1、22.1CHAPTER 22 PIPE SIZINGPressure Drop Equations . 22.1WATER PIPING 22.5Flow Rate Limitations. 22.5Hydronic System Piping 22.6Service Water Piping 22.8STEAM PIPING. 22.13Low-Pressure Steam Piping . 22.14High-Pressure Steam Piping . 22.14Steam Condensate Systems 22.14GAS PIPING 22.18FUEL OIL PIPING
2、22.19HIS CHAPTER includes tables and charts to size piping forTvarious fluid flow systems. Further details on specific pipingsystems can be found in appropriate chapters of the ASHRAEHandbook.Two related but distinct concerns emerge when designing a fluidflow system: sizing the pipe and determining
3、the flow/pressure rela-tionship. The two are often confused because they can use the sameequations and design tools. Nevertheless, they should be determinedseparately.The emphasis in this chapter is on the problem of sizing the pipe,and to this end design charts and tables for specific fluids are pr
4、e-sented in addition to the equations that describe the flow of fluids inpipes. Once a system has been sized, it should be analyzed withmore detailed methods of calculation to determine the pump pres-sure required to achieve the desired flow. Computerized methodsare well suited to handling the detai
5、ls of calculating losses aroundan extensive system.PRESSURE DROP EQUATIONSDarcy-Weisbach EquationPressure drop caused by fluid friction in fully developed flows ofall “well-behaved” (Newtonian) fluids is described by the Darcy-Weisbach equation:p = f (1)wherep = pressure drop, Paf = friction factor,
6、 dimensionless (from Moody chart, Figure 13 in Chapter 3)L = length of pipe, mD = internal diameter of pipe, m = fluid density at mean temperature, kg/m3V = average velocity, m/sThis equation is often presented in specific energy form ash = (2)whereh = energy loss, mg = acceleration of gravity, m/s2
7、In this form, the fluids density does not appear explicitly (al-though it is in the Reynolds number, which influences f ).The friction factor f is a function of pipe roughness , inside diam-eter D, and parameter Re, the Reynolds number:Re = DV/ (3)whereRe = Reynolds number, dimensionless = absolute
8、roughness of pipe wall, m = dynamic viscosity of fluid, PasThe friction factor is frequently presented on a Moody chart (Fig-ure 13 in Chapter 3) giving f as a function of Re with /D as a param-eter.A useful fit of smooth and rough pipe data for the usual turbulentflow regime is the Colebrook equati
9、on:= 1.74 2log (4)Another form of Equation (4) appears in Chapter 21, but the twoare equivalent. Equation (4) is useful in showing behavior at limitingcases: as /D approaches 0 (smooth limit), the 18.7/Re term dom-inates; at high /D and Re (fully rough limit), the 2/D term domi-nates.Equation (4) is
10、 implicit in f; that is, f appears on both sides, so avalue for f is usually obtained iteratively.Hazen-Williams EquationA less widely used alternative to the Darcy-Weisbach formulationfor calculating pressure drop is the Hazen-Williams equation, whichis expressed asp = 6.819L (g)(5)orh = 6.819L (6)
11、where C = roughness factor.Typical values of C are 150 for plastic pipe and copper tubing,140 for new steel pipe, down to 100 and below for badly corroded orvery rough pipe.Valve and Fitting LossesValves and fittings cause pressure losses greater than thosecaused by the pipe alone. One formulation e
12、xpresses losses asp = K or h = K (7)The preparation of this chapter is assigned to TC 6.1, Hydronic and SteamEquipment and Systems.LD-V22- pg- f LD-V22g- =1f-2D-18.7Re f -+fVC-1.8521D-1.167VC-1.8521D-1.167V22- V22g- 22.2 2013 ASHRAE HandbookFundamentals (SI)where K = geometry- and size-dependent los
