Psychrometric Analysis Quick Reference Guide

Psychrometric analysis is the study of thermodynamic properties of moist air, a critical discipline in heating, ventilation, and air conditioning (HVAC), building science, and industrial process control. At its core lies the psychrometric chart—a graphical representation of the thermodynamic state of moist air—where each point corresponds to a unique combination of dry-bulb temperature, humidity ratio, and other derived properties. The analysis relies on well-established physical laws, including the ideal gas law applied separately to dry air and water vapor, Dalton’s law of partial pressures, and conservation of mass and energy during air–water vapor interactions such as cooling, heating, humidification, and dehumidification. Key processes—like sensible heating/cooling, adiabatic saturation, constant enthalpy (evaporative cooling), and mixing of airstreams—are visualized as lines or curves on the chart and governed by corresponding analytical models. Accurate psychrometric analysis supports precise load calculations, equipment selection, control strategy development, and compliance with indoor air quality standards (e.g., ASHRAE 55 and 62.1).