AUF question

[berkshires]

Hi Folks,

Considering adding AUF to my little evaporator. I'd get a little squirrel cage blower. Not sure how many CFM I need. The actual firebox on my evaporator is about 14" x 18". With such a little fire, I don't want to overdo it and blow it all into the stack. On the other hand, I don't want to buy a blower that is under-sized and winds up doing the same (or less) than the natural draft I have now.

Anyone know the best way to figure this out? I definitely don't want to buy three and return two!

Thanks!

[mol1jb]

Maybe the easiest and surest way would be to get a little bigger blower and plumb it in with a damper in line so that you can turn the air down if need be.

[RileySugarbush]

You don't need much pressure or power for AUF. A little centrifugal blower like this one: https://www.grainger.com/product/DAYTON-Rectangular-Permanent-Split-45NM96 will work fine. You can probably fine something similar on craigslist or eBay.

If it puts out to much, make a damper on the inlet to the blower. For my first one, i just put a piece of cardboard over half of the inlet with a binder clip. You can easily regulate how much flow you get that way.

[phil-t]

Iused a vent fan off a propane water heater and did like has been mentioned, regulate the intake at the fan to control airflow into the fire. Works great. If you get a variable speed fan, you can regulate airflow that way. AUF is a great addition to an evaporator.

[Super Sapper]

A piece of duck tape over part of the inlet works also.

[berkshires]

Thanks for all the quick responses! Sounds like there's general agreement that the best way to go is to overshoot by a bit and then damp down to my needs. A few follow up questions:

- Riley, the CFM of the fan you linked is over 270. That is much more than I would have guessed for my little tiny evaporator. But of course that's why I'm asking - I don't know the right size. Even damped down, this won't be too big?
- To generalize the last question - should I be looking in the range of 70 - 150 CFM, or more like 200 - 300?
- Does it do any long-term damage to the engine to partially block either input or output? Seems like it would create stress on the motor.
- Some of you (mol1jb) have suggested a damper in the pipe between the blower and the firebox, while most of the others have suggested partially blocking the input to the blower. Does it make a difference, and is one better or worse than the other for the motor?

Also, I have no electricity in my sugar-shack, so I'll be running it off a deep-cycle battery (likely with an inverter inline). So I'd like to minimize the amps I need. Riley, if I'm reading it right, the one you referenced puts out over 270 CFM, while drawing only .77 amps. Others I was looking at by the same company with much smaller output seem to use much more electricity. For example, this one (http://www.electricmotorwarehouse.com/dayton-model-1tdp2-blower-104-cfm-2836-rpm-115v-60hz-4c763/#sthash.LsscvhMH.dpbs) puts out less than half the CFM, but soaks up more than twice the juice. Is it a different kind of motor? How can I narrow my search to more efficient motors?

Thanks!

[maple flats]

As long as there is still some air flow, it will not hurt the motor to block air air flow with a damper, but needing to block 75% means you are paying for more electric just to radically restrict it. I suggest you look in some of the maple catalogs. Most sell AUF blowers. Find on the right size for your rig and then maybe upsize 1 size. Then, even if you get a bigger rig, that blower should work, on this one, just make a damper, pop rivet it near the inlet, and then slide it to cover a portion as needed. You can also attach it with a sheet metal screw but be careful not to use one too long and have it interfere with the fan part turning.

[RileySugarbush]

Actually the motors use much less power when starved for inlet air. The load from the blower goes way down and the motor speed goes up. As Dave said, as long as there is enough flow to keep them cool, you are fine choking the inlet.

For your small rig, I'd guess anywhere from 100 CFM up will work fine, throttled down to what works best. My 2x6 worked well with a low pressure blower much like the one I suggested.

[red dorakeen]

I'm not sure if it relates to the blower motors considered here but I'll contribute it to the discussion.

When researching greenhouse exhaust fans I found that if there wasn't enough air inlets for a given size fan the fan motor would likely burnout sooner.

I'm guessing it would be good to find a blower as close to the CFM anticipated so choking could be kept to a minimum.

But I'm only guessing. Maybe it doesn't matter with squirrel cage blowers as much as fans.

[TYSC]

I was looking for info on this last year and found this info in another thread here. It was posted by Jeffb in a thread called blower cfm (http://mapletrader.com/community/showthread.php?28804-blower-cfm)

I tried to link to the thread, hope it worked.

[berkshires]

TYSC - the calculation at the start of your thread would mean that for my six inch stack I'd need a blower with 424 CFM. Pretty sure that's not right LOL!

Thanks, everyone, for the info. I'm thinking about buying this: http://www.electricmotorwarehouse.com/dayton-model-2c647-blower-134-cfm-1500-rpm-115-volts-60-50hz/#sthash.sHdqcmau.Dh8yCJxb.dpbs But this one and most of the others seem designed to mount onto a flat surface. Kind of a dumb question, but is there a straightforward way to attach it directly to a duct? The only obvious thing I can come up with is to attach the blower to a plate on one side, and and the plate to a duct on the other. This seems kind of cumbersome.

[maple flats]

Simply get a cap to fit the duct, then cut a hold the right size for the opening on the blower then bolt it on. Then put the cap on the duct and screw it in place. Depending on the size duct you have a cap will cost maybe $3-5. If the duct is crimped on the end you are attaching to, get a cap (fits outside the duct), if not crimped, use a plug (fits inside the duct). It will be cheaper at your local hardware stor, or Home depot or Lowes than online.
But personally I think you will gain more AUF just by adding 2' or even 4' to your stack than buying that small of a blower.

