Heard one that made me laugh.............

[heaterman]

I was at the Great Lakes Renewable Energy Association show this past weekend and one of the vendors there selling a downdraft gasifier was telling all who stopped by his booth that a Garn was susceptible to "cold shocking" (his words) or thermally induced stress cracking (my words). I just laughed. I didn't know what else to do. Either the guy doesn't have a clue or he's an outright liar. How does one "cold shock" a vessel containing 1500 gallons of water? Submerge it in liquid nitrogen?....Maybe?

I do know this...........The amount of mis-information and absolute dis-information out there is inversely proportional to the technical knowledge and intelligence of the person spewing it out.

 

[Rick Stanley]

I heard a story, from a pretty reliable source, that Dectra put a Garn filled with water in a parking lot during the Winter. After it froze solid, they fired it. Iirc there were bends and buckles but no leaks. Sound right?

 

[mike1234]

What about the radiation leaks, he didn't mention those too? And heat warping (I mean if the water is 180 all the time, doesn't that warp the steel?) And, how in theory, they contribute to the formation of black holes?

I have 0 technical info about garns, but just know all these things. Good thing I was around to warn you. :cheese:

 

[pybyr]

I was at the Great Lakes Renewable Energy Association show this past weekend and one of the vendors there selling a downdraft gasifier was telling all who stopped by his booth that a Garn was susceptible to "cold shocking" (his words) or thermally induced stress cracking (my words). I just laughed. I didn't know what else to do. Either the guy doesn't have a clue or he's an outright liar. How does one "cold shock" a vessel containing 1500 gallons of water? Submerge it in liquid nitrogen?....Maybe?

I do know this...........The amount of mis-information and absolute dis-information out there is inversely proportional to the technical knowledge and intelligence of the person spewing it out.

It's the FUD factor- Fear, Uncertainty, and Doubt- (unfortunately) widely used (throughout commerce and especially politics) by those who have nothing more solid to hang on to.

 

[heaterman]

I heard a story, from a pretty reliable source, that Dectra put a Garn filled with water in a parking lot during the Winter. After it froze solid, they fired it. Iirc there were bends and buckles but no leaks. Sound right?

I know for a fact that they had one freeze solid in Alaska last winter. Supposedly the "neighbor was firing the unit while the owner was away" I'd like to hear how that turned out. At any rate, the lid on the manhole was raised about 6" off the top of the unit on a column of ice and the entire thing was solid. They got it thawed after about 6 days and other than some minor distortion on the metal everything was intact so they put it back into service.

 

[SolarAndWood]

That is one big ice cube. It seems the Garn guys thought of everything, even ice expansion.

 

[Jim K in PA]

I heard a story, from a pretty reliable source, that Dectra put a Garn filled with water in a parking lot during the Winter. After it froze solid, they fired it. Iirc there were bends and buckles but no leaks. Sound right?

I know for a fact that they had one freeze solid in Alaska last winter. Supposedly the "neighbor was firing the unit while the owner was away" I'd like to hear how that turned out. At any rate, the lid on the manhole was raised about 6" off the top of the unit on a column of ice and the entire thing was solid. They got it thawed after about 6 days and other than some minor distortion on the metal everything was intact so they put it back into service.

Awesome! I wonder how it would have faired in 304 stainless . . .

 

[sdrobertson]

This is one of the major problems with all product vendors...not so much with manufacturers I think. I have no problem with products having their selling points pointed out as this does help consumers pick and choose. The problem comes when they start to point out why they feel the others products don't work as well. Garn has thermal shook issues (crock), down draft gasifiers have dirty and creosoted upper chambers that proves they don't burn clean and efficiently (crock), and the list could go on and on. I have a EKO and I love it and would recommend it to anyone. I've seen the Garn and loved the simplicity and longevity and I would recommend it to anyone. All the European style downdrafter boilers - I would recommend to anyone as they have proved themselves over the years. It's like the Chevy/Ford comparison...yes there are little differences but they both operate and roll down the road using the same technology. In the boilers, when you spend more money, you get a nicer machine than the economy unit but both still use less fuel and are allot more efficient than the OWB technology.

