Recommended Reading | Application of Energy Performance Methods in Energy Management Systems

Energy performance refers to measurable results related to energy efficiency, energy use, and energy consumption. The improvement of energy performance depends on the interconnected elements of energy performance parameters and energy baselines, as well as the understanding and application of energy target indicators. Therefore, applying energy performance methods requires a full understanding of the intrinsic relationship between these elements and energy performance.

Energy performance parameters are core elements of the energy management system. As the name suggests, energy performance parameters are created to determine and calculate an organization's energy performance. Only by fully understanding and applying energy performance parameters can an organization objectively and accurately measure and compare its energy performance.

Simply put, energy performance parameters are the metrics used to measure energy performance. Considering the organizational level, departmental level, process level, and system or equipment level, these indicators measure performance. For example, in a refining enterprise, comprehensive energy consumption at the organizational level, comprehensive energy consumption per ten thousand yuan of output value, refining (unit) comprehensive energy consumption at the energy-using unit or device level, unit energy factor consumption, unit ethylene consumption, and at the equipment level, indicators such as heating furnace thermal efficiency, equipment power consumption, and equipment efficiency are energy performance parameters at different levels.

After determining energy performance parameters at various organizational levels, corresponding energy baselines and energy target indicators should be established. The data values of energy performance parameters at different organizational levels during a previously selected specific period (baseline period) constitute the energy baseline. In other words, the energy baseline is the value of energy performance parameters during the baseline period, used to determine energy performance during that period. The units and measurements used for the energy baseline are consistent with those of the energy performance parameters. For many enterprises in the petrochemical industry, based on stakeholder energy statistics reporting requirements, energy consumption data is usually collected annually, so it is common to set the energy performance parameter values from the previous year's statistical period as the energy baseline.

ISO 50001:2018 "Energy Management Systems — Requirements with Guidance for Use" provides definitions for targets and energy indicators. Targets may include overall improvement goals for the energy management system or specific, measurable energy performance improvement indicators. That is, targets can be quantitative indicators of energy performance improvement or qualitative measures of energy management system improvement. Energy indicators within energy targets refer to quantifiable goals for energy performance improvement. According to Note 1 in the standard's definition of "energy performance," the achievement/completion status of an organization's energy target indicators is also a representation of energy performance.

The energy baseline serves as a reference before and after the implementation of energy performance improvement measures or with or without such measures, based on data from specific periods and conditions. The formulation of energy targets/indicators is based on important energy performance parameters and baseline values; therefore, energy indicators must be superior to energy baselines.

The purpose of an organization establishing an energy management system is to improve energy performance and the performance of the energy management system. The energy performance method requires organizations to treat the establishment of energy performance parameters and energy baselines as key parts of energy management system planning.

Organizations obtain relevant statistical information on energy use through energy reviews, including past and current energy use and energy consumption. By identifying and analyzing, they can determine major energy uses and further identify and determine relevant variables affecting these major energy uses.

Based on the results of the energy review, after fully considering the characteristics of energy use and consumption (including factors related to energy users), organizations select appropriate types of energy performance parameters, determine energy performance parameters, and then establish corresponding energy baselines and energy target indicators. Usually, organizations compare the measured values of energy performance parameters during the statistical period with the energy baseline to calculate and analyze changes in energy performance and make corresponding improvements accordingly.

To achieve energy performance improvement requirements at different levels, enterprises should establish and apply energy performance parameters, energy baselines, and energy target indicators at different levels such as organization, department, process, system, and equipment facilities to calculate energy performance at different levels. For example, the comprehensive energy consumption of an oil production plant, oil (gas) production comprehensive energy consumption, and other energy consumption amounts can be directly used as energy performance parameters at the organizational level. By calculating and comparing the corresponding energy consumption data of the baseline period and the reporting period, information on changes in energy performance can be obtained. The comparative value of quantitative energy performance indicators is also the value of energy performance improvement.

An organization's energy performance is often affected by many related variables and static factors, which may be related to business conditions such as market demand, sales volume, and profit margin, or related to operating conditions, environmental conditions, output, changes, etc. To ensure the accuracy of energy performance comparison values, once significant related variables and static factors affecting energy performance are identified, the method of "normalization" should be introduced for energy performance comparison.

The revision process of ISO 50001:2018 clarified the requirements for normalization. For example, clause 6.5 on energy baselines in the standard explicitly states, "When data shows that related variables significantly affect energy performance, the organization shall normalize the energy performance parameter values and corresponding energy baselines." However, enterprises and certification bodies applying the standard still have many issues in understanding and applying "normalization."

What is "normalization"? "Normalization" is a method used to accurately calculate the degree of energy performance improvement. Simply put, the purpose of "normalization" is to achieve equally comparable energy performance, that is, to create conditions for equally comparable energy performance.

