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Topping off the tank

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by VeggieFarmer, Oct 4, 2008.

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  1. VeggieFarmer

    VeggieFarmer New Member

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    1) What sort of storage-tank temperatures are people achieving? I've read talk of 170 to 175 in some other posts but have only managed 162 F myself, after a half dozen fires. I'm hoping to reach 170 after I insulate the boiler-to-tank pipes (25 foot run, losing 6 to 8 degrees along the way.) Any other tricks out there?

    2) Any consensus on how much to push the gasifier once the fan starts modulating? On the one hand, having the wood smolder between fan bursts seems inefficient, but on the other, once the boiler is hot, it seems a shame not to try to push the storage temp. as high as possible.

    3) Any simple control method for preventing the boiler circulator from pulling heat back out of the storage tank as the fire goes out? In the case of the EKO-40, the circulator comes on at 60 C and stays on as long as the water temperature stays above 60 C. If the storage tank has been pushed to 72 C, the circ. will pump heat out of the tank for hours until either the fuel light come on or I remember to turn off the fan/power. Seems like there ought to be a better way.

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  2. Nofossil

    Nofossil Moderator Emeritus

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    Good questions. This is what happens when theories meet the real world. I'm assuming that you have a heat exchanger in the system - perhaps an unpressurized tank? I have the exact same issues, although I've reached 170 a few times. Usually, I end with a tank top closer to 160. I didn't appreciate the heat exchanger issue when I built the system. As the storage gets closer to the boiler output temp, the heat exchanger's effective heat transfer capacity drops off pretty dramatically. That's the main reason I now recommend pressurized storage where practical.

    I tend to build my fires in the late afternoon or evening. Part of my thought is that when the storage starts to get hot, it would be helpful if the house called for heat once in a while. That's more likely when it's dark and cold outside.

    Idling is really bad when you're in the earlier phases of a burn - when a lot of wood gas is being produced and moisture is being driven out of the wood. Later in the burn, you're mostly oxidizing charcoal. The efficiency hit for idling is pretty minimal then, and I expect a bit of fan cycling in the last hour or so of a burn.

    As to your last question, the answer is 'no', at least with my limited skills. I've never found a simple solution to that problem. You need to be able to compare two temperatures and make a control decision based on the difference. I ended up with a computer to do that for me.

    The only thing I can think of that falls into 'simple' would be to put the EKO on a timer. It would take some experimentation, but perhaps you could estimate closely enough so that you could have it shut down somewhere close to the right time.
  3. steam man

    steam man Minister of Fire

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    [3) Any simple control method for preventing the boiler circulator from pulling heat back out of the storage tank as the fire goes out? In the case of the EKO-40, the circulator comes on at 60 C and stays on as long as the water temperature stays above 60 C. If the storage tank has been pushed to 72 C, the circ. will pump heat out of the tank for hours until either the fuel light come on or I remember to turn off the fan/power. Seems like there ought to be a better way.[/quote]

    The solution I use is what nofossil mentioned:comparing two temperatures. I only have a wood stove with heat exchangers right now but I use a solar differential controller to compare the heat at the wood stove exchangers to the storage tank. I use about a 20 deg start and shut it down at about 5 deg differential. This way the boiler has to be higher than the storage for the circ to run. If you wired it in series with your 60c controller it should work fine. Mine does. You can probably get what you need for under 150 bucks.

    Mike
  4. jebatty

    jebatty Minister of Fire

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    Hitting the 160-165 is pretty easy. I can get to the 175 area with cycling of the draft fan, which works best as nofo says towards the end of the burn, definitely not the early part. My plate hx on the high end will achieve just about a 5* temp differential between water in from boiler and temp out to storage. The main issue is that the Tarm draft fan shuts down at about 185 and that is as high as it can be set. If it could be set higher, then higher temps could be delivered to storage. However, I honestly don't need higher than 165.

