that at times 100° warmer air will not rob energy(BTU's) from the combustion process .    Now I have seen the argument that a 2000° flame will be un affected by this....but It can be calculated by number crunchers here exactly how many BTU's  are saved      For me its not worth the time to figure out the exact difference, and "hang my hat" on the fact that it does in fact save BTU's...=   ....$$$ 

Neigh Sayers...have fun...


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## Monica in France (Feb 28, 2014)

(N)iceguy4 : I agree that my statement was not precise.

I should have said < better than any other OAK installation>
For me It so obvious to use an OAK it did not occur to me to add this.
I certainly have one. When I was installing the stove , and before I found a suitable tube to connect it to my hole in the wall my feet were freezing. One felt that much more cold air was coming though the hole than was being sucked into the stove.
But whether an OAK is more than a health and comfort device I'm not sure.
The Hot air is going up the chimney anyway. The less the better agreed.
This air is coming from the outside either way. Directly or indirectly ( if its not you have a health problem ). Perhaps being pre-heated in the house (by the stove) but certainly by the combustion process. So maybe pre-heating it with concentric tubes ups efficiency as Chickenman claims.

The density of the air is not pertinent , correct combustion is talking relative weights. The hotter the air - the more you need.

I thought that the formation of creosote was from incorrect combustion : not from condensation of
the H2O and CO2 produced by correctly burnt pellets ?


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## iceguy4 (Feb 28, 2014)

First off let me state I meant NO disrespect  and followed my cooking comment with LOL in an effort to show I meant humor in my response. ( I pay attention...you said you can't cook)  Whats more then that is some people can't see different perspectives...I get that. I cant see "art" ...or artistic things like others.  For me that part of my brain is reserved to my mechanical aptitude.   I can see things mechanical and "harmonize " almost immediately..



Monica in France said:


> For me It so obvious to use an OAK it did not occur to me to add this


  For me Its obvious too and you didn't need to add this.     So again I posted to help people with "corrective lenses"  ...To  "SEE" 



> "The density of the air is not pertinent , correct combustion is talking relative weights. The hotter the air - the more you need



Lets turn this around...the hotter the air , the less you supplie.     This statement follows my theory ...pellet burners are supplied with too much air.  Thus lowering efficiency.



> . So maybe pre-heating it with concentric tubes ups efficiency as Chickenman claims


   IMHO   this statement is true...


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## Monica in France (Feb 28, 2014)

Iceguy4 : no sweat , but your reference to my cooking abilities suggested you could have misinterpreted my position.
LOL  - I learned only recently : but what does IMHO mean ? Is it rude ?

The objective of a stove must be to supply as little air ( MASS not volume) as possible to enable correct combustion. And this under varying fuel loads. And to keep it <clean>. And ...
I want to do some arithmetic before replying further : so – 'til tomorrow.


DLZ-Damon : yes , that is a very interesting paper. I've come across it a few times in different contexts. I think it started off life in Norway .
Your version seems to be orientated Wood and not Pellets per se. But is there a difference ?
60 % of the energy comes from the gasses ! Wow.


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## iceguy4 (Feb 28, 2014)

Monica in France said:


> Iceguy4 : no sweat , but your reference to my cooking abilities suggested you could have misinterpreted my position.
> LOL  - I learned only recently : but what does IMHO mean ? Is it rude ?
> 
> The objective of a stove must be to supply as little air ( MASS not volume) as possible to enable correct combustion. And this under varying fuel loads. And to keep it <clean>. And ...
> ...


 In My Humble Opinion


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## hyfire (Feb 28, 2014)

What happens if you reduce the flue gas temperature too much and how do you know what is a safe flue temp and what is not?  I don't think restricting the intake air is a good thing, and lowering exhaust blower either, I can do both in the programming and it netted a bad result.(smoke smell in room) .and put it back to factory settings.


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## Bioburner (Feb 28, 2014)

hyfire said:


> What happens if you reduce the flue gas temperature too much and how do you know what is a safe flue temp and what is not?


A careful read of chickenmans post tells you the parameters of the flue temp vs water condensation, soot etc. Smarter stoves will not be easily  modified because they change fan speeds etc fouling his mods. I think ?


