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Boiler Efficiency - Direct Method

Direct (input-output) efficiency: useful heat in steam vs. fuel energy. Fast and accurate when steam flow and fuel flow are metered.

SteamBoiler
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Formula, assumptions, and limits

η=ms(hshfw)mfLCV\eta = \frac{m_s \cdot (h_s - h_{fw})}{m_f \cdot \text{LCV}}
SymbolMeaningUnit
msm_sSteam producedkg/h
hsh_sSteam enthalpykJ/kg
hfwh_{fw}Feedwater enthalpykJ/kg
mfm_fFuel consumedkg/h
LCVLCVLower calorific valuekJ/kg
ηηDirect efficiency

Source: ASME PTC 4 - Fired Steam Generators

In short

Direct (input-output) efficiency: useful heat in steam vs.

Learn the theory Marine Auxiliary Engines and Generators