Abstract

Improving energy and water efficiency in irrigation pumping systems is essential for sustainable resource management in irrigation-dependent regions. Although variable frequency drives are widely used, their overall impact on energy-water performance under real-world irrigation operating conditions remains insufficiently quantified. Laboratory and full-scale field experiments were conducted, including testing at the Teshiktosh-1 irrigation pumping station in Uzbekistan. Pump, electric drive, and overall unit efficiencies were evaluated using dimensionless indicators normalised to nominal rotational speed. Statistical analysis was used to derive empirical efficiency-frequency relationships. Pump and drive efficiencies decrease nonlinearly as rotational speed decreases. 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. Variable frequency drives 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 a partial reduction in efficiency at lower rotational speeds.