Need help dialing in a navien ncb 240e

Discussion in 'Boiler Forum' started by seemarc, Jan 9, 2017.

  1. seemarc

    seemarc New Member

    Joined:
    Jan 9, 2017
    Location:
    New Jersey
    This is my first winter with my Navien ncb-240e and I need your help.

    I have the house set to 68 degrees and it is maintain that temperature. However

    It seems to be running most of the time. I called Navien tech support and he told me to raise the outgoing temp from 140f to 150f and if that didn’t help I would need to have a professional call on my behalf.
    I haven't noticed a difference with the increase of temperature so i was hoping someone here can help.


    I searched the site and came up with setting the k factor but I think that was for the previous model. I also found that maybe having the outdoor temperature sensor would help.

    Any help making this work more efficiently for me is greatly appreciated.

    My house is 1700sf and 70% recessed radiators and 30% baseboard heat.

    I replace the 60 year old boiler with this navien unit 5 months ago. I do not know the btu of old boiler but I know it was “oversized”
     
  2. NY_Rob

    NY_Rob Member

    Joined:
    Feb 23, 2016
    Location:
    New York
    Mod-cons are supposed to run "most of the time" unlike cast iron boilers that cycle.
    In theory- if the boiler is sized correctly for your home/radiators and the outdoor reset curve is setup properly the boiler should run 20+ hrs per day just keeping up with your homes heatloss without overshooting it.


    FWIW- unless your 1700SqFt home is un-insulated... at 118K BTU's your boiler is way oversized.
    I live out on LI, so our weather is similar to yours- my 1700 SqFt house (same as yours) is 1960's construction and it keeps toasty warm with a 80K BTU Mod-con which I have limited to 60K BTU's firing rate. Even the last couple of days with single digit morning temps it has no problem keeping the house warm.

    Is your boiler heating your home adequately?
    Are you using night time setback?

    What are the four values you're using for the reset curve?
    Outdoor low temp:
    Outdoor high temp:
    SWT high temp:
    SWT low temp:
     
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  4. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    If it's keeping the place warm and running super-long burn cycles, and running with return-water temps less than 125F out you're in the Goldilocks zone- don't steal defeat from the jaws of victory!

    Almost all Navien's are plumbed primary/secondary, and won't be delivering 90%+ efficiency until the output temp is under 130F, so if there's any tweaking to be done, it's to move the temperatures LOWER, not higher.

    A typical older but insulated 1700' house 2x4 framed house with clear-glass double panes would come in with a heat load in the ~25,000 BTU/hr (+/-5000) range at the typical 10-15F NJ outside design temps. So with ~17,000 BTU/hr out at minimum fire in condensing mode the thing should be running nearly 100% of the time whenever the temperature is below 30F or so, assuming a steady average indoor temp of 70F.

    With a modulating condensing boiler there is very little, and sometimes negative fuel savings to using overnight setbacks. To achieve maximum condensing efficiency requires the lowest water temperatures that still keep up, but unless the boiler has a "boost" mode it won't have reasonable recovery times from setback unless you raise the water temperature, which lowers the combustion efficiency. Read this primer to figure out how that works. By measuring up the radiation and estimating the whole-house load it's possible to come pretty close to nailing the ideal water temperatures and outdoor reset curve with just the napkin math.
     
  5. seemarc

    seemarc New Member

    Joined:
    Jan 9, 2017
    Location:
    New Jersey
    Thank you both for your response!

    I didn't know its supposed to be running up to 20 hours a day. It has been keeping the temperature at 68 I was just comparing it to the boiler I replaced which cycled much more frequently . I don't do a night time set back. I do have a nest thermostat that goes into eco mode that senses nobodies home and drops to 65. There is rarely nobody home here so that doesn't happen very often. Should I turn that feature off?

    Should I reset the outgoing temperature to 140 degrees before I changed it? The house was built in 1950 and is decently insulated. But has original windows with storm windows installed.

    I was told that the unit was oversized but was ok because it would "self modulate"and act like a smaller unit if need be. Now I think it wont be as efficient as the lower btu model? Im still working on my manual J number that Dana suggested to do....I couldn't find a simple program. Im not good at napkin math!

    How do I know what reset curve the boiler is set at?
    It looks like the outside temp is set at 22? Is that celsius or fahrenheit?
    I don't know what swt refers to but theses are all the numbers.

    A 118
    B 93
    C 102
    D 74
    E 0
    F 22
    G ---
    H 0
    I 12.6
     
  6. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    A typical tight 1950s 2x4 rancher with clear glass storms over wood-sashed double-hungs will usually run between 15-20 BTU/hr per square foot of conditioned space @ 0F, depending on whether it has an un-insulated vs. insulated full basement (or sealed crawlspace), and the total number of occupants, plug-loads etc. At +15F (coastal NJ) that would be more like 12-16 BTU/hr per square foot. So it's likely your true load is in the 25K range, but if you have some old gas bills that can be verified with a fuel-use based heat load calculation , which is simpler than a Manual-J.

    Without the load numbers and the radiation sizing there is no way to suggest temperature points on the curve.

    The whole point of a modulating boiler with outdoor reset is to have long steady burns, letting it modulate the firing rate up /down with the outdoor temperature.

    The English language versions of the manual and control are set in Fahrenheit degrees. << The outdoor reset discussion starts on p56 of that manual.

    Since the recessed cast iron rads (right, not fin-tube convectors?) have fairly linear response even at low water temps as well as substantial thermal mass it would be fine to set the minimum output temperature to 100F or so- there's not much efficiency to be gained by going lower. If that keeps up and doesn't short-cycle the boiler great- set it for 100F at all temps and just leave it there. Odds are 100F isn't enough though, and you'll have to figure out a couple of points on the curve.