Organizations can achieve normalization in two ways: they can normalize the energy baseline according to changing conditions to compare it with the energy performance during the statistical period under the same conditions; or they can normalize the energy performance parameter values of the statistical period according to baseline period conditions and compare them with baseline data to calculate energy performance improvement.

A typical approach is to use regression analysis for data normalization. GB/T 13234—2018 "Calculation Method for Energy Savings of Energy-Using Units" provides several methods for regression analysis calculation. Appendix F of GB/T 36713—2018 "Energy Management Systems — Energy Baselines and Energy Performance Parameters" provides examples of "normalization." Organizations can use univariate linear regression or multivariate linear regression methods to normalize energy performance parameter values or baselines based on the number of related variables.

There are various methods for calculating (accounting) energy performance improvement or continuous improvement for an organization, which may include energy savings calculation, comprehensive energy consumption reduction, product unit consumption reduction, energy efficiency improvement, and slowing down the conventional downward trend to confirm energy performance improvement. This article only describes several common situations below.

(1) Energy Savings Calculation Method

In many cases, enterprises use energy savings to evaluate energy performance, such as calculating energy savings for energy-consuming units, energy-consuming units, and energy-saving calculations for technical transformation projects. Many national and industry standards provide specific calculation methods for energy savings, with clear formulas that consider the impact of related variables. For example, the natural decline rate of oilfields and the comprehensive water cut rate significantly affect the comprehensive energy consumption of oilfield enterprises. When accounting for energy performance, the impact of the natural decline rate and comprehensive water cut rate should be considered. The GB/T 35578—2017 "Calculation Method for Energy Savings of Oilfield Enterprises" quantifies these two influencing factors into an oilfield development impact correction coefficient k. By comparing the comprehensive energy consumption data of oil and gas production in the statistical period and the baseline period, the oilfield energy performance is calculated, as shown in Example 1.

Example 1: Calculation of Energy Savings for Oil and Gas Production Output Value

An oilfield enterprise had a comprehensive energy consumption of 0.734 tce/10,000 yuan of output value in 2018; in 2019, the comprehensive energy consumption per unit output value was 0.784 tce/10,000 yuan, and the total industrial output value (2010 constant price) in 2019 was 4,902.6 million yuan.

According to the "Calculation Method for Energy Savings of Oilfield Enterprises" (GB/T 35578—2017), calculate the energy savings of oil and gas production output value for 2019 and 2018. The calculation method is as follows:

ΔEz = (ebz - k·ejz) · Gbz = (0.784 - 1.156 × 0.734) × 490260 = -31621.8 tce

Where:

ΔEz is the energy savings of oilfield production output value, in tons of standard coal;

ebz is the comprehensive energy consumption per unit industrial output value during the statistical reporting period, in tons of standard coal per 10,000 yuan. The enterprise's 2019 unit output value comprehensive energy consumption is 0.784 tce/10,000 yuan;

ejz is the comprehensive energy consumption per unit industrial output value during the baseline period, in tons of standard coal per 10,000 yuan. The enterprise's 2018 unit output value comprehensive energy consumption is 0.734 tce/10,000 yuan;

Gbz is the total industrial output value (comparable price) during the statistical reporting period, in 10,000 yuan. The enterprise's 2019 total industrial output value (2010 constant price) is 4,902.6 million yuan.

k is the oilfield development impact correction coefficient.

k = [1 - (1 - σ) * δ] / (1 - δ), if k exceeds 1.36, it is calculated as 1.36.

Where:

σ is the baseline period oilfield comprehensive water cut rate, expressed as a percentage (%); it was 92.78% in 2018.

δ is the natural decline rate of the oilfield during the statistical reporting period, expressed as a percentage (%); it was 14.39% in 2019.

k = [1 - (1 - 0.9278) * 0.1439] / (1 - 0.1439) = 1.156

(2) Single Factor (Related Variable) Calculation Method

For single-factor related variables, normalization is relatively easy and can be done in various ways. A common approach is to use a simple ratio method to determine energy performance parameters, normalizing a single influencing factor into directly comparable parameters to calculate whether energy performance has improved.

This method is actually a special case of linear "normalization," which can only be used when the base load is relatively small, allowing simple ratios to normalize energy performance participation. Several commonly used unit consumptions by enterprises fall into this category, such as: product unit output comprehensive energy consumption (i.e., the ratio of comprehensive energy consumption of an energy-consuming unit producing a certain product or providing a certain service during the statistical reporting period to the qualified product output in the same period) is an energy performance parameter normalized only by product output as the related variable; unit output value comprehensive energy consumption (i.e., the ratio of comprehensive energy consumption to the total output value or industrial added value of the energy-consuming unit during the statistical reporting period) is an energy performance parameter normalized only by output value as the related variable; the refining enterprise's refining (unit) comprehensive energy consumption is an energy performance parameter normalized by crude oil processing volume as the related variable.

