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not your grandpa's garn

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by TCaldwell, Jan 15, 2012.

  1. bigburner

    bigburner Feeling the Heat

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    I still would like more meat & potato's, this is a great project, the garn may not have seen a bunch of improvement, the designer built it like a carburetor and the new controls make it like fuel injection, some HP gains, better fuel economy and if he could drive up a mountain it would adjust for elevation,I am sure. My system could benefit from these control because of the amount and quality of the wood I burn. I would like to see & hear more. FYI these are my numbers from to other day one hour after reload [they need some work] O2% 15.7,CO2%5.0, CO PPM 580, Flue temp 192.2, Inlet Temp 45.5, EFF G[c] 82.4, Losses 17.6, XAIR% 301.9,CO/CO2 .0114, CO air free 2331

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  2. TCaldwell

    TCaldwell Minister of Fire

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    Bigburner, last night ran a load and checked with the testo 327 fluegas analyser,
    75lb mixed load firewood, 4 minutes from liteoff to 1200deg in secondary burn chamber, 3 minutes after that
    flue temp 277, co12.65 ,ex air56.7 , ppm co780 , ppm coaf1224 , o2%7.6 , net eff84.7, 30 minutes later,
    ft 267 co 12.55 ex57.7 ppmco 1224 ppmcoaf 1965 o2 %7.8 net eff 84.8

    The wood mc was a little on the high side, not sure how these numbers compare to others
  3. heaterman

    heaterman Minister of Fire

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    You talking net or gross flue temp?
  4. TCaldwell

    TCaldwell Minister of Fire

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    Steve, what are the ranges these fluegas numbers should be in? will higher mc wood cause high ppm co?
  5. heaterman

    heaterman Minister of Fire

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    For those of you who want to learn a little about combustion, here is a really good guide written by Jim Bergman, (a good lad with roots in Northern Michigan) who used to work at Testo. It's written in plain English and deals mainly with gas and oil burning equipment but much of the info is valid for solid fuel also. Pay attention to the graph of the relationship between O2, CO2, CO and excess air. Once you understand how that works you'll be able to make any burner sing a happy tune.......if you have the right equipment.

    http://www.aikencolon.com/assets/images/Testo/3161/pdfs/CombustionGuide.pdf

    You can also go here

    http://www.testo.com/online/abaxx-?$part=PORTAL.USA.Applications&$event=show-from-menu&categoryid=2735668

    and download the pdf field guide titled flue gas.
    That one is more technical and will make your eyes cross unless you're a chemistry/physics geek but there is some good info on solid fuel combustion in it.
  6. allan

    allan Member

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    Tom, nice work! I appreciated all your input when I was building my "garnlike" boiler. I also installed the tubalator in my last pass and it made a big difference. I thought about doing more to my boiler, but the truth of the matter is I like the simplicity. The other side of me wants to do what you did. It is a battle between the two sides. I have a balancing mechanism call my wallet unfortunately.
  7. bpirger

    bpirger Minister of Fire

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    Tom, did you find that your mixing pump allowed you to store considerably more heat in the Garn in a firing? I assume you can get the bottom of the tank to warmer temps. I know my front panel sensor seems to read at least 15 degrees warmer than the water out of my supply line....a couple of hours after a burn and onward. I assume mixing more thoroughly during the burn would allow the water at the bottom to get warmer....hence more heat in storage.

    I know heaterman says the mixing is quite pronouced during the burn, and I'm sure the convection makes it so, and without sensors on the bottom of the tank I don't know what it actually does get to....but I assume an adequate mixer would really help.
  8. TCaldwell

    TCaldwell Minister of Fire

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    aside from the old style gage i have 3 external sensors on the garn, 2 are on the front the first on the tank bottom face and the second at the tank top water line. typically right after a burn and the mix loop has shut off the 3 front sensors all read within 5deg, after say 6 hrs of load the gauge and top sensor might read 175 and the bottom sensor will read 140ish. If i start a fire within 10 minutes all will read the homoginized temp 155ish, you get the idea. the third sensor is on the actual supply pipe leaving the garn, it might read 156 before I fire. the piping for the loop is about 25ft 1.25inch bi a calefi dirt cal 2 pressure gagues a pair of isolators and a taco 0013. Suprisingly the type k thermocouple in the first section of class a fluepipe reads about the same temp as the sensor on the supply pipe, after the fire is out.
  9. Como

    Como Minister of Fire

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    What sort of budget are we talking about for the testing equipment?
  10. TCaldwell

    TCaldwell Minister of Fire

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    not sure what you mean by testing equipt
  11. Como

    Como Minister of Fire

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    You mentioned all the readings you took and what the various numbers should be, so I guess you have a gas analyzer of some sorts and I am not sure what else. Recording equipment?
  12. heaterman

    heaterman Minister of Fire

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    Optimum for 20% wood is around 5-6% O2, CO2 in the 14-15% range and CO would be <100ppm. Difficult to hit optimum with wood because of all the variations in the fuel itself which present a moving target....something your setup should be able to deal with though.
    Higher MC (25%+) will produce more CO because of incomplete combustion, lower efficiency and raise the dewpoint of the flue gas.

    I just ran out to my kids place to see what numbers his 4 year old 2000 is cranking out. Long story short.....he hasn't cleaned the flues since he put it in operation. :(

    I checked it with the Testo 330 just for kicks anyway.
    He's getting virtually no secondary burn due to reduced air flow, the CO the thing is putting out (which you want to be careful of with wood) will kill the sensor in your 327 in about 30 seconds, the CO2 is way low (6-7%) and the O2 is way high 13-14%. Flue temp at the outlet is running about 320 and it should be lower by about 30-50*. Efficiency though is still running 74% which is a testimony to the extraordinary heat transfer a Garn is capable of.
    Needless to say, we have an appointment with a couple of brushes this weekend...........
    His wood is mostly red oak which was cut into 8 foot lengths 2 years ago and made into firewood this spring. It still hits 20-25% MC in the middle of a fresh split.
  13. heaterman

    heaterman Minister of Fire

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    Budget!!?? Weee don neeed no steeenking budget!! :)
  14. Como

    Como Minister of Fire

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    Well the Testo is $1700, so that is not on my shopping list.
  15. Tonttu

    Tonttu Member

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    Wow...this is really impressive and way above this simple wood gnome's understanding right now, but the links to the charts and to the combustion theory literature that have been provided will make for some interesting reading for the cold winter nights ahead.
    For the simple layman (as I am), how does the efficiency for your setup compare to the basic Garn controller system, and to the Garn digital controller system?
  16. bigburner

    bigburner Feeling the Heat

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    Heaterman -"You talking net or gross flue temp?" The NETT is 146.5
  17. Sawyer

    Sawyer Minister of Fire

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    I cleaned my Garn after one year of continuous operation and found very little residue, maybe 2 cups + what blew out the flue when the motor started. My temps at the fan are still hitting 500-550* at peak weather I am burning 20% hard maple or 15% pine. Is this cause for concern? Did I not do a good job of cleaning and heat transfer is hindered? I will also try to get a temperature reading at the outlet.
  18. heaterman

    heaterman Minister of Fire

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    Peak temp will vary not only based on MC but also load volume and density. Try varying how much wood you stack in it and also location front to back. 500 range for a peak temp would not be considered abnormal. You would expect to see that for maybe 15-20 minutes before beginning to drop.
    As for the cleaning issue, I would dare say you did a fine job. I think my son's problem is letting ash build up in front of the lower air inlet to the point that some fell into the air collar and is restricting air flow there.
  19. Sawyer

    Sawyer Minister of Fire

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    Thanks Steve, I have been getting these temperatures with any 3/4 to full loads. I just checked moisture and the last load's moisture content was 15%. Perhaps it help if I put a half brick approximately 4" in front of the air inlet to slow the burn. I do split 6"-8" logs once as it seems the "rollers" never seem to want to dry easily. I will also check to see how long the 500+ flue is maintained before dropping.
  20. bpirger

    bpirger Minister of Fire

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    George....I've been getting up into the 500-550 range as well...wondering the same thing. Burning mostly cherry and ash...cut and split since this past early Spring. I wonder the same thing....I guess I need to measure my actual outlet temperature.

    But I have been filling more than 3/4 typically....pretty much filled.

    I think for next year I'm going to cut a whole bunch of cookies and set one of those in front of the pile, to help deflect some of the primary air from the bottom upward....and then it will burn right up. I'll use a small cut off chunk now if I have one...and it seems like it does help it burn cleaner...
  21. Sawyer

    Sawyer Minister of Fire

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    Good idea Bruce. I can throw a couple of logs on the sawmill and cut them into hardwood 2x4's, sticker, and by mid summer they will be dry. I could cut a couple of logs worth for you if you care to drive on over and pick them up. ;-)
  22. TCaldwell

    TCaldwell Minister of Fire

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    tonttu,
    If you go back on this thread you will see a link to two graphs, one represents a stock garn and the other with o2 control. the stock graph represents a a typical burn trend of a low o2 level for a period of time and slowly escalates till end of burn, due to the combustor and air delivery system the garn handles this efficiently with no smoke, that hot fast burn is the garn's trademark. My opinion is that maintaining a relatively static o2% throughout the burn is more efficient. There would be several criteria monitored for many burns needed to actually determine if one approach is better than the other, other than trading some flue analyser numbers for comparison, it was a fun project.
  23. Sawyer

    Sawyer Minister of Fire

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    Tom, what part does your tabulator play in this formula? Significant? What model did you buy?
  24. heaterman

    heaterman Minister of Fire

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    Just for everyone's info, Garn is now using a turbulator/flow straightener/diffuser or whatever you want to call it in the current units. It is a V shaped piece of metal about 3' long that lays on it's side in the last pass of the heat exchnager right after the combustion blower. I believe it will retrofit in all Garns of recent manufacture.
  25. Sawyer

    Sawyer Minister of Fire

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    It appears that the forum members are not the only ones benefiting from forum discussions. ;-)

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