Document LMNKn2jpw5Xk7qk54gmGpqBw

408 CHAPTER 28 FLOW OF WATER IN GALLONS PER MINUTE 1960 Guide low te of chart it bated on 20-deg temperature cfifferaoce beftraw flow and ratera rimrs. To tod frtcfioo when teaperafwe drop omer Aon 20 deg, ufKp<y (6* actual fiec! conveyed by t20-i-acted temp. drop) and reorf (he cane^ondfog friction. Ftper 100 ft Macndm per ft Cooversion Ft/(I00 RJ to MiBadm/Ft 0.J 1 2 3 60 120 240 360 4 480 5 600 Fig. 6.... Friction Loss duo to Row of Water in Type L Copper Tube Table 2----- Iron and Copper Elbow Equivalents** * * * Hum, Iren Pipe Copper Tubing Elbow, 90-dec........................................ Elbow, 45-deg......................................... Elbow, 90-dec long turn................. Elbow, welded, 9tf-deg...................... Reduced coupling........................... Open return bend............................... Angle radiator valve.......................... Radiator or convector....................... 1.0 0.7 0.5 0.5 0.4 1.0 2.0 3.0 1.0 0.7 0.5 0.5 1.0 3.0 4.0 Boiler or heater............................... Open gate valve.......................... ... Open globe valve................................ 3.0 0.5 12.0 * See Tsbk i tar eguirelent length at ooe elbow. 0.7 17.0 should be calculated. The friction loss at design Sow for all individual sections of pipe and for all fittings in the longest piping circuit should then be summarized. Table 2 shows the number of elbow equivalents foT various fittings. These equivalents can be converted to equivalent feet of pipe by use of Table 3. Fig. 7 shows the elbow equiva lents for determining .friction los in tees. If the pipe size calculation indicates a required pump head different from that of a standard pump, pipe sizes in the system may be changed to establish a closer relationship between the two. The relationship between systems and pump heads is dis cussed in the section Circulating Pumps. If there are more circuits than one in a system, the fric tion loss for the longest circuit should be used to determine Vsfcfpt 1 5 6 Table 3.... Equivalent Length of Pipe for 90-Deg Elbows Ftp* Six* XH m IX 2 2M 3 1.2 1.7 2.2 3.0 3.5 4.5 5-4 6.7 1.4 1.8 2.5 3.3 3.9 5.1 6.0 7.5 1-5 2.0 2.7 3.6 4.2 5.4 6.4 8.0 1.5 2.8 3.7 4.4 5.6 6.7 8.3 1.6 2.2 2.9 3.9 4.5 5.9 7.0 8.7 1.7 2.3 3.0 4.0 4.7 6.0 7.2 8.9 1.7 2.3 3.0 4.1 4.8 6.2 7.4 9.1 1.7 2.4 3.1 4-2 4.9 6.3 7.5 9.3 1.8 2.4 3.2 4.3 5.0 6.4 7.7 9.5 2.5 3.2 4.3 5.1 6.5 7.8 9.7 3X 7.7 8.6 9.2 9.6 10.0 10.3 10.5 10-8 11.0 11.2 4 -5 8.6 9.5 10.2 10.6 11.1 11.4 11.7 11.9 12.2 12.4 10.5 11.7 12.5 13.1 13.6 14.0 14.3 14.6 14.9 15.2 6 12.2 13.7 14.6 15.2 15.8 16.3 16.7 17.1 17.4 17.7 8 15.4 17.3 18.4 19.2 19.8 20.5 21.0 21.5 21.9 22.2 10 18.7 20.8 22.3 24.2 25.5 26.1 26.6 27.0 12 26.5 28.8 31.0 31.6 32.0 Hot Water Heating Systems the pump head requirement. Piping in the other circuits should be sized to obtain the same total friction loss. Effects of Antifreeze Fluid*. Antifreeze solutions arc some times used in heating systems when the danger of freezing exists. They should not be used in direct-fired boiler applica tion. Corrections must be made in flow rates, pipe size, and pump capacity relative to water when antifreeze solutions are used. See Chapter 49, Snow Melting. SaECTiON OF PIPING ARRANGEMENT The type of distribution system selected for any particular building will depend primarily on the structural and archi tectural characteristics of the building, the need for separate control of different zones, the pressure head due to the height of the building, the space available for piping, and the rela tive cost of different arrangements of piping. Consequently, mains may be run in basement, separate floors, or in space above highest heating units. There are four distinct arrangements of main piping: (1) the two-pipe reversed-return system, (2) the one-pipe sys tem, (3) the series-loop system, and (4) the two-pipe directreturn system. The last is not recommended unless elaborate pipe sizing technique and provision for adjustment are em ployed. Two-Pipe Reversed-Rehjm System--Description and Design The two-pipe reversed-return main system, Fig. 8, has two mains, one supplying water to the heating units or to risers 409 to heating unite, and one collecting water returned from these units. The piping is arranged in such a manner that the sum of the equivalent length of supply and return piping to any unit is approximately equal to that of any other unit. Compared with a one-pipe system, the two-pipe system may. 1. Have a smaller average pipe size. While two raaina are re quired, the rites of the vary as water passes from one main through the heating unit to the other. The maximum size of either main is no larger than the size of a one-pipe main. 2. Be more flexible in its application because larger friction loss may be used in the heat-transfer unit circuits. 3. Require a minimum pumping head because the heating unit resistances are in parallel. 4. Permit adjustment of flow through individual units of ra diation over wider limits. .4 Rg. 8.... A Two-Pipe Reversed-Return System Note* I. 77m chart lt bated off itraight tee*, ifid it, braathet A, B, and C era A* tone oxe. 2. Hoad loss in desired a'rcuif H obtained by teiaeting proper atrm oeeordbig to Bturiratioru, determining the flow at the orated branch, end cndtipfyinQ A* bead ha for the tamo dte elbow of (he flaw rate m (he csrded branch by Ae gw'veferrf elbowi indicated. 3. When Ae nze of on outlet b reduced Ae equivalent elbows tbawn fa) Ae dtert do not apply. The maximum ha for any dread for any flow wiB not exceed 2 elbow eqwVafeafi at Ae maximum flow (gpm) occurring in any brand) of Ae tee. 4. The top curve of Ae dtert it Ae overage of 4 curvet, one far eodi of Ae tee ctrcuite {Outvoted. Rg. 7,... Elbow Equivalents of Tees at Various Flow Conditions111 Continuing the comparison, some disadvantages are: 1. Two mains may require more pipe fitting labor than a single main. 2. Some additional pipe may be required to achieve a re versed return. 3. A two-pipe system will be slightly more expensive for ffmall systems. 4. The piping for two mains may be unsightly in occupied spaces. Important considerations in the design of a two-pipe reversed-return distribution system are: 1. The head which the pump must generate is equivalent to the friction drop through the circuit having the highest resist ance. At design flow, the resistance through the distribution system to any one heating unit should be the same as that through any other unit. Where the length of pipe required to obtain distribution to a particular section must be shorter than to other sections, it is desirable to dvm'gn that section with a higher friction less. 2. A reversed return, as indicated in the section Adjustment of Flow and Capacity, will reduce the need for adjustments neces sary to obtain equal total head through each heating unit cir cuit. 3. Fan-type air-heating units with extended-surface coils can be used with a higher water temperature drop than that recom mended for direct radiation. It is necessary to avoid a difference in air temperature across the face of the coil in such unite. One method of minimising thin difference is to install a minimum of two serpentine coils in each unit, one in front of the other. Coil s' I .]