Setting Targets

Internal benchmarking (see “Energy Saving Tip” #54, in May’s Plastics Engineering, p. 57) is the starting point for setting targets for energy use based on the actual plastics throughput of the site. The performance characteristic line (PCL) shows you how much energy you should be using. If your actual use is higher (worse) than predicted or lower (better) than predicted, then you can quickly see this.

Control charts (similar to SPC charts) can be used to show when/if deviation from the PCL is significant, but the best tool for setting targets is the cumulative sum (CUSUM) chart. This looks at the cumulative sum of the deviations from the standard; it’s sort of like looking at your bank balance—if it’s heading in the wrong direction, then you have to do something!

CUSUM charts can be used to set a “challenging but achievable” target based on the best previous actual performance.

Actions:

Look for a period of sustained good performance and create a PCL based only on this period. You know this performance is achievable because the site has done it in the past.
Challenge the site personnel to perform consistently to the best level they have previously achieved, and not to the average of what they have previously achieved.
Avoid simple targets such as “reduce energy use by 15%.” These are not related to production volume and may not be challenging enough to bring out the best performance.

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.