1. Welcome Hearth.com Guests and Visitors - Please enjoy our forums!
    Hearth.com GOLD Sponsors who help bring the site content to you:
    Hearthstone Soapstone and Cast-Iron stoves( Wood, Gas or Pellet Stoves and Inserts)
    Caluwe - Passion for Fire and Water ( Pellet and Wood Hydronic and Space Heating)

Efficiency misconceptions........

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by heaterman, Feb 1, 2012.

  1. Jim K in PA

    Jim K in PA Minister of Fire

    Joined:
    May 22, 2008
    Messages:
    621
    Loc:
    Pocono Mountains, PA
    Steve - The answer I think is "both".

    I think it comes down to a couple of factors, neither of which have anything to do with efficiency. The customer that does not have a convenient way to house the GARN and does not want to build a shed will opt for the solution that "fits" their physical parameters. The other issue is that for some, the PERCEPTION that a more "technically sophisticated" solution will provide better results rules the day, irrespective of data. I am also a follower of Occam's Razor, so I always look for the simplest solution first. However, a smaller unit that can fit within the desired space, plumbed with divorced storage, with cost and complexity equal to or greater than a GARN, is still a better solution than an old smoke dragon in the backyard or a hungry oil burner in the basement.

    I also lost a sale of a GARN due to nothing more than the physical constraints of the customer's situation. The customer WANTED the GARN, but the consequential costs of accomodating its size put it out of his budget. For those of us lucky enough to have the room to install one, well we just have to count our blessings . . . :)

    Helpful Sponsor Ads!





  2. goosegunner

    goosegunner Minister of Fire

    Joined:
    Oct 15, 2009
    Messages:
    1,238
    Loc:
    WI
    I am quite amazed and very happy running with 1000 gallons of storage. Lambda users posting the load it, light, walk away method makes me think I should have maybe went that way. Though a recent post seems as that is not quite always the case. The expensive controls kept me from buying a Lambda boiler.

    I originally steered away from the Garn because of my Forced air requirement of hotter water. I was told that the Garn might not be the best choice with a Forced air and heat exchanger in the plenum.

    After running with 1000 gallons storage this winter and running down to 140 on the tank my system is fine. Most days I can go 24 hours. Cold days I do 2 smaller fires. If I had the Garn with 1500 I think it would only be better.

    If I would have known last year what I do now, I would most likely have a Garn....

    gg
  3. I avoided the lambda boilers because it seemed like the small increase in efficency was not worth the increased complexity. The associated repair costs and longer wait times for parts didn't seem worth it to me. I Remember someone on here said the froling computer was over a grand to replace. I can cut a lot of wood for that price.

    Would have gone with a garn if I could have put it in my daylight basement. Just didn't have the room for another outbuilding close enough to the house with zoning setbacks and existing infrastructure.

    Seems to me that making sure you have well seasoned properly prepared wood is the biggest variable that can be controlled when it comes to getting the most out of a gasser.
  4. jebatty

    jebatty Minister of Fire

    Joined:
    Jan 1, 2008
    Messages:
    4,289
    Loc:
    Northern MN
    Heaterman, this statement is difficult to address because it subsumes one method of burning which by definition may (but I'm not sure) allow only the conclusion which you suggest. Obviously I agree that burning well-seasoned (20% MC) wood in a well-designed gasification boiler with storage sufficient to absorb the full btu output is very efficient, whether in a Garn, Tarm, Wood Gun, Froling, etc. etc. I think, however, that this statement blurs what people face in operating a gasification boiler in a real world operating environment. The fact is that many people do not have space for "sufficient" storage, even if they have space for some storage. And, not everyone loads and burns loads of wood in a manner which permits even, fast and complete burning. And, not everyone has ideal MC wood, of a size and dimension best suited for even, fast and complete burning. And there are other real world factors that enter the equation.

    Given the great many variables in real world operation by real people, superior efficiency, reduced emission levels, and hassle free operation leaves plenty of room for a variety of boiler styles, capacities, control systems, and storage capacities, such that it is not reasonable to assert one method only, except in the laboratory.

