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Is Munchkin 96% or 92%?

R. Kalia
R. Kalia Member Posts: 349
if you look at the Munchkin brochure:
<a href="Munchkin_brochure">http://www.htproducts.com/literature/lp-60.pdf</a>
it sayd "96% efficiency" on the first page (to the right of the picture) but the AFUE is given as 92% elsewhere.

If the AFUE is 92%, what is 96?


  • R. Kalia
    R. Kalia Member Posts: 349
    Munchkin brochure

    if you look at the Munchkin_brochure,
    it says "96% efficiency" on the first page (to the right of the picture) but the AFUE is given as 92% elsewhere.

    If the AFUE is 92%, what is 96%?
  • hr
    hr Member Posts: 6,106
    Depeends on when you measure it!

    I started one this weekend. The slab and return was at 41° F. Supply at 118, the analyzer indicated 96.1%.

    As the return temperature climbed up the efficiency dropped to 92%.

    hot rod

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  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    Seems to have some REAL problems when rating TRULY modulating boilers as the "standard" refuses to allow it to be rated doing what it is supposed to do! AT BEST it is rated as a two-stage appliance. The "other" number is their best estimate of efficiency when it is allowed to act in the method in which it is designed to operate.

    Write the US Department of Energy and complain. They administer the AFUE program through ASHRAE provided numbers. ASHRAE probably won't change anything unless forced by the DOE. The bulk of their $$$ and members are in air--not water.
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928
    Question HR

    Presume this was peak efficiency at full fire...

    Was the lower number the "bottom" before the unit modulated?

    Did the t-stat shut unit down before it had time to find its modulation state for maintenance?

    It would be interesting to measure efficiency with T-T jumped and the unit modulating on its reset curve ;)
  • Mark   Eatherton
    Mark Eatherton Member Posts: 49
    It's both!

    The lower listing is the A.F.U.E. rating, and the upper is the thermal efficiency.

    I've seen my lil' Muncher at 99.8% thermal efficiency NUMEROUS times. I also reduced my utility bill by 30% with a colder winter.

    I have another customer who nearly doubled the square footage of his home, and his gas consumption remained the same for worse exposure!

  • Murph'_5
    Murph'_5 Member Posts: 349
    ok then

    is the analyzer inside at the time or outside? inside the readings are coming from warmer ambient temps, outside is the intake air thats it using Hmmmmmmm.......

  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928
    That's one of the \"problems\"...

    ...with combustion analysis. By the time you can actually measure the temperature the process is already done.

    The energy transfer that occurs as a result and consequence of combustion is what matters but by the time we can ever measure it's too late to understand (and use) what happened...

    While I truly love and appreciate old things it seems much of our CONTEMPORARY knowledge is still rooted in coal and steam.

    Systems without thermostats and boilers [appearing] to operate at 100%+ efficiency will become more and more the "hot" topic here I believe.
  • hr
    hr Member Posts: 6,106
    With all the

    jobsite noise, it was hard to hear which speed the fan was at. I just checked it randomly throughout the day. Seems the highest numbers were the early ones, not sure about modulation levels, however.

    I'll be sure to observe that more carefully, next time :)

    hot rod

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  • hr
    hr Member Posts: 6,106
    I wonder that

    a lot of the combustion air is in fact ambient, inside air. Those cases don't seal well at all judging by the amount of sheetrock dust, etc that seems to get inside the blower vanes. Air takes the path of least resistence. Seems the leakage in the case would be easier pickings than 30 feet of PVC intake pipe?

    Actually this one pulls all the air from inside. The building is very volumesunous (I made that word up) It also has plenty leakage around the overhead doors.

    hot rod

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  • Mark Eatherton1
    Mark Eatherton1 Member Posts: 2,542
    With the remote readout...

    if you push and hold S4 for a few seconds, you can see EVERYTHING thats going on in real time.

    Supply temps, return temps, fan speed, flame ionization current, pumps status... EVERYTHING.

    It's actualy kind of addicting. I get real frustrated working on the other equipment I have because I can't see whats going on without strapping 20 pieces of equipment on them...
  • S Ebels
    S Ebels Member Posts: 2,322
    Famous last words

    It Depends...........

    It depends entirely on the return water temp and the actual operating temp of the system.

    Any condenser that I have ever tested out in the field has run at 88-89% when you run it at 180* supply, 160* return. Munchkin, Vitodens, Hydropulse (Gak! choked when I said that word) Pinnacle, all of em. However, when you start dumping <100* return water into any of these, look for efficiencies to be 93-94%. Same boiler, running at the same input and pumping the same flow rate. The difference is in the better rate of heat transfer into the cooler return fluid. I was just talking to my Viessmann territory manager today about this very thing. He fired up the big Vitodens on an all slab job that was 20,000 sq ft. The return water temp was 33*. (first heat in building all winter) His analyzer was reading 99.6% efficiency. The boiler was making a 5 gallon bucket of condensate every 45 minutes. I asked him if he checked the temp of the condensate and he said he hadn't but that when he stuck his finger in the bucket it felt like about 50*. We lit off another Vito on a slab on grade job a couple weeks ago. Parts of the slab were below freezing. That boiler also read nearly 100% efficiency. As the floor temp came up the efficiency settled out at 95% with return temps running in the 70* range.

    In other words the lower your system temp the higher the efficiency. The Munchkin, or about any other condenser, will run "in the 90's" depending on the system temp. Simple as that!
  • Floyd_5
    Floyd_5 Member Posts: 418
    Okay....with all of this in mind....

    where do we draw the line of say more pipe = higher eff.
    If I design a radiant slab heat system with design temps. say @ 115 and returns in the 90's... will I get enough extra eff. out of a condensing boiler so that if I can run it @ 95 and return temps in the mid 70's to pay for the extra pipe say in five years?????
    The other thing to bear in mind with the Mod. boilers is that the eff. increases as the boiler modulates toward low fire, with low fire being the best eff.
    With a modulating boiler the stack temps. will be at or near the return water temps. when it is running @ low fire... when it is running @ high fire the stack temps. will be much closer to the supply temps.
    It would seem that when using a modulating high eff. boiler and trying to get max. eff. out of the boiler, it may pay to oversize the boiler a bit and then also design the system for the lowest possible return water temps.

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