Lochinvar KBN211 lockout outlet ARHL

Discussion in 'Boiler Forum' started by eringuet, Oct 26, 2020.

  1. eringuet

    eringuet New Member

    Joined:
    Oct 26, 2020
    Location:
    Ontario, Canada
    Hello! New member here but I've been reading the forum for some time now.

    I've recently installed a KBN211 in my detached workshop. The boiler wasn't a choice, I just happened to get it at a really good price used. My system is just in-floor heating with 3 circuits totaling about 1000 ft of 1/2 pex fed by a 3/4 inch manifold.

    I have been having lockout issues and I suspect that potentially flow might be an issue. I only have a system pump (can't recall the model, 1/25hp). I've basically followed the installation guide but didn't install a boiler loop, although I do have the pump supplied from Lochinvar with the boiler. To be honest, I didn't really understand the loop shown in the "near boiler piping" in figure 6-2A of the installation manual.

    I am not a plumber, I just thought it was a good challenge to install myself and the stakes were pretty low since it's in the barn. My plumber doesn't have experience with Lochinvar, he usually installs Navien combi-boilers, which is what I have in my house.

    Any advice would be appreciated.
     
  2. fitter30

    fitter30 Active Member

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    Retired service tech
    Location:
    Peace valley missouri
    Whats the fault code? What turns on the boiler and pump?
     
    Last edited: Oct 26, 2020
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  4. eringuet

    eringuet New Member

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    @fitter30 it just says "outlet ARHL", there's another fault for "outlet MRHL"
     
  5. Dana

    Dana In the trades

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    Jan 14, 2009
    Location:
    01609
    A few comments:

    According to the manual the min-fire input to that beast is 42MBH, which is probably more than you'd be emitting even with ~1000' of half-inch PEX embedded in concrete. How big is this workshop- 500 square feet? 800 square feet? Is it a radiant slab, or something else (please describe).

    All example piping configurations in the manual indicate some sort of hydraulic separator/low-loss header. In figure 6.2A the hydraulic separator is a pair of closely spaced tees (a MINIMUM pipe size of 1", unlike a 3/4" manifold). The pump they shipped with the boiler should be able to deliver adequate flow thorough the loop to the hydraulic separator, but would NOT be specified to drive the necessary boiler flow through your restrictive radiation. The flow rates indicated are 11-20gpm, (11 gpm even for the 35F delta-T application, which isn't what you get out of a radiant slab or staple-up radiant floor). If you're pumping direct rather than primary/secondary (a boiler loop driven by it's own pump) through three parallel loops of ~333' of PEX you're unlikely to achieve anywhere near the minimum flow requirements with a 1/25 HP pump. See pages 37 through 39.

    It HAS to be plumbed primary/secondary (not just a 1/25HP secondary pump driving the radiation flow) to have any hope of working, and even then it's going to cycle a lot due to the gross oversizing of the boiler relative to your radiation.

    If you plan to forge ahead building your own hydraulic separator using closely spaced tees, follow these guidelines for starters:

    [​IMG]

    Use only 1" pipe for the boiler loop, but it's fine to reduce that to 3/4" off to your PEX manifolds. You might consider using a 1" x 3/4" purging tee (keeping the ball valve open) to save plumbing time & space, since the tees are already sufficiently close to work well:
    [​IMG]


    With a radiant slab there's at least some chance in hell that it won't short-cycle on you, but there isn't enough thermal mass in 1000' of PEX alone to fully prevent that.

    Alternatively, a cheap scratch & dent electric water heater could be employed as the hydraulic separator, using the hot port at the top and the drain valve port at the bottom as the supply and return for the secondary (radiation) runs to your manifolds. Pull the electric heater elements and use those ports for the primary (boiler) loop. Even a 40 gallon water heater has over 300lbs of thermal mass to work with to suppress short cycling no matter how slowly the radiation is sipping heat from the tank. While there are purpose-made versions (BoilerBuddy, etc) a cheap electric water heater would be a cheaper (and still effective) alternative. It effectively becomes one of these:

    [​IMG]

    Your 1/25HP system pump would be effectively the blue triangle in this diagram, whatever they shipped with the boiler would be the orange triangle.
     
  6. eringuet

    eringuet New Member

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    Oct 26, 2020
    Location:
    Ontario, Canada
    @Dana thanks for this really informative post.

