Survivalist Forum

Advertise Here

Go Back   Survivalist Forum > Survival & Preparedness Forum > Disaster Preparedness General Discussion
Articles Chat Room Classifieds Donations Gallery Groups Links Store Survival Files



Disaster Preparedness General Discussion Anything Disaster Preparedness or Survival Related

Advertise Here
Reply
 
Thread Tools Display Modes
Old 12-12-2010, 02:32 AM
ctwo ctwo is offline
Hiker
 
Join Date: Jan 2010
Posts: 679
Thanks: 175
Thanked 432 Times in 242 Posts
Default



Advertise Here

Lets clear up an important point:
Is the pipe that goes from my car engine to my muffler called an exhaust pipe or a flue, and what is the difference?

From what I can tell, the rocket mass heater has an exhaust pipe, under pressure from the fire. So yeah, any carbon monoxide produced by the fire is going to want to get out of that exhaust pipe and into your house. Is hippy-mud impervious to carbon monoxide? I don't know. Does the magic hippy fire produce any carbon monoxide? I don't know - one assumes some amount is produce. Does it produce enough and does enough of it make it through the magic hippy-mud to be a health (death) concern? I don't know.

What is confusing to me is that none of those questions are addressed in the video. If this is so awesome why didn't someone pay some post-doc slaves to do a little testing on it? Maybe Bill Gates can fork over 100k to see how many lives this will save/end.

ETA: At great risk to my street cred, I have to admit I don't actually hate hippies, they are just an easy target to make fun of.
Old 12-12-2010, 10:40 AM
NedReck NedReck is offline
Prepared
 
Join Date: Nov 2010
Posts: 370
Thanks: 80
Thanked 374 Times in 184 Posts
Default

Quote:
Originally Posted by Pinhead View Post
Try that with a conventional stove and then tell me the flu/exhaust/chimney serves the same purpose in both designs.
Trying to nit pick a single sentence that was clearly defined as "generic" is the sure fire evidence one need to conclude a total lack of merit.

I know you seek to present this design as something highly effective because you believe in it and I understand that, however that does not change the actual principles that it works on.

The claims that are made about efficiencies are false, between 10 and 18% of the heat loss up the flue is going to be latent heat in the form of water vapor which completely eliminates the 90+% claims completely. The byproducts of combustion are not simply CO2 and water vapor, there is a LOT more in there and much of it like CO is orderless. Wood stoves/furnaces also tend to produce a significant amount of sulfur.

In case you are not aware or have not tested, there is a huge variance in wood as far as heat, moisture, and chemical content not to mention burn temperature. Without damper control you simply can not speak to the stack temperature to ensure proper lift from one log to another. The wood from the trunk of a single tree would have pretty similar rates.

You have thought about the temperature of the stack obviously, would you like to really tweak the performance of your stove if you really do have one?
Old 12-12-2010, 12:06 PM
Hick Industries's Avatar
Hick Industries Hick Industries is offline
Live Secret, Live Happy
 
Join Date: Apr 2009
Location: Star Killer Hollow
Posts: 8,132
Thanks: 6,549
Thanked 12,611 Times in 4,643 Posts
Default

Quote:
Originally Posted by ctwo View Post
Lets clear up an important point:
Is the pipe that goes from my car engine to my muffler called an exhaust pipe or a flue, and what is the difference?

From what I can tell, the rocket mass heater has an exhaust pipe, under pressure from the fire. So yeah, any carbon monoxide produced by the fire is going to want to get out of that exhaust pipe and into your house. Is hippy-mud impervious to carbon monoxide? I don't know. Does the magic hippy fire produce any carbon monoxide? I don't know - one assumes some amount is produce. Does it produce enough and does enough of it make it through the magic hippy-mud to be a health (death) concern? I don't know.

What is confusing to me is that none of those questions are addressed in the video. If this is so awesome why didn't someone pay some post-doc slaves to do a little testing on it? Maybe Bill Gates can fork over 100k to see how many lives this will save/end.

ETA: At great risk to my street cred, I have to admit I don't actually hate hippies, they are just an easy target to make fun of.
I earned a great deal of my tuition money measuring data and capturing flu gas from small scale coal burning stoves. So at least one university has been testing such designs. I am assuming that every reliable wood and coal stove pays some outside lab to test their designs before putting them on the market.

I am always skeptical when backyard mechanics promote ideas without subjecting them to the most basic level of testing. From what I saw on the vid, they did not seal the primary burn chamber where CO is produced. Mud drys out and cracks, so it does not count.

