M&V Case Study: VFD Installed on a Milk Vacuum Pump

Description of Project: A variable speed drive was installed on an existing constant speed 10 HP milk vacuum pump. Since the maximum capacity of the vacuum pump was not needed for the operation of the milking facilities, the VFD allowed the vacuum pump to run at a fraction of its maximum load thereby saving energy. Demand savings for the measure was claimed during ISO winter performance hours.

Measurement & Verification Approach: Cx Associates developed a plan to:

  1. Verify that the pump actually ran during ISO winter performance hours (5PM – 7PM).
  2. Meter the actual pump operating characteristics during the winter performance hours.
  3. Calculate the demand reduction during that period.

Cx Associates metered the vacuum pump over a period of two weeks during the winter using three split-core current transformers connected to a data logger. The meter set-up measured the duty cycle of the pump and the magnitude of its current draw. From this data, CxA calculated the verified kW savings during the ISO winter hours.


Forecasted kW savings: 2.124

Verified kW savings: 2.970

Cx Associates' experience in demand resource verification has indicated that there is significant variability between engineering savings estimates and the actual demand reduction realized in the field. ISO NE requires that savings portfolios have 90% confidence and +/-10% accuracy which increases the need for pre-installation metering to ensure that custom measures in submitted portfolios meet the standard. Cx Associates provides consultation on pre-installation metering to help ensure metering protocols result in data that fulfills the requirements of FCM verification.