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Setpoint met quickly on new Combi boiler

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  • BoilOver2
    BoilOver2 Member Posts: 38
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    I owe you all some decent pictures but to my homeowner's eyes, it is placed as prescribed in the install manual on the system supply side.

    Here's what I have observed with some reasonably close temp values.

    Scenario: No calls for heat for 8-10 hrs and then the first zone calls for heat.

    Setpoint:125
    System sensor at start up: 90

    Boiler ramps immediately to Max percentage (currently 55%)

    Outlet temp might go to 140 - 150 before system side gets to 125, boiler stays at Max allowed fore the whole time

    Boiler then starts to ramp down slowly (slower then I'd expect) when system hits 125, but system temp keeps climbing because the boiler outlet is so high (I think because boiler side flow> system side in this case)

    At 134 system temp, boiler finally gets close to min fire but it's too late and shuts off at system a few seconds later when system sensor hits 135.

    System pump then runs for several minutes which causes the system temp to lower to 115 at which point the boiler fires again. Boiler outlet temps are still pretty hot (125-135 if I'm remembering correctly)

    Boiler again goes close to high fire and the process repeats with short cycling until another zone opened or I "helped" remove heat by opening a hot water faucet to bring the boiler outlet temp down to approximately 125.

    In this work around case, after shutting off the hot water faucet, system would fire if I got it just right at basically min fire and then keep nice long steady cycles (would stay at 10-15% fire rate for up to an hour or two) until a second zone opened in evening.

    Under similar weather, I've worked around the short cycling by disconnecting the system supply. Now the boiler control doesn't let boiler outlet temps get nearly as high and all appears well. ( No short cycling even at evening srartup, house is being warmed)


    Even though it's fairly close, the system can clearly dump enough BTUs to keep the boiler running for long times at min fire even with just the smallest zone open.

    I believe that the control logic may be a little too quick to go to high fire rather than trying to maximize cycle length by starting at min and slowly working is way up when it is clear that the current firing rate will not meet system setpoint in a reasonable time ( But could totally be misunderstanding somewhere). It sounds like some of the systems with more advanced control options would have let me tweak this setting.

    Either way, I think I found something that worked.


    Anyone know of good reasons why I should reconnect the sensor?


    Regarding flow:

    Flows on boiler side is whatever the pump does normally (maybe someone can point me to specs on this?) I don't know if the onboard pump is variable or fixed speed.

    Flow on system side shows 2-3 gallons (as accurate as the alpha 2 indicator is) when that first zone valve opened.

    Flow on boiler side likely exceeds system side in this single zone case.

    Alpha 2 is set to dp2 mode, but I messed with them all and it didn't seem to make much difference.


    Thanks all, you guys are great.
  • DZoro
    DZoro Member Posts: 1,048
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    What is your Max outlet temp. at? Is the max heat fire rate at 15%? Do you know approx. how many ft of tubing is in the small loop? Earlier you mentioned the sensor was close to the Tee's can you strap it on and insulate it farther down the supply line?
  • BoilOver2
    BoilOver2 Member Posts: 38
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    There's a lot going on because it's a tight space, but here are a couple of pictures that show the closely spaced tee and the sensor. Pump flow is towards the bottom out to the rest of the system. Pipe insulation is done because we have little ones that love to touch everything.
  • DZoro
    DZoro Member Posts: 1,048
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    Above the pump is that a tee going down to the pump? Hard to see with the insulation.
  • BoilOver2
    BoilOver2 Member Posts: 38
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    @DZoro

    Tried to take a couple shots, it's not a tee, it elbows around to connect in with the expansion tank
  • DZoro
    DZoro Member Posts: 1,048
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    Thanks for the pictures. Was a bit of a illusion on the piping, the sensor is in a good location. Maybe back up a bit and make sure there is no air in the boiler heat exchanger. Those boilers like to hold/hide air inside them. On the top of the boiler open the relief valve, listen and feel for any air bubbles. Make sure max fire rate is set at 15-20% no higher, at least for now.
  • BoilOver2
    BoilOver2 Member Posts: 38
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    I guess I'm a little confused. Regarding the max rate, I see the boiler rate at up to 35-50% in steady state. Setting it to something low like 15-20% seems like it would not keep up at night. It's mid 30's here when this picture was taken and the rate is 26%. (Not all zones are currently open).

