Efficiency of condensing boilers in non-condensing mode?

[Jasper_1]

Anyone have real world observations on the efficiency of condensing boilers while operating in non-condensing mode? Are they as/or more efficient than a non-condensing boiler? Or will a non-condensing boiler outperform at higher temps?

From what I can find, most people assume the efficiency will be between 80%-85%, same as a good non-condensing boiler. However, I am having trouble finding good documentation of this that isn't from a boiler manufacturer.

The application is for a buildings with fin tube radiators, being taken off a central hot water plant and receiving new boilers. Because the existing FTR will not be replaced, hot water return temp will likely be 160F or higher most of the year, but there may be some opportunity to operate in condensing mode during shoulder seasons.

 

[Compositepro]

If the condensing boiler is run in non-condensing mode, then it is a non-condensing boiler. I think what you don't realize is that there is a lot of water vapor (steam) in a flame due to combustion products. It takes considerable heat to turn water into steam. The extra heat that is extracted from the flue gas due to condensing this steam is what increases the "efficiency". The reason that most boilers are non-condensing is that flue gas condensate is corrosive.

 

[Jasper_1]

Compositepro,
Thank you, I'm tracking the physics behind the higher efficiencies of condensing boilers. What I'm asking is if there is any difference in efficiency between a typical "Condensing Boiler" (i.e a boiler designed to handle operating at condensing temperatures) and a "Non-condensing" (i.e. a boiler designed to only operate above condensing temperatures) when they are both run at a return water temperature that won't allow for condensation to occur (160F).

I would assume there is not a significant difference, but the project O&M staff is convinced that a "Condensing Boiler" is significantly less efficient than a "Non-condensing" boiler when operated above condensing temps. I'd like to find some data to support either conclusion, but have not been able to find anything so far, so hoping someone can point me in the right direction.

 

[LittleInch]

Try this

http://jmpcoblog.com/hvac-blog/ener...-golden-rules-of-condensing-boiler-technology

or search condensing boiler water return temperature. All very similar graphs.

Then compare to non condensing.

You still have the same HX as below, just not getting the extra 10% efficiency from the water condenation.

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