Experimental air/air Hx for Seton

[mole]

Ever wonder just how much heat the air inlet tubes recover from the exiting exhaust of a Seton type bioler?

About a year ago I set up some thermocouples at various places in my Seton to study its operation and see if there were ways to improve the efficiency. One of these thermocouples was placed in one of the inlet tubes about an inch from the inside end where the tube rests in the hole in the ceramic "wall". The temperature in the tube was observed periodically for about a year. The results were not particularly impressive. The air is warmed from room temperature(60-70degF) up to 105-135). It takes a real hot fire (about 500deg+ stack) to get to 135F. It was sort of disappointing to see so little of the "prewarming" of the comsbustion air that is talked about in the literature for these things. It doesn't seem to matter too much how clean the inlet tubes are either. They may pick up a little performance after a cleaning, but not more than maybe 5degF. On average, the exhaust is going up the stack at 450F after only warming the exhaust by about 60degF.

This looked like an opportunity for improvement. So after about 20 drawings, many beers, and many modifications, the end result was the "'74 Pinto" you see in the pics. (My brother was kind enough to fab the prototype for me, so I'm sort of obligated to share his humor!). It's been in the boiler over a month now and the solder (yes, ordinary solder!) is holding up pretty well so far. It looked fine after its first dusting last week. The first picture (if they attach -I've never done pics before) should be a top view of the new hx installed in the boiler between the ordinary inlet tubes. The second pic is a side by side view of the Pinto and the stock hx tube. The third pic is an end view that shows the end dimensions and the interior baffles in the hx. The inside baffles may not be performing up to their potential because they're just riveted in, (no solder) so the contact with the outer shell may not be great.

This Hx shows a higher and wider performance range relative to the original inlet tube. It will run 160F (on a cool fire, or on startup) all the way up to 220F on a hot fire with 500F exhaust. It's averaging about 180-185F overall vs 120-125F for the stock muffler. It doesn't appear to impede the air flow, although I have not gotten any actual measurements to verify this. If it lasts a year without corroding or the solder melting, I may make a couple more.

 

[mole]

This pic shows through the center of the hx. As you can see, the 2" copper pipe is only at the ends. the center is open except for the baffles.

 

[Pat53]

Nice work mole, interesting. A while back in one of my threads someone commented that by preheating the air it was actually causing a LOSS of efficiency because that warmer air held less oxygen, and thus a poorer environment in the combustion chamber and less efficiency?

Pat

 

[mole]

Nice work mole, interesting. A while back in one of my threads someone commented that by preheating the air it was actually causing a LOSS of efficiency because that warmer air held less oxygen, and thus a poorer environment in the combustion chamber and less efficiency?

Pat

Thanks, Pat.
I'm not sure I buy the loss of efficiency argument. The oxygen content in air is something like 21%, regardless of temp. If you were putting it in an internal combustion engine, I could see that point being true, since warm air will contain less moles air per volume than cold gases ans so you might not have enough oxygen to burn the fuel completely if you overheated the air. I suspect that these boilers generally run on the lean side (an excess of air), so we're usually diluting the heat created with some cool air, which decreases efficiency. The only hard data I have to back this opinion is the light black soot deposits I get on the tubes occasionally when I put too much surface area of wood in at a time, running too rich. But generally speaking, I think prewarming combustion air should give a cleaner burn by getting the combustion temperature higher. It should also increase the heat extraction efficiency since the delta T between the combustion gases and the water tubes is higher, no? I think wood stoves and the the Tarm/econoburn type boilers preheat secondary combustion air for the same reasons.

 

[Pat53]

Yes, that makes sense to me also mole. Are you thinking about replacing all the air tubes with "Pinto's" ? LOL

I've decided that at the end of the season I am going to modify my HX by getting it more into the flame/exhaust path. I think it can only help with heat transfer and make it easier to clean when/if needed. Might even try to make a few Pintos of my own !

Pat

 

[mole]

Yes, that makes sense to me also mole. Are you thinking about replacing all the air tubes with "Pinto's" ? LOL

I've decided that at the end of the season I am going to modify my HX by getting it more into the flame/exhaust path. I think it can only help with heat transfer and make it easier to clean when/if needed. Might even try to make a few Pintos of my own !

