How to calculate boiler efficiency by Direct Method ? - ASKPOWERPLANT

How to calculate boiler efficiency by Direct Method ?

How to calculate boiler efficiency by Direct Method

How to calculate boiler efficiency by Direct Method ?

in this article we discussed about the boiler efficiency how it calculated by direct and indirect method what are the factor responsible for the boiler efficiency . advantage or disadvantages of direct and indirect method  for calculating boiler efficiency

Boiler Efficiency:-

Thermal efficiency of boiler is defined as the percentage of heat input that is effectively utilized to generate steam. There are two methods of assessing boiler efficiency.

1) Boiler Efficiency by Direct Method:  Where the energy gain of the working fluid (water and steam) is compared with the energy content of the boiler fuel.

2) Boiler Efficiency by Indirect Method: Where the efficiency is the difference between the losses and the energy input.


  1. Boiler Efficiency by Direct Method This is also known as ‘input-output method’ due to the fact that it needs only the useful output (steam) and the heat input (i.e. fuel) for evaluating the efficiency. This efficiency can be evaluated using the formula:-
Direct- Method- boiler -efficiency
Direct Method boiler efficiency

Parameters to be monitored for the calculation of boiler efficiency by direct method are :

  • Quantity of steam generated per hour (Q) in kg/hr.
  • Quantity of fuel used per hour (q) in kg/hr.
  • The working pressure (in kg/cm2(g)) and superheat temperature (oC), if any
  • The temperature of feed water (oC)
  • Type of fuel and gross calorific value of the fuel (GCV) in kcal/kg of fuel
Direct Method boiler efficiency
Direct Method boiler efficiency

Where, hg – Enthalpy of saturated steam in kcal/kg of steam

hf – Enthalpy of feed water in kcal/kg of water

Advantages of Boiler Efficiency by direct method:

*Plant people can evaluate quickly the efficiency of boilers

*Requires few parameters for computation

*Needs few instruments for monitoring

Disadvantages of Boiler Efficiency by direct method:

*Does not give clues to the operator as to why efficiency of system is lower

*Does not calculate various losses accountable for various efficiency levels


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