This step is relevant to section 4.4.5 of the ISO 50001-2011 standard.
Energy performance metrics or indicators (called “EnPIs” in ISO 50001) are quantitative measures of energy performance and are used to determine improvements in energy use, energy consumption and energy efficiency. They can be defined at a variety of levels within the energy management system (EnMS). For example, EnPIs can be established at the level of your entire organization or at the level of a specific facility, piece of equipment, system or process.
As quantitative measures, EnPIs are measured values, ratios or models that are accepted by your organization as meaningful representations of energy performance. Improvement in energy performance is determined by comparing current EnPIs against the initial values from the relevant energy baseline(s). Energy baseline(s) are addressed in Step 2.8 and they serve as a reference against which future changes in energy performance are evaluated.
Responsibility for determining the EnPIs typically rests with the management representative and may involve other members of the energy team. It is top management’s responsibility to ensure that the EnPIs are appropriate for your organization and to provide the resources needed to establish, track and evaluate the EnPIs.
How to do it
There are two tasks associated with determining performance metrics:
2.7.1 Determine energy performance indicators (EnPIs)
EnPIs are developed using the information from the energy review (Steps 2.2 through 2.6). The responsibility of developing a list of potential performance indicators falls to the management representative and any others that may be assigned to assist.
Stakeholder needs can vary significantly and their requirements should be considered in EnPI development. It may be necessary to develop different EnPIs for different stakeholders. Top management typically will be interested in an EnPI that is related to your organization’s strategic business goals and improving the bottom line. Operations or production personnel want a metric that provides guidance for operating equipment and systems at maximum efficiency. External agencies may require specific performance metrics to provide information related to regulatory or other requirements.
There are no limits on the number of EnPIs that your organization can have. EnPIs are developed where they are needed for monitoring or measuring energy performance. The Checklist of Potential EnPIs provides examples and can assist with determining potential EnPIs. The Checklist does not show every possible EnPI, but it can serve as a thought starter for your organization’s formulation of appropriate energy performance metrics. The Checklist of Other Factors Affecting EnPIs can be helpful in identifying the relevant variables that might have an impact on energy performance and the identified EnPIs.
EnPIs are typically established in one of three forms:
A single metric, such as consumption;
A ratio or per unit basis such as Btu/square foot or Btu/pound or Btu/unit
A more numerical model that accounts for relevant variables
A single metric, such as consumption, is frequently adequate to determine and monitor energy performance if the equipment, system or process is not affected by other variables or the relevant variables are constant. Following are two examples:
A warehouse with no heating or cooling, equipped only with lighting, and operates on a set schedule every day would be expected to have consistent energy consumption. Any changes would be a reflection of facility changes (e.g., adjusted schedule, facility expansion) or changes in energy performance (e.g. installed high efficiency lighting, removed excess fixtures).
A motor operated 24 hours a day at a constant load. A change in consumption may indicate motor problems or if the current motor is replaced with an energy efficient motor a consumption decrease would be expected.
In these examples, monitoring consumption as the EnPI provides guidance on the operational status of equipment or information on the results of changes.
A ratio or a per unit basis EnPI may be desired so comparisons over time at different output levels or at different locations of a similar process are possible. These EnPIs typically relate energy consumption, cost or environmental impact to an appropriate organizational output. One form of a ratio EnPI that relates performance to production or to one single output is commonly referred to as simple energy intensity. An energy intensity EnPI is defined and calculated by dividing energy consumption by productive output for an organization, facility, department, product, equipment, system, process or other part of the organization under consideration.
When calculating the EnPI, the energy measurement must accurately capture energy consumption for the unit under consideration and the production measure must cover the same time frame as the energy consumption. Following are some examples:
For a commercial operation, an EnPI may be Btu/occupied-sq. ft. or Btu/type-sq. ft. or use (e.g. a commercial warehouse may calculate an EnPI for refrigerated square footage and another EnPI for dry goods square footage).
For an industrial plant, an EnPI may be Btu/unit produced or Btu/$-value added to product.
For an organization that makes bricks a typical EnPI is Btu/lb. or Btu/ton of bricks. A change in this EnPI provides an indication that some parameter in the process has changed and warrants investigation.
A model may provide a more meaningful measure of energy performance than a single metric or simple ratio to accurately represent the relationship between operational activities and energy consumption. In this case, more sophisticated models that allow the use of multiple factors for estimating energy consumption may be required. Depending on the needs of your organization, regression analysis or calculations using engineering theory may be required to provide a sufficiently accurate model. Modeling based on regression analysis or engineering theory can be a complex subject and typically requires analysis by someone skilled in the systems, processes, operations or equipment being modeled. The U.S. Department of Energy offers a regression EnPI tool. The documents and other resources available with the EnPI tool provide more discussion and review on the process of developing regression modeled energy performance metrics. The U.S. Department of Energy also lists several energy modeling and software programs that are available from various sources.
2.7.2 Record methodology for determining and updating EnPIs
The methods you use to determine and update your organization’s EnPIs must be recorded and reviewed on a regular basis. Regular reviews help ensure that your methods remain valid. Some organizations document their methods within an energy manual, which is not required, but can be useful as a “roadmap” to the EnMS (see Energy Manual Guidelines for additional information). Other organizations address their methods for determining and updating EnPIs within their procedure for energy planning. Another approach used is to create and maintain a record of the method or calculation used and the updates performed each time the EnPIs are reviewed.
EnPIs are reviewed on a regular basis to ensure continuing applicability for the energy performance being measured. Changes in facilities, equipment, systems, processes, operating procedures, materials, relevant variables and many other factors could result in a change in the validity of the EnPI used to measure energy performance. When changes occur they are evaluated so the EnPI can be updated as needed. Top management is responsible for ensuring that the EnPIs are appropriate for your organization (Step 1.9). Usually this is accomplished through management review (Step 5.1) which evaluates energy performance based on updated comparisons of the EnPIs to the associated baselines. (Step 2.8 addresses establishing energy baselines.)
Resources & Examples
The following resources provide examples of EnPIs and factors that can affect EnPIs:
