Document Z4G94v6N0ZMnBMY1xMRdEvzeJ

jil .504 CHAPTER 24 1949 Guide Hot 'Water Heating Systems and Piping 505 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- indans of a pump driven by electricity, steam, or other source of energy. As Table 1. Iron and Copper Elbow Equivalents* Fitting Elbow, 90-deg-----------------Elbow, 45-deg-----------------Elbow, 90-deg long turn... Elbow, welded, 90-deg.-- Reduced coupling.-----------Open return band------------Open gate valve-________ Open globe valve------------- Iron Pips 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 Radiator or convector___ Tee, per cent flowing through branch: inn 5ft 25.__________________ Iron Pips 2.0 3.0 3.0 1.8 4.0 16.0 Copper Tubinc 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 pipe of the same nominal eize and 25 diam long. Hence one elbow equivalent in feet of pipe equals 25 dism (in inches) divided by 12. IriilkvaHiWIKVaoUk.SM'aMIWMnMIlH.'HiMmMBSMIMHMBMi F R IC T IO N ---------- M IL IN C H E S P E R FO O T O F P IP E Fig.T.Heads Re3ULTinq 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 head 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 equiv- jj-8 fill i I I 1 -" V O O OOg 8| | | FLOW IN POUNDS OF WATER PER HOUR "" Fig. 2. Friction in Black Iron Pipes Based on Flow in Pounds per Hour 1 alent number of elbows of the same pipe size which would have the same' friction loss. An elbow is assumed to have the same friction loss as a straight pipe having a length equal to 25 diameters (nominal) of the elbow-. The resistance of various types of fittings expressed in equivalent elbow resistance is shown in Table 1.