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Electronic Wood Stove Control

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by ControlFreak, Jan 25, 2008.

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  1. ControlFreak

    ControlFreak Feeling the Heat

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    "The unit you are designing is for OEMs. Have you thought about something for the rest of us?"

    Yes, eventually. First we need to establish a reliable name. That would be very hard to do, starting out by sending off kits to people with various skills and stove configurations.

    One way you can help is by going to our website and taking our survey. www.inveninc.com Look for the white "Take Our Survey" link at the lower left. Gathering this data is essential to a successful launch. Oh by the way, there will be a drawing for an Ipod Shuffle when the survey is completed. The winner will be announced here, so you can be sure that we're not just "blowing smoke."

    Dan

    Helpful Sponsor Ads!





  2. Rob From Wisconsin

    Rob From Wisconsin Minister of Fire

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    Being an Engineer that has developed products that have been under the scrutiny of UL/CSA/CE,
    ('nuff said of my credentials)......
    Most safety underwriting agencies don't fully trust electrics/electronic in a safety critical operation.
    They tend to "smile" at mechanical safety interlocks, that in turn cause the energy source to fall to
    its lowest possible potential, if immediate injury/harm can reasonably be prevented. For example,
    spring loaded solenoid valves that return to their resting "closed" position when power fails, or any one of a set of "critical" faults occur - overtemp, controls self-check failure, etc.....
    Also, in extreme critical control, redundancy is required. Such an example would be if one of the overtemp. sensors failed (regular or backup), the controlling unit would "fail" & remained de-energized until both regular & backup sensor were restored to their "normal" operating states.

    In all sincerity, your proposed system sounds like a fairly easy system to implement & design
    "fail safe". The only potenial problems I see are the "nuscience" shutdowns that will likely occur
    from a system that may need to be "over-safe" (i.e. - pellet stove problems). But w/ time,
    even the Pellet Stove industry seems to be getting it right.......

    Hope this gets you in the right direction.....
    Rob
  3. Andre B.

    Andre B. New Member

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    When I think about designing something like this, here are some of the first things that come to mind.

    There should be two manually set air controls.
    One in parallel with the automatic control, this one is used by the operator to set the minimum airflow.
    And a second in series with them, this one is used to set the max airflow.
    This way the automatic control can be limited on both min and max airflow by the operator.

    Then how to make things fail safely.
    First a spring on the auto air valve to close it in case the power drops out do to an ice storm or some sensor trips the E-Stop system.
    Then I think, springs eventually fatigue and break so change it to a weight, gravity never fails.
    Now need some way to physically disconnect the servo from the air valve when the power fails, otherwise the weight needs to be enough to back drive the unpowered servo, which means the servo will be constantly using enough electrical power to hold up the weight, can't have that in something that may well be running off batteries. So put an electromagnet between the servo and the valve, still needs constant power but not much. It does require that the servo run down to valve closed position on power up to pick up the valve, but then it is not a bad idea to do a range of motion and limit switch test anyway. Should also monitor the servo current and report a possible problem.

    Etc..

    Attached Files:

  4. ControlFreak

    ControlFreak Feeling the Heat

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    Do you think that people who heat with wood have an aversion of mixing high-tech stuff with the low-tech tradition and simplicity that's prevalent in wood stoves?

    Dan
  5. Woodrat

    Woodrat New Member

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    Quite likely ---- esp. "older" ones.
  6. singed

    singed Member

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    Well, I'm here because I went out searching for "wood furnace" "control" OR "controller" and was disillusioned.

    When I found this thread, I had to sign up, log in, and say, "Go, Dan, go!"

    We just bought a house west of Madison, WI. It has an owner-built wood furnace as a secondary heat source in parallel with an LP.

    It's an odd duck. There is, what I've come to understand, a line-voltage thermostat in the first-floor hall which powers a rotisserie motor rigged to lift the air draft to full-open when heat is demanded. The lever arm on the motor shaft which lifts the draft gate also serves to stall the motor when it hits the "limit bolt."

    A second plenum-mounted thermostat actuates the blower when plenum temperature hits the setpoint. Meanwhile, the rotisserie motor stays in stall mode until the hallway thermostat hits its setpoint and drops power.

