Refrigeration, air-conditioning and cooling technology - 2007.pdf

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PLH_KKK_32_85.QXP 25.05.2007 10:11 Uhr Seite 64EXAMPLES FOR THE PUMP SELECTION IN THE CONDENSER CIRCUITThe selected pump is the Wilo-TOP-S 50/43-PN 6/10.Cavitation can be ruled out since this is a closedcircuit. For protection, the condenser circuitshould have its own safety valve and beequipped with its own diaphragm extensionvessel for a volume expansion of 2 to 5 %.Delivery head H [m]5,04,54,03,53,02,52,01,511,00,50 5min2max10 15 20 25 30Flow Q [m³/h]Note!The pump must constantly circulate the requiredwater volume when the refrigerating machine isin operation. This is to be ensured by a hydraulicswitch, heat exchanger, differential pressurevalves or bypasses.Operating data specificationsFlow 8.62 m 3 /hDelivery head4.09 mPumped fluidWaterFluid temperature 70 °CDensity 0.9777 kg/dm 3Kinematic viscosity 0.4084 mm 2 /sVapor pressure0.3121 barHydraulic data (duty point)Flow 8.88 m 3 /hDelivery head4.3 mPower consumption P1 0.295 kWSpeed2600 rpmThe necessary cooling towers are to be designedwith their own pump, as described before. Whenantifreeze is added, system separation with heatexchangers is recommended.64 Subject to change without prior notice 02/2007 WILO AG
PLH_KKK_32_85.QXP 25.05.2007 10:11 Uhr Seite 65EXAMPLES FOR THE PUMP SELECTION IN THE CONDENSER CIRCUITGround collector systemTo protect against freezing, the system is filledwith a glycol mixture (40% Antifrogen N + 60%water). The circulated volume is determined asfollows:Formula for the pressure / the delivery head HH Ges = (H geo + H A ) · f pH A = H VL + H VAFormula for volume flow V PUQ· NV·PU =m 3 /h0.97 · ∆ϑCalculationH Ges = (H geo + H VL + H VA ) · f pCalculationH VL= R · IH VA= Z + collector resistanceV·PU =2000.97 · 6m 3 /hH VL = 50 · 75H VL= 3 750 PaZ = Σζ ·ρ · w 22PaV·PU = 34.29 m 3 /hZ = 109.63 ·1 070 · 0.8 22PaThe desired pump head results from the pipelinerequirements. PVC pipeline material is selectedwith a nominal diameter of 125. The R value is50 Pa/m at a flow rate of about 0.8 m/s. Basedon the installed fittings, bends and the condenserresistance, the addition of 8 bends and2 shut-off valves results in a value of 109.63.Another 20 kPa are to be included in the calculationfor the collector and the pipe length to beconsidered is 75 m.Z = 37 537 PaResultH Ges = (H geo + H VL + H VA ) · f pH Ges = (0 + 3 750 Pa + 57 537 Pa) · 1.47H Ges = 90 092 PaA pump with a flow rate of Q = 34.29 m 3 /h andH = 9.0 m is to be selected.AbbreviationDescription1.16 Spec. heat capacity [Wh/kgK]∆Dimensioned temperature difference[K]10-20 K for standard systemsQ NH AH geoH GesH VLH VARHeat demand [kW]Pressure loss of the system in PaGeodetic pressure head difference in Pa (1 m WS ˜ 10 000 Pa)Total pressure loss in PaPipeline pressure loss in PaFitting pressure loss in PaPipe friction resistance in Pa/mLPipe lengthζResistance values in Paρ Density of fluid in kg/m 3w 2 Flow rate in m/s 2ZΣPressure loss in fittings in PaTotal lossesWilo Planning Guide - Refrigeration, air-conditioning and cooling technology 02/2007 65
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