AOF/AUF Blower size.

[vach50]

I’m rebuilding my homemade evaporator this summer and am adding AOF/AUF. I’ve tried searching again and can’t find what size Koala blower people are using for a 2x6 evaporator. I thought it was a Koala 680 but was hoping to double check before buying. What size should I buy? Thanks.

[bmbmkr]

I'm runnin a 650 cfm dust collector blower on my 2x6.

[minehart gap]

University of Vermont, Proctor has a website that you can find papers written about various maple related topics. I believe that one of those papers is the one that you are looking for.

Or look at mapleresearch.org.

[red/one]

I have a home built 2x6ish AUF and I have this. https://www.amazon.com/gp/product/B00LOCE356/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1 Very happy with it.

[mol1jb]

Any bouncy house blower should get you in the ball park

[maple flats]

This will give you the answers https://mapleresearch.org/wp-content/uploads/combeffic.pdf
Once you find the recommended blower from Graingers, get the specs of that blower and compare it to the jump house blower. They are the right type of blower and are much lower cost, but you still want to get close to the same CFM. You may want the next larger blower, ($129?), still far below the grainger units.

[vach50]

The Maple research org web site lists a specific Grainger model. Grangers description of that model list no CFM and no pressure specs. It also costs $421 without a motor. I know the Koala 680 will get me close, but I’d kinda like to more certain than just taking a stab at it. I know someone on here had some specific info about the Koala and proper sizing, but my search can’t find it again.

[maple flats]

I used to buy from Graingers quite often back 20-30 years ago when I was in the heating business. Back then once I had Grainger's number, I could go to that item and get all of the specs. I'll bet you still can. From the item listed in the https://mapleresearch.org/wp-content.../combeffic.pdf
get the item number, then look it up on Graingers web site or in their catalog. All specs will be there.

[vach50]

I’ve looked at both the Grainger and Dayton sites. They have a list of 30 specs that must include every size dimension for that blower, but neither site mentions cfm or output pressure. Guess I’ll try and call Dayton tomorrow.

[vach50]

Well that was easy. Not! Four phone calls to four different Dayton Companies directed by four different recommendations and I never did get the Dayton Company that builds blowers. I ordered a Koala 680 1/2 hp blower because I think it’s the right size, but after many hours of work I still am not certain it is. Time to move on and do something else with my life.

[vach50]

Thought I’d give an update and ask a couple questions. Second cook with new blower today and very happy with results. First cook I had way too much AOF. Today I started cutting that back and was steady at 25 gph for my 2x6 with flat pans and a poor preheater, no hood. That’s 40% more than last year. Very pleased.

There are a few things I question though. I’m using less AOF than AUF. My boil rate and stack temp both improved with this setup. Sounds like most others use more air over?

I have two or three times more area open in the floor of the firebox than recommend. Should I be closing that up some?

I also think I’m still blowing too much air. I add 5-8 pieces of white pine slab wood every 5 minutes. Black smoke out the chimney only lasts 60 seconds or less then no smoke and just heatwaves. I am blowing more embers out the chimney than ever before. No ash left in fire box after 5 hours of cooking.

I also think I have to start shutting air off when I fire up. I have 2 seconds to throw wood in and get door closed before I have flames shooting out door.

Thanks in advance for any comments or suggestions.

[maple flats]

Maybe this will help https://mapleresearch.org/wp-content/uploads/combeffic.pdf
With a 2x6 or smaller you can often use an old oil burner gun, no oil hooked up, but the blower on them is ca high pressure blower. The link I referred has suggested blowers for larger arches. They go by width, length doesn't really matter. If you see a bounce house blower try to check the CFM of the grainger recommended blower and compare that with the bounce house one you are considering. Remember, high pressure doesn't mean high volume, but if you use a high pressure blower that puts out at least 3" WC (water column) a measure of the air pressure, the CFM will help you match the amount of air pressure needed to create the turbulence in the firebox necessary to get near complete combustion.

[vach50]

Thanks for the reply Dave but I’ve already sized and installed the blower and was hoping to get some response to my new set of questions and observations from my most recent post.

[RileySugarbush]

It's hard to figure what the volume of air is or should be.

I think of it like this: AUF is the throttle. More air and your burn rate is higher, more energy into the arch. Too much and a lot of the heat goes right past the pans and up the stack, increasing boil rate but reducing efficiency and increasing stack temp. It is the combination of AUF volume and how much surface area of wood is in the box at a time that determines amount of heat generated. A tough balancing act.

AOF is for efficiency. You only want enough to burn the hydrocarbons that are unburnt in the exhaust of the fire. The stuff that would reignite as a flame out the top of the stack if you didn't have AOF. It is much better to burn it as it starts under the pans.

AOF should be introduced at high velocity into the area above the fire, to mix the air with the unburned gasses. That is why the nozzles are arranged all around the fire. Also why a high pressure blower is needed. Pressure at the nozzle is what determines the velocity. Then, size and number of jets determine the amount of AOF volume. If you adjust the AOF with a valve, you are lowering the pressure at the nozzles and that reduces mixing along with air volume. Better in my opinion to keep the line from the blower to the nozzles unrestricted and adjust the AOF to what you want by correct nozzle number and size.

For reference, the velocity is proportional to the square root of the pressure. At 3" H2O velocity is 50 mph At 5" it is 64mph. Mine is 8" and that give 81 miles per hour jets. Great for mixing but 50 mph is pretty good too.

I throttle the AUF and leave the AOF alone once I have my system tuned. I have a quick flap valve that stops inlet flow to both for firing.

Here is my AOF setup:
http://mapletrader.com/community/attachment.php?attachmentid=22189&stc=1
http://mapletrader.com/community/blob:http://mapletrader.com/9bc59a55-18d0-460a-93f1-af986be2f5aa

[vach50]

I did a quick check and had less than 3” wc on my 3/8” id nozzles. Inserted some 1/8” pipe with .269” id and had close to 8” wc. Will try that tomorrow on a cook and I think it may help. Also rigged up damper to easily close off air during fire up. Thanks.

[RileySugarbush]

Looks like you had so much nozzle area you were putting almost the full unthrottled flow of the blower onto the bottom of your pans. You should see a big improvement.