The different makers of radiators publish in their catalogues, tables giving the square feet of heating surface for different styles and heights, and these can be used in determining the number of sections required for all special cases.
If pipe coils are to be used, it becomes necessary to reduce square feet of heating surface to linear feet of pipe; this can be done by means of the factors given below.
3 = linear ft. of 1 -in. pipe 2.3 = " " 11-in. " Square feet of heating surface X 2 = " 11-in. " 1 .6 = " " 2 -in. " The size of radiator is made only sufficient to keep the room warm after it is once heated; and no allowance is made for warming up; that is, the heat given off by the radiator is just equal to that'lost through walls and windows. This condition is offset in two ways first, when the room is cold, the difference in temperature between the steam and the air of the room is greater, and the radiator is more efficient; and second, the radiator is proportioned for the coldest weather, so that for a greater the time it is larger than neces sary.
1. The heat loss from a room is 25,000 B. T. U. per hour in the coldest weather. What size of direct radiator will be required? ANs. 100 square feet.
2. A schoolroom is to be warmed with circulation coils of 11 inch pipe. The heat loss is 30,000 B. T. U. per hour. What!length of pipe will be required? ANS. 230 linear feet.
Location of Radiators. Radiators should, if possible, be placed in the coldest part of the room, as under windows or near outside doors. In living rooms it is often desirable to keep the windows free, in which case the radiators may be placed at one side. Circulation coils are run along the outside walls of a room under the windows. Sometimes the position of the radiators is decided by the necessary location of the pipe risers, so that a certain amount of judgment must be used in each special case as to the best arrangement to suit all requirements.
Systems of Piping. There are three distinct systems of piping, known as the two-pipe system, the one-pipe relief system, and the one pipe circuit system, with various modifications of each and combina tions of the different systems.
Fig. 23 shows the arrangement of piping and radiators in the two-pipe system. The steam main leads from the top of the boiler, and the branches are carried along near the basement ceiling. Risers are taken from the supply branches, and carried up to the radiators on the different floors; and return pipes are brought down to the return mains, which should be placed near the basement floor below the water-line of the boiler. Where the building is more than two
stories high, radiators in similar positions on different floors are con nected with the same riser, which may run to the highest floor; and a corresponding return drop connecting with each radiator is carried down beside the riser to the basement. A system in which the main horizontal returns are below the water-line of the boiler is said to have a wet or sealed return. If the returns are overhead and above the water-line, it is called a dry return. Where the steam is exposed to extended surfaces of water, as in overhead returns, where the con densation partially fills the pipes, there is likely to be cracking or water-hammer, due to the sudden condensation of the steam as it comes in contact with the cooler water. This is especially noticeable when steam is first turned into cold pipes and radiators, and the con densation is excessive. When dry returns are used, the pipes should be large and have a good pitch toward the boiler.
In the case of sealed returns, the only contact between the steam and standing water is in the vertical returns, where the exposed sur faces are very small (being equal to the sectional area of the pipes), and trouble from water-hammer is practically done away with. Dry returns should be given an incline of at least 1 inch in 10 feet, while for wet returns 1 inch in 20 or even 40 feet is ample. The ends of all steam mains and branches should be dripped into the returns. If the return is sealed, the drip may be directly connected as shown in Fig. 24; but if it is dry, the connection should be provided with a siphon loop as indicated in Fig. 25. The loop becomes filled with water, and prevents steam from flowing directly into the return. As the condensation collects in the loop, it overflows into the return pipe and is carried away. The return pipes in this case are of course filled with steam above the water; but it is steam which has passed through the radiators and their return connections, and is therefore at a slightly lower pressure; so that, if steam were ad mitted directly from the main, it would tend to hold back the water in more distant returns and cause surging and crack ing in the pipes. Some times the boiler is at a lower level than the basement in which the returns are run, and it then becomes necessary to establish a false water-line. This is done by making connections as shown in Fig. 26.