Air over fire/what size feed pipe

[Windy Acres]

Ok guys, we are getting concrete tomorrow, and i am unsure on the size of pvc to bury, i am bringing the air in from outside, should i use 3 or 4 inch? 2x8 evaporator, 1/2 hp blowe

[n8hutch]

Just Used 4" , my slab is getting poured on monday.

[Windy Acres]

Thank you, thats what i was thinking, the opening on the blower is 3.5x3.5 so it should be a good match

[johnpma]

Can you educate a newbie on what air over fire is please

[wiam]

Can you educate a newbie on what air over fire is pleasedo a search on here "aof"

[Flat Lander Sugaring]

im going to go 4" of my blower and when i get closer to the arch going to put a Y in drop to 3". reason for that is I got two 3 " pvc ball valves for free. I really want butterfly valves but those are wicked expensive

[n8hutch]

im going to go 4" of my blower and when i get closer to the arch going to put a Y in drop to 3". reason for that is I got two 3 " pvc ball valves for free. I really want butterfly valves but those are wicked expensive I am going to do something similar under the evaporator I'm going to have a 4x3 Y and 2 valves most likely.

[maple flats]

4" is good, but only use long sweep ells, that results in less friction loss.

[Windy Acres]

4" under the slab and 3 drains!14537

[Windy Acres]

Got the manifolds built, and nozzles installed, just need to notch the top row of bricks and put the under fire air tube back in, then i can plumb it all up!

[Windy Acres]

147301473114732

[pipeline]

almost ready looks nice !!

[Windy Acres]

Thanks pipeline!

[Windy Acres]

A few steps closer!14735147361473714738

[gmc8757]

Very nice work, it looks great.

Can you tell us more about the blower you are using? Is it a cage blower, "bouncy house" type blower, or something else? I always thought aof needed high pressure while auf did not?

Is the idea that the high pressure for aof is created by starting with 4", reducing it down to what looks like 2", then reducing it down to small nozzles? All while the auf gets the full 2"?


Sent from my iPhone using Tapatalk

[Sugarmaker]

Can you educate a newbie on what air over fire is please

John,
Air over fire systems come in many variations. Basically duct work, either internal or external to the arch to supply air under pressure, near the upper portion of the fire box. Usually multiple small nozzles direct the air into the fire box. The turbulent flow helps burn the gasses above the fire and get more heat out of the wood being consumed. It is a means to improve the efficiency of the wood burning maple syrup arch.
Regards,
Chris

[Windy Acres]

John, thank you, and yes, im using the specified dayton high pressure blower that is in the uvm research, if you need the numbers i could get them for you later

[RileySugarbush]

Very nice work, it looks great.

Can you tell us more about the blower you are using? Is it a cage blower, "bouncy house" type blower, or something else? I always thought aof needed high pressure while auf did not?

Is the idea that the high pressure for aof is created by starting with 4", reducing it down to what looks like 2", then reducing it down to small nozzles? All while the auf gets the full 2"?


Sent from my iPhone using Tapatalk

To get high pressure for the AOF flow you need a blower designed for high pressure. A squirrel cage blower won't do it. The bounce house blowers are good and cheap for this and that is what I use. Radial vane industrial blowers work as well but are more expensive. I had one of those but it's output pressure was only 4" H20. Output pressure on my Koala blower is 8" H20 when blocked and when mostly blocked. That much pressure at the nozzles is what gives the high velocity jets that help with the mixing above the fire. To make sure the nozzles see that much upstream pressure, the AOF manifold needs to have at least a couple of times as much cross sectional area as the sum of the nozzle areas.

For AOF flow, pressure at the nozzle determines the jet velocity.