I see a benefit from thermal mass wood stoves. I see a benefit from building your own stove on site and incorporating it into the hearth of a new home.

But combustion science, thermodynamics, and heat transfer are the basis of Mechanical Engineering and Rocket Propulsion. You dont just slap this stuff together. You design, build prototypes, test, and modify.

I would not touch this contraption with a ten foot pole.
The Following 2 Users Say Thank You to Hick Industries For This Useful Post:
Old 12-12-2010, 02:02 PM
NedReck NedReck is offline
Prepared
 
Join Date: Nov 2010
Posts: 370
Thanks: 80
Thanked 374 Times in 184 Posts
Default

Quote:
Originally Posted by Hick Industries View Post
But combustion science, thermodynamics, and heat transfer are the basis of Mechanical Engineering and Rocket Propulsion. You dont just slap this stuff together. You design, build prototypes, test, and modify.

I would not touch this contraption with a ten foot pole.
Your comment "this contraption" is spot on. The furnace concept is not totally flawed, though it is extremely exaggerated on performance by the fan club.

The counter flow design is not bad, however it is not really good either and the same goals in performance can be achieved without the inherent risk.

The primary improvement by this design is simple, it has a larger area, attempts to balance the exhaust rate with the buoyancy counter pressure. The problem is the fuel is by no means consistent, the flue system may drop well below the due point of the exhaust vapor and draft lost.

Take that barrel, lay it horizontal, weld in some baffles to force the flue gases in a serpentine form, put the fire brick in the bottom, cut a fresh air intake port in the lowest possible location that is ducted to the outside, put a cheap flapper control damper in it, put another on the exhaust flue which heads STRAIGHT up if at all possible, dial your combustion air damper 50% closed, get your fire started fairly decent, check your stack temp post warm up and be sure you are at least 50 degrees above the dew point in the exhaust vapors, close your exhaust damper down to about 50% and open the combustion air damper up to run it hotter, reset your stack damper according to the dew point and your done.You put a second barrel in series with it also with baffles and perhaps using pipes through it end to end to increase convection flow in the space.

You could do the same thing with this so called rocket stove (which is really just a term to make it sound cool and manly to start folks into buying into lore) but the fire brick laying on the floor and the "rocket" chamber also being on the floor instead of elevated really hinder performance, increase impingement problems and does little to nothing to heat the space.

The basis for the above design as described being far suprior to the design in the video which indeed was extremely dangerous is simply the outside air being ducted in for combustion air.

For some reason a lot of folks never really get their head around this simple concept but in old Ned simple terms, all that smoke going out the stack, well that is air with smoke in it, that air fed the fire, the fire did not make it so there you have it, it had to come from SOMEWHERE and that would be from OUTSIDE, into your space, into the fire and then up the flue. See that problem? It brought the 0 degree air from outside into the space before it headed to the furnace/stove/fireplace. It is MUCH more efficient to duct a combustion air feed from the outside to feed the fire, not to mention stops drafts.

Make no mistake, this is not the most efficient design. The most efficient design should not even be considered for post SHTF. Adding a catalyst to the above baffle system could bring the efficiencies and reduce the emissions into fantastic levels, but the problems remain the same, inconsistent fuel, burn rates and contamination.

No matter what design one chooses, getting it up about 1 foot above the floor, sealing the combustion system in its entirety and keeping the exhaust at the outlet significantly above the dew point are key factors to heating the space efficiently and safely. If it is below that other than at start up and shut down you are going to have creosote and sooting problems not to mention corrosive liquids eating the metals within your system. Post SHTF is not the time to have a flue fire or have uncontrolled amounts of poisonous gases spilling into your living space.

A real good BS detector for internet lore surrounding stove/furnace performance, without induced or forced draft you are NEVER under ANY circumstances get over 80% efficiency, if you light an open fire in the middle of the floor you can't manage that one!
The Following User Says Thank You to NedReck For This Useful Post:
Old 12-12-2010, 07:14 PM
ZootFenster ZootFenster is offline
Member
 
Join Date: Jun 2009
Location: Hot Humid Houston
Posts: 73
Thanks: 57
Thanked 84 Times in 38 Posts
Default

And draft, ya gotta have draft! Either higher flue temperatures or higher flue outlets create more draft. NedReck's analysis is sound. From someone who does this for a living on an industrial scale.
Old 12-14-2010, 09:19 AM
Doc Simonson's Avatar
Doc Simonson Doc Simonson is offline
Just the facts, Ma'am.
 
