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Post by nedreck on Dec 19, 2010 21:40:42 GMT -8
Possibly answering my own question (after thinking while typing)... if the exhaust gas cools to its dew point then the fly ash would percipitate out in the flue. Yes and this was a portion of the argument that set me on this path to where I am now. A lot of folks cool the heaters below the dew point on a regular basis and even on purpose. These products have some corrosive properties etc. I am trying to explore the overall safety parameters of these units. |
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Post by northriver on Dec 20, 2010 7:45:35 GMT -8
Possibly answering my own question (after thinking while typing)... if the exhaust gas cools to its dew point then the fly ash would percipitate out in the flue. Yes and this was a portion of the argument that set me on this path to where I am now. A lot of folks cool the heaters below the dew point on a regular basis and even on purpose. These products have some corrosive properties etc. I am trying to explore the overall safety parameters of these units. If the dew point were being reached in these systems there would be evidence ... corrosion and failure of the flue. Anecdotally, I have not seen discussion of failed flue systems in reading that I have done (also, I imagine most RMH's are not old enough to start developing problems?). I have also not seen a lot of hard numbers on flue exit temperature. Has anybody else? |
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Post by Donkey on Dec 20, 2010 9:34:53 GMT -8
No hard numbers.. A lot of subjectives like cool to the touch, etc. A lot of people are DEFINITELY getting condensate in their benches. It's fairly common. Seems to me that yer not hearing about corrosion because the pipes are buried in cob.. How would you notice? Even if the pipes completely disappeared, the cob would still do the job. Now, if you've been following my advice and pouring sand around the pipes, you would notice a failure at some point.  |
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Post by nedreck on Dec 20, 2010 10:46:23 GMT -8
Over all it depends and I can not state with any certainty at all. The products of combustion are known to be corrosive, but the study of corrosion is an industry in and of itself. Within this stove design it remains very unclear as to what may indeed be destroyed by the afterburner and what may remain.
When operating points within the system are below the dew point, what is certain is that whatever remains will certainly pose a corrosion risk. A simple Ph test of the condensate would give one some information, however, due to how corrosion comes about, it might not completely apply. Acids and alkaline solutions certainly pose a risk and the added heat can make both of those processes much more aggressive. There is a third issue that is far different that can occur in even ph neutral fluids called chelating. It is more prone in soft metals. In its most simple explanations, the solution does not dissolve the metal, it simply lifts part of it off, sort of like how a water softener trades a salt for a lime molecule, not exactly but the general idea. That process is often driven by temperature as well.
The other pressing concern is what is this condensate actually condensing on when it happens. If it is on the steel then you have X amount of time before it has structural issues and may begin to leak, if it is on firebrick how will it impact the components of the brick and begin to fail, if it is the cob, how will it attack the masonry and organic matter in the cob.
While a great many folks might and well DO argue about it and the importance of it, the corrosion factor will have to be considered long before any “approvals” of this design get past their infancy. I have observed so many claims about exhaust temps it is mind boggling. Claims as low as 70-90 up through 120 and the goal each time is “more efficiency” which is not really the case but what the heck. While I am not capable of “signing off” I have been involved in getting a few things approved. I can tell you that without any doubt what so ever if this unit were presented to me for review, one of the very first questions I would ask is “how is the hazardous waste stream handled?” Right after that “Where is the condensate drain and proof of content?”
I have yet to read the book on these things, but I question whether those types of questions will indeed be answered. I know they will have to be answered just as they are for any other heating device using combustion of fuel as the prime mover, no matter what fuel it is, you just can’t say “safe” unless you can prove it.
I think at this point in the game so to speak, the real evaluation regarding sucking all the heat out is to simply seek out the answer to “is it worth it” and go from there. If you extract all the heat out required to hit the dew point at the bottom of the barrel and it is going to ultimately fail due to the corrosion of the relatively thin material (16 or 18 gauge) in 4 years, that makes the barrel consumable, is it worth the extra energy extracted if you have to do that? What if it only takes 50 more degrees discharge not to have that issue?