    Immediately, I wondered why-in-the-world there wasn't a controller to read all the inputs and control the draft-door position in a closed loop with the flue (and perhaps, I thought, the plenum) temperature. Immediately after, I started dreaming about a design.

    I appreciate the wisdom of you wood-stove-loving aficionados who have distilled that wisdom from years of observation and experience. You need to tell me how to run a furnace because I am an idiot (and have the PhD to prove it), but my point is that--more and more of us are going to have to try wood to cut our energy costs--and the normal distribution being what it is, the preponderance of us are not going to love it.

    So, we're going to burn green wood and run our stoves way too hot and just generally be a danger to ourselves and our neighbors.

    An acquaintance has regaled me with the wonders of his pellet stove ("No ash! Think of it! 100% burn!") and while looking for that elusive after-market controller, I heard of Greenfire (http://www.greenfirefurnaces.com/products.html) which I took to mean wood-log combustion can be very efficient too.

    That's what brought me to thinking about and looking for a controller to optimize the process, and now I'm fairly convinced from earlier posts that, having set a match to the wood, I mostly want to make sure the fuel burns most completely. It will be nice if it can be damped down to reserve some of the fuel for later if it's not needed immed., but I'd rather it be burned up for the sake of clean air than left half-unburned going up the chimney.

    Echoing what was desired earlier re: retrofit kits, I'm reminded of my first computer (a Zenith Z-100 from "Zenith [TV] Data Systems"). ZDS published a magazine for their customers that had articles on "things to do" with, and to, your Z-100. It came with as I recall 192K (that's 'kay') of RAM, but one of their engineers explained how he'd managed to use 256K chips to expand the memory to 768K. (I'll tell you we wet our pants at the prospect!)

    But here's the kicker: at the end of three issues, I had the complete set of instructions, with photos, of the modifications, and one weekend I proceeded to take out the "motherboard" (new term for me) and CUT traces hither and yon with an Xacto knife while BENDING OUT PINS from specified ICs and soldering jumpers all over the place. I put it back together without a second thought and powered it up and began using my new gofast machine. It was only years later (I had been in my 20s at the time) that I realized what a delicate instrument I'd been fiddling with.

    But, being the idiot that I am, I desperately want to drill holes in my furnace, bolt things on the side and top of it, wire in jumpers and have something that behaves like a decent human being for once.

    As far as cost goes, you can sell me ANYTHING at ANY PRICE, after you prove to me that it's actually SAVING me money over N years. The pellet-stove guys have my attention that way.

    Thanks for all the great comments in here.

    Go, Dan, go! (One way to save costs: move from MA to IA...) :^)
  7. Gooserider

    Gooserider Mod Emeritus

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    Welcome to the forums Singed, this is definitely the place to learn about messing w/ wood burning... If you haven't gotten to it yet, it sounds to me like you'd be interested in talking to the guys over in the "boiler-room" forum, as they are more the experts on heating with central systems - as opposed to the Hearth room which is more about stoves, etc... They are also doing quite a bit with controls and such - lots of good info there.

    Gooserider
  8. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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    Yeah you got that right. Those old guys just can't grasp new technology.
  9. swestall

    swestall Minister of Fire

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    Hey BB, what are we going to do if we can't adjust the air?
  10. singed

    singed Member

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    Thanks, Gooserider. It's good to wake up among savants.

    Rooms? You say there's rooms?! :^)

    I'll wander over.
  11. ControlFreak

    ControlFreak Feeling the Heat

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    Hey Singed,

    I grew up over there in Watertown, WI. Graduated from UW Madison with a EE in 83. Maybe we'll see you this summer while we visit.

    Dan
  12. singed

    singed Member

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    Hey, Dan, I PM'd you. Yeah, come see me at UW.
  13. jotul8e2

    jotul8e2 Feeling the Heat

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    As it happens, I too have been wondering about this issue. When it comes to automated controls, compared to a wood fire burning oil, gas, or even coal is child's play. Microelectronics undoubtedly make it tempting to think it can be done.

