psychrometric

Psychrometrics is the branch of thermodynamics that studies the physical and thermodynamic properties of moist air—the mixture of dry air and water vapor—and the processes that change those properties. It provides a framework for understanding how temperature, humidity, and moisture content interact in air at a given pressure.

Key variables in psychrometrics include dry-bulb temperature, wet-bulb temperature, relative humidity, humidity ratio (the mass of water vapor per mass of dry air), dew point, enthalpy, and specific volume. These properties are interrelated by thermodynamic relationships and are often represented on the psychrometric chart, a graphical tool that shows how conditions move through heating, cooling, humidification, and dehumidification.

Measurement is commonly performed with a psychrometer, which uses a dry-bulb and a wet-bulb thermometer, or with electronic humidity sensors. Data can be read directly from a psychrometric chart or converted into state properties such as RH, humidity ratio, and enthalpy using standard formulas and reference assumptions about atmospheric pressure.

Applications of psychrometrics span several fields. In heating, ventilation, and air conditioning (HVAC), it is used to design systems and calculate cooling and dehumidification loads. In meteorology, it helps describe atmospheric moisture and weather phenomena. Industrial drying, food processing, and packaging also rely on psychrometric analysis to control moisture content, energy use, and product quality.

The term psychrometric also refers to the methods and instruments used to evaluate moist air conditions, enabling assessments of comfort, process efficiency, and energy requirements.