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

PLH_KKK_32_85.QXP 25.05.2007 10:11 Uhr Seite 72MEXAMPLES FOR THE PUMP SELECTION IN THE COLD WATER CIRCUITAdmixing circuit for temperature controlAdmixing circuit with three-way valves andpump performance adjustment18 °CMMM250 kWThe pumping pressure of 16.5 m is taken fromthe pipework calculation. To protect from frost,the system is operated with a Tyfocor/watermixture (40 % to 60 %). To stabilise the valveauthority at the load controllers, a constantdifferential pressure is demanded at the pump.Instead of a differential pressure valve or a differentialpressure controller without auxiliarypower, only a controlled pump for energeticallyfavourable operation is taken into consideration.MM75 kW450 kWDelivery head H [m]36322824201632 m24 m16 m22 °C12848 m1For optimum power adjustment, an admixingcircuit directly on the load was selected. Temperaturemaintenance is not required for theload circuit. The required volume flow is determinedas follows:Formula for volume flow V˙PUV·PU =Abbreviation Description1.03 Spec. heat capacity [Wh/kgK]∆Dimensioned temperature difference[K]10-20 K for standard systemsQ NCalculationV·PU =Q· N1.03 · ∆ϑ7751.03 · 4V·PU = 188.11 m 3 /hm 3 /hHeat demand [kW]m 3 /hNPSH [m]Shaft power P2 [kW]1210864202824201612840Operating data specificationsFlow 188.1 m 3 /hDelivery head16.5 mPumped fluid Tyfocor L (40%)Fluid temperature 18 °CDensity 1.061 kg/dm 3Kinematic viscosity 4.14 mm 2 /sVapor pressureHydraulic data (duty point)1 barFlow 188 m 3 /hDelivery headPower consumption P1NPSH0 40Impeller diameterMinimum volume flow80 120 160 200 240 280 32016.5 m13.1 kW6.58 m0 mmFlow Q [m³/h]40 80 120 160 200 240 280 320Flow Q [m³/h]40 80 120 160 200 240 280 320Flow Q [m³/h]20 m 3 /h at ∆p=16.5 m72 Subject to change without prior notice 02/2007 WILO AG