Calculating The Energy Saving For Fluid Flow Machines - Siemens SINAMICS G120 Operating Instructions Manual

6.30

Calculating the energy saving for fluid flow machines

Fluid flow machines, which mechnically control the flow rate using valves or throttle flaps,
operate with a constant speed corresponding to the line frequency.
Figure 6-71
The lower the flow rate, the poorer the efficiency of the fluid flow machine (pump). The fluid
flow machine (pump) has the poorest efficiency when the throttle or valve is completely closed.
Further, undesirable effects can occur, for example the formation of vapor bubbles in liquids
(cavitation) or the temperature of the medium being pumped can increase.
The inverter controls the flow rate by appropriately varying the speed of the fluid flow machine.
As a consequence, the fluid flow machine has the optimum efficiency for each flow rate, and
draws less electric power in the partial load range than for closed-loop control concepts based
on valves and throttle flaps.
Figure 6-72
Function
Converter with the CU240B-2 and CU240E-2 Control Units
Operating Instructions, 01/2017, FW V4.7 SP6, A5E34259001B AD
6.30 Calculating the energy saving for fluid flow machines
Flow control with pump and throttle connected to a 50 Hz line supply
Flow control with pump and inverter
Advanced commissioning
The inverter calculates the ener‐
gy saving from the flow character‐
istic associated with a mechanical
flow control and the measured
electric power that is drawn.
The calculation is suitable for cen‐
trifugal pumps, fans, radial and
axial compressors, for instance.
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