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A South West Water (SWW) optimisation project into the operating costs of their pumps identified VSD savings in both energy use and maintenance costs. Moreover, extending this over several sites achieved significant reductions from energy expenditure, extended lifespans, and minimising premature drive replacements.

The VSD saving initiatives reduced annual energy costs by up to £25,000 per drive whilst also minimising the frequency of filter changes. Furthermore, the projects mitigated the expense of early drive replacement.

At SWW’s Restormel Water Treatment Works in Cornwall, SWW identified a significant energy-saving opportunity. The site consisted of eight drives from 315 to 523kW controlling the motors used for reservoir pumps. Before, the associated cooling fans operated non-stop, even when the drives were not pumping.

VSD savings from clogged filters

The continuous operation of the cooling fans caused filter clogging issues, at sites close to wooded areas. Pollen and biological debris drawn into the filters reduced cooling efficiency. Because the £130 filters needed replacing five times more often than expected, SWW were incurring significant replacement and labour costs. Additionally, raising the drives’ temperatures by 10°C could reduce its lifespan by half.

In response, SWW developed a timer solution to switch off the fans half-an-hour after the drive stopped working. This generated energy savings of about £1,000 for each of the eight drives. Considering the retrofit solution’s cost of £1,000, the payback time for each drive is only 12 months. The same optimisation to reduce fan running times on other duty/standby pumps also resulted in VSD savings of £900.

ABB’s VSD flux optimisation provides the motor with the best voltage for any operating speed and load. This reduces the flux current needed and improves the efficiency of the motor. Thus, controlling pump speeds via a feedback loop achieved the best efficiency point of the pumps on the pump curve.

Shayne Fielding, Efficiency Manager for SWW, highlights the welcome reduction in energy costs resulting from these optimisation projects. Depending on the drive’s loading and power rating, energy cost savings of up to £25,000 are achievable. As a matter of fact, the most significant advantage was the reduction in capital costs by avoiding early drive replacements.