Key Points on the Energy Sustainable Development of the Food Industry – Case Study of the Portuguese Sausages Industry

Renewable and Sustainable Energy Reviews 57 (2016) 393–411

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Renewable and Sustainable Energy Reviews

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Key points on the energy sustainable development of the food industry – Case study of the Portuguese sausages industry

J. Nunes a, Pedro D. Silva b, L.P. Andrade a, Pedro D. Gaspar b,n a Politechnic Institute of Castelo Branco, Av. Pedro Álvares Cabral nº12, 6000 Castelo Branco, Portugal b University of Beira Interior, Electromechanical Engineering Department, Calcada do Lameiro, 6200-001 Covilhã, Portugal article info abstract

Article history: Sausage is an ancient food type that is nowadays considered as a delicatessen. Sausages are categorized Received 10 February 2015 within the deli sector as meat sub products. It is a food product preferred by consumers due to its Received in revised form nutritional value and organoleptic characteristics (wide range of flavors and textures). The heating and 3 August 2015 cooling processes during sausages production are indispensable technologies to ensure both the specific Accepted 10 December 2015 organoleptic characteristics and properties conservation through time. Energy is a major cost in the Available online 5 January 2016 operation of these facilities. This paper starts with a review of the research related to energy consump- Keywords: tion, energy efficiency measures and energy indicators in the food industry. Additionally it describes the Food industry major cost-effective electricity savings (improved door protection, defrost optimization, control settings Energy consumption and repairs) that can be applied to this industry. Later a case study that characterizes the production Energy efficiency measures process and the energy consumption of sausages processing industry in Portugal (20 industries) is pre- Energy indicators Sustainability sented. The results from this case study show that energy consumption of this type of industries is mainly fi Sausages of electricity (82%). The annual average speci c energy consumption (SEC) of electricity is 660 kWhe per Refrigeration tonne of raw material. Correlations were developed that show the relationships between tons of raw material and electricity consumption, volume of cold stores and compressors nominal power. A strong relationship between SEC and the usage of cold rooms was determined. Several electricity savings, estimated in 24%, can be achieved by implementing simple practice measures in the refrigeration systems. & 2015 Elsevier Ltd. All rights reserved.

Contents

1. Introduction ...... 394 2. Energy consumption in the food industry ...... 394 3. Energy efﬁciency in the food industry ...... 396 4. Energy consumption indicators...... 397 5. Cold storage facilities ...... 399 6. Case study of Portuguese sausages industry ...... 401 6.1. Productive process...... 402 6.2. Material and methods ...... 402 6.3. Results analysis and discussion...... 403 6.3.1. Facilities ...... 403 6.3.2. Refrigeration systems ...... 403 6.3.3. Energy consumption ...... 404 6.3.4. Speciﬁc indicators ...... 405 6.3.5. Refrigeration system modeling ...... 406 7. Best practice measures and technologies ...... 406 8. Conclusions ...... 408 References...... 409

n Corresponding author. E-mail addresses: [email protected] (J. Nunes), [email protected] (P.D. Silva), [email protected] (L.P. Andrade), [email protected] (P.D. Gaspar). http://dx.doi.org/10.1016/j.rser.2015.12.019 1364-0321/& 2015 Elsevier Ltd. All rights reserved. 394 J. Nunes et al. / Renewable and Sustainable Energy Reviews 57 (2016) 393–411

1. Introduction In Portugal, the industrial food sector is made up mostly by micro, small and medium industries, that having energy intakes The industrial sector is comprised by a diverse set of industries lower than 500 tonnes of oil equivalent (toe) do not require by that are globally responsible for 37% of a worldwide energy con- government diploma an evaluation of their energy performance. sumption and 36% of carbon dioxide emissions (CO2) [1]. The main The energy profile and the main features that contribute to its industries of this sector are manufacturing industries within energy performance, with special attention to refrigeration sys- which stands agrifood industries [122,123]. At European level, the tems, were not known for this specific type of industry. food industry represents a universe of 286,000 industries with This paper provides a review of the research related to energy 4.2 million direct jobs and had in 2014 a turnover of 1048 billion consumption, energy efficiency measures and energy indicators in euros [32]. the food industry. The review starts with the description of these In Portugal, the food industries follow the European trend, topics in the general industrial sector to the specific sector of meat being also the largest group of manufacturing industries in the processing. It is provided a review of the research developed in country (13.2%). In 2011 reached a business turnover of 9340 several countries focusing on the energy consumption, energy million euros [51]. Within the food industry, the largest sector efficiency measures and energy indicators values in the food corresponds to the meat industry. In 2010, this sector was repre- industry. The energy savings potential is quantified in terms of sented by 1159 industries with a turnover of 1130 million euros, procedures and technologies. To highlight the relevance of this representing 12.3% of total volume sales volume of food industries approach, this paper also presents a study with the results of 20 [51]. The main products of the meat industry sector are the cured sausages factory audits located in central region of Portugal to sausages. Based on the results of 2012, these industries produced assess the characteristics of energy consumption, with particular 87,400 tonnes of cured sausages, representing 46.8% of all indus- emphasis on electrical energy. The characteristics of the infra- trial production of meat products and corresponding to a turnover structures, refrigeration systems, energy consumption, energy of 249.4 million euros [50]. In Portugal, as in many European performance and potential savings of electricity are analyzed. A set countries, there has been an increased production of cured sau- of mathematical equations that relate the main parameters that sages. It was registered an increase of 10.6% in 2012 comparing influence the performance of cooling systems, such as: raw with the previous year [127,52,99]. materials, cold rooms volume, electrical energy consumption and In general, industries in this sector use two types of energy: the nominal compressors power are obtained. Using these corre- electricity and fossil fuels. The electricity is used primarily on lations, the owner of a sausage company can evaluate how much operating the cooling systems to comply with food safety competitive is his company in terms of energy efficiency compared requirements due to the high degree of spoilage of meat with his national counterparts. Knowing this value, the owner can [108,113,122]. In the particular case of cured sausages manu- apply a set of practice measures with different payback times to facture, about 25% of the total industrial energy is used for cooling achieve energy savings that can go up to 24%. These general and refrigeration processes, and 48% for food processing [81]. recommendations, some of them very cost-effective, may help However, during the production period, the cooling systems can companies' competitiveness through energy sustainability consume 45–90% of total electricity. In non-production periods measures. (retention periods), they are responsible for all electricity con- Globally, the review and the case study results are used to sumption [84,97]. present the key points on the energy consumption, energy effi- The energy consumption in sausages factories depends on ciency measures and energy savings potential to encourage the various factors such as the type of production process, the size and energy sustainable development of food industry. structure of the product, the chemical and physical properties of raw materials, the technology used, the mechanization level of the factory and the usage of installed capacity [128,129,44,61]. In order 2. Energy consumption in the food industry to maintain a sausages industry competitive taking into account the rising of energy costs, it is necessary to have a good energy and The energy consumption of refrigeration systems in the food environmental performance. Thus, these industries should use the industry has been growing due to increasing production of food best available techniques and production practices, with major and the requirements imposed by quality, hygiene and food safety emphasis for its energy efficiency [17–19,22,87]. standards [97]. The cooling systems are considered as intensive In general, for evaluating the energy efficiency of an industrial energy consumption systems due to the high degree of use in unit is common to use a normalized scale, often defined by the many industrial processes [131,132,75]. The specific characteristics ratio of energy expended during production and the result of the food industry business within the various countries, which obtained from such production [97,98,129]. Thus, indicators of is composed by a large number of small sized manufacturing food Specific Energy Consumption, SEC, (electrical and thermal) are industries, result on a very high electrical energy consumption obtained, that allow the evaluation of the performance of an [97]. In the EU, the majority (99.8%) of these industries was small industrial unit by comparison with indicators that belong to others and medium enterprises (SMEs) –about 20.9 million– and more units with the same category for similar activities and technolo- than nine out of ten companies (92%) employed less than 10 gies [129]. workers. This scenario is more relevant in the member states of There are some SEC values for these two types of energy in southern Europe, such as Italy, Spain and Portugal [25]. A few sub- related literature, although they correspond to industrial units sectors had an improvement of energy consumption resulting with different dimensions, technology level and world regions from increased activities and simultaneously by increased use of [104,18,19,35,97,129]. None of these studies deals specifically with refrigeration systems [97]. In fact, the electrical energy consumed sausage-making industries and furthermore they only use one by refrigeration systems may reach 85% of total energy con- pilot plant or fictional scenarios. Nevertheless, these indicators sumption [121]. In the UK, 11% of final energy is consumed by the allow to find the best practices and procedures for the reduction of food industry and some sectors are using more than 90% of elec- energy consumption in this type of industry. Fritzson and trical energy into the refrigeration system [107]. Many economic Berntsson [35] estimated that the energy savings in cooling meat sectors require the use of a fast cooling technique to remove the products could achieve 10% of in modern industries and 15% in the initial thermal load of products before the cold storage. Swain et al. oldest ones. [107] points out that in the UK there are six categories where it is J. Nunes et al. / Renewable and Sustainable Energy Reviews 57 (2016) 393–411 395

Nomenclature RM Annual amount of raw materialsÀÁ processed (tonRM). 3 ÀÁ Vtotal Total volume of cold rooms m . fi 1 P Nominal electric power of all refrigeration SEC Speci c Energy Consumption,ÀÁ kWh tonRM . total fi 3 compressors (kW). SECV Speci c Energy Consumption,ÀÁ kWh m . 3 UCR Usage of cold rooms volume tonRM m . toe Tonne of oil equivalent. NPC NominalÀÁ power of compressors per cold rooms EU European Union. volume kW m 3 . SME Small and Medium Enterprise. COP Coefficient of Performance LPG Liquefied petroleum gas. E Annual electrical energy consumption (kW h)

