• Some of the links on this forum allow SMF, at no cost to you, to earn a small commission when you click through and make a purchase. Let me know if you have any questions about this.

Pellet Smoker Design

rpolancot

Newbie
4
0
Joined Jan 10, 2016
Hi y'all:
I'm working on fabricating a Commercial Pellet Smoker, aiming cooking with very clean smoke, efficiency (pellet per hour) and stable/same temperature on all 22.5 cubic meters. For this I will use 1.5 inches insulation on all exterior and a forced convection system inside the smoker (as an industrial drying oven). I have read that, as air contains 21% oxigen, it still has 16-18% oxigen once it leaves a regular pellet smoker, with valuable smoke along it. My plan is to recirculate 75 % of this air to the intake fan on the pellet smoker system. I would have to circulate more air throug the burning pot as it will lack some oxygen, and with this recover temperature and smoke from exhaust.

In the end, the forced air out of the system/smoker should be less and more "good/clean" smoke in contact with the meat.

Any thoughts if this would work? or any other forum where I can share this concept?

Best regards,

Rodolfo
 

ofelles

Smoking Fanatic
SMF Premier Member
581
883
Joined Mar 16, 2019
Don't know about your science or calculations, but that is a big smoker. 22.5 cubic meters = 794.6 cubic feet or 1,373,034.2 cubic inches.
 

bill1

Master of the Pit
1,208
474
Joined Apr 25, 2015
I'd worry a bit that re-circulating the smoke through the pellet's induction fan could lead to soot or creosote build-up in the ducting and on the blades that will ultimately kill your fan. Maybe just put a separate fan inside the cook chamber to move the smoke around your meat a bit more before it exits the smokestack? (Usually works best to put the motor outside the chamber but have a long enough shaft so that just the fan blades are inside.)

I'm also a fan (no pun intended) of being able to switch in resistance to slow down the speed of a pellet machine's induction fan. And a I use a small water heater element inside a bread pan to greatly increase the humidity over just a "water pan". Or at least I'd make sure your design doesn't preclude these features even if you don't find them that useful.
 

rpolancot

Newbie
Thread starter
4
0
Joined Jan 10, 2016
Don't know about your science or calculations, but that is a big smoker. 22.5 cubic meters = 794.6 cubic feet or 1,373,034.2 cubic inches.
Thanks for the response and interest. You are right and it's my mistake, it is 22.5 square feets!!! Sorry!!!
 

rpolancot

Newbie
Thread starter
4
0
Joined Jan 10, 2016
I'd worry a bit that re-circulating the smoke through the pellet's induction fan could lead to soot or creosote build-up in the ducting and on the blades that will ultimately kill your fan. Maybe just put a separate fan inside the cook chamber to move the smoke around your meat a bit more before it exits the smokestack? (Usually works best to put the motor outside the chamber but have a long enough shaft so that just the fan blades are inside.)

I'm also a fan (no pun intended) of being able to switch in resistance to slow down the speed of a pellet machine's induction fan. And a I use a small water heater element inside a bread pan to greatly increase the humidity over just a "water pan". Or at least I'd make sure your design doesn't preclude these features even if you don't find them that useful.
Thanks for the response. The design has a recirculating fan included as you described it (fan in motor out). I like your idea of managing air intake-induction fan. I've always felt a lot of air is needed to ignite, but once lit, the air flow seems too much. Definitively I'll be playing around with it this weekend to see how it goes. I guess less air could make combustion less complete, the key would be to level out inducted air to no more that what is needed to burn the pellets complete. Thanks a lot!!!!
 

bill1

Master of the Pit
1,208
474
Joined Apr 25, 2015
...I've always felt a lot of air is needed to ignite, but once lit, the air flow seems too much. Definitively I'll be playing around with it this weekend to see how it goes. I guess less air could make combustion less complete...
If you look through the dozens of replacement induction fans on amazon, a few give fan details of 400mA or 45watts so they're about 270ohms resistance at full (~3000rpm) speed. (I've meant to verify that with a wattmeter but never seem to get to it.)

But I've seen those values at least 3 different places so I bought a half dozen 10W 100ohm resistors and wired them in 3 clusters of 2P, 1S, and 2S (50, 100, 200ohms) with a switch across each of the 3 clusters so I can add series resistance of 50, 100, 150, 200, 250, 300, or 350 ohms to the stock fan value via the 3 switches. I find that works out well. (<$10 for the resistors and the switches. Great mod.) Makes no difference in combustion or ash left in the crucible, you just greatly reduce the amount of pellets you use. Like you said you need quite a bit of air to get them red hot on start-up, but after that, whatever the auger feeds in will ignite via the high heat in the crucible.