Those are economic calls that involve your labor, only you can answer them. A testing agency is going to really want to know because when that barrel gets microscopic hold in it as the corrosion progresses those nasties are coming into the living space. A sound engineered practice will have to be shown to deal with the corrosive nature or proof of non-corrosive nature of the condensate before it is going to gain approvals with exhaust below the dew point driven by combustion, there is simply no way around it.
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Post by canyon on Dec 20, 2010 11:02:10 GMT -8
Thank You Ned! Being a passionate individual myself I value you and yours! I met another passionate pyro at a wood energy conference in Fairbanks AK a few years ago who I am sure you know and gained hugely from the experience and with just a few posts from you I have that same feeling I had then. I am grateful!  |
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Post by nedreck on Dec 20, 2010 12:37:20 GMT -8
No need to thank me, I look forward to the fun! |
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Post by northriver on Dec 20, 2010 22:39:01 GMT -8
I was flipping through the Rocket Mass Heater book by Ianto Evans this evening as I worked on my cold air intake ...
With this thread in the back of my mind I came across his discussion of flue temperature. While discussing maintenance of his stove (pg 55 of the 2nd edition) he mentions a probe-type thermometer that he maintains in the exit flue after it exits his cob bench.
He discusses using this probe to tell him if pyrolysis is happening. He seems to expect a temperature of 200-300 degrees F here. If the temperature drops to the low end of this range he assumes that the stove needs adjustment (more fuel, bridged fuel, ash blockage).
My own experience is fairly limited to date and I have not yet got my hands on a temperature probe of any description. Qualitatively, the flue immediately after the heat exchange barrel is too hot to handle. The exit flue is also quite warm although I have not yet finished my bench. I would be very curious to see other solid numbers as my impression from the book is that he does not expect 'cool' temperatures in or after the bench.
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Post by Donkey on Dec 21, 2010 3:25:29 GMT -8
Over all it depends and I can not state with any certainty at all. The products of combustion are known to be corrosive, but the study of corrosion is an industry in and of itself. Within this stove design it remains very unclear as to what may indeed be destroyed by the afterburner and what may remain
Sounds like we need some condensate samples..
Anybody got condensate in their pipes they'd like to stick a Ph strip in or send to have tested??This comes from the popular thought form that (assuming a good hot fire and clean burn) keeping more heat inside the (home) space means you need to burn less fuel for the same payoff.. It's generally perceived that cooler chimneys equals more heat in the house. By the way, usually us hipnecks don't start counting "flue" till the pipes leave the bench/mass and turn vertical to leave the space. I'll have to review the book.. It's been a little while since I looked at it.. Yeah, they mention condensate. It's recommended that pipe runs for 8 inch systems be somewhere around 25 - 30 feet. In my experience, that seems about right. After the bench and all the cob parts are dry, the condensation point is often a few inches to a foot or so past the end of a short vertical stove pipe. I like to see fog just past the end. I've never seen condensate (once the works are dry) anywhere near the barrel.. It's far down the horizontal run if it's inside AT ALL. Better to tune as above. |
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Post by nedreck on Dec 21, 2010 6:05:33 GMT -8
With this thread in the back of my mind I came across his discussion of flue temperature. While discussing maintenance of his stove (pg 55 of the 2nd edition) he mentions a probe-type thermometer that he maintains in the exit flue after it exits his cob bench. He discusses using this probe to tell him if pyrolysis is happening. He seems to expect a temperature of 200-300 degrees F here. If the temperature drops to the low end of this range he assumes that the stove needs adjustment (more fuel, bridged fuel, ash blockage). My own experience is fairly limited to date and I have not yet got my hands on a temperature probe of any description. Qualitatively, the flue immediately after the heat exchange barrel is too hot to handle. The exit flue is also quite warm although I have not yet finished my bench. I would be very curious to see other solid numbers as my impression from the book is that he does not expect 'cool' temperatures in or after the bench. While you may not have ventured over to the argument that got me involved in this, this is exactly what got me started. My recommended numbers were/are indeed a bit higher, but that is from a very "generic" point of view having done 0 research or even thought. 350 was my minimum and there are other reasons as well. It is POSSIBLE that lower ranges can be used which is why I decided I needed to build one and get some operational parameters that folks could use and stay within acceptable safety limits that would indeed vary by fuel content, air pressure changes, moisture content etc. While it might not make much difference in a large "hut", in fairly well sealed homes thee can be significant differences according to wind alone. Remember when "mom" used to tell you to "open the windows" when a tornado warning was in effect? With the very minor pressure differences this stove is operating on, it could have impact enough to stall operation, staying away from aka above that point has merit to give yourself a cushion. Back to the trade off of efficiency vs value of gain, while you might be able to reach 90%, the cushion 85% gives you is more important than the 5% increase. |
