Heat transfer is a fundamental concept in HVAC. It involves the movement of thermal energy from one object to another. There are three methods of heat transfer: conduction, convection, and radiation.

Conduction is the transfer of heat between objects that are in direct contact with each other. This is the most common method of heat transfer in HVAC systems, and is responsible for heat flow through walls, ceilings, and floors.

Convection is the transfer of heat through a fluid, such as air or water. In HVAC systems, convection is used to distribute heated or cooled air throughout a building. This is achieved through air handlers and ductwork.

Radiation is the transfer of heat through electromagnetic waves. This method of heat transfer is not commonly used in HVAC systems, but is important in understanding the behavior of heat energy.

Overall, understanding the principles of heat transfer is critical in designing and maintaining HVAC systems that efficiently and effectively manage thermal energy.