"the correct Stoichiometric ratio"

[iceguy4]

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

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)

 

[Monica in France]

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 .

 

[iceguy4]

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

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

 

[iceguy4]

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...

 

[Monica in France]

(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 ?

 

[iceguy4]

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..

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...

 

[Monica in France]

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.

 

[iceguy4]

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.

In My Humble Opinion

 

[hyfire]

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.

 

[Bioburner]

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 ?

 

[hyfire]

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...

 

[Bioburner]

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

 

[Bioburner]

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.

 

[Bioburner]

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.

 

[Bioburner]

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.

 

[Lake Girl]

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!

 

[Monica in France]

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.

 

[DZL_Damon]

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

 

[Monica in France]

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.

 

[Monica in France]

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.

 

[Monica in France]

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.

 

[chken]

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!

 

[John Ackerly]

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: (broken link removed to 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. (broken link removed to http://www.forgreenheat.org/decathlon/stove.html)

 

[NYBurner]

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?

 

[John Ackerly]

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 (broken link removed to http://www.forgreenheat.org/decathlon/teams.html)). The team starting with the Vogelzang will be posted later today on that page.