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Greenwood seminar; no water tank?

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by jklingel, Oct 26, 2007.

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  1. jklingel

    jklingel Feeling the Heat

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    I "attended" the Greenwood webinar yesterday, and learned a lot. I specifically asked if their boiler would run more efficiently if hooked to a water storage tank, and was told "no. we keep a lot of heat in the refractory cement", of which there is 1000 pounds. Still, I can not see the harm in having a BIG volume of fairly dense material retaining heat (water). What is your take? j

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  2. webbie

    webbie Seasoned Moderator Staff Member

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    Always depends on the application. One of the engineers here can easily tell us how much heat is stored in 1000 ls of refractory, but I doubt it is very much because you cannot calculate this based on a large temperature drop.

    Bottom line is that if you tried to run your GW when it was 55 and sunny during the day, it would probably run less efficiently.

    Another point is this - one of the reasons for water storage is that it make the boiler last longer since it is fired hotter - less bad acids in the firebox etc.- GW is correct on this point, that because they do not have a "wet" firebox, that boiler may be less likely to corrode when turned down.

    So, as usual, there are a lot of facets to the story. One size (storage) does not fit all, but does have advantages for certain apps.
  3. jklingel

    jklingel Feeling the Heat

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    Ah, enlightenment! I think I will just stick w/ what the factory engineers recommend: KISS. For now I will assume that they know their stuff.... that said, I will also ask another individual at GW, and see what the dealer up here has for empirical data.
  4. jpowell1979

    jpowell1979 Member

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    I've been running my new Greenwood for about a month now. I installed it with a Tekmar 262 two-stage boiler control with my existing Weil-Mclean oil boiler. The Tekmar controller has run-time stats for each boiler and by oil boiler had run less than 2 hours in the last month with a ~2000 sq. ft. house and temps around 20 degrees outside. The only time the oil boiler fires is in the morning to heat up the DHW before I have a change to reload the firebox after taking showers.

    I'm burning birch and can go 8-10 hours between reloading. The nice thing about the refractory of the Greenwood is that it stores heat for a long time after the fire dies out. I can stir the coals after 18 hours and just throw a couple fresh logs on and it starts right back up. So far I'm very happy with my new Greenwood. With heating oil prices of $2.85 I will recover my initial cost in less than 3 years.
  5. Nofossil

    Nofossil Moderator Emeritus

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    Plenty of threads discussing heat storage here. In my case, I've got 6400 pounds of water - that stores enough heat for a day or so, which means that I can fire the boiler every other day if it's not bitter cold. It also means that I still have hot water three or even more days after firing the boiler.

    Refractory cement is nowhere near as good a heat storage medium as water on a pound-for-pound basis. It takes 4 to 5 times as much heat to change a pound of water one degree as it does to change a pound of cement. 1000 pounds of refractory cement would have the same heat storage as a 30 gallon barrel of water at the same temperature. Of course, you can heat refractory cement to higher temperatures ;-)

    My boiler is far smaller than yours (80,000 BTU/hr) so your experience may be different. Bottom line is that heat storage is a pain, but it adds to the efficiency and livability of the system. No practical material is better than water for heat storage. on a cost / volume / performance basis.
  6. jklingel

    jklingel Feeling the Heat

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    Reason: The reason I was given for no storage tank, btw, is that the ceramics then cool off and have to be re-heated. I did not get into whether or not that is bad for them, or just takes time to re-heat, etc. Food for further investigation.
  7. KeithO

    KeithO Minister of Fire

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    Mr Klingel (as in ringing - german translation)

    If your boiler is a very good match to your heat load (in other words not oversized) in which case it would need to be continuously fired, then the water storage may be a moot point unless you would like to leave home for a couple of days, in which case you need a alternative source of heat. This is not a common scenario however, most of the time the boilers are rated for much more than the constant heat load, which means they need to cycle. It is exactly this cyclic operation that is the problem. Every time the boiler comes out of an idle condition it will not burn clean for a while. If the cycles are short enough, the unit may spend a lot of time in "dirty mode". Cycling is not good for refractory or steel either.

