LAN contracted with Saginaw-Midland Municipal Water Supply Corporation (SMMWSC) to provide a feasibility study to investigate the operational cost savings for operating select pumps at variable speeds at the 285-mgd Whitestone Point Pumping Station. Currently, to provide water flows below 42-mgd, the pumps are operated against partially closed valves thereby increasing the total dynamic head on the pumps resulting in higher energy use. With the use of VFD’s on the motors, speed can be used to reduce the pump capacity/head curve resulting in energy savings.

The tasks performed by LAN included investigating available manufactured variable frequency drives, inverter rating of selected pump motors, and space needed to locate variable frequency drives; modifying the existing electrical systems, station and ventilation control systems; and identifying operational energy savings. Three options were presented to the client for review and selection. LAN recommended the third option as the most economically attractive at an implementation cost of $740,800, which will provide a payback in 6.5 years based on a projected savings of about $114,000 per year.

SMMWSC retained LAN to provide design and construction management services for two 1200-HP VFD units, medium voltage, secondary transformers and new 5KV switchgear. The selected medium voltage VFDs are 2400/4160 volt, dual rated and are manufactured by AB/Rockwell Automation. Equipment bids were received from multiple venders, with the lowest bid in the amount of $701,750. This equipment was installed by the client’s in-house forces. The first year power saving were approximately $122,000.