    That said, I return to my statement above, "Obviously I agree that burning well-seasoned wood in a well-designed gasification boiler with storage sufficient to absorb the full btu output is very efficient, whether in a Garn, Tarm, Wood Gun, Froling, etc. etc."
  5. Como

    Como Minister of Fire

    Joined:
    Jan 28, 2008
    Messages:
    866
    Loc:
    Colorado
    That was my reasoning, but not everybody has room for a Garn.
  6. SmokeEater

    SmokeEater Feeling the Heat

    Joined:
    Feb 10, 2011
    Messages:
    309
    Loc:
    Northeastern NY
    My father would look at a new car and decide whether or not to buy based on his idea of "if it's too complicated, it'll spend too much time in the repair shop". These beliefs were used by his choice of buying any "machine", and that would include wood boilers. I don't really know how the lambda equipped boilers work, but have an idea. Another way of looking at the wood boiler is to view it as a reactant vessel within which a chemical reaction occurs. If reactants are combining chemically there needs to be sufficient quantities of each to complete the reaction with each reactant being "consumed" completely in the reaction. In the boiler one of the reactants is the wood fuel that we all spend considerable time and money to acquire. The other is oxygen, present in the air, easy to obtain, and not too expensive(yet!). I think a lambda wood boiler has complex (ie. expensive) controls that try to determine the quantity of oxygen to supply to the fixed quantity and kind of wood fuel need to complete the reaction with no fuel reactants and no oxygen remaining after the last of the reactants (limiting reactant) is consumed. Not usually necessary. Many reactions use a specific quantity of reactant(wood fuel load) and supply an excess of the easy-to-obtain and inexpensive reactant, oxygen and the wood fuel reactant is completely consumed, whereas the excess oxygen simply leaves with the combustion products, as in the case of the Garn. No Lambda necessary. Maybe I've gotten it wrong, but that's how I see it. Keep it simple and it won't break as often and often times works almost as well as the complicated version.
  7. TCaldwell

    TCaldwell Minister of Fire

    Joined:
    Oct 26, 2007
    Messages:
    522
    Loc:
    860-868-9014 h 203 948 0864 c nw corner ct.
    There really are few arguements, even from me.
    I agree that the largest effiency contributors are thermal storage and dry wood to any and all batch fired cordwood systems. Also a efficient combustion hx design, that reduces flue temps to 400deg or lower, this becomes a challenge when limiting boiler return temps required on downdrafters, actually the garn benefits from this, because if you have a system requirement of 110deg supply water and wait to fire at 110, your flue temp will be low helping the efficiency to be high, rather than refiring at 140 as a example. fluestack effiency calculation [you can google the formula] is used in fluegas analysers to calculate effiency, if you do the math a very low o2 number if the fluegas temp is low will still yield a high efficiency, the garn is good at this as half its burn is below the stiometeric setpoint of 7% for wood, wich is the optimum situation because it maintains a low flue temp from firing in a large low temp body of water. Effiency decreases as the water temp increases, and that takes about a load of wood in the garn. The downside to the garn equation is the last 1/3 of the burn is overaired o2 is up, flue temp is influenced to some degree by water temp, excess air is up and effiency is low. As a example o2=15%, co2=5% flue temp 280 ambient air temp 70 nets a effiency of 58%, as the o2 rises the effiency decreases. This to some degree holds true at start of burn also, no matter what the control strategy some of this is unavoidable. It is my beliefe that o2 control is of benefit, anytime you can sustain the optimum burn parameters for 85% or more for the length of a burn you are MAINTAINING a high average effiency, not just occasional spot checks during high burn. I think downdrafters, due to the lower water mass and challenging flue temps benefit more than the garn style boiler to o2 control. O2 control may be picking hairs effiency wise vs dollars but will end up on most all boilers as is storage mandatory throughout most of europe. I still believe until shown otherwise that my boiler is maybee just a little more efficient than stock, not withstanding cost.
  8. heaterman

    heaterman Minister of Fire

    Joined:
    Oct 16, 2007
    Messages:
    3,002
    Loc:
    Falmouth, Michigan
    I wouldn't quibble with any of that Tom.
  9. leaddog

