Radiant heating and cooling system

A radiant heating and cooling system refers to temperature-controlled surfaces that exchange heat with their surrounding environment through convection and radiation. By definition, in radiant heating and cooling systems, thermal radiation covers more than 50% of heat exchange within the space.Hydronic radiant heating and cooling systems are water-based. It refers to panels or embedded building components (floors, ceilings or walls). Other types include air-based and electrical systems (which use electrical resistance for heating purpose mainly). Important portions of building surfaces are usually required for the radiant exchange.

Radiant heating and cooling systems can be used in commercial, residential, education, and recreational buildings, museums, hospitals, and other type of buildings. The application depends on the type of radiant system (see below types of radiant systems), on climate conditions and on ventilation system used.

Heat radiation is the energy in the form of electromagnetic waves emitted by a solid, liquid, or gas as a result of its temperature. In buildings, the radiant heat flow between two internal surfaces (or a surface and a person) is influenced by the emissivity of the heat emitting surface and by the view factor between this surface and the receptive surface (object or person) in the room. The heat transfer by radiation is proportional to the power of four of the absolute surface temperature.

The emissivity of a material (usually written ε or e) is the relative ability of its surface to emit energy by radiation. A black body has an emissivity of 1 and a perfect reflector has an emissivity of 0.

In radiative heat transfer, a view factor quantifies the relative importance of the radiation that leaves an object (person or surface) and strikes another one, considering the other surrounding objects. In enclosures, radiation leaving a surface is conserved, therefore, the sum of all view factors associated with a given object is equal to 1. In the case of a room, the view factor of a radiant surface and a person depend on their relative positions. As a person is often changing position and as a room might be occupied by many persons at the same time, diagrams for omnidirectional person can be used.

The operative temperature is an indicator of thermal comfort which takes into account the effects of both convection and radiation. Operative temperature is defined as a uniform temperature of a radiantly black enclosure in which an occupant would exchange the same amount of heat by radiation plus convection as in the actual nonuniform environment.

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