 

[leaddog]

I was at the same show and I heard the same statement about thermo shock in the garn but I took it with the same grain of thought as the 4 pic's on the garn showing the inside of a " Euopean Downdraft gasifier" with creasote covering the walls of the primary chamber and then the walls of a garn. It then said which one burns cleaner?????????? To someone that dosn't know any thing about them it makes the downdraft gasifier look like it burns dirty. But it's not apples to apples as the garn and the downdraft boilers work differenty. I know that we all like our product better than the others but I'd like to see positives stated and help people learn so more people go to gasification.
That said I am very satified with my eko, I really like the garn and have given info out on both to people as I think they all have there place. The garn was on my short list but I went with the eko for reasons that fit me.
I'm sure we are all guilty of putting out statements for and against other boilers and some of it is not true but I think most of us try and help. I'm VERY appreciated of all the help that is givin here and the PRO's have been very generous with there info and help

The other coment I heard was that there is alot of bad info here on this site. I had to agree as alot of the info put out there has come from people like me that has had to learn by trial and error. But with out this site alot of us would have given up. In the last 2 years there have been alot of good knowledge put out here and alot of people have been helped. The dealers, manufactures, distributors, and installers have started to use this site to get out the good info to help people like me. I hope that if I put out some bad info that someone will speak up and correct me as I'll be the first to admit that I know nothing except what I've learned here and from trial and error. This is another reason I hope correct info is stated by all the makes of gasifiers as it will make it easier for people to make informed choices.
leaddog

 

[ISeeDeadBTUs]

Not so sure about "Bad info on this site". I like everyone else, like to express my own opinion, and that's all I can do.

I made my decision on a GW before I knew about this site. For now I'm making the best of the GW till I can justify a step up.

I'm glad I didn't go with my initial consideration, which was a CB OWB. Do I wish I'd gotten a Viessmann? Yup.

But I can't trash talk the CB nor the Viessman cause I've never run either.

 

[heaterman]

OK I've been debating posting these here because I'm not looking to pick a fight or start a riot of any kind. What I'd like is some well thought out theories or ideas as to why these two combustion chambers look so different. Both of these units burned wood that was identical, came off the same truck. Mixed hardwood that tested at 25-30% moisture which is a tad higher than both manufacturers recommend. Both owners went through approximately 22-23 face cords of wood, although one was heating about 6500 sq ft and the other about 2500. I'm seeking enlightenment here so don't get all nasty with me. I am not going to make any claims regarding efficiency or emissions, I'm just trying to figure out why one has bare steel and dry ash coating the firebox and the other one is half an inch thick with tar.

 

[brad068]

Heat, do I dare ask what make is the firebox on the right?

 

[heaterman]

Heat, do I dare ask what make is the firebox on the right?

Nope Not naming any names. Suffice to say it's a typical downdraft design.

 

[Nofossil]

The firebox on the right looks like a typical gasifier. The one on the left appears to have much more combustion happening in the firebox than what I've seen with downdraft gasifiers.

What's of more interest to me is what the flue looks like.

 

[heaterman]

The firebox on the right looks like a typical gasifier. The one on the left appears to have much more combustion happening in the firebox than what I've seen with downdraft gasifiers.

What's of more interest to me is what the flue looks like.

On which one? You can see the beginning of the HX tube at the very back of the secondary chamber on the left. It looks like that all the way through. I know the one on the right needs to be cleaned.

 

[brad068]

Guys, I do like and support the dds but is that not unburnt fuel on the walls. Garns burn it all everytime.

 

[sdrobertson]

The firebox on the right looks like a typical gasifier. The one on the left appears to have much more combustion happening in the firebox than what I've seen with downdraft gasifiers.

What's of more interest to me is what the flue looks like.

On which one? You can see the beginning of the HX tube at the very back of the secondary chamber on the left. It looks like that all the way through. I know the one on the right needs to be cleaned.

With the one on the right I'm assuming that by needing to be cleaned you are referring to the heat exchangers. The right one looks like mine does, but the bottom chamber looks like the beginning of the left one. I do see the point now on the "unburnt" fuel coating the upper chamber but the "gasification" chamber is cleaner and white. I'm not sure how much efficiency the one on the right looses after it gets coated as I don't ever see it get beyond the point it shows in the picture. The coating gets to that point but it doesn't continue to build up and I'm not sure why. The one on the left is really interesting...I'm wondering if the left one burns hotter and faster in the loading chamber than the right as this is the only way I can see it staying so clean. Is the left one insulated from the water?

 

[Gooserider]

I may be spilling the beans, but the one on the left looks like a Garn, or possibly a clone. I'm not expert on the Garn, but as I understand it, they are designed with the idea that most of the combustion takes place in the main firebox, with the secondary chamber and flue cleaning up the leftovers - in this respect it is more like a secondary combustion non-cat wood stove than an EKO style downdraft gasser (which is my guess for the one on the right, though I don't know the brand). This means that you have more flame in the main combustion chamber, and that it would get hotter than the upper chamber in a gasser. It doesn't take all that high a temperature to burn off a layer of creosote - according to some stuff I've read on wood fired brick ovens, that happens around 7-800*F, a temp the Garn main chamber is supposed to reach if I've read their material right.

