AUF, AOF ad blower questions

[spencer11]

i am going to be building a 2x6 evaporator and want to have AUF and AOF. what are the advantages to each? what type of blower(s) should i use? where should i have the air come in under the fire? back or front or under the grates? i have an idea about how to do the AOF, but not sure how i would hook it up to the blower. should i use square or round tube for the AOF?

spencer

[500592]

I was wondering the same thing just for a 3x8

[Flat Lander Sugaring]

auf under grates or what ever you have, not sure about style of blower or cfm, you can always use a rheostat, AOF supposed to be high pressure, look back in archives here and you will find a lot of posts about this subject

[spencer11]

can i do auf through the drap/ash door under the grates? or do it through the back? i thik i know how im gonna do the aof but dont know what i need to use for a blower for either of them.

spencer

[Flat Lander Sugaring]

stick it in any where you want, but the front ash door be a PIA every time you go to load wood it gonna be in the way, I would go from back. Iv heard people using 250cfm blowers for AUF. 2x3 tubing down rails 6" under pans then ceramic blanket over it and behind it only have nozzles sticking out.

[500592]

I think I am gonna stick2x4 tubing or 3 in pipe for my 3x8

[nymapleguy607]

You want to make sure you make the firebox big enough to handle the extra air you are forcing in there, otherwise you will be pushing all your heat out the stack.

[spencer11]

im going with about a 2'x2'x20" fire box. i think that should be big enough. when it is mounted in the back does it need to have pipe running into the ash "area" and blowing air upward? or can i just run piping from the blower to the back? or would that blow ash out the draft door?

spencer

[wiam]

im going with about a 2'x2'x20" fire box. i think that should be big enough. when it is mounted in the back does it need to have pipe running into the ash "area" and blowing air upward? or can i just run piping from the blower to the back? or would that blow ash out the draft door?

spencer

Mine just goes into the back. No pipe inside. You will want to make draft door air tight.

[wiam]

im going with about a 2'x2'x20" fire box. i think that should be big enough. when it is mounted in the back does it need to have pipe running into the ash "area" and blowing air upward? or can i just run piping from the blower to the back? or would that blow ash out the draft door?

spencer

Mine just goes into the back. No pipe inside. You will want to make draft door air tight.

[spencer11]

so you have the ash door closed while running the blower? i was woried about having to much air and having it kill the fire, is it possible?

spencer

[nymapleguy607]

im going with about a 2'x2'x20" fire box. i think that should be big enough. when it is mounted in the back does it need to have pipe running into the ash "area" and blowing air upward? or can i just run piping from the blower to the back? or would that blow ash out the draft door?

spencer

Ok lets be clear, are you building completly new or are you modifying existing. If you building new you are don't need to build a draft door thats the purpose of the forced air. I have never seen a fire blown out from too much air, unless its just starting, in most cases if you let the kindlin catch you start the blower and then never shut it off until you are done. A 2x2x20 firebox will be to small on a 2x6 with AOF and AUF. On most of the commercial wood evaporators with over fire air the firebox is 2/3 the length of the evaporator. So using that assumption your firebox should be around 48". Best advice is to look at some of the commercial built units and go from there.

[spencer11]

i will be new. and i guess if i need a draft door for some reason i can cut one in. 4 feet for a fire box seems pretty long on a 2x6 arch? i am trying to go to the bascoms open house so i could look at comercial ones there

spencer

[nymapleguy607]

Spencer,

The reason for the larger firebox is it gives the wood gasses a place to mix and burn. If your using a high pressure blower you will easiy pressurize the firebox and then you start to blow your heat up the stack. You will find the commercial ones have no ramp in the back of the firebox either, its just a straight wall. For a 2x6 one high pressure blower will give you all the air that you need on my arch my air comes into a box then I have dampers for the overfire and under fire air. The over fire will run wide open and under fire will vary depending on the wood and how fast you want to boil. Think of the underfire air as the accelerator the more it opened up the faster it will go, but you burn more fuel.

[spencer11]

would a 3 foot deep fire box be deep enough? do you know what size blower or fan or whatever i should get, so i could use it as both? thanks

spencer

[Flat Lander Sugaring]

Ok lets be clear, are you building completly new or are you modifying existing. If you building new you are don't need to build a draft door thats the purpose of the forced air. I have never seen a fire blown out from too much air, unless its just starting, in most cases if you let the kindlin catch you start the blower and then never shut it off until you are done. A 2x2x20 firebox will be to small on a 2x6 with AOF and AUF. On most of the commercial wood evaporators with over fire air the firebox is 2/3 the length of the evaporator. So using that assumption your firebox should be around 48". Best advice is to look at some of the commercial built units and go from there.

