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Not so fast troubleshooting buckaroos!

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hot_rod
hot_rod Member Posts: 22,472
Guilty of this myself. You arrive on a boiler troubleshooting call, so you crank up all the thermostats and head to the boiler to see what goes on.

All boilers/ systems go through a transient condition for a period of time. This could be minutes, or hours depending on the system.

They are trying, and will find thermal equilibrium. The point where the distribution and the boilers output match. Some systems will never get to the operating point you want or expect, like meeting the operating set point on the control.

In a perfect system, the boiler actual output and the heat emitter output would match.

Attached see where the thermal equilibrium happens with an 8 loop radiant distribution., example below.

If the distribution exceeds the boiler output, you may never get the boiler up to boiler setpoint. There are no boiler adjustments you can make at the control aquastat to change this condition. Setting it to 240°F will not help :(

On the opposite end example 4-1 of thermal equilibrium if the control aquastats were jumped, pressure relief removed. (Do not try this at home:)!
This would probably present as a short cycling boiler, 11,000 btu of fin tube capacity connected to a 50,000 boiler output.

Graph 4-3 shows a 50K system, into a 70° space with 180 SWT. So the SWT "required" at any load condition can be determined. A prediction of thermal equilibrium.
Which, again plays to mod cons on 180F systems.

So get a differential temperature meter across boiler supply and return, observe that until the temperature stabilize, that is the indication you are at steady state, thermal equalibrium condition and can look for the problem.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 23,640
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    We all tend to go off half cocked, @hot_rod ! Thank you for that summary. The onlly thing I might add is that steam systems can be similarly misleading -- and take an astonishingly long time sometimes to get to equilibrium.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    ttekushan_3leonz
  • Dave Carpentier
    Dave Carpentier Member Posts: 604
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    Presume you're faced with a mod-con.
    What if you're not on-site during a period of design temp ?
    Would you fiddle with the burn% seeking an equilibrium state ?
    30+ yrs in telecom outside plant.
    Currently in building maintenance.
  • RayWohlfarth
    RayWohlfarth Member Posts: 1,552
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    @Hotrod that's fascinating. How often would you reach equilibrium? There's lots of factors going into that supposition; indoor temperature, water flow, water temperature, boiler operating temperature, when different zones call for heat or close. I hate that you get me thinking about this now. I will be thinking about it the few days LOL
    Thanks for sharing your expertise
    Ray
    Ray Wohlfarth
    Boiler Lessons
    mattmia2
  • hot_rod
    hot_rod Member Posts: 22,472
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    You will get to equilibrium regardless of the load.
    Recently I posted some pics of a 8 section cast radiator I was trying at different flow rates to see how velocity changed the output. I tested the IR "colors" at different periods of time at different flow rates.

    I sent the pics to Siggy for an opinion and he asked if I tested output a steady state, or if they were still in a transient condition. Which was a good question to ask, because I did not run them and check for S&R temperature stabilization :#
    I was looking for speed, but diid not consider final output at different flow rates at steady state.


    So the graph included, for that hypothetical example would allow you to go in at any load condition and see where equilibrium would be reached. In graph 4.3 to release 20,000 but/hr, ∆T between SWT and ambient air needs to be @ 44°F. 44F+70ambient= 114° SWT required. Or work it backwards.
    Or monitor that S&R.

    Certainly you will get a feel for what system will be fast and which will be slower, after years of watching boilers work. High mass systems, large piping and big radiators, cold concrete slabs would involve more "bucket" time.

    Oversized boilers on small fin tube distribution would be the dragsters.

    Gets me back to your question about portable flow or BTU meters. With good diagnostic equipment, you could watch that system from afar or over a longer period of time.

    Pete Skinner has a handful of those ultrasonic flow meters for his work, typically attached for 30 days on domestic water usage applications.
    With his data over years, 30 some systems he was able to show the error in Hunters Curve calculations developed in the 1940's. Convince the powers that be, the engineering community and code writers its time to rethink that calculation method. Our industry can be slow to change, sometimes.

    'And now the new IAMPO demand calculators, developed with his insistence of grossly oversizing piping and PRVs, thermostatics, etc. are being intergraded into the code books.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • hot_rod
    hot_rod Member Posts: 22,472
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    We all tend to go off half cocked, @hot_rod ! Thank you for that summary. The onlly thing I might add is that steam systems can be similarly misleading -- and take an astonishingly long time sometimes to get to equilibrium.

    Exactly!


    Do I dare ask this group if they consider a steam system is a hydronic system? :o
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    mattmia2Solid_Fuel_Man
  • mattmia2
    mattmia2 Member Posts: 9,949
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    see what happens if you try to run it without water then answer that question

    leonzSolid_Fuel_Man
  • mattmia2
    mattmia2 Member Posts: 9,949
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    Although I think I had the same question when reading the residential code.

  • RayWohlfarth
    RayWohlfarth Member Posts: 1,552
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    @hot_rod I wonder about steam because it would have a relatively steady temperature 218.5 @2 psig where a hydronic boiler would have a reset temperature

    Ray Wohlfarth
    Boiler Lessons
  • hot_rod
    hot_rod Member Posts: 22,472
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    I've defined hydronics as water or fluid based energy transfer. All hydronics radiant, geo, solar DHW recirculating.


    water turns to steam and back to water, so?..

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,835
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    @hot_rod

    Is that the same Pete Skinner that used to work for Carlin?

  • leonz
    leonz Member Posts: 1,180
    edited March 2023
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    If the steam is dry steam isn't it in a high energy gaseos state due to the expansion of the water droplets 1,700 times creating the wet steam and the heat from the wet steam passing from up a riser pipe or down to a drop header then to a second drop header while the condensate is dropping down to the drain pipe reaching the boiler water level.

  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
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    Ultimately, isn't steady state when yhe return water temp plateaus. Then a true deltaT can be measured across the radiation. Once flow is known, then thr exact output can be calculated

    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • hot_rod
    hot_rod Member Posts: 22,472
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    If you know the delta T by measuring S&R and know or estimate flow, then you have the numbers to calculate btus being transferred

    500 f (delta t)

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Solid_Fuel_Man
  • hot_rod
    hot_rod Member Posts: 22,472
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    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream