Stack temp, air flow and Btu output

[goosegunner]

I just cleaned my Econoburn 200 Friday. Today I installed a Thermocouple with PID digital display. I put the thermo couple in the flue outlet on the back of the boiler.

I had been using a magnetic gauge about 1' up from the outlet.

When the magnetic external read just under 250 the internal thermocouple read 625.

I have seen the magnetic one at 300 so internal temps will be higher than 625 at that point.


My fan butterfly is full open, does that reduce flue temp if I close it down a little?

What does that do to output if I close down the primary air a little?

The boiler will burn 90lbs of oak in less than 3 hours. I am calculating 4000-4200 btu's per lb of wood to storage. Would reduced air flow net more btu to storage if I reduce flue temp?

gg

 

[Singed Eyebrows]

I just cleaned my Econoburn 200 Friday. Today I installed a Thermocouple with PID digital display. I put the thermo couple in the flue outlet on the back of the boiler.

I had been using a magnetic gauge about 1' up from the outlet.

When the magnetic external read just under 250 the internal thermocouple read 625.

I have seen the magnetic one at 300 so internal temps will be higher than 625 at that point.


My fan butterfly is full open, does that reduce flue temp if I close it down a little?

What does that do to output if I close down the primary air a little?

The boiler will burn 90lbs of oak in less than 3 hours. I am calculating 4000-4200 btu's per lb of wood to storage. Would reduced air flow net more btu to storage if I reduce flue temp?

gg

GG, I don't think the bimetal stick on's are that accurate so I would just go by the probe. If the EB is like my Atmos reduced air will reduce temps. I would strive for about 400 degrees & if its not going up the chimney its going into the water. I cannot adjust primary & secondary independantly so hopefully an EB owner can help with that, Randy

 

[woodsmaster]

I have a candy thermomiter for flu temp and magnetic for external. The Magnetic for me is usually 100 F less than the prob.
600 F flu temp seems a little high. Can you slow the fan down to drop flu temp and se if you can measure a difference
in total output ? How was it to clean ?

 

[woodsmaster]

Any chance the sensor is off. I suppose to much air could be the cause to. If you can close the air down and still get a clean burn maybe that will lower flu temps ?

 

[goosegunner]

As far as I know the fan speed cannot be controlled. The air can be controlled by the plate on the fan, it also has adjustment bolts for secondary air.

I knew the Magnetic gauge was off but I was surprised by how much. I have checked the metal flue pipe with a infrared temp guns and the metal will read 500 so I believe the internal probe is accurate.

Over the last couple months as I started trying to calculate output I have wondered if it was supplying air too fast and losing a lot of btu's up the stack. It seems as though high stack temps and 4000 btus/lb to storage would point in that direction.

Will closing damper lower temps or will the velocity of air stay the same by using a plate to control air flow instead of speed?

gg

 

[TCaldwell]

the thermocouple is probably accurate, I would try recleaning the hx tubes first. do you have a clean burn wiht your current p/s air settings, is there no smoke?
if you only reduce the fan speed with your currrent settings the output will reduced, a lower btu output, might help, the lower fluegas velocity will have longer dwell time. If you increase the p air, a quicker initial start to gasification, however will produce too much woodgas for the secondary air to maintain setpoint, dropping o2 and losing gasification thus smoke, unburned fuel up the stack. decreasing p air will take longer for gasification startup, burn at a higher o2 level during gasification and you will be overaired towards end of burn. and too much secondary will give the same symptoms as too little primary, too little secondary will give the same results as too much primary. You can think of this as the primary air creates the woodgas and the secondary air reburns thoes gasses at the correct o2%, so at the beginning of a burn the p damper modulates to open and the s damper modulates to close, as the fire progresses both dampers will modulate towards open, and as the fire wanes it will act as the beginning of a fire. this holds true for a batch burn, you are retarding the fire at the beginning and letting it out as the fire progresses and forcing it at the end. with static air controlls the best would be to find a happy medium, and the p/s ratios will change on wood mc. a inline damper will act the same as a lower fan speed, this is called a fan damper, they are controlled fire box pressure, maintaining a slightly negative pressure. less fire, less air and more fire more air, ehausto manufactures them.

 

[PassionForFire&Water]

I agree with Randy: reduced air = reduced temperatures

Check your sensor if you can.
Put it in an ice/water bath. Should read 32F
Boil water and stick it in. should read close to 212F
Now you know the temp curve reading are somewhat linear and correct

sorry, this procedure probably does not work with the magnetic ones. But it is interesting to do this experiment and see what the deviations are, so you can come up with correction factors

 

[willworkforwood]

gg,
Did you pull the turbs and clean the tubes and get them back down to metal? I know you have the new controller but, unless the Nimbus board has also been replaced, you can change fan speed via the Nimbus dip settings. 650 is high, and something is going on. In addition to the 2 items already discussed, how about draft - could it be getting pulled up the stack? Do you have a BD installed?

 

[goosegunner]

Yes I pulled the turbulators and wired brushed them with a drill. I am not sure how to controll fan speed with the new controller. I sure there is a way because it will slow fan when boiler hits 5 degrees below set point.

I do have a barometric damper set to proper draft. I monitor it with a manometer.

Econoburn website states flue gas temps of 280-400. Mine is running basically double that.

The boiler burns with clean exhaust at this point. I would think it would be best to control speed vs volume of air with butterfly plate.

Wouldn't the air velocity stay the same with plate adjustment?


gg

 

[willworkforwood]

Try cross-checking the probe for accuracy as previously mentioned. Then, if it's accurate and in the correct location according to the manufacturer, you should give Dale a call next week and give him the full scoop. Seems like your boiler is either pushing or pulling in extra air. He might have you change the Nimbus to reduce the fan speed, or perhaps the air P/S adjustment - or maybe something else entirely. There has to be some reason why you're running so high, and you're already beyond most of the obvious ones. Good luck with it!

 

[goosegunner]

I Checked the probe;

In a glass of ice water 36 degrees

In a pan water that just stopped boiling 200

I would think those numbers are correct since the water is not at freezing temp it was melting the ice and the hot water was not actively boiling when I put the probe in.

What do you think, close enough to call probe accurate?

gg

 

[salecker]

Hi GG
I have the magnetic probe in my chimmany,and i see numbers to match yours.My dealer is supposed to come and check the efficancy with a meter when they are out here.I have turned down the primarys 3/4 of a turn and havn't noticed any real differance.Seeing how my main attention and time is being concentrated on my house,i havn't pursued the problem.I know i have lot's of improvements on the heating system after the hopuse is done.Right now it is -40 C or F and we are warm,storage will last about 16 hours,last fire shut off at 11PM and will probly start one around 6pm tonight.
But i would really like to see lower stack temps!!
My wood is super dry and i get a lot of huffing at the begining of the burns.
Good Luck i'll be watching for thingd to try.
Thomas

 

[hobbyheater]

[quote author="salecker" date="1326669194"]

Port McNeill , Northern Vancouver Island its a balmy +20 F here today :exclaim: Just wondering which part of the North you are from?

 

[salecker]

Port McNeill , Northern Vancouver Island its a balmy +20 F here today :exclaim: Just wondering which part of the North you are from?

Hi Hobbyheater
I'm in the Yukon,100miles north of the big city of Whitehorse.I belive that there is a Jetstream keeping a house warm in town here.Been meaning to contact the guy to see if that is correct.
Thomas