Calculating The Energy Saving For Fluid Flow Machines - Siemens SINAMICS G120C Operating Instructions Manual

8.33

Calculating the energy saving for fluid flow machines

Overview
Fluid flow machines, which mechanically control the flow rate using valves or throttle flaps,
operate with a constant speed corresponding to the line frequency.
Figure 8-82
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 converter controls the flow rate by appropriately varying the speed of the fluid flow
machine. By controlling the flow rate, the fluid flow machine operates at the optimum
efficiency for each flow rate. This situation means that in the partial load range less electric
power is required than when controlling the flow rate using valves and throttles.
Figure 8-83
Function description
SINAMICS G120C Converters
Operating Instructions, 02/2023, FW V4.7 SP14, A5E34263257B AK
8.33 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 converter
Advanced commissioning
The converter calculates the en‐
ergy saving from the flow charac‐
teristic associated with a mechan‐
ical flow control and the meas‐
ured electric power that is drawn.
The calculation is suitable for cen‐
trifugal pumps, fans, radial and
axial compressors, for instance.
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