    I use a timer. With a full load of pine (my primary wood), 8 hours on the timer is about right. The load is usually done burning in about 6 hours, and the extra time is just to make sure. If it did shut down a little early, all that would be left would be charcoal embers and that would not pose any problem. A little issue here, though, too. The timer I have been using is an electronic digital timer, and if we have a power glitch, it shuts off. Not good if it shut down 1 hour into the burn. I will be getting a mechanical timer.
  5. Reggie Dunlap

    Reggie Dunlap Feeling the Heat

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    Steam Man- I have that problem. As the boiler comes down in temp it cools off the tank until the aquistat shuts off the circulator. I manually turn up the aquistat as the fire is dying to prevent this, but you have to be there.

    I don't know of any control that will work.
  6. steam man

    steam man Minister of Fire

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    Simply put, the circ stays on because of the heat coming back from the storage tank. It doesn't see a positve heat output from the boiler and doesn't know the difference. I use Tekmar, Thermomax, and Resol controllers. I would suggest maybe a simple Tekmar differential controller, maybe a model 155, http://www.tekmarcontrols.com/prod/155.shtml. It uses thermisters for sensing. Obviously there are others out there that will work.

    Mike
  7. deerefanatic

    deerefanatic Minister of Fire

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    Hey Nofo, I get 172 at the top and 156 out the bottom with my flat plate routinely. :) Course, 70 plate flat plates can do that for you.... And I'm getting plenty of idling at the end (about 40% on time, and 60% off time for the stove fans)
  8. Nofossil

    Nofossil Moderator Emeritus

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    I recently hit a tank top temp of 178, but the middle and bottom were only 162 and 160 respectively. Lots of idling is the price to pay in trying to get maximum tank temp through a heat exchanger.
  9. pybyr

    pybyr Minister of Fire

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    I'm still in the spot of acquiring and assembling parts (with the zeal of a man who cancelled his oil deliveries and does not want to freeze or starve)-- but

    with a tank that is not temp-limited like the liner types-

    and with a 150mbtu boiler,

    and with a 5"x12"x70 plate HX, and,

    with 4 way valves for counterflow across both sides of the plate HX, and,

    once I get the initial shakedown bugs out of my system,

    I aim to eventually "put the boots to" my tank, in the extreme, in hopes of pushing the tank as close as I can to boil without either hitting actual boil in the tank or getting cavitation in the circulator on the unpressurized side of things

    time will tell, and suggestions are welcomed!
  10. WoodNotOil

    WoodNotOil Minister of Fire

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    I am glad to see I am not the only one getting a lot of idling near the top end. My experience is similar to deerefanatics through my flat plate hx (but I only have 30 plates). I get the temp up between 160-169 usually. I haven't crossed over the 170 mark yet and don't intend to until I am certain my top tank temp reading is accurate. I don't want to exceed the limits of my EPDM liner. I end up with a stratification of 18-20*. I like seeing others data for comparison.
  11. Blevesque

    Blevesque Member

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    I'll second the tekmar control. I just picked up the 156, although its not installed yet I think it's going to make my system operate much better. Right now I have my Tekmar 374 reset control jumped out to run the wood boiler pump all the time. If i didn't the 374 shuts everything done when there is no call for heat. When the 156 is hooked up this will keep the wood boiler pump running to try and achieve the diff. in the tank until the fire dies down and shuts the pump off. Then when there a call from the house the 374 will call the pump back on. Last night I was able to get 186 in the tanks. Next I have to work on someway to shut the combustion fan off when the fire starts to die. If anyone has a cheap solution other then a timer switch let me know.
  12. free75degrees

    free75degrees New Member

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    I am getting to 175 at the top with no idling, which I am thrilled with. I was a little worried about my HX, because it is a configuration that isn't exactly like anybody else's who I have heard of. I have 4 coils of 1/2" copper in parallel, each one is about 85 feet total. I just got all three of my sensors working (Dallas semiconductor 1 wire sensors interfaced to a ts7800 arm SBC). The highest energy storage I have achieved is 176 at the top, 165 in the middle and 145 at the bottom. I confirmed the top temp with a mercury lab thermometer. Now that I have all 3 sensors working I plan to push the limit to see how much energy can cram in.

