Page:Encyclopædia Britannica, Ninth Edition, v. 11.djvu/626

of water in pipes. When the boiler or source of heat is very near the level of the pipes for heating the air, the average temperature which can be obtained in the pipes will be lower than when the vertical column is long. The heating surface must be regulated with reference to this difference of level. It may further be assumed that with small pipes, the temperature being constant, the velocity of flow in the pipe necessary to furnish a given amount of heat will vary in the ratio of the length of the pipe. When the water circu- lates through the pipes by virtue of the difference of temperature of the flow and return currents only, it is impossible to count upon a greater mean temperature of the pipes than from 160° to 180°, because above that temperature the water in the boiler begins to boil. To obtain a sufficient velocity of circulation for long dis- tances, or with small differences of level, a forced circulation may be resorted to. This has been done by Messrs Easton and Anderson at the county lunatic asylum at Banstead, in the following manner. The whole hot-water service is supplied from boilers placed at one end of the asylum buildings, which extend toa distance of several hundred yards. There are two pipes: one of them, which may be calle the flow pipe, is connected directly with the boiler, ter- minating at the point furthest from the boiler in a dead end; the other, which may be termed the return pipe, is parallel to the first, and terminates at one end ina cistern which is placed about 6 feet above, and supplies the boiler. At the other end furthest from the cistern the second pipe also terminates in a dead end. At each pavilion or place to which hot water is required to be conveyed, there is a connexion between the two pipes, which can be closed or opened at will; when it is opened, the water ean pass from the flow to the return pipe. In the second, or return pipe, near the point where it ascends to the cistern, is placed a rotatory pump, or fan wheel, which is always kept revolving. When the openings are all closed between the two pipes, this pump or fan simply slips through the water ; but as soon as the return pipe obtains a supply of water from any of the openings between it and the flow pipe, a circulation is established.

The following diagram, resulting from Mr Anderson’s experi- ments, published in the Journal of the Institution of Civil Engincers for 1877, shows the total units of heat given out by east-iron and wrought-iron pipes per square foot of surface per hour for various differences of temperature applicable either to hot-water or steam pipes. Suppose, for example, it is required to know how much heat will be given out by 4-inch cast-iron or 2-inch wrought-iron pipes at 190° in a room, the temperature of which is 60°; the difference of temperature is 130°, and corresponding to this will be found 232°7 units for 4-inch pipes and 356 units for 2-inch wrought-iron pipes per square foot per hour.

Units of Heat per Square Foot per Hour. 19.4 0 vu lu 20° 3% 40° Su? 69° 7U° bu° 90° 100" 110° 120° 130° 140° 150° 160° 17u° 180" 19U° 200°

Diagram for ascertaining the heat given out by 4-inch cast-iron and 2-inch wrought-iron pipes at various differences of temperature. The dotted line shows the 4-inch, and the solid line the 2-inch pipes.

The amount of heating surface to be afforded with hot-water pipes depends mainly upon tke volume of air to be admitted and removed, and the temperature desired to be maintained, but in any given building there are other circumstances to be taken into account, viz., the position, aspect, subsoil, temperature of locality, thickness of walls, size and" form of windows, and other influences affecting the temperature of the incoming air, or causing loss of heat. An empirical rule has been laid down that in a dwelling- house 1 square foot of heating surface is required for every 65 cubic feet of space to be warmed, and in a greenhouse 1 square foot to every 24 cubic feet. This empirical rule does not take into account the sanitary considerations as to the renewal of air.

Steam-heated pipes present important advantages in some cases over hot-water pipes for heating purposes, because of the higher temperature to which the pipes ean be raised, their consequent smaller size, and the facility of conveying the heat to a distance. Steam heating may be applied directly; and the waste steam from an engine is also applicable for heating.

