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Post in 'The Boiler Room - Wood Boilers and Furnaces' started by heaterman, Dec 31, 2008.
How is that setup working out? Is it a big advantage? Does it ever get "confused?"
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Hay guys don't get me wrong cause I REALLY REALLY like the garn and think that it should be looked at first in alot of situations. That said, There is a market for a residentual chip burner. Just look around and look at the available fuel supply. Chips are available every where locally. very little processing, cheap, easy to handle and you don't need to use valuable timber. You can also use cherry pits, peachpits, nuts, wood pellets, hay pellets. If you have one that modulates then you don't need storage and you are getting closer to having a easier boiler that everyone can run and understand. I'm getting older and someday I just might not beable to cut, split, stack, and handle wood. Thats one reason pellets was a very serious thought for me but pellets are still at the mercy of oil where chips are right here in my back yard.
Nice looking install,
Glad to hear america will soon have a national board stamped gasifier. I am looking forward to seeing one. What a major inprovement over most of these owb smoking away and rusting away fron the inside out.
I have a 48ft open top trailer that is set up for wood chips/hog fuel etc. I do this when there is extra work to be had. I would be concerned about the wood chips freezing and sticking together. If i haul clean chips, which is already debarked before they're chipped, it isn't too bad. Still have to put fuel down to keep them from sticking to the plywood walls and floor. These are only in the trailer for a few hours. And they'll slide right out when put up on the dumper. But you never leave a load on overnight(unless you store inside a heated garage, then it's still a risk). Not only do they freeze to the walls, but freeze together. This is green or dry wood. The hog fuel, which is the bark and other junk is just a crap shoot sometimes, freezes solid very easy. Knowing nothing about this, seems like you'd have to store the wood chips in a heated building. I can get about 35 to 38 ton of green hardwood chips in my trailer, that's 48ft x 8'6'' with a possum belly. Probably in the 135+ cu/yd range. If you compare tonnage, I plan on using about 12/13 ton of hardwood in my Tarm. If all is equal than about 1/2 a trailer load of dry wood chips(even though the RFO says it can burn green, still going to perform better with dry). You mentioned burning cherry pits etc. I wouldn't think that that type of material will have the btu's per ton as good wood chips. Even that amount I know would freeze if not in some kind of heated building. Unless you want to chip as you burn, which to me takes away some of the convience of it. My .02 but I haven't read anything for info in how they do it over there, so I'm sure they got it all figured out, they usually do.
chiptec in vermont makes several models of chip boilers,its not the cost of the boiler but the conditioning and delivery system of the chip that makes it out of residential reach. they use cleaver-brooks controls with a ametek in situ flue gas analyser. my experimentation so far with cordwood and 02 control is a ''estimated compromise'' because of the burning stages of cordwood , start-up, with a time period of 02 deficit , next stage a optimum combustion with a 2to 4 % 02 reading, next stage about 2/3 through burn, o2% will gradually rise to about 13% about 75% coals and a few small logs left. the last third basically just coals will rise from 13 to 20.9% end of burn. in the garn when it puffs the o2 reading is at 0%, so in a nut shell with a static fan speed , under aired for first third of burn a good o2 range for second third of burn and over aired for last third of burn. this cycle can be manipulated with size of splits, frequency of reload and moisture content. i suspect most '' lambda controlled'' cordwood boilers are designed to try to limit theses ''estimated compromises''by carefully designing fire box capacities and reccomending small splits, primary/ secondary air ratios and volumes to try to minimize the cordwood burn cycle swing. I am in the process of defining and testing programable runs in the allen bradley plc for different moisture content wood. one button for a program that will controll dry wood,another for average wood ,and a third for less than optimum wood., these programs basically differ in initial static fan speed start-up time, also looking to end burn with a declining flue temp for a given length of time, and of course a overide toggle to run manually. this experiment, ongoing is leading me to believe that a continious fuel delivered system, pelletts or chips for example is more successfully controlled with o2 control. i would appreciate any comments or ideas that you think might be incorporated, thanks
Tom, which way does the fan speed good when it starts puffing?
