Simple upgrade saves 90% in parts washer

Modern technology replaces commonly oversized set-up at Mercedes Benz plant

A small pump and electronic frequency converter have saved a German Mercedes-Benz plant 90% in energy costs and 33 tonnes of CO2 emissions a year in a washing system for connecting rods.

The system's previous set-up used an oversized, 18.5 kW pump running constantly at full speed, two ball valves, a throttle valve and a bypass line to adjust for system pressure between the cleaning media storage tank and the parts washer. The washer needed only 3 bar at 10 m3/h; the pump supplied a steady 10 bar.

"Such a set-up is common in many applications in factories all over the world - though not always with such an extremely oversized pump," according to Heinz Maier, Key Account Manager Automotive of Grundfos GmbH in Germany (see the diagram below).

Diagram 1

Daimler AG, which owns the Mercedes-Benz plant in Untertürkheim, had named this parts washer as a potential source of wasted energy. Daimler implemented Grundfos's proposal for improvement.

Small pump, no valves

Mercedes Benz replaced the 18.5 kW pump with a Grundfos 1.5 kW CR pump with integrated frequency converter. This frequency converter monitors system pressure, starting and stopping the pump as needed to maintain the required capacity of cleaning media in the parts washer. Mercedes Benz also removed the bypass line and valves, making the whole system simpler (see the diagram below).

Diagram 2

After a trial and quality assurance period, the plant measured the energy use with the new set-up. It reduced previous consumption from 57,000 kWh to 5,590 kWh, a 90% savings. Daimler measured CO2 emission savings from this one small application at 33 tonnes per year.

The new pump and installation cost EUR 3,800 - far below the annual energy cost savings of EUR 6,200, meaning payback time on the investment was just over seven months. This single application is now continuing to save the plant EUR 6,200 per year.

The German Energy Agency (DENA) highlighted the Grundfos-Daimler project as exemplary for energy efficiency in industry and business in its Energy Efficiency Initiative.