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BASIC CONDENSING THEORY ?

DUAL3
DUAL3 Member Posts: 1
I HAVE A CLIENT THAT HAS INSTALLED ULTRA HIGH EFFIC 95% TRIANGLE SOLO CONDENSING BOILERS AS PART OF A HYDRO AIR SYSTEM.  THEY ALSO HAVE INDIRECT WATER HEATER TO PROVIDE DOMESTIC.  AM I CORRECT IN ADVISING THEM THAT THEY WILL NOT ACHIEVE THE DRAMATIC EFFICIENCIES LISTED DUE TO THE NEED TO RUN HOTTER SYSTEM WATER TO THE HOT AIR SIDE AS WELL AS DOMESTIC SIDE WHEN IT CALLS.  MY UNDERSTANDING IS AS YOU GET NEAR 130 DEGREE SYSTEM TEMP , YOU CONDENSE VERY LITTLE IF AT ALL.  ANY ONE ANSWER THE FOLOWING PLEASE...   AM I GENERALLY CORRECT?  ARE THERE ANY GENERAL CHARTS AVAILABLE TO SHOW RELATIONSHIP BETWEEN EFFICIENCY AND SYSTEM TEMP AND LASTLY CAN I MAKE GENERAL STATEMENT THAT A SIMPLER 90%  CONDENSING GAS BOILER THAT IS 1/2 THE PRICE WILL PROBABLY PROVIDE THE SIMILAR OPERATING COST AS THE 95-99% MODELS IN THIS SITUATION.    THANKS

Comments

  • CMadatMe
    CMadatMe Member Posts: 3,085
    edited July 2010
    AFUE

    You will not see 90% of higher AFUE in a condensing boiler until you get in the 120-125 return water temp range. You need to get down to 110 or so to get the full 95%. The load percentage that you are using in the boiler also plays key. Attached is a Viessmann Vitodens 200 Tech Data Manual. Page 2 has a chart. I have searched in the past other mod/con mfgs manuals and Viessmann seems to be the only one that gives a chart in their manual.



    In the case of hydro air. The units are always oversized for the heat loss as they are sized for the cooling load. A typical 3 ton hydro air handler will provided 50,000 plus btu's. If you pull the hydro airs manual they general give btu's ratings at given water temps. Just need to know how many btu;s you need to heat the zone from the heat loss and adjust the boilers heating curve. Also follow any other recommendations from that particular hydro's manual.



    The same can go for the domestic side. You can limit the supply water temp. Just have to design around it. May need a larger volume tank. Again, you have to pull that tank mfg tech literature and design your domestic based on that tanks recovery at given btu's and water temps and your needs.



    Any piece of equipment installed is only going to give you what the installer has designed it to give you. That is sometime the difference from contractor "A" being higher priced than contractor "B". This aspect is what most homeowners are blind to. They see a lable and think that's what they are getting.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Tim McElwain
    Tim McElwain Member Posts: 4,480
    Dual 3 I agree with

    HVHEHCCA in all he posted.



    What I have done with Hydro-Air units is determine location, other than attics (possible cold temps) you can usually slowly lower the temperature going to each unit that will still keep duct temp above 100 degrees (F) coming out of the hydro-air unit, also if you can lower the blower speed on the unit for heating. Try doing this on a real cold day which would be the worst scenario.  The attic unit will need a minimum of 150 degrees to the coil, insulate piping right up to the unit. I put temp gauges into and out of the hydro-air unit both on piping and duct work and really dial it down to what will give comfort. it takes some work but when you inherit someone elses work you try to help the customer (for a price by the way).



    Same thing with the indirect work with the lowest temperature you can get away with and make sure pump is sized correctly. Insulating piping and lowering temps to the lowest they will go can bring efficiency up.



    You might also work with outdoor reset but be careful with temperature balance. A low loss header may also help.



    Is there any other emitters other than hydro-air?



    You might touch base with [email protected] he is a rep for Triangle Tube he may have some more ideas for you.
  • Charlie from wmass
    Charlie from wmass Member Posts: 4,195
    One thing to look at

    If the hydro air coils are getting old is replacing them with untis that will give the same out put of btu's at a lower water temperature. If they are new coils do as said above.
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
    https://heatinghelp.com/find-a-contractor/detail/charles-garrity-plumbing-and-heating
  • Royboy
    Royboy Member Posts: 221
    edited August 2010
    chris or tim or ?

    can someone help me understand why, according to the chart for the Vitodens 200, the efficiency of the combustion process looks to more affected by the size of the load than by the return water temp.



    one axis of their graph is labelled "partial load in %" which I would take to mean the actual load vs boiler capacity. if that's right, it looks like efficiency is much more enhanced by the boiler modulating down than by the return water temp dropping.



    got a feeling I'm misreading this ...
  • Tim McElwain
    Tim McElwain Member Posts: 4,480
    Royboy on high fire

    at 100% of heating load at a max of 167°F (highest temp possible on the 200) and a return temp of 140°F there will be less or perhaps no condensing hence the eff goes to 85 to maybe 85.5%.



