Document 6RoVxKbNyxQv4oE5K4G8d9BJ1

' ?~ 528 CHAPTER 22 1955 Guide ' of 150 milinches per foot, or 600 milinches for 4 ft. If the first floor radi ators are located 3 ft above the mains, second floor radiators 12 ft above the mains, third floor 21 ft, and fourth floor 30 ft, the heads are 450, 1800, 3150, and 4500 milinches, respectively. In forced circulation systems flow is produced mechanically by means of a pump driven by electricity, steam, or other source of energy. As Hot Water Heating Systems 529 Table 1. Iron and Copper Elbow Equivalents* Fitting Iron Copper Pipe . Tubing Fitting Iron Copper Pipe Tubing Elbow. 90-dee................... Elbow, 45-deg..................... Elbow, 90-deg long turn___ Elbow, welded, 90-deg.......... Reduced coupling................... Open return bend................... Open gate valve...................... 1.0 0.7 0.5 0.5 0.4 1.0 0.5 12.0 1.0 0.7 0.5 0.5 0.4 1.0 0.7 17.0 Angle radiator valve Radiator or convector.... Boiler or heater.................... 9n q n 3.0 . 4.0 3.0 4.0 Tee, per cent flowing through branch:1* 100....................................... 60 25....................................... 1.8 40 16.0 1.2 40 20.0 * The friction in one 90 deg standard elbow is approximately equal to the friction of a length of straight pipe of the same nominal size and 25 diam long. Hence, one elbow equivalent in feet of pipe equals 25 rliwrn (in inches) divided by 12. " Applies to conditions of flow in hot water heating system.1, * FLOW OF WATER IN GALLONS PER MINUTE Fig. 1. Heads Resulting from Temperature Difference (Gravity Systems) forced circulation velocities are higher than those in gravity systems, and as the friction in a heating system varies almost as the square of the veloci D a given error in the calculation or assumption of the velocity is less portant in a forced circulation system than in a gravity circulation syste ' and, consequently, it is easier to design a satisfactory forced circulat system than a satisfactory gravity circulation system. FRICTION LOSS Values of friction loss due to flow of water in the various parts of a h^' ing system must be known in order to design either gravity or forced c lation systems. The friction loss of fittings is customarily expressed m eqm . Fig.. 2. Friction in Black Iron Pipes i. To ?c^e of chart is based on 20 deg temperature difference between flow and return risers. (no *nction when temperature drop is other than 20 deg, multiply the actual heat conveyed by actu^f^mp and read the corresponding friction.