    Having water storage allows for the best of both worlds: A boiler with a high output and not needing to run intermitantly. The boiler runs through an entire load of fuel while heating the water in the storage tank. This may allow for an idle time of more than a day until the next cycle. And under these conditions, the boiler will run at peak efficiency, make virtually no smoke and consume the least wood. Your neighbors will love you and you will smile at the guy in the mirror when there is no need to re-load the firebox in the middle of the night when it is 50 below,...
  8. jklingel

    jklingel Feeling the Heat

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    KEITHO:
    Mr Klingel (as in ringing - )...JA. RICHTIG. EHR IST EIN "DING A LING".

    If your boiler is a very good match to your heat load... GOOD POINTS. THAT IS WHAT IS LOGICAL TO ME, AND THAT IS WHAT EVERYONE HERE IS SAYING, LOGICAL FOLKS THAT THEY ARE. ANY ENGINE RUNS CLEANER NEAR WOT THAN AT IDLE, AS FAR AS I KNOW, AND I DON'T SEE WHY A WOOD BURNER SHOULD BE ANY DIFFERENT. I AM CERTAIN I WILL BE INSTALLING A WATER BOX OF SOME KIND.

    CHEERS, AND YOU SHOULD SEE WHAT "KEITH" TRANSLATES TO! J
  9. jklingel

    jklingel Feeling the Heat

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    Akwoodburner: I sent you a pm. BTW, why are you paying $2.85 for heating oil? I am about $2.25.... not that that is cheap....
  10. jpowell1979

    jpowell1979 Member

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    You are in for a surprise on your next oil delivery. www.fairbanksgas.com has local heating oil prices. The cheapest price is $2.85. For a small deliveries the price is about $3.10/g. I'm sure glad that I don't have to depend on oil anymore to heat my house. I just checked my Tekmar control and my oil burner fired for 4 hours during the last month. My Weil-McLean boiler burns about 1g/hr. so I probably burned 4 gallons for October. The only time that the oil boiler is firing is in the morning to reheat the hot water before I have a chance to refill the firebox my Greenwood boiler. I probably saved 50-80 gallons and burned about 1/2 cord in October. So far I've saved about $200, still have a long way to go till I break even the costs for this project.
  11. jklingel

    jklingel Feeling the Heat

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    Woodburner: Thanks for the warning, even though it ruined my day almost as much as these pics. Dumb mistake that I hope I never make again. Gathering future heat....

    Attached Files:

  12. jklingel

    jklingel Feeling the Heat

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    here's another. we righted it in a few minutes; i was very lucky.

    Attached Files:

  13. ISeeDeadBTUs

    ISeeDeadBTUs Guest

    Hey all! Installed my GreenWood 100 back in January, to a 20 plate HX into a Viessmman. 4000[] of residence (Pex radiant) of which 1800[] is slabs (basement and attached garage)

    First let me say that other than the original salesman at GW, the company is awful at customer service. The refractory holds heat, yes, but

    It cracks terribly, and
    heat in the refractory will not refire fresh wood. A few coals will eventually, but hot refractory material does no ignite wood.

    Anyway . . .

    I didn't go with Tarm because I wasn't going to spend $7k on a tank, and I'm burning birch and oak which have laid on the forest floor, so we boil the water out first, then we produce heat :coolhmm:

    Since I need to use this GW for a while I need to make my cash nback, I need some mods. . . . I want to 'ramp' the bottom of the firebox so that the chunks and coals move to the back of the box where the air enters. Any ideas on configuration and materials for this 'ramp'?

    Jimbo
  14. Eric Johnson

    Eric Johnson Mod Emeritus

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    Welcome to the Boiler Room, ISDB.

    We've got a couple people here who like to soup up and otherwise customize stock boilers in their spare time, so I bet you'll get some good ideas.

    Other than all that refractory mass, how does the Greenwood work? Does it have a wood combustion chamber on top and a gasification chamber on the bottom. Does it have nozzles (or a nozzle) between the two. Does it have a blower? I seem to recall somebody saying that it's natural draft.

    I've heard about the refractory cracking on Greenwoods. Not a big deal if everything stays put, but no fun all the same on a new boiler.
  15. ISeeDeadBTUs

    ISeeDeadBTUs Guest

    I didn't buy a Central Boiler because I read the then AG Spitzer's report on how that huge volume of water surrounding the combustion chamber was making them inefficient aka, smoke. Now that I've spent the money on a GW, I've talked with enough people and observed enough Centrals working to know I should'a just bought one insteada the GW, which required a building around it . . .