    The displayed parameters you reported are, according to the discussion starting on p54 mean:

    A 118 < --- (= the current space heating output temperature setpoint if under supply output temperature control)
    B 93 < --- (= the current space heating return setpoint when under input temperature control)
    C 102 < --- (= the programmed domestic hot water output temperature)
    D 74 <--- (= the sensed incoming domestic hot water temperature)
    E 0 <--- (= the sensed domestic hot water flow rate, which being zero, explains why the incoming sensed temperature is so high.)
    F 22 <--- (= the sensed current outdoor air temperature)
    G --- <--- (= outdoor reset not currently in use set it to either 3 or 6, for cast-iron radiation- try 3 first)
    H 0 <--- (= boost interval time. Setting it to zero turns that function off, which is fine.)
    I 12.6 <--- (= heating system pressure, in pounds per square inch- 12.6psi is just fine.)

    Try programming the low temp at your your 99% outside design temp (guess, based on the nearest listed city), and set the highest temperature to 60F (a guesstimate, based on where you set your thermostats it'll probably do just fine during the colder seasons. If it keeps up, drop the programmed lowest temperature by 10F, see it still keeps up. Repeat until it doesn't keep up with the load over night, then raise the low temp 5F, and bump it up or down a degree at a time until it keeps up.

    In the spring as temperatures rise keep an eye out for short-cycling behavior. Burn times will be shorter when the load is low, and is guaranteed to cycle on/off above some outdoor temperature. As long as burns are at least 3-4 minutes long, with no more than a handful of burns per hour it'll be just fine. But 1-minute burns and 10 burns or more per hour are an efficiency & wear & tear disaster. The thermal mass of the radiators will probably keep that from happening, but be aware of how it's behaving when it's say, 45F or higher outside.

    The 5F setback function on the Nest will screw this all up, and won't really save you much, if anything. When you have it dialed-in without the reset function, you can try enabling that function on the Nest, and enabling the Boost function, set to 15 minutes or something.
     
  7. seemarc

    seemarc New Member

    Joined:
    Jan 9, 2017
    Location:
    New Jersey
    I read your post a few times and need a little clarification...

    When you say "it would be fine to set the minimum output temperature to 100F or so-" Does that mean parameters at A and B set at 100F and monitor and increase both 10 degrees till I get long burn times? Im sorry Im confused!

    Can you clarify... Try programing the low temp at your 99% outside design temp?is this parameters C and D?

    Should I take any action with parameters D and E? You mentioned D was high.

    Thanks again I just want to make sure I adjust the proper functions and I think the manual refers to them slightly different than you did
     
  8. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    If your system does NOT have the outdoor reset option installed, you set the space heating water temperature by hitting the mode button once, then bumping it up or down with the "+" and "-" buttons. See page 53 of the manual and the "Setting the Parameters" section starting on page 55. If it doesn't short-cycle with the maximum set to 100F or 110F and it still keeps the place up to the thermostat settings even when it's cold out you'll be getting 95-98% efficiency out of the thing. If it doesn't keep up you have to bump the temp up until it does. But if the return water temps go above 125F or so it won't be condensing, and efficiency will be in the 87% range.

    So when in doubt, keep bumping it down- the cooler the water temp, the higher the efficiency. But below 100F there is really no more efficiency gains left to be had. As the temps go ever lower, if the thing starts short cycling (= burn times less than 3 minutes, more than 5 burns per hour during continuous calls for heat), bump it back up 5F at a time, then observe it's behavior.

    If your system DOES have the outdoor reset option installed (recommended), change parameter G to either 3 or 6. If you don't know if that option is installed, it should give you an error message if you change it to something other than "---". Or dig further into the documentation, or take a close look at the installation- is there an outdoor temperature sensor wired to the thing? The sensor looks like a little domed disc, but the connection wire could look like thermostat wire, spliced into to the pigtail that plugs into the unit. See page 80 of the manual.:

    [​IMG]

    C & D don't have anything to do with the space heating side.

    C is your domestic hot water temperature - probably the sensed temperature at the output , not the programmed hot water temperature, but it could be the programmed temperature though 102F would be pretty tepid for showering, and downright cool for bathtub fills. If you hit the "mode" button twice you can bump the temp up or down with the "+" and "-" buttons. If that changes the number displayed by C, it means it's telling you the programmed temperature, not the current temperature when there is no flow.

    D is the temperature of the incoming water on the domestic hot water end, and is not a programmable parameter. When there is no hot water being drawn, the temp of the incoming water side rises, being heated by the residual heat in the heat exchanger. Try opening up a hot water tap and reading what C & D are again while the hot water runs. I expect C will either be a bit higher or stay at 118F, and D will be MUCH lower, like 40F or something.
    E is just reporting the flow rate- if nothing is running, it should be zero. It is not a programmable parameter, but tells you if there is a hot water tap running somewhere.
     
  9. seemarc

    seemarc New Member

    Joined:
    Jan 9, 2017
    Location:
    New Jersey
    Thank you very much! I now understand. I do not have the outdoor sensor. But for $60 sounds like it pay for itself in sort time
     
  10. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    It will pay for it mostly in comfort rather than fuel costs if you have enough radiation that the place always stays warm set to 120F or lower. (My system needs 125F water when it's 0F outside- YMMV.)

    If your system needs 150F water to keep the house warm on the coldest days of the year, adding the outdoor reset function will pay for itself in the first heating season.
     
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