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# explanation of boiler efficiency curves examples in EP?

Apologies for what is almost certainly a very dumb question but I'm struggling to understand what the boiler efficiency curves in the EP example files actually represent.

Looking at InputOutput reference for the formula and plotting the biquadratic condensing boiler efficiency curve data given in the boilers.idf file gives Eff = 112% at 0.1 part load and Twater = 50oC for example. The coefficients for the curve define the curve completely so I'm not sure what the nominal thermal efficiency field is used for. I've looked at the Veissman technical guide referenced in Boilers.idf and while it contains a graph showing the curve I've plotted it doesn't have any other explanation. I thought the part load efficiency was the thermal efficiency but guess I must be wrong or it shouldn't be over 100%

I've had a look for other boiler efficiency curves and the only other data I could find was in the ACM reference manual for california building code compliance. The coefficient values there give a very different curve for a condensing boiler, ie. Eff = 96% at 0.1 cartload and Twater = 50oC.

My overall aim is just to model a non-domestic condensing boiler that is available in the UK but unfortunately have very little data on efficiency:

Boiler efficiency Part load 30% at 50/30°C (gross) 97.4 %

Boiler efficiency Full load 100% at 80/60°C (gross) 88.2 %

If anyone could enlighten me I'd be very grateful!

Thanks,

Pamela

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Question title might be more clear if it was changed to something like "what is boiler nominal thermal efficiency used for". As it stands it initially sounds like a much broader question than it is.

( 2018-01-30 07:38:27 -0500 )edit

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The coefficients for the curve define the curve completely so I'm not sure what the nominal thermal efficiency field is used for.

From the I/O Reference, the 'Normalized Boiler Efficiency Curve' describes the normalized heating efficiency (as a fraction of nominal thermal efficiency) of the boiler’s burner.

The nominal thermal efficiency is the equipment efficiency at full load and design outlet temperature. The output of the efficiency curve modifies the nominal efficiency based on the runtime (part load, temperature) conditions.

My advice would be: in lieu of more complete data about your system, use the curve that best fits the data that you have.

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Thank you - that makes much more sense now!

( 2016-06-27 07:17:55 -0500 )edit