    For the 3rd question, I don't know of a simple solution. I am planning on doing something lik nofo where he compares the boiler output temp to the tank temps to decide whether to keep charging the tank.
  13. mpilihp

    mpilihp Feeling the Heat

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    The solution I use is what nofossil mentioned:comparing two temperatures. I only have a wood stove with heat exchangers right now but I use a solar differential controller to compare the heat at the wood stove exchangers to the storage tank. I use about a 20 deg start and shut it down at about 5 deg differential. This way the boiler has to be higher than the storage for the circ to run. If you wired it in series with your 60c controller it should work fine. Mine does. You can probably get what you need for under 150 bucks.

    Mike[/quote]

    Hi Mike could you explain how the solar differential controller works? Where are the sensors and how its configured? Sorry im new to the concept and I cant wrap my mind around it. Your saying the boiler output has to be higher than the storage for the circ to run. Is this circ the wood boiler circ or one just for circulating to the storage? IE I have a aqusat on the wood boiler that at 170D to start and run, with the Diff set to 5 which I think means it will shut off at 165. IE start running at 170 and above and stop running at 165 deg. Are you putting a sensor on the output pipe of the wood boiler and as long as the temp of the water in the pipe there is hotter than the storage temp it will allow the circ to run? so would I put this in series with the aqustat on my wood boiler that activates the wood boiler circulator?? Or would it just replace this aqustat?

    Sorry for the confusing questions..

    ~ Phil
  14. Hansson

    Hansson Feeling the Heat

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    I can reach 220 in the top of the tank and 203 in the bottom of the tank.
    My boiler don't have the modulating fan thing. The boiler stops the fan when the temp is to high

    I now some people here are modifying the temp sensors on the Orlan Super to reach higher temperatures.
  15. steam man

    steam man Minister of Fire

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    Hi Mike could you explain how the solar differential controller works? Where are the sensors and how its configured? Sorry im new to the concept and I cant wrap my mind around it. Your saying the boiler output has to be higher than the storage for the circ to run. Is this circ the wood boiler circ or one just for circulating to the storage? IE I have a aqusat on the wood boiler that at 170D to start and run, with the Diff set to 5 which I think means it will shut off at 165. IE start running at 170 and above and stop running at 165 deg. Are you putting a sensor on the output pipe of the wood boiler and as long as the temp of the water in the pipe there is hotter than the storage temp it will allow the circ to run? so would I put this in series with the aqustat on my wood boiler that activates the wood boiler circulator?? Or would it just replace this aqustat?

    Sorry for the confusing questions..

    ~ Phil[/quote]

    This thread has been around. No problem. The problem with the aquastat is that it only sees the boiler temp. On at 170-of at 165. Say you heated the tank up during a cycle to above 165. As long as it stays there it just keeps circulating back to the boiler. If the boiler is not generating a positive heat output, it will stay at whatever temperature water the tank is sending to it until the water cools below 165 and the circ shuts off. Now the tank has given up its heat to the boiler. If you use a differential controller to measure both the boiler and the tank, you can shut the pump off while it still has a slightly positive heat output which is before the tank starts to give up heat to the boiler. The Tekmar 155 is pricey but there are other differential controllers that may work and are are used for wood boilers. A good controller can be programmed for minimum boiler temp, maximum tank temp, and other variables. It can just replace the aquastat. Note that they are not used for safety shutdown devices so that has be a consideration when installing. In that case a series wiring may be all that is needed. The sensors need to be where you can measure accurately with a good response. Probably at the outlet pipe close to the boiler. The tank temp most likely near the lower part inside a well.
    I know mine works flawlessly.

