Industry: Water
Application: Water Pumps and Drives
Challenge:
Southwest Water identified an energy saving opportunity at its Restormel Water Treatment Works near Lostwithiel in Cornwall. The eight drives at this site are of three ratings, 315 kW, 485kW and 523kW. The VSDs control the motors used to run the reservoir pumps, altering the speed of the motors to meet the actual pumping demand. The drives operated their cooling fans constantly, even when the drive was not being used for pumping.
The fans are used to maintain various parts of the drive enclosure at temperatures within the drive’s operating range. The fans involved were the door fan, the main drive fan and the fan used to cool the LCL harmonic filters.
APDS Solution:
ABB and APDS developed a solution using an ABB timer circuit on the internal 115V supply that would switch the fans off, via a relay, half an hour after the drive is shut down.
The resultant savings in energy costs amount to around £1,000 for each of the eight drives. With the retrofitted solution costing £1000, payback time for each drive is only 12 months.
As well as wasting energy, this constant operation also caused a problem with clogging of the filters on the door fan. Situated in a wooded area, cooling fans suck in the pollen and the filters become clogged with this and other biological debris, reducing the cooling efficiency of the fans.
The project extended to other treatment works including Littlehempston, Tamar Lakes and Pantacridge. At Pantacridge, the drives run on a duty/standby arrangement where one drive is always running, and the other is always on standby. By preventing fans from running on the standby drive, it was calculated that around £900 per year could be saved.
APDS has also used flux optimisation at most of the 120 sites where ABB drives are fitted. This selectable Drive parameter technique maintains the speed of the pump motors at 44 to 46 Hz via a feedback loop to achieve the Best Efficiency Point of the pumps on the pump curve. Flux optimisation provides the motor with the optimum voltage for any operating speed and load. This reduces the flux current needed and improves the efficiency of the motor by 10-15%.
Benefits:
- APDS solution saves £25,000 per year
- No Filter fan clogging
- Reduced frequency of filter changes.
- Extend lives of existing drives
- Impacts lower bills for customers
Conclusion:
Shayne Fielding, Efficiency Manager for SWW, says: “The reduced energy costs are welcome – depending on the loading of the drive and the power rating, some drives can save up to £25,000 in energy costs. However, the major benefit is the significant reduced capital costs from avoiding early replacement of the drives. These cost savings help towards keeping customer bills as low as possible.”
Shayne Fielding added: “The clogging of the filters meant we had to replace them five times more often than we would expect. At £130 per filter this was a significant added expense. Blocked filters also reduce the cooling effect. Raising the temperature of a variable speed drive by 10C can halve its life.”
Footnote:
Please note these customer-approved stories are collected since 2000. While some company names may have changed during this time, the principles and methods described to save energy or improve productivity are applicable today. contact APDS Ltd Bristol: 01179 822 049 www.apds.co.uk
Have a similar project or application? Why not contact us to discuss your needs?