    leaddog Minister of Fire

    Joined:
    Sep 24, 2007
    Messages:
    912
    Loc:
    Hesperia, Michigan
    First of let it be known that I think the garn is a great boiler. I looked at them when I was going to buy. In my case I have the time to do the work, I have the time to scrounge up parts so cost became the deciding factor. I put the 2000 gal of storage against the house so any heat loss is going partly into the house. I only have less than $9000 total in my system including all the mistakes I've made along the way. I almost bought a wood gun but because of price difference during the time of looking and then dealers coming into the picture they got to high. At the time the eko was the best buy for ME. If I was to change now I probably would check out one of the newer efficient models because I have my storage and every thing in place. I do think they would be esier to run.
    With that all being said if I hadn't been able to install every thing cheaper I love the garn. If the price is the same and I have the room etc the garn wins every time.
    leaddog
  10. thecontrolguy

    thecontrolguy Member

    Joined:
    Mar 17, 2009
    Messages:
    78
    Loc:
    Northern British Columbia
    If I might add to the mix, after a LOT of reading, industrial bio-mass experience, and an old farm-house heated with (a lot of) wood in a modified RSF100 wood furnace, I feel that the cleanest most efficient burns come from full-tilt batch burns from devices built like the old "Jetstream" or anything else emulating its burn characteristics. Perhaps a further squeeze of efficiency into the Jetstream would be a Lambda sensor controlling the amount of air injection into the burn, but the high-temps and no creosote problems reported consistently from users in its 30 years of history can't be wrong. Also, simple to operate, re-buildable, and long-lasting. Lets see where these fancy all-electronic multi-damper lambda controlled variable-fan speed boilers will be in 25 years? I would really be pleased to see someone offer a kit form of the Jetstream, with the user pouring his/her own vermiculite and the inner refractory liner poured by the user with good instructions to follow. This would lead the user to trust their skills and be able to use the boiler long into the future, and the factory keep the shipping costs down to a minimum. However, I also feel strongly that NO wood boiler should be installed without some type of accumulator installed to prevent the boiler from short-cycling or otherwise going into a turn-down or idle mode. Creosote, condensation, corrosion. Not good for a boiler ..
  11. bioman

    bioman Burning Hunk

    Joined:
    Dec 25, 2010
    Messages:
    230
    Heaterman
    Saving the world, one wood boiler at a time. Once again Heaterman tells it like it is. I like simple, Garn is simple, built like a tank. don't need no 02 sensor to burn out if you don't see no smoke then something is going right. just my 02.
  12. jebatty

    jebatty Minister of Fire

    Joined:
    Jan 1, 2008
    Messages:
    4,289
    Loc:
    Northern MN
    Maybe it's important to keep this discussion focused on the premise, which is burn efficiency. We all pretty much agree that a full tilt batch burn at gasification temperature results in very high burn efficiency. TCaldwell has accurately pointed out that
    when water temps get above 140F. And with regard to the Garn WHS3200, that is exactly what Dectra has advised, that efficiency drops off with water temps above 140F.

    If we all want the discussion to move from burn efficiency to boiler - system interface efficiency and usefulness/practicality, then I think the discussion may start to change considerably. And if we want to look at other design constraints of the Garn which reduce its efficiency in delivering btu's to the system, then the discussion also may start to change considerably. A number of points in these regards already have been made. Based on things stated in this thread and things not stated, there are many reasons to choose a boiler of one brand over another, and they are not all based on ignorance. There are good and valid reasons why everyone has not purchased a Garn.

    Brand hyperbole and brand bashing both need to be avoided.
  13. woodsmaster

    woodsmaster Minister of Fire

    Joined:
    Jan 25, 2010
    Messages:
    2,433
    Loc:
    N.W. Ohio
    Garn was on my short list when looking at boilers. Came down that to that is was simply out of my budget. Also size was
    big and that translated to more money for a building to put it in. I'm happy with my decision and think I would have been
    just as happy with a garn. Especially the first few weeks when I was adjusting air for the optimal burn. I was originally
    going to get a conventional OWB until I found this sight and became more educated. I'm happy with the efficiency
    of the biomass. I heat my house shop and DHW with only about 20 - 25% more wood than it took me to just heat
    most of the house with my old wood stove and I have some heat lost to the outdoors by having it in
    a shed, But that's one trade off I was willing to make for thr sake of the mess.
  14. jebatty

    jebatty Minister of Fire

    Joined:
    Jan 1, 2008
    Messages:
    4,289
    Loc:
    Northern MN
    I have reported high efficiency numbers for the Garn WHS3200 in prior posts, although not quite this high. It would be very helpful as an aid in improving the 3200 performance to get more information on the Garn 2000 tests, such as:

    1) what was the exact MC of the wood, and was it uniform for all wood burned;
    2) what were the dimensions of the wood burned, how much difference between splits;
    3) what was the weight and volume of the ash and coals remaining in the firebox at the end of the burn;
    4) what was the condition of the firebox and the hx tubes, that is, well cleaned such as a user might have after cleaning the Garn before starting a new burn season, or in the condition that might exist after a half season of substantial use;
    5) was the Garn 2000 in factory delivered condition, other than installation of sensors;
    6) what was the chimney configuration and dimensions used during the test;
    7) what was the weight of the wood burned; was it more than one single load; how much by weight loaded and at what times during the burn;
    8) what was the low heat value used for the wood:
    9) what was the starting temperature of the water in the Garn and was it uniform in temperature;
    10) what was the ending temperature of the water in the Garn and was it uniform in temperature;
    11) what flue temperatures were measured during the burn and at what location and times were the measurements taken;
    12) was the standard, one speed blower used during the entire burn, what CFM; and if not, what was used and what was the CFM;
    13) what was the length in time of the burn; was it measured from first lighting until the end; was it measured during some mid-point period of the burn;
    14) at what point and why was it determined that the burn was completed;
    15) was the water mixed during the burn or after the burn; what method was used to mix the water during or after the burn, what circulator, what gpm, etc.;
    16) what was the air temperature in the structure housing the Garn during the test;
    17) what was the outside air temperature during the test;
    18) what and how much insulation was placed around the Garn for the test;
    19) did the efficiency calculations account for heat loss into the structure during the test;
    20) did the test measure O2 or other components of the combustion process, other than particulates, and if so what were the components and the measurements.

    I think this will help all of us in using our gasification boilers to achieve higher efficiency and greater satisfaction in our gasification boiler experience.
  15. jebatty

    jebatty Minister of Fire

    Joined:
    Jan 1, 2008
    Messages:
    4,289
    Loc:
    Northern MN
    I was able to locate the test report on the Garn WHS1500, but not the WHS2000. Will need more time to review the report.

    Test Garn WHS1500
  16. MarcM

    MarcM New Member

    Joined:
    Dec 4, 2007
    Messages:
    140
    Loc:
    CT/MA/RI border
    I don't know if it's just my crap browser, but the link didn't work for me.

    For anyone else with the same issue, here's the full URL:

    "http://garn.com/wp-content/themes/Chameleon/forms/G100248857MID-006R Test Report signed(3).pdf"

    Do a copy/paste
  17. Tennman

    Tennman Minister of Fire

    Joined:
    Mar 4, 2009
    Messages:
    629
    Loc:
    Southern Tenn
    Great discussion, I'm learning a lot. Hopefully won't be in the market for a new boiler for a while but can't help collecting data and Garn was way up on my list. I'm surprised to learn a Garn is less than idea for a forced air HX system. So as the Garn's stored temp gets higher it's efficiency drops off... because the water to exhaust gas temp differential gets less?? I guess that would be true for all boilers. I'm getting this from TC's comments regarding increase in flue temps which I'm taking that as the water to exhaust gas differential decreases the gas transfer rate decreases. Makes sense. But for my forced air system I routinely see 185F for the majority of the burn. Garns never get their water this hot? It's just interesting to me that some boilers may be more suitable for forced air. I'm stuck forever with forced air. Is that what ya'll saying here?
  18. Frozen Canuck