    Mike
  16. NHFarmer

    NHFarmer Feeling the Heat

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    I have built the same HX as Free75.With the Tarm Solo 40 I have been able to get the top of the tank to 170* with no problem.So far,one burn per day is all I need to meet my needs.I am sure it will be different once it really gets cold,but so far it has been working great!!!!
  17. Nofossil

    Nofossil Moderator Emeritus

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    I only ever do one burn per day. On cold days, though, the burn could be 12 hours.
  18. NHFarmer

    NHFarmer Feeling the Heat

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    Boy would that be nice
  19. free75degrees

    free75degrees New Member

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    How many refills do you need to keep it going 12 hours? I was a bit suprised at how quickly I go through 1 full load of wood - about 3 hours at full gasification. Is this normal? Should I be reducing my primary air?
  20. NHFarmer

    NHFarmer Feeling the Heat

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    Free75 I also go thru a full load in about 4 hours if I don't top it off half way into the burn.I do cut my wood 16"long and that does leave some empty space in the firebox.I was thinking that was why I had such short burn times
  21. chuck172

    chuck172 Minister of Fire

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    Has anyone come up with another solution to prevent the wood boiler circulator from removing heat from storage as the fire dies down? I believe so far the only options are a timer, a differential control, manually turning up the aquastat.
  22. pybyr

    pybyr Minister of Fire

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    I am hoping- when I get that far- to put a thermal switch on the stack, so that once the fire goes out, that thermal switch, by way of a relay, kills power to the boiler's blower and the boiler's circulators. My plan is to have a temporary-on timer with a push-button switch to briefly override the temp switch for when the fire is first lit and getting started.
  23. chuck172

    chuck172 Minister of Fire

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    I'd think you would need more precise control. If the storage tank is 180*, the controller should stop circulation to the tank if under that temp. But in my case still feed zones which call for heat till I hit a low limit of about 140*
  24. Nofossil

    Nofossil Moderator Emeritus

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    I get about 5 hours on a really full load, plus another hour or two of cool down where there's still heat being generated. I'll refill every three or four hours as needed. On a typical winter day I'll do an initial load that's good for an hour or so, then a three hour load, and then one last three hour load at bed time.

    My control system is differential on steroids. I'll actually select loads and circulator speed to keep the boiler outlet temp in the range that I need. As the storage tank gets hot, I'll slow the circ to raise the boiler outlet.
  25. mwk1000

    mwk1000 Member

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    This has been an excellent place to learn. I am glad I found it before I finished my install. I would never have caught the reverse heat drain. Until after I was done of course ! I will be adding the tekmar to my design. My plans look similar to much that I have seen here. I built an 8x6x5 ( Inside dimensions ) tank in my basement with the boiler in the garage. I have a HX 5x12-70 with a pump each on the tank and the boiler side. I will add the teckmar to the two input sensors on the HX and when the tank and boiler temps flip ( or get to close ) I can shut down the tank side pump. I'll leaved the boiler circuit alone. It will pump but it should cool down normally without stealing from the tank

    This tip.

    The paraffin wax on top for evaporation I liked.

    The stability of polystyrene ( That one may cost me some rework since that is what I used ) I have a couple of chunks of my materials in a boiling pot for the last 12 hours to see how they do at 190 and I'm hoping for the best. FYI the pink home depot stuff expanded and got soft at 212 but the blue was a MUCH better. It did distort but only slightly at boiling for 1 hour. So far no distortion of either at 190. I'm torn since 12 hours does not = 10 years. But I was planning on a 175 tank temp 180 tops if I could hit it. I may loose some capacity by lowering the temps, There is OSB over the Insulation so if the boiling blocks look ok tonight I'm going to run with it.

    Some of the code clearances -- I'm in Michigan and someone mentioned an 18" off the floor requirement.

    I was planning 1 burn per day based on my BtU calcs for the house and tank and boiler. The discussions here make me think it might happed. The house is 84,000 BTU / hr at -15 so I figured on the tank for 16 Hours.

    Thanks to all for the comments you have saved me some future grief I am sure.

    my stuff:

    EKO 60, DIY tank at 1500 usable gal 60 foot run of 1" Pex-al-pex to garage based boiler. two zones using an air exchanger in existing furnaces draw from tank side of HX. Tank is done, Chimney is done, Line set is run and insulated. Setting Boiler and plumbing to lineset and chimney is next ....
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