OTOH the EKO style downdraft gasser is more intended to have the main combustion action happen in the secondary chamber, with only enough fire in the top chamber to generate the gas to feed the lower flames. This doesn't take as high a temperature as it does to burn off a creosote layer, so you get some buildup, which is presumably self limiting by excessive thickness flaking or melting off and flowing down into the lower chamber where it gets burned...

My take is essentially that it just shows two different styles of burning, but doesn't mean anything significant in terms of efficiency - only way it would make a difference that I see is that the first few loads through the gasser might be a bit less efficient until it builds up the creosote layer, and you might potentially have a similar loss any time you cleaned that layer off (unless you saved the creosote to toss in the firebox and burn it later...)

Gooserider

 

[Floydian]

OK I've been debating posting these here because I'm not looking to pick a fight or start a riot of any kind. What I'd like is some well thought out theories or ideas as to why these two combustion chambers look so different. Both of these units burned wood that was identical, came off the same truck. Mixed hardwood that tested at 25-30% moisture which is a tad higher than both manufacturers recommend. Both owners went through approximately 22-23 face cords of wood, although one was heating about 6500 sq ft and the other about 2500. I'm seeking enlightenment here so don't get all nasty with me. I am not going to make any claims regarding efficiency or emissions, I'm just trying to figure out why one has bare steel and dry ash coating the firebox and the other one is half an inch thick with tar.

Such incendiary remarks could very well spark the Great Boiler Riots of '09. ;-)

I think the big difference is a 3/4 HP fan on the left making sure all available smoke and gases are pulled into the secondary chamber at a very high rate. The downdraft on the right is probably using 50 to 100 watts to pull or push (depending) the gases down through a relatively small nozzle. I have read enough of your posts to know that you understand all of this far better than me.

Heaterman, can we get more info to compare these two heating systems more fairly, like:

Is the wood in these face cords cut to same length? Around here when someone says face cord there is a lot of room for discrepancy.
Most of the downdrafts I am looking at take wood lengths of around 20" whereas a Garn would take up to 32" pieces.

Is the downdraft set up with storage? Obviously idling is an efficiency killer. Also, is it a forced draft or induced draft and would this make a difference in how the upper chamber looks?

Are the doors, windows, air infiltration, and insulation quality the same in these houses?

I am curious to know the differences of these heating system and houses as I don't think the look of the fireboxes has a lot to do with the 22 or 23 face cords that each house used.

Noah

 

[Hansson]

The firebox on the right looks like a typical gasifier. The one on the left appears to have much more combustion happening in the firebox than what I've seen with downdraft gasifiers.

What's of more interest to me is what the flue looks like.

I agree on that. The one on the left look like it have what we say a Flashover.

Some words on combustion
(broken link removed to http://translate.google.se/translate?prev=hp&hl=sv&js=y&u=http://www.afabinfo.com/aldehydforbranning.asp&sl=sv&tl=en&history;_state0=)

 

[Piker]

I can't speak to all the ins and outs of a garn type boiler, but I do know that the downdrafts are not designed to achieve an efficient combustion in the upper chamber. There is no need for it. The only reason that we are even taking any heat off of the upper chamber at all is because it's best to have water on the other side of any steel that is exposed to flame in order to prevent thermal stress on the boiler plate. In my opinion, it would actually be better if ZERO heat were taken off of the upper chamber, and ALL the heat produced was transfered to the waterjacket in the lower chamber and heat exchanger... it would deal with the issue of balancing burn times and load size with efficiency... ie you could put a giant firebox on a gasser for good burn times... but the material in the upper chamber would really have to take some serious abuse from the heat, and would be expensive if it were to have a long service life.

There are definitely higher combustion temps in the firebox on the right than the one on the left. Again, this is not an issue of efficiency... any heat not transferred to the water by the top chamber's jacket will be absorbed as the air is forced through the combustion chamber and heat exchanger, which will remain spotless on any downdraft gasser, especially if installed with thermal storage. The buildup in the upper chamber may affect overall Btu output a bit, but not efficiency.

I believe that the reason creosote is self limiting in the upper chamber is this: as the creosote layer builds, thermal transfer will be reduced through that layer... at some point in the "growth cycle" of this layer of creosote, it becomes possible to maintain a high enough temperature on the surface of the creosote coating that any additional creosote that is formed there will burn off.

cheers

 

[heaterman]

OK I've been debating posting these here because I'm not looking to pick a fight or start a riot of any kind. What I'd like is some well thought out theories or ideas as to why these two combustion chambers look so different. Both of these units burned wood that was identical, came off the same truck. Mixed hardwood that tested at 25-30% moisture which is a tad higher than both manufacturers recommend. Both owners went through approximately 22-23 face cords of wood, although one was heating about 6500 sq ft and the other about 2500. I'm seeking enlightenment here so don't get all nasty with me. I am not going to make any claims regarding efficiency or emissions, I'm just trying to figure out why one has bare steel and dry ash coating the firebox and the other one is half an inch thick with tar.

