This section is from the book "A Treatise On Architecture And Building Construction Vol4: Plumbing And Gas-Fitting, Heating And Ventilation, Painting And Decorating, Estimating And Calculating Quantities", by The Colliery Engineer Co. Also available from Amazon: A Treatise On Architecture And Building Construction.
Size of Pipe in Inches.
Area of Direct Heating Surface in Square Feet.
If the area of heating surface exceeds the amount given, the fall of temperature will exceed 20°, and if it be less, the fall will be less correspondingly. If the connections are long or crooked, less heating surface can be operated, or a larger drop in temperature will occur.
218. In order to find the proper sizes of pipes for indirect-heating apparatus by means of the tables given, it is necessary to convert the area of indirect-heating surface into an equivalent area of direct-heating surface. This should be done by adding 50 per cent. to the actual area of the indirect radiators.
219. The manner of determining the proper sizes of the various parts of a hot-water pipe system by means of the foregoing tables will be explained by the aid of Fig. 80. This is a diagram showing the area of heating surface required at each radiator, the height of the various risers, and the length of the horizontal branches and mains. The vertical lines represent risers, the horizontal lines represent mains, and the oblique lines indicate horizontal branches extending at right angles from the pipes to which they are attached. The horizontal dotted lines indicate the several floor levels. The figures having the symbol □ attached to them (thus, 60°) indicate the area in square feet of the radiator at that branch. The risers are numbered No. 1, No. 2, etc., for convenience in reference. The length of each horizontal branch is noted in feet, and the lengths of the several parts of the mains are also noted.
220. Having a suitable working drawing, the work of computing the diameters of pipes should begin at the point most remote from the boiler, which, in this case, is the radiator on the 4th floor on riser No. 4-
The riser must supply water sufficient for 60 square feet of heating surface at that point. Referring to Table 19, it appears that on the 4th floor a 1-inch pipe is best adapted to 48 square feet, while a 1 1/4-inch pipe will serve 80 square feet. If the 1-inch pipe is used, the fall of temperature at the radiator will be more than 20°; therefore, it is wise to use the 1 1/4-inch pipe.
The pipe leading from the 2d to the 3d floor must supply the 60-foot radiator on the 4th. floor and also the 66-foot radiator on the 3d floor-a total of 126 square feet. The table shows that 126 feet on the 3d floor will be nearly supplied by 1 1/2-inch pipe, while the next size, 2-inch, is much too large. If there were no radiator on the 2d floor, it would be advisable to use the 2-inch pipe from the 66-foot radiator down to the mains.
The riser from the main to the 2d floor must supply three radiators, aggregating 210 square feet. The table shows that 2-inch pipe is a little small, while 2 1/2inch is larger than necessary. But it should be noted that there are elbows at the foot of these pipes; therefore, it is wise to use the 2 1/2-inch diameter.
The sizes of the other risers should be determined in a similar manner. The horizontal lines may then be considered. That part of the mains extending from No. 4 riser to the connections to No. 3 must supply a first-story radiator in addition to No. 4 riser, aggregating 312 square feet. The length of the flow pipe is 100 feet, which, added to the same length of return pipe, makes a circuit of 200 feet. Referring to Table 18, it appears that 312 square feet of surface, on a 200-foot circuit, requires a 3 1/2-inch pipe. This size is a little larger than that actually required, and will compensate for the elbows at b.
At the point c another circuit is attached, No. 3, which supplies 240 square feet of heating surface, making the total surface to be supplied at that point 240 + 312 = 552 square feet. The distance between the points c and d is 75 feet, making the circuit 150 feet long. The table shows that 552 square feet of surface, on a 200-foot circuit, requires a 4 1/2-inch pipe. The return may be continued to the boiler with that size, but the flow main should be enlarged at d to provide for the radiator at c.
The length of the connections to this radiator is so much greater than ordinary that the circuit should be considered as a 100-foot circuit. The table shows that 120 square feet of surface requires 2-inch pipes.
It will be noted that this radiator is also provided with an independent return connection, as shown at f. This construction insures a good circulation, more positive and rapid than if the return were connected into the return main at d. The difference is owing to the length of the horizontal branches. If the radiator were located close to the mains, there would be no considerable advantage in providing it with an independent return.
The circulation in circuit No. 2 would probably be improved by providing the return pipe g with an independent connection to the boiler, instead of connecting it into the return main, as shown in the drawing.
The radiator h, on circuit No. 2, has long connections. It is explained in Art. 211 that a given size of pipe will supply 1.7 times as much heating surface on the third floor as on the first; therefore, this radiator corresponds to one on the first floor having 48 ÷ 1.7 = 28 square feet of surface. Table 18 shows that a radiator of that size on a 100-foot circuit requires 1 1/4-inch pipes.