In terms of human comfort, radiation is basically the transfer of heat energy from one surface to another.
The body is heated if the surrounding air is warmer than the skin's temperature – examples you're familiar with include the radiant energy of the sun, a fire, the heating elements in an oven, or a radiator.
In the same way, the body can lose heat when the surrounding air or surface is colder.
This is why tile or metal surfaces can feel cool indoors when a room is otherwise a comfortable temperature, because the warmer body temperature is radiated to the cooler surface.
But the same metal cafe chairs may feel perfectly comfortable in a patio restaurant in the summer. In winter or cooler climates, the designer can consider covering cold surfaces with fabrics, rugs, or using draperies and insulating panels to keep occupants feeling “warm”.
Heat is transferred in 3 ways:
- Conduction: The transfer of heat between substances which are in direct contact with each other. Conduction occurs when heat flows through a solid.
- Convection: The movement of gases and liquids caused by heat transfer. As a gas or liquid is heated, it warms, expands and rises because it is less dense resulting in natural convection.
- Radiation: When electromagnetic waves travel through space, it is called radiation. When these waves (from the sun, for example) hit an object, they transfer their heat to that object.
Similarly, by minimizing drafts, you can keep people comfortable in a cool environment.