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## hyfire (Feb 28, 2014)

Bioburner said:


> A careful read of chickenmans post tells you the parameters of the flue temp vs water condensation, soot etc. Smarter stoves will not be easily  modified because they change fan speeds etc fouling his mods. I think ?



Sorry he posted while I was writing that... My stove is designed to run up to 400F exh temp. the normal temp is min 200, some people run at 300, no way you can get this to 120F...


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## Bioburner (Feb 28, 2014)

Now the Bixby was heat scavaging with dual piping and runs up the room fan to keep flue temps down.


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## Bioburner (Feb 28, 2014)

chickenman said:


> In some cases you are right Bioburner but these stoves are not really that smart.  The good things about modding like this is that you can see what is happening almost straight away and adjust accordingly.  Yes I have found stoves we cannot help and it usually comes down to fire pot design and inflexible electronics.  No stove has actually outsmarted us yet....AS you have lots of experience you would agree that the technology has not really gone that far over the years.  Compare an 83 car with a new one.  Fair bit of difference there.  It just goes to show how good the original stoves were.


Comes with trying to match the demands of the EPA. So they ramp up the fans to blow more air to thin out the bad air to meet the new rules. I have a original Whitfield 1983 and the output temp is very low and with single wall pipe you can easily put your hand on it.


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## Bioburner (Feb 28, 2014)

chickenman said:


> See the old codgers knew what they were doing.
> It just goes to show that the testing regime is wrong when you need to lose efficiency to pass the tests.  Here in Australia our testing is based on particulate matter per kg of fuel burned.  That is far better I reckon.  That is probably why our efficiency is better than yours - we are not forced to blow heat out the flue to pass some dicky test.
> Far be it from me to suggest you do any thing that goes against EPA standards but surely what you do in your own home is your own business.  The EPA cant tell wood burners to only burn clean wood, why should pellet burners be constrained to crazy regs?


Welcome to this side of the jungle I ran that old Whit for 20 years and still have it and will use it this spring in a greenhouse.


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## Bioburner (Feb 28, 2014)

chickenman said:


> Well done Bio!  Next thing you will be tellin is you use it to make moonshine like the Wiseway boys!


Going down to Knob Creek Kentucky next month Japanese bought the Jim Beam brewery couple months ago.


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## Lake Girl (Mar 1, 2014)

While not strictly related to the original topic, a study you may appreciate ... http://www.nyserda.ny.gov/Publicati...opment-Technical-Reports/Biomass-Reports.aspx  #11 European Wood Heating Technology

Enjoy!


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## Monica in France (Mar 1, 2014)

I said <maybe> , Iceman4 said <IMHO> , Chickenman < agreed totally> but didn't actually prove it : but do we need to dapple in conjecture ?
Between us we have enough facts and arithmetic to calculate the effect of preheating the input air.
I was hoping to do 'a tour de force' and show you but I got hopelessly bogged down in different units and realized I was making assumptions which maybe were not justified.
But on this forum we surely have enough knowledge between us to hammer this out ?

Let us start with pellets at room temperature ( 20°C ) , exterior temperature of 0°C and the smoke output temperature given by Chickenman of 120 °C.
With this stove we will burn one gm of pellet in the best possible manner which will produce about 4.7 watts of energy.
All we need to do is to add up where the heat comes from and where it is going.


In the best possible manner we have : ( = stoichiometric )

*1 gm of DRY pellets + 6.4 gms of AIR = 1.83 gms CO2 + 0.52 gms H2O + 5.05 gms N2.*


The specific heats are ( SI units )
Wood 1.76 : Water 4.14 : Steam 2.08 : Air 1.01 : CO2 0.84 : N2 = air

So we start with the heat inherent in one gm of pellets at room temperature and 6.4 gms of fresh air = Init_Heat.
We burn it which adds the 4.7 Watts = Input_heat
and pumps hot air into the flue = Waste_Heat
So our efficiency is ( Input_heat - Waste_heat ) / ( Input_heat )

Have I made a mistake already ?
And now I need help . I've tried and tried – but failed miserably.
Who can fill in the numbers ? The units don't matter , use the ones you are used to.
That done we can vary the input air temperature and see what sort of effect it has on the result.
I think the result will be positive but not significant – prove me wrong. Please.