13、s coefficient (Tables1 to 4).Example 1. Determine the pressure drop for 15C water flowing at 1 m/sthrough a nominal 25 mm, 90 threaded elbow.Solution: From Table 1, the K for a 25 mm, 90 threaded elbow is 1.5. p = 1.5 1000 12/2 = 750 PaThe loss coefficient for valves appears in another form as Av, a
14、dimensional coefficient expressing the flow through a valve at aspecified pressure drop.Q = Av(8)whereQ = volumetric flow, m3/sAv= valve coefficient, m3/s at p = 1 Pap = pressure drop, Pa = density of fluid 1000 kg/m3for water at temperatures below 120CSee the section on Control Valve Sizing in Chap
15、ter 47 of the 2012ASHRAE HandbookHVAC Systems and Equipment for moreinformation on valve coefficients.Example 2. Determine the volumetric flow through a valve with Av=0.00024 for an allowable pressure drop of 35 kPa.Solution: Q = 0.00024 = 0.0014 m3/s = 1.4 L/sAlternative formulations express fittin
16、g losses in terms of equiv-alent lengths of straight pipe (Table 8 and Figure 7). Pressure lossdata for fittings are also presented in Idelchik (1986). p35 000 1000Table 1 K Factors: Threaded Pipe FittingsNominal PipeDia., mm90EllReg.90EllLong45EllReturn BendTee-LineTee-BranchGlobe ValveGate ValveAn
17、gle ValveSwing Check ValveBell Mouth InletSquare InletProjected Inlet10 2.5 0.38 2.5 0.90 2.7 20 0.40 8.0 0.05 0.5 1.015 2.1 0.37 2.1 0.90 2.4 14 0.33 5.5 0.05 0.5 1.020 1.7 0.92 0.35 1.7 0.90 2.1 10 0.28 6.1 3.7 0.05 0.5 1.025 1.5 0.78 0.34 1.5 0.90 1.8 9 0.24 4.6 3.0 0.05 0.5 1.032 1.3 0.65 0.33 1
18、.3 0.90 1.7 8.5 0.22 3.6 2.7 0.05 0.5 1.040 1.2 0.54 0.32 1.2 0.90 1.6 8 0.19 2.9 2.5 0.05 0.5 1.050 1.0 0.42 0.31 1.0 0.90 1.4 7 0.17 2.1 2.3 0.05 0.5 1.065 0.85 0.35 0.30 0.85 0.90 1.3 6.5 0.16 1.6 2.2 0.05 0.5 1.080 0.80 0.31 0.29 0.80 0.90 1.2 6 0.14 1.3 2.1 0.05 0.5 1.0100 0.70 0.24 0.28 0.70 0
19、.90 1.1 5.7 0.12 1.0 2.0 0.05 0.5 1.0Source: Engineering Data Book (Hydraulic Institute 1990).Table 2 K Factors: Flanged Welded Pipe FittingsNominal PipeDia., mm90EllReg.90EllLong45EllLongReturn BendStandardReturn Bend Long-RadiusTee-LineTee-BranchGloveValveGateValveAngleValveSwing Check Valve25 0.4
20、3 0.41 0.22 0.43 0.43 0.26 1.0 13 4.8 2.032 0.41 0.37 0.22 0.41 0.38 0.25 0.95 12 3.7 2.040 0.40 0.35 0.21 0.40 0.35 0.23 0.90 10 3.0 2.050 0.38 0.30 0.20 0.38 0.30 0.20 0.84 9 0.34 2.5 2.065 0.35 0.28 0.19 0.35 0.27 0.18 0.79 8 0.27 2.3 2.080 0.34 0.25 0.18 0.34 0.25 0.17 0.76 7 0.22 2.2 2.0100 0.3
21、1 0.22 0.18 0.31 0.22 0.15 0.70 6.5 0.16 2.1 2.0150 0.29 0.18 0.17 0.29 0.18 0.12 0.62 6 0.10 2.1 2.0200 0.27 0.16 0.17 0.27 0.15 0.10 0.58 5.7 0.08 2.1 2.0250 0.25 0.14 0.16 0.25 0.14 0.09 0.53 5.7 0.06 2.1 2.0300 0.24 0.13 0.16 0.24 0.13 0.08 0.50 5.7 0.05 2.1 2.0Source: Engineering Data Book (Hyd
22、raulic Institute 1990).Table 3 Approximate Range of Variation for K Factors90 Elbow Regular threaded 20% above 50 mm Tee Threaded, line or branch 25%40% below 50 mm Flanged, line or branch 35%Long-radius threaded 25% Globe valve Threaded 25%Regular flanged 35% Flanged 25%Long-radius flanged 30% Gate
23、 valve Threaded 25%45 Elbow Regular threaded 10% Flanged 50%Long-radius flanged 10% Angle valve Threaded 20%Return bend(180)Regular threadedRegular flangedLong-radius flanged25%35%30%Flanged 50%Check valve Threaded 50%Flanged +200%80%Source: Engineering Data Book (Hydraulic Institute 1990).Pipe Sizi
24、ng 22.3Table 4 Summary of K Values for Ells, Reducers, and ExpansionsPastaASHRAE Researchb,c1.2 m/s 2.4 m/s 3.6 m/s50 mm S.R.eell (R/D = 1) thread 0.60 to 1.0 (1.0)d0.60 0.68 0.736100 mm S.R. ell (R/D = 1) weld 0.30 to 0.34 0.37 0.34 0.3325 mm L.R. ell (R/D = 1.5) weld to 1.0 50 mm L.R. ell (R/D = 1
