Document kx7Z1d7drdL0najQRN618NB

502 CHAPTER 21 1951 Guide milinches per foot, or 600 milinches for 4 ft. If the first floor radiators 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 503 Table 1. Ikon and Copper Elbow Equivalents* Fitting Iron Pipe Fihow. 45-dee____________ Elbow. 90-deg long turn_. Elbow, welded, 90-deg-- Reduced coupling------------Open return band------------Open gate valve--------------Open globe valve-------------- 1.0 0.7 0.5 0.5 0.4 1.0 0.5 12.0 Copper Tubing Fitting 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_______ .-- Tee, per cent flowing through branch: 100.. ---- ------------ 50. . --------- 25 ---------------- - Irok Pipe 2.0 3.0 3.0 1.8 4.0 16.0 Copper Tubing 3.0 4.0 4.0 1.2 4.0 20.0 * The friction in one 90 deg standard elbow is approximately equal to the friction of a length of straight nine of the same nominal siae and 25 diam long. Hence, one elbow equivalent in feet of pipe equals 25 diam (in inches) divided by 13. Fio. 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 velocity, a given error in the calculation or assumption of the velocity is less im portant in a forced circulation system than in a gravity circulation system, and, consequently, it is easier to design a satisfactory forced circulation system than a satisfactory gravity circulation system.. FRICTION LOSS Values, of friction loss due to flow of water in the various parts of a heat ing system must be known in order to design either gravity or forced circu lation systems. The friction loss of fittings is customarily expressed in equiy- Lower scale of chart Is based on 20 deg temperature difference between flow and return risen. To find, friction when temperature drop is other than 20 deg, multiply the actual heat conveyed' by ( actual top. drop ) and read the oorr3pondill riotk,n'