    At 50% (roughly 20° to 30°F outdoor temp) of heating load same temps efficiency goes to 94% due to modulation and some condensing.



    Also as supply temp goes down and return temp is lowered more condensing occurs at 50% of heating load and eff goes to 97.5%.



    I also believe that chart assumes ODR.
  • Royboy
    Royboy Member Posts: 221
    edited August 2010
    OK, I'm getting it

    the "partial load in %" axis is not load as a % of boiler capacity, but load as a % of design load. and then the supply/return temp lines are labeled for temps at 100% of design load and reflect increasing amounts of ODR as you move to the left.



    that makes much more sense.



    thanks ...



    nice to see that concept in a graphical/visual mode ...
  • CMadatMe
    CMadatMe Member Posts: 3,085
    Spot On

    Tim is spot on. I wish the other boiler mfg would post the same type of graph in their lit.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Royboy
    Royboy Member Posts: 221
    as long as everyone's here

    Tim - you said: "At 50% (roughly 20° to 30°F outdoor temp) of heating load same temps efficiency goes to 94% due to modulation and some condensing."



    are you saying that part of the efficiency gain is due to modulation alone?



    if so, how does that work?
  • Royboy
    Royboy Member Posts: 221
    yeah

    considering that one of the main selling points for the technology is the added efficiency through condensation, its really nice to get a sense of how/where that comes into play.



    I'd like to see 2 graphs - one showing efficiency as a function of return temp and one showing return temp as a function of outdoor temp (for a "typcial" ODR curve)
  • Tim McElwain
    Tim McElwain Member Posts: 4,480
    MODULATION is a very

    important part of the total concept. On most systems it is the combustion air blower ramping up and down based on demand and controlling the amount of gas and air being premixed before burning.

    In a conventional non-condensing boiler, hot combustion gases from the burning of fuel heat water contained in a heat exchanger. The waste gases are still quite hot (350°F-400 °F) and significant heat is lost to the atmosphere.

     

    In a condensing boiler working at peak efficiency, the water vapor produced by the burning fuel in the boiler is condensed back into liquid water. Provided the returning water is sufficiently cool, the vapor condenses to liquid water, hence the name condensing boiler. Some of the extra efficiency of the condensing boiler is due to the cooling of the exhaust gases, but the majority of the energy recovered is from the condensation of the water vapor in the exhaust gases. This releases the latent heat of vaporization of the water (2,260 J/g, or 970 BTU/lb, of condensate) into the heat exchanger.

     

    The actual operating efficiency of a condensing boiler depends on the temperature of the return water stream: if it is too warm then little condensation takes place and little extra energy is extracted. Because of this, a newer generation of condensing boilers (so-called modulating control boilers) have microprocessor-controlled combustion that modulates the quantity of gas/air fuel mixture which is supplied to the burner using a configurable embedded algorithm that considers outdoor air temperature, water temperatures supplied and returned to the boiler, and time at a specific temperature. The most sophisticated algorithms learn the building requirements at specific outdoor air temperatures, more successfully returning cool water that condenses the vented exhaust gases and recovering the heat of vaporization. Modulating control units also minimize on-off cycling to increase efficiency. They attempt to supply only the amount of heat to the building that the building loses at a specific outdoor air temperature.

     

    The new Vitodends 200 with Lamda Pro actually controls the gas valve using the microprocessor signal (microamps) from the flame to the sensing rod to control the modulation of the gas valve electronically. This means on each cycle the burner flame is dialed in for maximum efficiency and is not affected by the BTU content of the gas or its specific gravity.
  • Royboy
    Royboy Member Posts: 221
    thanks, Tim

    appreciate your time laying this out so succinctly!



    I gained a better sense of the role that microprocessor controlled combustion nuances play in this technology.



    left with the impression that modulation per-se doesn't necessarily increase efficiency (other than perhaps by reducing short-cycling), but that the subtle control of the modulation can add to efficiency by optimizing the whole combustion scene.
  • CMadatMe
    CMadatMe Member Posts: 3,085
    Now that's a Mouth Full

    Tim again hits it spot on again. The only thing I would like to add is that the measure of condensate is a sign of btu extraction. For every 1 gallon of water of condensate the boiler makes it has extracted roughly 8,700 btu's of that latent heat.  A basic Little Giant Condensate Pump holds 1/2 gal of water and pumps 1.2gpm at 5' head. Next time your in the boiler room with a mod/con in action listen for the pump  For every 10 minute run you just pulled a therm of gas that would normally escape the flue.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • NRT_Rob
    NRT_Rob Member Posts: 1,013
    modulation is key

    and also there is big difference in many cases between atmospheric and sealed combustion units that doesn't show up in AFUE or combustion analysis. That is, whether you're pulling cold air into the house or just the boiler.



    that's actually pretty significant in many cases. sealed combustion, modulation with no condensation would still be a significant efficiency increase for a lot of projects.



    if you run your temps lower on the hydroair just make sure you keep your air temps up or that you are not blowing air directly on anyone.
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
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