    Anyway . . . the GW is natural draft. Basically an aquastate opens the damper at the back of the combustion chamber when the water temp drops, then closes it when it gets back to temp. 10 degree differential on either side. No partial open/close; it's either open or closed. Because I HAVE to tinker, I want to replace the aquastate with a data logger. Then I can program the damper based on outdoor temperature and boiler water temp, just like the indoor Viessmman.

    Maybe a variable speed pump to slow down the circulation when the water drops below 160 degrees?

    All kinds of ideas . . .I just hope the GW holds up another 6 years so I can get my money back:S

    BTW, only a couple hours S of you . . .we had snow here this AM. . .

    Jimbo
  16. Eric Johnson

    Eric Johnson Mod Emeritus

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    I work in the Adirondacks and we've got snow on the ground. Just rain now at home.

    What do you do for low temp return water protection, if anything?

    I have a Taco 007 that circulates water from the top of the boiler to the bottom when the boiler is running. I have an aquastat on the return line that shuts off the circulators (I have two) when the return water temp goes below 160. This supposedly keeps the boiler temp in the best range for gasification (around 170).

    I think Spitzer is right about the waterjacket around OWBs. You'll never get secondary combustion or gasification in that firebox, which is going to mean smoke and higher wood consumption. Central is the premier OWB mfg., and I'm fairly confident they've wrung about all the efficiency out of that design that they can. Which ain't much, relatively speaking.

    Tinkering. I prefer to call it "upgrading" the heating system, but tinkering is what it amounts to.
  17. ISeeDeadBTUs

    ISeeDeadBTUs Guest

    I burned bass last year, then when it finally got cold for a while in Feb, I went on the weekends and picked up red oak. When I was a kid we used woodstoves and burned beech and cherry, so I never realized how this oak can sit in the woods for years and still give BTU's

    The great thing with the GW is I just cut and roll it in the door . . . well, 'cept I cut down this hard maple that goes 30" . . . . but that stuff will burn all day!!

    Anyway . . .back to my original question . . . I find that sometimes late in the burn cycle the coals and one last chunk are at the opposite end of the combustion chamber from the flame path and air inlet, hence my idea for a 'ramp'.

    One bad thing about tinkering - and I read this in someone else's post too - DON'T tinker aka, 'stoke' an OWB/Hydronic wood gasifier/whaterUwant2CallIt!! Build a good fire, then leave it alone untill the temp drops below 160, then build your next fire. Hence the need for a data logger so I can KNOW when to add wood while sitting inside sipping on Black Label instead of running out in the cold every 20 minutes and cussing out Greenwood louder every time!!

    Jimbo
  18. Eric Johnson

    Eric Johnson Mod Emeritus

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    I second the Black Label.

    The way I've heard it told, with a gasifier the best approach is to get a good fire going and initiate gasification, then load it to the gills and come back again hours later when it's all burned out. With my old, conventional wood boiler that worked too, but it smoked so bad with a full load of wood that I took to building a lot of small, hot fires. Of course, on a cold night when the wind was right I'd load 'er up and to go to bed. But that can bite you if the wind shifts in the middle of the night and your neighbor is on the phone at 2:00 a.m. wondering why his house is full of smoke.

    Since I don't have my tank hooked up yet (getting therel!), I still make smaller fires in the EKO, part out of habit and partly because I don't have any place to put the excess heat. Plus, It's fun to fool around with different wood and loading strategies and "make observations" about how it's working.
  19. ISeeDeadBTUs

    ISeeDeadBTUs Guest

    Damn neighbors anyway . . .they're probably the same ones that don't want wind towers . . .

    Fortunatly my neighbors are far enough away (and many also burn wood) so smoke has never been an issue. Not sure how scientific this is, but I say


    White smoke is not smoke (unburned particulate) but is mostly water
    thin blue smoke is DGF (Damn Good Fire!!)
    dark brown/black smoke is over-fueled fire, in my case burning dimensional lumber :lol:

    BTW, during the summer I have found I can burn a load of dimensional lumber and heat my inside boiler and DHW, which is enough for two showers, aload of dishes and a load of clothes every couple of days. That's a 50 Gal DHW tank. I hope to get an Eltron Stribel 160 gal tank this spring which should mean a fire only every other day. . .plus I am eyeing solar . . . .

    Jimbo
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