Jet velocity multiplied by the total nozzle area will tell you how much air your AOF is adding to the combustion. Too little and the AOF is ineffective. Too much and your flue gasses blow past the flue pan so fast all you get is high stack temperatures and low efficiency.
Here are the numbers for my system this year:



AOF flow calculations

















NozzleDiameter
0.25
inches



NumberOfNozzles
14




Pressure at nozzle
8
inches of h20


Velocity of AOF jets
81
mph



total AOF Flow
34
CFM





You can use the high pressure blower to feed the AUF as well, but you need to regulate how much air goes that way or all of it will since that becomes the low resistance path. That will burn wood like crazy and drop the pressure so much AOF jets don't do anything. I use a blast gate on a branch off the output of the HP blower to throttle down the AUF flow and feed it under the grate.

[maple flats]

Windy acres, before you cover it in, I have a question on the nozzles. Are they aimed straight out (level)? If they are it may be an issue. The reference from Proctor says they should face down 10 degrees. That creates more turbulence and thus more complete combustion. Mine face down the 10 degrees and it works wonderfully. I don't know if aiming them level across above the fire will do the same.

[Windy Acres]

Maple flats, yes they face down at 10 degrees, and the ohes by the oor face forward about 5 degrees

[Windy Acres]

Maple flats, yes they face down at the 10 degree angle that was recommended n the research

[maple flats]

Sorry, in the pictures I thought they looked to be pointing straight out, not down, my bad. It sounds like you are on the right path.
Based on my experience, you will burn about 30% less wood and boil about 25-30% faster. That's a win-win.

[Windy Acres]

No biggie Maple flats, are you using your original grates?

[Windy Acres]

1474714748got the front door sight glass done, and air is all done, ready for grates!

[Wanabe1972]

Windy, What did you use for glass in your door? I've always wanted to do this to set up my Under and Over the fire air. Jeff

[Windy Acres]

Wanabe, its high temp. Glass circles out of McMaster Carr, 1/8" thick, the pipe is a sch.80 1-1/2" pipe nipple that goes through the door, flush with the insulation, and the ring is a slip nut from the plumbing section from most any hardware store

[1ruralmailman]

i gotta stop by and check this setup out windy.

[Windy Acres]

Sounds good!

[mellondome]

For valves, use gate valves.. cheap if you look for the ones used in wood shops on their dust collection systems.

It looks like you used screws to hold the fittings together. Are you also going to glue them?

[Windy Acres]

After i boil with this setup, and am sure the piping is how it should be, i will glue all joints, the valves i used are gate valves

[Windy Acres]

well we've been able to boil enough to get the AOF/AUF adjusted and what a HUGE difference! we went from firing every 5-6 minutes, to now every 14-15 minutes, and it holds 900 on the stack with very little smoke, and im sure we picked up around 15-20 gallons an hour, well worth the time and effort!

[maple flats]

I want to clarify from my post (reply # 8). 4" is good for my size rig (3x8), I'm sure a much bigger rig will need 6" and some possibly even 8". I think the way to know will be the discharge outlet of the high pressure blower. The pipe should be a little lafer than that measurement. In my case the discharge is 3" and I used 4" pipe.
Someone asked if I used the original grates, yes I did and still have them. When those grates need replacing, I will be making a floor in my arch out of refractory, it will have plenty of air passage under, with fire half bricks to hold it up, then the refractory floor will have holes of about 3/4" and tapering larger at the bottom all over the floor (I'll make non corrugated cardboard to make cones to make the holes while casting). My AUF is also high pressure, valved off the HP blower using 2 3" brass ball valves. The AOF is open about 60-70% and the AUF is open about 25-30%. Those settings never change.

[RileySugarbush]

Dave,

Have you ever measured your nozzle pressure? Your rig is wider than mine but I would like to compare it to my numbers. I haven't fired up the new extended pan yet. This year, 2x8 with 8"h20 pressure at the nozzles, with fourteen nozzles of .25 inch diameter. I figure jet velocity of 81 mph and total AOF flow of 34 CFM. This is reduced from last year when my stack temps were too high and I am anxious to see how it changes.