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Efficiency misconceptions........

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

  1. heaterman

    heaterman Minister of Fire

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    I bring this up because of correspondence with a Hearth member here who recently purchased a Lambda controlled gasser and is anticipating the addition of 2000 gallons of storage. Let me say at the outset that I do not disparage his choice in any way. I questioned why not just go with a Garn and he cited the "technology" of the boiler he purchased. While I don't disagree that the boiler he chose is a very good product, I think there is a fundamental disconnect in the thinking that high tech controls and O2 sensors are required to obtain hydronic nirvana. ;)

    I would humbly submit for discussion here, the premise that storage and dumping all the heat from a wood load into such, is a much more hassle free method of obtaining superior efficiency and reduced emission levels. Recent tests have shown that even with very high quality, O2 controlled units emission levels rise dramatically and efficiency drops when these units are subjected to low load situations. As any astute person here is aware, full boiler output is needed less than 5% of the heating season. That being the case, our heating systems are subjected to operation at less than full load for the majority of the winter. The person I referenced above is doing it right by adding significant storage that will allow flat out burns until all the fuel is consumed under most circumstances. He will likely not have any issues other than the routine maintenance/replacement required with any lambda (O2 controlled) system.

    Using numbers [shown below] from a test on a production Garn 2000 using cordwood (not the faulty EPA test), you can see that efficiency and emissions from a good basic unit that burns the entire load of wood and does not idle are such that there is virtually no room for realistic improvement.

    For those who are unfamiliar with it, the Garn is a 30 year old design that was done right in the first place. It uses no controls other than operator input and a button to start the combustion fan when fueled.

    The test was conducted by Intek in accordance with the Thermal Storage Appendix XI of ASTM Document E 2618 – 09, using oak cordwood just like you and I burn rather than the kiln dried cribwood in the EPA protocol.
    It was done at the Garn facility using a standard dilution tunnel sampling method and it gave the following results.


    88.4% delivered efficiency and more tellingly, only .088 lbs of particulate/million BTU’s delivered output.


    This emission result is 72% less than the current EPA Phase II Limit of .32 lbs of particulate per million BTU’s delivered.
    For the sake of clarity, it should be noted that wood heating efficiency is currently based upon the lower heating value of fuel industry wide.
    The efficiency achieved simply physically cannot be any better or a person would encounter issues with condensation of flue gas and the resulting disaster in your heat exchanger.

    So I would ask the following question; is "the answer" simply storage and good design, or are high tech controls going to be the best long term choice? I tend to fall into the KISS category but I am willing to learn if I'm missing something here.

    Let's hear what you think.

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  2. Singed Eyebrows

    Singed Eyebrows New Member

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    It would be hard to fault Garn for heat transfer capabilities when the "boiler" is in the tank & I don't think too much more could be extracted from the fuel. I think for most people the efficiency comparison wasn't to the Garn, it was to small non Lambda boilers & there would be a difference with these. Could I ask why the Garn is rated as a gasification boiler? Dectra doesn't put too much info out there. I know the fuel load is burned basically horizontally. My guess would be that the reaction chamber glows red hot & secondary air is introduced in there somewhere, correct? wrong? Randy
  3. ewdudley

    ewdudley Minister of Fire

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    Speaking for myself, the unit is set up to drop the burn latch relay, shut down the exhaust fan, and seal off the draft inlet as soon as storage is maxed-out, so there's no idling or smoldering.

    As far as efficiency, it would take many decades to pay for the increased efficiency of a closed-loop combustion control, even supposing the lambda units have an efficiency advantage, which I doubt. Not to mention the expense of having a full inventory of replacement parts on hand should some oddball one-year one-model Elbonian control decide to wig out.

    But I can definitely see a future for any unit that can legitimately claim to minimize emissions in urban settings, alpine valleys, or other places that may well be unable to tolerate 'a little smoke on start up'.

    --ewd
  4. heaterman

    heaterman Minister of Fire

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    Randy, the Garn does use gasification to sustain that level of temperature (1600*+) in the secondary chamber. (When wood gas is present of course) It is configured differently than a downdrafter in that the airflow is horizontal through the fuel and combustion chamber rather than downward, which can make it a little easier to light up. More like Viessmann's wood boiler which burns horizontally at the bottom.
    With their design, primary air enters at the bottom and impinges directly on the fire while secondary air goes across the top, gets superheated and then mixes with the smoke/gas when it enters the secondary chamber where it ignites.
    The point I am bringing up is not so much controls and high tech boilers as it is the issue of storage being a simpler path to good burn characteristics.

    EW, you kind of hit the nail on the head when you mentioned smoking at startup. It's virtually impossible to do and that is the advantage, as I see it, in a batch burn/storage type system where there is only one start per load. Your other comments are dead on as usual as far as I can see.
  5. benjamin

    benjamin Minister of Fire

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    I couldn't agree more. I come at this from the cobbled together end of the spectrum, so I can't imagine how there could be a critical mass of demand for high tech wood burning systems. Where I was raised, if you got $20,000 you don't buy a wood burner, you buy a double wide and retire. If you add up the materials and a qualified contractor to install some of these systems, then geothermal starts to look like a bargain IMHO.

