How do you evaluate energy savings from installing a VFD on an existing pump?

Evaluation process: establish baseline power consumption and flow profile (daily/seasonal variations), construct system curve (static head + friction), apply affinity laws to predict power at various flows. Energy savings = integral of (baseline power - VFD power) over operating profile. Key factors: proportion of static vs friction head (VFD saves more with high friction proportion), flow variation range, current control method (throttling vs recirculation), motor efficiency at reduced speed. Include VFD losses (3-5%) and motor efficiency variation. Simple payback typically 1-3 years for good applications.