    The shop is 28x22, the floor is 567 sqft. The pipe isn't in the slab, I just put vapor barrier, laid 2x4 sleepers 24 o.c. and 1/2 rigid insulation and added 3/4 osb on top. Each 24 in cavity has 3 runs of pipe. The walls and roof are insulated to R22.

    here's my setup... remember, not a plumber, just an IT guy who wants to learn...

    [​IMG]

    Working with a bit of a tight spot, if I understand correctly, I'll have to have 1" pipe with a minimum of 8" before the purging tees and a minimum of 4" after. The tees go to my feed and return.
     
  7. fitter30

    fitter30 Active Member

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    Feb 2, 2020
    Occupation:
    Retired service tech
    Location:
    Peace valley missouri
    ARHL&MRHL are both high outlet temp 200* auto high limit200* & manual reset high limit 210*. This boiler only holds 1.7 gallons of water so tripping on high limit will shorten the life of the boiler. Can get all the manual here
    https://www.supplyhouse.com/Lochinvar-KBN211-170000-BTU-Output-Knight-High-Efficiency-Boiler
    Max differential water temp is 35* between in & out minimum 20*. What is the brand & model off pump? Looks like 6 loops size and lenght of loops?
     
  8. eringuet

    eringuet New Member

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    @fitter30
    Hi, my pump is a UPS15-58FC, 3 loops, 1/2 pex, roughly 300ft per loop.
    Any settings I can change?
     
    Last edited: Oct 27, 2020
  9. Dana

    Dana In the trades

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    Jan 14, 2009
    Location:
    01609
    Even assuming a few windows & doors the design heat load of that building isn't more than 15,000 BTU/hr( assuming there is glass in the windows and doors that close.) If you think that's wrong, run a CoolCalc or LoadCalc load Manual J(-ish) estimate.

    There is no WAY the 1000' of PEX in contact primarily with just air (and not the subfloor) is going to emit anywhere near the minimum-fire output of the boiler (which is >35,000 BTU/hr) at temperatures that would not melt the PEX! At the very least it would need aluminum heat spreaders tight to the PEX and your sub-floor. The radiation you installed will be able to emit 10-15,000 BTU/hr (at the maximum boiler temp), not more.

    With 35KBTU/hr coming out of the boiler and only 10-15KBTU/hr leaving the PEX the excess BTUs rapidly heat the water to the max, cycle the burner off, wait until it cools down repeat. This sort of short-cycling is hard on the equipment and takes a huge toll on efficiency, since it's spending almost as much time purging the flue prior to re-ignition (and blowing heat out of the heat exchanger with every purge) only to fire up the burner for another few tens of seconds. At the boiler's maximum temp you might get 85-87% combustion efficiency out of it, but with the short cycling the net efficiency will be on the order of 75%. Lowering the temperature into the condensing zone for higher raw combustion efficiency won't really fix that, since even LESS heat will be emitted from the PEX, leading to even shorter burn cycles.

    This boiler is GROTESQUELY oversized for both your radiation and heat load. You'll NEVER get this to work without more thermal mass in the system- either a buffer tank or a massive hydraulic separator.

    Also without a much bigger pump you'll never get the delta-T across the boiler down to something reasonable, and chronically running it beyond it's specified maximum temperature delta mechanically stresses it- it WILL destroy the boiler over not a huge number of weeks.

    Given the very low thermal mass of your radiation you won't be able to make it work with a purging tee as the hydraulic separator. A thermally massive hydraulic separator (like a re-purposed electric water heater) could.

    So, where do you go from here?

    It's silly to spend extra on buffer tanks etc. just to be able to use a King Kong sized boiler to serve a Stuart Little sized load, using Stuart Little sized radiation. Were I personally to inherit this project I'd the KBN211 up on Craigslist or something, run the heat load numbers, estimate the water temp requirements for getting it out of the not-so-thermally coupled PEX, and find something more suitable as aheat source for that radiation.

    Or, abandon the radiant and heat (and cool) the place with a 3/4 ton or 1 ton ductless mini-split heat pump. A 110V version of a Pioneer or Senville etc (all made by Midea) DIY mini-split with 16-25' of pre-charged refrigerant line runs about USD $800 at internet pricing. Check your wiring & breaker panels before buying- most 110V versions need 25A breaker and 10/3 wiring. (Read up on the manual for what it needs.)
     
  10. eringuet

    eringuet New Member

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    Oct 26, 2020
    Location:
    Ontario, Canada
    @Dana very insightful comment again, thank you.

    I paid only $380 CAD for the boiler, I wasn't looking for something this big, I just assumed it would heat everything quickly.