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Post by nedreck on Dec 21, 2010 11:55:44 GMT -8
This comes from the popular thought form that (assuming a good hot fire and clean burn) keeping more heat inside the (home) space means you need to burn less fuel for the same payoff.. It's generally perceived that cooler chimneys equals more heat in the house. By the way, usually us hipnecks don't start counting "flue" till the pipes leave the bench/mass and turn vertical to leave the space. In the words of an undecorated educator, shit, piss, cock-sucker, mother-fucker, tits! I love it when things start to come together. When folks seek out perfection they overlook the details and even when the details want to smack them in the face they continue to remain blind. There is a major piece missing and however trivial it might seem, its not at all. I have downloaded the book and am going to read it today from a technical perspective. I believe I may have discovered a slight design flaw. If I am correct an improvement that makes a large step towards design considerations may be made that would render the design more accepted to “approval” and increase safety. I could be wrong, but at this point I am placing my money on this hypothesis. |
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Post by nedreck on Dec 21, 2010 14:52:29 GMT -8
Major paradigm shift required!
Really cool brain shit happening lol.
A huge thank you to ya Donkey, your honest and open feed back has been invaluable. More should practice what they preach on it instead of thinking they are protecting the idea by hiding the pitfalls of the design.
Was quite refreshing to see Ianto brought the same issues forward and openly.
I have to study this some more to see about paths to fixing some of the issues, but they are by no means outside the box or beyond field unskilled adaptation. There is a pretty sensitive balance at work inside here, but gathering information on that balance and expanding it is very possible. What that means is basically this pup can be whatever size and capacity you want it to be. Never should have been labeled a “rocket” as that leads one astray of the operation completely.
A lot of my theory on operation fits, just not exactly in the same manner! I only wish I was 20 again and had my buddy Dave to get crittered with and bounce ideas back and forth over the weekend! Damn I love the feeling of one’s brain running full speed in 30 directions. Gotta hit the bricks and head home, this is going to be an interesting week that’s for sure!
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Post by josephjcole on Dec 21, 2010 15:09:42 GMT -8
Looking forward to hearing more of your thoughts, and possible improvements.... Thanks
Joe
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Post by careinke on Dec 22, 2010 22:44:59 GMT -8
Hi Ned,
As a fellow INTJ, I think you are going to be a great addition to this board.
On an earlier post you wrote: "I have read some folks saying that they are getting a positive pressure on the exhaust side of theri stove any one here make such claims?"
Well, I guess I would have to make that claim. If I can run my exhaust out below the elevation of my fire, Without a chimney, wouldn't I have to have a positive pressure on the exhaust side? Maybe I am missing something here, but I cannot see how you can exhaust like that without positive pressure. The exhaust is certainly not being drafted/pulled out from the end of the exhaust.
Not trying to be confrontational here, just wondering why you seem to think that is not possible. Perhaps we are not talking about the same thing.
Cliff
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Post by nedreck on Dec 23, 2010 11:28:24 GMT -8
Not trying to be confrontational here, just wondering why you seem to think that is not possible. Perhaps we are not talking about the same thing. Cliff Vapor pressure pushes in all directions equally. It moves from a high pressure to a lower pressure. Typical designs are going to have -.010-.02"WC over the fire and about -.04"WC at the breech of the stove. Note those are negative pressures so .01 is much greater than.04 This is a large part of my paradigm shift this week. I am working up a post so to speak this week that will address this issue more. It has already significantly altered testing plans. I am going to try and speak with Ianto and Donkey on this very soon. |
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Post by zoidberg on Jan 28, 2011 8:08:56 GMT -8
So what came out of this interesting discussion ? Any yummy results yet ?
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