Download: Heating: method of calculating the efficiency of a condensing boiler

Helps establish thermal combustion efficiency in a condensing or high efficiency boiler For use by professionals. By Rémi Guillet.


Establishing the performance of thermal generators is a delicate operation which requires heavy equipment. It is even more so with condensing generators!

We present here a simple method to use, not very demanding in measurement equipment and particularly adapted to the case of generators called condensing or even high efficiency.

It is assumed that combustion is complete (CO check performed!). This is an indirect approach to thermal performance, therefore based on the
knowledge of the “combustible” energy entering the generator and that conveyed by the combustion products (in gaseous and possibly liquid phase) discharged at the outlet nozzle. The losses “on the walls” and the energy consumed by the auxiliary devices are therefore not taken into account (in the case of recent generators, these elements are generally negligible compared to their nominal thermal power).

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In any case, we are talking here about “thermal efficiency of combustion” and we will call it Rt.

The reference conditions for the expression of the enthalpies of the various “H” flows being specified (in temperature and humidity), the value of Rt is written “Rt = 100 + Ha + Hc - Hpc” 

Expression where the quantities Rt, Ha (enthalpy of the flow of air entering the generator), Hc (enthalpy of the incoming fuel flow), Hpc (enthalpy of the rejected combustion products) are expressed in% of the heating value.

Since these are primarily condensing generators, then the calorific value chosen a priori is the superior calorific value (Pcs), that is to say that which takes into account the heat of condensation of the water formed during of combustion.

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