25、.5) weld 0.50 to 0.7 100 mm L.R. ell (R/D = 1.5) weld 0.22 to 0.33 (0.22)d0.26 0.24 0.23150 mm L.R. ell (R/D = 1.5) weld 0.25 0.26 0.24 0.24200 mm L.R. ell (R/D = 1.5) weld 0.20 to 0.26 0.22 0.20 0.19250 mm L.R. ell (R/D = 1.5) weld 0.17 0.21 0.17 0.16300 mm L.R. ell (R/D = 1.5) weld 0.16 0.17 0.17
26、0.17400 mm L.R. ell (R/D = 1.5) weld 0.12 0.12 0.12 0.11500 mm L.R. ell (R/D = 1.5) weld 0.09 0.12 0.10 0.10600 mm L.R. ell (R/D = 1.5) weld 0.07 0.098 0.089 0.089Reducer (50 by 40 mm) thread 0.53 0.28 0.20(100 by 80 mm) weld 0.22 0.23 0.14 0.10(150 by 100 mm) weld 0.62 0.54 0.53(200 by 150 mm) weld
27、 0.31 0.28 0.26(250 by 200 mm) weld 0.16 0.14 0.14(300 by 250 mm) weld 0.14 0.14 0.14(400 by 300 mm) weld 0.17 0.16 0.17(500 by 400 mm) weld 0.16 0.13 0.13(600 by 500 mm) weld 0.053 0.053 0.055Expansion (40 by 50 mm) thread0.16 0.13 0.02(80 by 100 mm) weld 0.11 0.11 0.11(100 by 150 mm) weld 0.28 0.2
28、8 0.29(150 by 200 mm) weld 0.15 0.12 0.11(200 by 250 mm) weld 0.11 0.09 0.08(250 by 300 mm) weld 0.11 0.11 0.11(300 by 400 mm) weld 0.073 0.076 0.073(400 by 500 mm) weld 0.024 0.021 0.022(500 by 600 mm) weld 0.020 0.023 0.020Source: Rahmeyer (2003a).aPublished data by Crane (1988), Freeman (1941), a
29、nd Hydraulic Institute (1990).bRahmeyer (1999a, 2002a).cDing et al. (2005)d( ) Data published in 1993 ASHRAE HandbookFundamentals.eS.R.short radius or regular ell; L.R.long-radius ell.Table 5 Summary of Test Data for Pipe TeesPastaASHRAE Researchb,c1.2 m/s 2.4 m/s 3.6 m/s50 mm thread tee, 100% branc
30、h 1.20 to 1.80 (1.4)d0.93 100% line (flow-through) 0.50 to 0.90 (0.90)d0.19 100% mix 1.19 100 mm weld tee, 100% branch 0.70 to 1.02 (0.70)d0.57100% line (flow-through) 0.15 to 0.34 (0.15)d06100% mix 0.49 150 mm weld tee, 100% branch 0.56 100% line (flow-through) 0.12 100% mix 0.88 200 mm weld tee, 1
31、00% branch 0.53 100% line (flow-through) 0.08 100% mix 0.70 250 mm weld tee, 100% branch 0.52 100% line (flow-through) 0.06 100% mix 0.77 300 mm weld tee, 100% branch 0.52 0.70 0.63 0.62100% line (flow-through) 0.09 0.062 0.091 0.096100% mix 0.88 0.72 0.72400 mm weld tee, 100% branch 0.47 0.54 0.55
32、0.54100% line (flow-through) 0.07 0.032 0.028 0.028100% mix 0.74 0.74 0.76aPublished data by Crane (1988), Freeman (1941), and Hydraulic Institute (1990).bRahmeyer (1999b, 2002b).cDing et al. (2005).dData published in 1993 ASHRAE HandbookFundamentals.22.4 2013 ASHRAE HandbookFundamentals (SI)Equatio
33、n (7) and data in Tables 1 and 2 are based on the assumptionthat separated flow in the fitting causes the K factors to be independentof Reynolds number. In reality, the K factor for most pipe fittings var-ies with Reynolds number. Tests by Rahmeyer (1999a, 1999b, 2002a,2002b) (ASHRAE research projec
34、ts RP-968 and RP-1034) on 50 mmthreaded and 100, 300, 400, 500, and 600 mm welded steel fittingsdemonstrate the variation and are shown in Tables 4 and 5. The studiesalso present K factors of diverting and mixing flows in tees, rangingfrom full through flow to full branch flow. They also examined th
35、evariation in K factors caused by variations in geometry among manu-facturers and by surface defects in individual fittings.Hegberg (1995) and Rahmeyer (1999a, 1999b) discuss the ori-gins of some of the data shown in Tables 4 and Table 5. The Hydrau-lic Institute (1990) data appear to have come from
36、 Freeman (1941),work that was actually performed in 1895. The work of Giesecke(1926) and Giesecke and Badgett (1931, 1932a, 1932b) may not berepresentative of present-day fittings.Further extending the work on determination of fitting K factorsto PVC piping systems, Rahmeyer (2003a, 2003b) (ASHRAEre
37、search project RP-1193) found the data in Tables 6 and 7 giving Kfactors for Schedule 80 PVC 50, 100, 150, and 200 mm ells, reduc-ers, expansions, and tees. The results of these tests are also pre-sented in the cited papers in terms of equivalent lengths. In general,PVC fitting geometry varied much