    However, once you have decided that a stove that plugs into a wall outlet is acceptable (and many inserts, and all outdoor wood furnaces are electrically dependent already), then why not take the leap and hook up to a gas supply (lpg or propane) as well? A very small, microprocessor controlled gas burner in the secondary combustion chamber, combined with automatic primary and secondary air controls (possibly mechanical?), could ensure efficient, clean burns for all those times when the wood, the loading, the temperature, or whatever, is not optimal. The suggestion made above that forced air may be required is likely correct. And when conditions will not allow a seconary burn (wood too green, too wet, etc.) it could just shut off the air intake and allow the fire to go out, rather than sit there and smolder uselessly.

    Something along these lines could make those dirty, inefficient outdoor wood furnaces far more appealing.

    Mark
  14. Gooserider

    Gooserider Mod Emeritus

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    No thanks... I burn wood in order NOT to burn gas... I don't want anything to do with a gas burner in the wood burner as that would defeat the entire purpose...

    I suppose there might be something to be said for having a small gas burner to make starting fires easy, but I'm not sure just what, as once you know how it is almost trivially easy to start a fire w/ newspaper and kindling...

    Gooserider
  15. jotul8e2

    jotul8e2 Feeling the Heat

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    I'm not thinking of a gas fired appliance with supplemental wood heat. I'm suggesting the possibility of a small, electrically ignited, temperature controlled flame source to ignite secondary gasses earlier and more consistently. A little gas (or oil, I suppose), to make a wood appliance function more or less automatically could be attractive in some applications. In fact, some outdoor furnaces already use gas or oil as a backup heat source. Why not take it a step farther and use a trivial amount to acheive a much larger btu output from the wood fuel? If someone burning six cords of wood a season could get the same btu output for, oh, say five cords and five gal. of propane, then why not?

    Of course the answer may well be that it would not work that way.

    I should have noted above that I personally don't want such a furnace either. My stove has to function independently of any inputs beyond wood and my time. But I can see where such an automated wood fuel stove could be desirable.

    Mark
  16. ControlFreak

    ControlFreak Feeling the Heat

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    "why not take the leap and hook up to a gas supply (lpg or propane) as well?"

    I think it will come down to cost. Adding such a thing is certainly possible, and I have given this some thought, but in my opinion the complexity + cost vs benefit makes this impractical.
  17. MishMouse

    MishMouse Minister of Fire

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    There is also another thing with adding propane to a wood stove, especially if your stove over fires, or the ash and heat cuases the connection of the propane to degrade.

    B O O M !

    No more heating problems.... :lol:
  18. tradergordo

    tradergordo Minister of Fire

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    Believe it or not, this has actually been invented already. I stumbled across it in a patent search I was doing.
    A guy from the EPA, Robert Hall, has a patent called "Woodstove for heated air forced into a secondary combustion chamber and method of operating same

    Abstract
    A resistance heater heats air forced by a fan into a woodstove secondary combustion chamber having an ignitor. The fan, heater and ignitor are controlled by a temperature sensor for gas flowing from a primary combustion chamber to a secondary combustion chamber. Two ignitors, extending through the stove back wall into the secondary combustion chamber, are controlled by the temperature sensor.

    Anyway, in his patent, he mentions:

    "Other techniques for sustaining combustion in the secondary combustion chamber have involved the use of a natural gas powered flame and electrical ignitors; see Spolek et al., "Secondary Combustion in a Dual-Chamber Woodstove," ASHRAE Transactions Vol. 91, Part 1, pages 1138-1146, 1988. Laboratory measurements of woodstove emissions using natural gas powered flames have demonstrated a substantial decrease during limited testing. However, experimentation with natural gas powered flames was suspended because of practical problems associated with supplying an external natural gas source to a woodstove. In experiments we conducted with electrical ignitors, wherein the ignitors were located on the secondary combustion chamber outside wall, it was found that the electrical ignitor did not result in complete combustion of products in the secondary chamber. "

    An object of the invention is to provide a new and improved dual chamber woodstove having secondary chamber combustion control and method of operating same.