necessary to remove this energy, which are milk (corresponding to According to DEFRA [14], the refrigeration systems used in the an energy consumption of 532 GW h year1), meat UK dairy industries have an average energy consumption of (114 GW h year1), potatoes (59 GWh year1), other 250 GWh year 1. Moreover, the energy used in the refrigeration vegetables (36 GW h year1), fish (6.5 GWh year1) and fruits sector plays a very important role in the total energy needs of a (5.9 GWh year1). It also states that using the best cooling tech- dairy facility, often representing more than 40% of the electricity nologies available in the UK, an annual energy savings of 154 GWh consumed. The amount and type of energy used depends on the can be reached in potatoes cooling, 128 GWh in milk cooling and type of products manufactured. from 51 to 80 GWh in carcass cooling. Also in the UK, Burfoot et al. Regarding the Australian dairy industries, in particular for [9] found that the chilled food sector had an annual energy con- cheese production, the electrical and thermal energy correspond sumption of 9.27 109 GW h, and about 18% of this value was to 27% and 73% of the total energy, while in milk production for consumed in the industry to maintain low temperatures to pre- human consumption these values are around 66% and 34%, vent the growth of microorganisms in food. respectively [91,92]. Concerning the meat sector, Gigiel and Collett The refrigeration systems in France are responsible by 4% of the [39] emphasize that in 1982 the refrigeration systems in UK industry electricity consumption and almost 7% of the country slaughterhouses consumed 75 GW h of electricity in the cooling electricity consumption. It is estimated that the consumption of process and cold storage of pork carcasses. In addition, the energy electricity in the French dairy sector is roughly of the order of consumption in the Spanish meat sector increased 22.7% from 2.9 TW h. Furthermore, 25.5% of this amount, corresponding to 1996 to 2001 reaching 333.20 ktoe. The electrical energy and the fi approximately 740 GW h, are exclusively consumed by refrigera- fuel consumption (as propane gas, heating oil or rewood) cor- tion systems [38]. In terms of electrical energy consumed with respond to 61% and 39% of the total energy consumption in processed meat products (sausages). In slaughterhouses the fractions refrigeration systems, the dairy industry ranks fourth, after the of the electrical energy and other fuels consumption (propane and large food distribution (3.6 TWh), the cold storage industry natural gas) are about 64.3% and 35.7%, respectively [69]. (2.45 TW h) and trade proximity (1.4 TW h). This consumption is The results of energy audits performed to 51 Spanish meat above the electricity consumption in other food activities such as production and processing industries are presented in ICAEN [45]. cattle slaughterhouses (370 GW h), the delicatessens (369 GW h) A number of 441 cooling chambers were diagnosed corresponding and breweries (203 GW h) [38]. Dairy establishments, particularly to a production of 478,697 tonnes with a total energy consumption in the manufacture of cheese and meat processing are particularly of 110 GW h year 1 and an energy cost of € 7,713,299 year 1. energy demanding, because they need it for both cooling and The electrical energy corresponded to 66 GW h year 1 (60%) of heating processes. For example, Ramirez et al. [96] point out that the total energy consumption and the thermal energy to in the Netherlands the production of dairy products, and the 43 GW h year 1 (40%). Regarding the electrical energy consump- production, processing and preservation of meat accounts for 1 tion, the energy balance points out 60 GW h year (81.2%) to about 15% and 9% of the total energy consumed in the food sector, refrigeration systems, 1.8 GW h year1 (2.9%) for compressed air, respectively. Also according to Ramirez et al. [96], in 2000, the 7.1 GW h year1 (10.8%) for process machinery, 2.7 GW h year1 11 dairy sector consumed approximately 1.444 10 GW h, (4.1%) and lighting 0.7 GW h year 1 (1%). The main fuels were 11 11 11 0.944 10 GW h, 0.444 10 GW h and 0.388 10 GW h of natural gas (45%), biomass (19%), heating oil (16%), heavy oil (15%) primary energy in France, Germany, the Netherlands and the UK, and LPG (5%). respectively. A study about energy consumption in Irish meat industry In 1998, the USA food industry represents 4.4% of electricity shows that globally between the years 2003 and 2008 there was consumption in the industrial sector [70]. Regarding this country, an increase of 4.5% of electricity consumption and a decrease of within the manufacturing industries sector, dairy products have 4.4% in the consumption of thermal energy [20]. This study indi- huge highlight, with electricity consumption in 2002 and 2006 of cates that cooling is used intensively and shows that total energy 11 11 0.236 10 GW h and 0.266 10 GW h, respectively. There has consumption in the sector of beef processing increased by nearly been an increase in electric energy consumption by 3.1% during 1% between 2003 and 2008, reaching a value of 395 GW h. this period. Although the production of dairy products has grown, According to that study, in 2008, the average energy consumption an opposite trend was registered in the Netherlands, with a in the slaughter process of a bovine head process was 889 MJ reduction of electricity of 9.3% between 1998 and 2002. This by head. reduction result from effective measures of energy savings [132]. A similar study performed to Spanish slaughterhouse category In South Africa, the manufacturing sector has the largest elec- presents the following values of energy consumption [69]: refrig- tricity consumption (68% of 40 GW h). The energy consumption eration, 22 MW h day1 (54.4%); electric motors, 15 MW h day1 increased by 22% between 1992 and 2000, with the greatest (36.7%); lighting, 0.8 MW h day1 (2.1%); and compressed air, growth in the agricultural sector (25%) [116]. 2.8 MWh day1 (6.8%). The main meat industries of this country are 396 J. Nunes et al. / Renewable and Sustainable Energy Reviews 57 (2016) 393–411 manufacturing small-scale industries which still perform all the and milk storage equipment (20%). The main consumers of ther- meat processing steps (slaughterhouse, cutting plants, cold storage mal energy are the heating systems and dryers (40%). and manufacture of sausages and ham). However a split on In general, large energy savings can be achieved in food slaughterhouses and sausages activities begins to occur in this industry with the implementation of efficient management and industry [22]. For Portugal, according with the Regional Directorate monitoring systems of the energy consumption [132,2,35,70] and of Agriculture and Fisheries Center (DRAPC) there is an effective with a good maintenance of the existing systems and technologies split between slaughterhouses and sausages activities with each [39,49,56]. Moreover, the energy savings can also be achieved if sub-sector performing by itself. the current systems are improved, for example, using high- efficiency electric motors [130,18,19], deploying variable speed motors Tassou and Qureshi [94,110,111,100,1], or developing new 3. Energy efficiency in the food industry food preservation technologies with very low potential for environmental impact along with the reduction of food waste Given the high-energy consumption, the food processing [109,57,63,85]. In addition, in some cases we can also reuse the industries face the need to adopt measures and actions to promote waste heat from condensers and condensates [34,58]. good use of energy. In fact, the implementation of energy effi- Moreno [69] states that the process of drying products such as ciency measures improves the reduction of energy costs, main- sausages, ham and cheese is the most costly in terms of energy tenance costs, improve safety, increase productivity, contribute to and therefore considers that one of the possibilities to reduce a better matching between refrigeration equipment and thermal energy consumption is to take advantage of outside air conditions load, a better working environment and a reduced resource con- for the drying process. Energy savings of about 25% can be sumption and greenhouse gases emission [121]. The energy- achieved with this procedure. According to the same author, savings value in refrigeration systems is related to the number another possible technique to reduce energy consumption during and the type of measures applied and the quality of the technology the drying of sausages and hams is the use of desiccants or used. The improvement of the operating practices in the facilities absorbent materials in the air circulation circuit of the dryer. or a careful building up of industry facilities can often provide a Energy savings of about 50% can be obtained with this technique. reduction of energy consumption by 15%, or even more, while the However, it has the disadvantage of being very expensive. Even on technical improvement of the components of the refrigeration dry ham, Ortega et al. [83] discloses a related technique with the system can achieve an energy consumption reduction potential operation time of the air-handling units: in well-controlled con- between 15% and 40% [121,40,64]. According to Victoria [121] the ditions, these devices may be turned off during controlled periods energy efficiency improvement on existing systems can be of time when energy is more expensive. During machine stop, the achieved by an action plan involving the following steps: i) temperature and relative humidity must be within desired para- required cooling capacity analysis, ii) thermal insulation require- meters to prevent any damage to the produce. In this case, the ments, iii) assessment of the refrigerant distribution in the system, environmental conditions inside the drying chamber are main- iv) assessment of the control system equipment and heat rejection tained due to thermal storage (cold storage). This technique allows processes; v) maintenance optimization and finally vi) re- a 5% saving of electrical energy and a 50% reduction of the evaluation of the system performance. For new installations, the electrical power. main steps are i) integrated system design; ii) appropriate selec- Sarvisé [103] presents the results of energy audits carried out in tion of the compressor; iii) selection of evaporators and con- the meat, fruits and dairy sectors. Regarding the meat sector, 31 densers; iv) selection of the heat transfer fluids and refrigerant v) meat establishments were audited presenting a total energy con- reuse of waste heat; and finally vi) whole year estimation of the sumption of 22,669 toe of which 10,337 toe corresponded to system efficiency. The details of each one of these steps in the electricity (45.6%) and the remaining 12,332 toe correspond to energy efficiency of the refrigeration system can be found in IIR thermal energy (54.4%). After being applied some energy saving [49], Reindl et al. [98] and Victoria [121]. Landymore [59] reports measures (e.g., automation of refrigeration plants, improving the that significant improvements in the technology of refrigeration insulation of refrigeration chambers and control of defrosting the systems was already achieved, however some of the solutions are evaporators) a total energy saving of 2058.5 toe year1 was too costly to be implement for small and medium companies. As in obtained in the refrigeration facilities corresponding to 19.9% of refrigeration systems the compressor accounts for about 70% of the electricity consumed. Regarding the fruit sector, 31 facilities the electrical energy consumption of the installation, one of the were audited featuring a total energy consumption of 4304 toe technologies with great energy saving potential is an electronic and 49 GW h of electricity consumption. The final diagnosis esti- device that lower compressor operating time up to 30%. mated energy savings of 885.5 toe, representing approximately According to Gautherin et al. [38], in the French dairy sector, 20.5% of the consumption of electricity. The main energy saving where the electrical energy by the refrigeration systems is measures to be implemented in this case are: automation of the approximately 740 GWh, it was implemented a number of energy refrigeration system; control of the defrost system; installation of efficiency measures in terms of proper refrigeration facilities and evaporative condensers; enhance the surface of the evaporators; production processes and manufacturing. Within these measures, installation of high performance humidifiers; and the cool rooms the authors highlight the lowering of the condensing temperature, walls repair. Finally, in the dairy products industry, the energy the increase of evaporation temperature, the use of variable speed audits in 12 stores showed an energy consumption of 11,945 toe of drives, the use of advanced control on cold rooms, the resizing of which 2,461 toe corresponded to electricity (20.6%). These indus- pasteurizers, the assessment of energy savings, the evaluation of tries present a good technological level and a 2.7% electrical the equipment used in the processes and its energy consumption. energy savings was achieved. The suggested measures were the The energy savings achieved when compared with the initial improvement of the cold storage systems performance and the use consumption values are between 10% and 20%. of evaporative condensers. Mirade et al. [67] points out that the accurate analysis of energy In ICAEN [45], energy audits are carried out in the meat sector consumption in the cheese manufacturing industry allows high- 51 establishments and 441 cooling chambers and providing a set lighting the main energy consumers. In terms of electrical energy of energy efficiency measures. A total energy consumption of consumers there are two main groups, pumps, fans, motors of the 109 GW h year1 distributed by 66 year1 of electricity (60%) and roller transmission and lighting systems (35%) and cooling systems 43 GW h year1 of thermal energy (40%). The electrical energy J. Nunes et al. / Renewable and Sustainable Energy Reviews 57 (2016) 393–411 397 savings in refrigeration are expected to reach 20 GW h year1 by 4. Energy consumption indicators implementing a set of energy efficiency measures: air curtains usage to decrease the cold losses (with an energy savings potential The evaluation of the energy performance and energy effi- of 22.6%); implementation of evaporative condensers (46.7%); ciency of food manufacturing facilities can be performed through fi change of defrosting systems of evaporators (4.2%); improvement benchmarking, which method involves comparing the speci c energy consumption (SEC) among facilities with similar char- of evaporators performance through implementation of electronic acteristics [98]. For conducting a benchmarking is usual using up valves (23.6%) and changing the refrigerant (2.9%). indicators for SEC that are usually defined by the ratio between In ICAEN [46], a study of 50 energy audits fruit plants is pre- energy consumption of a particular process (electrical or thermal) sented which involved 818 cooling rooms. A total energy savings 1 and a physical quantity such as raw material, production, volume, potential of 6 GW h year was determined. The proposed energy among other [131,96,97] or monetary (energy costs) [98]. fi ef ciency measures are: implementation of evaporative con- According to Reindl et al. [98], this analysis, also known as "nor- densers (with an energy savings potential of 7.2%), improving the malized performance analysis" is a formal process designed to operation of the evaporators (23.9%), refrigerant replacement eliminate or minimize the influence of one or more uncontrolled (8.4%), reduction of cold/heat losses (10.5%), replacement of the variables that influence the performance measurement. The nor- evaporator defrosting process (16.5%) and using of variable speed malization allows comparing performance data obtained under electric motors (33.6%). different conditions in a consistent and meaningful way. The A set of measures to improve the energy use in a slaughter- normalization process also allows researchers to identify the fac- house are also presented in a European Commission report [17]. tors that may contribute to the excessive energy consumption. The Energy efficiency measures implemented include both thermal change of the normalized indicator indicates a change in the sys- and electrical components. The measures included the monitoring tem performance. This change may be useful in evaluating the results and efforts to improve energy efficiency. An unexpected of electrical energy and fuel consumption, improving the thermal change is an indication of a variation in the system performance, insulation, sealing leaks in compressed air system, monitoring the or a system response in relation to factors affecting the energy use. operation time of refrigeration systems. In addition, an alarm The SEC is an energy indicator commonly reported in the lit- system was also installed to avoid that the doors of the chambers erature to evaluate the energy efficiency of industrial facilities or may be left open. economic sectors [115,65,72]. This indicator was recently used in Table 1 provides an overview of the main measures for energy the energy analysis in meat manufacturing industries [77,78], in efficiency referred in this section and complemented with other horticultural industries [80] and in cheese industries [73] as well proposals by other authors. as in the development of computational tools for the energy

