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Gas Turbine Inlet Cooling Calculator
Estimate how far evaporation can cool the compressor inlet during a hot dispatch hour. Add a turbine-specific output curve to see how many extra megawatts the plant could export.
Site conditions
Use outdoor dry-bulb and wet-bulb readings from the same location and hour.
90% is an editable screening assumption. Use measured effectiveness or a supplier’s design value where available.
Add turbine and dispatch data (optional)
From two points on the same OEM curve, divide the increase in gross output by the temperature drop. Use the same operating mode, elevation and load limits for both points.
Include incremental compressed-air, water-treatment and control loads. Zero assumes no auxiliary draw. Blank headroom means no generator cap is applied.
Examples replace all inputs, including an illustrative 0.40 MW/°F slope and 0.50 MW auxiliary load.
Estimated compressor inlet
72.5°F
22.5°F cooler than ambient.
- Available wet-bulb depression
- 25.0°F
- Gross output gain after cap
- Add OEM slope
- Net export change
- Add OEM slope
- Net energy for entered hours
- Add slope and hours
How is turbine inlet temperature calculated?
Subtract the wet-bulb temperature from the dry-bulb temperature to get the available cooling range. Multiply that range by the evaporative effectiveness, then subtract the result from the dry-bulb temperature.
Inlet temperature = dry bulb − effectiveness × (dry bulb − wet bulb). Enter 90% as 0.90 in the equation. This model assumes complete evaporation upstream of the compressor and excludes both the extra sensible cooling from Smart Fog’s cold spray and any wet compression. Smart Fog reports approximately 39°F at the nozzle without a water chiller. That temperature is not the bulk compressor inlet temperature.
Two 95°F afternoons, two different MW estimates
| Illustrative case | Dry afternoon | Humid afternoon |
|---|---|---|
| Wet bulb | 70°F | 85°F |
| Inlet at 90% effectiveness | 72.5°F | 86.0°F |
| Gross gain at 0.40 MW/°F | 9.0 MW | 3.6 MW |
| Net after 0.50 MW auxiliaries | 8.5 MW | 3.1 MW |
Both examples assume sufficient generator headroom. Net MWh = net MW × hours at the entered conditions. For a season, calculate each weather and dispatch interval separately and sum its MWh. The worked numbers are illustrative.
What can change the result?
Can I use this calculator without a turbine curve?
Yes. You can calculate inlet temperature and cooling range from weather alone. The power and energy results require the local slope of a gross MW-versus-inlet-temperature curve. For a nonlinear curve, read both endpoint outputs directly or split the interval into smaller segments.
Why can net export be negative?
If generator headroom is exhausted, or humid air leaves little evaporative potential, cooling-system auxiliaries can consume more power than the turbine gains. A negative result represents the modeled change if those auxiliaries continue running.
Does the estimate include a combined-cycle steam turbine?
It covers the machine represented by the entered curve. For a gas-turbine curve, downstream heat-recovery steam generator and steam-turbine effects are excluded. Use plant performance software for combined-cycle net output, inlet pressure losses, heat rate, icing limits and part-load dispatch.
Engineering references: ASHRAE Handbook, Combustion Turbine Inlet Cooling and GE Power Systems GER-4200 (PDF).