Secondary Air Distribution System

Re: Secondary Air Distribution System

PostBy: Lightning On: Mon Jan 06, 2014 12:16 pm

Hey thanks man! Excellent way to mark the holes. I've been using caps with different sized openings for different parts of the burn cycle. I'm very happy with the results so far :D
Lightning
 
Hand Fed Coal Furnace: Clayton 1537G
Coal Size/Type: Nut/Stove Size Mix

Re: Secondary Air Distribution System

PostBy: Lightning On: Mon Jan 06, 2014 12:27 pm

Oops lol
Lightning
 
Hand Fed Coal Furnace: Clayton 1537G
Coal Size/Type: Nut/Stove Size Mix

Re: Secondary Air Distribution System

PostBy: Lightning On: Mon Feb 10, 2014 3:15 am

Had a blond moment last night and didn't put the "salt and pepper" caps back on my secondary air inlets after burn off of a fresh load. I woke up for work this morning and noticed, so I thought it would be a good time for a quick experiment. I put the caps on which significantly lowers the secondary air volume. In the matter of 20 minutes pipe temp dropped from 198 to 189, the over the load door temp increased from 316 to 329 and my warm air duct increased 116 to 119. I realize its an increase of 3 degrees but that 3 degrees is added to a huge volume of forced air.

The quick experiment only proved what we already know :lol: excessive secondary air will carry heat out the chimney that could have been kept in the house.. :D Nice to see the "givens" doin their thing..
Lightning
 
Hand Fed Coal Furnace: Clayton 1537G
Coal Size/Type: Nut/Stove Size Mix

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Re: Secondary Air Distribution System

PostBy: Sunny Boy On: Mon Feb 10, 2014 7:16 am

Yup, it's good to have a "re-cap" :D , . . of your previous test results.

Sorry, Lee, . . . could not pass that one up ! :D

Paul
Last edited by Sunny Boy on Mon Feb 10, 2014 10:11 am, edited 1 time in total.
Sunny Boy
 
Hand Fed Coal Boiler: Anthracite Industrial, domestic hot water heater
Baseburners & Antiques: Glenwood range 208, # 6 base heater, 2 Modern Oak 118.
Coal Size/Type: Nuts !
Other Heating: Oil &electric plenum furnace

Re: Secondary Air Distribution System

PostBy: KingCoal On: Mon Feb 10, 2014 9:45 am

Lightning wrote:Had a blond moment last night and didn't put the "salt and pepper" caps back on my secondary air inlets after burn off of a fresh load. I woke up for work this morning and noticed, so I thought it would be a good time for a quick experiment. I put the caps on which significantly lowers the secondary air volume. In the matter of 20 minutes pipe temp dropped from 198 to 189, the over the load door temp increased from 316 to 329 and my warm air duct increased 116 to 119. I realize its an increase of 3 degrees but that 3 degrees is added to a huge volume of forced air.

The quick experiment only proved what we already know :lol: excessive secondary air will carry heat out the chimney that could have been kept in the house.. :D Nice to see the "givens" doin their thing..


cool, as you say this gives more credibility to the idea that less secondary over a mature fire gives more heat.

now how can i use this to understand how my DSM 1400 w/ fixed secondary air supply manages to pull less secondary under higher WC of draft and more under less draft !?!

that right there is going to bug me for ever, even when i change to an antique cylinder or base burner stove.

thanks,
steve
KingCoal
 
Hand Fed Coal Stove: Comforter Stove Works
Baseburners & Antiques: 2014 DTS C17 Base Burner
Coal Size/Type: Nut Anth.
Other Heating: none

Re: Secondary Air Distribution System

PostBy: Sunny Boy On: Mon Feb 10, 2014 10:28 am

Steve,
The answer to that may be in how large the fixed secondary air holes are, how many there are, and their size relationship to the primary air inlet ?

With Lee's set up, the small holes he drilled inside the secondary air tubes have their own airflow limiting ability by proof that the flames at the rear-most holes are the same size and are being redirected out across the coal bed, as the holes nearest the front opening of the tubes - even without the "salt and pepper shaker" caps in place.

The caps having fewer holes, just add more resistance (control).