Pat

I have 5 intake tubes in mine. I guess the next step will be to put the Pintos in 1,3,5, some time next year, leaving 2,4 stock, and see how that works for a while. Then I'll decide from there if I should do the last two. You'll have to tell us how that works out moving your water tubes. Sounds interesting!

 

[bigburner]

Keep us posted- the preheat air is a feature that I liked about the green wood and have been going to add something like that to my stove. I did wonder how much heat that they actual picked up be so short, looks like no much. If copper is your choice of material you can use a product called Harris-15 and braze it all together [super simple to use]

I was thinking more along the line of pulling flue gas directly from the vent - adding some air and injecting it back in the fire box.

 

[mole]

Keep us posted- the preheat air is a feature that I liked about the green wood and have been going to add something like that to my stove. I did wonder how much heat that they actual picked up be so short, looks like no much. If copper is your choice of material you can use a product called Harris-15 and braze it all together [super simple to use]

I was thinking more along the line of pulling flue gas directly from the vent - adding some air and injecting it back in the fire box.

Can you tell me more about this Harris-15?

 

[bigburner]

Harris-15 is used in the refrigeration game for gas welding copper pipes together. You have to heat the pipe to a dull red [mapp gas will do it ,but it's slow] we use ox-acel for the purpose. It flows like honey when hot and no pre cleaning is required on the copper unless it real nasty.
It 's like brazing but flows better and won't develop pin holes. When used in piping you will have a big leak or no leak there is never a small leak. Google it for more specs, there may be other brands also but this is what I have used for 25 years.

 

[mole]

Thanks Bigburner. I'll check that stuff out.

 

[Pat53]

Hey Mole, I was toying around with some ideas this weekend about how to increase the air temps into the firebox and was thinking about this: what about a sort of manifold on each end of the tubes with just a whole bunch of 1" copper pipe inbetween, each with about 1/2" or so of space between them. You could put a double or even triple row of them in. They would have to be checked often tho to make sure they weren't getting plugged up with soot and ash. Am I dreaming? LOL

Pat

 

[mole]

Hey Mole, I was toying around with some ideas this weekend about how to increase the air temps into the firebox and was thinking about this: what about a sort of manifold on each end of the tubes with just a whole bunch of 1" copper pipe inbetween, each with about 1/2" or so of space between them. You could put a double or even triple row of them in. They would have to be checked often tho to make sure they weren't getting plugged up with soot and ash. Am I dreaming? LOL

Pat

Yeah, but It's a GOOD dream! LOL! I was thinking about that sort of thing too. I almost did something like that. I figured it would take four 1" pipes just to equal the cross sectional area of a 2" pipe. With friction losses, you'd probably need more. I'm guessed it would take like six 1" pipes per 2" diameter tube to move the same volume of air. I don't know how to do the calculations, so I may be way off. It sounded like thought the spacing of the pipes in the manifold might get a little tight. So I was leaning more towards a reducing wye from 2" to 1-1/2" pipe with one pipe high and the other beneath it give two 1-1/2" rows from each 2" inlet tube. You could even rotate them to a 45degree angle so it would function more like two offset rows of 1-1/2" tubes.

You know what would be real cool.... if you were building a boiler from scratch, (like you already did!), you could build the air inlet door and the refractory wall with all the holes for 1" (or 1-1/2"tubes). Maybe three staggered rows with 10 tubes per row? Or four rows of eight tubes . Then you wouldn't have to build any expensive or complicated manifolds. I'll bet the heat tranfer would kick ass if you could get the right air flow. I'm sure it would suck to clean all those tubes, but it might be worth it.