    I looked at mini-splits but I'm not sure it works well in our cold Canadian weather. As far as I know they don't work below -5c. I could be wrong though.

    Also, electricity is really expensive around here so gas was my choice. I looked at different solutions I could implement with my goals and skill level. Mainly, I wanted: gas, separate burn chamber since it's a woodworking shop, no loud fans, even heat. I really like infloor heating and now that it's installed, I want to keep it.

    When I purchased the boiler, I was also looking at a tank domestic hot water heater. I figured I could try the boiler and could always fallback to the DWH, the plumbing in place would still be usable. My friend has a garage of similar size and it seems to work for him.

    I'll look a different options, thanks again for the advice and explanation.

    Thanks
     
  11. Dana

    Dana In the trades

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    Jan 14, 2009
    Location:
    01609
    It heats up the system water VERY quickly, but there isn't enough radiation to get it from the water into the room as the same rate as the boiler output even at minimum fire, which is THE major problem here.

    There are MANY mini-splits with vapor injection scroll compressors that deliver their full "rated" capacity down to -15C/+5F, and others that have a specified output even as cool as -22F/-30C.

    Even those with simpler compressors are usually fully rated down to +17F/-8C, with lesser output specified at temps well below that.

    What is your local 99% outside design temperature, approximately?

    Mini-split blowers are really quiet. Most 1-tonners are only as loud as a refrigerator when running at their highest fan speed, and quieter than a whisper on low. Even the DIY versions are easier to install properly than a KBN211. A cold-climate 1-tonner can usually deliver about 15-16,000 BTU/hr @ -15C, and even the simpler compressor types (such as most 110V DIY versions) deliver more than 10,000 BTU/hr @ -15C.

    If you have 230VAC available in the shop there are more options, some that are good to -22C.

    Electric heating is only expensive if it's resistance heating at a coefficient of performance (COP) of 1. A pretty-good cold climate mini-split will have a seasonal average efficiency of 3 or more, delivering 3x as much heat per kwh as an electric space heater. Even in expensive electricity areas it's not much more expensive to run than a properly sized 80% efficiency gas burner, and usually quite a bit cheaper than #2 oil or propane.

    Figure out the design heat load first using one of the better freebie online load calculators I linked to previously in response #8. Without the load numbers there is no way to then figure out the water temp requirements for making the radiant floor work. Without knowing both heat load and the water temp requirements it's impossible to specify the heat source.

    I suspect your water temp requirements will be higher than a typical tank type water heater can deliver without modification. Even though the tank liners and other components can usually handle up to 80C the aquastats don't allow them to be adjusted that high (due to extreme scald risk in residential applications.) But it's easier to suppress short-cycling with a tank type water heater due to the substantial thermal mass you have to work with.
     
    Last edited: Oct 28, 2020
  12. fitter30

    fitter30 Active Member

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    Retired service tech
    Location:
    Peace valley missouri
    Pump is to small in both gpm and head. Flow switch was listed in optional equipment so you will to see if theres one but boiler needs one for protection. BMS connection in service manual can limit firing rate. Dana wrote your system is grossly oversized. 900' 1/2" pex 31,500 btu's. System only holds 17 gallons of water boiler alone 1.7 gallons larger volume of water wold also help with short cycling.
     
    Last edited: Oct 29, 2020
  13. Dana

    Dana In the trades

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    Jan 14, 2009
    Location:
    01609
    The 31.5 KBTU/hr seems extremely optimistic without even so much a staples holding the PEX in contact with the subfloor let alone heat transfer plates. In reality it can't emit more than half that. His description in response #5 was:

    The pipe isn't in the slab, I just put vapor barrier, laid 2x4 sleepers 24 o.c. and 1/2 rigid insulation and added 3/4 osb on top. Each 24 in cavity has 3 runs of pipe.

    That reads to me like the PEX is simply between the sleepers, flopped on top of the foam insulation, no gypcrete, no heat spreaders, no staples, with only random very occasional points of contact with the 3/4" OSB flooring. The O.D. of the PEX is less than 0.75" so there's going to be on average a quarter inch of air between the PEX & OSB, which is fairly insulating compared to gypcrete. Getting anywhere near 35BTU/hr per foot of PEX requires solid thermally conductive contact between floor layers and the PEX, such as aluminum heat spreaders or embedding the PEX in concrete. As described I'd hazard somewhere between 10-15,000 BTU/hr (best case) with an entering water temp of 180F, but I can't say I've designed or implemented a radiant floor that way.
     
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