38、more from one manufacturer toanother than steel fittings did.Losses in Multiple FittingsTypical fitting loss calculations are done as if each fitting is iso-lated and has no interaction with any other. Rahmeyer (2002c)(ASHRAE research project RP-1035) tested 50 mm threaded ellsand 100 mm ells in two
39、 and three fitting assemblies of severalgeometries, at varying spacings. Figure 1 shows the geometries,and Figures 2 and 3 show the ratio of coupled K values to uncou-pled K values (i.e., fitting losses for the assembly compared withlosses from the same number of isolated fittings).The most importan
40、t conclusion is that the interaction betweenfittings always reduces the loss. Also, although geometry of theassembly has a definite effect, the effects are not the same for50 mm threaded and 100 mm welded ells. Thus, the traditionalpractice of adding together losses from individual fittings gives ac
41、onservative (high-limit) estimate.Calculating Pressure LossesThe most common engineering design flow loss calculationselects a pipe size for the desired total flow rate and available orallowable pressure drop.Because either formulation of fitting losses requires a knowndiameter, pipe size must be se
42、lected before calculating the detailedinfluence of fittings. A frequently used rule of thumb assumes thatthe design length of pipe is 50 to 100% longer than actual to accountfor fitting losses. After a pipe diameter has been selected on thisbasis, the influence of each fitting can be evaluated.Table
43、 6 Test Summary for Loss Coefficients K andEquivalent Loss LengthsSchedule 80 PVC Fitting KL, mInjected molded elbow, 50 mm 0.91 to 1.00 2.6 to 2.8100 mm 0.86 to 0.91 5.6 to 5.9150 mm 0.76 to 0.91 8.0 to 9.5200 mm 0.68 to 0.87 10.0 to 12.8200 mm fabricated elbow, Type I, components0.40 to 0.42 5.9 t
44、o 6.2Type II, mitered 0.073 to 0.76 10.8 to 11.2150 by 100 mm injected molded reducer 0.12 to 0.59 1.2 to 6.2Bushing type 0.49 to 0.59 5.2 to 6.2200 by 150 mm injected molded reducer 0.13 to 0.63 1.9 to 9.3Bushing type 0.48 to 0.68 7.1 to 10.0Gradual reducer type 0.21 3.1100 by 150 mm injected molde
45、d expansion 0.069 to 1.19 0.46 to 7.7Bushing type 0.069 to 1.14 0.46 to 7.4150 by 200 mm injected molded expansion 0.95 to 0.96 10.0 to 10.1Bushing type 0.94 to 0.95 9.9 to 10.0Gradual reducer type 0.99 10.4Fig. 1 Close-Coupled Test ConfigurationsFig. 2 Summary Plot of Effect of Close-Coupled Config
46、urations for 50 mm EllsFig. 3 Summary Plot of Effect of Close-Coupled Configurations for 100 mm EllsPipe Sizing 22.5WATER PIPINGFLOW RATE LIMITATIONSStewart and Dona (1987) surveyed the literature relating to waterflow rate limitations. Noise, erosion, and installation and operatingcosts all limit t
47、he maximum and minimum velocities in piping sys-tems. If piping sizes are too small, noise levels, erosion levels, andpumping costs can be unfavorable; if piping sizes are too large,installation costs are excessive. Therefore, pipe sizes are chosen tominimize initial cost while avoiding the undesira
48、ble effects of highvelocities.A variety of upper limits of water velocity and/or pressure dropin piping and piping systems is used. One recommendation places avelocity limit of 1.2 m/s for 50 mm pipe and smaller, and a pressuredrop limit of 400 Pa/m for piping over 50 mm. Other guidelines arebased on the type of service (Table 8) or the annual operating hours(Table 9). These limitations are imposed either to control the levelsof pipe and valve noise, erosion, and water hammer pressure or foreconomic reasons. Carrier (1960) recommends that the velocity no
