Navien NCB manifold piping

Discussion in 'Tankless Water Heater Forum' started by cadobe, May 28, 2019.

  1. cadobe

    cadobe New Member

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    Location:
    Seattle
    My configuration install looks 100% similar with the attached image, having only one zone. Anyhow I can control the temperatures on each individual room by either using the smart thermostat or/and the TRV's.

    - Pump: Taco VR1816
    - Heat emiters: Myson panel radiators with TRV's on all of them
    - Relay: Taco switch relay for only one zone
    - Ecobee thermostat.
    [​IMG]

    My question is this: Is it possible not using the Navien manifold primary for NCB series? Just simple supply and return lines (in /out ) .
     
  2. Dana

    Dana In the trades

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    The heat exchanger in the Navien is a water tube type with a high pumping head, and isn't designed for high flow rates, but also requires a minimum flow rate to avoid microboil on the heat exchanger from becoming macro-boil, reducing heat transfer efficiency.

    That said, if you do the math you may very well be able to find a pumping rate that meets the requirements of both the Navien and the radiation. If you don't do the math you're just hacking, and all bets are off (possibly including the warranty.) You may have to replace the internal pump inside the NCB (labeled "H" in the lower left corner of the diagram) with something else to make it work. That pump is sized correctly for the heat exchanger's pumping head assuming only a modest amount of pumping head from the exterior plumbing (such as the pre-engineered hydraulic separation manifold you're trying to get rid of.) Your radiation loop has substantially more pumping head than just the hydraulic separator, but for your system the radiation pumping rates probably don't need to be very high.

    [​IMG]

    It's also possible to use something other than Navien's pre-engineered manifold as the hydraulic separator, either your own closely spaced tees made up from fittings, or a massive high volume hydraulic separator to mitigate against short cycling.
     
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  4. cadobe

    cadobe New Member

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    So the pre-engineered manifold is just to protect the heat exchanger?
     
  5. Dana

    Dana In the trades

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    I don't know about "...just to protect the heat exchanger..." - it's a system design issue. As with any hydraulic separator it's there to be able to allow different (both higher and lower) flows to the radiation than through the boiler. Fat piped low-head cast iron boilers aren't very sensitive to flow rates. Water tube modulating condensing boilers are sensitive to flow rates, so primary/secondary plumbing separating the radiation & boiler flows are customary with that type of boiler.

    Fire tube mod-cons are less sensitive to flow rate than water tube boilers, and can often be drop-in replacements for systems previously heated by cast iron without hydraulic separation. If you're going to be doing this in hacker-mode, no math you'll probably have better luck at finding success with an HTP UFT-Combi than with an NCB, due to it's fire tube heat exchanger, which can be direct-pumped over a much broader range of system configurations, even though all the examples in the manual show closely spaced tees as hydraulic separators. It comes in both wall hung and floor mounted versions (floor mount shown.) Westinghouse sells the exact same combi boilers through the orange box stores.

    [​IMG]

    Note, these too come with an internal pump and expect somewhat lower pumping head on the exterior plumbing.
     
  6. cadobe

    cadobe New Member

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    Yeah, I am not a hydronic engineer, but I do hacking, yes I am a software developer and I will do all the installs on my own. Honestly, I saw so many contractors out there having no clue about and/or asking fortunes to get this "proper" installed, so I am taking the risk doing by myself. At least if something goes wrong I will blame myself not crying for the money I spent on so called "contractors".
    The think is I am trying to understand why do I need that manifold, since I have only one single loop which delivers heat on the thermostat call. I do not need even a bypass or mixing valve since is a combi boiler separating on its own the DHW and Heating, and all radiators has TRV's except one which allows the flow going through all the time. Simple as is. If there is no call for heat, there is no flow or any other moving part/s.

    PS. I am originally from Europe. We are used to have only ONE SINGLE device doing everything you need. This is the reason I stick with Navien, which I already purchased. Moreover, I never saw a combi boiler with an additional expansion tank attached to the plumbing.
     
    Last edited: May 28, 2019
  7. Dana

    Dana In the trades

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    Sure there's only flow when there's a call for heat but is it the right flow for both the radiation and the boiler?

