Newbie has questions re Navien NCB-240E

Discussion in 'Boiler Forum' started by Heinz Wittenbecher, Mar 12, 2019.

  1. Heinz Wittenbecher

    Heinz Wittenbecher New Member

    Joined:
    Mar 3, 2019
    Location:
    Langley, BC
    I just went through the pain (and expense) of a boiler replacement.
    Located in Langley, BC.

    Some background here: http://www.smallrvs.ca/?p=1345

    After doing more research elsewhere and from what I read here I do seem to have oversized.
    My own fault. Should'a listened to the installer.
    Comes from the "bigger is better" thinking process acquired over the years.
    Seems that thought process doesn't apply here :)

    Our old boiler was 135k BTU's running at 160 degrees.
    Piping in boiler room (closet) is copper but distribution to baseboard fins is Poly B.
    House is baseboard fins, 2 floors, and a garage has infloor heating.
    No Poly B in the concrete, it was done later.
    Best I can tell, no plastic fittings with Poly B but of course I can't see all of them.

    240E replaces boiler and hot water tank.
    We have the Outdoor Reset Control.
    B. is set to 1

    I would like to limit Supply temp to 160 so as to maintain max temps we used to have, mainly for the benefit of the Poly B.
    Currently boiler temps are running 140-150. During the night we dip into mid 20's.
    I did see 161 on one check but only once, early morning.
    I do like it warm so the thermostats are set at 71 degrees 24/7. House is occupied 24/7.
    4 baseboard zones + garage zone with mixer valve. 1 baseboard zone is on second floor.

    Now for the question... Does the N. setting override the default settings of B. 1?

    Hoping it does, I have set N. to 160.

    If it doesn't override the B. 1 I'm guessing I have to do a custom setting for B?
     
  2. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    Setting parameter B to 1 puts the outdoor reset curve to respond properly to the non-linearites of fin tube baseboard. Setting N to some fixed number will indeed limit the maximum temperature whatever you've entered, independently of what the curve might be calling for. In many/most systems it's better to set parameter B to 7 and fine tune the curve, setting DIP SW2 position #1 to "on" to put it under return water temperature control. (Setting N still limits the max output even when under return water control.)

    Did you set up the reset curve, or did the installer do that?

    Have you tried adjusting a custom reset curve?

    Almost no system out there needs 160F water out to the radiation. Most will do just fine with 140F even at temperatures below the 99% outside design temperature. (In Langley that's about 21F, comparable to Bellingham WA, slightly cooler than Vancouver.) At output temperatures north of 140F there is no condensing efficiency to be had, so the way it's running it sounds like it will only deliver about 87%. But to get a handle on that, take a look at the return water temperatures. Condensing starts at about 127F entering water temperature, where it's delivering 88-89% efficiency, but doesn't hit 95% efficiency until the entering water temperature is under 115F or so.

    The NCB almost always has to be plumbed primary/secondary with another pump driving the radiation flows, and a hydraulic separator to limit the interaction between radiation flows & boiler flows. This is often done with the Navien's pre-engineered manifold directly below the boiler, but it doesn't look like that was used here. It's not entirely clear from the pictures, but it's likely that the closely spaced tees by the right-most pump in the picture is providing that function.

    With any primary/secondary setup the temperature of the water going out to the radiation is strictly cooler than the water coming directly out of the boiler. This is because the water going out to radiation is a mixture of boiler output and return water, the mixing occuring in the hydraulic separator. So just because the boiler output was 161F doesn't mean the boiler going out through the zone valves or elsewhere are anywhere near that hot. With a pistol-grip infrared thermometer and strips of hockey tape on different pieces of plumbing you can directly measure within a few degrees F what the supply temperatures to the different zones are, and how much cooler that is than the stub directly tied to the boiler output is. Bare copper isn't emissive enough in the infra red to take those measurements, but hockey tape, or any non-metallic spray paint is.

    To get a handle on what supply temps are needed to the zones, start by measuring the baseboard lengths separately zone by zone. Then run a fuel-use based whole-house load calculation. In combination with the radiation data would be good enough to ballpark a custom curve, and it can be fine tuned from there.
     
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  4. Heinz Wittenbecher

    Heinz Wittenbecher New Member

    Joined:
    Mar 3, 2019
    Location:
    Langley, BC
    Installer did. I looked on with nose in manual.
    Not sure what the settings are for dip switches as they were done earlier.

    Have not adjusted further, yet. Gathering intel :)

    I'm using the 160 as a Max. In reality I hope it never gets there or at least infrequently.
    I need about 140 when cold or the upstairs doesn't get to my desired 70/71. I'm hoping that as spring rolls around that temp will adjust itself downward. How did I get to the 140? Trial and error when B. was off.

