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It is increasing crucial to improve the sustainable use rate of energy and contribute to carbon neutrality and environmental footprints reduction. This work features cutting-edge selected extended papers and developments that were presented at the 25th Conference on Process Integration, Modelling and Optimization for Energy Saving and Pollution Reduction, held on 5–8 September 2022 in Bol, Croatia. More than 400 papers were accepted and presented at this conference. Out of these papers, the 45 contributions in this Virtual Special Issue represent a selection of the most cutting-edge developments in the topic of the Sustainable Use of Energy Contributes to Carbon Emissions Neutrality and Environmental footprint reduction. This paper provides a review of these contributions and above, and groups them into four research themes: (1) Energy Conversion, Storage, Recovery and Efficiency Improvement, (2) Energy Management, Planning and Optimization, (3) Energy, Environment and Economy, and (4) Heat Transfer, Heat Pumps and Heat Convection. [ABSTRACT FROM AUTHOR]

This paper investigates the existence of environmental Kuznets curve in Croatia for the period of 1992Q1-2011Q1. To fulfil to goals of the paper, Autoregressive Distributed Lag (ARDL) and VECM method has been applied. Results show the existence of inverted U-shape relation between CO 2 emissions and economic growth in long run that is the validity of EKC. Granger causality based on VECM approach shows bi-directional causality between CO 2 emissions and economic growth in short run and uni-directional causality from economic growth to CO 2 emissions in long run. DOLS and FMOLS results confirm the robustness of long run results. Variance decomposition and Impulse response also show similar results. Beauty of the paper is the consistency of results from different techniques. [ABSTRACT FROM AUTHOR]

In the light of European energy-climate package and its measures for increasing security of supply, decreasing the impact on environment and stimulating sustainability, Croatia as a new EU (European Union) member state needs to reconsider and develop new energy policy towards energy efficiency and renewable energy sources. Croatian long-term energy demand and its effect on the future national GHG (greenhouse gas) emissions are analysed in this paper. For that purpose the NeD model was constructed (National energy demand model). The model is comprised out of six modules, each representing one sector: industry, transport, households, services, agriculture and construction. The model is based on bottom up approach. The analysis has shown that energy policy measures, identified through this paper, can potentially achieve energy savings up to 157 PJ in the year 2050, which presents a 40% decrease to referent (frozen efficiency) scenario. Results obtained in this paper were also compared to the Croatian National Energy Strategy for the years 2020 and 2030. It was shown that if already implemented policies were properly taken into account the actual final energy demand for the year 2030 would be 43% lower than projected by the Croatian National Energy Strategy. [ABSTRACT FROM AUTHOR]

Abstract: The transport sector in Croatia represents one of the largest consumers of energy today, with a share of almost one third of the country's final energy demand. Considering this fact, it is very challenging to assess future trends influencing that demand. In this paper, long-term energy demand predictions for the Croatian transport sector are presented. Special emphasis is given to different influencing mechanisms, both legal and financial. The energy demand predictions presented in this paper are based on an end-use simulation model developed and tested with Croatia as a case study. The model incorporates the detailed modal structure of the Croatian transport sector, including road, rail, air, public and water transport modes. Four long-term energy demand scenarios were analysed till the year 2050; frozen efficiency, implementation of EU legislation, electrification and modal split. Based on that analysis, significant savings can be achieved through energy efficiency improvements, electrification of personal vehicles fleet as well as gradual modal split. Comparing the frozen efficiency scenario and electrification scenario for the year 2050, it can be concluded that energy consumption, with the heavy electrification of personal vehicles fleet, can be cut by half. [Copyright &y& Elsevier]

Abstract: The Energy Strategy of the Republic of Croatia was adopted by the Croatian Parliament in 2009 for the period until 2020 in order to harmonize national energy goals with goals and time framework of strategic documents of the European Union. The adoption of the Energy Strategy Implementation Program with associated measures is still in process. The goal of the Strategy was to create sustainable energy system that will make a balanced contribution to the security of energy supply, competitiveness and environmental protection in Croatia. In this paper an overview of the energy production, final energy consumption and planned development of energy infrastructure is given. The intention of the paper was to research and stress out the abilities and opportunities of Croatian energy system and to give recommendations for Energy Strategy implementation and practical realization of planned energy infrastructure projects for improvement of security of energy supply and competitiveness of energy system of the Republic of Croatia. [Copyright &y& Elsevier]

