Heat transfer is the process by which thermal energy moves from regions of
higher temperature to regions of lower temperature. In building physics, this
transfer occurs through distinct physical mechanisms: conduction, convection,
radiation, and latent heat exchange. Understanding these processes
is essential for improving thermal comfort.

Conduction is heat transfer by direct contact of particles. In a solid wall,
fast-moving (hot) molecules collide with slower ones and pass on energy.
That’s why heat flows from the warm inside to the cold outside if the wall is
not sufficiently insulated.

Convection is heat transfer by the movement of fluids such as air. Warmair is less dense, rises, and is replaced by cooler, heavier air that sinks. Thiscirculation carries heat with it, for example near windows or in poorly sealedrooms.

Radiation is the emission of energy as electromagnetic waves (mainly infrared).It does not need a medium. A warm surface radiates energy to colder surroundings - for instance, you can “feel” the cold wall even without touching it.

Latent heat is hidden heat bound in phase changes. It is the energy thata material absorbs or releases when it changes its physical state, such asfrom liquid to vapor or from vapor back to liquid, without any change in temperature.When water evaporates, it absorbs energy from the air (cooling effect).When it condenses, it releases that energy back.

This diagram illustrates how the human body exchanges heat with its surroundings.Heat is transferred through conduction, convection, and radiation,while evaporation of sweat helps cool the body. Together, these processesregulate body temperature in different environments.

This diagram shows how the human body loses heat at different temperatures.At low air temperatures, most heat is lost through radiation, because of thelarge temperature difference to the body (36 - 37°C) and air is large. As theroom warms up, this heat exchange rate become smaller. At high temperaturesclose to body temperature, the body can no longer lose heat by radiationor convection and relies mainly on evaporation of sweat to stay cool.