Psychrometric Chart

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This Demonstration of a psychrometric chart calculates the relative humidity [%], absolute humidity [kg water/kg dry air], dry bulb temperature [ºC], and specific volume SV [m³/kg dry air] for different pairs of temperature and absolute humidity at a pressure of 101.325 kPa.


You can drag the locator to see values at points on the saturation line and points with relative humidity less than 100%. The blue line represents the saturated air; the purple lines are the lines with relative humidity equal to 80%, 60%, 40%, 20%, and 10%.

The equations used to simulate this psychrometric chart are:




Contributed by: Mariana Sobreiro (March 2011)
Open content licensed under CC BY-NC-SA



Psychrometric properties are relevant for processes involving acclimatization, refrigeration, cooling and freezing, humidifying and dehumidifying of air, drying and dehydration of humid products, and in ambient control and meteorology. The most common variables in such processes are: dry bulb and humid bulb temperatures, relative humidity, absolute humidity, vapor pressure, specific volume, specific enthalpy, sensible heat, and the dew point temperature.

The use of psychrometric charts requires skill by the user, which restricts their use. Thus, mathematical modeling of the equations and subsequent computer simulation of psychrometric charts significantly simplify their use, eliminating reading errors.

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