Energies 2019 , 12 , 247
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performance within an organization, and how to determine whether the energy performance meets the targets set by the organization. Energy performance is understood as the “measurable results related to energy efficiency, energy use” [17]. When establishing EnPIs, different characteristics of the energy use, such as base load (e.g., fixed energy use) and variable loads, affected by production, occupancy, weather and other factors, should be taken into consideration. The energy performance can be influenced by different variables (weather conditions, production parameters, operating hours and operating parameters) and by static factors connected to changing business conditions such as market demand, sales and profitability. The relevant variables that can influence the energy performance should be defined, quantified and isolated in terms of significance (ranging from no influence or little influence to significant). The organization sets quantitative references, meaning EnBs for each EnPIs in order to compare EnPIs values over time and to quantify the changes in energy performance. The results of energy performance can be expressed in SEC (e.g., kWh/unit), and when multiple forms of energy are used, conversion to a common unit of measure should be performed in such a way that the conversion process includes the total energy used and the losses. When comparing energy performance results, it is recommended that the EnPI and its corresponding EnBs are normalized by modifying the energy data so that the changes in relevant variables which affect energy performance are considered and the comparison is carried out under equivalent conditions [17]. According to SS-EN 16231:2012 (standard [9] on energy efficiency benchmarking methodology), when aiming to evaluate and compare performance between or within different entities, the performance data of comparable activities should be collected and analysed. This is basically the process of benchmarking, and different types exist, from internal benchmarking, which involves a comparison of energy performance at different locations within the same organization, to external benchmarking, which can be used to establish a series of EnPIs for either an installation or a product, within the same sector. Benchmarking boundaries should be clearly defined and limited to the process installation, facility, product, building or organization in such a way that the correction factors (e.g., weather conditions, product or service and associated technology, production level and quality of feed stock used) will be applied as little as possible. In energy efficiency benchmarking, the energy use of processes with the same output is assessed, and comparability of processes can be achieved in exceptional cases by the use of correction factors, i.e., well-defined adjustments of the SEC. In energy efficiency benchmarking, SEC is used as an indicator of energy use per (physical) unit of output, and the output can be a product, an activity or a service, e.g., GWh per kt of paper, GJ per tonne of steel, annual kWh per m 2 , or kWh per full-time employee [9]. SS-EN 16212:2012 (standard [37] on energy efficiency and savings calculations, top-down and bottom-up methods) also defines SEC as the energy use per physical unit of output, and describes it at subsector level and relates the annual energy use to annual physical production. It connects the total energy use to the number of systems, in this case the equivalent of mean yearly energy use per system, e.g., GWh per kt of paper, GJ per tonne of steel, kWh per m 2 of dwelling, kWh per refrigerator or L/100 km for vehicles. The change in SEC value over time is used as an energy efficiency indicator for top-down energy savings calculations, as it relates the energy use to a physical output or to the number of systems using energy. When carrying out a top-down savings calculation, energy indicators will be selected and used. The choice of energy savings indicators starts with the definition of energy savings, which is dependent on the types of drivers (economic, technical or behavioural factors) behind the changes in energy use. When technical efficiency is assessed, SEC per physical unit is calculated. The steps for performing a general calculation of top-down energy savings are: definition of indicator types, calculation of indicator values and calculation of energy savings per indicator. Examples of SEC usage as indicators for these calculations are: (i) SEC at sub-sector level, which relates energy use to physical production (e.g., GWh/kt paper, MJ/tonne of steel, etc.) for a given period, usually a year; and (ii) SEC for energy using systems, which relates total energy use for specific systems to the number or size of systems.
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