    Looks like I may not have the full benefits of condensation. At least I will have similar to old boiler but still some advantages. Burner adjusting flame/temp and not having the blowtorch effect of full on or full off should have some benefits.

    The pump on the left feeds the in-floor of the garage, in associating with a mixing valve with temp sensor on the garage feeder pipe.

    Thank you for the hockey tape hint. Definitely going to try that.

    Thank you very much for your comments and suggestions to help me become a more informed home owner. For the installation itself I pretty well had to rely on the installer but since I don't want him to live in my house I take it upon myself to learn what I can so that I can get the maximum benefit out of the install. Maximum benefits meaning benefits for my particular installation as there are seldom 2 alike.
    You have given me lots of useful information and home-work :)
    Thank you
     
  5. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    In addition to spot-checking the entering water temp at the boiler you should be able to tell if when it's condensing by looking at the condensate PH-neutralization cartridge that's hooked up to the white PVC plumbing to right of the boiler. If it looks bone-dry all the time it's not condensing much at all.

    There is no settable "off" for parameter B. To turn the outdoor reset on/off is parameter A. When the display for A is showing the null "-- -- --" indicating it's off, parameter B will show the same thing.

    When measuring the baseboard you may want to run this bit o' napkin math on it to see just how low the water temps can be before it starts short-cycling.

    As a dumb rule of thumb typical fin tube baseboard emits about 200 BTU/hr per running foot at an average water temp of 120F, which will probably occur on your primary/secondary plumbed system at an output temp of 125-130F. The minimum fire output of the NCB 240E is about 17,000 BTU/hr, so it takes about 85' of baseboard to emit the full 17K at condensing temperature. It can still work just fine at condensing temps with just 50' of baseboard on zone by tweaking parameters L & M- hopefully you have at least that much baseboard on your shortest zone. If they are shorter than that it's worth running experiments to determine the minimum burn times & duty cycles with just the smaller zone calling for heat.

    If all the zone baseboards are short enough to induce short cycling you may be able to get something out of tweaking parameter H. but that's a bit tricky, since you could end up in a scenario where programming a long delay with H limits the duty cycle enough that it can't even heat the house when it's cold outside.
     
  6. Heinz Wittenbecher

    Heinz Wittenbecher New Member

    Joined:
    Mar 3, 2019
    Location:
    Langley, BC
    Sorry, actually meant A.---. Brain induced typo :)
    Thank you for the additional info/suggestions.
     
  7. Heinz Wittenbecher

    Heinz Wittenbecher New Member

    Joined:
    Mar 3, 2019
    Location:
    Langley, BC
    A supplemental question... I'm adding an automatic whole house water shut-off.
    Do I have to worry about if/when the Navien running out of water?
    Will the Navien take care of itself or do I need to add power off for the outlet the Navien is plugged into.
     
  8. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    On page 18 of the manual they described the operation of the internal low water cut off and automatic water replenishment system.

    There is quite a bit of self-monitoring of the operation and a few dozen conditions that will cause the thing to automatically stop, displaying an error code on the front panel. See section 5.2.

    I personally would always install a wall switch for cutting off the power to any boiler or tankless water heater. It's a cleaner way to turn it off for service & maintenance than yanking a cord out of a wall socket. I've never seen a combi-boiler or tankless that wasn't hard-wired for power (no plug, no outlet) but that may be a code requirement in my area. I've been using a tankless water heater as a boiler on my system for a decade or so, and nearly the whole system including zone controllers & pumps, not just the tankless can be powered off by a single switch mounted at the zone manifold panel. Power to a hydro-air handler located in another room has it's own separate switch since it's operating on 240VAC, the rest is all 120VAC.
     
  9. Heinz Wittenbecher

    Heinz Wittenbecher New Member

    Joined:
    Mar 3, 2019
    Location:
    Langley, BC
    Thank you Dana. We do have a wall switch for the works but the Navien is plugged into a receptacle, which is after the wall switch. My only concern was wether I need to pull power remotely if we loose water. Gone this far so I'll be adding remote off/on for the outlet the Navien is plugged into.
    This all for when away from home. While at home it's easy to throw the wall switch if needed.
    Thanks again for all the info. Lots to digest but it's all good.
     
  10. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    The boiler's internal error detection for loss of water pressure are usually adequate. I'm not even sure what remote sensors and controls would even be used for redundancy here.
     
  11. Heinz Wittenbecher

    Heinz Wittenbecher New Member

    Joined:
    Mar 3, 2019
    Location:
    Langley, BC
    My house is already somewhat setup with home automation so I'll simply add the boiler to it and when water shutoff emails/texts that water has been shut off, I can shut the boiler off as if I was at home. One less thing to worry about in time of crisis while away from home :)
     
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