Table 1 Major energy efﬁciency measures applied to the agrifood industry.

Measures Max energy savings (%) References

Refrigeration systems grouped by compression level 25% Gameiro [36], Langley [60], DEFRA [14] Regulation of refrigerant volumetric flow (scroll 20% Qureshi and Tassou [94], Gameiro [36], ICAEN [46], DEFRA [14], compressors) Landymore (2012) Monitoring and control of the refrigeration system 9% Gameiro [36], López et al. [62], DEFRA [14], Evans et al. [28] Sub-cooling increase 1% (medium temperature) 9% (low Gameiro [36], DEFRA [14], Evans et al. [28] temperature) Lowering the condensation temperature 2–3% by °C Westphalen et al. [125,24], Gameiro [36], DEFRA [14] Using a floating condensation pressure 30% Manske et al. [64], Reindl et al. [98], Christophe [11] Superheat reduction 1–1.5% Garcia and Rubio [37], Langley [60], Evans et al. [28] Electronic valves 20% DEFRA [14] Increasing the evaporation temperature 1–4% per °C ETSU [24], Gameiro [36], DEFRA [14] Increasing the diameter of suction line 1.5–2.5% Gameiro [36], DEFRA [14] Variable Frequency Drives (VFD) in motors 30–70% Gameiro [36], López et al. [62], Victoria [121], Widell and Eikevik [126], DEFRA [14] Evaporative condensers 6–12% Gameiro [36], EREN [22], ICAEN [45], Hajidavalloo and Eghtedari [41], DEFRA [14] Optimum level of refrigerant charge 1–4% Gameiro [36], DEFRA [14] Reduction of operating bad practices 4–8% Langley [60], DEFRA [14] Refrigerant replacement 10–15 % Gameiro [36], Pagan et al. [84], Langley [60] , ICAEN [46] Refrigeration system retrofitting 30-40% Nunes et al. [79] Proper thermal insulation (ducts and cold rooms walls) 1–5% Gameiro [36], Garcia and Rubio [37], Langley [60] Proper thermal insulation of building envelope 1–3% Garcia and Rubio [37] Regular evaporator defrost 5–10% Manske et al. [64], ICAEN [45,46] Doors protection of cold rooms (air curtain, plastic 10% Gameiro [36], López et al. [62], ICAEN [46], DEFRA [14] strips,…) Lighting control management 0.16% ICAEN [45] Implementation of an energy management plan 13% López et al. [62], Evans et al. [28] Cooling the lubrication oil of scroll compressors 3–10% Reindl et al. [98], Victoria [121] Regular maintenance 4–8% Reindl et al. [98],EC[18,19], Victoria [121], Evans et al. [28] Condensation heat recovery 12% López et al. [62] Using heat pumps in specific heating processes 8.6% López et al. [62] Using efficient lighting 70–80% of lighting energy ICAEN [45] Control and regulation of compressed air 30% ICAEN [45] Reducing products initial thermal load Variable James [55], Nunes et al. [80] Avoiding excessive nominal power design Variable Langley [60], DEFRA [14], Evans et al. [27] 398 J. Nunes et al. / Renewable and Sustainable Energy Reviews 57 (2016) 393–411 efficiency assessment in the agrifood sector [102,73,74,76]. The energy savings techniques, even outside the slaughtering hours SEC value is determined by Eq. (1). [31]. A study conducted in the United Kingdom (UK) in 1991 deter- E 1 SEC ¼ ðkWh ton Þð1Þ mined an average SEC of 85 kWh ton 1 for large slaughter- RM RM carcass houses that carry out the slaughtering, chilling and some freezing. where E represents the annual electrical energy consumption 1 This value varied from 36 to 154 kWh toncarcass [17]. The use of (kW h), and RM designates the annual amount of raw materials energy is not only in the form of electricity. Other forms of energy processed (ton ). RM were taken into account, and other indicator was used for the The specific energy consumption per volume unit of the cold specific consumption of fuel in the form of heating oil (SECfuel). In rooms [27,6,62,80] that can be calculated using Eq. (2): this case, 85% of the facilities involved in the study presented a E 1 ¼ ð 3ÞðÞ value of 440 kWh toncarcass, with an average value of 322 SECV kWh m 2 1 V total kWh toncarcass. In Italy, the pig slaughterhouses have a total SEC between 280– where V is the total volume of cold rooms. The study of Evans total 380 kWh ton 1 , being 1/3 of electricity and the remaining 2/3 et al. [27] concluded that store volume is the dominant factor carcass of thermal energy [17]. The available information suggests that no related to energy used by cold stores. Moreover, Nunes et al. [79] generalization can be made on single operations using electrical introduced additional specific performance indicators for the evaluation and comparison of operating conditions of food- energy and other energy sources. The study conducted in 1991 in refrigerated facilities. The usage of cold rooms volume (UCR) is the UK revealed that the facilities in Northern Ireland had a total one of the indicators used. It is a physical indicator determined by SEC higher than in Britain. The condition was attributed to the fact Eq. (3). that all facilities of Northern Ireland are licensed under the EC regulation. The higher consumption levels were attributed to RM UCR ¼ ðton m 3Þð3Þ electricity consumption associated with refrigeration require- V RM total ments imposed by the EC laws. The best practice reported by 1 According to authors, this indicator helps to evaluate the usage slaughterhouses was 36 kWh toncarcass (although it should be of cold storage with consequent implications for the energy noted that the temperature used in the cooling systems of meat consumption level. products was not investigated). The best SECfuel (5.86 fi 1 Other indicator de ned by these authors was used to quantify kWh toncarcass) was determined in a slaughterhouse using an the cooling power installed per unit of cold room volume (NPC). anaerobic digestion plant for the production of biogas from solid Therefore, this indicator expresses the quality of the sizing/usage waste of the slaughterhouse, thus only a small amount of extra of cooling systems. It is defined as nominal power of all refrig- fuel was required [17]. eration compressors, Ptotal, per cold rooms volume as shown in Eq. The distribution of the electrical energy consumption in a cattle (4): slaughterhouse in Denmark [17] was 45% for the cooling systems; 10% for the compressed air system; 10% for lighting; 10% for ¼ Ptotal ð 3ÞðÞ NPC kW m 4 machinery; 5% for ventilation and finally 20% others sinks. V total Refrigeration is the main consumer of electricity in slaughter- The SEC indicators are recognized as suitable for assessing the houses, around 55–75% of total electricity consumption [68].In energy savings potential and to help the implementation of best these type of facilities, there are still a large number of electric energy efficiency practices. Among these references, the works motors driving auxiliary equipment, including evaporator and presented by Helgerud and Sandbakk [42] and Sandberg and condenser fans, evaporative condenser pumps, ammonia pumps, Söderström [101] are pointed out, which identified an energy glycol pumps, air handling units and others. Comparatively, the savings potential of about 20% in the food and beverage sector in largest amount of energy used in a cooling system is related to Norway and Sweden, respectively. compressors [68]. Xu and Flapper [131] identified large variations in the SEC in dairy An UNEP report [117] indicates that about 80–85% of the total facilities (milk powder, condensed milk, butter and other dairy pro- energy consumed in slaughterhouses is supplied by thermal ducts) of various countries. These authors reported that the highest energy from fuels combustion in boilers. The thermal energy is indicators could be reduced from 50% to 80%, by changing technol- used to heat water for cleaning and meat processing and drying. ogies, energy management and improving maintenance. The remaining 15–20% of the energy is supplied by electricity, Moreno [69] states that the total (thermal and electrical) SEC which is used by the equipment working during slaughter and (SECtotal) for the production of fresh meat decreased from 315 kWh 1 – 1 deboning, for processing by-products, and for cooling and com- toncarcass in 199 300 kWh toncarcass in 2001, representing a decrease of energy consumption, although it must be taken into pressed air. Typical values of SECtotal are between 333 kWh 1 1 account the species of slaughtered animals. In the case of pro- toncarcass and 1334 kWh toncarcass. cessed products (sausages), the total SEC remained in the order of The MLA [68] reported the "Red Meat Processing Industry fi 767 kW h ton 1. Energy Ef ciency" in 12 slaughterhouses to assess the energy EREN [22] presented the plan of energy assistance for the meat consumption and the potential energy savings in this type of fi facilities. It was concluded that the total average SEC per facility sector. The Spanish ham manufacturing process has a speci c 1 consumption of thermal energy and electricity of 480 kW h ton 1 was 936 kWh toncarcass. The results of that study also showed that fi and 500 kW h ton 1, respectively. from 1998 to 2008 there was an improvement in energy ef ciency Slaughterhouses are the meat production facilities that use of 1.3% and that the energy savings potential still possible to electricity and thermal energy in the manufacturing process. These achieve is comprised between 15% and 60%. They also concluded facilities use energy, mainly electricity, even when there is no that although the thermal energy consumption is around 70% of production. This condition occurs in the meat storage phase inside total consumption, there is a great difference in the consumption the cooling rooms [31]. The specific energy consumed during the of the different slaughterhouses. On the other hand, it was also slaughter of a sheep in a Norwegian slaughterhouse was equal to found that despite the higher heat consumption, the electricity 1 356 kWh toncarcass and the annual average value was 1256 costs represent 65% of the total energy costs (30% of total energy 1 kWh toncarcass. This value reveals the importance of implementing consumption) [68]. J. Nunes et al. / Renewable and Sustainable Energy Reviews 57 (2016) 393–411 399

Table 2 Speciﬁc energy consumption values for the meat sector.