I get the same feeling that consistently sized wood, and equal MC would be necessary for the optimum control of the burn with the lambda system. I also think that with a Garn setup you will be needing to control the primary and secondary air to get better control over the burn. The Garn would have to be re figured in construction to completely separate these two air sources. But the original garn setup is so simple and so effective that I don't think it can be changed.
Hey Tom, how's the guys with the switzers doing? I haven't heard any updates.
Brad, at 70hz you get away from the puffing but will still read 0%o2 at 80 hz fan speed. i agree that the primary/secondary air would have to be reconfigured to optimize, have not talked to or heard from the switzer boys, i should call them.
The biggest advantage of a chip burner is being able to vary the fuel load. When you can change the rate of fuel feed going to the burner as well as the air you have a bio-mass fired appliance which will be very close to the efficiency of the best gas and oil fired equipment. In addition, be able to throttle the firing rate can nearly eliminate the need for storage which as most of you know is expensive any way you slice it.
As far as burning cordwood goes, the Garn is an excellent choice due to the ability to burn wide open for the entire burn cycle. Could it be better? Yes, but at what cost and added complexity? The beast works so well and so simply in its present form that what little can be gained in efficiency may not support the extra mechanical pieces and costs. Gaining an additional 3-5% by utilizing O2 sensor and a variable speed blower would show marginal ROI in the long run but it sure is fun to play with and think about. You really can't get much more efficiency than that or a person would wind up with a condensation problem of epic proportions.
RE secondary air: I've often wondered what would happen if the secondary air stream in a Garn was "ducted" directly into the refractory chamber..........just thinking out loud.
Sorry to jump in here, but I thought about this too. However, in the early stages, and/or when you have insufficient air supply (puffing) situations, you would want to have the upper nozzle air supply dump 100% into the primary chamber, then as the O2 readings improve, transfer or redirect the flow of air from the upper nozzle from the primary chamber to the secondary reaction chamber via some heavy walled piping/duct path. It sure would be nicely pre-heated by the primary chamber before it got to the secondary!
Just a thought.
Guys, I and High E experimented with all different setups and settled on the original concept. One test run, I made up a tubing grate that the wood and coals sat on and it was stuck into the bottom combustion air hole and ran at a slight incline to the start of the secondary chamber. It didn't do any better than the original and actually the thermometers that are in my flue passages read lower.
One experiment/ setup that I often tried and still do is to place a flat piece of cardboard with a piece of glass fastened to it and place it over the door opening. When looking through the glass you really get the full effect of the burn. What I noticed is that when the air exits out the bottom hole into the primary chamber it slams it the wood/coals and really strips off the gases and coals which in-turn causes great turbulence in the chamber for good mixing.
My opinion to split the primary/secondary is that you would have to take the secondary chamber and place it below the primary then exit out the back of it with the traditional garn flues. That way the wood is at a constant distance from the nozzle helped out by gravity.
Man - my hat is off to you Captain G (and High E). Thinking/theorizing/dreaming is cheap and easy. You put in the time and $$ to try this stuff out.
I am sure Martin Lunde has thought of and tried most of what we are kibitzing about, and many more ideas as well.
I have no desire or need to modify my GARN, but I just can't help being fascinated by it and its function.
heaterman, gary switzer built a boiler for ed forest, a hearth member that i saw in action last may. It was similar to a garn in concept of a primary chamber/secondary reaction chamber, the dimensions were different than a garn, however it had a 2 inch dedicated secondary air supply that was damper controlled by a flue stack thermocouple, it terminated on the back vertical wall about 18 inches away from the secondary reaction chamber. when the flue temp reached ? the damper opened introducing o2 next to the src, but not in it. switzer claims about 850kbtu/hr out of a 6'' id refractory chamber that is 5ft long. he has 3000gal water in storage. the best readings with the testo 327 were in the high 70% range.
