AUF or AOF ??? what gives the best results

[miller maple]

i have a 3x8 traditonal wood fired arch, and want to add forced air for the 2013 season, im gowing to modify the arch and try to make it a little more air tight,and was wonding what is the better route to go, with the AUF or the AOF. thanks

[maple flats]

Do both for best results. I run 1 high pressure fan, split the flow with valves on both. I do not need to adjust the valves after I initially set them. My fan pressurizes a 4" PVC pipe. The 4" splits to 2- 3" pipes, one AUF and one AOF. The AUF valve I have about 25% open and the AOF valve is about 65% open. When testing early on I tried opening the AUF valve about 50% but that burned more wood with almost no gain in boil rate. The most important one for efficiency is the AOF. That is causing turbulance of the wood gasses and they then burn much more completely, under the pans where it does the most good. I can't speak for an airtight front since mine is still the original cast doors but I will likely do airtight someday. When I installed the AOF I saw my boil rate rise and my wood consumption drop and both were rather good changes. I don't remember the boil rate change now, but my fueling went from every 7 minutes to every 10. I have tried intervals of 8, 10, 12, 15 and even 20, but I finally decided I liked 10 minutes best. I do not need to slow the AUF when I open to add wood, I just open and put the wood in, as quickly as I can and close the doors. When this goes fast enough the boil only slightly slows and when the door closes again the boil is back at full almost instantly. I get no sparks,smoke or ashes out the doors when open after the fire and stack are hot. The only time I ever get any smoke is on the initial lighting of the fire and that is very brief. I light with a large flame thrower torch, aim the flame over the wood for 3-5 seconds to warm the stack and then direct the flame at the wood to light. It all usually takes less than a minute to get it fully involved, burning the 500,000 BTU torch at maybe 1/2 throttle. I only use about 25-30% of a 20# propane tank for the entire season.

[meadster02]

where did you get the high pressure blower or do you think a squirrel cage blower would work too

[maple flats]

My high pressure blower came out of an old factory that had closed. A squirrel cage will not work, they are high volume not high pressure. You need a blower with low volume and high pressure. New they are not cheap, but Graingers is one source, there are others. Refer to this paper on AOF: http://www.uvm.edu/~pmrc/Combustion.pdf

[miller maple]

how did you take your 4'' pvc downt to the nossles or what kind of manifold did you set up like it was talking about it the link that you posted

[miller maple]

What is ray gingerichs prices on his gas powered RO's

[Timberwolf]

In case anyone is interested, there are some high pressure blowers available on ebay much cheaper than Grainger.

[sandman6921]

I'm using two burners from a coal stoker. Anybody have an opinion if AOF would help me?

[maple flats]

Only opinion, but I think yes. My reasoning is that coal smoke can be smelled, and it smells like some gasses. AOF should burn those gasses. Other smells will not burn up in the exhaust.

[Woody]

Can you tell me how you take your 4'' pvc from the blower down to the nozzles or what kind of manifold you set up. I was thinking I would come off the blower with pvc then split into two runs and install the valves. Then I was going to transition to black pipe and run the manifolds on the exterior of the fire box and make penetrations for the nozzels. Are there better ideas out there? Thanks

[RileySugarbush]

My setup uses separate blowers, but maybe a useful example. I connect the manifold to the high pressure blower outlet using corrugated aluminum ducting that allows the clamp to distort round to rectangular. My manifold is welded of rectangular and square steel tube and resides inside the firebox, just above the top row of firebrick. The nozzles are stainless hydraulic tubing. Inside the box, the tubing and nozzles are protected by wrapping in ceramic blanket. Works well!

You can see the manifold before it was installed in this you tube video:

http://www.youtube.com/watch?v=LhiEyMjVx5g

[user587]

For me AOF and AUF both is definitely the way to go. I built an arch a few years ago, see ([URL="http://s1103.photobucket.com/albums/g478/user587/Arch%20Construction/"].

The AOF makes a nice hot fire into an inferno. When we turn the AOF off (to fire, etc...) the fire looks nice and it's hot - but the AOF kicks it up a notch. With Oak last year, and a real meter, we boiled 60gph on the 2x8 evaporator (2x5flue pan) last year.

As seen in the pics, I used PVC 4" for the air feed. I used the grainger paddle fan and 3/4hp motor - seems to be plenty. (I can look up p/n's if needed - let me know). It's easier to put it in now than later. :)

One note - I think the pics have the non-slant back end of arch - after 1 year I revised the arch to have the slant floor under the flue pan - the fire needs to have line-of-sight to the flues for radiation (my mistake on the original design - live and learn)

[maple flats]

I connect the fan to the 4" PVC using a fernco connector. After the 4" splits and goes to 3", for under and over each goes thru a 3" valve, the over air connects to the manifold that supplies the nozzles using a fernco again, but the under fire air just goes into a 4" stove pipe with the end capped. It is split where it joins the 3" valve so I just used a SS band clamp. The stove pipe then lays on the floor under the grates and has 3 rows of 5/16" holes, one top center, the other 2 point each to their respective side, these holes are spaced about every 4" and the last one is 8" back from the fill door. My manifold is under spec but it works very well. It is made of 2" sq. tube, 1/16" wall with the nozzles every 6" and pointed down 15 degrees. The nozzles are 3/8" black pipe if memory serves me, but maybe it was 1/4". The manifold is 6" under the pan and is protected with refractory cement.

[Timberwolf]

For me AOF and AUF both is definitely the way to go. I built an arch a few years ago, see ([URL="http://s1103.photobucket.com/albums/g478/user587/Arch%20Construction/"].



What kind of meter do you use? I would like to get a flow meter to measure my GPH.

[user587]

I use a WM75 for sap running into the evaporator, and a WM100 for sap when I'm pumping into the feed tank. These meters work very well for me. For the evap. meter, I plumbed a bypass for emergencies, but have never used it. Also it's mounted on the wall, removable with unions for *reasonably* easy cleaning. meters from http://assuredautomation.com/WM/index.php

I see the prices have gone up this year. I paid $76/136, now they are listed at $90/160. bummer!

I think I had seen some lesser type meters, but I'm really glad I have the old heavy style units.