Energies 2019 , 12 , 247
9of 22
The annual energy use may be normalized, meaning that it can be corrected for yearly deviations from average climate that influence energy use and include heating and space cooling. The value for SEC indicators is calculated using the formula below, where the normalized energy use (NEC) is divided by the driver quantity (DV) for the year t [37]:
NEC ( t ) DV ( t )
IND ( t )=
(5)
where IND is indicator value, NEC is normalized energy use, DV is quantity for driver and t is year of evaluation. The change in SEC indicator value is calculated as follows [37]: CIND = IND ( t 0 ) − IND ( t ) (6) where CIND is change in indicator value, IND is indicator value, t 0 is base year and t is year of evaluation. The energy savings per indicator are calculated as the change in indicator value multiplied by the driver quantity in the year of evaluation, as in the formula below [37]: ESPI = [ IND ( t 0 ) − IND ( t )] × DV ( t ) (7) where ESPI is energy savings per indicator, IND is indicator value, DV is quantity for driver, t 0 is base year and t is year of evaluation. When calculating energy savings for the industrial sector, SEC for energy-intensive industries is calculated as follows [37]:
Final energy use of the branch Production measured in physical units ( e.g., kt )
(8)
SEC =
As can be seen, SEC is presented and recommended as an energy performance indicator for energy efficiency and the formula presented is basically the same in all the reviewed standards. Practical guidance on the usage of SEC is presented, but more analysis on the challenges and usage of SEC is required. The calculations of SEC in the reviewed articles comply with the calculations recommended by the international standards. Additionally, the studies using SEC confirm that the usage of SEC also complies with the requirement to measure energy efficiency. 4.4. SEC Usage for Benchmarking In summary, according to the literature (e.g., [28,51]), the relationship between the amount of data and the precision of the identification for improvements can be as illustrated in Figure 1. In other words, the more disaggregated the level of benchmarking is, the more data is required [28]. For example, international benchmarking can be used to identify the potential for improved energy efficiency, but cannot specify where exactly the energy efficiency improvement measures can be found [51]. However, benchmarking at process level could identify such energy saving opportunities [51]. Notably, international benchmarking is generally challenging due to differences between the sectors, economic structure of the countries, etc. ([11,28]). In agreement, the reviewed studies confirmed that the more disaggregated the level such as e.g., process level, the more precision was required and given (e.g., [7,10,16]), whereas the more aggregated the level of benchmarking, the lower the precision (e.g., [6]). Some studies addressed one levels of benchmarking within their study (e.g., with the same study, e.g., [7,10,16]), whereas some of the other studies using SEC performed benchmarking at several levels within the same study (e.g., [52]).
Made with FlippingBook Digital Publishing Software