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. 22.15Low-Pressure Steam Piping . 22.16High-Pressure Steam Piping . 22.16Steam Condensate Systems 22.16GAS PIPING 22.20FUEL OIL PIPING
2、22.21HIS 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 headrequired to achieve the desired flow. Computerized methods arewell suited to handling the details of
5、calculating losses around anextensive 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, lbf/ft2f = friction factor,
6、dimensionless (from Moody chart, Figure 13 in Chapter 3)L = length of pipe, ftD = internal diameter of pipe, ft = fluid density at mean temperature, lbm/ft3V = average velocity, fpsgc= units conversion factor, 32.2 ftlbm/lbfs2This equation is often presented in head or specific energyform ash = (2)w
7、hereh = head loss, ftg = acceleration of gravity, ft/s2In 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/
8、(3)whereRe = Reynolds number, dimensionless = absolute roughness of pipe wall, ft = dynamic viscosity of fluid, lbm/ftsThe 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 dat
9、a for the usual turbulentflow regime is the Colebrook equation:= 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 limit-ing cases: as /D approaches 0 (smooth limit), the 18.7/Re termdominates; at high /D and Re
10、(fully rough limit), the 2/D termdominates.Equation (4) is 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 equat
11、ion, whichis expressed asp = 3.022L (5)orh = 3.022L (6)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 greate
12、r than thosecaused by the pipe alone. One formulation expresses losses asp = K or h = K (7)The preparation of this chapter is assigned to TC 6.1, Hydronic and SteamEquipment and Systems.LD-gc-V22- p-gcg-f LD-V22g- =1f-2D-18.7Re f -+fVC-1.8521D-1.167ggc-VC-1.8521D-1.167gc-V22- V22g- 22.2 2013 ASHRAE
13、HandbookFundamentalswhere K = geometry- and size-dependent loss coefficient (Tables1 to 4).Example 1. Determine the pressure drop for 60F water flowing at 4 fpsthrough a nominal 1 in., 90 threaded elbow.Solution: From Table 1, the K for a 1 in., 90 threaded elbow is 1.5.p = 1.5 62.4/32.2 42/2 = 23.3
14、 lb/ft2or 0.16 psiThe loss coefficient for valves appears in another form as Cv, adimensional coefficient expressing the flow through a valve at aspecified pressure drop.Q = Cv(8)whereQ = volumetric flow, gpmCv= valve coefficient, gpm at p = 1 psip = pressure drop, psiSee the section on Control Valv
15、e Sizing in Chapter 47 of the 2012ASHRAE HandbookHVAC Systems and Equipment for moreinformation on valve coefficients.Example 2. Determine the volumetric flow through a valve with Cv= 10for an allowable pressure drop of 5 psi.Solution: Q = 10 = 22.4 gpmAlternative formulations express fitting losses
16、 in terms of equiv-alent lengths of straight pipe (Table 8 and Figure 7). Pressure lossdata for fittings are also presented in Idelchik (1986). p5Table 1 K Factors: Threaded Pipe FittingsNominal PipeDia., in.90StandardElbow90 Long-RadiusElbow45ElbowReturn BendTee-LineTee-BranchGlobe ValveGate ValveA
17、ngle ValveSwing Check ValveBell Mouth InletSquare InletProjected Inlet3/8 2.5 0.38 2.5 0.90 2.7 20 0.40 8.0 0.05 0.5 1.01/2 2.1 0.37 2.1 0.90 2.4 14 0.33 5.5 0.05 0.5 1.03/4 1.7 0.92 0.35 1.7 0.90 2.1 10 0.28 6.1 3.7 0.05 0.5 1.01 1.5 0.78 0.34 1.5 0.90 1.8 9 0.24 4.6 3.0 0.05 0.5 1.01 1/4 1.3 0.65