 

[Pat53]

Hey Mole, I was toying around with some ideas this weekend about how to increase the air temps into the firebox and was thinking about this: what about a sort of manifold on each end of the tubes with just a whole bunch of 1" copper pipe inbetween, each with about 1/2" or so of space between them. You could put a double or even triple row of them in. They would have to be checked often tho to make sure they weren't getting plugged up with soot and ash. Am I dreaming? LOL

Pat

Yeah, but It's a GOOD dream! LOL! I was thinking about that sort of thing too. I almost did something like that. I figured it would take four 1" pipes just to equal the cross sectional area of a 2" pipe. With friction losses, you'd probably need more. I'm guessed it would take like six 1" pipes per 2" diameter tube to move the same volume of air. I don't know how to do the calculations, so I may be way off. It sounded like thought the spacing of the pipes in the manifold might get a little tight. So I was leaning more towards a reducing wye from 2" to 1-1/2" pipe with one pipe high and the other beneath it give two 1-1/2" rows from each 2" inlet tube. You could even rotate them to a 45degree angle so it would function more like two offset rows of 1-1/2" tubes.

You know what would be real cool.... if you were building a boiler from scratch, (like you already did!), you could build the air inlet door and the refractory wall with all the holes for 1" (or 1-1/2"tubes). Maybe three staggered rows with 10 tubes per row? Or four rows of eight tubes . Then you wouldn't have to build any expensive or complicated manifolds. I'll bet the heat tranfer would kick ass if you could get the right air flow. I'm sure it would suck to clean all those tubes, but it might be worth it.

Yes, it takes almost 4 -1" tubes to equal the same volume as 1 - 2" pipe. I have 7 air tubes on my system so I would need about 28-30 1" pipes to be roughly equal with air volume. What about adding an additional 3' or so of chimney? I would think that would help offset any small loss of air from the tubes? I have an extra 3' of class A stuff I'm not using right now as I have plenty of draft with the 15.5 feet of chimney I have now.

I'm definitely going to play around with this idea in the off-season and see what I can come up with. If I do decide to try something different I'm going to make the device easily removable so that it can be cleaned regularly without too much trouble.

And yeah, when I mentioned a "manifold" , it would encompass the entire area inside the air inlet door, sort of like a box that all of the 1" pipe would fit into, and then the same thing on the other end, and then just the 7 - 2" pipes entering thru the refractory. My air inlet door is 26" wide and 3" deep so I could easily fit in 32 - 1" pipes (in 2 rows) with 1/2" spacing side to side and between the rows. 1 1/4" pipe would probably also work. What do you think?

Pat

 

[roaring fire]

Congratulations Mole on your ingenuity. I really think you are on to something & your kindness in sharing will make all us Seton types a lot happier.
On a different note I cleaned my water tubes last wkend & I am amazed at the difference in performance with wood consumption down considerably.
My question : Both you & pat 53 have storage on your units, does your boilers perform better ie. require less cleaning of tubes?
The inventor Fred Seton doesn't recommend storage. He asserts the boiler cokes the wood during idling & doesn"t affect performance.
I have been on the fence on this issue for 4 seasons because storage is a big step for me & I want to make sure it is worth it.
Dan
Modified Adobe Boiler

 

[Pat53]

Congratulations Mole on your ingenuity. I really think you are on to something & your kindness in sharing will make all us Seton types a lot happier.
On a different note I cleaned my water tubes last wkend & I am amazed at the difference in performance with wood consumption down considerably.
My question : Both you & pat 53 have storage on your units, does your boilers perform better ie. require less cleaning of tubes?
The inventor Fred Seton doesn't recommend storage. He asserts the boiler cokes the wood during idling & doesn"t affect performance.
I have been on the fence on this issue for 4 seasons because storage is a big step for me & I want to make sure it is worth it.
Dan
Modified Adobe Boiler

Hi Dan, I added 500 gallons of storage in the offseason last summer. IMO, there is no doubt that the unit runs cleaner with the longer hotter burns.

Also, IMO, Fred Seton is dead wrong about the proper function of the Seton. Here are a few things he told me about the Seton:

"the Seton is more efficient the longer it idles" (if thats the case, just let it idle... forever! LOL)
"the Seton has a firebox temp of 3000F" ( hmm., but the refractory is only rated for about 2500F and the kaowool for 2300F ! oops )
"the Seton is self-cleaning, meaning any creosote that builds up on the water tubes is quickly burnt off when the boiler refires" (completely false)

Fred is a great guy, but I disagree completely about the most efficient way to run the unit. Bottom line, at least for me, is that running them full out, with storage, is the best way to run them.