    Thermal storage is definitely the way to go, whether that's steel water tanks, masonry stoves, adobe or concrete, depending on climate, needs etc. The garn is a simple, robust and effective product that has the disadvantage of size, cost, and an open system. The typical indoor gassifiers with added storage can do the same thing, but with more complex installation, more complex operation and similar cost. I just don't think there are enough Americans willing to pay the high price for quality components and custom installation, learn to operate the systems and still have to cut or buy wood.

    I would like to build-find-copy-design a woodburner similar to a garn in simplicity, refractory, blower and controls, without the built in storage. The drawbacks would be that the simplicity would not allow it to idle, and the separate storage would lead to boilover and/or overheating the boiler if circulation and backup fire damping failed. A simpler relatively high efficiency boiler would work great in conjunction with concrete shop floors, tight homes with at least moderate mass, DHW in multiple electric water heater tanks or propane tanks and heat exchangers. When all of these loads are drawn down they could easily store the output without additional water tanks.
  6. Como

    Como Minister of Fire

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    I am not aware of any wood boiler with lambada controls where the manufacturer does not specify storage. It is a requirement due to the nature of the beast.

    Depending on your situation there is a lot to be said for sizing the boiler to meet a bit less than peak load, so you burn at 100% much more of the time and then top up with something else.

    I can quite see that greater controls would improve efficiency a little and decrease emissions slightly over the course of a burn. Just look at your vehicle. The biggest gain would be to get the design right.
  7. hiker88

    hiker88 Burning Hunk

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    I'm one of the people considering a lambda based unit. However, if you and I had had the discussion, I wouldn't have mentioned efficiency as the reason to go with a lambda unit. From my massive amount of experience related to wood boilers (all gained on this forum in the last six months or so) - once you go with a quality gassifying boiler and hook it up to storage you're pretty much there efficiency wise. I see that the lambda units claim efficiency numbers a bit higher, but not to the point where the dollar difference makes it my reason.

    For me, it's the convenience factor. Some might scoff at that, but when you're trying to replace the convenice of oil and trying to get the family on board (who will also have to tend the boiler) this can be a factor.

    PS I agree that I've not come across a lamda unit that doesn't require storage.
  8. jhunter19

    jhunter19 Member

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    I like the idea of having some O2 sensors on the unit. I have a Biomass 40 and struggle to keep the unit in gassification mode. If I had some measurement of whether I was too rich or too lean, it might make adjusting easier. As it stands now, I tweek a llittle here and there but have no way of knowing what effect I am having on the unit. Very frustrating.
  9. pwschiller

    pwschiller Member

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    That was my thinking as well. An efficiency rating difference of 3-5% didn't matter to me so much, it came down to ease of use. Also important to me was having a negative draft boiler to minimize or eliminate smoke escaping indoors and a sensor to automatically shut down the fan near the end of the burn. The three lambda boilers that I'm familiar all have those features.
  10. Como

    Como Minister of Fire

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    For convenience, then pellet would be the way to go followed by wood chip.
  11. maple1

    maple1 Minister of Fire

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    On that note, might it be beneficial for some who are having tuning issues, to just install a simple a/f (lambda) meter in the exhaust outlet and use that to tune in their operating procedures?

    I am quite new to this stuff as well, but from all I have read on here, it does seem that the lambda aspect is more of an ease of use thing than an efficiency gain of any significance.

    EDIT: I typed too slow again, that was in response to jhunter.
  12. hobbyheater

    hobbyheater Minister of Fire

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    I"m a complete believer in heat storage. My association with heat storage predates the Jetstream and the Garn. Our first wood boiler was a round barrel type with a water jacket around the fire box. Burned 22 cords in the first year of operation. The second was a Tasso cast iron down drafter, the smallest unit they made. It burned 16 cords in a year. Both of these boiler were creosote dragons. A 1000 gallon storage tank was added with the hopes of eliminating the creosote problem. HA! On the storage tank, the creosote only got worse, not the boilers fault. I knew nothing about keeping the water in the boiler above 140 F plus. The upside of this is that the Tasso's wood consumption dropped to under 10 cords. The Jestream, in the same system, burns around 5 cords.
    There is also one more step in this. I had seen the improvement in the Tasso's efficiency when connected to storage, so I did some tests to determine just how much the oil boiler burned. A Hobbs meter was hooked up to the burner of the oil boiler to determine its fuel usage in heating and stand by mode. In the next step the oil boiler was connected to the storage tank and it cut the oil boiler's consumption of oil by 60% - yes, really 60%.
    Storage eliminates stand by and stand by loses can be huge.
  13. jhunter19

    jhunter19 Member

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    I have 500 gal storage on my Biomass 40, but my unit has never gone into stand by mode that I can tell. I wish is would. About as hot as I can get my storage is 150 deg F.
  14. heaterman

    heaterman Minister of Fire

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    True. Automated feed of wood chips or pellets is as near to oil/gas burning as you can get.

