Document e12gJqyyBxZZ1bJ0pgrkoD0ae

HEATING VENTILATINC AIR CONDITIONING GUIDE 1940 Table 6. Capacities of Mains in Mbh, foe One-Pipe and foe Two-Pipe Direct Return Gravity Circulation Systems with a Total Friction Head of 0.6 In., a Temperature Drop of 35 F, when the Mains are 4 Ft above the Center of the Boiler Pipe Sob (Inches) IK 2 2K 3 3K 4 Equivalent Length of Pipe (Frets) 3.0 4.0 4.5 5.0 5.5 6.0 Equivalent Total Length of Pq>b in Feet in Longest Circuit 75 1 100 125 150 175 j 200 | 250 | 300 | 350 Unit Friction Hear, in Miunches - 8,0 6.0 4.8 4.0 3.4 3.0 2.4 2.0 1.7 43.0 37.5 SS.0 30.0 27.0 25.0 22.2 20.2 18.7 83.0 72.0 6S.0 67.0 51.0 48.0 42.0 38.0 35.0 140.0 115.0 100.0 90.0 81.5 75.4 67.2 61.0 56.0 234.0 204.0 176.5 160.0 143.0 133.0 110.0 107.5 100.0 347.0 300.0 260.0 236.0 21A.0 200.0 177.0 160.0 146.0 490.0 422.0 370.0 334.0 297.0 278.0 248.0 223.0 205.0 the'vekKSty!TM316 1<!I,Bth f pipe in eQuivaknt to one elbow in friction head. This value varies wilh is used, the capacity will be 8.0 Mbh; if both risers are % in., the capacity will be 14.0 Mbh. The K->n- pipe is selected for both risers. To design the radiator connections, use Table 8 and note that for the first floor radiator connections the capacity of a K-in. flow and 1-in. return is 9.1 Mbh, and that of a 1-in. flow and a 1-in. return is 12.5 Mbh. The former is more nearly the correct size, but since it is difficult to secure a good flow through first floor radiators, the 1-in. flow and return connection is selected. For the two upper floors, the capacity of a %-in. flow and return connection is 10.5 Mbh, and that size is used. Table 7. Maximum Capacities of Risers* in Mbh, and Velocities of Water in Pipes In Inches Per Second for One-Pipe and for Two-Pipe Direct Return Gravity Circulation Systems with a-Drop of 35 F through Each Radiator Pipe Size (Inches) Flow I Return Equipalert Length op Pipe (Febic) lffr FuioBb Vd (In. per Seed) Mbh Flow I Retorn 2nd Floob MM 3ed and 4tb Flooks Mbh KK 1.0 KK K lK lK l l IK IK IK IK IK IK IK 1.5 2.0 3.0 3.5 9 2.3 2.3 12 3.2 2.0 18 2.5 2.5 21 3.0 2.0 26 3.0 3.0 34 4.0 2.5 AS. 3.0 3.0 .______________________________ ,,;i 6 6.4 10.1 12.8 20 26.2 43 6.2 8.0 14-0 17.1 26.0 u 65 1 This table is based on pressure heads of 450,1800, 3150, and 4500, respectively, for tbe first, second, third, and fourth floor radiators, and on friction heads of 200 miiinches for the first floor radiators and con nections, and 700 miiinches for all other radiators and their connections. bTbe riser branches, the piping which connects the risers to the mains, are to be one size larger than tbe risers. eApproximate length of pipes in feet equivalent to one elbow in friction head. This value varies with the velocity. dVelodties apply to tbe riser branches. 324 CHAPTER 17. HOT WATER HEATING SYSTEMS AND PIPING Table 8. Maximum Capacities of Radiator Connections in Mbh, for One-Pipe lA and for Two-Pipe Direct Return Gravity Circulation Systems with a Temperature Drop of 35 F through Each Radiator PzfbSjzb Flow Return Equivalent Length of Pipe (Feet) 1st Floob Mbh 2nd, 3rd, and 4th Floors Mbh '. K K K % 1 1 lK K K K 1 1 IK IK 1.0 1.5 2.0 3.0 4.1 6.2 7.0 9.1 12.6 17.6 23.3 5.9 7.5 10.6 13.0 17.8 23.2 33.2 Approximate length of pipe in feet equivalent to one elbow in friction head. This value varies with tbe velocity. As explained in the design of the forced circulation system of Fig. 5, the two-pipe direct return system of Fig. 8 will not function correctly unless its lour sets of risers are balanced among themselves. This neces sary balancing is accomplished by adding resistances to all risers, except the one farthest from the boiler, equal to the excess boiler pressure heads available for those risers above the boiler pressure head available for the farthest riser. For example, the first set of risers is 60 ft nearer the boiler than the last set. Since the flow and return mains are designed for a friction head of 3 miiinches per foot (see Table 6, Column 8), the boiler pressure head available for the first set of risers is 360 miiinches in excess of that available for the fourth set. The velocity in the riser branch is 3 in. per second (see Table 7) and, therefore, according to Table 5, an 0.65-in. orifice in a l}4-in. union should be used. This will provide a resistance of about 420 miiinches. In the same manner it is found that for the second set of risers a resistance of 240 miiinches is required and that an 0.70-in. orifice in a lM->n. union will provide a resistance of 285 Fig. 9. An Open Expansion Tank Fig. 10. A Closed Expansion Tank 325