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

PLH_KKK_U2_31.QXP 25.05.2007 11:01 Uhr Seite 13FUNDAMENTALSDelivery head H [m]Hydraulic flow rate of the pumpPumpBFlow Q [m³/h]Flowrate vThe electric power consumption P 1 is givenwhen the pump and drive motor form an encapsulatedunit, like with the so-called glandlesspumps. Here, it's even customary to put bothvalues P 1 and P 2 on the name plate.For aggregates where the pump and motor arecoupled via a coupling or rigid shaft connection,like with the glanded pumps, the required shaftpower P 2 is given. This is required for thesepump designs since the wide variety of motordesigns – starting with the IEC standard motorto the special motor – with their various powerconsumptions and efficiencies are installed onthe pump.Power requirement P [w]System curveBFlow Q [m³/h]Since in practice a shift in the duty point canalways be expected, the power of the drivemotor of a glanded pump must be set by approx.5 to 20% higher than the assumed requirementwould be.To calculate the operating costs of a pump, itmust be fundamentally distinguished betweenthe power requirement of the pump P 2 , oftenequated with the installed motor power, andthe power consumption of the drive motor P 1 .The latter is the basis of the operating costcalculation. If only the power requirement P 2 isgiven, this can also be used, but by simultaneouslytaking the motor efficiency into accountaccording to the following equation.The power consumptions of the pumps given inthe documentation of the pump manufactureralways refer to the water as the fluid in the areaof building engineering with:Specific density ρ = 1000 kg/m 3Kinematic viscosity ν = 1 mm 2 /sWhen there is a deviation in the specific density,the power consumption changes proportionallyto the same degree.Lower spec. density ^- Lower power consumptionP 1Higher spec. density ^- Higher power consumptionP 1This practically means that pumps which areoperated at high water temperatures, and thuslower spec. density of the fluid, usually requirelower motor power. For the temperatures andpump capacities which can be found in buildingengineering, this correction isn't carried out.Thus, on the drive side there is a certain motorreserve.When there is a deviation in the kinematic viscosity(by admixing to the fluid, only viscosityincrease relevant), there is also a change in thepower consumption.P 2P 1 =η MAbbreviationP 1P 2η MDescriptionPower consumption of the drivemotorPower requirement at the pumpshaftMotor efficiencyHigher viscosity ^- Higher power consumptionThe change is not proportional and must bespecially calculated.Wilo Planning Guide - Refrigeration, air-conditioning and cooling technology 02/2007 13