Lochinvar Knight 085 boiler temperature settings

Discussion in 'Boiler Forum' started by Ki23, Nov 15, 2019.

  1. Ki23

    Ki23 New Member

    Joined:
    Mar 14, 2019
    Location:
    Rhode Island
    Good morning,
    This is the first time it's been below freezing since installing my Lochinvar Knight 085 boiler. Last night it was about 30 degrees outside here in Rhode Island my boiler was heating the house with 132 degree water. Whenever my thermostat dropped below 67 (where i keep it 24/7) the boiler kicks on and runs for about 20-25 minutes until it reaches 67. The zone would keep the temperature for about 40 minutes and then turn the boiler back on.

    The boiler runs at 100% for a minute or two, then works it way down to 10% and stays there for a few minutes then moves back up and hovers around 30-40% for the remaining time. Is this normal?

    I just want to make sure I have my temperature setting correct because it seems like my boiler is running far longer (which I know is a good thing) than my old cast iron. I'm just concerned about the gas bill with the boiler running so much.
     
  2. Dana

    Dana In the trades

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    Jan 14, 2009
    Location:
    01609
    It sounds like the outdoor reset curve is set too high. When it's 30F outside it shouldn't be burning for 20-5 minutes at 30-40%, then off for 4o minutes, which is about a 35% duty cycle. With the reset curve dialed in it should be running a 90-100% duty cycle at 10-15% of max fire. The burst of 100% firing rate is due to the slug of now tepid return water from the high volume radiation at the beginning of the cycle after cooling off for 40 minutes. A thermostat with a narrower (or programmable) dead-band would shorten the on/off times and reduce the amount of 100% firing rate burn, but the low duty cycle would remain the same.

    With 132F out, 122F (?) entering water temp at the boiler and 30-40% firing rate it's only delivering about 90% raw combustion efficiency.

    At 132F out/122F back, and average water temp (AWT ) of 127F , the emittance of the radiators is about 65 BTU/hr per square foot EDR. If it's only running a 35% duty cycle it only needs to be emitting 0.35 x 65 = ~25 BTU/hr per square foot, which happens at an AWT of about 105-110F.

    Bumping the curve down to where it's delivering 110F out/105F back and 10-15% of max firing rate at nearly 100% duty cycle to deliver the same heat per hour it would be closer to 95% efficiency:

    [​IMG]
    [​IMG]
     
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  4. Ki23

    Ki23 New Member

    Joined:
    Mar 14, 2019
    Location:
    Rhode Island
    My only issue is that I don't seem to have reliable heat when I have my temperatures set that low (anything under 125 is shaky at best). My fin baseboards are from the late 70s and probably aren't that efficient. I will post my setting when I get back home to make sure I'm speaking realistically.

    Also, I never really get a big difference between my outlet and inlet temperatures. Is something wrong with that? I've attached some photos of my screen if that helps.
     

    Attached Files:

  5. Ki23

    Ki23 New Member

    Joined:
    Mar 14, 2019
    Location:
    Rhode Island
    actually found a note on my phone with the settings, sorry about that. my settings are:

    Space heat 1 setpoint - 132F
    SH1 low outdoor temp - 10F
    SH1 setpt @ low outdoor temp - 135F
    SH1 high outdoor temp - 65F
    SH1 setpt @ high outdoor temp - 120

    DHW tank setpt - 140F
    DHW boiler setpt - 175F


    By reading your above post, I imagine I have to change the "SH1 setpt @ low outdoor temp" ?
     
  6. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    The very low delta-T between inlet and outlet is usually a symptom of excessive flow (on the primary loop, if plumbed primary/secondary.) If it's plumbed direct (one pump, no primary/secondary)

    The fact that your curve has a 120F @+65F outside and 135F @ +10F means it isn't really changing much over large changes in outdoor temperature. Older fin-tube (and even some newer) can be very non-linear at 120F, which is why it may seem unreliable at output temps below 125F. At warmer outdoor temps the non-linearity doesn't matter as much. But go ahead and set SH1 setpt @ low outdoor temp to 125F @ +10F, see if it keeps up.

    The 20+ minute burns and 1 burn per hour is fine, but it would be better for efficiency if the entering water temp were lower. What pump(s) are currently on the system, and if multi-speed, what settings? And is it pumped direct, or primary/secondary? As long a the boiler is getting it's minimum flow rate under all operating conditions it's fine to back off the flow to achieve a higher delta-T. Ideally you could get a 10F delta out of it and still have reasonable room-to-room temperature differences on the loop, but even 5F would make a measurable difference in efficiency when the output temp is ~130F, since the combustion efficiency at an entering water temp of 128-129F is about 2% lower than it is at 125F. With an output of 125F the return water temp is guaranteed to be in the condensing zone even with a small delta-T.

    Operating with a tighter dead-band thermostat yielding 5-10 minute burns and 2-4 burns per hour would still be fine, and would probably provide better comfort.
     
  7. Ki23

    Ki23 New Member

    Joined:
    Mar 14, 2019
    Location:
    Rhode Island
    Ok I will change my SH1 setpt @ low outdoor temp to 125F @ +10F . Tonight will be a decent test as it's going to be around 20F.

    I am not entirely sure if it's plumbed primary/secondary. I'm doing my best to learn as I go and I have already learned a ton from this site, so thank you. I posted some pictures of my setup that may help. I have the grundfos variable speed pump (the black one) and I have three zone pumps (the green 007e's also variable I believe)

    I'm not sure how to "back off on the flow" I don't see any setting for that in boiler menu.

    As far as deadband thermostats I use the ecobees on my zones.
     

    Attached Files:

  8. Dana

    Dana In the trades

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    It looks like the black pump in the picture is driving the primary loop, with the closely spaced tees a foot or so above the pump providing the hydraulic separation between the secondary( radiation loop) flows and the primary (boiler loop) flow. The other picture shows a few Taco 007e driving the secondary loops:

    [​IMG]

    [​IMG]

    Schematically your system looks a bit like this:

    [​IMG]

    But the Lochinvar fire tube boilers do NOT have a "... high head loss characteristic" like the boiler in the schematic, and can probably handle the full radiation flow pumping direct (no hydraulic separator), if the pumps are sized correctly and you simply do the math.

    Backing off the flow is not a boiler parameter setting- it's a pump setting or valve adjustment issue. What model is the primary pump (the black one)? If multi-speed, what speed is it set to?

    For experimental purposes one could use either one of the ball valves just below the hydraulic separator to throttle back the flow on the primary, but it's not clear if that will fully do the trick, especially if the radiation is being over-pumped. Take some temperature readings to determine the delta-T of each of the radiation loops (separately).
     
  9. Ki23

    Ki23 New Member

    Joined:
    Mar 14, 2019
    Location:
    Rhode Island
    The pump main pump is a grundfos that came with the boiler. It’s variable speed so I think the speed changes as needed?

    I have been running 122-126 degree water for a few days now and the house is keeping up. The return temps have been under 125 so I’m happy. I’ve also attached a comparison from my old cast iron to the lochinvar for the month of October. Granted, it may have been colder last year but it’s still pretty impressive.
     

    Attached Files:

  10. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    Plotting the therms against average temperature during the billing periods is a better comparison than calendar time. Some September/October seasons are quite a bit colder than others.

    What model Grundfos, and what is it set to? Even the "Auto Adapt" modes on the Alpha2 have different settings, and can be set to a fixed speed if needed/desired:

    [​IMG]
     
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