Psychrometric%

Psychrometric Algorithms and References

CYTSoft Psychrometric Chart uses the formulations developed by Hyland and Wexler to calculate

thermodynamic properties of moist air, which model moist air as a REAL gas, rather than an ideal gas.

Atmospheric Pressure and Altitude (U.S. Standard Atmosphere)

The atmospheric pressure for the altitude range of -5000 to 11000 m is given by

Water Vapor Saturation Pressure

The saturation pressure over ice for the temperature range of −100 to 0 °C is given by

The saturation pressure over liquid water for the temperature range of 0 to 200 °C is given by

Saturation Humidity Ratio

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Relative Humidity

Humidity Ratio

Wet Bulb Temperature

The wet bulb temperature is calculated iteratively through the following equations

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References

[1] 2005 ASHRAE Handbook – Fundamentals. Chapter 6: Psychrometrics.

[2] Hyland, R.W. and Wexler, A. 1983a. Formulations for the thermodynamic properties of dry air from 173.15 K to 473.15 K, and of saturated moist air from 173.15 K to 372.15 K, at pressures to 5 MPa. ASHRAE Transactions 89(2A):520-535.

[3] Hyland, R.W. and Wexler, A. 1983b. Formulations for the thermodynamic properties of the saturated phases of H2O from 173.15 K to 473.15 K. ASHRAE Transactions 89(2A):500-519.

[4] Hyland, R.W. and Wexler, A. 1973a. The Enhancement of Water Vapor in Carbon Dioxide-Free Air at 30, 40, and 50 °C. J. Res. NBS 77A:115-131.

[5] Hyland, R.W. and Wexler, A. 1973b. The Second Interaction (Cross) Virial Coefficient for Moist Air. J. Res. NBS 77A:133-147.

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