Year Country Meat facilities Product Energy type SEC [kWh/ton] References

1991 United Kingdom Slaughterhouse Carcass (bovine, pig) Electrical 36–154 [54] 1999 Denmark Slaughterhouse Pig animal Total (traditional) 125 [128] Total (med. tech) 50 Total (High-tech) 30 1999 Denmark Slaughterhouse Bovine animal Total (traditional) 300 [128] Total (med. tech) 125 Total (High-tech 70 1999 Canada Slaughterhouse Pig carcass Electrical 70–300 [118] Thermal 138–250 1999 Canada Slaughterhouse Bovine carcass Electrical 70–250 [118] Thermal 56–138 1999 Norway Slaughterhouse Lamb carcass Total 1256 [17] Sheep carcass 2000 Spain Slaughterhouse Carcass Electrical 55–193 [10] 2000 Italy Slaughterhouse Pig carcass Total 280–380 [17] 2001 Spain Slaughterhouse Carcass Electrical 124 [69] Thermal 176 2001 Spain Slaughterhouse Carcass Total 757 [69] 2001 Spain Sausages Sausages Electrical 289 [69] Thermal 477 2002 Ireland Slaughterhouse Pig carcass Electrical 310–740 [31] Thermal 360–600 2002 Ireland Slaughterhouse Beef carcass Electrical 180–220 [31] Thermal 160–220 2002 Finland Sausages Sausages Electrical 180–740 [31] Thermal 160–1000 2002 Finland Sausages Sausages Electrical 750–1300 Torensen (2001) Thermal 450–1240 2003 Australia Sausages Sausages Total 944 [5] 2005 Italy Slaughterhouse Carcass Electrical 94–127 [10] Thermal 186–253 2005 Spain Slaughterhouse Carcass Electrical 197 [62] 2005 Spain Sausages Sausages Electrical 460 [62] 2007 Benchmarking Slaughterhouse Bovine carcass Total 90–1094 IFC (2007) Pig carcass 110–760 2008 Spain Slaughterhouse Bovine carcass Total 500 [45] 2008 Spain Sausages Ham Electrical 500 [22] Thermal 400 2008 Europe Sausages Sausages and ham Electrical 1000–1300 [53] Thermal 450–1000 2008 Spain Sausages Sausages and ham Total 1920 [45] 2008 Australia Sausages Sausages Electrical 271 [68] Thermal 664 2009 Ireland Slaughterhouse Bovine animal Electrical 117 [20] Thermal 132 2009 South Africa Sausages Sausages Total 258–1407 [71] 2010 OECD Slaughterhouse Pig carcass Electrical 139 [118] Thermal 250 2013 Europe Sausages Sausages and ham Electrical 263–438 [86] Thermal 870–1450

In literature, there are few values of indicators of specific process machinery, storage facilities, refrigeration systems, etc... energy consumption and those that are public are presented in with the consequent increase of the energy consumption. reports, usually as result of energy audits. The evolution of SEC values for the meat sector (thermal and electrical energy) can be found in COWI [13], OME [82], UNEP [117], FEI [31], Canales and 5. Cold storage facilities Vidal [10], IFC [47,48] and EREN [22]. Table 2 presents a summary of the specific consumption values of electricity and fuels for the The increase in electricity consumption provided by the high meat sector. use of refrigeration systems in the storage of chilled or frozen It is noted that there are different energy consumption values foods has been a strong concern among researchers. to achieve the same activity. Several factors influence the pro- There are studies that analyze the energy consumption in cold cesses within the food industry, such as environmental conditions, stores, as the studies developed by Poulsen and Singh [88] and species characteristics, characteristics and age of technology. These Singh [105]. These studies evaluated the effects of storage air factors may present small variations among countries and there- temperature, ambient air temperature and of the storage volume fore it is acceptable some divergence of the figures. As shown in on the electrical energy consumption of a cold store. Both authors Table 2, during the last two decades, the average SEC values for concluded that these variables have a strong influence on energy meat industry remained almost constant. Although the technolo- consumption. The research works of Bosma [7], Elleson and gical evolution occurred during this period, the production has Freund [21] and ETSU [23] analyzed the consumption of electricity increased over the years requiring the increase of the number of in different cold stores located in various places in the world and 400 J. Nunes et al. / Renewable and Sustainable Energy Reviews 57 (2016) 393–411 estimated values of SEC for the facilities of these locations shown iii) speed control of the fans. The study recorded a potential for in Table 2. reducing the annual energy consumption by about 9.5%. Faramarzi et al. [30] state that the refrigeration systems of cold In addition, Evans [26] studied three cold storage facilities in the stores account for over 70% of the total energy consumption. UK. In the study, a comparison between the consumption of elec- According to these authors, the performance of the refrigeration tricity and the thermal loads in the three facilities is performed. The equipment in a storage facility can benefit from energy efficiency electrical energy consumption of each facility was compared with solutions, thereby reducing energy consumption and improving the calculated heat load, divided by the coefficient of performance food security providing desirable air temperatures of conservation. (COP) of the refrigeration system. The COP was calculated for each In this sense, they present an energy efficiency study in a cold environment, under stable operating conditions and including the store in California. The installation was subject to the following energy consumption of the compressor, fans, evaporators and interventions: i) defining the area of the loading dock; ii) imple- condensers. The conclusions of the study point out the most sig- mentation of efficient cooling with dehumidification in that area nificant thermal loads are the heat transmission through the walls, to reduce the thermal load inside the pier; iii) construction of new heat dissipation by the fans of evaporators, the heat load o fair refrigeration equipment with the best state of the art available, infiltration through doors and finally the products temperature. In considering advanced control systems; iv) floating condensing relation to the thermal load by heat conduction through the walls, pressure; v) sub-cooling evaporators; vi) installation of high effi- energy savings of 35%, 47% and 67% can be achieved of the wall ciency condensers (evaporative) and motors with variable speed. thickness of 122.5 mm (original thickness) was changed to 203 mm, These measures allow reducing the daily energy consumption by 245 mm, and 330 mm, respectively. For the thermal load of air more than 5%, reducing the peak power absorbed by more than 5% infiltration through the doors, the author adds that protective sys- and increasing the cooling area by 17%. Furthermore, the cooling tems such as curtain with plastic tapes, air curtain and revolving system started operating at higher suction pressures and lower doors, could achieve electrical energy savings around 47–59%. In condensing pressures. The new facility allows reaching daily relation to the actual performance (SECV) of the three cold stores energy savings of 102 kW h. analyzed in that study, the results were 57.3 kW h m3, In relation to cold storage for conservation, Merts and Cleland 71.1 kW h m 3 and 57.9 kW h m3, respectively. [66] state that the storage industry in new Zealand has 460 cold In 2006, the Department for Environment, Food & Rural Affairs stores and has an annual energy consumption of 571 GW h, (UK) funded a project to identify, develop and stimulate the representing 5.2% of the electrical energy used in the industrial development and application of more efficient refrigeration tech- sector of that country. The savings achieved in the food storage set nologies in terms of energy and business practices to use (refrigeration, freezing and mixed) if all stores reached the best throughout the food chain without compromising the safety and reference consumption was estimated at 22%, which is 125 GW h. quality of food [56]. The research program involved three topics: i) The potential energy savings for chilled, mixed and frozen storage assessment of energy consumption; ii) identification of new would be 26%, 23% and 15%, respectively. The same author energy-efficient technologies; iii) Viability studies of promising developed a set of predictive correlations to estimate the elec- technologies. The ten cooling technologies considered priorities by tricity consumption of a cold storage equipment based on the the study were chilling in retail, catering refrigeration, refrigerated main parameters of the facility. The actual energy consumption for transport, cold storage, ready meals cooling, freeze hot potato, that facility was at least 35% higher than expected, suggesting that milk cooling, dairy processing (cheese), potato storage and finally there were significant opportunities to improve energy efficiency. carcass cooling. Swain [106] presents details of these processes. To assess the specific electricity consumption in refrigerated Singh [105] assessed the energy consumption patterns of con- facilities in California, Singh [105] developed a web-based servation cold stores. The study included three objectives: devel- benchmarking tool to compare the use of electricity of a facility oping a survey to collect information; survey the type of energy based on the survey on various facilities. This benchmarking tool conservation technologies; development of a benchmarking web- allowed comparing the energy performance between facilities. tool for receiving data and provide information to operators of the Since the tool was developed using information gathered in a facilities to improve their energy efficiency. The study included 42 survey, it presents some limitations, as for example, not including responses to the survey and concluded that the specific energy the effects of local weather conditions or product input conditions. consumption of the refrigerated facility decreases with increasing In addition, this tool also does not disclosures the energy savings size of it. potential, i.e. the energy efficiency that facilities can achieve be The results obtained in this study are consistent with those implementing best practices. The abovementioned studies are obtained in other studies in New Zealand, Netherlands, United based on the determination and use of the SECV to represent the Kingdom and United States of America, and are shown in Table 3. energy efficiency of a facility. Studies performed in various In the same work, nine energy-saving measures to be applied industrial cold rooms located in Europe, New Zealand and USA in that kind of cold stores are presented. The advanced measures 3 show that SECV may vary greatly, between 19 kW h m and are: i) replacement of the thermal insulation; ii) cooling of roofs or 379 kW h m 3, as shown in Table 2. Duiven and Binard [16] esti- covers; iii) use of efficient lighting; iv) use of evaporative con- mated that the cold stores had a SECV between 30 to densers; v) thermosiphon oil cooling; vi) implementation of an 50 kW h m3. automatic control mechanism of the refrigeration system; vii) use According to Swain [106], the annual consumption of electrical of variable speed drives in the fans of condenser and evaporator; energy in the storage sector in the UK is 900 GWh with expected viii) floating condensing pressure; ix) installation of door sensors. savings of 20–40% with the application of energy efficiency mea- With the implementation of these measures as a whole is achieved sures. The author emphasizes that between 1994 and 2006 there energy consumption improvements ranging from 22% to 74%. was a reduction of 7.5% in the annual energy consumption in the Also with the aim of developing a benchmarking tool web- sector and that the most efficient facilities use about 78% less based, Prakash and Singh [89] constructs a model that predicts the energy compared to less efficient. thermal loads and the use of energy of a cold facility on a monthly In New Zealand, Brown and Lewis [8] studied a set of energy or yearly basis. Fundamentally, the research work was developed efficiency measures to reduce energy consumption in a cold sto- in three steps: determination of the thermal load on the refri- rage facility. The study focused on three areas of opportunity: gerated warehouse (heat conduction through walls, hot air infil- i) condensing pressure; ii) options for control of suction pressure; tration through the doors, workers activity, forklifts activity, J. Nunes et al. / Renewable and Sustainable Energy Reviews 57 (2016) 393–411 401

Table 3 Service/Maintenance/monitoring Benchmarking studies on cold storage facilities.