But if Lee were to drill larger holes in the tubes, they would flow more air at the same WC pressure then they would now. At some point the holes would be large enough that the air speed through them would drop and they would no longer throw an equal flame at each hole because then, some holes would be able to meet most of the demand for air more easily then others near the back. Plus, at slower air speeds, the flame at the holes would start to soften, be less defined, and likely bend more toward the firebox outlet to the stack.

Paul


Paul
Sunny Boy
 
Hand Fed Coal Boiler: Anthracite Industrial, domestic hot water heater
Baseburners & Antiques: Glenwood range 208, # 6 base heater, 2 Modern Oak 118.
Coal Size/Type: Nuts !
Other Heating: Oil &electric plenum furnace

Re: Secondary Air Distribution System

PostBy: Lightning On: Mon Feb 10, 2014 3:19 pm

Hi Steve, I wish I had a good answer for that puzzle lol. What bothers me about that is what it implies.

For example, let's make fact that stronger negative pressure means less volume of secondary air. What would happen if we continued to strengthen negative pressure towards a vacuum? Would air stop flowing thru the secondary air inlets? Given the above fact, it appears that would happen but it doesn't really seem possible.

Now let's make fact that weaker negative pressure means more air thru the secondary inlets. What would happen as the negative pressure weakened to zero reading on the manometer? Would more air enter the secondary air inlets? What would be its motivation to enter the stove at equilibrium?

I'm trying hard to not discount your observations but the paths lead to places that, in my mind don't work out.

What's your take on these scenarios partner? :D
Lightning
 
Hand Fed Coal Furnace: Clayton 1537G
Coal Size/Type: Nut/Stove Size Mix

Re: Secondary Air Distribution System

PostBy: KingCoal On: Mon Feb 10, 2014 3:40 pm

i fully agree with the expectation of failure at the far ends of the paths of logic you put forward.

the problem as i see it is that i have seen something that answers to the out come you yourself observed this morning.

that being that somewhere in the middle of the logic my stove appears to be self regulating secondary air intake thru a fixed tract and openings and shows the same increase or decrease in temps. coinciding with the amount of secondary being admitted.

i think Paul has made a pretty good case.

believe me, i'm baffled, even though i can make it happen over and over on demand.
KingCoal
 
Hand Fed Coal Stove: Comforter Stove Works
Baseburners & Antiques: 2014 DTS C17 Base Burner
Coal Size/Type: Nut Anth.
Other Heating: none

Re: Secondary Air Distribution System

PostBy: Lightning On: Mon Feb 10, 2014 3:57 pm

Man, I wish I could get in front of your stove so I could see what the heck is going on there! :lol:
Lightning
 
Hand Fed Coal Furnace: Clayton 1537G
Coal Size/Type: Nut/Stove Size Mix

Re: Secondary Air Distribution System

PostBy: KingCoal On: Mon Feb 10, 2014 4:08 pm

is there any chance that the lay out, of the secondary intake tract on this stove has a bearing ?

your tubes run parallel to the fuel bed and "inline" with the path of the "draw" ( front to back ) of the draft.

mine is across the width of the front of the fuel bed, 90* "off line" from the "draw". both are closed tracts that aren't supplied from primary.

from other input in this thread, i have a problem with the diff. according to the law of equality or some such that says any pressure ( + or - ) inside an area must act the same thru out.

did i get that right ?

maybe i'll see if i can get some help to make some video.
KingCoal
 
Hand Fed Coal Stove: Comforter Stove Works
Baseburners & Antiques: 2014 DTS C17 Base Burner
Coal Size/Type: Nut Anth.
Other Heating: none

Re: Secondary Air Distribution System

PostBy: Sunny Boy On: Mon Feb 10, 2014 4:18 pm

Just spit balling here, but, . . .

But one of the factors that can affect WC readings in a flue pipe is not just pressure difference,but exhaust gas speeds too. You can see examples of this variation in readings by plumbing vacuum gauges in at different sized areas (carb venturi, intake manifold runners, intake manifold plenum, etc. ) of an automotive intake system.

Another thing that may be happening that also limits how much the secondary's "pull" air is if at higher WC , the fire is burning hotter (as measured downstream in the flue pipe, not the firebox) , therefore producing more exhaust gases and even though to you see the WC reading increasing at the flue pipe, that WC may "appear" to be higher, because of the higher exhaust gas speeds from the increased heat output of the firebox. Meanwhile, back in the firebox where you can't get a WC reading, the increased exhaust gas "volume" in the firebox is now actually at a lower WC, so that the secondarys see less pressure difference ???