Happy New Year Tom and all of you here at Hearth.com,
The Switzer has been a wonderfull addition to the Forest family. I burn for @ 5-6 hrs every other evening to bring my 3000 gal of water storage up to 200-220* depending on the weather report. If next day temps are predicted in the 40's then i'll stop @ 180*.
It takes 10 cu ft per load to fill the fire box and the average fire these days takes 2 full loads. We keep the house @ 70* first fl and 68 - 70* second fl. The kids spend most days running about sock-less and shirtless so 24 hr warmth in our 3600 sq ft cape is a priority. The wood I burn is a mix of pine, maple, poplar, oak, lumber scraps, and "mystery wood". I have it easy now but next year when the 3700 sq ft barn is on line I'll need to burn daily. I must say even with oil so cheap( which I haven't burned since May) I'm glad I control the fuel cost/demand for my home. My boiler is simple to use and easy to maintain. I spoke with Scott(smangold) recently and he has the same situation but without the additional storage he must burn daily.
correction: the secondary air intake is a full 4"at the rear of the fire box on the left side which is @ 18" from the ceramic lined secondary chamber. As you noted the secondary air is controlled by stack temp as is the primary upper and lower air .
another thing worth mentioning; the Switzer never blows smoke out the load door because the draft inducer is located outside of the boiler mounted to the masonry chimney. My boiler has a draft switch that kicks the fan on high whenever the top door is opened. I can almost place my head inside the 30" round x 36" long fire box at the beginning or end of a burn without MELTING the grey hair my wife considers sex appeal. Bottom line, I love my Switzer boiler. I'm hesitant to post these days because so many guys seem to struggle with there installs and I hate to sound like a braggard. But maybe I'm delusioned and burn way to much wood.
All you Garn Guys: how much wood do you burn for heat and DHW.
BTW I resolved the "puffing" issue if any are interested...
Here's a link to the Roxul......http://www.roxul.com/sw42877.asp
Click on the blanket type
Ed-it sure sounds like you have an excellent setup. Glad to hear it. And don't be "afraid" to post your positive experiences. It gives others the inspiration to keep trying. I am very happy with my GARN, but have room for improvement.
With temps in the high teens to low 20s, I burn twice daily, probably 40-60 lbs each burn. I am keeping my GARN in a fairly narrow window between 150 and 190. I am very happy with the performance. Each burn is ~2 hours, seperated by anywhere from 9-14 hours.
Do tell. I have figured out how to keep my GARN from puffing when burning small scrap wood 90% of the time. It's all technique on loading.
with my heatload, i average2 cords per month in the winter, ok ED, how did you do it? tom
Tom and Jim K
The Switzer is a GARNlike vessel for the most part but the controls are very different. Gary uses limit control switches by Honeywell that are set into the stack before the draft inducer. He uses 4 limit switches with different settings. Some break on rise only or drop only, some break and/or open on rise/drop. 3 of the switches control the 3 Dayton shutter motors that open and/or close the 3 draft doors on the face of the boiler depending on stack temps. Upper and lower primary air on the load door and ash door, and secondary air to front of firebox. The 4th switch is for draft inducer control. The inducer is two speed and can be forced to stay on high via a timer switch or it will drop to low on stack rise until end of burn when stack temps drop and the limit control switch turns the inducer to high until stack cools enough to turn the entire system off.
As for the puffing. I don't know if this will help with a garn because of the different controlls but the solution was very simple for me.
fill the beast with as much wood as you can but never put wood closer than 10" to the load door both vertical and horizontal.
My fire box is 30" diameter x 36" long but my splitter can only handle 25" logs so this is convenient. I have loaded the box from front to back with shorter splits and the puffing was so bad that the fire fire dept showed up after my alarm went off. It was a little embarasing but they thought it was a "grilling mishap" so my pride was left intact until I did it again a week later and had to fess up.
Since then I rarely experience puffing with careful loading and if it does puff it only does it for a few seconds after the lower primary draft door closes on stack rise (after loading or reloading only).