Join Date: Oct 2010
Location: Stalag 22, Minnesota
Age: 56
Posts: 2,054
Thanks: 4,295
Thanked 2,681 Times in 1,178 Posts
Default

I've ordered the book by Ianto Evans and Leslie Jackson, the sort of inventors of the RMH. Mr. Evans was involved in a lot of projects to help people in third world countries use less fuel and clean up their environment by reducing the pollutants emitted through the burning of wood. I'm pretty sure he wouldn't want people to build heaters that would kill them. It's bad for your reputation. Since these heaters are homemade, I suspect that they can be made badly. But the technology seems to work well, and I haven't found any references to deaths due the using a Rocket Mass Heater. That doesn't mean there aren't any, just that I haven't found any yet. I am hoping to contact the authors of that book and ask them the questions you've asked in this thread.

I have to say that I was surprised at the intensity of emotion coming from the folks who spoke out against the RMH.

Last edited by Doc Simonson; 12-14-2010 at 09:19 AM.. Reason: I can't spell to save my life.
The Following 2 Users Say Thank You to Doc Simonson For This Useful Post:
Old 12-14-2010, 01:35 PM
NedReck NedReck is offline
Prepared
 
Join Date: Nov 2010
Posts: 370
Thanks: 80
Thanked 374 Times in 184 Posts
Default

Quote:
Originally Posted by Doc Simonson
I have to say that I was surprised at the intensity of emotion coming from the folks who spoke out against the RMH.
That is not hard to explain at all sir, it is the penalties for improper design that drive my passions about it. The "rocket stove" is a heat concentration device for cooking, very efficient and if designed properly as safe as can be.

The rocket stove "mass heater" is a real good example of what one should NOT do at all. You will find that the folks whom wrote the book make it clear that dropping the flue temps too low makes the stove "smoke out" or some similar term. In other words instead of coming out the flue, the exhaust gases spill out through the fire box.

CO poisoning is so pitiful a way to watch a person pass. Yes, I said WATCH. Once you have a 30% level in your blood stream there is NOTHING that can be done. The person can be fully awake and your talking to them and there is not a thing you can do to save them, even the hospital can only administer pure oxygen and hope.

There is a REASON building codes do not allow horizontal flue systems, they are VERY dangerous and can lose draft any time. In most states I think you would find a MINIMUM 1-12 pitch requirement meaning a minimum of 1 inch of rise for every foot of length absolute minimum, and then only if proper flue temps are maintained due to the increased friction and buoyancy losses. I have never designed a system with any less than a 45 degree angle myself simply due to the liability issues one would have for doing so.

Again in answering your question regarding the emotional response to it, while I may not be the most friendly person one would ever cross, senseless deaths from stupid ideas infuriate me. While I highly doubt this involves a rocket stove, I simply hope I am not contacted to perform an inspection or act as a professional witness for this recent event of 3 days ago:

ST. CLAIR, MO (KTVI - FOX2now.com) — A St. Clair, Missouri family is dead and carbon monoxide poisoning may be to blame. The bodies of four family members were discovered in their home in St. Clair Missouri around 11 p.m. Thursday. The youngest victim is 3 the oldest is 29. When 27 year old Ryan Yoder did not show up for work for a few days people became concerned.

Two individuals went to Yoder's residence and when they arrived they saw Yoder's body through a window inside the home.

They called police and a forced entry was made. The bodies of three others were also found. Yoder's two children, 4 year old son Devin and 3 year old daughter Tessa as well as 29 year old Angela Sohn. All were pronounced dead at the scene.

Photos and the rest of this tragic story are : http://www.fox2now.com/ktvi-carbon-m...,6469862.story
Old 12-14-2010, 02:43 PM
Doc Simonson's Avatar
Doc Simonson Doc Simonson is offline
Just the facts, Ma'am.
 
Join Date: Oct 2010
Location: Stalag 22, Minnesota
Age: 56
Posts: 2,054
Thanks: 4,295
Thanked 2,681 Times in 1,178 Posts
Default

Quote:
Originally Posted by NedReck View Post

CO poisoning is so pitiful a way to watch a person pass. Yes, I said WATCH. Once you have a 30% level in your blood stream there is NOTHING that can be done. The person can be fully awake and your talking to them and there is not a thing you can do to save them, even the hospital can only administer pure oxygen and hope.

