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Primary circ pump - playing with speed settings - your thoughts?

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by stee6043, Nov 4, 2009.

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  1. Gooserider

    Gooserider Mod Emeritus

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    One thought I've had that would seem to address both the boiler protection question and the pumping speed issue if it would work, is whether or not one of the new temp-responsive ECM pumps would be good - not necessarily having any kind of close boiler return loop, or possibly just some sort of mix valve, with the TC pump watching the return water and boiler out temps and turning just fast enough to keep the boiler out from exceeding the idle triggering temp... Would this work, or is there still to much risk of the boiler return being to low?

    Gooserider

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  2. kabbott

    kabbott Member

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    This is basically what i am saying only managed via a control system(NFCS in my case) instead of the ECM pump. Same thing only different. ;-)

    I still think you need a bypass of some sort be it a pump or mechanical valve. If you have a tank full of water @room temp it doesn't matter how slow you run
    the pump, I think it's gonna cause problems.
  3. jebatty

    jebatty Minister of Fire

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    I suppose essentially what you need to do is charge the tank to about 165F at bottom of tank. My tank is horizontal, not that that necessarily makes any difference, but when my bottom of tank is 165 and charging is continuing, bottom of tank temp is rising rapidly, which means that the water column above quickly becomes much hotter. I don't have mid tank sensors (could be done, though), but I suspect that in this situation about 190F water sits in at least the top 2/3 or more of the tank. Returning 165 water to the bottom of the tank might not be giving up many btus. But as you say, radiant would be much better.

    This is the point I'm making above.

    I think this is somewhat problematical, and is highly related to the engineering design of the boiler and the firetubes. I have 8 tubes, 3" diameter, and x" long. The velocity of the flue draft will determine how long and how hot the hot gases are in the firetubes. Controlling the draft, faster or slower, seems to be the primary way to control the ability to extract heat from the firetubes in a typical home boiler. How much heat is extracted by the surrounding water/water flow will depend on the interior design of the boiler water jacket and how that water flows through the firetube matrix and mixes as it flows from the bottom return to the top supply. Increasing the speed of that flow does not necessarily equate with the ability to extract more heat in any determinable fashion, except by trial and error with measurement. The flow will take the path of least resistance, which likely is not through the firetube matrix. While some additional heat may be extracted, I suspect it will not be linear with increase in flow. And second, in all cases increasing flow is limited by the capacity of the plumbing, pump head, etc.

    A differential controller should largely solve this problem. When return temp is less than ___* less than supply temp, the circ should shut down.

    An interesting side note. I've been involved as a lay adviser in a non-profit institution installing a Garn and a Woodgun for primary heating, to replace heating previously provided by 4 LP staged boilers. The LP boilers will remain to supplement, as needed. Beautiful looking install, but two issues have quickly surfaced and were not dealt with by the HVAC contractor: 1) no return water protection for the Woodgun, and 2) at this point believed to be inadequate specs/design on the HX a) to transfer to the pressurized system all the btus that the Garn can produce and b) to operate in a reverse direction to transfer excess Woodgun btus to the Garn storage to prevent the Woodgun from idling. The HX issue highlights what we know well, and appears not to have been adequately considered or understood by the HVAC contractor: as delta-T closes it takes a lot more capacity to move btus. It will be intriguing to see how this is worked out.
  4. stee6043

    stee6043 Minister of Fire

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    Do they offer pumps that can monitor both inlet and output temps in a stand alone setup? I've seen the pumps with single temp triggers but not two. I like this idea but the only problem I see is that in my case I could have 180 coming off the boiler but still have 120 on the bottom of my storage tanks. Without some kind of mixing valve still in place I'm still going to have some risk of low return temp. Alas, I'm back to wanting more sophisticated controls...

    I like where this thread has gone. Great read....
  5. Nofossil

    Nofossil Moderator Emeritus

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    I agree. There have been a few dark days where I question the time and effort that I've put into control design and theory. This thread is a good reinforcement of the reasons I started down this path. At the end of the day, I believe that you can get much better performance out of almost any system if you have the right control logic.
  6. jebatty

    jebatty Minister of Fire

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    Based on the color of the bottom link or two of the chain turbulators (where the hot gases enter the firetubes) in my Tarm, it appears that some of the firetubes are receiving hotter gases than others, and/or that water circulation around some of the firetubes is better than others, resulting in some tubes being hotter than other firetubes. Whether and how much this makes a difference in the temp of the gases as they exit the firetubes I do not know. Might demonstrate the point made above.
  7. barnartist

    barnartist Minister of Fire

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    wouldnt it be great to know the temp of each fire tube and then be able to adjust how the heated air flows through each tube to improve the efficiancy even more?