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## DZL_Damon (Mar 1, 2014)

I think you might be mixing the 2 methods into one: the Direct method and Indirect method for calucalting boiler efficiency?

Direct method uses Heat Out (Qo) measured from water temperature rise & flow and  Heat in (Qi) is from known fuel values. Dividing Qi/Qo=Efficiency.

The Indirect method primarily utilizes Excess air (or Excess O2) and inlet temperature of air and exhaust temperature of air. It involves a lot of balance chemical formulas like you were demonstrating before. It has a greater margin of error since you are calculating the heat losses vs the heat utilized. Therefore, a small error or assumed value while calculating something that should only be 10-20% of the accounted fuel energy will yeild a larger error than if you were calculating where 80-90% of the energy goes.

The most difficult part I have struggled with while using the Indirect method is knowing the correct composition of C, H, N, and O for the fuel you are using. I get quarterly pellet samples taken from our 2 suppliers. The numbers are not consistant it appears since pellets take wood from several species more often than not


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## Monica in France (Mar 1, 2014)

Suddenly realized where I was going wrong.
Corrected it and came up with a result I did not expect.

I won't share it with you – *I would prefer someone else confirmed my findings first.*


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## Monica in France (Mar 1, 2014)

DZL_Damon : I get this feeling that you know much more about this subject than me : have even forgotten more than I know. I know nothing at all about 'methods' : I thought I was arguing from first principals. 
But I get your point , and its the sort of point I was hoping people would make :  But even if I am mixing methods : is my *LOGIC* correct ?
I know I picked the easiest formula – it was the only one I could get a handle on. But could you bear with me and do the arithmetic for me ? 
Then we can argue about margins of error and why the result is not realistic.

I've put my figures into a tableur and played with them. Frankly I would prefer that I've got it wrong.

I simulated a petrol engine last winter in much the same way. The actual simulation is worthless but you learn so much while writing it.


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## Monica in France (Mar 2, 2014)

Pour faire une omelette *il faut casser des oeufs,*
Agreed : but the danger is to break the eggs without making an omelette.
And you forget – I can't cook. Iceman is not wrong there.
But you are not the first to accuse me of mental masturbation.

Probably I will get my hands dirty when the heating season is over but not before I know what I am trying to do. You mentioned the advances in car technology – this is not due  'playing around until it works' – that finished in the 70's . It came from computer simulation of the motor. They discovered amongst other things that the people polishing the inside of the inlet manifold were making things worse not better. Yes - I know that people are still polishing away : but there are people who think OAKs are a waste of time as well.

I received your certification report - it was very interesting - especially the appendixes
I always like reports with a section < uncertainty of measurement statement >.
Whilst they were not explicit I understood that their definition of efficiency was :

*Efficiency = Heat in the room / Heat paid for.*

I would suggest that neither of the two standard options ( Combustion and Thermal - see Damon above) is appropriate to a domestic pellet stove. Something in a boiler room - perhaps , but not a stove in your living area. All energy going into the stove – and that includes fans and triac heatsinks is being used to heat the room. The only energy being wasted is that going up the chimney.


I very much like this definition of efficiency for pellet stoves.


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## chken (Mar 2, 2014)

chickenman said:


> Sorry guys, I made a mistake.  I should have said 120 Celsius not F.  So the temp we aim for is 250 F.  Hyfire is right you can't get down to 120F.


Oh my god, for a few days there, I had been thinking about my stove and trying to figure out how to lower the air rate to get to 120F exhaust temp when my room blower won't even come on unless it's 175F exhaust temp!


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## John Ackerly (Nov 10, 2015)

Great thread guys.  Just came across it.  We tested 6 popular pellet stoves and found average excess air was usually in the 14 - 19% range: http://www.forgreenheat.org/decathlon/efficiency.html.

Most folks say that other objectives - like clean glass - get prioritized over efficiency, so they allow too much air into the firebox to keep the glass clean. In our upcoming pellet stove competition, we have some folks taking existing pellet stoves and trying to retrofit them with an oxygen sensor to see how hard it is to improve efficiency.  If anyone knows how to do this, please consider entering our competition - or attending the event in April to see how these folks tried it. http://www.forgreenheat.org/decathlon/stove.html


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## NYBurner (Nov 11, 2015)

This was an interesting thread, and if I am understanding this correctly then burning 'rich' is more efficient at the expense of black glass?  Also there will not be creosote build up provided the 'rich' burn is kept within a range?

Im assuming the reasoning for more efficiency is that hot air is held in the chamber longer allowing more time for heat transfer before it gets pumped up the chimney?


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## John Ackerly (Nov 11, 2015)

NYBurner said:


> This was an interesting thread, and if I am understanding this correctly then burning 'rich' is more efficient at the expense of black glass?  Also there will not be creosote build up provided the 'rich' burn is kept within a range?
> 
> Im assuming the reasoning for more efficiency is that hot air is held in the chamber longer allowing more time for heat transfer before it gets pumped up the chimney?



I would like to think that you can get a efficient burn and keep the glass clean at the same time.  Creosote does happen from some pellet stoves burning some pellets, but many pellet stoves avoid creosote altogether, and they really should be able to design pellet stoves that work well enough not to make creosote.  Pellet stoves aren't as sophisticated as many people may think.  The Enviro M55 has a sensor right in the firebox and also in the exhaust stream, but others have few sensors that can change the air to fuel mixture on the fly.  Most seem to work on factory settings established for good quality pellets.  We just heard a team from the University of Maryland is buying a Vogelzang pellet stove and testing it at its factory settings, and will then see how much they can optimize it.  And, the great thing is that they will share all the steps they went through to improve the efficiency.  I hope pellet stove manufacturers are paying attention to this experiment!  Here are teams vying to be finalists so far, including one university team starting with the Quadra-Fire Classic Bay 1200. (See http://www.forgreenheat.org/decathlon/teams.html). The team starting with the Vogelzang will be posted later today on that page.


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## Pelleting In NJ (Nov 11, 2015)

John Ackerly said:


> Great thread guys.  Just came across it.  We tested 6 popular pellet stoves and found average excess air was usually in the 14 - 19% range: http://www.forgreenheat.org/decathlon/efficiency.html.
> 
> Most folks say that other objectives - like clean glass - get prioritized over efficiency, so they allow too much air into the firebox to keep the glass clean. In our upcoming pellet stove competition, we have some folks taking existing pellet stoves and trying to retrofit them with an oxygen sensor to see how hard it is to improve efficiency.  If anyone knows how to do this, please consider entering our competition - or attending the event in April to see how these folks tried it. http://www.forgreenheat.org/decathlon/stove.html


The challenge will be to develop a method to keep the oxygen sensor from fouling-up from the combustion by-products. Also, probably need a heated ox sensor, as the stove exhaust temps may not be hot enough for the ox sensor to function, especially if the stove is made more efficient (which will lower the exhaust temp). I suspect because of the above reasons it is not practical to utilize and ox sensor for a pellet stove.


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## Pelleting In NJ (Nov 11, 2015)

John Ackerly said:


> Great thread guys.  Just came across it.  We tested 6 popular pellet stoves and found average excess air was usually in the 14 - 19% range: http://www.forgreenheat.org/decathlon/efficiency.html.
> 
> Most folks say that other objectives - like clean glass - get prioritized over efficiency, so they allow too much air into the firebox to keep the glass clean. In our upcoming pellet stove competition, we have some folks taking existing pellet stoves and trying to retrofit them with an oxygen sensor to see how hard it is to improve efficiency.  If anyone knows how to do this, please consider entering our competition - or attending the event in April to see how these folks tried it. http://www.forgreenheat.org/decathlon/stove.html


The challenge will be to develop a method to keep the oxygen sensor from fouling-up from the combustion by-products. The exhaust from a gasoline car is way cleaner than what comes out of a pellet stove!  Also, probably need a heated ox sensor, as the stove exhaust temps may not be hot enough for the ox sensor to function, especially if the stove is made more efficient (which will lower the exhaust temp). I suspect because of the above reasons it is not practical to utilize and ox sensor for a pellet stove.


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## maple1 (Nov 11, 2015)

Oxygen sensors are used in some wood boilers - should be OK for pellet exhaust.


