Evaluating the Effectiveness of VFD Retrofit Under Operational and Manual Control Constraints in a Kenyan Petroleum Depot

Globally, downstream petroleum operations face increasing pressure to optimize energy use and reduce carbon emissions, with electrically driven pumping systems representing the dominant site-level electricity load. This study investigates why anticipated energy savings from a variable frequency drive (VFD) retrofit were not realized in a Kenyan petroleum depot. High-resolution PLC-SCADA data at 1 s intervals were analysed over a six-month period using a custom Pump-Arm Modelling framework, reconstructing pump operation and energy consumption as a function of loading arm demand, runtime, and control mode. Results show that, despite VFD installation, pump speeds remained effectively fixed, and energy consumption was governed by discrete loading arm demand rather than speed modulation. Eight months billing data confirmed that post-retrofit energy intensity increased, from an average of 0.493 to 0.555 kWh/m3, demonstrating that expected efficiency improvements were not achieved. Stratified analysis further showed that idle running due to manual overrides accounted for approximately 3% of total depot electricity consumption. To contextualize this performance gap, idealized affinity-law scaling was applied to observed partial-load intervals, revealing unrealized energy savings potential of approximately 92 MWh, equivalent to a depot-level savings potential of 28.4% ± 1.4%. The findings indicate that limited energy savings were attributable to open-loop control architecture, partial digital integration, and legacy equipment constraints rather than VFD hardware limitations, highlighting the need for demand-aware, closed-loop energy optimization in retrofitted petroleum depots.