    What a hobby this burning of wood has become.
  8. kabbott

    kabbott Member

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    Good observation. Slowing the flow like I was thinking could certainly make this more pronounced. Has anyone ever had a problem with to little
    flow creating "hot spots" while outlet temp is still below idling temp with the modern gassers? Do any of the manufacturer's recommend a minimum flow?

    If there were an easy way to measure the temps/flow you could probably balance this by adding/removing links from the chain. When I was considering
    building my own I had a design that had the firetubes on the wide side of the boiler allowing more tubes but thought there might be a problem with the center
    tubes taking the majority of the flow.
  9. barnartist

    barnartist Minister of Fire

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    I don't mean to stray to far from the flow subject...
    I would love to have a digital readout of my secondary burn temp, and then I could use that measurement in conjuction with the stack temp, then if I had a way to adjust flow I could experiment a bit. Nofossil has probably done all of this.

    How do I look for such a temp probe/display, or does anyone know where to buy one already? I know I have asked this in the past seasons-sorry. Maybe the answer is buried in the sticky"tweeking the Eko"
  10. Gooserider

    Gooserider Mod Emeritus

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    I think NoFo has such a sensor in his setup - might be worth looking on his site for details on what he's using... I know that it's a non-trivial thing, as you are looking at temps in the secondary of a gasser that are outside the range of most type K sensors and the like.

    Gooserider
  11. Nofossil

    Nofossil Moderator Emeritus

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    I do use thermocouples as part of my control logic. I use 1/8" diameter stainless jacketed Type K probes from Omega, and I keep them out of the direct secondary combustion flame. I have one near the side of the secondary chamber and one in the flue. I ruined an inconel jacketed probe ($$$$) by putting it in the direct flame.

    I just (yesterday) designed and ordered a batch of thermocouple signal conditioning circuit boards for the NFCS system. Basically, they allow a thermocouple to be used interchangeably with all the other sensor types that I have. I like sensors, and at this point I have three different semiconductor sensor types, thermistors, thermocouples, and pressure sensors all supported. It might be overkill, but it keeps me off the streets. Probably a good thing for society in general ;-)
  12. Gooserider

    Gooserider Mod Emeritus

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    What about "Dallas One Wire" type sensors? Seems like those would be a worthwhile addition since they are relatively cheap, you can use as many as you want, and they come in several different sorts. As I understand it, once you have the basic DOW interface, interpreting the different sensor types is mostly a question of software... I know there was a recent link to a monitoring system that looked very impressive, using DOW sensors, only downside was it didn't have any control output capability, only monitoring and logging (seemed rather pointless, why collect all that data and not USE it for something?)

    Gooserider
  13. kabbott

    kabbott Member

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    I have 1-wire sensors setup on the same hardware that is running my NFCSS, the problem is tying it into Nofossils software package. For now they are
    read only. He has limited support through a network 1-wire interface i believe. I am using the ds9490r usb interface. This is going to be one of my next
    projects, even if i just help get some of the pieces together and have to bribe Nofo to finish it. :bug:
  14. barnartist

    barnartist Minister of Fire

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    I'm not sure if I wil ever get to a software based monitoring sytem, although it would be freakin awsome, but a sensor that I can read right at the Eko would be nice. Just something to help me tell how my air settings are and the differences in load (wood species. etc).
  15. TCaldwell

    TCaldwell Minister of Fire

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    i think type k reads to nearly 2400degf, in direct flame path omega sells a slip over ceramic protective sheath, sofar 5 months in, is still good, barnartist checkout red lion instruments, panel meters, the cub 5 tc, maybe what you are looking for
  16. leaddog

    leaddog Minister of Fire

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    http://cgi.ebay.com/Thermocouple-K-...emQQptZLH_DefaultDomain_0?hash=item3a5482fdd9

    Here is a K probe with ceramic., They have pid's and other meters. I use a k and a pid meter to moniter my stack temp. I picked up my pid's on ebay. I also use one to run my 3-way valve. Pid's and probes cost me less than $40. I thought about putting one in the bottem to check the gasification temp but haven't yet. It shouldn't be hard. just drill a small hole at the door and lay on the fire brick.
    leaddog
  17. DaveBP

    DaveBP Minister of Fire

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    To bring the thread back on topic I have another angle on this balancing act of varying the circulator speed through the boiler to get the more of the heat the boiler is producing out into the storage.

    On the other side of the equation from varying the flow rate through the boiler is varying the output of the boiler itself.