Pat

 

[mole]

Congratulations Mole on your ingenuity. I really think you are on to something & your kindness in sharing will make all us Seton types a lot happier.
On a different note I cleaned my water tubes last wkend & I am amazed at the difference in performance with wood consumption down considerably.
My question : Both you & pat 53 have storage on your units, does your boilers perform better ie. require less cleaning of tubes?
The inventor Fred Seton doesn't recommend storage. He asserts the boiler cokes the wood during idling & doesn"t affect performance.
I have been on the fence on this issue for 4 seasons because storage is a big step for me & I want to make sure it is worth it.
Dan
Modified Adobe Boiler

Dan,
Thanks for the support. It's nice to have something to share with the people here that I've learned so much from. I strongly agree with everything Pat said. And the storage makes the boiler burn 10x cleaner. I used to scrape creosote from the overhead tubes weekly to keep it running reasonably efficiently. It's amazing how much heat transfer you lose with 1/8" coating on the tubes. With storage, I don't scrape tubes at all. I run a nylon bristle brush between the tubes DAILY to dust off the ash. It's probably not necessary to do it that frequently, but I'm a little obsessed, and it takes under 5 minutes to dust the top and about 1/2 way down the rear tubes. Even the rear tubes require only a dusting to keep them clean. One disclaimer though: I designed my storage system so there is no cycling of the draft door (idling) at all during the fire. To do this, you have to be able to remove heat faster than the boiler can produce it, which gets difficult as the delta T between the boiler water and the storage tank shrinks and the tank is coming up to temp. If you end up with the draft door cycling, I'm not sure if it will still be "scrape-free".

 

[mole]

[/quote]


Yes, it takes almost 4 -1" tubes to equal the same volume as 1 - 2" pipe. I have 7 air tubes on my system so I would need about 28-30 1" pipes to be roughly equal with air volume. What about adding an additional 3' or so of chimney? I would think that would help offset any small loss of air from the tubes? I have an extra 3' of class A stuff I'm not using right now as I have plenty of draft with the 15.5 feet of chimney I have now.

I'm definitely going to play around with this idea in the off-season and see what I can come up with. If I do decide to try something different I'm going to make the device easily removable so that it can be cleaned regularly without too much trouble.

And yeah, when I mentioned a "manifold", it would encompass the entire area inside the air inlet door, sort of like a box that all of the 1" pipe would fit into, and then the same thing on the other end, and then just the 7 - 2" pipes entering thru the refractory. My air inlet door is 26" wide and 3" deep so I could easily fit in 32 - 1" pipes (in 2 rows) with 1/2" spacing side to side and between the rows. 1 1/4" pipe would probably also work. What do you think?

Pat[/quote]

Pat,
I didn't get what you were saying the first tme around about the manifold. Yeah, a single manifold sounds a whole lot better than what I was thinking. Sounds do-able. Hell, if you can build your own boiler, this should be a piece of cake!

 

[Pat53]

Mole, OK, that settles it, I'm going to build something this summer LOL

BTW, I didn't build my boiler myself, I had help from a guy who is a really good welder. Without him I wouldn't even have attempted it. But yeah, building this manifold thing SHOULD be "a piece of cake" but probably won't be as easy as I think...LOL

Pat

 

[roaring fire]

Thanks Mole & Pat 53. I really value both your opinions on these boilers.
You both have given me the push I needed to get this done.
It is in keeping with a wise old tradition I learned long ago
" When you decide to buy a car talk to the man who drives one,
not to the man who sells it."
Again thank you both, will keep you posted on my progress.
Dan

 

[Pat53]

Thanks Mole & Pat 53. I really value both your opinions on these boilers.
You both have given me the push I needed to get this done.
It is in keeping with a wise old tradition I learned long ago
" When you decide to buy a car talk to the man who drives one,
not to the man who sells it."
Again thank you both, will keep you posted on my progress.
Dan

No problem Dan. One thing I will add is that if I had to do it over again I would go with at least 1000 gallons of storage. I only had room for a 500 gallon propane tank, but mole has 1000 gallons. Good luck and yes, keep us posted. Mole will probably give you a few good suggestions also. Make sure you use good size pipe for your connections, 1 1/4" or even bigger.

Pat