The direet application of steam heating on a large scale has been made at Lockport, New York. About 200 houses in the city are heated from a central supply through about 3 miles of piping, radiating from a boiler-house, which contains two boilers 16 feet by 5 feet, and one boiler 8 feet by 8 feet. ‘These boilers are fired during the winter to a pressure of 35 Tb to the inch, with a con- sumption of 4 tons of anthracite coal in twenty-four hours. The Loiler pressure of 35 T in winter and 25 tb in summer is maintained through a total length of 3 miles of piping up to the several points of consumption, where there is a eut-off under the control of the consumers. The first 600 feet of mains from the boilers are 4 inches in diameter. There are 1400 feet of 3-ineh pipes, 1500 feet of 23- inch pipes, and 2000 feet of 2-inch pipes. The supply pipes from these mains to the houses are 14 inches in diameter, and within each house §-inch pipes are used. In addition to the cut-off tap from the main under the control of the consumer, there is a pres- sure valve regulated to a 5-Ib pressure under the coutrol of the company ; and beyond this is an ingeniously constructed meter, which indicates, not only the total consumption in cubic feet of steam, but also the quantity of steam in each apartment. At each 100 feet of main an expansion valve, like an ordinary piston and socket, is inserted, allowing an expansion in each section of 100 fect of 12 inehes for the heat at 35-tb pressure. No condensation oecurs in the mains. They are covered with a thin laycr of asbestos paper next the iron, then a wrapping of Russian felt, and finally manilla paper, and the whole is encased in timber bored out three- quarters of an inch larger than the felt-covered pipes, and laid along the street like gas-pipes. The distribution of heat in the apartments is by means of radiators consisting of inch pipes, 30 inches long, placed vertically cither in a circle or as a double row, and connected together at top and bottom, with an outlet pipe for the condensed water, which eseapes at a temperature a little below boiling, and is sufficient for all the domestic purposes of the house, or it may be used as accessory heating power for horticultural and other purposes. The steam has also been applied at a distance of over half a mile from the boilers for motive power, and two steam engines of 10-horse and 14-horse power are worked from the boilers at a distance of half a mile with but a slightly increased consump- tion of fuel. The laid-on steam is also used for cooking purposes, for boiling, and even for baking. As in the case of gas supply, the steam supply company lay their pipes up to the houses, the con- sumer paying for all internal pipes, fittings, and radiators. Ina moderately-sized eight-roomed house the expense of these amounted to $150, and in larger houses with costlier fittings to $500.

3oulton’s system of heating with exhaust or waste steam is devised to cause the steam froma steam engine to travel long distances without any back pressure on the engine. It is especially applicable to drying rooms in which 150° Fahy. has been obtained by a large heating surface ; for a lower temperature less heating surface is required. The capacity of heating by exhaust steam is neatly ina ratio with the fuel expended in the boiler. There is some cooling in passing through the engine, and in the conveyance along the pipes to the rooms to be heated, but this loss is compara- tively small if the pipes and the cylinder are covered with a good non-conductor, and the condensed water is taken back hot into the boiler. Thus, if the steam be taken from the boiler direct to the pipes at five atmospheres, the temperature would be 307°, and if a comparative capacity of steam were allowed to pass through the engine to create power, and discharged into the pipes at one atmo- sphere, it would decrease in temperature to 213°; but it would increase in bulk according to the expansion ; and thus to obtain nearly the same temperature in the room the heating surface should be increased.

With an engine of 17-inch cylinder and 25-horse power nominal, the exhaust steam has been made to travel 200 yards in a direct line, as well as to pass into various branches, amounting in the aggregate to about 2386 yards (or 14 miles) of 14-inch pipes. After this it warms the water for the boiler, and the steam is not all used up. The whole efficiency of the system depends upon so arranging the pipes as to prevent back pressure. Mr Boulton assumed that one-horse power if properly applied should warm about 30,000 cubic feet of space, subject to reductions for window space, wall space, the number of cubic feet of air allowed to eseape for ventilation, and other considerations, and lays down the follow- ing empirical rule, viz.:—1 square foot of steam pipe 18 allowed for cach 6 square fect of glass in the window, 1 for every 6 cubic feet of air escaping for ventilation per minute, and 1 for every 120 fect of wall, roof, or ceiling, adding about 15 per cent. for contingencies. .

Wrought-iron pipes 14-inch bore are the most economical for steam, as they afford a large heating surface with small area. In heating living rooms by steam, the high temperature of the pipes affords one of the advantages of an open fire, viz., warmth by radiation, and combines with this the advantage which hot-water pipes possess of directly warming the air.

(d. g.)

HEAVEN. See Eschatology, vol. viii. p. 537.