Country New United The Netherlandsc (West California condenser fans Zealanda Kingdomb Coast) (USA)e USAd evaporator fans

No. of 34 – 56 11 28 other facilities – – – – Storage 4640 4000 60,000 32,000 20,000 compressor volume 93,221 230,000 210,000 171,0 00 (m3) Defrost optimisation SECV (kWh 26–379 34–124 35 19–88 15–132 m 3) Energy saving potential Infiltration/door protection Issues detected a Werner et al. [124]. 0 5 10 15 20 b ETSU [23]. Mean % c Bosma [7]. d Elleson and Freund [21]. Fig. 1. Mean average percentage of issues detected in facilities and its corre- e Singh [105]. sponding energy savings potential (selected from [28]). (For interpretation of the references to color in this figure legend,the reader is referred to the web version of products input, lights, evaporator fans and defrost. Then, the this article). electricity used by cooling systems to remove heat gains in storage fi is determined. Finally, the electricity consumption of all ware- energy savings potential was also quanti ed. The energy savings – house equipment was determined to obtain the total consumption potential ranged from 8 72% of the annual electricity consump- of electrical energy used in the facility. The tool allows the user to tion. Fig. 1 shows the mean average percentage of some of the enter basic data, such as location, size of the facility and operating issues detected in the facilities and its corresponding energy sav- conditions. As result, the tool estimates the energy consumption ings potential. These issues were particularly selected from the work of Evans et al. [28] because they are in line with the results of and SECV reference values. This study shows that: i) it is possible to estimate the electricity the present study, as will be shown in the following section. The consumption in frozen storage facilities using the theoretical bal- results show a large variability in annual energy used in cold stores. SEC ranged from 4 to 250 kW h m3, 6 to 240 kW h m3 ance of thermal loads and the theoretical values of SECV. The V 3 deviation of around 11% for the frozen facility selected for vali- and 23 to 157 kW h m for chilled, frozen and mixed cold stores respectively. Computer programs to estimate the electricity con- dation; ii) the lighting system affects substantially the SECV values. sumption in the facilities were developed in the study [33]. A more efficient lighting improves SECV 20%—using lighting levels 2 2 Hilton [43] presents the energy efficiency measures imple- of 8 W m instead of 10 W m , SECV can be reduced 2.30 kW h m3 (710%); iii) the thermal energy of product load mented in one of the largest refrigerated and frozen facilities in Australia. Although the storage capacity increased from 2009 to can significantly affect the SECV. If all products enter the facility at 2010, the energy efficiency improved from 53.5 kW h m3 to a temperature 20 °C higher than the storage temperature, the SECV 3 can increase about 60%; iv) compared to other thermal loads, the 37.6 kW h m . The main measures implemented were: i) con- load corresponding to the infiltration is generally small. It construction of new buildings and installation of new refrigeration equipment with high energy efficiency standards; ii) gauging the tributes less than 5% of the total amount of SECV. The model fi developed was implemented in FlashTM (Adobe Systems Inc.) in a energy ef ciency of the refrigeration plant; iii) monitoring and computer environment in order to be accessible via online by the controlling the temperature of the cold rooms; iv) improving the facilities managers to simulate their data stores. doors design to reduce infiltration; v) replacement of lighting Evans et al. [27,28] present the results of a research project equipment by LED type lamps; vi) variable-speed drive moder- entitled “Improving Cold Storage Equipment in Europe” (ICE-E) nization for the screw type compressors, evaporators fans and aimed for the creation of tools for reducing the energy con- evaporative condensers; vii) oversizing of evaporative condensers. sumption and the emission of the greenhouse gas effect of the According to Raeisi et al. [95], electricity in refrigeration sys- refrigeration industry through the implementation of more effi- tems can also be saved by inactivating the system for certain cient equipment, taking into account the energy and environ- periods of time or even by reducing the system capacity, through mental standards of the EU. The project developed a number of the thermal energy storage application in the cold rooms. The technical initiatives that included: i) benchmarking; ii) energy author states that this technique allows: i) changing the use of audits of cold stores; iii) information analysis; iv) use and devel- electrical energy of the cooling system to off-peak hours, with the opment of mathematical models; v) educational programs and potential of lower electricity prices; ii) increase the operating project results dissemination and finally vi) financial advice to range of the refrigeration equipment, which can reduce the food identify and implement the initiatives with efficient energy con- losses in case of power failure or equipment malfunction; iii) sumption. The main data collected were the temperature control provide opportunities for transport and sale of food products in point (set point), the floor area and the storage volume, the remote locations or without electricity supply. amount of product and the annual energy consumption. The Data collected on 329 cold stores involved 21 European countries including Portugal. 6. Case study of Portuguese sausages industry The volumes of the chilled, frozen and mixed food stores varied between 57 and 225,000 m3, 100 and 291,280 m3 and 9100 and A case study is presented to exemplify how the key points on 180,000 m3, respectively. energy consumption, energy efficiency measures and energy sav- Twenty-one deficiencies were identified in the energy audits. ings potential in the sausages industry are accessed and evaluated. The correction of these issues may contribute to improving the Before describing the materials and methods used to evaluate the energy efficiency of refrigerated and frozen products facilities. In profile of electrical energy consumption in processing industries of general, 2–12 deficiencies were identified in each facility. The cured sausages and to characterize their cooling systems, the 402 J. Nunes et al. / Renewable and Sustainable Energy Reviews 57 (2016) 393–411 productive process of cured sausages will be described to provide RECEPTION OF RAW MATERIAL an insight of the energy consumption systems and devices. MEAT STORAGE T 6.1. Productive process Chilling Storage Chamber ( = 0 ºC to 2 °C) Freezing Storage Chamber (T= -18 ºC)

The sausages are foods that are prepared with minced and MEAT CUTTING IN A GRINDER MACHINE spiced meat. In general, in Portugal the sausages include three Cutting Room categories of products obtained from pig meat: sausage cured by (T ≤ 12 ºC) scald (there are different types of sausages known in Portugal as MIX AND SALTING IN A MACHINE MIXER morcela, chouriço de sangue, cacholeira, and alheira), dry cured Manufacturing Room sausage (known in Portugal as linguiça, chouriço, painho, salpicão, (T ≤12 ºC) paio, alheira, farinheira, and chouriço mouro) and ham. This wide variety of products results from the different characteristics of the MEAT MATURATION raw material used, of the various types of seasonings and of the Chilling Storage Chamber (T ≤ 6ºC; RH= 85% to 90%; 24 to 48 hours) productive processes. The manufacturing process of cured sausages by scalding and MEAT SEASONING IN A MACHINE MIXER drying, comprises several consecutive steps, which include: (Manufacturing Room T ≤ 12 ºC) reception the raw material, meat conservation in cooling or freezing chambers, thawing meat, meat cutting (pieces less than FILLING T 2 cm), mixing and salting of the meat paste, maturation (24–48 h), (Manufacturing Room ≤ 12 ºC) meat seasoning, stuffing, drying, and final stabilization of the Traditional Smokehouse Artificial Drying products, packaging and shipping [112,3]. The ham is obtained Smoked/Steaming/Drying Streaming/Drying T from whole pigs legs (10–12 kg) through an artificial process (1ºday m = 60 ºC then 30 ºC – 40 ºC) (Tmax.= 26 ºC; RH= 65% to 80%) consisting of several stages that are carried out over a time period (Aprox. 1 to 5 Days) (Aprox. 1 to 7 Days) of about 180 days. The process involves several stages, although FINAL STABILISATION ° the importance of salting, post-salting, drying (to 15 C), steaming Controlled atmosphere Chamber (to 26 °C and RH 60–85%) and final stabilization must be high- (T=12 ºC to 14ºC; RH=50% to 65%) lighted. Each stage takes place in environments of different temperature and relative humidity during a certain period of time, as PACKAGING/EXPEDITION described by Ventanas and Andrés [120], Arnau et al. [3] and Nunes et al. [77]. Fig. 2. Diagram of the productive process of dry cured sausages. After the filling stage, the cured sausages by scalding are placed in a container of hot water at a temperature between 60 °C and 6.2. Material and methods 61 °C for 10 min [119]. Afterwards, it are subjected to a steaming fi and drying process in a controlled atmosphere chamber or in a In order to evaluate the pro le of electrical energy consump- traditional smokehouse using heat and smoke resulting from oak tion in processing industries of cured sausages and to characterize wood burning [119,90]. their cooling systems, audits were performed in 20 sausage fac- – The drying of the cured dry sausage in a traditional smoke- tories located in central region of Portugal. Industries, named CS1 house consists in performing an initial stage of steaming, by slowly CS20, do the same type of activity and have a similar production increasing the temperature to reach 65 °C and then the drying process. fi stage is obtained slowly lowering the temperature to values within The audits were developed in two phases. In the rst phase, fi 30–40 °C. This whole process takes from 24 h to 48 h for the each company was visited for the purpose of lling in an inquiry thinner product and about 3–5 days for the medium size and with a set of pre-defined questions. Specifically, the following about 1 month for thicker products. aspects composed the inquiry: i) identification and location of the The drying process of the dry cured sausages by artificial facility; ii) infrastructure characterization; iii) characterization of methods is the most common method. It is performed in climatic the activities developed; iv) identification and characterization of chambers fitted with air treatment units. Initially, sausages the production process; v) identification and quantification of undergo a steaming stage (26 °C with high relative humidity) for energy types; vi) characterization of the electrical tax and its several hours. Afterwards, the drying stage is accomplished by consumption; vii) disaggregation of consumption by sector and slowly lowering the temperature to values within 14–18 °C, for equipment; viii) characterization of cold rooms; ix) determination time periods varying according to the size of the products. Typi- of the environmental conditions inside and outside of industrial cally, thinner products require between 1 and 3 days, medium size facility and within the cold rooms; x) identification and char- products require 3–7 days and thicker products require in average acterization of refrigeration systems; xi) characteristics of com- 1–2 months [29,3,93]. pressed air systems; xii) practice measures of energy efficiency After the drying process, the dry sausages obtained either by already implemented. traditional smokehouse or by artificial methods are placed in In the second phase, industries were visited again but now controlled climatic chambers for the final stabilization of the with the objective of measuring the relevant parameters for its product at an approximate temperature of 12 °C [69]. characterization. Thus, in this second stage and with the assistance The typical flow process of dry cured sausages is shown in of several measuring equipment, the following parameters were Fig. 2. The process of manufacture of artificial dried cured sausages quantified: i) dimensions of cold rooms; ii) inside and outside have four typical temperature levels in the production process; rooms temperatures and relative humidity; iii) electricity con- meat freezing (18 °C), meat chilling and the paste meat sumption of different equipment, in particular of cooling systems; maturation (0–6 °C), cooling of the manufacturing rooms where iv) nominal compressors power and v) overheating degree of the different operations are performed: meat cut, mixing, filling and refrigerant. Additionally, facilities were inspected in order to check chambers of final stabilization (12–14 °C), steaming and drying for any failures in the surroundings of cold rooms and possible (temperatures below 26 °C). maintenance flaws in refrigeration systems. J. Nunes et al. / Renewable and Sustainable Energy Reviews 57 (2016) 393–411 403