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## NYBurner (Nov 11, 2015)

John Ackerly said:


> Great thread guys.  Just came across it.  We tested 6 popular pellet stoves and found average excess air was usually in the 14 - 19% range: http://www.forgreenheat.org/decathlon/efficiency.html.
> 
> Most folks say that other objectives - like clean glass - get prioritized over efficiency, so they allow too much air into the firebox to keep the glass clean. In our upcoming pellet stove competition, we have some folks taking existing pellet stoves and trying to retrofit them with an oxygen sensor to see how hard it is to improve efficiency.  If anyone knows how to do this, please consider entering our competition - or attending the event in April to see how these folks tried it. http://www.forgreenheat.org/decathlon/stove.html



John - I read the article regarding efficiency but was left wondering what the conclusion of the testing was?  I see that the usage was ~1 ton per stove over a month cycle, but it does not discuss how the stoves were configured, feed rates, damper settings, etc.. so what was the final conclusion?
  I understand the idea of 'excess' 02 measured at output but were any steps taken to adjust feed to compensate?  Also flue temp was not explained in relevance to efficiency, is this explained as more efficient heat exchange or result of improper combustion?
  Also in terms of this thread discussion relative to intentionally running rich for wood pellet stoich combustion, is the intent to slow air travel and allow a longer heat transfer time or more a function of burn time relative to the fuel to create a complete burn?
  Sorry for all of the questions, I am just trying to understand this correctly.


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## smwilliamson (Nov 12, 2015)

Lake Girl said:


> Your stove is set up for your installation set-up?  Pelleting in NJ probably sent you both manuals...  From there, you can make minor adjustments to air and pellet drop - press buttons 6 & 7 together to get pellet and draught.  This would accommodate pellet change.
> 
> These stoves have multiple heat sensors but that really doesn't say much about the efficiency of the burn...  I have noticed the combustion blower will change slightly but not quite sure what triggers that as the temp remains fairly steady (state stove).


Ravelli uses a hall sensors on the motor housing of the combustion blower to maintain variable known RPMs in the system logic. The older controllers and I'm not sure on the latest models, there was a recipe the installer had to set according to the vent length. This increased or decreased overall percentages of full power to the combustion blower across all heat settings. However, when fire is achieved, the stove creates positive pressure in the vent via heat (draw) so the hall sensors allow the controller to change output to the combustion blower.


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## Pelleting In NJ (Nov 12, 2015)

The newer Ravelli / Ecoteck stoves, with the new RDS feature, don't need the "install recipe" setting (based on the installers opinion of the flue vent restriction/configuration). That was replaced with the RDS initial setup routine,  done one-time when the stove is installed, which actually measures the restriction of the flue vent system that was installed, and sets the baseline RPM of the combustion blower (for each of the "power" heat settings P1 thru P5). The RDS system can do this because it has a mass-airflow sensor in the intake air path, which can measure the volume of intake air. The controller adjusts the RPM of the combustion blower to get the measured intake air volume to match the factory preset values, one for each P power level. This RDS system is effectively an auto-adjusting combustion air damper, and can maintain the same amount of combustion airflow even as the flue and burn-pot becomes more restrictive due to ash build-up. When the ash build-up becomes too large to be compensated for (by ever increasing the combustion blower RPMs), the stove then trips an alarm that tells the user to clean out the stove.

The "old" Rika Austroflam Integra stoves were the first stove to use an intake mass-airflow sensor, but they did not have an adaptation routine like the Ravelli RDS, to adjust for different exhaust flue pipe restrictions/configurations that are unique for each installation.


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## NYBurner (Nov 13, 2015)

Hey Guys - just hoping to bump this so someone in the know can answer my questions on this (post #54 right above).  With discussions bouncing back and forth regarding o2 sensors, mass air, etc....I feel there is 3 different focus of discussions taking place that all have different requirements, clean emissions, ideal burn, and stove heat efficiency.  Either that or I am totally missing something very apparent to everyone else so would really appreciate the clarification/education!


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## smwilliamson (Nov 13, 2015)

NYBurner said:


> Hey Guys - just hoping to bump this so someone in the know can answer my questions on this (post #54 right above).  With discussions bouncing back and forth regarding o2 sensors, mass air, etc....I feel there is 3 different focus of discussions taking place that all have different requirements, clean emissions, ideal burn, and stove heat efficiency.  Either that or I am totally missing something very apparent to everyone else so would really appreciate the clarification/education!


