radiant heating: see heating.

heating, means of making a building comfortably warm relative to a colder outside temperature. Old, primitive methods of heating a building or a room within it include the open fire, the fireplace, and the stove. In ancient Rome a heating system, called a hypocaust, warmed a building by passing hot gases from a furnace through enclosed passages under the floors and behind the walls before releasing them outside. The principal modern systems that are used to heat a building are classified as warm air, hot water, steam, or electricity. In the warm-air system air, heated in a furnace, rises through warm-air ducts and enters the rooms through outlets, while cooler air in the rooms passes into return ducts that lead back to the furnace. The air circulates through the system by convection, i.e., the tendency of a fluid such as air to rise when warm and sink when cool. In newer buildings the circulation is assisted by a fan. The hot-water system has a boiler for heating the water that is sent through connecting pipes to radiators and convectors, the latter devices being metal enclosures containing hot-water pipes surrounded by metal fins. The circulation is maintained by pumps or, in older buildings, by convection. In the steam-heating system, steam generated in a boiler is circulated by its own pressure (sometimes aided by a vacuum pump) through radiators. There are many kinds of electric heating systems. In one type current is sent through wires into electric resistors that are contained in convectors in rooms. The resistors convert the current into heat. In a radiant panel heating system a room is warmed by heat emitted from wall, floor, or ceiling panels. They are warmed by the circulation of warm air, hot water, or steam or by an electric current in resistors within or behind the panels. Experiments are being made to utilize solar energy for heating buildings. In many large buildings, such as theaters, public libraries, and municipal buildings, the heating, ventilating, and air-conditioning units are combined in one system. In district heating, heat is distributed from a heating plant to buildings in a section (usually commercial) of a city.

Use of solar radiation to heat water or air in buildings. There are two types: passive and active. Passive heating relies on architectural design; the building's siting, orientation, layout, materials, and construction are utilized to maximize the heating effect of sunlight falling on it. A well-insulated building with a large south-facing window, for instance, can trap heat on sunny days and reduce reliance on gas, oil, or electricity. Brick, stone, or tile capacity walls are often incorporated to absorb the sun's energy and radiate it into the interior, usually after a time lag of several hours. In active solar heating, mechanical means are used to collect, store, and distribute solar energy. In liquid-based systems, a blackened metal plate on the exterior absorbs sunlight and traps heat, which is transferred to a carrier fluid. Alternatively, fluid may be pumped through a glass tube or volume of space onto which sunlight has been focused by mirrors. After picking up heat from the collector, the warm fluid is pumped to an insulated storage tank. The system can supply a home with hot water from the tank or provide space heating with the warmed water flowing through tubes in floors and ceilings.

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Method of raising the temperature of an electrically conductive material by subjecting it to an alternating electromagnetic field. Energy in the electric currents induced in the object is dissipated as heat. Induction heating is used in metalworking to heat metals for soldering, tempering, and annealing, and in induction furnaces for melting and processing metals. The principle of the induction-heating process resembles that of the transformer. A water-cooled coil (inductor), acting as the primary winding of a transformer, surrounds the material to be heated (the workpiece), which acts as the secondary winding. Alternating current flowing in the primary coil induces eddy currents in the workpiece, causing it to become heated. The depth to which the eddy currents penetrate, and therefore the distribution of heat within the object, depend on the frequency of the primary alternating current and the magnetic permeability, as well as the resistivity, of the material.

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Process of raising the temperature of an enclosed space. Heat can be delivered by convection, radiation, and thermal conduction. With the exception of the ancient Romans, who developed a form of central heating, most cultures relied on direct heating methods such as fireplaces and stoves. Central heating, adopted for use again in the 19th century, is a method of indirect heating: heat is produced away from the occupants and then conveyed to them. In warm-air heating, air heated by a furnace rises through ducts to rooms above, where it is emitted through grills. In hot-water systems, a pump circulates water from a boiler through a system of pipes to radiators or convectors in rooms. In steam systems, steam is generated in the boiler and led to radiators through pipes. The high temperature of the steam makes it hard to control, and steam heating has been largely superseded. A common type of electric heating system converts electric current to heat by means of resistors that emit radiant energy. Seealso radiant heating, solar heating.

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