What is conduction in terms of heat transfer?

Conduction refers specifically to the transfer of heat through direct contact between materials. When one object or substance is heated, its particles begin to move more quickly and collide with neighboring particles, thereby transferring thermal energy. This process occurs without the movement of the material itself, meaning that the heat is transferred through the solid or between solids primarily through molecular interactions.

In HVAC applications, understanding conduction is essential, as it plays a crucial role in how buildings retain or lose heat. For example, when warm air inside a building comes into contact with cooler walls or pipes, heat transfer happens through conduction, affecting the overall thermal performance and energy efficiency of the system.

The other options describe different types of heat transfer mechanisms: movement of heat through air relates to convection, transfer of thermal energy through a medium can apply to all forms of heat transfer including conduction, convection, and radiation, and cooling of air via fans involves forced convection rather than conduction. Each of these does not accurately define conduction on its own.