Document x1MYaKkOK8ab3ev0z9gZBNj9g

94 CHAPTER 6 1962 Guide And Data Book in feet. The length of run is not usually known at the out set; hence, it may be necessary to assume some pipe size at the start. Such an assumption frequently is considerably in error, and a. more common and practical method is to assume the length of run and to check this assumption after the pipes are sized. For this purpose the length of run usu ally is taken as double the actual length of pipe. BASIC CHART FOR STEAM PIPE SIZING Fig. 22 is the basic chart for determining the weight-flow rate and velocity of steam in Schedule 40 pipe for various values of pressure drop per 100 ft,..based on zero psig saturated steam. By. use of the multiplier charts it may be used at all saturation pressures between 0 and 200 psig. TABLES FOR PIPE SIZING FOR LOW-PRESSURE The basic chart, Fig. 22, can be used for siring pipe on low-pressure systems. The values in Table 5 which are taken from the basic chart provide a more rapid means of selecting pipe sizes for the various pressure drops listed and for systems operated at 3-5 and 12 psig. The weight-flow rates shown for 35 psig can be .used for saturated pressures from 1 to 6 psig, and those shown for 12 psig can be used for saturated pressures from 8 to 16 psig with an error not exceeding 8 percent. Both Fig. 22 and Table 5 are for use where the flow of Table 6.... Steam Pipe Capacities for Low-Pressure Systems - (Far Use oa Oat Pip* System* or Two-ftp* Systems tn which Condensate Row* Against Ota Sfeam'Row) Thb tab!* b based on data developed through research nvestigations of the American Society of Heating, Refrigerating and Air-Conditioning Engineer* Capacity In Pound* per Hour Nominal Rpe Size, Indies Two-Pip* Systems Condensate flowing against steam Vertical Horizontal One-Pip* Systems Supply upfeed Rodiotor valve* and vertical connections Radiator and riser A H m. U? 2 2H 3 3H A 5 6 8 10 12 16 3* 8. 14 31 48 97 C* __ 9 19 27 49 159 282 387 511 1,050 99 175 238 425 788 1,800 3,750 7,000 11,500 22,000 1,400 3,000 5,700 9,500 19,000 D> 6 11 20 38 72 116 200 286 380 -- _ _--_ -- _ 7 16 23 42 ____ -- ____ -- ft 7 7 26 16 23 42 65 119 186 278 5___45 -- Ncu: Steea at an average presura ef 1 paif b used a* a boas of calculating capacities. * Do n<* m Column B tor pressure drop* ot ks than Hi pm per 100 ft f equivalent run. Use Fig. 83 or Table 5 instead. k Do not use Column D tor pmit,ire drape 1m than H, pa per 100 ft ctf equivalent run except on ebea 8 in. and over. Uae Fig. S3 or Table 8 instead. * Pitch at horizontal runouts to'rken and radiators sboold be oot less than H in- per ft. Where this pitch cannot be obtained, runoute over 8 ft in length bo one pipe sbe larger than called for in thb table. condensate does not inhibit the flow of steam. Columns B and C of Table 6 are for cases where steam and condensate flow in opposite directions as in risers or runouts that are not dripped. Columns D, B, and P are for one-pipe systems and include risers, radiator valves and vertical connections, and radiator and riser runout sizes, all of which are based on the critical velocities of the steam to permit the counterflow of condensate without noise. Return piping may be sized with the aid of Table 7, where pipe capacities for wet, dry, and vacuum return lines are shown for several values of pressure drop per 100 ft of equivalent length. It is customary to use the same pressure drop on both the steam and return sides of a system. Example t: What pressure drop should be used for the steam piping of a system if the measured length of the longest rue is 500 ft, and the initial presure is not to be over 2 psig? Solution: It will be assumed, if the measured length of the longest run is 500 ft, that when the allowance for fittings is added, the equivalent length of run will not exceed 1000 ft. Then, with the pressure drop not over one-half of the initial pressure, the drop could be 1 psi or less. With a presure drop of 1 psi and a length of run of 1000 ft, the drop per 100 ft would be 0.1 psi. while if the total drop were 05 psi, the drop per 100 ft would be 0X15 psi. In both cases .the pipe could be sized for a desired capacity according to the 0.1 and 0JQ5 pressure drop lines in Fig. 22. On completion of the sizing, the . drop could be checked by taking the longest line and actually calculating the equivalent length of run from the pipe sizes de termined. If the calculated drop is less than that assumed, the pipe size is all right; if it is more, it is probable that there are an unusual number of fittings involved, *"d either the linsm must be straightened' or the column for the next lower drop must be used, and the lines resized. Ordinarily, resizing will be un necessary. CHARTS FOR SIZING PIPE FOR HIGH-PRESSURE Many installations of heating systems for large industrialtype buildings have been designed for the use of high-pres sure steam, that is, without the use of pressure-reducing valves. Such systems usually involve the use of unit beaters or large built-up fan units with.blast heating coils. Pressures on these systems vary from 30 to 150 psi. Temperatures are controlled by a modulating- or throttling-type thermostatic valve or by face or bypass dampers controlled by the air temperature in the room, fan inlet, or fan outlet. Figs. 23, 24, 25, and 26 provide charts for sizing steam piping for systems of 30, 50, 100, and 150 psig at various pressure drops. These charts are based on' the Moody Fric tion Factor, which takes into account the Reynolds number and the roughness of the internal pipe surfaces, and contain the same information as the basic chart of Fig. 22 but in a more convenient form. Return pipe capacities given in Tables 8 and 9 are based on the following assumed pressures in the return piping: Pressure Orop lb/100 Ft X 8 X l 2 Pressure in Return Line (Psig) 30 p*i System X 1 2 3 4 150 psi System ix 2X 5 7X 10 20 The pressure loss and. line loss as given were substituted in the Babcock steam flow formula, and the resulting capac ity was multiplied by 12 for 30-psig systems and by 16 for steam Heating Systems 95 Table 7___ Return Main and Riser Capacities for Low-Pressure System--Pounds per Hour (Referaac* to An table win b* mode by column latter G through V) _. is bas*d on pip* size data developed through the research krvertigatiora of The American Sodety of Heating, Refrigerating and Air-Conditioning Engineer* 150-psig systems to obtain tbe values given in-Tables 8 and 9. The return-line pressures used were found by observation of operating systems. The Babcock formula was used in this case since information on condensate flow in return lines based on the Moody Friction Factor is not readily available. - SIZING PIPING FOR ONE-PIPE GRAVITY SYSTEMS Gravity one-pipe air-vent systems, in which Tbe equivalent loigth of run does not exceed 200 ft, should be sized by means f Tables 5,6, and 7 and Fig. 22 as follows: 1. For the steam main and dripped runouts to risers where the steam and condensate flow in the same direction, use He P8* drop (Table 5 or Fig. 22). N 2. Where the riser runouts are hoi dripped and the steam and condensate flow in opposite directions, and also for the radiator runouts where the same condition occurs, use Table 6, Column F. 3. For up-feed steam risers carrying condensate back^from the radiators, use Table 6, Column D. A. For down-feed systems, the mein risers of which do not carry any radiator condensate, use Table.6, Column B. 5. For the radiator valve size and the stub connection, use Table 6, Column B. 6. For the dry-return main, use Table 7, Column 0. 7. For the tvet-return main, use Table 7, Column N.