The transportation sector is one of the major energy consumers in most energy systems and a large portion of the energy demand is linked to road transport and personal vehicles. It accounted for 32.8% of the final energy consumption of Croatia in 2011 making it the second most energy demanding sector. Because of their higher efficiency, a modal switch from conventional ICE (internal combustion engines) to EVs(electric vehicles ) has the potential to greatly reduce the overall energy demand of the transport sector. Our previous work has shown that a transition to EVs in a combination with a modal split from air and road to rail transport can reduce the energy consumption in Croatia by 99 PJ, which is approximately 59%, by the year 2050 when compared to the business as usual scenario. The goal of this paper is to model the hourly distribution of the energy consumption of EVs and use the calculated load curves to test their impact on the Croatian energy system. The hourly demand for the transport sector has been calculated using the agent-based modelling tool MATSim on a simplified geographic layout. The impact EVs have on the energy system has been modelled using EnergyPLAN. [ABSTRACT FROM AUTHOR]

Abstract: Today, tourism represents one of the backbones of Croatian economy and one of the main factors of its growth. Combined with catering trade sector, tourism represents a significant energy consumer that has the tendencies of future growth. Since services sector, which tourism–catering trade sector is a part of, is not yet well described regarding future energy balances it would be very interesting to see how could possible future growth in tourism influence energy consumption of the services sector in Croatia. Through this paper long term energy demand projections of tourism–catering trade sector were studied with special emphasis on future growth of tourism in Croatia as well as different mechanisms that might lead to certain energy savings. Bottom-up approach was chosen as the most suitable one since it allows better quantification of different measures, technological or legal, that would influence future energy demand. Downside of this approach is extensive input data that is required to analyse and model future energy demand which is roughly divided into heating/cooling section and all other consumption. Results show that additional energy savings in the tourism–catering trade sector are possible if careful and rational demand side planning is in place. [Copyright &y& Elsevier]

Abstract: Many of the modern practices in waste management at the same time represent means of reduction of greenhouse gas (GHG) emissions. The main focus in this paper is given to the measures for recovering energy from municipal solid waste (MSW): Utilization of landfill gas for electricity production, Utilization of refuse derived fuel (RDF) in cement industry, Thermal treatment (Incineration) of MSW, Mechanical-biological treatment, and to one measure without energy recovery – Landfill gas flaring, for all of which it was found that could generate substantial GHG emission savings. The economic side of the implementation of these measures, considering the GHG emission reduction, is analysed in order to determine the priority between them. With respect to the cost-effectiveness, marginal costs (expressed as € per ton of reduced or avoided CO2eq) are calculated for all the measures. It was determined that around 1 million tons of CO2 can be avoided in 2020, which is 2.7% of projected GHG emissions in Croatia, while the energy that could be recovered from waste is 8.3 PJ in 2020, which represents about 3% of the total final energy consumption in 2008. The measures Utilization of landfill gas for electricity production and Landfill gas flaring showed the greatest economic benefit. [Copyright &y& Elsevier]

Abstract: A dominant share of Croatian cogeneration capacity and future cogeneration potential belongs to district heating systems currently operating in almost all bigger mainland and coastal towns. Since public cogeneration and public heating plants cover only 10% of heating requirements of households and services sectors it is reasonable to assume that in future energy supply district heating could take a bigger relative and absolute share even in conditions of reduced heat demand imposed by implementation of Energy Performance of Buildings Directive. However, development of future district heating projects will inevitably depend on capability to bridge financing barriers usually manifesting in large investment costs and long pay-back time. The public involvement will be necessary either at state or/and at municipal level since private companies are focused on short-term profitability. In this paper comparison of various concepts of district and individual buildings heating has been performed with respect to efficiency and environmental indicators. Taking a midsize town as an example profitability of operation of both biomass and of natural gas fired district heating cogeneration plants have been analysed. Calculated results indicate levels of financial support required for sustainability of district heating projects in specific conditions of Croatian energy market. [Copyright &y& Elsevier]

Abstract: This paper provides methodology for regional analysis of biomass energy potential and for assessing the cost of the biomass at the power plant (PP) location considering transport distance, transport costs and size of the power plants. Also, methodology for determination of an upper-level price of the biomass which energy plant can pay to the external suppliers has been proposed. The methodology was applied on the case of Croatia and energy potential of biomass in the Croatian counties was calculated, using different methodologies, for wheat straw, corn stover and forestry residues, types of biomass considered economically viable at the moment. Results indicate that the average energy potential of wheat straw is 8.5PJ, corn stover 7.2PJ and forestry residues 5.9PJ. [Copyright &y& Elsevier]

