Direct (input-output) efficiency: useful heat in steam vs. fuel energy. Fast and accurate when steam flow and fuel flow are metered.
Formula
$$ \eta = \frac{m_s \cdot (h_s - h_{fw})}{m_f \cdot \text{LCV}} $$
Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| $m_s$ | Steam produced | kg/h | steam meter |
| $h_s$ | Steam enthalpy | kJ/kg | steam tables |
| $h_{fw}$ | Feedwater enthalpy | kJ/kg | feedwater tank |
| $m_f$ | Fuel consumed | kg/h | flow meter |
| $LCV$ | Lower calorific value | kJ/kg | ISO 8217 |
| $η$ | Direct efficiency | - | result |
Sources
- ASME PTC 4 - Fired Steam Generators.