Sub-metering, EMIS or EMS: What’s the difference?
September 11, 2018 - Various terms are used in relation to collecting and processing energy consumption data. Some of the more common include sub-metering, energy management information system (EMIS), monitoring and targeting (M&T) and measurement and verification (M&V). Although these terms relate to overlapping activities, they are not equivalent with respect to their content, cost and, most importantly, value for business. As such, understanding the distinctions between them can mean the difference between achieving massive savings or adding a maintenance headache.
Energy use sub-metering
Sub-metering is the process of measuring the energy consumption of a particular machine—such as a plastic moulding machine—or an entire system—such as a chiller or production line.
Sub-metering requires the installation of one or several additional metering devices. The measured data is typically collected either by reading the meter or by downloading information from a data logger. How the data is then analyzed and reported is not part of the sub-metering process.
By itself, sub-metering adds little to no value for companies, while creating additional work for floor personnel and increasing maintenance costs. As a result, sub-meters are often neglected. Their measured data is collected irregularly, if at all, and with no analysis, it does not lead to action.
An EMIS builds on sub-metering by adding automatic data transfer to a computer for analysis.
Data processing can be undertaken at different levels, from drawing graphs to performing statistical analysis, depending on a company’s needs and capabilities. The depth of analysis is what sets different EMISs apart.
With a basic EMIS, energy use analysis is presented as a dashboard with graphs and gauges. As a visual representation of spreadsheets, these are easy to grasp, but any actual analysis must be done by a user.
A more advanced EMIS will allow the user to set an ‘alarm’ for when measured parameters exceed certain thresholds, thus automating a simple level of analysis. The challenge is to set sensible thresholds for energy consumption when production conditions are subject to change. With narrow thresholds, the user may be too frequently alerted by false alarms; but with wide thresholds, it is easy to miss energy performance deviations and malfunctions. To address this issue in a practical manner, many maintenance managers will set a wide threshold, but also rely on other means of monitoring performance.
The best EMISs allow users to set thresholds that will change with dynamic operational conditions, such as production levels or weather conditions. Multi-variable regression analysis can estimate how much energy a machine should consume under given operational conditions. This way, energy consumption analysis can be automated to save the energy manager’s time.
Using regression analysis, the energy manager can report savings achieved in actual operational conditions to the plant manager. So, the next time the plant manager brings up energy bills and questions the results of efficiency projects, the energy manager can produce accurate calculations of savings that have been yielded through best practices, rather than having to explain how savings may be ‘masked’ by increased production or a hot summer. (The best practices in question, of course, are compiled in ISO 50001, Energy management systems.)
Does this mean the best EMIS guarantee a company will reap all the benefits of energy management? Not necessarily. When data has been accurately measured through sub-metering, then collected and analyzed with an EMIS, the process creates reports and, thus, increases the energy manager’s awareness of the situation. Results, however, can only come when appropriate actions are taken in response to these reports.
This is where an energy management system (EMS) comes into play. An EMS is a set of policies and procedures to co-ordinate actions within an organization toward more effective and efficient use of energy.
Software and hardware, on their own, do not generate value for the company; actions do.
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