Clean emissions and ideal burn are kinda the same thing. 


NYBurner said:


> Hey Guys - just hoping to bump this so someone in the know can answer my questions on this (post #54 right above).  With discussions bouncing back and forth regarding o2 sensors, mass air, etc....I feel there is 3 different focus of discussions taking place that all have different requirements, clean emissions, ideal burn, and stove heat efficiency.  Either that or I am totally missing something very apparent to everyone else so would really appreciate the clarification/education!


Stoitiometry as it relates to the air and fuel in the combustion of a pellet stove has to take in to consideration a lot of variables that are not known or may be a variable. The common ratio in wood combustion is 35 parts air to 1 part fuel as they meet and combust in the combustion zone. Pellet stoves, because they have controls and induced draft for a very long time enjoyed a default efficiency of 78% as it was thought that through these controls, optimum efficiency was going to be achieved. I believe this myth as been busted. All manufacturers seems to go about this achievement in all sorts of ways and if I had to put money on it, from the testing I've been privy to in the lab as well as my vast knowledge of equipment out there, I'd have to say that very few, if any, are able to get to and maintain that sweet spot and here's why. As I said above, there are variables.

For example, a pellet stove rated for 3" diameter venting that has 3 90 degree offsets, rises 7 feet in height and travels 2 feet horizontal will have much more restriction than a direct vent installation of 3' straight out horizontal through a wall. These two installation types are common and both quite short runs but will perform different, especially once they are dirty, whether they are warm or cold and whether there may be additional influences such as leeward or windward issues relating to the side of the house they may be installed on. Additionally the same unit may be vented in to a masonry liner, insulated or not and extending 40 feet above a roof pitch. All the same stove.

Some installation requirements want the installer to start and run the stove and set dampers, such as the case with all Sherwood products. Harman may have a default impeller that is used below 4000 feet in altitude or another one used above.

All of this plays into how much air is allowed to enter the machine. Most stoves have an excess of air. This allows the unit to run and operate the same when it's clean as when it's slightly neglected but this approach will lower the overall combustion efficiency as well as emissions.

The correct ratio of air required cannot be attained in an all-in-one blanket approach. As stated above, Sherwood allows a damper to be set for the installation by measuring the draft and making the required corrections but j can tell you most installers just don't do it. It adds an additional 1 or 2'hours to the install, most don't own the equipment etc etc

Back in the day or Austroflamme, now Rika and also the engine for todays Hearthstone pellet stoves, a mass airflow sensor was used in the intake path that allowed the controls to measure and ramp up or down the combustion fan to try and create a perfect air to fuel ratio. If the vent was in a tall chimney liner, there would be an assist once the liner became warm and this would pull air through the machine. The control board can see the RPMs rising and slow the motor. If the system had a direct vent and it was very dirty, the airflow would be restricted and to some extent the draft blower could speed up and deliver more air....however, there are some drawbacks; the controls are ONLY measuring the air flow and bouncing that info off a preprogrammed known variable written in to the logic. Also, it can only measure the intake air from the intake. Of the stove has an air wash, gasket leak etc, combustion efficiency is affected. This system is far from perfect. While it seems to know what going on in the stove for air, it doesn't really know what going on on the fuel side.

From a measurement standpoint it seems to me that if one is trying to create the "perfect burn" one MUST measure the stove's combustion efficiency such as with a oxygen sensor as well as mass air flow and perhaps even a fit of temp sensor and white your at it, toss a sensor on the vent too.

It's a lot to consider and try and work out. I can tell you this, no manufacturer seems to want to let the end user know too much about what actually going on and perhaps that's an issue the service sector of this industry needs to try and figure out.

I spent a couple days with this dude Norbert, a builder of masonry heaters up in Canada. We was saying that they passed  some regulations in his parts where technicians as part of a chimney service actually have to test the system for efficiency and make adjustments as necessary. The test adds $100 or so to the cost of a service call and requires an upfront investment of $6k or so for the equipment, but in his view it's worth it. For one it gives a bit of credibility back to the trade as we are actually measuring something and making improvements AND it kind of thins out those who are charging for a service that they may or may not be doing correctly. That's a whole new thread.


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## NYBurner (Nov 13, 2015)

Scott- I agree with what you are saying (except that emissions focus and perfect burn focus are identical......often similar but not the same) however, that is my question.  What is the focus of determining the parameters of a 'perfect burn'??  The test paper posted above had some very interesting information but the relevance and intended data support was never given.  (ie...If my emissions have high relative O2 but my flue temps are safe.....why is that inefficient/bad and how does it correlate to heat output into my house?)

  I, like everyone on this forum love to tinker with the stove and see what it can do..learn how to make it better.  At the same time its main objective in my opinion is to heat and reading what is in this thread, I am being advised that I need to choke down my stove for a 'better' burn.  So I am asking....what constitutes a 'better burn' relative to direction given by the Green Heat Team and the info posted?  Is this more emissions oriented, or better for me heat transfer oriented?? When I am thinking efficiency I am thinking of thermal efficiency into my home.

  Running lean in a race motor is associated with running hot.  However a race motor runs under compression and a pellet stove running under very low vacuum are two completely different things and I am trying to understand.


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## velvetfoot (Nov 13, 2015)

As far as I understand it, my pellet boiler takes the inputs of water temperature, flu temperature, and time and varies pellet feed rate and induced fan speed according to some magic algorithm.  Windhager touts its system as requiring less maintenance and provide just as good results as, for example, Fröling's lambda sensor, which I'm sure Fröling would contest.  I would imagine one could stick a probe from a device similar, or maybe the same, as that used by an oil burner service tech, to determine efficiency.  I think one indicator of efficiency could be flue temperature-the lower the better, above the condensation point.  I have read that there are condensing pellet boilers in Europe.


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## smwilliamson (Nov 13, 2015)

NYBurner said:


> Scott- I agree with what you are saying (except that emissions focus and perfect burn focus are identical......often similar but not the same) however, that is my question.  What is the focus of determining the parameters of a 'perfect burn'??  The test paper posted above had some very interesting information but the relevance and intended data support was never given.  (ie...If my emissions have high relative O2 but my flue temps are safe.....why is that inefficient/bad and how does it correlate to heat output into my house?)
> 
> I, like everyone on this forum love to tinker with the stove and see what it can do..learn how to make it better.  At the same time its main objective in my opinion is to heat and reading what is in this thread, I am being advised that I need to choke down my stove for a 'better' burn.  So I am asking....what constitutes a 'better burn' relative to direction given by the Green Heat Team and the info posted?  Is this more emissions oriented, or better for me heat transfer oriented?? When I am thinking efficiency I am thinking of thermal efficiency into my home.
> 
> Running lean in a race motor is associated with running hot.  However a race motor runs under compression and a pellet stove running under very low vacuum are two completely different things and I am trying to understand.


Yes agree, heat transfer efficiency and emissions efficiency are two completely different things. Harman stoves, specifically speaking, the 52i insert (that's what we tested ourselves) has a fantastic heat transfer on low to medium burns, it could be seen by monitoring the flue temps. But as we increased up to high burn rates, the flue temps went up considerably as compared to the lower and medium settings. This really has all to do with the heat exchangers thermal transfer capability. One the one hand, we want the stove produce as much heat as required but on the other hand one is limited by the design. Suppose that's one of the reasons why we tested stoves.

A perfect burn is subjective and subject to interpretation I suppose. I can tell you this, stoves are primarily "decorative" appliances. If manufacturers were super interested in achieving the highest efficiencies, both transfer and emissions, they would get rid of the glass. Glass is a problem as its not insulated and to keep it clean air that could be used solely for combustion is diverted to that glass suave to keep it clean via friction, which I'll add also cools the firebox. This is another topic altogether but part of getting these efficiencies up, you need to insulate the firebox and direct the whole amount of heat to the exchanger. Focus there. From my point of view, a stove really needs to monitor efficiency and have some kind of a variable heat exchanger that can  transfer heat at as close to 100% as possible across all heat levels. Water jackets do this fairly well in boilers. I've done a few prototype drawings using mineral oil. 

Perfect burn... Nothing's perfect. One thing for sure, there's plenty of room for new technology in a system that hasn't seen much innovation since it was conceived 30 years ago.