    It is another object of the present invention to provide a new and improved dual chamber woodstove having a secondary combustion chamber wherein the stove is efficiently operated and emissions, including particulates, are substantially reduced, even though fuel is being burned in a primary combustion chamber of the stove at a medium or low burn rate. "
  19. cbrodsky

    cbrodsky Member

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    Dan,

    Very interesting - this is something we've discussed on hearth.com many times in the past - making a wood stove almost as idiot-proof as a pellet stove. It looks like you've spent quite a bit of time on this and it seems like a very professional product that no matter where it goes, would certainly have a niche market on hearth.com among the many engineers.

    What price range are you targeting? The survey seemed to indicate you are looking at $400+ as the lowest option, which could be a significant challenge. I think many of us technical types would be interested in this but it probably needs to be a cheaper product for broad mass market adoption - it will definitely be a challenge to get people to mix high tech controllers with wood heating. I have been looking at spending $100 or so for a digital thermocouple with alarm for overfires and would gladly add $100 more for a draft control. But I suspect many people would weigh the cost against a bimetallic system with a calibration adjustment and say that it's "good enough" for $10. I don't think I could justify $400+.

    The auto-calibration idea for the draft controller could be really helpful for aftermarket applications.

    I noticed you list this as a "patent pending." I was curious and took a look but didn't see a published application yet on the USPTO site. I'm curious which aspects you believe are novel, presuming you've already filed to protect those claims.

    -Colin
  20. begreen

    begreen Mooderator Staff Member

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    CF, I understand the nature of the product proposed is to control the stove, you might also want to consider an offshoot product from this technology. I think you could do well to produce a good stove monitor. I other words, the same device but without the output side servos and air controls. If it can be tied wirelessly to a computer, even better.
  21. ControlFreak

    ControlFreak Feeling the Heat

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    Guys,

    The monitor idea is not something we had thought of. However, this is a subset of SmartStove. So, considering how easy that would be to do, it would make a lot of sense to offer a stripped-down version which is a thermal monitor with settable alarms. I don't see any reason why we wouldn't do this. We will be discussing this for sure.

    Dan
  22. cbrodsky

    cbrodsky Member

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    I would definitely be interested in the $150 or less range. And I think it may help you get higher volume sales to help bring costs down for active controls. Make sure you consider catalytic stove applications as well - catalytic users are often more interested in maximizing efficiency.

    -Colin
  23. Gooserider

    Gooserider Mod Emeritus

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    I would second the interest, and also suggest doing a search on past threads, it's been a while since the topic has come up, but there have been several previous discussions of desirable features and so forth. There is a definite market opportunity here as I don't know of anyone offering a product that really matched up with what a lot of us seemed to want. I would suggest trying "Digital Thermometer" as a search string, mostly in the Hearth Room and Gear forums.

    Quick summary as I recall it -
    2-4 inputs, probably "Type K" thermocouples
    Large display, LED or backlit LCD, able to be read across the room...
    AC power (wall wart?) w/ battery backup, no automatic shutoff
    Alarms for over-fire temps, and possibly low temp / add wood
    Some sort of ability to output to a PC - I prefer wired ethernet, other folks liked USB or Wireless, needs to be in a documented format so that any O/S can use it, not just Micro$oft

    Gooserider
  24. mayhem

    mayhem Minister of Fire

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    I hope this helps.
  25. scotty

    scotty Member

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    Colin, the "novel" test was degraded some years ago. I think that you know that, but I thought I'd elaborate for those who don't. Today a patent doesn't have to be quite as new or unique as was once the case....it can simply be an improvement on an existing process. In other words, a unique manner (proprietary electronic circuitry) of achieving a desired effect (combustion control) would be very patentable. The test for "improvement" is that the new process solves a "known problem".

    BTW, At one time the patent office preferred that the inventor submit a working model with the patent application. They can still require a model, but now they prefer drawings and data as they are running out of storage space.
    ......MORE STORAGE SPACE...now that would be a great invention!

    scotty

    >I noticed you list this as a "patent pending." I was curious and took a look but didn't see a published application yet on the USPTO site. I'm curious which aspects you >believe are novel, presuming you've already filed to protect those claims.

    -Colin[/quote]
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