Air temperature and relative humidity were measured using 6.3. Results analysis and discussion digital multifunction equipment, Testo 435-2 with temperature (20 to þ70 °C) and relative humidity (0–100%) probes with The two phases of the survey carried out in the processing accuracy of 70.3 °C and 7 2%RH, respectively. It also was mea- industry of cured sausages provided a wide range of data about sured the outside surface temperature of cold rooms to evaluate these industries, which stands out: the year of facilities con- thermal bridges. A general observation with infrared thermo- struction, amount of raw materials processed annually, number of graphy equipment, Testo 880-4, was performed and then, in more cold rooms; total volume of the rooms, nominal electrical power of sensitive areas, the surface temperature was measured with the compressors, annual electrical consumption, SEC, UCR and NPC Testo 435-2 equipment using a contact temperature probe (60 to indicators. This data is shown in Table 4 and is analyzed in detail in 300 °C) with accuracy of 7 2%. In particular, to evaluate the the following subsections along with other data collected. overheating level of the refrigerants, the temperature and suction 6.3.1. Facilities pressure at the compressor inlet and temperature at the eva- According to the survey, 45% of the sausage factories feature a porator outlet were measured. covered area up to 1000 m2 and 55% between 1000 and 2000 m2. The inner dimensions of cold rooms were determined with an As shown in Table 4, most of the plants have 11–20 years old (50%) infrared rangefinder with a maximum range of 60 m and an and 21–30 years old (30%). The walls of buildings are mostly built accuracy of 70.01 m. in brick masonry. Only 20% of plants have building walls con- Global consumption of industries as well as the partial energy structed with polyurethane panels. The largest constructive solu- consumption in refrigeration systems were measured using digital tion for building covers is the fiber cement sheets (75%). In gen- power analyzers, Elcontrol – Energy Explorer, with a measuring eral, the zone between the cooling chambers ceiling and loft is not range of 15–750 V and 20–1000 A with an accuracy of 0.53–2V ventilated. and 0.04–2 A, respectively. Globally, there are 138 cold rooms, i.e., an average of 7 cold The nominal electric power of the compressor was determined rooms per plant with an average volume of 67 m3. The construc- based on the measured values of the evaporation and condensation characteristics of these cold rooms are divided in 45% of tion temperatures, and the overheating level, by consulting cata- brickwork coated with cork panels or polyurethane panels (55%) fi logs and using speci c calculation software provided by com- with thicknesses between 60 and 80 mm. Some of the cold rooms pressors' manufacturers. To validate this methodology, some of older facilities show clear signs of quality loss of the thermal compressors were randomly selected and the nominal electrical insulation (cracks and thermal bridges), visible through images power was determined through experimental measurement of obtained with the thermographic camera. Furthermore, the door characteristics, namely: voltage, electrical current and power fac- seals of the cold rooms are damaged in its majority, and do not use tor, using a digital multimeter and a clamp meter, Escort ECT-620. any protection device to prevent from thermal entrainment in The comparison between nominal power values obtained by open door position. these two methods allows to conclude that the difference between the calculated and measured values is below 10%, thus validating 6.3.2. Refrigeration systems this approach. The sausages factories use four levels of temperature: freezing In order to evaluate the energy performance of the industries in (18 °C), cooling (0–6 °C), controlled atmosphere (14–26 °C) and this case study, the abovementioned indicators, SEC, UCR and NPC, climate (12 °C). In general, these industries use cooling systems to were used. perform the treatment and conservation of raw materials and The statistical analysis of all data collected was performed processed products and to air conditioning in processing rooms using the SPSS program. In the correlations development, the and corridors. points that do not satisfy the Chauvenet criterion were excluded As required cooling capacities are small, due to the small quantity from the sample [4]. of products to cool and reduced air volume to be conditioned, the type

Table 4 Characterization of sausages plants based on the annual data collected locally and on calculated indicators.

Plant Year of Raw material No. of cold Total volume of Compressors nominal Electricity consump- SEC (kW h UCR NPC 3 1 3 3 constr (tonRM) rooms cold rooms (m ) power (kW) tion (MW h) tonRM ) (tonRM m ) (kW m )

CS1 1998 38.5 4 80.0 7.8 23.7 616 0.48 0.098 CS2 1992 45.3 4 188.0 11.8 38.2 844 0.24 0.063 CS3 1997 104.8 5 172.7 8.6 44.1 421 0.61 0.050 CS4 1992 877.2 12 675.0 44.0 245.0 279 1.30 0.065 CS5 1990 76.5 6 248.6 19.0 68.7 897 0.31 0.076 CS6 2003 450.4 9 679.0 71.6 232.4 516 0.66 0.105 CS7 1998 149.9 4 126.0 17.8 47.4 316 1.19 0.141 CS8 1994 78.5 8 516.0 27.8 144.5 1840 0.15 0.054 CS9 1995 198.0 6 547.0 31.6 66.1 334 0.36 0.058 CS10 1995 315.8 6 321.0 27.2 82.8 262 0.98 0.085 CS11 1998 55.5 3 26.0 9.3 27.3 491 2.14 0.358 CS12 1995 1040.9 9 850.0 94.6 258.0 248 1.22 0.111 CS13 1982 178.3 7 866.0 55.4 194.1 1088 0.21 0.064 CS14 1990 31.1 2 14.0 3.8 12.6 405 2.22 0.271 CS15 1970 178.1 9 764.0 24.5 145.8 818 0.23 0.032 CS16 1993 80.3 4 173.0 13.3 39.5 491 0.46 0.077 CS17 2003 45.5 4 175.0 12.9 25.5 560 0.26 0.074 CS18 1995 68.0 4 122.0 4.2 33.5 494 0.56 0.034 CS19 1995 1003.0 23 2,077.0 126.7 673.3 671 0.48 0.061 CS20 1986 92.3 9 510.0 21.4 148.7 1611 0.18 0.042 404 J. Nunes et al. / Renewable and Sustainable Energy Reviews 57 (2016) 393–411 n

of refrigeration system preferred is the individual small refrigeration o i

t 100 unit (condensing units or refrigeration plants with a compressor or p

m 90 u small refrigeration plant). s

n 80 o

The industries analyzed in this study use the following cooling c 70 y g systems: 31 vapor-compression refrigeration systems with one r 60 e n

e 50 compressor (29%), 29 condensation units (27%), 18 direct cooling (%) e

h 40 circuit plants (17%), 14 air handling units with air-to-air heat pump t f

o 30

(steaming and drying) (13%), 12 air handling mini-units (steaming e

g 20 a and drying) (11%) and ﬁnally 3 refrigeration systems of compact t n 10 e c

type (3%). r

e 0

Globally, the cooling systems contain 128 compressors: 29 P CS4 CS9 CS1 CS3 CS5 CS6 CS7 CS8 CS2 CS18 CS20 CS12 CS13 CS14 CS16 CS19 CS10 CS11 CS15 hermetic type (22.5%), 89 semi-hermetic (69.5%) and 10 of open CS17 type (8%). The nominal electrical power of the industrial refrig- Sausages factories eration compressors stands between 4 kW and 127 kW. Fig. 3. Consumption profile of electrical and fuel in sausages factories. ( : Elec- The operation time of compressors has the following distribu- tricity; : Fuel; : Average electricity; ■: Average fuel). (For interpretation of the tion: 41% have a running time between 21 and 40 years, 49% references to color in this figure legend,the reader is referred to the web version of between 11 and 20 years and only 10% has a running time between this article). 1 and 10 years. From these results, a large number of compressors has a long operation time that may commit their energy perfor- 2% mance. According to Coquinot and Chapon [12], the average life of most equipment used in cold systems production should be 16% between 15 and 20 years (compressors, fans, air treatment units). Their energy efficiency decreases beyond this period. The refrigeration systems use 107 condensers, all cooled by forced air. The most commonly refrigerants used are the R22, R404a and R134a. 82% In addition to the thermal equipment already presented, some industries still have greenhouses that can be heated by electrical energy or using firewood. Throughout the fieldwork it was found that many compressors suffer from a lack of maintenance and had oil leakage, some Fig. 4. Balance of energy consumption in sausages factories ( : Electricity; : fi condensers were dirty and clogged and were installed in poorly Propane; : Diesel). (For interpretation of the references to color in this gure legend,the reader is referred to the web version of this article). ventilated areas or near heat sources, and finally, the cooling systems had a long time of operation (i.e., old equipment). 4,8% 6,9% 6.3.3. Energy consumption The results show that all factories use electrical energy, propane gas or heating oil. Some factories still use firewood to cure the sausages. The electrical energy is used to power the electric 38,7% equipment of which stands out cooling systems, such as compressors, evaporator fans, condensers, electric heaters, air treat- 48,5% ment units, electric saws, grinders, mixers, filling machines, compressed air systems, lighting, pumps and office equipment. Propane or heating oil are burned in heat generators (boilers) for water heating to use in the process (meat cooking) or cleaning operations. Firewood is also used in drying operations. From Table 1 it can be seen that the annual electrical energy 1,1% consumption of sausages factories lies between 13 MW h and Fig. 5. Annual distribution of electricity consumption for typical sausage factory 673 MW h with an average value of 127 MW h. -2066 tonRM and 1037 MWhe-( : Refrigeration system; : Motors; : Lightning; Fig. 3 shows the individual and average electrical and fuels : Compressed air; : Other). (For interpretation of the references to color in this consumption (propane gas or heating oil) of sausages factories of figure legend,the reader is referred to the web version of this article.). this study. The results show that the average annual electrical energy consumption is 82% and the fuel consumption is 18%. Some factory processing 2066 ton of raw materials and consuming sausage factories only use electrical energy because they use 1037 MW h of electrical energy. As shown in Fig. 5, electrical energy electric water heating cylinders (CS6, CS12, CS14 and CS15) as is the main type of energy used by the sausages factories and the shown in Fig. 4. larger consumers are the refrigeration systems (48.5%) and electric In sausages factories, most of the equipment (grinder, mixers motors (38.7%). However for smaller sausage factories with less fi and llers) works only during certain time periods of day or week. activity, the distribution of consumption changes with cooling Refrigeration systems works continuously most of the time. Fig. 4 systems assume even a larger share of the electricity consumption. shows the balance of energy consumption in sausages industries. For a sausage factory annually processing 104.8 ton of raw materials The set of industries consumed during the year, a total 667.4 toe and consuming 4.42 MW h of electrical energy, the distribution of distributed by 548.7 toe of electricity (82%), 108.3 toe of propane (16%) and finally 12.4 toe of heating oil (2%). In average, each electricity consumption is 79.2% for cooling systems and 11.1% for fi industry consumed annualy 33.4 toe. electric motors. These results con rm that cooling systems are the Fig. 5 shows the annual average distribution of electricity con- major electrical energy consumers as referred by Okos et al. [81], sumption by the main energy consumers of a typical sausage Pagan et al. [84] and Ramirez et al. [96]. J. Nunes et al. / Renewable and Sustainable Energy Reviews 57 (2016) 393–411 405

