Abstract

Improving energy and water efficiency in irrigation pumping systems is essential for sustainable resource management in irrigation-dependent regions. Although variable frequency drives (VFDs) are widely applied, their integrated impact on energy–water performance under real irrigation operating conditions remains insufficiently quantified. Laboratory and full-scale field experiments were conducted, including testing at the Teshiktosh-1 irrigation pumping station (Uzbekistan). Pump, electric drive, and overall unit efficiencies were evaluated using dimensionless indicators normalized to nominal rotational speed. Statistical analysis was used to derive empirical efficiency–frequency relationships. Pump and drive efficiencies decrease nonlinearly with decreasing rotational speed. At moderate speed reductions (up to ~50% of nominal speed), electric drive losses dominate, whereas at lower speeds, pump losses become the primary contributor to total energy losses. The obtained relationships differ from classical affinity-law assumptions. Field validation confirmed their applicability. VFD implementation enabled water savings of about 313.6 thousand m³ (≈16%) and seasonal energy savings of about 107,700 kWh (≈14%). The findings demonstrate that variable-speed control improves overall energy–water performance despite partial efficiency reduction at lower rotational speeds.