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Modulation Range of Condensing Boilers?

SpeyFitterSpeyFitter Member Posts: 422
I'm curious what you guys see in the future of Condensing Boilers and their modulation range and/or technology. Do you think we might see systems that modulate significantly lower? Is the Burner technology there? Could we see 20 to 1? 30 to 1? 50 to 1? Smart control systems that can virtually match the boiler load to the heat loss and adapt as neccessary to ensure this is the case?

I know of one boiler with a 10 to 1 modulation range, but most seem to be 3-5 to 1 right now. 
Class 'A' Gas Fitter - Certified Hydronic Systems Designer - Journeyman Plumber


  • don_9don_9 Member Posts: 395
    What ever for

    If the load was ever to get that low then I would simply tell them to put on a sweater bc, the heat is being turn off on warm weather shutdown.

    I'm still on the fence with the issue that modulating equipment will save on fuel verse it more gear toward comfort and zoning.
  • Tim McElwainTim McElwain Member Posts: 4,373
    Not so sure

    if modulation is the answer. I am inclined to want to see better system design with accurate temperature control to the system emitters. It is my long standing opinion and in some cases I have proved that firing at full rated input is the better way for overall efficiency. Working to insure the condensing feature is met on all phases of firing will also improve overall efficiency. When we can effectively use every BTU produced to actually end up in the dwelling is the real efficiency.

    This is also why I do not like two stage systems as they tend to cause people to constantly override the thermostat when the system does not heat up quick enough. This also by the way is usually a problem with system design.

    Putting a high efficiency boiler or furnace on a poorly designed system or one that has not been modified to work in conjunction with the high end heater is a real waste.
  • CMadatMeCMadatMe Member Posts: 3,066
    Couldn't Agree with you more Tim

    I have always taking the stand that system efficiency is more important than boiler efficiency. How an appliance makes its energy is great but how you use the energy produced from the fuel you pay for is most important. This is the main reason that I am a big Viessmann fan. They take a system approach with their products unlike any other boiler manufacture in the world.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • SpeyFitterSpeyFitter Member Posts: 422
    Why modulate then?

     My biggest concern is the lack of smaller boilers out there for smaller applications and/or areas with more moderate climinates, and I am specifcally interested in Viessmann for their known quality.  Viessmann's smallest Vitodens 100 which fires at 37,000 BTUH's input in some cases is as much as twice the design day heat loss, of some houses I know of. So it would/could be short cycling like a MOFO on shoulder days, which is a significant portion of the heating season. Perhaps we could do some things to mitigate how the system acts to perform with the higher output of the boiler, but it would also be nice to know the boilers BTUH output would more closely match the heat loss, or be more suited to it.
    Class 'A' Gas Fitter - Certified Hydronic Systems Designer - Journeyman Plumber
  • CMadatMeCMadatMe Member Posts: 3,066
    edited December 2009
    Vitodens 100

    Keep in mind that you would be using a LLH (low loss header). Boiler supply water temp max is 176 on the Vitodens 100 leaving the boiler to the LLH (when your curve is set to 6). You are only getting  roughly 170 degree water on the system side of the LLH. This is all based on a 20 degree delta-t and flow rates. So let's say you only need 37K or 3.7 GPM on the boiler side and your delivery water temp out the boiler is 115 degree water to the LLH. Water temp on the system side is going to be alot colder leaving the LLH probably 100 degrees or so. Board would be only putting out roughly 120 btu's a foot. I don't think short cycling will be an issue. The boiler is going to run as long as the zone thermostat asks the boiler to run. A perfect example of why the heat loss and emmiter sizing is key to  system efficiency.  Another way to combat is go to a 30 degree delta-t instead of a 20. Average water temp at design would be about 160and your board output at 1gpm and 160 water is about 430 btu's a ft.

    Just my thoughts welcome to any others.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • EricAuneEricAune Member Posts: 432
    edited December 2009
    Viessman system is nice, but

    Too large of a boiler is just that.  I really like the LLH approach but in cases where the boiler is just too darned big I start looking at other heat sources.

    This is an area of the market where buffer tanks could be used more appropriately.  The cost of those tanks also has to come down, but thats another thread.
    "If you don't like change, your going to like irrelevance even less"
  • CMadatMeCMadatMe Member Posts: 3,066
    I think That is Where

    Boiler control technology needs to get. To give the ability to run the boiler at what btu you want on design day. I'd like to see a mod/con that gives the ability to run down to 10,000 btus and all the way up to 120,000.  The installer via the control would be able to select the desired btu and water temp he wants on his deisgn degree day. The boiler would then modulate and reset based on his inputs. Grapevine has it there is another Vitodens on Steriods coming out. Don't know if that means bigger or smarter but I wouldn't be suprised if they were the first ones out the gate with this type of burner and control technology.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Tim McElwainTim McElwain Member Posts: 4,373
    It will require

    special burner technology to have that broad a differential in BTU's in the same chamber. Poor Port Loading on the burner on the low end would create a low flame temperature which could cause carbon monoxide issues. The burning speed of natural  gas which is a slow burning fuel would definitely have a problem.

    I would be more inclined to see new boiler concept with 10,000 to 30,000 BTU's available for small heat loss application. That way burner design could be made to fire at these rates.
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