HOT WATER HEATING.
Another method of heating is by a similar application of direct hot water radiation. This consists in circulating hot water through radiators, which are placed in the rooms as in the case of direct steam heating. The hot water i.s conducted from the main heater in the cellar through the pipes and radiators, and the air is warmed by the direct radiation from these sources. The principle of this circulation is found in the difference in density and volume between hot and cold water. Water is at its greatest density at about 39 degrees F. When heated its density decreases and its volume increases, so that as soon as the fire in the boiler is started the circulation begins, and the water becoming lighter flows up through the pipes and radiators giving off its heat, until becoming colder and heavier it flows back through the return pipes to the heater. This process is continuous as long as any heat is applied to the water in the boiler, the velocity of flow depending upon the difference in temperature between the supply and return, and the height of the radiators above the boiler.
Hot Water Piping. The system of hot water piping consists of a free circulation of water from the heater to the radiators and back to the heater again. The supply pipe is taken off at the top of the heater and main and branches are run with an incline upward, the return pipes being parallel to these and connected with the bottom of the heater. Misers are taken off the tops of the mains and return pipes connected to the return mains in a like manner. (Fig. 65.) As this system depends upon the force of gravity to keep up its circula tion an expansion tank (Fig. 60) must be provided, high enough above the highest radiator to insure free circulation, and the pipes should be run so that any radiator may be shut off without interfering with the general circulation. This tank should be supplied with a glass gauge and an overflow to some convenient place, and an open vent pipe should be taken from the top. The connection from the heating system enters at the bottom and an automatic connection should be made with the train water supply. Al water connection should also be made at the heater to be used when the system is first filled, as by this means the air is driven upward and discharged through the vent on the tank.
The expansion tank should be large enough to contain a gallon of water for every forty square feet of radiation.
Valves. Special valves are made for use with loot water radia tors, the main advantage being a device for quick closing, a half turn being usually sufficient to open or close the valve. Connections with the radiators may be made at the top or bottom, the return pipe being always at the bottom. Only one valve is necessary to stop the flow of water through the radiator and this is put on the supply pipe, the return connection being made by a union elbow.
The ordinary "pet cock" is generally used for an air valve, but there are several forms of automatic valves which are operated by a float which allows the air to escape when the water line is lowered but closes upon the flowing in of the water.
Hot Water Heaters. The heater differs from a steam boiler mainly in the omission of the space allowed for steam, the hot water heater being filled with water in circulation instead of steam, so that it is essential that the heat should strike the surface in such a manner as to increase the natural circulation.
Radiators. Radiators for use with hot water differ from the ordinary steam radiators in hav ing a passage at both bottom and top, as shown in the illustration, Fig. 67. 'Phis is necessary in order to draw off the air which gathers at the top of each loop. These radiators may be used for steam as well as hot water and are arranged for either top or bottom connections. Sometimes the pip ing is so arranged that, instead of running pipes to each radiator from the beater, a single riser is carried up to the expansion tank from which pipes are run to supply the drops to which the radiators are connected. (Fig. (S.) In this case the radiators are supplied at the top and emptied at the bottom, and as the air in this system rises at once to the ex pansion tank and escapes through the vent, no air valves are required on the radiators.
Other methods of Beating are by indirect steam, indirect hot water, and a combination of hot air and steam, and the same general principles will apply to these methods as to those which have been consid ered. The indirect application of steam or hot water is the system by which fresh air is brought to each register, after being heated by passing over a coil of steam or hot water pipes, and while it is the most satisfactory of all means of heating, the expense of installation and maintenance i5 a bar to its employment for ordinary country or suburban horse heating