Sub-Metering

Interval data (see last month’s E-Saving Tip #62) is valuable, but sub-metering is even better. The only problem is that sub-metering costs money, whereas interval data is generally free.

Sub-metering allows you to look at energy use by area, machine, or any other activity that you want to meter. This means that you can see what an area, machine, or service is using in real-time and how efficient you are. You can look at patterns, rogue events, and all of the other things the interval data does, but with more accuracy.

Good sub-metering systems (and there are many) will allow you to set alarms to warn you if the maximum demand approaches a penalty limit, will record all your energy use, and give you the ability to look at small changes in demand for exception reporting.

Actions:

As a general rule, a reasonable sub-metering system for a plastics processor will cost approximately 2% of the annual electricity bill, but it will pay for itself very quickly. The savings achieved can be up to 20% of the electricity bill.
Sub-metering generates lots of data very quickly. Check that any system has good data-handling controls.
Go for area-level measurement first, and only extend this to machine-level measurement when you have experience with data handling. As a general rule, any area, service, or process using more than $75,000 of energy per year should be sub-metered (energy mapping will quickly give you a good idea of these areas).
Look for good web access so that you can look at the data remotely.
Look for good displays so that you can communicate energy use to the staff.

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.