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Ashrae Psychrometric Chart Si Units Pdf Download

Ashrae Psychrometric Chart Si Units Pdf Download

A psychrometric chart is a graphical representation of the thermodynamic properties of moist air at a constant pressure. It is widely used in the fields of heating, ventilation, air conditioning, and refrigeration to analyze and design various processes involving moist air. A psychrometric chart can show the relationships among dry-bulb temperature, wet-bulb temperature, relative humidity, dew point temperature, humidity ratio, enthalpy, and specific volume of moist air.


ASHRAE, the American Society of Heating, Refrigerating and Air-Conditioning Engineers, is a professional organization that develops standards and guidelines for the HVAC&R industry. ASHRAE publishes several psychrometric charts in both I-P (inch-pound) and SI (International System of Units) units for different pressure levels and climatic zones. These charts are available in PDF format on the ASHRAE website or as an interactive app for iOS devices. The app allows users to plot points and processes on the chart, save and email the results, and access climatic data from the ASHRAE Handbook.

In this article, we will focus on the ASHRAE Psychrometric Chart #13 (SI), which is based on a standard atmospheric pressure of 101.325 kPa and covers a dry-bulb temperature range from -10C to 60C. This chart is suitable for most engineering calculations involving moist air at sea level or low altitudes. The chart consists of several curved and straight lines that represent different psychrometric properties and processes. The following table summarizes the main features of the chart:





Dry-bulb temperature (T)

The temperature of moist air measured by a thermometer with a dry bulb.


Humidity ratio (w)

The mass of water vapor per unit mass of dry air in moist air.


Wet-bulb temperature (Tw)

The temperature of moist air measured by a thermometer with a wet bulb that is kept moist by evaporating water.


Dew point temperature (Td)

The temperature at which moist air becomes saturated when cooled at constant pressure and humidity ratio.


Relative humidity (φ)

The ratio of the partial pressure of water vapor to the saturation pressure of water vapor at the same temperature.


Enthalpy (h)

The total energy per unit mass of moist air, consisting of sensible and latent heat.


Specific volume (v)

The volume per unit mass of moist air.

To download the ASHRAE Psychrometric Chart #13 (SI) in PDF format, you can click on this link or scan this QR code:

To learn more about the theory and applications of psychrometrics, you can refer to these resources:

  • : A lecture note that explains the basic concepts and equations of psychrometrics in SI units.

  • : A webpage that provides information about the ASHRAE Psychrometric Chart app and other psychrometric products and publications.

  • : A book that serves as a reference manual and a basic refresher course for psychrometrics.

We hope you found this article helpful and informative. If you have any questions or feedback, please feel free to contact us. Thank you for reading!


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