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  1. #1
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    Electric Boiler Control

    I have been retrofitting this building, for about a month and now its down to the boiler. Its driving me a little crazy, it has a kele sequencer and 0-10vdc signal from a unt controller staging the sequencer. The old control was to reset the HWST from OSA, I have changed that to Space demand, and OSA Lockout. The problem is that the boiler is a very large electric boiler,and is very difficult to control with a 8 stage sequencer chasing setpoint all over, and overshooting bad, this reset was a function of the UNT by others. I have thoughts of adding a return sensor, and trying to control from that, or scraping PID control and coming up with staging in the frontend. I was wondering what approach you guys would take??. Any ideas would be much appreciated.

  2. #2
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    I did a PI* on the last one I did (from memory), sounds like the same setup. I will see if I can find the PID settings - took awhile to get it tuned correctly. Made it worse that the maintenance guy kept overriding the reset setpoints....and manually forcing it on to a fixed setting....

    *BTW - you're still in Western Washington right? Just making sure you're not taking over my old building! LOL... **Never mind read UNT...
    Last edited by crab master; 12-19-2011 at 09:59 PM. Reason: *PI not PID *BTW **
    "How it can be considered "Open" is beyond me. Calling it "voyeur-ed" would be more accurate." pka LeroyMac, SkyIsBlue, fka Freddy-B, Mongo, IndyBlue
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  3. #3
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    Yep still in the rainy side of Wa. I might also explain that when the old 135 OHM control was removed, that several stages were joined together to except new 8 output sequencer which doesn't help matters. Also would like to add that today, I played with controlling the output from the frontend.This is a FX-60 using that loop ,not so much luck!!!. By the way Crab, I think this is your building!!. Will you come fix this???

  4. #4
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    I was on the Eastern side, so not mine...
    When I get home tonight/tomorrow morning I will try to look up those settings for you - granted TAC controls, but should get you in the ballpark...

  5. #5
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    >that several stages were joined together to except new 8 output sequencer which doesn't help matters.

    You can add another Kele card and gang them together such that 0-10v is now 16 outs or whatever is needed. That may help. IMHO return water temp control is a mess and nothing but problems.
    Propagating the formula. http://www.noagendashow.com/

  6. #6
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    I don't think this is the latest, I will keep searching as I know I have updated parameters somewhere....but I see I used 2 separate Kele output cards 0-100% were stages 1-4 and 100%-200% were stages 5-8.

    I assume I started out -
    control interval - 1 second
    Gain - 10
    Integral - 5
    Deadzone - 1 deg F
    Stroke - 1800 seconds
    Max Output - 200%

  7. #7
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    The more I think about this, this was definitely the earliest version - don't use those numbers as I know I used a much less stroke time, a slow gain and an aggressive integral...just can't find the latest parameters...

  8. #8
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    Hey guys, thanks for all the input. I have to get back to the site, I do like the idea of adding another sequencer. I think that boiler is to large, and with the elements wired as such it heats the water very fast. So adding more stages, I think will be my route. Crab have friends in Eastern WA, I visit there a lot Tri-Cities Area.

  9. #9
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    IMHO in most situations controlling a boiler to supply temp will leave you chasing your own tail. Try looking at return temp. I bet things will settle down.
    IV IV IX

    use your head for something other than a hat rack.......Gerry


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  10. #10
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    Quote Originally Posted by viceman View Post
    IMHO in most situations controlling a boiler to supply temp will leave you chasing your own tail. Try looking at return temp. I bet things will settle down.
    Interesting - While it can be a bit of a challenge, but I prefer supply temp control as I've yet to see a boiler trip on too high of a return temp.

    Yep one leads to the other, but supply temp give much quicker feedback as to what the boiler is doing. Also such sequences can be written in to cover higher supply temps with return temp control, but then it tends to get convoluted....
    "How it can be considered "Open" is beyond me. Calling it "voyeur-ed" would be more accurate." pka LeroyMac, SkyIsBlue, fka Freddy-B, Mongo, IndyBlue
    BIG Government = More Dependents
    "Any 'standard' would be great if it didn't get bastardised by corporate self interest." MatrixTransform
    My 5 yr old son "Dad, Siri is not very smart when there's no internet."


  11. #11
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    Quote Originally Posted by crab master View Post
    Interesting - While it can be a bit of a challenge, but I prefer supply temp control as I've yet to see a boiler trip on too high of a return temp.

    Yep one leads to the other, but supply temp give much quicker feedback as to what the boiler is doing. Also such sequences can be written in to cover higher supply temps with return temp control, but then it tends to get convoluted....
    the boiler should have two limits. one manual reset
    and the other is a operating control. the manual reset will be set above the operating control. the operating control will cycle the boiler before the manual reset high limit trips. in my experience controlling to supply temp will cause excessive cycling of the boiler. as soon as the boiler stages up the supply temp will climb quickly and your control will begin staging back.that being said i don't see to many electric boilers around my area. in my service days i have seen boilers sooted up or electric staging contactors burned from excessive cycling.
    IV IV IX

    use your head for something other than a hat rack.......Gerry


    We have freedom because somebody fought for it.
    We keep it because we are willing to fight for it.
    We lose it because we are not willing to fight for it.

  12. #12
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    Agreed, but I've seen too many boilers that end up operating off the operating control top end, not the controls setpoints. I prefer to not hit the operating control at all. It makes me do a better job with tuning the PID, then it gives me an 'operating' safety and I set the hi limit above that.

  13. #13
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    Hey guys, a little update I ordered another 8 stage kele board today and will be installing it next week. I will be making 16 stages instead of 8 to get more staging, and also there is no return sensor so it will stay off of supply water temp control. I agree that it stay's and controls off of the high end of the operating control now, and the goal is to get it to control at setpoint. This boiler draws 710 Amps when all stages are on,and this is one of those energy projects so if I get this thing to control, this board will pay itself back in no time flat.

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