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© 1982, The Board of Regents of the University of Nebraska on behalf of the University of Nebraska–Lincoln Extension. All rights reserved.


This NebGuide describes how to use a simplified psychrometric chart to better understand the relationships between air temperature and relative humidity.

Air is a vital component of our everyday lives. Air properties are important whether we are ventilating a livestock housing unit, drying grain, or determining relative humidity in the home. In a livestock building, temperature, moisture, odors, and toxic or noxious gases must be controlled. Since the moisture holding capacity of air increases with increasing temperature, heat may be added in grain drying to aid in removing moisture from the grain kernel. In the home, moisture can either be added to or removed from the air to change the relative humidity. In each case, air provides the link between the controls and the mechanical equipment, and air properties influence the results of the processes.

Psychrometrics refers to the properties of moist air. A psychrometric chart graphically illustrates the relationships between air temperature and relative humidity as well as other properties. A better understanding of air properties and the psychrometric chart can aid in the selection and management of a livestock building ventilation system, a grain drying system, or a home humidifier.