I dont know about 2/3 of the evap. But deffinately the entire syrup pan. If you talk to Leader people they say you can't really do a gasification unit on any thing smaller than 30x10 because like you said Jeff a lot of room is needed for the mixture of high pressure air and gases for it to work. I am doing same thing this summer but adding 18" to 2' to lenght of arch adding a hot air chamber box so I am going to be blowing very hot air back in AOF. You need approx. 1200 deg in fire box area for gasification to happen. Two blowers one for AUF and one for AOF.

[spencer11]

i changed the design for my arch so it has a 3 foot fire box instead of 20" deep. i think it should be big enough. what size blower should i use for auf?

spencer

[spencer11]

okay so i got a 2.5x8 raised flue evaporator and what size blower will i need for aof? i plan on using a blower from an old furnace i have(cant have my mom find out) in the basement. i dont know the cfm until get it out but we use them at the race track to cool the cars and it seems like alot of air and its moving pretty quick, is this a good blower for auf? can it be used for aof? i know i havent given a ton of info but this is all i know so far

[spencer11]

got the blower out, the motor is a GE 1/4 hp at 1725 rpm if this helps

[RileySugarbush]

Spencer,

It will be more than enough for AUF. You will likely need to throttle it down with an inlet baffle to keep your wood construction reasonable. It will be a poor choice for AOF. Lots of volume but not enough pressure to get the high speed jets of air you need.

[spencer11]

what kind of blower should i use for aof? i know high pressure but what does everyone else use? for a 2.5x8

[spencer11]

would this blower work for aof?
http://www.ebay.com/itm/4-High-Output-165-CFM-In-line-Duct-Exhaust-Fan-Air-Scrubber-Filter-/120931725552?_trksid=p3284.m263&_trkparms=algo%3DSIC%26its%3DI%26itu%3DUCI%252BIA% 252BUA%252BFICS%252BUFI%26otn%3D21%26pmod%3D130712 782653%26ps%3D54#ht_3556wt_1185

or could i put a bigger motor on the blower i already have?

[Waynehere]

This is what you might want to look at, although you might not need one so big.

http://www.grainger.com/Grainger/DAYTON-High-Pressure-Direct-Drive-Radial-4C108

I am planning on using it for my 2x6, but have a smaller motor on it.

[spencer11]

they have those on ebay for under 200, what size motor for a 2.5x8? what size motor are you planning on for a 2x6?

[maple maniac65]

for a 2.5x8 a 1250cfm variable speed blower will be enough. Most of the time I run mine about 300cfm's and only run it on full speed when I am trying to push the heat out to shut it down for the night.

[spencer11]

you are talking about AUf correct?

[maple maniac65]

my arch is auf/aof designed by Leader

[spencer11]

what blower do you run at 300 cfm?

[802maple]

When I build a 2x6 econo-fire as i call it, which is the restyled instens-o-fire that I originally designed, I use a 1/2 horse blower by Grainger #70747 high pressure unit. The firebox should be 2/3rds the length of the pans for proper gasification or combustion which ever you chose to call it. It blows into a plenum that divides the airflow thru a damper system,to the AUF and AOF. 75 percent of the air should go to the aof. In my unit there is air at the back of the firebox and the front of the firebox thru the frame of the door and the door itself. My finished fire box is 27 inches high x 22 inches wide and 48 inches long. I use 27 inches of grate and i never fill the firebox more then 2/3rds full.

[spencer11]

the fire box on my 2.5x8 is about 1/2-2/3's the size of the whole thing. i have a blower for auf already could i still just use that one for aof? i was looking at this for a blower
http://www.ebay.com/itm/Dayton-4C329-High-Pressure-Direct-Drive-Radial-Blade-Blower-G2-/230807319894?pt=LH_DefaultDomain_0&hash=item35bd303556#ht_1875wt_905

now are rpm for the blower motor more important the the HP? or reversed?