There is a REASON building codes do not allow horizontal flue systems, they are VERY dangerous and can lose draft any time. In most states I think you would find a MINIMUM 1-12 pitch requirement meaning a minimum of 1 inch of rise for every foot of length absolute minimum, and then only if proper flue temps are maintained due to the increased friction and buoyancy losses. I have never designed a system with any less than a 45 degree angle myself simply due to the liability issues one would have for doing so.
Nedreck, please don't call me sir. There is nothing about me that deserves that honor. Call me Doc (purely a nick name) or Dave. I certainly don't want to trivialize the dangers of CO poisoning. Being a biologist by training, I understand that the irreversible bond of CO to hemoglobin can be a very difficult thing to treat. And since it is a suffocation event, it is painful and horrible.

If building codes don't allow for a horizontal run, it seems to be a moot point. You can't legally install a RMH in your home I would assume. I am still interested in knowing what the facts are regarding it's performance. I'd like to see technical data on one in action. So far, I have found nothing. I am hoping the book I ordered will point me to something a bit more scientific in nature.
Old 12-14-2010, 03:38 PM
NedReck NedReck is offline
Prepared
 
Join Date: Nov 2010
Posts: 370
Thanks: 80
Thanked 374 Times in 184 Posts
Default

Quote:
Originally Posted by Doc Simonson View Post
If building codes don't allow for a horizontal run, it seems to be a moot point. You can't legally install a RMH in your home I would assume. I am still interested in knowing what the facts are regarding it's performance. I'd like to see technical data on one in action. So far, I have found nothing. I am hoping the book I ordered will point me to something a bit more scientific in nature.
They can run horizontal, they just have to have the right pitch, most competent engineers design 1" per foot. The uniform mechanical code requires an absolute minimum of 1/4" per foot, the extra that is standard by design is for site issues and settling. As steep as possible is almost always the default.

Here are some other UMC minimal standards:

The horizontal length of a vent connector to a natural draft chimney or vent serving a single draft hood appliance shall not be more that 75% of the height of the vertical portion of the chimney above the connector. [NFPA 1992 (7.10.10)].

The vent connector can only be 1.5’ per inch of diameter.

No more than 2- 90 degree elbows in the vent.

Vent to be as short as possible, long runs get too cool and create condensate, rust, soot and debris build up.

Wood burning stoves are to maintain flue temps in excess of 300 degrees even with inducer draft systems to prevent condensate which will contain sulfuric acids, form creosote, etc. Most natural draft wood burning appliances are going to operate with stack temps in excess of 400 degrees.

Pinheads claim of increase efficiency by dropping the flue temps into the 150 degree range come about from ignorance of the science behind it and in reality it is operating less efficiently. There is no reason to bother arguing about it with someone whom simply is not educated on the subject, I do not have time to explain the technical concepts to someone without the basic understanding to start with. The claims and fabricated information on these stove/mass heaters exist for only one reason, no one manufactures them so no one can be held accountable for claims made. What is even more amazing is the mass of information that is available on the internet about these contraptions.


The rocket stove for cooking is fine but adding this thermal mass to convert it into a heater of sorts has some really serious design flaws. The rocket stove as a cooking appliance directly vented outdoors is much much more efficient than an open fire, turning the flue horizontal and then capturing the heat from it is so dangerous it is not even funny.

As the temp drops the stack effect drops meaning the draft is reduced. If you were to tune the stove with hickory and then were to switch to pine or even hickory with a higher water content, the performance would change significantly, if it drops too far your going to get combustion gas into the space. There is a ton of REALLLLLLLY bad stuff in wood burning exhaust!

carbon monoxide, methane, aldehydes, formaldehyde, acrolein, propionaldehyde, butyl aldehyde, acetaldehyde, furfural, substituted furans, benzene, alkyl benzenes, toluene, acetic acid, formic acid, nitrogen oxides, sulfur dioxide, methyl chloride, naphthalene, substituted naphthalenes, oxygenated monoaromatics, guaiacol, phenol syringol catechol , cyclic di-and triterpenoids, dehydroabietic acid, isopimaric acid, lupenone, friedelin, chlorinated dioxins.

And the list goes on and on and on, I am not a tree hugger saying do not burn wood, I am a scientist and engineer that is saying do not take any risk of letting all that into your house through misguided designs.

A natural draft systems operates with about .3” of water column pressure differential, lowering the stack temps lowers that and when you drop below .25 you can find yourself flirting with down draft and spilling all that crap into your home and it could be as simple as tuning the draft system with high BTU content and then burning only slightly lower heat content fuel.

http://books.google.com/books?id=TxK...20wood&f=false

This is a reference to wood boiler flue design that might give you a bit of insight.