    If things are keeping us warm with no short cycles, is there a need to use the sensor supply? (I don't really understand the advantage of modulating on this sensor versus just using boiler outlet temp-- as I'm reasoning it seems like the worse that could happen is that the system sees slightly lower temps than the one curve prescribes) I feel kinda bad to not use something they took time to install, but I'd rather not keep fighting the short cycles when a single zone was open. If you know of something I'm missing regarding the sensor, I'm super interested in that.


    I am kinda curious about what system temps are being seen though , is there a sensor that I could strap on with a digital read out?
  • DZoro
    DZoro Member Posts: 1,048
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    You mentioned no calls for heat for 8-10 hours. IMO that is because when you do have a call for heat, your water setting is too high. Thus taking the slab on a big roller coaster ride. Slab gets too hot for 8-10 hours then too cold for the rest of the day/evening. That ride needs to be flattened out. That is what the outdoor sensor and the boiler really want also. Would like to see very minimal low water temp rises=minimal slab swings=more constant house temps. Lower the boiler water temps, set up ODR properly. Let the ODR do its thing. You will be amazed how few btu's it will take to do this. This is also a VERY SLOW temperature changing system. Don't expect results in hours, it will take days instead. That's a lot of mass that moves very slowly, slow and steady is the key here.

    Your boiler is certainly capable of going fast, but your system is not capable of going fast.

    D
    Gordyratio
  • BoilOver2
    BoilOver2 Member Posts: 38
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    Hadn't thought of it that way, that makes sense. Do you have suggestions for dialing in the ODR curve? I think it'll be a little trickier than perhaps some environments because 1) fairly large daily outside temp swings (typically 20-30 degrees) 2) many of the zones are areas in the house that pick up a lot of solar gain heat in the winter (when it's sunny, which is most days)

    I think my current parameters are 140F at Design Day and 110F at 70 degrees.

    I'm planning on keeping a little log with different settings tried, how long, etc with observations on what the system did and how the inside responded.
  • DZoro
    DZoro Member Posts: 1,048
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    Slab sensing thermostats, Teckmar 519, no set backs, water temp will be a little experimental I would start with 120* max design temp 65* @ 70* out side air temp.
    I'm still thinking 120 is probably still on the high side, IMO.
    Brewbeer
  • hot_rod
    hot_rod Member Posts: 22,253
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    My thoughts are that a high mass radiant nis not an ideal application for residential where you see often and wide temperature swings. even with ODR the mass becomes hard to manage. Low mass or mid mass thin pours works better from my experience in a climate that does see those weather swings.

    A few weeks back we went from 67f to 17F in a couple days, then back into the high 50's
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • DZoro
    DZoro Member Posts: 1,048
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    @hot rod_7 , I'd agree but the system is already installed. But think it could be managed better with minimal water temp swings. With the solar gain, and all. A fast recovery system could be a mini-spit heat pump would pair up nicely with this. But again keeping slab water temp to its minimum.
  • BoilOver2
    BoilOver2 Member Posts: 38
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    I adjusted the warm day setpoint down from 105 to 70 and I believe the system has been running a much larger percentage of the day with the lower water temps (and I can now confirm that my condensate pump is working properly). Still trying to figure out if I'd like it a little warmer first thing in the morning, but it's a step in the right direction.

    I have noticed that the little bit of chill I was noticing in a couple spots in the evening has improve.

    It's possible that it has been running 24 hrs a day since I made the change, but I need to observe some more to know for sure.

    I'll post back about tuning progress
  • DZoro
    DZoro Member Posts: 1,048
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    Thanks for the report, that change should make a huge difference! Your on the right track, any change now will take a couple of days to settle in. I'll bet that boiler is condensing a lot now ;)
    Slow and steady wins the race.

