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

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PLH_KKK_32_85.QXP 25.05.2007 10:11 Uhr Seite 80EXAMPLES FOR THE PUMP SELECTION IN THE V- CIRCUITVaporiser circuit with measuring orificeFlow rate control in the vaporiser circuitVaporisers which have a distributor pump andmixing circuit pumps in their hydraulic systemcan have different flows. In order to maintaingood controllability of the circuit, a constantvolume flow is required under certain preconditions.By means of a measuring orifice and apressure transducer, the pump can keep theflow constant within its duty chart.At a power reduction of 350 kW cooling capacity,a volume flow of 50 m 3 /h is required. If all secondarycircuits are closed, this volume flows viathe short circuit. If all secondary circuits pull waterout of the primary circuit, an additional differentialpressure of 3 m is created. This meansthat the primary circuit pump no longer has tobuild up a differential pressure of 5.8 m, but onlyof 2.8 m.Delivery head H [m]141312 12 m max111098710 m8 m6543216 m4 mmin2 m0 5 10 15 20 25 30 35 40 45 50 55 60 65 70Operating data specificationsFlow 50 m 3 /hDelivery headPumped fluid5.8 mWaterFluid temperature 6 °CDensity 0.9989 kg/dm 3Kinematic viscosity 1.474 mm 2 /sVapor pressure0.1 barFlow Q [m³/h]Secondary circuitM16°C18°CHydraulic data (duty point)Flow 50 m 3 /hDelivery head5.8 mPower consumption P1 1.45 kWVaporiser∆pPrimary circuitM M M M M M6°C12 °CThe selected Wilo-Stratos 100/1-12 keeps thevolume flow constant (within the regulation differenceof the PID controller) in connection witha Wilo CRn system. The differential pressure iskept constant via the measuring orifice; a constantvolume flow is automatically set. The valvein the bypass is to be set so that only 50 m 3 /hflow through this at full speed. In the controlrange of the reduction in the secondary circuits,a pressure drop is created in the feed and a pressurerise in the return. As a result, the flow viathe bypass valve will approach zero.Cavitation can be ruled out since this is a closedcircuit. For protection, the vaporiser circuit shouldhave its own safety valve and be equipped withits own diaphragm extension vessel for a volumeexpansion of 5 to 7 %.80 Subject to change without prior notice 02/2007 WILO AG
PLH_KKK_32_85.QXP 25.05.2007 10:11 Uhr Seite 81Wilo Planning Guide - Refrigeration, air-conditioning and cooling technology 02/2007 81
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