800 200 program for managing the production activity, which consists of n o

i 700 t performing manufacture on certain days of the week and inactive p 600 150 m in the remaining days in order to minimize the use of refrigeration u

s 500 n systems. It has a direct-circuit cooling plant and maintenance plan o

c 400 100

y of refrigeration systems. All these positive factors provide this t (MWh) i 300

c 1 i industry with the lowest SEC value, 262 kWh ton . This result r RM t

200 50 (kW) Power c

e allows to conclude that the quality of the infrastructure materials, l 100 E 0 0 namely of walls, roof and cold rooms are a major factor in achieving these results. Furthermore, the energy use of thermal CS1 CS2 CS3 CS4 CS5 CS6 CS8 CS9 CS7 CS19 CS20 CS10 CS11 CS12 CS13 CS14 CS15 CS16 CS17 CS18 energy for the cure of sausages, and the use of a centralized Sausages factories refrigeration equipment, with a good energy management and ﬁ Fig. 6. Relationship between contracted power ( ), nominal power of compressors maintenance contribute to an improved energy ef ciency. ( ) and electricity consumption ( ). (For interpretation of the references to color The sausage factory that has the highest SEC value is CS8. The in this ﬁgure legend,the reader is referred to the web version of this article.). infrastructure of this sausage factory was built in 1994 with masonry and with a metal cover plate. The cold rooms are made of polyurethane panels with 60 mm thick. It also has an unvented °

) 2000 loft, where temperature reach values higher than 50 C. Further-

RM 1500 more, it has a compact cooling equipment installed inside the facility, resulting in heat dissipation of the condenser inside the 1000 facility as result of a faulty location of the equipment. To maintain 500 the interior environment of the climatic facilities, particularly of

SEC (kWh/ton 0 the processing room and hallways, the temperatures in these spaces are set to 8–10 °C (below the standard temperature of CS1 CS9 CS2 CS3 CS4 CS5 CS6 CS7 CS8 ° CS15 CS16 CS18 CS19 CS10 CS11 CS14 CS17 CS20 CS12 CS13 12 C). This industry also works below its nominal capacity as shown in Table 4, with the lowest value of UCR, which is Fig. 7. SEC values of sausages factories ( : SEC of sausages factories; ( : average 3 SEC; : reference SEC). (For interpretation of the references to color in this figure 0.15 tonRM m . On the other hand, it is also one of the industries legend,the reader is referred to the web version of this article). that have the lowest NPC, 0.054 kW m 3. Improper installation of refrigeration equipment and the use of low evaporation tem- From the analysis of the industry electrical taxes, the hourly peratures, combined with a large thermal load inside the facilities, tariffs are the most used with contracted power between 19 kW force the cooling systems to present a high consumption of elec- and 190 kW (average of 55.3 kW). trical energy. All these factors contribute to this industry present 1 It was still found that 8.7% of industries pay reactive energy due the largest SEC, 1840 kWh tonRM, far above the average of 660 1 to a power factor less than 0.92. This cost can easily be avoided by kWh tonRM. installing a capacitors battery. Another example of an industry with a SEC value above average Fig. 6 shows the graph relating the contracted power, the is CS5. The infrastructure of this sausage factory was built in 1992 nominal electrical power of compressors and also the electrical in double masonry wall and a marseille tile roof, it was a well energy consumption for the industries in study. As shown in Fig. 6, ventilated loft and a concrete slab separating the loft from the there is a very narrow relationship between the two types of working area. Despite showing infrastructure in good conditions of power and with the electrical energy consumption. This relation- conservation and possessing excellent materials for the cold rooms ship allows to conclude that the electrical power of refrigeration (polyurethane panels with 80 mm thick), the refrigeration systems compressors takes a leading role both in the choice of contracted have a high operation time and without planned maintenance in power and in the electricity consumption. such way that the condensers of the refrigeration systems were clogged. These factors affect the energy efficiency of refrigeration 6.3.4. Specific indicators systems and, in particular, the energy performance of the facility. The specific consumption of total energy (electrical and heat) of Consequently, this plant presents a SEC value well above average, 1 1 sausages factories of this study lies between 248 kWh tonRM and 898 kWh tonRM. From this example, it is concluded that the 1 1 2080 kWh tonRM, with an average value of 660 kWh tonRM,as operation time of refrigeration equipments and it maintenance are shown in Fig. 7. These results are higher than the values (110–760 also two key factors for the energy performance of refrigeration 1 kWh tonRM) presented by benchmarking [48], but within the systems. – 1 range reported by Toresen et al. [114],600 1040 kWh tonRM, and The set of factors described above are some examples that 1 López et al. [62], 460 kWh tonRM. contribute to the result of the energy performance of sausages As can be seen in Fig. 7, there is a wide range of SEC value industries. These results allow to conclude that there are potential among the different industries. During the fieldwork, the sausages savings of electrical energy that can be achieved if the several factories that present the highest and lowest SEC values were inefficiencies detected were corrected. Assuming that all indus- analyzed in detail. tries with a higher value than the average SEC (see Fig. 7) imple- By comparing the SEC values of the sausages factories, it is ment practice measures to improve the energy efficiency in order possible ascertaining the most efficient and what are the main to achieve this average value, it should be expected an overall factors contributing to the differences in energy efficiency potential of 24% of reduction consumption of electrical energy. In between themselves. this case, the procedure presupposes sharing the best practices of The sausage factory that has the lowest value of SEC, CS10, was energy use in this sector. This savings translates into an annual constructed in 1995, and has the surroundings and cold rooms value of 337 MWh. In relation to the reference value [104], where constructed in polyurethane panel with a thickness of 120 mm and the average value of the electrical energy consumption for the 1 the cover with 40 mm polyurethane panels. In addition, it also has sausages processing is 465 kWh tonRM (see Fig. 7), the value of a loft of identical height to the work zone (4 m) and is well ven- energy savings obtained is 37%, corresponding to an annual value tilated. This industry also uses thermal energy from a boiler in air of 1813 MWh. It should be noted that the Spanish industries treatment units used in drying the cured sausages. It even has a incorporate in the production process other forms of energy 406 J. Nunes et al. / Renewable and Sustainable Energy Reviews 57 (2016) 393–411

2,50 0,400 ) 3 2,00 0,300 /m 0,200 RM 1,50 0,100 1,00

NPC (kW/m3) 0,000 0,50 UCR (ton CS5 CS7 CS8 CS9 CS1 CS2 CS4 CS6 0,00 CS3 CS12 CS10 CS11 CS13 CS14 CS16 CS17 CS19 CS20 CS15 CS18 Sausages factories CS8 CS1 CS3 CS4 CS5 CS7 CS9 CS2 CS6 CS20 CS18 CS10 CS13 CS14 CS15 CS19 CS12 CS17 CS16 CS11 Sausages factories Fig. 10. NPC values of sausages factories. (For interpretation of the references to color in this ﬁgure legend,the reader is referred to the web version of this article). Fig. 8. UCR values of sausages factories. (For interpretation of the references to ﬁ color in this gure legend,the reader is referred to the web version of this article). 6.3.5. Refrigeration system modeling Table 5 shows the mathematical equations that relate the various variables and other indicators obtained during the statistical 2000 analysis of results. 1800 Fig. 11 shows the graphical representation of experimental 1600 values of sausages industries and the linear regression obtained

] by the model and the upper and lower limits that correspond -1 1400 y = 382,84x-0,674

RM ﬁ 1200 R² = 0,84 to a con dence interval of 95% for each one of the relationships. Fig. 11(a) shows the relation between volume of cold rooms (m3) 1000 and annual processed raw material (tonRM); Fig. 11(b) relates 800 nominal power of compressors (kW) with raw material; Fig. 11(c)

SEC [kWh ton 600 relates the annual electrical energy consumption (MWh) versus 400 raw material; Fig. 11(d) shows the relation between electrical power of compressors and volume of cold rooms; Fig. 11(e) relates 200 the electrical energy consumption and the volume of cold rooms 0 and finally Fig. 11(f) relates the electrical energy consumption with 0,00 0,50 1,00 1,50 2,00 2,50 the electrical power of the compressors. UCR [ton m-3 year-1] RM As shown in Fig. 11, the data points are concentrated within the Fig. 9. Correlation between SEC and UCR for sausages factories. (For interpretation range of 95% confidence. The high values of the coefficients of of the references to color in this figure legend,the reader is referred to the web determination R2 indicate a good relationship between the version of this article). experimental points and the model equations. Owners or managers of sausages manufacturing companies can use these corre- besides electricity [104], contrary to Portugal where the energy lations [76] to assess the energy performance of his company. It sources rely primarily on electricity and some biomass to perform must be pointed out that the predictions are solely indicative and the drying and smoking operations. This feature explains the large allow the user to be aware of the positioning of his company in difference in electrical consumption observed between the relation to the national average in terms of energy efficiency. An industries of the two countries. in-situ energy audit is required to provide a deeply and detailed Fig. 8 shows the UCR results. The UCR values show that not all analysis. Nevertheless, the results may help the user on the deci- sausages factories have a proper volume utilization of cold rooms sion making of practice measures for the improvement of the in a similar manner. This result shows that the total installed energy efficiency. The next section provides an overview of cost- capacity of sausages factories is not used (low UCR value). Con- effective best practices measures that can be considered to sequently, sausages factories using below their nominal cold sto- improve the energy sustainable development of sausages industry. rage capacity show higher SEC values, meaning a decrease in their energy efficiency. For example, CS4, CS7, CS10, CS11, CS12 and CS14 have higher SEC values than CS2, CS8, CS13, CS15, CS17 and CS20. 7. Best practice measures and technologies From this analysis it is concluded that for the activity of sausages factories, the partial load contributes to reduce the energy The following key points on the energy sustainable develop- fi 3 ef ciency. Globally, the average UCR value is 0.712 tonRM m .A ment of sausages industry are based on failures and inefficiencies strong inverse relationship is found between UCR and SEC, i.e., the detected in the fieldwork. Some of the best practices measures fl underutilization of cold room capacity is re ected on the increase proposed are in line with the findings of related studies [27,28]. of energy consumption. As UCR increases, i.e., the average usage of These energy efficient practice measures can offer savings on the cold room per year achieves its nominal value, the SEC value several levels such as reducing the energy and maintenance costs, decreases, as shown in Fig. 9. For this industry, and assuming the improving facilities security, increasing productivity and compe- same criteria as for the correlations development, a power rela- titiveness and improving the environmental impact of a company: 2 ¼ tionship with R 0.84 given by Eq. (4) was found. Infrastructures: The surroundings of an infrastructure including : fi SEC ¼ 382:84 UCR 0 674 ð4Þ coverage are most relevant key-points in terms of energy ef - ciency. Surroundings that facilitate heat input contribute to Fig. 10 shows the NPC results. It can be seen that there is a increase the electricity consumption of refrigeration systems. certain uniformity of results for this indicator, from which it can be Some audits disclosure companies which infrastructures were concluded that the sizing or the cooling capacity used for activity built with (1) poor thermal resistance materials provided by of sausages factories presents a certain standardization. Excep- reduced wall thickness and/or poor quality of the insulating tionally, CS11 and CS14 have much higher values than the other materials; (2) high thermal conductive roofing materials; sausages factories. However, these two sausages factories also (3) closed recesses, among others. However, as shown by Evans have the highest values UCR and the results are in agreement. et al. [28], although improvements associated with building Globally, the average NPC value is 0.1 kW m3. infrastructure and new layout designs have a high energy savings J. Nunes et al. / Renewable and Sustainable Energy Reviews 57 (2016) 393–411 407

