Psychrometric State Calculator
Enter dry-bulb temperature plus one humidity input to compute the complete moist-air state — dew point, wet-bulb, RH, humidity ratio, vapor pressure, enthalpy, specific volume, density, and degree of saturation.
Inputs
Moist-Air State Result
Formula & Calculation Basis
All values are computed server-side by the PsychroLib v3 API (ProExergy), which implements the ASHRAE psychrometric formulations for perfect-gas moist air.
| Symbol | Meaning | Unit (SI) |
|---|---|---|
| T_db | Dry-bulb temperature | °C |
| T_wb | Wet-bulb temperature | °C |
| T_dp | Dew-point temperature | °C |
| φ | Relative humidity | – (0 to 1) |
| p_w | Partial pressure of water vapor | Pa |
| p_ws | Saturation vapor pressure at T_db | Pa |
| W | Humidity ratio | kg water / kg dry air |
| h | Specific enthalpy of moist air | J/kg dry air |
| v | Specific volume of moist air | m³/kg dry air |
| μ | Degree of saturation | – (0 to 1) |
| p | Total atmospheric pressure | Pa |
Calculation sequence: resolve total pressure (sea level, altitude, or manual) → send dry-bulb + chosen humidity value + pressure to the matching endpoint (/api/v1/calc/from-rel-hum, from-wet-bulb, from-dew-point, from-hum-ratio, from-vap-pres, or from-enthalpy) → API solves the remaining state variables and returns the full PsychroState object.
Assumptions & Limits
Included effects
- Moist air treated as an ideal-gas mixture of dry air and water vapor.
- Enhancement factor for saturation vapor pressure over the working range.
- Altitude-based standard atmosphere (ISA) when pressure is derived from elevation.
Excluded effects
- Non-standard atmospheric composition (e.g., contaminants, CO₂ enrichment).
- Local micro-climate pressure deviations not entered manually.
- Supersaturated / fog states below the saturation curve.
Valid input range: approximately −100 °C to 200 °C dry-bulb (SI) at standard-atmosphere pressures; wet-bulb and dew-point must not exceed dry-bulb; relative humidity 0–100%; humidity ratio and vapor pressure ≥ 0.
Engineering Notes
- Enthalpy is referenced to 0 °C dry air / liquid water (ASHRAE convention) and is per unit mass of dry air, not total moist air.
- Degree of saturation μ differs slightly from relative humidity φ; μ = φ only in the ideal-gas limit and they diverge near saturation.
- For data-center and cleanroom work, cross-check computed dew point against ASHRAE TC9.9 allowable/recommended envelopes.
- Method reference: PsychroLib (ASHRAE Fundamentals 2017, Ch. 1) as implemented by the ProExergy PsychroLib v3 API.
- API reference: ProExergy.com/.
Revision: v1.0 — initial release, calls PsychroLib v3 endpoints for RH, wet-bulb, dew-point, humidity ratio, vapor pressure, and enthalpy inputs.
