Energy characterisation and benchmarking of factories Rasel Mahamud, Wen Li, Sami Kara (1)* Sustainable Manufacturing and Life Cycle Engineering Research Group, School of Mechanical and Manufacturing Engineering, The University of New South Wales, Sydney, Australia 1. Introduction Energy and the associated emissions are of great concerns in today’s world. The manufacturing industry, in particular, is affected from this since manufacturing sector consumes nearly one-third of the global energy generated [1]. Improving energy efficiency in manufacturing can be considered as a pragmatic and an attractive solution, because it assists manufacturers to address the mentioned concerns as well as reducing their production cost, ultimately enhancing their competitiveness in the market. In order to systematically improve the energy efficiency, it is essential to identify improvement potentials and to monitor the progress at the factory level. One approach is to derive references or targets through benchmarking which is a well-established management tool [2,3]. The present development in energy benchmarking for factories is mainly based on industrial surveys for a specific sector. For example, the Energy Star1 industry programme uses statistical analysis to determine a probabilistic frontier for automotive industries [4]. The BEST (benchmarking and energy savings tool) uses a bottom-up approach to compare each unit process with a hypothetical best process from a sector- specific survey (e.g. iron and steel industry) [5]. However, those methods are limited to available industry surveys which require great efforts and need to be updated regularly. In addition, it is often unfair to compare with an external practice due to the variety of products, processes and factories. Alternatively, benchmarking can be performed through the comparison with a theoretical limit [2]. In the context of energy benchmarking, the concept of minimal/theoretical energy require- ments can serve as an unbiased reference for a given manufactur- ing system. Therefore, this paper aims to develop a generic methodology to derive such reference points for a given factory. 2. Analytic approach and its limitation In order to provide the theoretical background, the analytic approach from a thermodynamic perspective is first discussed in this section. This approach is based on ‘exergy’ that has been defined by Sciubba and Wall [6] as ‘the maximum theoretical useful work obtained if a system S is brought into thermodynamic equilibrium with the environment by means of processes in which the S interacts only with this environment’. Gutowski et al. [7] introduced an exergy framework for manufacturing systems. Under this framework, all types of input and output streams (e.g. energy, material, waste) can be converted into a unified form, exergy. Also, this quantification offers the opportunity to estimate the minimal/theoretical energy require- ment for producing one unit of product. However, this approach requires a significant amount of detailed information, which limits its applicability. To further explore the required efforts, an exemplary case is presented, which is an aluminium remelting facility in Australia. Firstly, all main input and output streams were identified through a material and energy flow analysis. The amount of the input energy, input material, output product, and by-product (i.e. slag) was obtained from the company database, whereas the exhaust gas from the furnace was estimated theoretically. In addition, it is necessary to obtain the chemical composition and physical status (e.g. temperature, altitude) of each stream to derive the exergy coefficients. Then, the exergy due to system loss (e.g. radiation) was calculated based on the exergy balance as Eq. (1): X Ex m þ X Ex en ¼ X Ex p þ X Ex w þ X Ex l (1) where all quantities with Ex refer to the exergy, and subscripts m input materials, en input energy streams, p output product streams, w waste streams, and, l aggregate loss in the system. CIRP Annals - Manufacturing Technology xxx (2016) xxx–xxx A R T I C L E I N F O Keywords: Energy efficiency Factory Energy benchmarking A B S T R A C T Energy efficiency is imperative for enhancing the competitiveness of today’s manufacturing. Benchmarking can provide guidance for developing improvement strategies, which requires energy characterisation to determine the current performance, reference points and improvement potentials. However, the present developments in energy benchmarking cannot be applied to a wide range of manufacturing industries. Therefore, this paper presents a generic methodology to characterise the energy efficiency at a factory level and to derive the reference points for benchmarking. A case study is used to demonstrate the validity and applicability of the proposed method. ß 2017 Published by Elsevier Ltd on behalf of CIRP. * Corresponding author. G Model CIRP-1568; No. of Pages 4 Please cite this article in press as: Mahamud R, et al. Energy characterisation and benchmarking of factories. CIRP Annals - Manufacturing Technology (2017), http://dx.doi.org/10.1016/j.cirp.2017.04.010 Contents lists available at ScienceDirect CIRP Annals - Manufacturing Technology journal homepage: http://ees.elsevier.com/cirp/default.asp http://dx.doi.org/10.1016/j.cirp.2017.04.010 0007-8506/ß 2017 Published by Elsevier Ltd on behalf of CIRP.