Danfoss VLT AQUA Drive Design Manual

Also see for vlt aqua: Instructions Design guide Instruction manual Operating instructions Design guide

Contents

2.7.3. Example of energy savingsAs can be seen from the figure (the laws of proportionality), the flow is controlled by changing the rpm. By reducing the speed only 20% from the ratedspeed, the flow is also reduced by 20%. This is because the flow is directly proportional to the rpm. The consumption of electricity, however, is reducedby 50%.If the system in question only needs to be able to supply a flow that corresponds to 100% a few days in a year, while the average is below 80% of therated flow for the remainder of the year, the amount of energy saved is even more than 50%.The laws of proportionalityThe figure below describes the dependence of flow, pressure and power consumption on rpm.Q = Flow P = PowerQ 1 = Rated flow P1 = Rated powerQ 2 = Reduced flow P2 = Reduced powerH = Pressure n = Speed regulationH 1 = Rated pressure n1 = Rated speedH 2 = Reduced pressure n2 = Reduced speedFlow :Q1Q2=n1n2Pressure :H1H2= (n1n2 )2Power :P1P2= (n1n2 )32.7.4. Example with varying flow over 1 yearThe example below is calculated on the basis of pump characteristics ob-tained from a pump datasheet.The result obtained shows energy savings in excess of 50% at the givenflow distribution over a year. The pay back period depends on the priceper kwh and price of frequency converter. In this example it is less thana year when compared with valves and constant speed.Energy savingsPshaft=Pshaft outputFlow distribution over 1 yearVLT® AQUA Drive Design Guide 2. Introduction to VLT AQUA DriveMG.20.N4.02 - VLT® is a registered Danfoss trademark 172