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KHN startup first report.

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  • Leon82
    Leon82 Member Posts: 684
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    Lowering the fan speed would lower output because less gas will enter the combustion chamber maintain the air fuel ratio.



    There can be a situation where the boiler can suck the line below 4 inch of water, or what ever the cut off is, from an underside gas line. Limiting fan speed will prevent it from doing this as a bandaide.

    My tank less water heater says this in the manual. It even allows you to raise the minimum speed as well.
  • keyote
    keyote Member Posts: 659
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    a square makes sense from behavior the fan micro mod i describe might be just the very beginning of modulating before its able to register as a percent of modulating. It does a great job of anticipating so far its never had to modulate more than 5% for the DHW and that only happens in the last minute
  • Gordy
    Gordy Member Posts: 9,546
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    Hatterasguy said:

    Gordy said:

    Hatterasguy said:

    Gordy said:



    I want to address the fan speed limit for DHW so that there is no confusion about it.

    In theory, this parameter is absolutely not required, If the indirect cannot accept the full output of the boiler, the boiler simply modulates down...............just like it does with CH.

    The only reason it is present is under the condition where the indirect can only accept a fraction of the capability of the boiler. Under this circumstance, the boiler might climb to HL before it has sufficient time to modulate down. With a fan speed limit, this problem is eliminated.

    Under any reasonable scenario where the boiler is not 200K with a small indirect, this parameter is most definitely not required.

    It is no different than the CH limit. A bandaid for the control system to prevent a HL trip. In theory, the boiler shouldn't require it.

    Then why is it a parameter to be used specifically for DHW?

    How does fan speed relate to the burner output?

    What is the goal of a DHW call in priority?


    CH has a similar parameter for the same reason..........prevent a HL trip,

    Reduce fan speed and the burner output reduces with it. It's not a linear relationship, however. My guess is that it is a square function.

    Clearly, the goal of a DHW call in priority is to end the call ASAP.

    That's my point Hat. End the call asap. the fan speed gives a little fudge. However with the modulation there is no need to treat it the same as CH. I'm sure that is how Lochinvar sees it. Satisfy the DHW demand when in priority mode asap. Then the CH can pick up where it left off as soon as possible. CH demands usually fall in the same time frame as a DHW call in the early morning when OAT is inherently lowest.
  • keyote
    keyote Member Posts: 659
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    before i set up DHW I talked to them because of Boons problems. Dont think I gopt their best tech but for what its worth he said it doesnt modulate in DHW the way it does in CH. In other words in CH it mods to the SWT SP but in dhw it mods to the tank temp. Now this doesnt quite Jibe with my bucket analysis. But I think his point was its trying to satisfy the call asap, that said it DEFINITELY never crossed my 185 setting whats more it has never hit the 185 until the last 2 minutes.
    BTW guys just posted the first ch adventure in another discussion

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