Examines the cumulative effects of deteriorating values of motor and variable frequency drive (VFD) efficiencies and the speed of a pump is reduced in a closed fluid distribution system. Uses published values of these efficiencies to show that the power required at the inlet of a pump-VFD configuration is significantly higher, especially for oversized motors, than the power predicted by the classic pump law that states that Power is proportional to the cube of the speed. Constructs non-dimensional power curves to calculate power requirements relative to the shaft power at nominal operating conditions as a function of flow rate. States these curves can be used for any closed systems where pump efficiency at the nominal operating conditions can be assumed to remain constant when speed is reduced where motor and VFD efficiencies obey the presented curves. Finally, evaluates yearly energy consumptions for four different utilisation scenarios. Shows that energy consumption can be significantly higher than the energy consumption predicted by the Power proportional to the cube of the speed relationship, especially when mostly low flow rates are used.
Citation: ASHRAE Journal, vol. 41, no. 12, December 1999
Product Details
- Published:
- 1999
- Number of Pages:
- 4
- File Size:
- 1 file , 590 KB
- Product Code(s):
- D-9308
