This lecture introduces the fundamentals of Heating, Ventilation, and Air Conditioning (HVAC) systems, covering topics such as thermal comfort assessment, psychrometric processes, key components of HVAC systems, and common HVAC processes like heating, cooling, and dehumidification. The lecture also explores the historical development of HVAC systems, from Willis Carrier's invention of modern air conditioning to the role of HVAC in indoor climate quality. Practical examples and exercises are used to illustrate the application of psychrometric principles in HVAC design and operation.