    Frozen Canuck Minister of Fire

    Joined:
    Dec 14, 2009
    Messages:
    863
    Loc:
    North central Alberta, Canada
    I think the discussion is mixing a few variables here.
    Namely the physics of heating water at different temps.
    It takes more energy to heat water from 150 -190 than it does to heat it from 110 - 150. Same 40 delta, so what's up with this?
    We all think it should be a straight line right? Nope like most things it's a curve.
    Once one reads up on this one begins to understand why a country like Germany has rules in place that lower the max temp of fossil fired boilers into the high eff range 150"s as opposed to the 190"s & above that you will see on this side of the pond.
    Tennman you are right these variables will apply to all boilers as they all heat the same medium - water.
    No boiler is better or worse suited to delivering any type of water based heat, as the medium (water) is the constant.
    What is often misinterpreted as boiler trouble is in fact the poor matching of boiler to load requirement, lousy plumbing, worse pump & component selection & no thought as to what the whole system should look like/function as before someone starts cobbling parts together & calling it a system.
    Just my $.02. For me I look at it the same way I do a structure.
    A structure is the assembly of thousands of components, that when assembled correctly work very well with minimal maintenance.
    When assembled incorrectly...well it's just a pile of badly assembled parts that isn't working like it should.
    99/100 it's operator/assembly error.
    Just the way it is as we (humans) are the largest most uncontrollable variable in the equation.
  19. heaterman

    heaterman Minister of Fire

    Joined:
    Oct 16, 2007
    Messages:
    3,002
    Loc:
    Falmouth, Michigan
    For clarification:

    The Intertek testing was done in accordance with the ASTM protocol for thermal storage units that I mentioned above. Efficiency is measured not at a single point in the burn or even multiple points.

    The numbers generated for efficiency in that regimen are the average over a given period of time which include everything from lighting the match to total exhaustion of the wood supply + standby losses encountered over the entire length of the test. With a thermal storage system like the WHS2000 used in the test this could be from as little as 6-8 hours under maximum btu draw to as long as 24-26 hours when measuring efficiency at 15% of output. It is not designed to be a snapshot of a single point in the burn cycle. Measurements of that type will in all cases tend to give a false picture of what is really going on. They are just a single point "snapshot" and don't do anything but indicate what is going on right at that moment.

    Water temp is measured at the beginning and at the end to determine total btu's going into the storage as I understand it. For the testing done on the Garn beginning water temp was 120-125* and ended at 170-180*. The wood load was split red oak with a moisture content in the 23-25% range.

    I wish I could publish all the entire report but it is copyrighted and considered intellectual property so I best not go there.
  20. heaterman

    heaterman Minister of Fire

    Joined:
    Oct 16, 2007
    Messages:
    3,002
    Loc:
    Falmouth, Michigan
    DP'd
  21. heaterman

    heaterman Minister of Fire

    Joined:
    Oct 16, 2007
    Messages:
    3,002
    Loc:
    Falmouth, Michigan
    Someone is watching..........I just got this in an e-mail from Garn. It may help to answer some of the questions posed about the test method and the unit itself.



    · The efficiency is based upon the total burn (strike of match to no remaining fuel, thus no fire). Standard GARN digital control used to turn off blower at end of burn.

    · 8 hours of stand-by losses were deducted from the total energy stored to arrive at the overall efficiency of 88.4% (not just “combustion†or heat exchange efficiency).

    · Standby losses were measured at 170F. Unit insulated with 8†batt fiberglass.

    · Tank was thoroughly mixed pre and post burn to obtain a non stratified average temperature. Temperature determined via multiple thermocouples located within the tank.

    · De-stratification pump was not run during the test.

    · Test storage temps began at approximately 124F and ended at approx 179F.

    · Stock WHS 2000 unit installed per manual with about 4 months of use on the unit prior to the test.

    · 6†Class A vertical flue. Flue gases collected by dilution tunnel per ASTM E2515-09. Dual vacuum sample trains used to collect particulates.

    · Standard GARN WHS single speed blower.

    · Approx 160 lbs of red oak at 23 to 24 % MC, dry weight basis per ASTM Spec was used for each test. MC was determined at 6 locations for each piece of cordwood.

    · Cordwood size was 3†to 10†across and 24†in length. Some split some not split. Purchase from the “open market†of MN and WI.

    · Three (3) tests conducted over a one week period in October.



    The tests were set up and executed in full compliance with ASTM Document E2618-09, Appendix XI for Thermal Storage Equipment and conducted by Intertek Testing of Madison , WI. The full details of how the test was set up and conducted can be found in the two ASTM Documents referenced. The two documents describe the standard method for testing cordwood fired equipment that incorporates full thermal storage (not partial thermal storage).


    Gotta run. Just got a call from someone who ran into their wood boiler with their truck. Never know what a day will bring................ :)
  22. jebatty

    jebatty Minister of Fire

    Joined:
    Jan 1, 2008
    Messages:
    4,289
    Loc:
    Northern MN
    Garn deserves credit for posting the test report on the 1500; hopefully it will do the same for the 2000. And I hope other boiler mfrs post similar information, in detail. This kind of information will help shed light on many of the things that we discuss on the forum.
  23. jebatty

    jebatty Minister of Fire

    Joined:
    Jan 1, 2008
    Messages:
    4,289
    Loc:
    Northern MN
    I reviewed the efficiency calculation on the WHS1500 as contained in the test report and compared it to other information to roughly test the outcome. Does the following make sense?

    The report uses HHV of 8550 btu/lb, which is wood at 0% MC, and calculates the weight of the wood in the test burns as if at 0% MC. Total btu input then is 8550 x dry weight. Without quibbling over any rounding, btu input = dry weight x 8550. Using Run 4 as an example, dry fuel weight of 55 kq x 2.205 = 121.28 lbs x 8550 = 1,036,012 btu input (vs 1,029,557 in test report, and I have no issue with this variation).

    The efficiency calculation is (heat stored) / (input) = 744,056 / 1,029,557 = 72.2% (vs 71.6% in test report, again I have no issue, the small variation may relate to standby loss and heat stored in the steel mass of the Garn).

    For a comparison, based on 20% MC and 400F stack temp, wood has 6050 btu/lb. Energy in Wood This means that (fuel load weight) x 6050 = (143.75 + 2.2) x 6050 = 882,998 btu input. And efficiency then is 744,056 / 882,998 = 84.3%. I didn't see a flue temperature number in the test report, so it is not possible, except by speculating, to adjust this based on a lower or higher flue temperature.

    Question: I need to think this through more, but what might be the reasons for the variation in efficiency calculation? Shouldn't the 6050 btu/lb account for the difference between a dry weight calculation and a 20% MC calculation?

    The 84% efficiency number for the 1500 compares to 80% efficiency I calculated for the 3200. Garn 3200 - Part 6 But my calculation was based on btu's supplied to the system, and my calculation did not account for standby losses or heat stored in the steel mass of the Garn. Regardless, it would not be reasonable to assume that efficiency of the 1500 and the 3200 are necessarily the same.

    I think two other things would be reasonable:

    1) if I could account for standby losses and heat store in the steel mass of the 3200, the efficiency calculation would be closer to the method used in the test report and efficiency would increase above 80%, and

    2) my method of measuring efficiency by btu's supplied to the system is closer to what a user might expect in actual performance in use of a Garn (or any other boiler), because standby loss and heat stored in the Garn likely is not usable heat for a structure (unless the Garn is in the heated structure). I measured btu's supplied to the system by delta-T temperature measuring: (supply temp - return temp) x 500 x gpm.

    I wish every boiler mfr had this kind of data available for review and scrutiny. While efficiency is not the end all in selection of a boiler, it is one important consideration.
  24. PassionForFire&Water

    PassionForFire&Water Minister of Fire

    Joined:
    Jan 14, 2011
    Messages:
    567
    Loc:
    Billerica, MA
    Hi Jim,
    You can find the calculations in this link: http://www.epa.gov/burnwise/pdf/owhh.pdf
    This is the revised EPA phase2 partnership program. Date 10/12/2011. The Test done was much earlier in 2011. So probably not 100% in line with the newer calculations.
    Also this new revision allows for overall efficiency calculation according CSA B415, known as Stack Loss Efficiencies.
    Calculations start on page 30.
    MC is used in these calculations and then the BTU value for wood will come close to your value.
    I do have an Excel spread sheet based on the older phase2 program.
    PM me if you are interested.
  25. jebatty

    jebatty Minister of Fire

    Joined:
    Jan 1, 2008
    Messages:
    4,289
    Loc:
    Northern MN
    The link to the EPA site produces an EPA page saying File Not Found. Maybe EPA no longer has this on its website, or EPA moved it without a cross-link.

Share This Page