I really have no idea why I bothered with this actually, I consider it actually Darwins job to sort this stuff out, but when I see the unbelievable and 100% false claims being touted by non-peer reviewed CRAP and it can actually harm folks, I feel compelled to comment.

Furnace design is much like juggling, you can certainly learn to do it, but if you start off with chain saws you are not likely to succeed.
The Following 2 Users Say Thank You to NedReck For This Useful Post:
Old 12-14-2010, 07:24 PM
Pinhead's Avatar
Pinhead Pinhead is offline
Hunter
 
Join Date: Nov 2009
Posts: 1,400
Thanks: 11,947
Thanked 2,106 Times in 795 Posts
Default

Quote:
Originally Posted by NedReck View Post
Pinheads claim of increase efficiency by dropping the flue temps into the 150 degree range come about from ignorance of the science behind it and in reality it is operating less efficiently.
How can you claim that a drop in exhaust temperatures of a RMH indicates a drop in efficiency? It simply means more heat is extracted from the hot gasses and put to use. You are greatly underestimating the strength of the draft in this design. In fact, it got it's "rocket" name from the sound it makes when in use. Here is a good video; you can hear the "rocket" sound from the airflow.

After seeing and demonstrating quite a few installs, all of which have exhaust temperatures well below 300°F, there have been none that have had problems with back-flow. The insulated burn chamber and heat riser cause such a strong draft that as long as the RMH is designed correctly, the temperature after the heat riser is inconsequential.

The key is being designed correctly. For example, if you have your exhaust pipe sticking straight out horizontally of the north side of your house and get a 40mph wind out of the north you'll probably get back-flow. A 6" feed tube and 2" heat riser and exhaust pipe it won't work, either; relative dimensions are critical.

I have a Magnehelic pressure differential gauge with a max reading of 2" of water. I plan on measuring the pressure differential between various points in the system, as well as measuring temperatures at those points.

Let me ask you this, NedReck, what are the pressure differential points? Base of the flue and the living space? Base of the flue and the top of the flue?
Old 12-14-2010, 09:18 PM
NedReck NedReck is offline
Prepared
 
Join Date: Nov 2010
Posts: 370
Thanks: 80
Thanked 374 Times in 184 Posts
Default

Quote:
Originally Posted by Pinhead View Post
How can you claim that a drop in exhaust temperatures of a RMH indicates a drop in efficiency?

I have a Magnehelic pressure differential gauge with a max reading of 2" of water. I plan on measuring the pressure differential between various points in the system, as well as measuring temperatures at those points.

Let me ask you this, NedReck, what are the pressure differential points? Base of the flue and the living space? Base of the flue and the top of the flue?
First item, because that is exactly how it works.

Second item, I would not use a magnahelic, it is an expensive accurate tool but is not really designed for flue gases. Get a Dwyer incline manometer graduated in hundredths of an inch, that is what they are made for.

If you do not even know where to measure haw can you claim to even understand it sir?

With all due respect, you have already explained my education and certifications are worthless to you and then you clearly demonstrated you do not even understand the simplest principles in question, I have a great deal of difficulty even bothering to respond. You are simply going to argue misunderstandings of terms to try and justify your position as you already have and it will be an exercise in futility.

I have no idea if you are truly interested in learning WHY it is a bad idea or if you just seek to argue. If you really want to understand it in layman's terms I will take you through it step at a time without insult,
Old 12-14-2010, 09:31 PM
ctwo ctwo is offline
Hiker
 
Join Date: Jan 2010
Posts: 679
Thanks: 175
Thanked 432 Times in 242 Posts
Default

The earlier point about using warm inside air to 'push' the exhaust out is a good one. The rocket stove is not just using interior oxygen, it is pulling a lot of warm nitrogen with it. Maybe a better design would be to a closed loop from outside (oxygen) to fire then through the mass (heat and waste gases) and back outside.
Assuming you can make a really closed loop (no joints leak under whatever pressure can occur), then the back draft problem goes away - it back drafts outside.
Some wood stoves have air tight gaskets on the loading door, so maybe the same could be used on the rocket stove for loading in fuel.
Old 12-14-2010, 09:35 PM
NedReck NedReck is offline
Prepared
 
Join Date: Nov 2010
Posts: 370
Thanks: 80
Thanked 374 Times in 184 Posts
Default

Pulling combustion air from the outside is most certainly the largest improvement one can make to the efficiency numbers, however while sealing the flue perfectly sounds great it is not required. Maintaining the proper flue temp is very important however and while I can understand how some see that as wasted energy it is not because of how the entire process works.
Old 12-14-2010, 10:06 PM
6556 6556 is offline
human
 
Join Date: Nov 2010
Posts: 2,580
Thanks: 208
Thanked 2,462 Times in 1,167 Posts
Default

The arguments for and against the rocket stove both sound good.
However I'd like to see these arguments taken to the http://www.permies.com/permaculture-forums/10.0 Site where there are a number of these rocket stoves both in use and being built.

