Solution – Wastewater Lift Station Energy Cost Reduction

Case Study:  Lift Station Pump High Energy Costs

Customer:  Greenville Sanitary District

PLC Type:   SLC 5/04

Drive Type:  Powerflex 750

Problem:  Customer was having trouble with frequent starts on a lift station pump causing high energy costs.  The customer requested that we look at the call to run for the pump to find a solution to reduce the number of starts, which would cut energy costs.

Observations:  The pump would ramp up to speed and run at that speed for the entire time it was running.  This was causing the increased amount of starts because it pumped the station down so quickly.

Solution:  The PLC at the customer site was hard wired into the VFD.  It had the ability to control the speed of the pump but this ability was not currently in use.  We tested the system for a minimum frequency we could run the pump at without back pressure stopping it and set the minimum frequency on the VFD at this number.  Then we tested the system for the maximum frequency we could run the pump at without the current running out of the service factor of the pump.  This was set as the VFD’s maximum frequency number.   The pump was then placed under a speed control based upon the level of the lift station.

Results:  The customer reported a dramatic decrease in the number of starts on the pump and expressed their interest in surveying other parts of the Water/ Wastewater system to cut more costs.

J.Schrubbe 6/15