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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 stovestove,
device used for heating or for cooking food. The stove was long regarded as a cooking device supplementary to the fireplace, near which it stood; its stovepipe led into the fireplace chimney. It was not until about the middle of the 19th cent.
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. 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 radiatorsradiator,
device used to heat an area surrounding it or to cool a fluid circulating within it. The familiar radiators of steam and hot water heating systems in buildings are misnamed, as they operate principally by convection, in which heat is transferred by air currents, rather
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 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.

Bibliography

See F. Porges, Handbook of Heating, Ventilating, and Air Conditioning (1982).

Heating

Raising the temperature of an interior space, either by a fire in a fireplace, hot air from a furnace, gas heater, electric heater, or radiator.

Heating

 

the artificial warming of premises during the cold season in order to compensate for heat loss and maintain a comfortable temperature or to meet the temperature requirements of a production process. The term “heating” is also used in reference to the equipment or systems that perform this function.

Thermal comfort is first of all a function of room temperature. Thus in dwellings, for example, a temperature of 18° to 20°C is considered to be the most favorable, while in the dressing rooms of bathhouses a temperature of 23°C is preferred. It is very important that the temperature be uniform over the whole floor area and at all heights. The extent to which such even heating can be maintained depends on the type and positioning of the heaters, the thermal-insulating properties of the outer enclosures (walls, floors, ceilings), and the degree to which outside air can penetrate these enclosures.

According to current Soviet standards, the capacity must be sufficient to compensate for heat losses during periods when the outside temperature is equal to the average temperature for the coldest five-day period on record in a particular locality. In Moscow, for instance, this temperature is —26 °C; in Yakutsk, -52°C; and in Tashkent, -13°C.

In industrial enterprises, where heat is continuously given off by equipment, the capacity of the heating unit can be correspondingly reduced. Vital physiological processes in humans also involve the evolution of heat and its release, mainly by radiation and convection, into the environment. This heat is transferred to the air and to the walls, floor, and ceiling, which help create the microclimate in any room. There is continuous change in all the components of heat loss in a room, as well as change in the amounts of heat given off by machinery, people, electric lighting, or solar radiation. It is therefore necessary to regulate the amount of heat that is supplied by a heating system; the amount supplied constitutes the difference between the thermal losses and the heat liberated. The most effective regulation of heat transfer is provided by an automatic heating system that takes thermal inertia into account as well as the heat liberated or lost. Regulation is also achieved by means of control valves on heater units.

Heating systems are classified as central or space-heating. In the central heating systems, heat is produced in a boiler room or heat and power plant that is separate from the space to be heated. The heat is then transferred through pipelines to the various rooms and buildings. Central heating systems are subdivided, according to the type of heat-carrying agent, into hot-water, hot-air, and steam heating systems. The most common system, used mainly in dwellings, public buildings, and sometimes in industrial buildings, is hot-water heating, with various types of heating units. Also in extensive use, chiefly in public and industrial buildings, is hot-air heating, which can be combined with ventilation and air-conditioning systems. In dwellings, public buildings, and industrial buildings where the requirements for air purity are higher than usual, panel heating and radiant heating are used extensively. Because of the inherent disadvantages of steam heating for modern construction, its use in currently constructed buildings is being curtailed. Combined steam and water systems are more often used. In these systems, a boiler is replaced by a water heater, which is heated with the steam.

In low buildings, space-heating systems that combine the heat generator with the heating unit are used. The heating stove is a very common type of space heater. However, it is gradually being displaced by more efficient and economical central heating systems and by other forms of space-heating such as gas and electric units and apartment heating units. This last type differs from central heating in that the heat generator supplies heat for one apartment, is usually located in the kitchen, and often combines a heater and a cooking range.

Heating is an essential consideration in the USSR because much of the country’s climate is characterized by low temperatures, which necessitates a lengthy heating season. The heating of residential and public buildings alone uses approximately 30 percent of all the solid and gaseous fuels extracted in the Soviet Union. The cost of heating equipment generally amounts to 46 percent of total construction costs. Operating costs depend to a great extent on fuel costs. The greatest operating efficiency is achieved by the centralized heat supply systems of the cities and industrial regions.

Heating technology has a long history. The first heating devices appeared in the Stone Age. At the beginning of the Common Era heating stoves with smoke pipes to remove the combustion products made their appearance. These stoves, with improvements, long remained the principal type of heating. The creation of central heating systems was an important step in the development of heating technology. The earliest such systems used a network of ducts beneath the floor, through which passed the smoky gases from a stove. As early as the 15th century, hot-air heating was used; air heated by contact with the surfaces of a stove was transferred to the room. Hot-water and steam heating systems were developed in the 19th century. In the early 1900’s radiant heating and panel heating were developed, along with centralized heating systems, district heating systems, and centralized heat supply systems.

REFERENCES

Stroitel’nye normy i pravila, part 2, sec. G, ch. 7: Otoplenie, yentiliatsiia i konditsionirovanie vozdukha; Normy proektirovaniia. Moscow, 1964.
Otoplenie i ventiliatsiia, 2nd ed., part 1. Moscow, 1965.
Semenov, L. A. Pechnoe otoplenie, 3rd ed. Moscow, 1968.

I. F. LIVCHAK

heating, ventilating, and air-conditioning system (HVAC system)

A mechanical system designed to satisfy the environmental conditions within an air-conditioned space, usually controlling the temperature, relative humidity, distribution and movement of air, and air cleanliness. Types of systems differ, but a basic system often includes an outside-air intake, chiller, preheater, dehumidifier, heating coil, humidifier, fans, duct-work, air outlets, and air terminals.