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Psychrometric Calculator

// MOIST AIR PROPERTIES - HVAC - THERMODYNAMICS

Unsaturated ASHRAE 2017/2021
Psychrometric Chart
Saturation (100% RH)
Constant RH
Enthalpy
Volume
Wet Bulb
Current State
Controls
Professional Engineering Tool - Disclaimer of Liability

FOR ENGINEERING AND EDUCATIONAL USE ONLY. This tool calculates moist air properties using ASHRAE standard equations. Results are theoretical and assume ideal gas behavior.

NO WARRANTY. This software is provided "AS IS" without warranty of any kind, express or implied, including warranties of merchantability, fitness for a particular purpose, or accuracy. The entire risk as to quality and performance is with you.

ASSUMPTION OF RISK. Psychrometric calculations are sensitive to input accuracy, atmospheric pressure, and measurement errors. Do not use for safety-critical systems without independent verification. Incorrect inputs or edge cases may produce misleading results.

VERIFICATION REQUIRED. Always cross-check critical calculations against ASHRAE Handbook charts, published tables, or validated software. This tool does not account for all real-world effects (contaminants, non-ideal gas behavior, aerosols).

Units
Pressure: kPa
Input Mode
Input Parameters
Standard pressure at altitude: 101.325 kPa
Process States
State A
Not set
State B
Not set
Save A and B to compare states.
HVAC Processes
No process applied.
Chart Overlays
Current Properties
Unsaturated Air
Dry Bulb (Tdb) 25.00 °C
Wet Bulb (Twb) 17.89 °C
Dew Point (Tdp) 13.86 °C
Rel. Humidity (RH) 50.0 %
Humidity Ratio (W) 9.88 g/kg
Enthalpy (h) 50.32 kJ/kg
Specific Volume (v) 0.858 m³/kg
Sat. Vapor Press 3.169 kPa
Part. Vapor Press 1.585 kPa
Input Parameters
Dry Bulb Temperature 25.0 °C
Relative Humidity 50.0 %
Atmospheric Pressure 101.325 kPa
Primary Calculations
Saturation Vapor Pressure (ASHRAE Ch.1, Eq. 5 ice / Eq. 6 water)
ln(Pws) = C1/T + C2 + C3*T + C4*T^2 + C5*T^3 + C6*ln(T)
Pws (at Tdb) 3.169 kPa
Pw (partial) 1.585 kPa
Humidity Ratio (W) 0.009881 kg/kg
Dew Point (Tdp) 13.86 °C
Energy Properties
Specific Enthalpy (ASHRAE Eq. 30)
h = 1.006 × Tdb + W × (2501 + 1.86 × Tdb)
Enthalpy (h) 50.32 kJ/kg
Wet Bulb (Twb) 17.89 °C
Physical Properties
Specific Volume (v) 0.858 m³/kg
Air Density (rho) 1.168 kg/m³
Degree of Saturation (mu) 0.498
Solver Details
Dew Point Solver Newton-Raphson
Wet Bulb Solver Bisection Method
Iterations (Twb) PsychroLib internal
Validation Checks
Tdp ≤ Twb ≤ Tdb Pass
0% ≤ RH ≤ 100% Pass
Pressure in valid range Pass
Engineering Disclaimer: This tool is provided for educational and informational purposes only. While algorithms are based on ASHRAE Fundamentals Handbook (2017/2021) equations, the software is provided "as is" without warranty of any kind, express or implied. The authors assume no liability for errors, omissions, or damages resulting from the use of this tool. Users must verify all critical calculations against standard engineering references.