[802maple]

Thats a lot of blower, that is the one i use for a 5' wide evaporator. I had a typo on the blower for above, 7D747 is the blower i use for a 2 and 2.5 evaporators. I am assuming your firebox slopes up from the grates. AOF will work on those but not as efficient. The square back box works the best because there is more room for combustion behind the fire. Although i have retrofitted a quite a few old arches like yours to AOf and most people have been happy for what they had.

[spencer11]

it dos has the slope in the back of the fire box, but i could possible stack bricks up for bend some sheet metal for that , but it would make the fire box slightly smaller. and i will look at grainger for that blower

[spencer11]

what about putting a smaller, 1/2 hp motor, put on the same blower i put the link in for? just cause it would be cheaper. or it that not a good idea?

[802maple]

The 12 1/2 inch wheel would work a 1/2 horse awful hard. and besides by the time you bought the 1/2 motor and that blower you would be near the same price for the new one from Graniger. You only need one blower to run the whole evaporator with a damper setup out of a plenum.

[Waynehere]

they have those on ebay for under 200, what size motor for a 2.5x8? what size motor are you planning on for a 2x6?

I am starting with a 3/4 HP at 1700 rpm. After I get the tubes and nozzles installed, I will test my pressure to see if I am getting enough. If not, then I will upgrade the motor to the recommended rpms to see if I can get it up there.

[spencer11]

i will get the blower from grainger if i have can afford it when i need it, but other wise its just be auf, which i have a blower i could use already. if i just use the grainger blower how can i divide the air flow at 25 auf and 75 aof?

[maple flats]

I run mine splitting with valves. I have an antique high pressure blower. I run a 4" pvc from the blower outside to under the arch. There I split into 2 pipes, 3" pvc. Each has a valve, the one feed AUF I open about 1/3 and the one that feeds AOF I open about 3/4. This works good. I have no idea if that is 25/75 or whatever. I do know it is pumping much more air AOF than AUF but fluid dynamics are above my ability to be sure. If you do similar and send a little under and the greater over you will be fine. When you are operating you can experiment with differing valve settings. When I first hooked mine up I tried different settings, but when I found the most efficient setting it stays there. I have not moved my valves since that first season, they stay where they are all the time.

[spencer11]

i would try that if i get the blower and get it set up, that seems like a good idea

[500592]

I plan on using a leaf blower for my aof and furnace blowers for auf this should work right:confused:

[802maple]

When i build an arch, i divide it up with 2 dampers like I mentioned above out of a plenum. Without really gettin into the science of the unit, a good way to determine if you have your mixtures right would be go out and look at the exhaust. no smoke or sparks and you are pretty close, if you are blowing out a ton of sparks, you have to much air under the fire, If you have a ton of smoke and no sparks, you need more over air. You only need enough air under to maintain the fire and not create a torch. and enough over to burn the smoke.

[spencer11]

500, i am also using a furnace blower i just too off out furnace for auf if i dont get the high pressure blower for aof this year

[maple flats]

Both a leaf blower and a furnace blower are high pressure. You can use it but AUF only needs a cheaper squirrel cage type blower. The AOF is where the high pressure is needed. Also, most leaf blowers are not built for continuous operation. Even if buying or finding used look for a blower that can last. The last complication you need while boiling is to lose a fan, but if one were to fail, far better the under fire one as long as you can open the original draft door.

[maple flats]

Think of things this way, under fire air burns wood faster, over fire air make the burning efficiency go higher.

[802maple]

If you can find a old oil burner, preferably something newer then 25 years old, they will give decent pressure for your small evaporator and they will run constant for a long time

[500592]

802 would two or three furnace blowers work for a 3x8 just like spencers except it is 3x8 and has both stainless pans

[RileySugarbush]

Both a leaf blower and a furnace blower are high pressure. You can use it but AUF only needs a cheaper squirrel cage type blower. The AOF is where the high pressure is needed. Also, most leaf blowers are not built for continuous operation. Even if buying or finding used look for a blower that can last. The last complication you need while boiling is to lose a fan, but if one were to fail, far better the under fire one as long as you can open the original draft door.


Dave,

I haven't checked specifically, but am surprised that a furnace circulation blower is high pressure. Do you know how high a SP they have when stopped down to 100 CFM or so? I consider that the minimum pressure you would want at the inlet to the nozzles would be 3.5 in h20. More would be better.

