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Tuning gas valve on aging modcon to revitalize factory AFUE

wcs5050
wcs5050 Member Posts: 142
in THE MAIN WALL
Does anyone know what happens in the gas valve that throws off factory AFUE? I had my combustion analyzer on a WM series 2 Ultra today. Ox2, CO2, CO were all in range that manual indicated, but AFUE was 89%, as opposed to 92%(still not impressive, but decent for an older offering). Any way to cheat this back? Which way would the O2,CO2 go within the mandated range to raise AFUE. I've heard that gas valves on mod/cons need adjusting after a certain amount of years.

Comments

  • delta T
    delta T Member Posts: 884
    what were the numbers?
  • Zman
    Zman Member Posts: 7,611
    I would not put much faith in the efficiency numbers. It is calced by the analyzer using the combustion numbers and the flue temp. It is a serious SWAG.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    njtommyGordySWEIkcopp
  • njtommy
    njtommy Member Posts: 1,105
    edited November 2015
    Not to mention your firing rate and water temp will change the efficiency numbers.
    But 89% is not bad at all.
    kcopp
  • SWEI
    SWEI Member Posts: 7,348
    What were the water temps at the time of the test?
  • ChrisJ
    ChrisJ Member Posts: 16,485
    Not to mention combustion efficiency and AFUE are two totally different things.

    Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.

    wcs5050
  • vaporvac
    vaporvac Member Posts: 1,520
    njtommy said:

    Not to mention your firing rate and water temp will change the efficiency numbers.

    But 89% is not bad at all.

    I wonder if this is why my numbers are so improved. I've recently thought my boilers may not be getting the rated btus.

    Two-pipe Trane vaporvacuum system; 1466 edr
    Twinned, staged Slantfin TR50s piped into 4" header with Riello G400 burners; 240K lead, 200K lag Btus. Controlled by Taco Relay and Honeywell RTH6580WF
  • wcs5050
    wcs5050 Member Posts: 142
    Have to look at my job notes for levels. Low fire water temp was about 105, high fire about 150.
  • Tim McElwain
    Tim McElwain Member Posts: 4,651
    Your combustion analyzer gives you combustion efficiency which will always be less than AFUE as they are two different things. Typically combustion efficiency is 8 to 10% less than the advertised AFUE. At best as someone else stated efficiency with the analyzer is a calculated reading not pure from a sensor such as O2 and CO along with net stack temperature. That along with draft are the important numbers.

    It is not a good idea to adjust Mod/Cons different than what the manufacturers specs call for.
    kcopp
  • wcs5050
    wcs5050 Member Posts: 142
    edited November 2015
    Lochinvar indicates otherwise in regards to KBN500 gas valve adjustment, years in. Im not talking about tweaking outside range called for. Wondering how to get back to optimum. I realize combustion eff and unit eff are separate, yet proportional.
  • Zman
    Zman Member Posts: 7,611
    Lower O2, Higher CO2 with CO safely within the limits will generally get you close to the sweet spot of efficiency.
    All these numbers of course need to be within the manufactures limits.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    SWEI
  • wcs5050
    wcs5050 Member Posts: 142
    Thx zman. That's what I was looking for.
  • SWEI
    SWEI Member Posts: 7,348
    If that 89% you saw was at high fire, and the 150°F was either a return temp or a supply temp with a small ΔT, it looks about right.

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