    Without looking up the specs or doing any of the math...

    Lets say you need 4 gpm on the radiators to get the right amount of heat into the system with the given radiation, and the heat exchanger on the NCB needs to operate between 1-3 gpm. How are you going to do that with one pump, and no hydraulic separation?

    Conversely, lets say you only want 1 gpm on the radiation and the minimum flow requirement for the NCB is 2 gpm. That might be do-able without hydraulic separation, but you have to design it.

    Then let's say both the radiation and boiler are happy with 2-3 gpm. How do you know if you'll be able to achieve that flow with internal pump in the NCB without doing the math on the pumping head for the radiation loop?

    To date I have never done the math on pumping direct with the NCB with either it's internal pump or a different pump, and I don't know the actual specs on what it really needs. But as with any water-tube boiler I absolutely WOULD do that math if I were contemplating pumping direct, to be damned sure it would both deliver the necessary heat and not burn itself up.

    Also, dealing with big (150K+) modulating burners requires doing the math on the gas plumbing and getting that right too. Pulling a permit? Are you even allowed to install gas fired equipment in WA without a gasfitters license? (I don't actually know the answer to that.)

    Seriously, if you're not going to do the math, use a condensing tank type water heater and a flat plate heat exchanger, an approach highly tolerant of gross hackery-tinkery (unlike water tube mod-cons):

    [​IMG]

    A smallest 50 gallon HTP Light Duty PH76-50 with the 76K burner is fine for most 2 bathroom houses with a sub-30K heat loads. (Westinghouse rebrands those and sells them through box stores too.)

    Whether combi-boiler or tank type water heater, even if you DIY the installation it's important to have a qualified tech do the final review and commissioning, testing your gas pressure drops at different burn rates, verifying the combustion efficiency etc. Installing modulating burners and heating systems is way more than just a "hookin'-up-the-plumbin'& wirin' " type project if you want to work efficiently & safely, and last for more than a few years, even if that's what you did with your original water heater version.
     
  8. cadobe

    cadobe New Member

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    I said that I have already an external pump which is Taco Viridian VR1816. This gives you
    3 operating modes:
    • - Fixed speed ( ) - infinitely adjustable min/max settings
    • - Constant pressure ( ), variable speed - 3 constant pressure differential curves (5, 10, or 15 feet of head)
    • - Proportional pressure ( ), variable speed - 3 variable pressure differential curves (High, Med, or Low).

    So you have different options to choose from, obviously the one that fits your system.

    That pump just satisfied my heating needs this winter using yes a dedicated regular water heater with no plate exchanger, separating DHW.

    The flow rate for Navien 180 is max 3.4 from the manual?

    custom.jpg
     
    Last edited by a moderator: May 30, 2019
  9. Dana

    Dana In the trades

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    Yes you already have an external pump- I'm quite familiar with the VR series Tacos. You still have to do the math on all of the plumbing to know if the VR1816 is going to work. (Probably will, but you still design it, don't just hack at it.)

    Just because it with a low-head heat source (the tank type water heater) doesn't mean it will auto-magically deliver the same performance with the impedance of a high pumping head heat exchanger in the loop. With the low impedance manifold in the heating loop rather than th heat exchanger it almost surely will perform comparably, (even if turns out that the radiation is too skimpy and will short-cycle the boiler.)

    The 3.4 gpm flow rate is the maximum that it can deliver on the domestic hot water side at a 77F rise, and has no relevance to operations on the heating side. Regarding domestic hot water flow rates, it can go higher at a lower temperature rise. A typical tub fill is 110F, a 75F rise from your wintertime incoming water low of about 40F, so at times you'd be maxed out at about 3.5gpm, and it would take fully 10 minutes for a standard size tub fill.. In your area the Even at a tedious 10 minute tub filling rate you don't have any margin to support other draws, you'll have to schedule other hot water use around tub fills and showers, and it would not support simultaneous 2.5gpm low-flow showers. That is is why the -180 is a lousy choice for a 2-bathroom house at your incoming water temps.

    Using a water heater dedicated to heating-only is expressly disallowed in some states- not sure about WA. Running a radiator loop directly from a potable water heater without isolation from the potable supply is a code violation in most states, due to the pathogen growth potential in stagnating water over the summer. What is your other water heater's input BTU rating? Are you keeping it?

    It doesn't take hard math to figure out your heat load from prior use, or to figure out the maximum heat emittance of your radiators across temperature (particularly at condensing temperatures, if contemplating a modulating condensing system.) Those are the first-order priorities for figuring out what would be an appropriate heat source for the system.
     
  10. cadobe

    cadobe New Member

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    The label states clearly that:
    [​IMG]

    which 99.99% of "contractors" have no idea, not saying that customers, they chew what are they told. Indeed the water heater is separated from potable water, I know that the image from previous reply is not that clear, but it is separated. The other water heater is 50 gal/40,000 BTU's, which by now they both are in place probably few more weeks.

    Define that statement Dana.
    What if the DHW is coming out at 140 degrees or more? I know that is scalding but we mixed that right? The 2.5gpm is taken in account only for the hot water not mixed. Even if you get your hot water at 110, you still mix that. Obviously having the vent flue changed accordingly to CPVC instead PVC.

    Meanwhile I will do my math.
     
    Last edited: May 30, 2019
  11. Dana

    Dana In the trades

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    Is your water heat at combi tank with an internal heat exchanger?

    If not, just because the manufacturer specifies that it's suitable for space heating it doesn't mean the local codes allow that. Many states allow water heaters like that to be used as "open" combi systems if there is less than 100' of plumbing and it's feeding a hydro-air coil rated 50,000 BTU/hr or less, with some variation on that theme. I'm not up on what's currently allowed in WA (haven't lived there in decades.)

    No matter what the output temperature is set to, the burner is BTU limited, and it has to raise the incoming water mixed to ~105F at the shower head. It's simple arithmetic:

    A 2.5 gpm shower is about (2.5 x 60 min. x 8.34lb/gal.=) 1250 lbs/hr.

    When the incoming water is 40F, it needs to raise the temperature 65F to hit 105F at the shower. That means it needs an input rate of:

    65F x 1250 lbs/hr = 81,250 BTU/hr for one shower

    ...and...

    162,500 BTU/hr to support two showers.

    The NCB-240E can deliver the the 162.5 K-out with margin (enough margin to cover your likely heat load plus the two showers.)

    The NCB-210E would just barely squeak by, with less than 10 KBTU/hr of margin

    The NCB-180E doesn't even take in 162.5 KBTU/hr at it's input, let alone output.
     
  12. cadobe

    cadobe New Member

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    You take in account only the how water and not mixed
     
  13. Dana

    Dana In the trades

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    I'm absolutely accounting for the BTU/hr rate it takes to deliver 2.5gpm of 105F water when the incoming water is 40F. How it is mixed in the middle doesn't matter. Whether it's raising the hot side to 140F and mixing down or raising the hot side to 105F with zero cold mixing in at the shower mixer in it's still the same BTU rate. By definition it's 1 BTU/lb per degree F, and if the pipe coming into the house is delivering 40F water, split between the water heater flow and cold flow then remixed to deliver 105F water at 2.5gpm it doesn't matter what the peak temperature was on the hot side.

    The peak temperature on the hot side determines how much flow has to go through the water heater- if raised to 140F the flow rate through the water heater drops to about 1.6 gpm, and the cold side of the shower mixer increase to about 0.9 gpm, but the BTU rate it takes to elevate it to 140F at 1.6 gpm remains the same. 40F to 140F is a 100F rise, 1.6 gpm is ~800 lbs, for 100F x 800lbs= ~80,000 BTU/hr. (The difference is just the rounding errors in both examples, made to keep it simple enough to do in my head.)
     
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  14. Dana

    Dana In the trades

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    Try this tool for verifying the mixing math of 140F water with 40F water to hit 105F output (or write your own app :)), but it's about right. (More than 2 significant digits would require bigger napkin to scribble on, and won't make a meaningful difference.)
     
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