  • BoilOver2
    BoilOver2 Member Posts: 38
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    Boiler is definitely condensing plenty, at dinner time I've heard the pump turn on each of the last three days.

    After I tried it, I was surprised that the system would stay on so long and that so many zones would stay open. I initially had higher temps because I was concerned about only one zone staying open and short cycling.

    This is a bit of an aside, but...

    What's interesting is the tradeoff between the boiler being more efficient due to lower temps (decreased gas usage ) and the increased electrical usage fom having the system running longer (two pumps and fan) from say 12 hrs a day to 24 at low fire rates. (~200watts x extra 12 hrs a day)

    I bet that part is roughly a push or even a little more with the extended runtime, which gets one back to the question of comfort.

    One other question

    Any other potential downsides to having the system on for longer periods of the day?

    One that comes to mind is that I have Cooper tubing (currently leak free) that I'd like to not have to replace any time soon.

    Any extra wear/tear on that infrastructure by having water flow all the time?


    Thanks y'all. I've been reading this site for almost three years before going ahead with the project and I've learned so much.

    I'm definitely glad I have some "adjustment knobs" to turn as a few things have definitely still surprised me. (Specifically needing every bit of a 10x turndown)
  • SuperJ
    SuperJ Member Posts: 609
    edited December 2018
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    Lochinvar has some ramp settings, so you can limit the firing rate initially. I think there are to 5 steps. This would be worth setting up to avoid the overshoot.

    Since you are high mass you could probably make your turn on offset smaller:
    - currently it looks like it has to drop 30F below setpoint before it starts.
    - Try maybe 5 deg,
    - leave your shutoff offset at 10.

    This means assuming a 120f setpoint, starts at 115f (limit modulation to min fire for 5-10min), shutoff at 130f.
    You could tighten this up until your boiler starts to cycle more than 1 or 2 times an hour.
  • SuperJ
    SuperJ Member Posts: 609
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    Regarding power and wear and tear:
    Modern ECM pumps don't draw much power, especially compared to fans. Often it's less than 50watts per pump, might be more like 50-100watts per pumps for a non ecm.
    I wouldn't worry about wear and tear with wet rotors.

    My Grundfos Alpha is usually running 9-12watts constantly but I have a variable flow setup so it's often only moving 1-2gpm.
  • Gordy
    Gordy Member Posts: 9,546
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    So long as the velocity of the flow rate isnt unrealistic the tubing should be fine. I sold a house with a mile of copper tubing for radiant built in 52. Leak free still. That’s 66 years old.
  • Gordy
    Gordy Member Posts: 9,546
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    For electrical consumption this is why zone valves are better.
  • BoilOver2
    BoilOver2 Member Posts: 38
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    @Gordy

    I believe the velocity is reasonable, just one alpha2 pumping 4 zones in a fairly large home
  • BoilOver2
    BoilOver2 Member Posts: 38
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    > @SuperJ said:
    > Lochinvar has some ramp settings, so you can limit the firing rate initially. I think there are to 5 steps. This would be worth setting up to avoid the overshoot.
    >
    > Since you are high mass you could probably make your turn on offset smaller:
    > - currently it looks like it has to drop 30F below setpoint before it starts.
    > - Try maybe 5 deg,
    > - leave your shutoff offset at 10.
    >
    > This means assuming a 120f setpoint, starts at 115f (limit modulation to min fire for 5-10min), shutoff at 130f.
    > You could tighten this up until your boiler starts to cycle more than 1 or 2 times an hour.


    Missed this one previously...

    Good idea, though the Noble doesn't have nearly as many control options as models such as the Knight. Perhaps to be able to offer it at a lower price?

    (Unless there's a secret menu some place)
  • Leon82
    Leon82 Member Posts: 684
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    > (Unless there's a secret menu some place)
    >

    There is an installer menu with a password. The manual has it in it. I'm not Sure if it's is the same or different for each model of boiler