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## smwilliamson (Nov 13, 2015)

velvetfoot said:


> As far as I understand it, my pellet boiler takes the inputs of water temperature, flu temperature, and time and varies pellet feed rate and induced fan speed according to some magic algorithm.  Windhager touts its system as requiring less maintenance and provide just as good results as, for example, Fröling's lambda sensor, which I'm sure Fröling would contest.  I would imagine one could stick a probe from a device similar, or maybe the same, as that used by an oil burner service tech, to determine efficiency.  I think one indicator of efficiency could be flue temperature-the lower the better, above the condensation point.  I have read that there are condensing pellet boilers in Europe.


Awe I thinks it's more complicated than "sticking a probe from a similar device"! There needs to be some logic to read the input and then all that data needs to be bounced off all of the other data that's being considered. I've written some ladder logic and man, you have like three lines of of code for one event and then you add another data set and then you have 12 lines of code and the. You add another data set and you have 36 lines of code....to a system that may have 1200 lines of code or more adding another data set is like rewriting 3600 lines of code!


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## velvetfoot (Nov 13, 2015)

I was referring to the Bacharach combustion analyzer, or whatever, that the oil techs use to measure the efficiency of an oil burner.  You referred to that earlier to analyze the efficiency of a biomass burner.


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## smwilliamson (Nov 13, 2015)

Right, gotcha, like a Testo or such. But I agree, someone should use something to see what's relevant to the issues atbhand


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## velvetfoot (Nov 13, 2015)

That's the name I was thinking of.


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## NYBurner (Nov 16, 2015)

smwilliamson said:


> Yes agree, heat transfer efficiency and emissions efficiency are two completely different things. Harman stoves, specifically speaking, the 52i insert (that's what we tested ourselves) has a fantastic heat transfer on low to medium burns, it could be seen by monitoring the flue temps. But as we increased up to high burn rates, the flue temps went up considerably as compared to the lower and medium settings. This really has all to do with the heat exchangers thermal transfer capability. One the one hand, we want the stove produce as much heat as required but on the other hand one is limited by the design. Suppose that's one of the reasons why we tested stoves.
> 
> A perfect burn is subjective and subject to interpretation I suppose. I can tell you this, stoves are primarily "decorative" appliances. If manufacturers were super interested in achieving the highest efficiencies, both transfer and emissions, they would get rid of the glass. Glass is a problem as its not insulated and to keep it clean air that could be used solely for combustion is diverted to that glass suave to keep it clean via friction, which I'll add also cools the firebox. This is another topic altogether but part of getting these efficiencies up, you need to insulate the firebox and direct the whole amount of heat to the exchanger. Focus there. From my point of view, a stove really needs to monitor efficiency and have some kind of a variable heat exchanger that can  transfer heat at as close to 100% as possible across all heat levels. Water jackets do this fairly well in boilers. I've done a few prototype drawings using mineral oil.
> 
> Perfect burn... Nothing's perfect. One thing for sure, there's plenty of room for new technology in a system that hasn't seen much innovation since it was conceived 30 years ago.



Ok this kind of walks back to what I was thinking and I wanted to make sure of in my head before I commented in this direction.  Moving away from the glass, liquid transfer, etc...the reality is we all bought pellet stoves for the ambiance as well the heat.  Attempting to turn these into blast furnace style stoves would defeat the purpose really, and people looking for something of that style can get one (furnace/boiler).  So basically at the end of the day this all really comes back to a thread I had posted a month or two ago regarding turning up the convection blower manually.  

Via the test data, high flue temps indicate that the maximum heat transfer is occuring in most all of the stoves via their thermal capacity, except the Enviro (which is more apparent by the o2 data suggesting non ideal burn although Im not sure I agree with this).   In reality, creating guidelines or research into a 'more efficient' burn are some what pointless.  Either a catalyst afterburn can be added similar to a blazeking wood stove to increase both thermal output and emissions cleanliness, greater mass needs to be added to the stoves, and/or higher output convection blowers to increase the temp delta between burn and exchanger.  Correct?

I really like the idea of improving efficiency, and tinkering in general.....but this smells like a big marketing push via the industry to 'add on' a bunch of sensors/complexity/service and COST to a system that really just needs a bigger fan/plate of metal added.  I love innovation, but at this point the basic crude design is not even perfected.


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