[RileySugarbush]

Actually, I did just check. Home furnace air blowers look like I expected. Very high volume but low pressure. You can see the curves here. I don't think you could get much over 2 inches SP out of these.

http://www1.eere.energy.gov/buildings/appliance_standards/residential/pdfs/furnaces_boilers/fb_tsd_appendixi_0906.pdf

[nymapleguy607]

802,

Have you ever used the area under the flue pan as a plenum/ heat exchanger for the combustion air. I'm working on a new arch and am debating trying this to see if it helps drop the stack temp.

Thanks.

[spencer11]

so is the furnace blower like i have high pressure? or high volume? and could it be changed?

[RileySugarbush]

so is the furnace blower like i have high pressure? or high volume? and could it be changed?
You should figure it out for yourself. It easy.

Clamp your blower securely and add a couple feet of duct. Cardboard will do. Wire it up safely with a switch or plug. To figure out the static pressure, use a manometer. Look it up on the web. It is just a u shaped bit of clear hose, with the bottom of the u filled with water. One open end should be stuck in th side of the duct, perpendicular to the air flow. The other open to the shop. With the blower off, the water level in each side of the U will be even. That is zero static pressure. Now turn on the blower. The water levels will change very slightly. If you progressively close off the outlet you will see the levels change. This is the "inches of water" we have been talking about With the flow totally blocked you should see the maximum static pressure of the fan. I'm guessing you will not see much over 2". If you see over 4" then you could use it for over fire air. More would be better.

If you had an easy way to measure the CFM at each blockage you could plot CFM vs SP and that would be the fan curve shown in the link I posted.

Fans cannot be changed from low to high pressure. It would involve changing the shape, number, spacing, length of the vanes as well as the housing. That's everything! High pressure blowers are typically loud and not likely to be found in a furnace.

Write up this experiment and you will have next years science fair project done in advance!

[spencer11]

okay before i can do that test i need to find out whats wrong with my blower. its a furnace blower and when i plug it in it turns on then the motor stop and it starts slowing down, then it starts again and goes full speed for a couple more seconds then does that for a third time then shuts off completaly. it has a 1/4 hp GE motor on it. any idea on whats wrong or what i need?

[RileySugarbush]

Try starting it with the outlet blocked off about half way.

[spencer11]

so just put like cardboard over half the outlet so there is back pressure?

[RileySugarbush]

yup. If the problem is overspeed due to no load condition this will tell you.

[spencer11]

wow it works! `why does it do that? now i just gotta put a switch in..

[spencer11]

got the switch in. i had some 1/4" clear hose laying around and put a whole in the cardboard i had over the front(i had the whole front blocked off) and i had a little over an inch of "difference" in the water, so not a high pressure one

[RileySugarbush]

Nice work! That is what I expected. It will make a super under air blower.

[500592]

The leaf blower I have is an electric toro that we used it before all day to blow air into our old oil tank arch and it never got hot or anything it worked great

[spencer11]

thats what i plan to use it for if i dont get something for both auf and aof...would a leaf blower actually work for aof? cause im sure i could get one cheap, even new

[RileySugarbush]

Probably not well. That is another high volume application. Plus to get AOF on your rig would be at least 1HP.

[spencer11]

i think im gonna go test our leaf blower...it is gas powered but just to see what it does and if it actualy might work. ill let you know how it works!

[spencer11]

just tested it and at full throttle i got around 18" of difference, just idleing i got about 2. would that leaf blower actually work? btw its a husqvarna 125 bt gas leaf blower

[RileySugarbush]

Did you check it with the end closed off and little to no flow?? If you just stick the open tube of the manometer into the end of the open leaf blower nozzle, you are measuring the velocity of the air, not the static pressure. That is called a pitot tube and is how airplanes measure airspeed! Look it up on wikipedia.

[spencer11]

i blocked it off with duct tape and then stuck the tube in and taped around it

[802maple]

I would say that you guys are trying something that is already been tried, it will in the end, cost you more then buying a good blower that blows into a plenum and then the air divided up out of that plenum by using 2 exits with dampers to divide the air. Been there done that with leaf blowers etc., unfortunately they are not made to run hour upon hour and will fail. the good ones that will last, cost twice as much as the blower used from Grainger.

The used oil guns that I mentioned will work and have used them, one for over air and one for under air. You still will need to control the air from them with somekind of damper. I do recommend not to try to force the air into a small tube for air transfer to your air injectors. Again I have been doing this since 1992 and have seen what works and what doesn't, all your ideas will work to a certain extent, but you need to get maximum air to your fire box for the best efficiency.