I suppose the reduced flow rate of smoke past the meat could reduce the smoke flavor, but I don't think a stock pellet machine has near enough smoke flavor so I have other tricks to fix that.
 

rpolancot

Newbie
Thread starter
4
0
Joined Jan 10, 2016
Thanks for the details! I've ordered an AC motor speed regulator (7 bucks) and intend to regulate air flow, as my induction fan is AC. I've ordered also a wind speed meter to measure wind output and assess mininal flow to keep pellets burning. I'll see where this gets me.
 

bill1

Master of the Pit
1,208
474
Joined Apr 25, 2015
...I've ordered also a wind speed meter to measure wind output...
If possible, I'd put the meter on the air intake to your cooker instead of the hot exhaust. It's probably calibrated for room-temp air and air density and viscosity are quite temperature-dependent. I haven't done the calc, so this might be negligible, but there's also the issue that burning wood converts O2 to CO2 so what comes out isn't really air. Plus, most anemometers have plastic construction and don't tolerate cooking or smoking temps very well, so if you do use it on exhaust, you might want to make it easily removable so you can just take a quick measurement on a periodic basis.

I bought a cheap one myself, although to be honest I'm not exactly sure what to do with the data. :emoji_wink: It's really the velocity moving past the meat that counts and with the exception of something ideal like hamburger patties in a horizontal duct, is going to vary quite a bit with most meats in most heated spaces.
 

G8trwood

Fire Starter
49
28
Joined Mar 18, 2022
Been thinking about this a bit myself lately. Efficiency vs flavor, i.e. are pellet grills too efficient for their own good. I have wondered if beyond startup, they would benefit more from an HVLP approach than their high velocity air stream. More pellets consumed for more flavonoids but not burning like a jet engine.

But, it seems figuring this out would involve math ….
 

bill1

Master of the Pit
1,208
474
Joined Apr 25, 2015
Any smoker wastes a lot of "flavanoids" (love that word) out the stack that never come close to sticking, flavoring, or in any way coming near the meat. So any attempt to "duct" the smoky air more closely around the meat (with minimal parallel exit paths elsewhere) increases the efficiency of flavoring your meat with the precious flavanoids. This is never really easy to do, but given some steel flashing, tin snips, and hog rings it's a lot easier in a vertical pellet smoker than a grill-like one, although there are other ease-of-use advantages of the grill (single-grate) style that makes it my "daily driver". (I have both.) There is really no down side to this, although I suppose if you got very aggressively narrow with the ducting, that the increased pressure drop could put an added load on the induction fan and possibly wear it out slightly quicker.

The reduced flow approach being mentioned, and that I find beneficial to reduce the stock air velocity in a pellet smoker (esp once I've reached temperature) is a definite design change. And there is a major safety caveat here which is why vendors sell them the way they are. Namely you do increase the risk your crucible fire goes out and your control system continues feeding pellets to overflowing. That alone is not so bad, but many folks upon getting an undertemp error code, instead of disassembling things and verifying this hasn't happened, just merrily restart their units, resulting in a huge flare-up issue, which can be frightening and dangerous too, if you've located your cooker too close to wood structures like sheds, eaves of a home, etc. And now, if again like me you've replaced your factory grease-control parts with smoke-generating paraphernalia, you have a grease build-up on the bottom of your pellet machine, making a flare-up particularly interesting.

So in making mods to commercial equipment, make sure you understand why things are the way they are so that when removing one control you've added another (even if it's just never leaving the unit unintended) to make up for the risk you've incurred.
 

SmokinEdge

Master of the Pit
OTBS Member
★ Lifetime Premier ★
3,952
4,010
Joined Jan 18, 2020
Interesting topic. Though in the end I’m thinking it’s just a dog chasing tail. That said, the first pellet grill I had was a Green Mountain, the fan on that machine once up to temp would start “huffing” for lack of a better word. More like a bellows, so there wasn’t a constant air speed. Then when temp got 5* low the fan would kick up to full speed until temp was reached then back to bellows. Repeat and so forth. I really think the smoke flavor was much better from that grill than my current Yoder, which runs the fan constantly.
 

G8trwood

Fire Starter
49
28
Joined Mar 18, 2022
My old first gen Traeger with 30 degree swings has better flavor than my pid controlled rock steady grill.
On the Flavanoid :) front, I don’t think you want a direct air stream as that dries stuff out too much, but a broader high volume low speed draw that swaddles dat brisket.
 

Latest posts

Hot Threads

Top Bottom
  AdBlock Detected

We noticed that you're using an ad-blocker, which could block some critical website features. For the best possible site experience please take a moment to disable your AdBlocker.