It can be seen that the determination of such energy performance parameters has already considered the impact of related variables, and their values can be directly compared and calculated to confirm the degree of energy performance improvement.

(3) Multi-factor (Related Variable) Calculation Method

(1) Multiple Regression Method

For multi-factor related variables, multiple linear regression can be used for normalization, or statistical models or engineering models can be established for normalization.

For complex production and energy consumption processes such as refining enterprises, the complexity of energy consumption in different organizations and processes must be fully considered for normalization. The commonly used unit energy factor method considers the number and complexity of refining units, energy consumption of storage and transportation, sewage treatment energy consumption, thermal loss, transmission and transformation loss, energy factors, and temperature effects, systematically normalizing the impact of various factors on the comprehensive energy consumption of refining enterprises (see GB 30251—2013 "Energy Consumption Limits for Refining Unit Products"). The unit energy factor can also be used to compare energy performance among similar organizations.

(2) Multi-factor Simplification Method

It is also possible to consider selecting one or two relatively prominent factors among multiple factors and applying appropriate methods multiple times for normalization, simplifying complex problems.

For example, based on the characteristics of oil well production in oilfield enterprises, considering that the natural decline rate and comprehensive water cut rate of oilfields are continuously changing and have a significant impact on comprehensive energy consumption, these two influencing factors are quantified into an oilfield development impact correction coefficient k. This is a typical method of simplifying two variables into one variable for normalization. By "normalizing" baseline period data with correction coefficient k and comparing the comprehensive energy consumption data of unit oilfield oil and gas production in the statistical period and the normalized baseline period, the method for calculating oilfield production energy savings is shown in Example 3.

Example 3: Using the same oilfield enterprise data as in Example 1, select the organization-level energy performance parameter—unit output value comprehensive energy consumption to compare energy performance improvement between 2019 and 2018.

Considering the significant impact of oilfield comprehensive water cut rate and natural decline rate on unit output value comprehensive energy consumption, normalize the 2018 data and compare it with the 2019 data as follows:

Normalization calculation of 2018 data:

Comparison of 2019 and normalized 2018 unit output value comprehensive energy consumption:

(4) Year-on-Year Comprehensive Energy Consumption Comparison Method

Year-on-year comprehensive energy consumption (unit product year-on-year comprehensive energy consumption) is an energy performance parameter normalized for environmental temperature, which is what we commonly refer to as period comparison. Many organizations use year-on-year methods to measure improvement levels.

(5) Special Period Exclusion Method

For situations with special conditions during specific periods, normalization can be done by subtracting the energy consumption of special operating conditions. In such cases, the same operating conditions and time periods should be selected for comparison. For example, if energy consumption changes significantly during major maintenance, the energy consumption during the maintenance period should be excluded, and then compared with the same conditions in previous periods, which is also an acceptable form of "normalization."

Mature large enterprises generally have the need for benchmarking against industry organizations. Therefore, many enterprises set energy targets based on baseline and advanced values, with advanced values often considering industry benchmark values. Some high energy-consuming industries have issued energy consumption limits, energy access, and energy benchmarks for products or processes; the country has issued the "Energy Efficiency Benchmark Levels and Baseline Levels for Key Areas in High Energy-Consuming Industries," which clarifies the baseline and benchmark values for energy consumption of high energy-consuming enterprises. The selected energy consumption indicators are actually the energy performance parameters (values) used for comparison among peer industry organizations.

Additionally, for energy performance of different organizations within the same industry, product unit output comparable comprehensive energy consumption can be used (i.e., the comprehensive energy consumption per unit product output calculated by adjusting for various factors affecting product energy consumption to achieve comparable final product energy consumption within the same industry). Comparison is made by calculating the product unit output comparable comprehensive energy consumption value for the statistical period. For example, the Energy Intensity Index (EII) method is a typical internationally accepted product unit output comparable comprehensive energy consumption method suitable for refining enterprises. It comprehensively considers factors such as unit type, feedstock nature, operating conditions, and product quality to determine the standard unit energy consumption as the basis for comparison, thereby enabling energy performance comparison within the industry and being adopted by major oil companies.

In summary, energy-using industry enterprises should establish and use energy performance parameters and energy baselines, reasonably set targets and energy indicators, measure and quantify energy performance changes of equipment, facilities, processes, and systems, and deeply understand energy performance methods while flexibly applying normalization methods to calculate (verify) energy performance improvements, thereby effectively managing their energy performance.