This book presents a practical guide to the application of the psychrometric chart in heating, ventilation, and air-conditioning (HVAC) systems. The chapters are structured to guide readers from basic principles to real HVAC applications. Key psychrometric processes such as cooling, heating, humidification, dehumidification, and air mixing are explained with clear examples. Special attention is given to tropical climates such as Malaysia, where high temperature and humidity strongly influence cooling load and building energy consumption. The book also introduces simplified mathematical models to estimate hourly temperature and relative humidity when limited weather data is available.To strengthen practical understanding, the book includes laboratory exercises and examples involving common HVAC systems such as split units, fan coil units, and air handling units. This book is intended for students, lecturers, and HVAC practitioners who wish to develop a practical understanding of psychrometric analysis and its application in air-conditioning systems.