18、0.33 1.3 0.90 1.7 8.5 0.22 3.6 2.7 0.05 0.5 1.01 1/2 1.2 0.54 0.32 1.2 0.90 1.6 8 0.19 2.9 2.5 0.05 0.5 1.02 1.0 0.42 0.31 1.0 0.90 1.4 7 0.17 2.1 2.3 0.05 0.5 1.02 1/2 0.85 0.35 0.30 0.85 0.90 1.3 6.5 0.16 1.6 2.2 0.05 0.5 1.03 0.80 0.31 0.29 0.80 0.90 1.2 6 0.14 1.3 2.1 0.05 0.5 1.04 0.70 0.24 0.2
19、8 0.70 0.90 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., in.90StandardElbow90 Long-RadiusElbow45 Long-RadiusElbowReturn BendStandardReturn Bend Long-RadiusTee-LineTee-BranchGlobeValveGateVal
20、veAngleValveSwing Check Valve1 0.43 0.41 0.22 0.43 0.43 0.26 1.0 13 4.8 2.01 1/4 0.41 0.37 0.22 0.41 0.38 0.25 0.95 12 3.7 2.01 1/2 0.40 0.35 0.21 0.40 0.35 0.23 0.90 10 3.0 2.02 0.38 0.30 0.20 0.38 0.30 0.20 0.84 9 0.34 2.5 2.02 1/2 0.35 0.28 0.19 0.35 0.27 0.18 0.79 8 0.27 2.3 2.03 0.34 0.25 0.18
21、0.34 0.25 0.17 0.76 7 0.22 2.2 2.04 0.31 0.22 0.18 0.31 0.22 0.15 0.70 6.5 0.16 2.1 2.06 0.29 0.18 0.17 0.29 0.18 0.12 0.62 6 0.10 2.1 2.08 0.27 0.16 0.17 0.27 0.15 0.10 0.58 5.7 0.08 2.1 2.010 0.25 0.14 0.16 0.25 0.14 0.09 0.53 5.7 0.06 2.1 2.012 0.24 0.13 0.16 0.24 0.13 0.08 0.50 5.7 0.05 2.1 2.0S
22、ource: Engineering Data Book (Hydraulic Institute 1990).Table 3 Approximate Range of Variation for K Factors90 Elbow Regular threaded 20% above 2 in. Tee Threaded, line or branch 25%40% below 2 in. Flanged, line or branch 35%Long-radius threaded 25% Globe valve Threaded 25%Regular flanged 35% Flange
23、d 25%Long-radius flanged 30% Gate 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 (Hy
24、draulic Institute 1990).Pipe Sizing 22.3Table 4 Summary of K Values for Ells, Reducers, and ExpansionsPastaASHRAE Researchb,c4 fps 8 fps 12 fps2 in. S.R.eell (R/D = 1) thread 0.60 to 1.0 (1.0)d0.60 0.68 0.7364 in. S.R. ell (R/D = 1) weld 0.30 to 0.34 0.37 0.34 0.331 in. L.R. ell (R/D = 1.5) weld to
25、1.0 2 in. L.R. ell (R/D = 1.5) weld 0.50 to 0.7 4 in. L.R. ell (R/D = 1.5) weld 0.22 to 0.33 (0.22)d0.26 0.24 0.236 in. L.R. ell (R/D = 1.5) weld 0.25 0.26 0.24 0.248 in. L.R. ell (R/D = 1.5) weld 0.20 to 0.26 0.22 0.20 0.1910 in. L.R. ell (R/D = 1.5) weld 0.17 0.21 0.17 0.1612 in. L.R. ell (R/D = 1
26、.5) weld 0.16 0.17 0.17 0.1716 in. L.R. ell (R/D = 1.5) weld 0.12 0.12 0.12 0.1120 in. L.R. ell (R/D = 1.5) weld 0.09 0.12 0.10 0.1024 in. L.R. ell (R/D = 1.5) weld 0.07 0.098 0.089 0.089Reducer (2 by 1.5 in.) thread 0.53 0.28 0.20(4 by 3 in.) weld 0.22 0.23 0.14 0.10(6 by 4 in.) weld 0.62 0.54 0.53
27、(8 by 6 in.) weld 0.31 0.28 0.26(10 by 8 in.) weld 0.16 0.14 0.14(12 by 10 in.) weld 0.14 0.14 0.14(16 by 12 in.) weld 0.17 0.16 0.17(20 by 16 in.) weld 0.16 0.13 0.13(24 by 20 in.) weld 0.053 0.053 0.055Expansion (1.5 by 2 in.) thread0.16 0.13 0.02(3 by 4 in.) weld 0.11 0.11 0.11(4 by 6 in.) weld 0
28、.28 0.28 0.29(6 by 8 in.) weld 0.15 0.12 0.11(8 by 10 in.) weld 0.11 0.09 0.08(10 by 12 in.) weld 0.11 0.11 0.11(12 by 16 in.) weld 0.073 0.076 0.073(16 by 20 in.) weld 0.024 0.021 0.022(20 by 24 in.) weld 0.020 0.023 0.020Source: Rahmeyer (2003a).aPublished data by Crane (1988), Freeman (1941), and
29、 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,c4 fps 8 fps 12 fps2 in. thread tee, 100% branch 1.20
30、to 1.80 (1.4)d0.93 100% line (flow-through) 0.50 to 0.90 (0.90)d0.19 100% mix 1.19 4 in.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 6 in.weld tee, 100% branch 0.56 100% line (flow-through) 0.12 100% mix 0.88 8 in.weld tee, 100% branch 0.
31、53 100% line (flow-through) 0.08 100% mix 0.70 10 in.weld tee, 100% branch 0.52 100% line (flow-through) 0.06 100% mix 0.77 12 in.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 0.7216 in.weld tee, 100% branch 0.47 0.54 0.55 0.54100% line (f
32、low-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 HandbookFundamentalsEquation (7) and data in Tab
33、les 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 projects RP-968 and RP-1034
34、) on 2 in.threaded and 4, 12, 16, 20, and 24 in. welded steel fittings demonstratethe variation and are shown in Tables 4 and 5. The studies also presentK factors of diverting and mixing flows in tees, ranging from fullthrough flow to full branch flow. They also examined the variation inK factors ca
35、used by variations in geometry among manufacturers andby 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 Freeman (1941),work that wa
36、s 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) (ASHRAEresearch project RP-1193) foun
37、d the data in Tables 6 and 7 giving Kfactors for Schedule 80 PVC 2, 4, 6, and 8 in. ells, reducers, expan-sions, and tees. The results of these tests are also presented in thecited papers in terms of equivalent lengths. In general, PVC fittinggeometry varied much more from one manufacturer to anothe
38、r thansteel 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 2 in. threaded ellsand 4 in. ells in two and three fitting assemblies of seve
39、ralgeometries, 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 important conclusion is that the interaction
40、betweenfittings always reduces the loss. Also, although geometry of theassembly has a definite effect, the effects are not the same for 2 in.threaded and 4 in. welded ells. Thus, the traditional practice ofadding together losses from individual fittings gives a conserva-tive (high-limit) estimate.Ca
41、lculating 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 selected before calculating the detail
42、edinfluence 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 6 Test Summary for Loss Coefficient
43、s K andEquivalent Loss LengthsSchedule 80 PVC Fitting KL, ftInjected molded elbow, 2 in. 0.91 to 1.00 8.4 to 9.24 in. 0.86 to 0.91 18.3 to 19.36 in. 0.76 to 0.91 26.2 to 31.38 in. 0.68 to 0.87 32.9 to 42.18 in. fabricated elbow, Type I, components0.40 to 0.42 19.4 to 20.3Type II, mitered 0.073 to 0.
44、76 35.3 to 36.86 by 4 in. injected molded reducer 0.12 to 0.59 4.1 to 20.3Bushing type 0.49 to 0.59 16.9 to 20.38 by 6 in. injected molded reducer 0.13 to 0.63 6.3 to 30.5Bushing type 0.48 to 0.68 23.2 to 32.9Gradual reducer type 0.21 10.24 by 6 in. injected molded expansion 0.069 to 1.19 1.5 to 25.
45、3Bushing type 0.069 to 1.14 1.5 to 24.26 by 8 in. injected molded expansion 0.95 to 0.96 32.7 to 33.0Bushing type 0.94 to 0.95 32.4 to 32.7Gradual reducer type 0.99 34.1Fig. 1 Close-Coupled Test ConfigurationsFig. 2 Summary Plot of Effect of Close-Coupled Configurations for 2 in. EllsFig. 3 Summary
46、Plot of Effect of Close-Coupled Configurations for 4 in. 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 the maximum and minimum velocities in pi
47、ping 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 undesirable effects of highvelocities.A variety
48、 of upper limits of water velocity and/or pressure dropin piping and piping systems is used. One recommendation places avelocity limit of 4 fps for 2 in. pipe and smaller, and a pressure droplimit of 4 ft of water/100 ft for piping over 2 in. 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
