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Psychrometric Moist-Air Properties Calculator — result sheet
Estimate saturation pressure, vapor pressure, humidity ratio, dew point, specific volume, and moist-air enthalpy from dry-bulb temperature, relative humidity, and air pressure.
Inputs used
Results
Visual chart
Breakdown
Calculation steps
Returned data table
Formula and methodology
Formula: Saturation pressure uses pₛ = 0.61094 exp(17.625T/(T+243.04)) kPa over the bounded liquid-water range; vapor pressure pᵥ = φpₛ; humidity ratio W = 0.621945pᵥ/(p−pᵥ); dew point uses the inverse saturation relation; specific volume v = 0.287042(T+273.15)(1+1.607858W)/p; moist-air enthalpy h = 1.006T + W(2501+1.86T).
This calculator describes one moist-air state from three directly entered properties. It keeps pressure explicit because the same temperature and relative humidity produce different humidity ratios and specific volumes at different pressures. The compact saturation-pressure relation is intended for ordinary HVAC and classroom comparisons in the stated range; it is not a replacement for a full property package, psychrometric chart, or equipment design review.
This result follows the calculator's declared inputs, precision, validation boundaries, and model limits.
Input contract
- Dry-bulb temperature — °C; minimum 0; maximum 60
- Relative humidity — %; minimum 0.01; maximum 100
- Total air pressure — kPa; minimum 20; maximum 120
Worked example
| Input | Value |
|---|---|
| Dry-bulb temperature | 25 |
| Relative humidity | 50 |
| Total air pressure | 101.325 |
The estimated state has about 1.58 kPa vapor pressure, a humidity ratio near 0.00988 kg/kg dry air, a dew point near 13.86 °C, and a specific volume near 0.858 m³/kg dry air.
Assumptions and limits
- Dry-bulb temperature is between 0 °C and 60 °C, the relative humidity is above zero and at most 100%, and total pressure is entered in kPa absolute.
- The saturation-pressure relation is an approximation for water vapor over liquid water in the bounded temperature range; ice saturation, fog, supersaturation, and condensation processes are not modeled.
- Humidity ratio is kilograms of water vapor per kilogram of dry air; specific volume and enthalpy are also reported on a dry-air mass basis.
- The moist-air relations use ideal-gas behavior with constant dry-air and water-vapor gas constants; real-gas corrections and contaminant gases are excluded.
- Relative humidity is treated as a state input, not as a measurement uncertainty or a forecast of indoor comfort.
- Use a validated psychrometric property method and qualified HVAC review for equipment sizing, condensation control, or safety-critical work.
Calculator note
Source and methodology
Use the official WorldCalculate methodology policy for the source, formula, precision, and boundary standards behind this calculator.
Planning estimate, not financial, medical, legal, or professional advice. © WorldCalculate — reuse with attribution. Built and curated by Hassan ALRowaie.
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