Internal Site Benchmarking

Energy Saving Tip of the Month #5 (Plastics Engineering, October 2009) introduced the concept of the performance characteristic line (PCL) for a site. This is found by plotting a scatter chart of twelve months of monthly electricity use against twelve months of production volume (amount of plastic processed). The PCL is the linear line of best fit to this data. The equation for the PCL is generally of the form: kWh = A x production volume + B (where A and B are constants from the line of best fit).

The PCL can be used to set targets and assess energy use. If the PCL for the site is: kWh = (1.5551 × production volume) + 48,106, and the production volume for the month is 70,000 kg, then the predicted energy use will be: kWh = (1.5551 x 70,000) + 48,106, or 156,963 kWh. This predicted energy use value is the target for the month and can be compared to the actual energy use.

The PCL allows internal benchmarking based on previous site performance.

Actions:

Plot twelve months of electricity use against production volumes. Find the line of best fit.
Establish the amount of material processed in a month and calculate the predicted energy use.
Determine the actual energy use for the month and compare this to the predicted energy use.
If the energy used is less than predicted, then the site performed better than target.
If the energy used is more than predicted, then the site performed worse than target.

Note: Dr. Robin Kent is the author of Energy Management in Plastics Processing, published by Plastics Information Direct, and managing director of Tangram Technology Ltd., consulting engineers specializing in energy management in plastics processing. rkent@tangram.co.uk.