    My question is this: How much can you lower the firing rate of any given downdraft gassifier before it starts to become less efficient? After all, each different make and model has some subtle design features that are built around some limited range of operation before it can't produce the desired burn efficiency. A 60 KW boiler won't be shut down to 15 KW and still run clean will it?

    Except on those design nights the boiler is producing more BTUs than are currrently needed. For many even those design nights are easy to keep up with.

    So can you reduce the draft fan speed and air settings to lower the BTU output of the fire and thus allow more time to get the heat out through the fire tubes to the storage. It's the same as picking up the speed of the water in the jacket around those same fire tubes to get the heat out. It's all about getting that heat through the walls of the heat exchanger into the water that carries it away to storage before it goes up the flue. One needs boiler that can keep up with the heat demand on those coldest nights but most of the time it doesn't need to fire that fast.

    So you guys that have run your boiler with properly dried wood for a season or two, how low can you run it without compromising the clean burn?Do they need to run at max to get the best efficiency or will they run well over a range? 10% under rated max? 25%?
    And how do you know that?
  18. Gooserider

    Gooserider Mod Emeritus

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    As I recall, Eric has done some experimenting with putting a firebrick over half the nozzle in his EKO, and had seemingly decent results from doing so. The discussion may be in the "tuning the EKO" thread.

    Gooserider
  19. barnartist

    barnartist Minister of Fire

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    Thanks TCaldwell and Leaddog. I will look up those probes...

    I did not have great results covering one of the nozzils, but even so, that needs to be done before the wood is placed into the boiler. The thinking is probably something more conveniant to adjust automaticly during the burn.
  20. DaveBP

    DaveBP Minister of Fire

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    I forgot about blocking the nozzle with a brick. I was only thinking of primary and secondary air adjustments tuned with varying the draft fan. I'll do some re-search through the past threads. Probably have more questions then.
  21. kabbott

    kabbott Member

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    Here is a video from the taco website that deals with some of the applications of variable speed pumps.

    edit: C&P entire link.
    http://www.taco-hvac.com/en/products/ Variable Speed Variable Voltage "00"<sup>®</sup> Circulator/products.html?current_category=194

    Video at the bottom of page. Shows some applications that may be useful to us wood burners.

    It looks like the variable speed variable voltage 00 circulator would interface nicely with the NFCS. Anyone know the cost of adding the variable speed variable
    voltage control to the taco pumps?
  22. Nofossil

    Nofossil Moderator Emeritus

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    The NFCS turns a standard Taco pump (like the 007) into a variable-speed pump. When all is said and done, four channels of NFCS variable speed works out to about $120 per circulator. With 007 circs going for around $70, that gives you VS circs under $200 each, with all the control logic and remote monitoring / access of the NFCS.
  23. kabbott

    kabbott Member

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    That's why I was wondering how much the 00-VV taco variable speed circulators run. They will take a 0-10V, 2-10V, 0-20mA, or 4-20mA signal. The 4-20mA option
    should be a perfect match for the analog out card. They should be cheaper than the variable speed pumps with control logic onboard however a quick search turned
    up no prices. I doubt it would be cheaper than your hardware but it never hurts to check.

    I know the price for pumps with control and sensor inputs onboard are absurd.

    I have two 00R pumps which could be setup with relays similar two your "poor mans variable speed", Do you have any Idea how these three speed pumps
    react to your variable speed control. Would you have to set them to high speed and adjust down from there?
  24. Nofossil

    Nofossil Moderator Emeritus

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    While the analog inputs on the TS9700 can read 4-20ma, unfortunately the TS9700 analog out is 0-5V, not 4-20ma. Voltage signals don't travel well, and it takes extra circuitry to make 0-5V into 4-20ma. That's what the variable speed breakout box does in my system - it has a little circuit card in it. It also takes a 16V or greater power supply to drive 20ma into most devices that use 4-20ma. I spent a fair amount of time pulling out what little hair I have left trying to find a simple solution. If the TS9700 had 4-20ma output or 0-10V output life would be simpler. Maybe a custom card down the road a bit....

    I'd use 3-speed pumps on high and slow them down, unless I knew that I'd never need full speed.
  25. kabbott

    kabbott Member

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    Oooooops... You are correct. I knew there was a 4-20mA singal involved there somewhere. Thats a bummer, I guess that would have been to easy.
    I very much doubt the taco option would compare in price anyway. Are the variable speed units something you can have ready to go without much
    notice or are you backed up with other systems. I may Email you in the next few weeks about it.

    Did you get a chance to check out the sudo.tar I posted on your forum?
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