I'd would like to see the responses (to the comments here) from those that are currently using them.
The Following User Says Thank You to 6556 For This Useful Post:
Old 12-15-2010, 12:24 AM
NedReck NedReck is offline
Prepared
 
Join Date: Nov 2010
Posts: 370
Thanks: 80
Thanked 374 Times in 184 Posts
Default

Ok, in simple and easy terms, please note that doing so can lend itself to slight discrepancies as far as total accuracy goes, however it will remain 100% accurate to the physics and principles the system operates on. Please take note I said SYSTEM and it indeed is one and each part depends on the other parts to operate properly.

The first thing we are going to do is separate the two, a rocket stove and a rocket stove mass heater, they are NOT one and the same. The rocket stove is a very efficient, low emissions cooking device. The mass heater is a furnace of sorts.

Now lets get some fundamental stuff out of the way. When you heat air it expands when it expands it weighs less per cubic foot. It is this fact that makes the hot air flow up the flue, it is lighter. Now please note, there is cold air in the flue that the hot air must push out of the way, in doing so it must build pressure. Now knowing that some things make simple sense.

The hotter the air, the faster it will move through the flue. Incase there is any misunderstanding, the flue connects to the exit of the heat exchanger and travels all the way out the roof where it may have a cap on it.

Now it is very important you remember that the cold air is indeed on top pressing down on the warm air impeding its flow. So now we have a system where X pounds of air presses down on X pounds of air that is warmer therefore has pressure pushing it. So now lets say for sake of illustration only that we have 0 degree air on top of the flue that weighs 10 pounds, on the bottom of the flue we have 250 degree air that weighs 8 pounds there fore it has 2 pounds of “lift” so it will rise. Now we raise the temp to 500 and the same volume of air now weighs 7 pounds and will have 3 pounds of lift so to speak.

The 500 degree air will rise and travel through the flue faster than the 250 degree air. I will assume everyone bothering to read along agrees with this basic concept as flawed as the numbers inserted might be. If you must test this law, take two balloons, file one 75% full of helium and the other 100% both being lighter than air and let them go at the same time and see which lifts faster. You might simply think about a hot air balloon, fire the burner get more rise.

Ok so now we have established the hotter the faster. Now lets talk about balance a bit. The leaner the burn the hotter the flame. Instead of going into the science, we fan an ember to get a flame in tinder, we fan the flame to make it hotter to light the kindling, we fan the kindling to light the logs. Scientifically we are increasing the oxidation rate which increases the temperature. We need to increase the oxygen flow to hasten the process.
Once the flames are burning we must constantly feed fuel and oxygen into the process to maintain the heat.

This is what a flue does, as the heated air flows up the flue it pulls air in the front of the furnace (front meaning the beginning stage, could be bottom, top, front side etc) this is bringing the oxygen to the fire. In a natural draft system, the flue is designed in such a way that it will draw the proper amount of fresh air into the front and maintain the proper lift to rise out of the flue. Now there is more to that but I will speak to it later in this blathering.

Now speaking directly to the question pinhead asked, “how does lowering the flue temp make it less efficient?” paraphrased by me. It lowers the efficiency by taking the system out of balance. Lowering the flue temp lowers the velocity of the air leaving it and since that air leaving it came in the front of it, it lowers the flow of combustion air which lowers the temperature the wood is burning at which lowers the fuel consumption which is indeed one of the plus items listed to a rocket stove (the cooking device) it also helps with the fuel consumption of a furnace as well.

I know, some of you are saying wait a second, did you not just agree? No, not at all. There is a lot more to the process than that. Pinhead’s position is that by removing additional heat from the flue and putting it into the space it is more efficient. The lowering of the flue temp, there by lowering the air intake, there by lowering the combustion (oxidation) temp, not all of the “fuel” of the wood gets burned. You wind up with “incomplete combustion” aka NOT stoichiometric combustion meaning 100% of the fuel value oxidizing. If air content is higher than the stoichiometric ratio - the mixture is said to be fuel-lean. If air content is less than the stoichiometric ratio - the mixture is fuel-rich.

