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barometric damper for gassifier - recommendations please

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by SteveJ, Dec 3, 2007.

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  1. jebatty

    jebatty Minister of Fire

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    Do a search on jebatty and you will find posts that pretty well describe my system. I started in the forums looking for help on "too high" stack temp, learned much from many of you, for which I am very thankful. I'm pretty tied up for the next month to get pix together, but will try in the future. Thanks for the inquiry.

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  2. Eric Johnson

    Eric Johnson Mod Emeritus

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    We really appreciate your contribution, Jim. I hope you keep us bookmarked.
  3. TCaldwell

    TCaldwell Minister of Fire

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    here is some interesting information about boiler efficiency through draft modulation, I wonder how much of this is non boiler specific? go to www.donegaloric.ie and click on alternative heat , then click on the leaflet on wood gassification specifically on the electronic controller, efficiency in its many guises, why bother with a storage tank,ect. Would be interested on your thoughts! tom
  4. SteveJ

    SteveJ Member

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    Jim,

    Thanks for the detailed informative post.

    What is the draft in your system? What is the altitude of your system? Where (in relation to exhaust) do you measure the draft? the exhaust temp?

    Anthony,

    I noticed that your exhaust temp gauge is about 6ft up your chimney and the draft gauge is in the smoke pipe about 6in from the exhaust.

    My draft gauge is connected in about the same spot but my temp gauge is in the same horizontal pipe as shown in the picture below.

    According to the manual from Fred that I received with my boiler on Sept. 30, 2007, (p.2 in the "Boiler Installation" section):

    This is consistent with Jim's fourth paragraph above. The manual goes on to specify draft of 0.06" wc to 0.08" wc and an exhaust temp of 350 to 450 with the draft open and the boiler up to temperature (Jim's ideal conditions).

    So, with all the different ways to measure the operation conditions, it appears that the exhaust temperature at the top of the chimney is the most critical for "clean" burns and to minimize creosote formation.

    Does anyone have a temperature at the top of their stack?

    I was thinking of using something like Oregon Scientific AW129 Wireless BBQ Thermometer with Probe Thermometer and Remote

    Has anyone used these with success?

    I have seen the thread on the use for water temps, but has anyone used them for top of the chimney stack exposed to the elements temperture measurements?

    Thanks,
    Steve

    EDIT: Looks like one reviewer with a wood furnace is using this one Pinzon Wireless Probe Thermometer with Remote - okay - which one of you is P. Chesterson from Naugatuck, CT?

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  5. jebatty

    jebatty Minister of Fire

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    "What is the draft in your system? What is the altitude of your system? Where (in relation to exhaust) do you measure the draft? the exhaust temp?"

    Easy answers first, then a little to mess it up. I have a Condor probe thermometer inserted in the black stove pipe about 12" vertical above the flue collar exit from the boiler (Tarm). I never have measured draft because of my belief that temperature and draft are directly related (and I did not have nor wanted to buy a draft gauge). Since I started with much higher temp, I know my draft is good, as I had to reduce the draft by partially closing the forced draft fan damper to bring my temperature down. This is the only air in point in my boiler, so the vacuum action of a good draft also is pulling air through this damper.

    We are located about 1000' above sea level. The boiler has 4-5' of black stove pipe exiting vertical from a 90 degree flue elbow diretly from the flue collar. The stove pipe connects through a celing fitting to 18' of 6" stainless, double wall, insulated chimney pipe, with a standard rain cap at the top. About 12' of the stainless chimney is in an unheated, well-ventilated attic and the remainder is above the roof. The top of the chimney is 2-3 feet above the roof peak. Outside air temp this winter has been a low of -26, with low's typically 5-15.

    Measuring flue temp or draft readings for the typical boiler owner will be guides to proper boiler operation and not scientific set points, as there are many variables from burn to burn and even during a single burn. Examples mentioned earlier and others include accuracy of temp or draft gauge, type of wood, mixture of wood types, moisture content, size of splits (surface area), outside air temp, outside wind speed and direction, clean/dirty heat hx tubes, presence of turbulators in hx tubes, load mix valve on boiler vs direct return from heating system, type of chimney (steel, clay, masonry, etc.), . . . .

    For me the goal was the reasonable minimum flue temp with the temp probe I had which also resulted in the heat I needed (within boiler capacity) and no smoke, no creosote, no condensation, practically no ash, and no problems. Based on info provided by others, I knew my flue temp should not be less than 300 (assuming an accurate probe; others have indicated material differences in readings between different probes, even of the same brand), and each 100 degree increase in flue temp translates approximately to 2.5% reduction in efficiency. My goal is not maximum efficiency all the time, but reasonable efficiency all the time in consideration of all the variables. As mentioned previously, with burning dry pine slab wood this is achieved with a probe temp of 450-500 during most of the burn, with a peak of just under 600, and end of burn down to 300-400. I found that if I pushed that peak temp much lower, while the early part of the burn was good, I did not seem to achieve the same good burn durning the latter part. So I compromised, knowing that 600 is above the most efficient temp but not dangerous, and the entire burn was reasonably efficient. I want to be able to fire my boiler and walk away without any adjustment during the burn.

    Another solution for some may be to add turbulators to the heat hx tubes. This will be particularly true if excessive flue temp is a problem which cannot be solved by draft adjustment, which was my case, as turbulators will result in more heat transfer, reduced flue temp, reduced draft, and also increase in efficiency. They also should add to efficiency in most other cases, so long as a good burn may be achieved and the desired flue temp/draft maintained, and draft adjustment likely will be necesarry if turbulators are added.
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