Abstract: Cities all around the world are faced with a rapid increase of urban population, and their crucial sustainable development issue becomes energy management. Moreover, the national energy management sector is slowly passing from government surveillance to the responsibility of local municipalities. The energy efficiency management in cities helps local governments to focus on important energy projects that have strong environmental aspects and financial feasibility. This paper analyzes the public lighting energy management in the Croatian city of Rijeka in order to determine the connection of the energy market liberalization and sustainable development in urban areas. Research results indicate a significant connection between investments in energy management of public lighting and its influence on lower emissions of carbon dioxide (CO2). [Copyright &y& Elsevier]

Abstract: In the Republic of Croatia there are some medium temperature geothermal sources by means of which it is possible to produce electricity. However, only recently concrete initiatives for the construction of geothermal power plants have been started. Consequently, the paper provides proposals of the possible cycles for the Republic of Croatia. On the example of the most prospective geothermal source in the Republic of Croatia detailed analysis for the proposed energy conversion cycles is performed: for Organic Rankine Cycle (ORC) and Kalina cycle. On the basis of analysis results both the most suitable cycle for selected and for other geothermal sources in the Republic of Croatia are proposed. It is ORC which in case of the most prospective geothermal source in the Republic of Croatia has better both the thermal efficiency (the First Law efficiency) and the exergetic efficiency (the Second Law efficiency): 14.1% vs. 10.6% and 52% vs. 44%. The ORC gives net power of 5270kW with mass flow rate 80.13kg/s, while the Kalina cycle gives net power of 3949kW with mass flow rate 35.717kg/s. [Copyright &y& Elsevier]

An analytic approach to determine appropriate regulatory strategies for the energy sector is proposed in this paper. A basic model of the regulatory system in the energy sector is defined, and the regulatory mechanism functions in this context are outlined. The basic problem of unknown factors (i.e., system entropy) is highlighted. An original algorithm developed to analyze regulatory background context and regulatory mechanism functions is discussed. A useful method for defining existing level of energy activities regulation is also presented using the Croatian regulatory framework as an example. [Copyright &y& Elsevier]

Following a strategic orientation towards sustainable development, the Government of the Republic of Croatia has changed its energy legislation and has put forward a framework for the systematic development and increased use of renewable energy sources and cogeneration. This paper focuses on changes in the regulatory context relevant to the cogeneration sector and also analyses the impact of energy market transition on cogeneration viability in municipal district heating, industry, services and the residential sector. Particular attention has been paid to the expected changes of heat, electricity and gas prices. We present a simple model for quantitative prediction of the cogeneration system profitability at different power levels under given national circumstances. Our findings support a need for a strong institutional support for initial penetration of the micro-cogeneration technologies into the Croatian energy system. [Copyright &y& Elsevier]

Abstract: The effective and rational energy generation and supply is one of the main presumptions of sustainable development. Combined heat and power production, or co-generation, has clear environmental advantages by increasing energy efficiency and decreasing carbon emissions. However, higher investment cost and more complicated design and maintenance sometimes-present disadvantages from the economical viability point of view. As in the case of most of economies in transition in Central and Eastern Europe, Croatia has a strong but not very efficient co-generation sector, delivering 12% of the final energy consumption. District heating systems in the country''s capital Zagreb and in city of Osijek represent the large share of the overall co-generation capacity. Besides district heating, co-generation in industry sector is also relatively well developed. The paper presents an attempt to assess the sustainability of Croatian co-generation sector future development. The sustainability assessment requires multi-criteria assessment of specific scenarios to be taken into consideration. In this respect three scenarios of Croatian co-generation sector future development are taken into consideration and for each of them environmental, social and economic sustainability indicators are defined and calculated. The assessment of complex relationships between environmental, social and economic aspects of the system is based on the multi-criteria decision-making procedure. The sustainability assessment is based on the General Sustainability Index rating for different cases reflecting different criteria and their priority. The method of sustainability assessment is applied to the Croatian co-generation sector contributing to the evaluation of different strategies and definition of a foundation for policy related to the sustainable future cogeneration sector development. [Copyright &y& Elsevier]