In other words, lowering the flue temp which lowers the air flow actually burns fuel rich aka not efficient. Now if you understand that the buoyancy of the temperature difference in the flue is the driving force behind the air flow, then understand it is your only control point for the intake combustion air. If you lower the exhaust velocities you lower the intake velocities and cool your fire down.

Now lets take a real good look at the other issue. We have spoken of heated air which is all fine and good, unfortunately that is not what flue’s carry away. They carry away a whole host of chemicals that are byproducts of wood burning. Most all of us know this, CO, water, sulfur and a lot of other stuff, many of these chemicals are NOT lighter than air and we depend upon the velocity of the flow in the flue to carry them out of the living space.
For those of you looking for a simple explanation, remember the fans they used to run with beach balls suspended in the air at the department stores in the 70’s? If you take a beach ball and place it in the air stream of a high velocity propeller type fan, it will lift the ball and hold it in the vortex the fan creates. On high speed it will hold it a few feet above, turn it to medium speed it holds it at about 1 foot, put it on low it falls all the way down.

The same thing happens with the heavier than air byproducts of combustion, if the velocity is high enough they are blown out the top of the flue and if it is not they fall back to the bottom where they build up and they have weight so as they build they create a downward pressure and push themselves back out the front of the furnace into the living space.

I have even observed a you tube video of some walking talking moron using a flue gas analyzer by testo at the outlet of the furnace talking about how amazed he is that it is burning so clean and has virtually no emissions from the furnace. Here is a clue for him, that is because all of the poison is spilling into the living space instead of leaving out of the flue you idiot! There are chemicals that come from wood buring that require temperatures in the tens of thousands of degrees to oxidize and it can not be done inside a wood stove/furnace, these products NEED to be in the flue gases and exit the space. Showing that they are not there does not mean they were magically burned up because some hippy says so, it simply means someone lowered the flue temps to such a level that the velocity of the flue gas allowed them to drop out and back draft into the space poisoning the folks inside.

I am not sure how much simpler I can explain it and I am sure that explaining it in technical terms and math would be a wasted effort. In order to maintain the proper combustion rate and flue gas velocities on a wood burning natural draft appliance you need to maintain a flue temp between 400 and 450 as a general rule. If you really put your work into it and burn a very consistent wood product and moisture content you can tune it SLIGHTLY lower than that, but without any doubt you can not approach 250 safely.

If you think so still, step up and prove it! No debate, no word twisting, flat out factually prove your buoyancy equations, velocity equations, combustion air fuel equations etc, anything else will be ignored as argumentative forum crap and I have no interest.
The Following 3 Users Say Thank You to NedReck For This Useful Post:
Old 12-15-2010, 12:41 AM
NedReck NedReck is offline
Prepared
 
Join Date: Nov 2010
Posts: 370
Thanks: 80
Thanked 374 Times in 184 Posts
Default

Quote:
Originally Posted by 6556 View Post
The arguments for and against the rocket stove both sound good.
However I'd like to see these arguments taken to the http://www.permies.com/permaculture-forums/10.0 Site where there are a number of these rocket stoves both in use and being built.

I'd would like to see the responses (to the comments here) from those that are currently using them.
Saw your post afterward. I have no interest in entering into a debate with even more folks whom have little to no idea of what they are talking about.

That said, my comments have been in direct regard for the system in the video. There are indeed better designs on that webspace even some with horizontal exhaust, there are still issues and when they speak about the fire burning up the wood instead of the wood collapsing into the fire pit, that is because of back draft.

I do not re-engineer for free nor do I train for free and I sure as heck am not going to go argue, train and re-engineer a bunch for free. The subject does not even have my interest enough to assign one of my thermo students a paper on them, it is real simple why the one we saw in the video is a very bad idea.

Think of it like Russian Roulette, you are five times as likely to drop the hammer on an empty chamber, not bad odds really, but when you consider the penalty you just don't take the chance.
The Following 2 Users Say Thank You to NedReck For This Useful Post:
Old 12-15-2010, 01:19 AM
velacreations velacreations is offline
Recent Blog: Pumpkins
Hunter
 
Join Date: Dec 2010
Posts: 1,140
Thanks: 621
Thanked 693 Times in 372 Posts
Default

CO is combustible, so, in theory, if you had a secondary air intake and high enough temperatures, you could combust most of the CO from an initial combustion.

That's how wood gas works for powering cars, H2 and CO combust in the presence of O2 creating H20 and CO2.