As it burns hotter it backs up in the firebox because it acts as a plenum, dropping the WC at that point as the gases have to speed up to exit.

One thing I've noticed about the box stoves is they can pull alot of WC on a mano gauge.

I think that, unlike our old stoves, that have such a smaller firepot in comparison to their 5 inch and 6 inch flue pipe size, your big box stoves are closer to the maximum firebox output for their flue sizes. Being that close in firebox to pipe size will give much different exhaust gas speeds, which you can only see as increase in mano readings, but not velocity.

Being that much closer to max firebox to flue ratio has to have an affect of how (and when) your secondarys draw.

Or not, .... :D

Paul
Sunny Boy
 
Hand Fed Coal Boiler: Anthracite Industrial, domestic hot water heater
Baseburners & Antiques: Glenwood range 208, # 6 base heater, 2 Modern Oak 118.
Coal Size/Type: Nuts !
Other Heating: Oil &electric plenum furnace

Re: Secondary Air Distribution System

PostBy: KingCoal On: Mon Feb 10, 2014 4:26 pm

and, i'll bet the extra baffle i installed in my stove to redirect the exhaust flow is adding activity of unknown impact.
KingCoal
 
Hand Fed Coal Stove: Comforter Stove Works
Baseburners & Antiques: 2014 DTS C17 Base Burner
Coal Size/Type: Nut Anth.
Other Heating: none

Re: Secondary Air Distribution System

PostBy: Sunny Boy On: Mon Feb 10, 2014 4:34 pm

KingCoal wrote:and, i'll bet the extra baffle i installed in my stove to redirect the exhaust flow is adding activity of unknown impact.


Quite possibly.

By the way, in a static system the pressure will be the same, but in a system with moving gases, such as a stove, flue pipes and chimney, there are slight pressure differences (easily within the range of a mano) as the gases have to speed up, or slow down as they move through different sizes areas, and as they change density with temperature change.

The WC readings you see at the flue pipe, highly likely not what you'd see inside the firebox, or at the top of the chimney. But it's the WC readings inside the firebox that's affecting your secondarys, so don't assume anything based on just the flue pipe WC readings.

Paul
Sunny Boy
 
Hand Fed Coal Boiler: Anthracite Industrial, domestic hot water heater
Baseburners & Antiques: Glenwood range 208, # 6 base heater, 2 Modern Oak 118.
Coal Size/Type: Nuts !
Other Heating: Oil &electric plenum furnace

Re: Secondary Air Distribution System

PostBy: KingCoal On: Mon Feb 10, 2014 5:18 pm

seems we are then indeed trying to grasp the wind.......................................
KingCoal
 
Hand Fed Coal Stove: Comforter Stove Works
Baseburners & Antiques: 2014 DTS C17 Base Burner
Coal Size/Type: Nut Anth.
Other Heating: none

Re: Secondary Air Distribution System

PostBy: Lightning On: Mon Feb 10, 2014 7:08 pm

KingCoal wrote:is there any chance that the lay out, of the secondary intake tract on this stove has a bearing ?
Anything is possible, but I would dare say that position wouldn't have bearing, for the reason below...

KingCoal wrote:from other input in this thread, i have a problem with the diff. according to the law of equality or some such that says any pressure ( + or - ) inside an area must act the same thru out.
If you are saying that pressure is equal throughout the fire box, I would agree.

Sunny Boy wrote:The WC readings you see at the flue pipe, highly likely not what you'd see inside the firebox, or at the top of the chimney. But it's the WC readings inside the firebox that's affecting your secondarys, so don't assume anything based on just the flue pipe WC readings.
I've taken mano readings above and below the baro, in the fire box and underneath the grates. All readings are equal EXCEPT under the grates it is .005" stronger negative pressure. I'm guessing the coal bed attributes a small amount of its own draft as air is heated and rises up thru it resulting in the .005" stronger there.. I know these readings go against what may seem but I've done them several times trying to get a different result and Einstein was right.. Running the same experiment while expecting different results will lead to insanity.. :lol:
Lightning
 
Hand Fed Coal Furnace: Clayton 1537G
Coal Size/Type: Nut/Stove Size Mix

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