Steam Heating

steam heating [′stēm ′hēd·iŋ]

(mechanical engineering)

A system that used steam as the medium for a comfort or process heating operation.

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Steam heating

A heating system that uses steam generated from a boiler. The steam heating system conveys steam through pipes to heat exchangers, such as radiators, convectors, baseboard units, radiant panels, or fan-driven heaters, and returns the resulting condensed water to the boiler. Such systems normally operate at pressure not exceeding 15 lb/in.² gage or 103 kilopascals gage, and in many designs the condensed steam returns to the boiler by gravity because of the static head of water in the return piping. With utilization of available operating and safety control devices, these systems can be designed to operate automatically with minimal maintenance and attention.

In a one-pipe steam heating system, a single main serves the dual purpose of supplying steam to the heat exchanger and conveying condensate from it. Ordinarily, there is but one connection to the radiator or heat exchanger, and this connection serves as both the supply and return. A two-pipe system is provided with two connections from each heat exchanger, and in this system steam and condensate flow in separate mains and branches.

Another source for steam for heating is from a high-temperature water source (350–450°F or 180–230°C) using a high-pressure water to low-pressure steam heat exchanger. See Boiler

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Steam Heating 

a type of central heating wherein steam is used as the medium of heat transmission. The steam is provided to a heating system by a central heat-supply network or by a steam boiler, which can be located either in the building being heated or nearby. Three types of steam heating systems are distinguished according to the initial steam pressure: subatmospheric systems with a pressure less than 100 kilonewtons (kN)/m² (1 kilogram-force/cm²), low-pressure systems (from 100 to 170 kN/m²), and high-pressure systems (from 170 to 600 kN/m²). The low-pressure systems are used most frequently (Figure 1).

Figure 1. Low-pressure two-pipe downfeed steam heating system with gravity return of the condensate to the boiler: (1) steam boiler, (2) steam main, (3) heat-emitting devices, (4) return main, (5) air escape, (6) modulating valves

Steam heating makes use of steam’s property of giving up its latent heat when it condenses in heat-emitting devices. The resuiting condensate (water) is returned through the return main to the steam boiler or to the central heat-supply network.

Steam heating systems are classified as upfeed and downfeed according to the location of the steam main relative to the heat-emitting devices. Depending on the method of connection of the devices to the system, we speak of two-pipe and one-pipe systems (by analogy with hot-water heating). To achieve gravity flow of the condensate (including the condensate formed as a result of cooling of the steam piping), emptying of the system, and removal of air from the system, all piping is installed with the required pitch.

Steam heating was widely used, particularly in industrial buildings, until the 1930’s or 1940’s, but it is being supplanted in modern construction by hot-water and hot-air heating. The advantage of these methods over steam heating is that they permit the heat supply to be easily controlled according to the outside air temperature through variation of the temperature of the heat-transmission medium. Regulation of the heat supply in steam heating is usually performed by periodic switching-off of all or a part of the heating system. This complicates the use of steam heating and results in a nonuniform distribution of heat in the building. In addition, the operation of steam heating is frequently accompanied by noise, particularly when a cold system is being filled with steam. Another drawback is that the very high temperature of the heat-dissipating surfaces of the heat-emitting devices in steam heating systems poses danger from the standpoint of health and safety. For this reason, the regulations presently in effect in the USSR prohibit the installation of steam heating in dwellings, children’s institutions, hospitals, educational institutions, and administrative buildings.

The use of steam heating is permitted in industrial buildings that are supplied with steam for technological needs and also when exhaust steam is made use of. Installation of steam heating is also appropriate where operating conditions require rapid heating of the heat-emitting devices and the cooling of the devices after the heating system is switched off. In this respect, steam heating is superior to hot-water heating, particularly if the heat-emitting devices—for example, radiators—have increased volumes.

I. F. LIVCHAK