Ingeniero

Energy 38 (2012) 331e345

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Energy
journal homepage: www.elsevier.com/locate/energy

Energy efficiency measurement in industrial processes
E. Giacone*, S. Mancò
Dipartimento di Energetica, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy

a r t i c l e i n f o
Article history: Received 18 March 2011 Received inrevised form 25 November 2011 Accepted 26 November 2011 Available online 29 December 2011 Keywords: Energy efficiency Specific energy consumption Energy management system Energy benchmarking Melting furnace LCA

a b s t r a c t
Although the meaning of energy efficiency is clear, different definitions exist and important issues relating to its implementation still need to be addressed. It is nowrecognised that complicating factors e such as complex industrial sites and energy flows, multiple products and fuels, and the influence of production rate on energy efficiency e render it necessary to adopt a structured framework to define and measure energy efficiency more precisely. In this paper, a methodology is proposed to build such a framework. The whole energy system of a site is represented usinga single matrix equation, which expresses the relationship between imported energies and energy drivers. The elements of the matrix are the specific energy consumptions of each single process. Mathematical process modelling, through statistical analysis of energy consumption data, is used to quantify the specific energy consumption as a function of the output. The results of this structured approachare relevant for energy benchmarking, budgeting and targeting purposes. Furthermore, this approach is suitable for implementation in an energy management system standard (e.g. EN 16001, ISO 50001) or LCA standard (e.g. ISO 14044). Glass and cast iron melting processes are presented in order to illustrate the application of the method. Ó 2011 Elsevier Ltd. All rights reserved.

1. IntroductionThe measurement of the energy efficiency of a system or process is an essential step towards the control of the energy consumption and energy costs. Numerous studies have recently been focused on industrial energy use and energy efficiency in various manufacturing sectors [1e6]. An analysis of existing literature concerning the definitions of energy efficiency pertaining to a process [7e13] has pointedout a variety of indicators of energy efficiency, such as thermal efficiency, specific energy consumption, energy intensity index, etc. The most widely used indicator in industry is the specific energy consumption (SEC) of a given output (or input) [7]. Despite the simple definition, several complicating factors arise in its implementation [7e13]:  complex production sites operate more than oneproduction process;  a production site may make various types of products, each with its own energy intensity factor;  considering that different variables can affect energy efficiency, a comparison between different installations using energy efficiency indicators can lead to misleading conclusions,

especially when it is difficult (or even impossible), in practice, to take into account all thevariables in an appropriate manner;  specific energy consumption depends on the production rate when, for example, there is a base energy consumption, whatever the utilisation of the production capacity;  unlike thermal efficiency, the definition of SEC does not provide information on whether energy is used or produced efficiently;  in the case when energy efficiency is compared over time or betweendifferent installations, it is particularly important to define suitable system boundaries to ensure that all energy users are considered equally. Moreover, many industrial companies still lack appropriate methods to effectively address energy efficiency in a comprehensive and practical manner [13]. Experience in trying to quantify the concept for monitoring processes has highlighted that a framework...