    As far as cordwood goes, there is nothing else as convenient as filling, pushing the start button and not thinking about it again until the storage temperature gets low. With an integrated storage unit like Garn there are no pumps, no piping, no controls, no wiring and no assembly required. And that I guess is the point of my initial question.

    Let me rephrase it.

    Does anyone have documentation that high tech controls add any significant benefit to a storage based system in terms of emissions and efficiency?

    I'm mentally comparing a "normal" gasser with storage or something like a Garn to a gasser with computer controlled combustion process. From the numbers I'm seeing for Garn and for normal gassers with decent (four figure) storage, the issue is storage and batch burning more than anything else.
  15. bpirger

    bpirger Minister of Fire

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    I'd say one of the things I like the most about the Garn is there is nothing to adjust. I don't have to tweak or twiddle to keep the gasification going. No vents to open/close, no smoke in the "house", no worries of boil over (unless you put on too much wood).

    Now, that said, I sometimes wonder how do I know if it is working....and the answer to that is look at the exhaust. No smoke? Gasification. Smoke? Something is not ideal. As I write this, I can look out the window and see no smoke coming from the 80+ pounds of wood burning in the Garn. Good! I will say that placing a small piece of wood in front of the "pile" to burn will deflect some of the primary air (entering the burn chamber at the bottom) upward. Sometimes without doing this, I might see a bit of smoke for a bit longer. Next year I will intentionally cut a bunch of cookies to use for exactly this purpose...about 2" thick, from maybe a 12-15 log, and half of it should be perfect. One could very legitmately argue this is required twiddling and tinkering.

    It would be interesting, and heaterman has this been done, to run a Garn without the refractory lining in the chambers and see/measure the output. Even with a full out burn, there should be a significant increase in the emissions. Has this been done by Dectra?
  16. heaterman

    heaterman Minister of Fire

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    I've seen it done inadvertently when people destroy the front half of the refractory. Put mildly, it definitely effects both emissions and efficiency. That refractory is in there to prevent any heat transfer in that area and create maximum temperature possible.
  17. bpirger

    bpirger Minister of Fire

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    But no actual measurements? I'd think it would be similar to a typical OWB burning full tilt.... Obviously one wouldn't want to DO this, other than just to measure the impact of the hot refractory chamber.
  18. heaterman

    heaterman Minister of Fire

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    I doubt it's ever been tested or tried that way purposely.
  19. Singed Eyebrows

    Singed Eyebrows New Member

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    I've talked up Lambda boilers as much as anybody on the forum because of the need to babysit my Atmos untill the Samson flap is down etc. For me, this would be a huge improvement in convenience. I see next to no advantage of a Lambda boiler over a Garn, I would expect the reaction chamber to heat about as fast as a coal bed is established on a downdrafter, so I doubt even a startup emissions advantage. Heaterman, I can understand you losing sales to someone needing to take a boiler down the basement steps. The others is kind of difficult, although I think thats being remedied fast here. Simple is good, & no computor no servos would be a plus for me as having the boiler right in the storage tank. Randy
  20. hobbyheater

    hobbyheater Minister of Fire

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    I like simple. Our system is simple. Boiler and storage tank share the same water with an opened expansion tank on the next floor, internal heat exchanger in the storage tank, one for domestic supply and the other for house heat. One circulator between the boiler and tank and another for the zones. The bottom of the storage tank is above the top of the boiler's heat exchanger so no need for any valving to prevent stack lost.
    Operation of the boiler is simple - scoop the ash out of the burn chamber before lighting the fire. Wood sizing is important with a 12" round split into three to five pieces being ideal.
    This system has had six operators, two of which could not operate it safely. (We had the house rented out.)
    My thought is this; if the systems get too complicated, the first generation operator is going to have no problem as he has likely has done the install and understands every thing. What about the second generation operator?
  21. Adios Pantalones

    Adios Pantalones Minister of Fire

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    I like these discussions.

    Mother Earth News had all sorts of plans for barrel-based rocket stoves that burned fast and hard, the exhaust going through a mass for storage much like a masonry heater.

    Simple, cheap, DIY, efficient- potentially dangerous but the short burn time meant that you could monitor it the whole time.
  22. Pat53

    Pat53 Minister of Fire

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    I would say that either your plumbing isn't right or perhaps your boiler is undersized or you're losing a lot of heat somewhere. With just about any boiler you should be able to get your tank up to at least 180F
  23. maple1

    maple1 Minister of Fire

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    I was just about to post something similar - something seems not quite right there. Another possibility is wet wood? We might be able to help with more info posted - but likely would be better off in its own separate thread though.
  24. maple1

    maple1 Minister of Fire

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    I also like simple, which is why my planning has me with a natural draft boiler as first choice, and good convection heat load flows for overheat & power outage conditions.
  25. Jim K in PA

    Jim K in PA Minister of Fire

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    The GARN has all those features, without O2 sensors that will require replacement, air flow controls that will require maintenance, or a sophisticated control schema. There is nothing simpler than loading, lighting, and walking away, which is what I have been doing for three seasons with my GARN. And mine doesnt even have the new-fangled controller!

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