Such incendiary remarks could very well spark the Great Boiler Riots of '09. ;-)

I think the big difference is a 3/4 HP fan on the left making sure all available smoke and gases are pulled into the secondary chamber at a very high rate. The downdraft on the right is probably using 50 to 100 watts to pull or push (depending) the gases down through a relatively small nozzle. I have read enough of your posts to know that you understand all of this far better than me.

Heaterman, can we get more info to compare these two heating systems more fairly, like:

Is the wood in these face cords cut to same length? Around here when someone says face cord there is a lot of room for discrepancy.
Most of the downdrafts I am looking at take wood lengths of around 20" whereas a Garn would take up to 32" pieces.

Is the downdraft set up with storage? Obviously idling is an efficiency killer. Also, is it a forced draft or induced draft and would this make a difference in how the upper chamber looks?

Are the doors, windows, air infiltration, and insulation quality the same in these houses?

I am curious to know the differences of these heating system and houses as I don't think the look of the fireboxes has a lot to do with the 22 or 23 face cords that each house used.

Noah

Here's the skinny on the two houses and systems.

House number 1 is just under 6500 sq ft, built in 2004 and is pretty tight. The unit feeds the house system from about 250' away in the pole barn. The pole barn itself is 40 x 56and is very light on insulation in the walls but has the ceiling blown with about 12" of cellulose. It is kept between 35-45* all winter also. The heating system in the house is a combination of radiant floor in the full basement and about half of the first level. (about 2800 sq ft total) The balance of the house is heated with steel panel radiators. 2 adults and 5 kids live in the house so the domestic hot water load is substantial. 2000 gallons of storage is integral in the unit. I quizzed the owner about the wood and he said he cuts it about 18-20" which allows him to get two rows of wood in the firebox if he wants. He also stated that his wood use was 8 and 9 actual pulp cords, 4'x4'x8'. Pulp wood cords are more standard than face cords as far a volume goes so we'll compare that way.

House number 2 is about 2500 sq ft of old farm house which.....shall we say doesn't present any problems with adequate fresh air supply. It is insulated pretty well but the foundation and some of the old windows are leakers. That boiler sits about 80' away from the house in an outbuilding and feeds into a 500 gallon STSS tank in the basement of the house. Both of the lines feeding the houses are insulated in the same manner, (sprayed urethane) and there is little measurable heat loss from the underground loop in either case. The system in the house about 300 sq ft of underfloor pex in the kitchen area and the rest of the house started the winter with a coil in the furnace plenum and a few panel rads. Through the course of the winter the furnace part was abandoned and more panel rads were installed. (No comparison in the comfort level) The actual wood use for that system was a full 10 pulp cord load plus he bought 3 face cords at the end of the winter so call his wood use an actual 11 pulp cords of wood. That's far different than the 22-23 face cords any way you slice it.

The interesting thing is that when I ran a heat loss on these two places it came out to within 8,000 btus with the smaller house being the lesser of the two. I do think however that system number two is losing more heat in the outbuilding than system 1 in the larger pole barn.

As to the draft question you posed, I'm assuming that you're asking whether it's positive pressure or negative pressure in the firebox. The clean one is negative and the black one is positive. I have a theory as to why this may contribute to the appearance of the two units but until I rig up the negative pressure unit with a piece of tempered glass in place of the door to allow observation, I'm just taking an educated guess..

 

[deerefanatic]

The reason is simple, DD's are true Gasifier's.... The pyrolize the wood to realease the gas, then burn it down below (which I might add is always spotlessly clean with no creosote..... Garns are more of an "inferno burner" that just plain incinerates the wood..... That little bit of creosote on the walls of the DD MIGHT be equal to one load of wood wasted..... If that.....

 

[Piker]

Heaterman,

Is the DD in an indoor environment? The air going into a downdraft gasser really needs to be tempered before it goes into the unit. If the secondary air is 0* it can cool the refractory down significantly to the point where gasification efficiency is effected dramatically. For instance, a DD in a three sided shed is a no-no for sure. It's best to enclose the unit inside an insulated room where the heat loss from the boiler itself can temper the air a bit before it enters the combustion path. The difference in fuel usage between a unit inside and one setting outside under a roof can be staggering.

cheers

 

[deerefanatic]

The heatloss from a DD sitting outside under a roof can be staggering too!