How do you raise 2000 gals of water 40* with only 40-60 lbs of wood? the math doesn't work. Are you using other sources to heat the water? I burn @ 300 lbs to raise 3000 gals 70* ( this is a guess based on cu ft because I've never weighed my wood).
One thing that I didn't like with the switzer design is that the primary and secondary combustion air is from inside the room, right? I think that is why your smoke alarm went off? The garn uses a direct vent from right outside so when the puffing starts the blow back goes outside., on my unit with the door latch that I have.
I would be interested in knowing what the secondary temps run in you unit. I don't know what mine will run right in the sec. chamber but it will glow bright orange and I have a 200-1000*F thermo in the first clean out and it will pass 1000 on start up and usually run @ 950*F.
Another thing that I think is of dislike is that the secondary chamber is to high in the back of the primary chamber. I found that lowering the chamber keeps the wood closer longer throughout the burn. Like the DD's gravity pulls the wood down to the nozzle where most of the refractory and heat is keeping the wood hot and releasing gases maintaining a good, hot, consistent burn.
LOL - "grilling mishap" - I gotta remember that. Sounds kind of like a "wardrobe malfunction".
I never actually weighed the wood, so my estimate is probably off by some, but not a lot. The GARN WHS2000 specs say that there is actually only 1860 gallons of water in an operating unit (I suspect the actual tank volume is 2000, but you don't fill it all the way). My delta T is in the 30-40 range. On most days (like this morning) I usually run it from about 152 to about 185-190. SO, I am raising 1860 gallons 35 degrees, on average, twice a day. I load in about 10 lbs of dry scrap lumber, and then 4-7 pieces of cordwood. So, perhaps 60-80 lbs is probably a better estimate. So, 1860*8.33*35= approx 542k btu. If I am getting 7k btu/lb of wood, that yields about 77lbs consumed. So, I am in the ballpark.
My wood is extremely dry, well seasoned hardwoods. I frequently get flue temps in the last pass of the GARN HX in the 425-475 range, without puffing. Depending on the heat load at the time, I can get a 10+ degree rise in less than 30 minutes from first light. This is consistent with the Dectra specs of max input for the WHS2000 of 425k Btuh.
you and I are burning the same amount of wood overall but I get it done in one burn every other day vs 2 burns daily. That is one advantage of a pressurized system. But never getting smoke in the house from puffing is great. Garn definitely has that situation under control. Switzer boilers must draw air from the room because of the numerous draft doors and their locations and therefore puffing puts smoke in the building.
My Switzer 1450 has been doing very well. This last cold spell has me burning between 400-500 lbs/day to get the temp up to 220F, but I'm heating a 2400sq ft. well insulated house and a 3000 sq.ft barely insulated house for my inlaws. (and hot water) The thermopex is doing well, no appreciable loss in a 250ft run to my inlaws' and a 75ft run to our house. This month will be almost a 2 1/2 full cord month, but 3 cords got me from Sept. to Jan 1st even while some plumbing bugs were being worked out.
The only time mine puffs back into the room (outside building) is when I've loaded too close to the door (as Tom mentioned). Even then the fire has to get the flue temp to 350+ so the primary air door closes before any puffing occurs. Since it's not in our house, it doesn't bother me much. All in all, a great unit, and I will post pics of my building. Maybe I'll snap some this weekend. -Too cold to do much else.
Tom, whats the best readings that you got out of the Garn?
My unit has performed exceptionally well in the low temps up until now. I don't know how I'm going to fix the catastrophe I am in now. I just don't understand how this could of happened after all the thought and time I invested in it that this failure was not foreseen..... oh yeah, you guessed it, I broke a firebrick!
High E got me on this one!!
What was the cost of such an install?
In deference to the owner I don't think I'll make that public knowledge here without his permission. PM me if you'd like. I do not know what the cost of his insulation job is as he and his mechanics did that work themselves.