54. Probable Efficiency of Indirect Radiators.-The velocity with which the air will move over radiators when heated a given amount can be readily computed as explained in Article 33. With a given velocity we can determine from the experiments cited the probable amount of heat that will be given off per degree difference of temperature per hour for natural and for forced circulation. The results deduced from. experiments are given in the following tables:

TABLE FOR NATURAL CIRCULATION.

TABLE SHOWING THE HEAT-UNITS PER DEGREE DIFFERENCE OF TEMPERATURE BETWEEN THE ENTERING AIR AND THAT OF THE HEATING SURFACE FOR DIFFERENT VELOCITIES OF AIR APPLICABLE IN FORCED CIRCULATION.

55. Temperature produced in a Room by a given Amount of Surface when Outside Temperature is High.

Guarantees are often made respecting heating apparatus that it shall be sufficient to maintain a temperature of 70 degrees when the external air is at some fixed point, as zero, or 10 below. As under the exact conditions of the guarantee the trial can only be made when the external temperature corresponds with that specified, it becomes of some importance to establish an equivalent temperature which would indicate the efficiency of the heating apparatus for any specified condition. The following method applicable for such computations and is expressed in the shape of a formula:

Let T equal temperature of radiator, ' that of room, and t that of outside air for the conditions corresponding to the guarantee. Let B equal loss from room for 1 degree difference of temperature; let c equal the heat-units from I square foot of radiator per 1 degree difference of temperature for conditions corresponding to the guarantee; let c' denote the same values for other conditions; let r equal resulting temperature of room, t' outside air for the actual conditions, R equal square feet of radiation.

When '70, T = 220, t = 0, and c = 1.8, we have

(3)

The coefficient of heat transmission d' grows less as the temperature in the room becomes higher, as already shown in Art. 46; so the equations can only be solved in an approximate manner. The following table gives the temperatures in column 4, which a room would have for various tempera

tures outside, provided there was sufficient radiating surface to heat the room to 70 degrees in zero weather. The temperature of the radiator in all cases is assumed to be that due to 3 pounds pressure of steam by gauge, or 220 degrees.

Example showing Application of Table.-To determine by a test of the apparatus, when weather is 60°, whether a guarantee to heat to 70° in zero weather is maintained, operate the apparatus as though in regular use and note the average temperature of the room. If the room has a temperature equal to or in excess of 104.7° F., it would have a temperature of 70° in zero weather, all other conditions, such as wind, position of windows, etc., being the same as on the day of the test.

*This table, although calculated for steam with radiator at temperature of 220° F., is practically correct for hot-water radiation or for steam at any pressure and temperature.

Value of c' in formulæ.

Vol. 1, Transactions American Society Heating and Ventilating Engineers.

CHAPTER V.

PIPE AND FITTINGS USED IN STEAM AND HOT-WATER HEATING.

56. General Remarks. In this chapter will be found a concise description of pipe and fittings to be had regularly of most dealers. Such a description is entirely unnecessary to those familiar with current practice in the industry of steam and hot-water heating; but as the writer has found by experience detailed knowledge on this subject is often required, the following descriptions are deemed necessary.

It may be remarked in a general way, that for conveying heated air, galvanized or tin pipe or brick flues are usually provided, but for the purposes of conveying steam or hot water wrought-iron pipe is used almost exclusively.

57. Cast-iron Pipes and Fittings.-Cast-iron pipe was used very largely at one time for both supply-pipe and radiating surface in hot-water heating, but at present it is used only to a limited extent in greenhouse heating. For this purpose one size of pipe only is used, and this is 4" outside diameter. The pipe weighs about 12 lbs. to the foot, and has a capacity of gal. per foot. The pipes are usually joined by socket-joints, for which purpose a socket is cast on one end of each pipe. The joints are formed by inserting one end of one pipe into the

FIG. 32.-CAST-IRON PIPE WITH SOCKET.

socket of another and filling the interspace either with melted lead, iron-filings and sal-ammoniac, sulphur, or cement, and calking thoroughly. The lead joint, which is ordinarily used, is formed by making a mould, by wrapping a hemp rope covered with clay around the joint, with a pouring-place on top, into which the melted lead is run. After the joint cools the lead is

driven into place with a calking-iron. The rust-joint is a very excellent joint, and often used. It is made with a cement formed by saturating for ten or twelve hours iron turnings or filings with sal-ammoniac. This cement is pressed into the socket, and then pounded tightly into place with a calking-iron. Joints made with Portland cement are sometimes used, but they are likely to crack from the heat, and cannot be recommended. The regular form of pipe and some of the principal fittings are shown in Figs. 32 to 36.

FIG. 33.-ELBOW FOR CAST-IRON
PIPE.

FIG. 34.-ROUND TEE FOR CAST-
IRON PIPES.

FIG. 35.-RADIATING SURFACE AND PAN FOR HOLDING WATER 10 MOISTEN AIR. Two or more lengths of pipe, supported on special brackets are usually run in parallel lines with a slight descent in the direction of the flow, and thus serve both for radiating surface and circulating pipes. For greenhouse heating, where the air is to be kept moist, a special pan to be filled with water, as shown in Fig. 35, supported by the pipes, is used at intervals.

For the purpose of checking or stopping the flow a stop consisting of a flat plate, which can be set at any angle with the pipe,

and of a form as in Fig. 36, is used. Each length of cast