If you had an insulated combustion chamber (like the Rocket Stove), you could definitely reach temperatures high enough to burn the CO.

So, as far as the CO is concerned in the exhaust, it is not inconceivable that the Rocket Stove exhaust contains less CO than a single combustion wood stove.

I would think that if there is considerable blowback, it would be obvious to the scores of folks that are using these. I haven't found much being mentioned about that in the countless blogs, sites, and videos about these things.

The real thing to do would be to build one in a sand box outside and test the exhaust and intake for pollutants. Also, we could measure temps in the burn chamber, and all along the flue.

A long piece of stovepipe within a cob bench doesn't seem to be the greatest heat exchanger to me, but again, it is hard to argue with so many people that are using these things.

Something must be working....
The Following User Says Thank You to velacreations For This Useful Post:
Old 12-15-2010, 06:57 AM
NedReck NedReck is offline
Prepared
 
Join Date: Nov 2010
Posts: 370
Thanks: 80
Thanked 374 Times in 184 Posts
Default

Quote:
Originally Posted by velacreations View Post

Something must be working....
Darwin's theory seems to be.
The Following User Says Thank You to NedReck For This Useful Post:
Old 12-15-2010, 08:20 AM
Bullets~n~Beans Bullets~n~Beans is offline
Fishing on a river
 
Join Date: May 2010
Location: East of the Clearwater River Valley, Idaho
Age: 54
Posts: 2,406
Thanks: 6,426
Thanked 3,627 Times in 1,440 Posts
Default

Quote:
Originally Posted by NedReck View Post
WOW!


The comment when the girl referred to the smoke as "unburned fuel" and at the end of the video when they said they checked outside and all that was coming out was "steam" are a direct reflection of the idiots whom built that contraption and it is a very dangerous setup.
Sorry to contradict you here but smoke IS unburned fuel.

---------------------------------------------------------------------------------

EDIT - After reading the rest of this thread I suppose I better qualify my statement. I have spent the past 31 years as a professional firefighter. I've been burned over twice in wildfires, experienced one backdraft and seen numerous flashovers and rollovers. Trust me, smoke IS UNBURNED FUEL. It WILL burn and can be extremely explosive. Those facts are very well known, and part of training in the fire service.

As for the rest of your arguments I can not comment. Yourself and others are far more qualified than I am.
The Following User Says Thank You to Bullets~n~Beans For This Useful Post:
Old 12-15-2010, 08:36 AM
ctwo ctwo is offline
Hiker
 
Join Date: Jan 2010
Posts: 679
Thanks: 175
Thanked 432 Times in 242 Posts
Default

The thing that is still unclear to me is: does the rocket mass heater have an exhaust pipe or a flue?
I've seen buses that have exhaust pipes at the level of the street, and I've seen them where they have an 8 ft vertical pipe to get it above people. Does that 8 vertical feet make a big difference to the engine? Any more so than an additional 8 horizontal feet?

If the rocket stove works fine with no flue at all - if it is used outside and just dumps the exhaust after the combustion chamber, then adding horizontal pipe just increases resistance - creating some amount of back pressure. How much more back pressure does a foot of vertical pipe create compared to a foot of horizontal? I suppose if the movement is slow enough it would act somewhat like a fractionating column and perhaps the heaver components would collect in it.

If the flames are getting pulled into the combustion chamber, then is it safe to assume no appreciable amount of combustion gases are coming out of the wood feed mouth? Is the problem that even when there is no smoke-back - lets say air is moving into the wood feed mouth at 1 cfm, there can be a dangerous amount of combustion gases making it out against that current and into the room?
The Following User Says Thank You to ctwo For This Useful Post:
Reply

Bookmarks

Tags
hearters wood stove



Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Rocket Stove MeadowMuffin DIY - Do It Yourself 4 05-24-2013 04:44 PM
Home Canning using a wood stove/ rocket stove Jasmine_xoxo Food and water 5 04-06-2011 10:21 PM
Hobo Rocket Stove Creek Walker Wilderness Survival, Hiking and Camping Forum 22 10-15-2010 12:55 PM
Rocket Stove nursegurly Disaster Preparedness General Discussion 19 09-09-2009 10:26 AM
rocket stove vegasrandall Wilderness Survival, Hiking and Camping Forum 3 09-10-2008 10:08 PM


All times are GMT -5. The time now is 07:06 PM.


Powered by vBulletin®
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Copyright Kevin Felts 2006 - 2012,
Green theme by http://www.themesbydesign.net