[berkshires]

Simply get a cap to fit the duct, then cut a hold the right size for the opening on the blower then bolt it on. Then put the cap on the duct and screw it in place.

Aha! That makes perfect sense, thanks!


But personally I think you will gain more AUF just by adding 2' or even 4' to your stack than buying that small of a blower.

Hmm... I'd guess I have about 12-16 feet of 6" smokestack now. As it is, a lot of the air seems to sneak around the fire, and I get a fair bit of coals. Part of what I hope the blower would do is allow me to cut a hole in the evaporator directly under the grate and direct air straight up through the fire and at the bottom of the front pan, reducing coals and putting more fire right on the pan. But who knows, maybe the blower won't do anything?

[maple flats]

I have high pressure AUF/AOF, get a super hard boil and I get lots of coals. I doubt the blower will reduce them.
I first fired a 2x3, then a 2x6 and then a 3x8 all using natural aspiration. Then I tried a blower for AUF on the 3x8, it increased to fuel consumption and the boil rate, but did not lessen the amount of coals. The same when I added high pressure AUF/AOF, no reduction in coals but the wood consumption dropped.
The only way to reduce coals is to give them more time to burn, but when making syrup is the primary goal so we don't burn the coals up, we keep adding more wood, most of us do it by the clock. This way, coals keep adding up, only to be burned up after our last fueling of a boil session. I do on mine, rake the coals forward, spreading them more evenly maybe every hour or so, basically when I notice them building towards the back of the grates.

[berkshires]

Reducing coals is not really my goal. Getting more heat on my pans is my goal. I want to see more air go through the fire, rather than around it. My hope is that this would increase the rate of the fire, and also have less cool air in the firebox. If I get coals burning off faster, great, but that's not the main thing.

[maple flats]

In that case, make sure the wood is dry, and split no larger than your wrist, fuel it every 7 minutes by the clock and run the blower, the one you indicated will need to run full open, no damper.

[RileySugarbush]

I'm surprised you still get coals, Dave. With AUF, I get almost none. They burn up as fast as I add new wood. Like you, when I added AOF, I used less wood for the same or a bit better evaporation rate.

[wiam]

If you have air going around the fire a blower is not going to fix that. Your wood should be covering the grates. When I had auf I had to put a 6” wide flat plate crosswise on top of the grates just inside the door. Too much air was going right up the front and cooling the pan.

[Super Sapper]

I've noticed that if I am getting coals built up that I am firing too often and the boil does slow down. Air going around the coals and wood will also decrease your boil. Keep everything spread out. I also added a brick just in front of the door to decrease the area the air has to travel and keep it on the coals.

[maple flats]

I still get coals, but not as much as I did before I added AOF/AUF. Before I added the AOF I had a squirrel cage blower for AUF, it was a 550 CFM but I blocked the inlet about 35%, but I'll bet it moved more than 65% of the 550 with the block. I fuel every 9 minutes using a timer. The timer gets reset before I open the doors to start again. Most of my wood is good hardwood but some is hemlock or other soft slab. A little of my wood is even tulip poplar and basswood.

[RileySugarbush]

I use a row of firebrick just inside the door like William does. Also, make sure you distribute the wood evenly when firing so there are no open spots for the air to bypass the fuel.

[maple flats]

Wood distribution is likely the biggest cause of the air bypassing the fire. Don't have any voids for air to bypass thru. I haven't in the past, but I'll try adding a row of firebricks just inside the door to see if I get an even better boil rate, good idea I hadn't thought of yet.

[Ken Letcher]

I use to have a Leader Half Pint, we added a centrifugal fan to the draft door. Not ever sure how many CFM the fan was, stole it off our old wood burner in the shop. But we run an electric cord to a switch box that we left on the floor right next to front door of the evaporator and then wired to the fan, the switch box has an on/off switch for when you are firing, and it also is wired through a rheostat (a light dimmer dial) so that we can easily adjust the air flow based upon our needs. You will find that sometimes you need to change air flow quite often, based on wood quality, stack temp, boil, etc., so the rheostat is extremely handy, and you don't have to worry about restricting air flow.

[Mark B]

Actually stumbled onto something that I think will work for auf. I found my old spray paint blower... I forget the make (cheapie Graco I think). Anyway, I have a a.c. motor variable speed control that I have adapted to it. My 2x4 is custom built so I am planning to trade for a few modifications including an adapter to the auf vent. If it all works out, I will post video in a month or so. Right now I have to get my uncles place ready for a renter in a month.

[mspina14]

I made a barrel stove and rigged up a blower fan.

16820

16821

I used a flexible metal dryer vent tubing, some black pipe, and duct tape to connect it to the bung hole in the barrel stove lid.

The blower was 125 CFM, if I remember. I had it plugged into a cheap rheostat that allowed the speed of the fan to be adjusted as needed.

16822

Worked great.

Mark

[Sugarmaker]

AUF: some air is way better than none, too much and you will know it. Some trial and error on that. But keep in mind that thousands of gallons of syrup have been made in the old days with no AUF. Just because it seems like everyone is doing it, you don't have too. A rig set up to have good draft will roar on its own with no AUF help. The amount you gain from wood savings and or increased boil rate is going to be hard to see and maybe hard to justify with no electric in the sugarhouse. Maybe a 5 to 15% improvement in efficiency????
Just my 2 cents. Have fun. Try it and let us know. Pictures are always helpful too!:)
Regards,
Chris

[berkshires]

I have some other improvements/fixes I need to make to my evaporator, and limited time (baby!) So I will at least start the season with the other improvements but without the AUF. If time allows, I may add it mid-season. That'll give me an apples-to-apples comparison of what kind of improvement just that makes in boil rate.

Gabe