![]() Radiant energy doesn’t have a temperature. This energy can be absorbed by other objects with a lower temperature. The primary source of radiant energy is the sun, but every object on earth radiates infared energy as long as it has mass and a temperature above absolute zero. It also works in a vacuum and it’s the most important form of heat transfer in outer space. Radiation doesn’t need a medium (like air or water) for heat transfer. More precisely, it concerns the part of the electromagnetic spectrum that’s called infrared radiation. Radiant energy is transferred through electromagnetic waves, similar to light or sound. Radiation, the third form of sensible heat transfer, works in a very different way from conduction and convection. This plume of warm air that rises from every object that is warmer than the surrounding air, is called convection. Its place is taken by cold air, which is heated in turn, expands, rises, and so on. However, the air that is warmed by conduction expands and rises. By itself, this effect is limited, because air has a high thermal resistance - that’s why it forms the basis of most thermal insulation materials. Each physical object that is warmer than the air that surrounds it, heats up the air in the immediate vicinity through conduction. This explains why, for instance, a cold metal object feels much colder than a cold wooden object, even though they both have the same temperature.Ĭonduction not only occurs between physical objects, but also between physical objects and gasses (like air), and between gasses mutually. The speed at which this happens depends on the thermal resistance of the substance.įor example, heat is transferred much faster through metal than through wood, because metal has a lower thermal resistance. Conduction concerns the transfer of energy due to the physical contact between two objects: heat will flow from the warmer to the cooler object. Conduction and convection are closely related. While convection implies the warming of each cubic centimetre of air in a space in order to keep people comfortable, radiation and conduction can directly transfer heat to people, making energy use independent of the size of a room or building.įirst, let’s have a look at the different methods of heat transfer in some more detail. The old way of warming was based upon radiation and conduction, which are more energy-efficient than convection. There are three types of (sensible) heat transfer: convection (the heating of air), conduction (heating through physical contact), and radiation (heating through electromagnetic waves). This seems an obvious choice, but there are far worthier alternatives. Most modern heating systems are primarily based on the heating of air. It would make a lot of sense to restore this old way of warming, especially since modern technology has made it so much more practical, safe and efficient. These people countered the large temperature differences with insulating furniture, such as hooded chairs and folding screens, and they made use of additional, personal heating sources that warmed specific body parts. ![]() They used radiant heat sources that warmed only certain parts of a room, creating micro-climates of comfort. In earlier times, our forebear’s concept of heating was more localized: heating people, not places. These days, we provide thermal comfort in winter by heating the entire volume of air in a room or building.
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