1200

) 140 3 1100 m ( 1000 120 s 900 n

o 800 100 o r 700 d

l 80

o 600 c 500 f 60 o 400 e 300 40 m u

l 200

o 20

v 100 0 Compressors power (kW) 0 0 50 100 150 200 250 0 500 1000 1500 Raw material (ton) Raw material (ton)

400 70 n

o 350 60 i t p 300 50 m u

s 250

n 40 o

c 200

l 30 a (MWh) 150 c i r

t 20

c 100 e l 10

E 50 Compressors power (kW) 0 0 0 250 500 750 1000 1250 0 150 300 450 600 750 900 Raw material (ton) Volume of cold rooms (m3)

300 400 ) h 350 W 250 M

( 300

n 200 o

i 250 t p

m 150 200 u s n

o 150

c 100

y 100 g r

e 50

n 50 E Energy consumption (MWh) 0 0 0 200 400 600 800 1000 0 20406080100 Volume of cold rooms (m3) Compressors power (kW)

Fig. 11. Correlations for characterization of the refrigeration systems of sausages industries. (For interpretation of the references to color in this figure legend,the reader is referred to the web version of this article). potential (around 15%), the average payback is so long (18 years) fluorescent or LED lighting allows substantial electricity savings that cannot be seen as cost-effective measures. (70–80%) in lighting with a payback around 4 years [28]. Cold rooms: The cold rooms walls shall be constructed with The doors must be well insulated with seals in good conditions. good insulating materials such as polyurethane panels with proper The replacement of rubber seals in cold room doors as well as its thickness for the environmental conditions where they are loca- periodic verification contribute to the reduction of energy costs. ted. In audits, several cold rooms constructed with polyurethane The use of air or plastic strip curtains are proper to avoid the panels with reduced thickness (60 mm) were found in locations output of cold air inside the cold rooms, eliminating the need for with high outside temperature. It is recommended that the cold constant cold replacement, and consequently reducing power rooms built in polyurethane panels have thickness of 100 mm and consumption. The energy savings potential for this issue is around 120 mm, respectively for chilled and frozen food products. 6% and has an average payback of 2 years. Regular practices per- As matter of energy savings, the doors of cold rooms should formed by cold room operators to check its operation (identifica- remain closed as long as possible. This is a very simple and cost- tion of damaged doors and its protection as strip curtains, air effective practice that only requires information and awareness of curtains, roll-up; frost formation on evaporators coil surface; mal- cold room operators to perform regular checks. The payback is functioning of evaporator fans) may provide energy savings ran- immediate. ging between 5% and 12% and reduce the payback [28]. Lights of cold rooms should be off when are not occupied. Other very simple practice is related with the correct dis- Another option is to use electronic controllers for lighting of all tribution of products within the cold room (correct stowage) to plant sections. Replacement of incandescent lighting with compact promote the uniform cooling of products. The awareness of this 408 J. Nunes et al. / Renewable and Sustainable Energy Reviews 57 (2016) 393–411

Table 5 Correlations for characterization of the refrigeration systems of sausages industries (Correlations signiﬁcant at 0.01 level).

Cold rooms volume Vtotal Compressors power Ptotal (kW) Electricity consumption E (m3) (MW h year1)

1 Raw materials RM (ton year ) Formula Vtotal ¼ 4.3795 RM87.42 Ptotal ¼ 0.0702 RMþ11.492 E ¼ 0.2376 RMþ24.18 R2 0.82 0.68 0.92 Standard deviation 130.53 14.20 23.24 Spearman correlation 0.83 0.86 0.93 coefﬁcient n 12 19 15 3 Cold rooms volume V (m ) Formula Ptotal ¼ 0.0572 Vtotalþ3.4135 E ¼ 0.3243 Vtotal6.8444 R2 0.93 0.96 Standard deviation 4.06 17.34 Spearman correlation 0.92 0.91 coefﬁcient n 15 16

Compressors power P (kW) Formula E ¼ 2.9045 Ptotalþ11.323 R2 0.90 Standard deviation 25.68 Spearman correlation 0.92 coefficient n 17 condition by cold room operators increases food safety and has air. The application of VSD controllers achieves energy savings up influence on the refrigeration system operation. Product place- to 20% with a payback of 3 years [1,15]. ment close the cold air inlets should be avoided not to block the air Steam generators: A regular check of the operating parameters flow at the outlet of the evaporator. As determined by the rela- of this equipment is critical to its performance, increasing its tionship between UCR and SEC, the use of partially loaded cold lifetime and reducing fuel consumption. It is recommend to per- rooms promotes energy waste. However, exceeding the maximum form regular inspections for boiler combustion regulation or storage capacity for which the cold room and the refrigeration cleaning of heating surfaces that can translate into energy savings. system were designed is also not recommended. The fuel feeding system must ensure it reaches the burner under Refrigeration systems: To improve the energy efficiency in appropriate conditions, either in quantity or in temperature and refrigeration systems, the following actions should be at least pressure conditions for good atomization and mixing with air implemented: (liquid and gaseous fuels). –Conducts must be well insulated to prevent high overheating, Features of electricity consumption: Given the current energy which reduces the efficiency of the refrigeration cycle. Energy prices, is desirable to perform a systematic analysis of energy bills. savings between 1% and 1.5% can be achieved, although the pay- This analysis should start describing the causes for smaller or back time can be long. larger power consumption, and detect irregularities in the power –Replace the refrigeration systems older than 10 years, mainly factor causing reactive power consumption. the old compressor, by new ones with high efficiency motors. The Renewable energy (solar thermal energy, biomass, solar pho- energy savings can go up to 30–40%, but the payback is the longest tovoltaic): Whenever possible, the use of renewable energy may [28]. be implemented. Although the payback periods may be long for –Install condensers in shaded ventilated areas and with proper same applications, the daily energy savings can be substantial. maintenance (cleaning). It is possible to save 2–3% of energy if the The above list provide the key-points for the energy sustainable condensing temperature is reduced 1 °C. Using well-sized or development of this type of industry, and for sure is applicable to oversized condensers promotes the reduction of condensing other manufacturing sectors. Several practice measures are very temperature and provides a slight sub-cooling of the refrigerant cost-effective and provide significant energy savings. Most of them resulting in an energy savings of 1–4%. These actions have a 2- are related with regular checks included in maintenance, mon- years payback. itoring and service tasks. The cost associated is the awareness and/ –Regular evaporators defrost. The defrost methods allow or training of company operators. Additionally, there are some obtaining savings from 5% to 10%, although it payback can go from practice measures with paybacks less than 4 years (which is a less than a year to several years. Recovering the heat released in suitable time for companies) that may provide interesting energy the condensation operation for heating water, which may serve to savings. For last, significant energy savings can be accomplished perform the defrost evaporators or heating spaces, is a measure with infrastructure retrofitting, equipment substitution, new that can achieve a 12% energy savings. designs and implementing renewable energy systems, although –Implement an energy management plan, as this measure the payback between one and two decades. contributes to achieve an energy savings of 13%. –The qualification and training of maintenance professionals (knowledge, certifications, etc.) must not be neglected because 8. Conclusions expensive equipment as the refrigeration ones require all the attention to work efficiently. This paper provides a review of the research related to energy Compressed air: This the second form of energy most used in consumption, energy efficiency measures and energy indicators in the manufacturing industry. Although some air leaks are unavoidable, food industry. The analysis gathers data from the general industrial detecting and repairing air leaks must be done regularity. A key sector to the specific sector of meat processing. The review is com- measure is the selection of the compressor in terms of flow rate plemented with a case study performed in 20 sausages factories sector and air pressure. If possible, it should have a soft starter, variable located in the center region of Portugal. The analysis considers infra- speed drive (VSD), not to work without load, and work with dry structures, manufacturing processes, refrigeration systems, energy J. Nunes et al. / Renewable and Sustainable Energy Reviews 57 (2016) 393–411 409 consumption, and evaluation of specific indicators. Mathematical can offer savings on several levels such as reducing the energy and correlations were developed that serve to characterize the energy maintenance costs, improving facilities security, increasing pro- performance of refrigeration systems and particularly these industries. ductivity and competitiveness and improving the environmental The sausages factories of this study, and generally in Portugal, impact of a company: are small industries that process annually an average value The most cost-effective measures that can yield energy savings 255 tonnes of raw material, and have a covered area around around 15% are related with regular checks of maintenance and 2000 m2. They are usually built of masonry and have fibrocement monitoring services. The awareness and/or training of company covering. The cold rooms are constructed of polyurethane panels operators is fundamental. Then, are practice measures can be with a 60–80 mm thickness and have an average volume of 67 m3. applied, with higher energy savings but with longer payback. Each The main products are dry cured sausages. These products involve conservation operations of meat, cutting, mixing, salting, plant requires a detailed analysis to achieve the largest energy maturing, filling, steaming and drying. These last two operations savings with the less investment. are usually performed in flues or controlled atmosphere rooms. The results here presented can help and advice for the energy The refrigeration systems are of classic type for conservation sustainable development of meat industries, since same ineffi- operations and air-handling systems of air-air heat pump type are ciencies may exist in other companies in other countries despite used for drying. the differences that may exist both on processing methods or cold The main type of energy used in this industry is electricity storage conditions. (82%) and fuel in a smaller scale (18%). The major electrical energy consumers are the refrigeration systems (48.5–79.2% of total electricity consumption). The specific total energy consumption (electricity and heat) is References 1 1 between 248 kWh tonRM and 2080 kWh tonRM. These results are higher than benchmarking considered as reference. Thus, the [1] Abdelaziz EA, Saidur R, Mekhilef S. A review on energy saving strategies in sausages factories in this study consume more energy. 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