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This paper focuses on the possible impact of the thermal soil regime on the occurrence of forest fires in the Zaječar administrative district in Eastern Serbia. The study uses data on soil temperature from the Republic Hydrometeorological Service of the Republic of Serbia and the ERA5-Land gridded reanalysis dataset for monthly temperature and volumetric soil water of the soil level 1 (0-7 cm), and soil level 2 (7-28 cm) with horizontal resolution of 0.1°C (approximately 12 km × 12 km) during the period of 2009-2021. Differences in soil temperature at depths of 2 cm, 5 cm, 10 cm, and 20 cm at the meteorological station in Zaječar for the periods 1961-1990 and 2009-2021 are observed. By analyzing the data on the registered number of forest fires for the period 2009-2021, pronounced oscillations in the dynamics of forest fires can be observed. The minimum number of forest fires (0) is registered in 2014, when the maximum of soil moisture in the soil levels 1 and 2 is observed. A high number of forest fires corresponds to high soil temperatures in 2012 and 2017. Soils drier and hotter than the average are registered in 47.0% of all months with the fire occurrences. About 50% of fires occurred in dry and hot soils during 2012 and 2017. This percentage was zero in 2014, when there were no fires. [ABSTRACT FROM AUTHOR]

Sustainable housing is a worldwide challenge, while the case of Serbia could be an example of how complex the circumstances can be and how difficult it is to see the path towards sustainability. This paper sets out to answer multiple challenges; can energy-efficient, low-impact housing enter the market and respond to the needs of its population, potentially contributing to a more affordable and futureproof housing reality in Serbia? And does this demand rather different measure than the ones conventionally explored in innovative housing approaches elsewhere? To answer these questions, the paper starts from the preview of circumstances, then the methodology is proposed and explained, after which the possible building materials and technical installations for pilot multi-apartment Passive House are selected, and in the end, results are given and conclusions are drawn. Since the building is intended for a housing co-operative, both the affordability of the proposed solution and the environmental footprint has been comprehended by the methodology proposed. In the end, by carefully balancing the benefits of individual measures – favouring those that are cost-effective and discouraging the implementation of measures that are not, a viable pilot project that could step into the market-oriented society is selected. [ABSTRACT FROM AUTHOR]

The Environmental Protection Agency of the Republic of Serbia continuously monitors and collects air quality parameters at numerous measuring points throughout the country. The results revealed that the levels of air pollution recorded during the lockdown differed from those recorded during the same period the previous years. In this paper, we examined pollutant concentration trends in 2020 and a few previous years to determine the underlying causes of these trends. Pollutants are measured at five stations in Belgrade from the beginning of March to the end of July between 2015 and 2020. Because no hourly data were available, NO2, SO2, and suspended particles PM10 and PM2.5 are average daily values, whereas CO and ozone are daily 8-hour maximums. Concentrations were compared and averaged only when data for the same period over time was available, i.e. when comparing 2020 to previous years. The results were compared to the annual and daily limit values (for ozone and CO 8 hours maximum, respectively), as well as the variations in concentrations over time. The goal of calculating and displaying these values is to specifically identify a change in air pollution during the COVID-19 virus pandemic isolation period. In general, for Belgrade in 2020, NO2 concentrations are lower at four stations, PM2.5 concentrations are lower at two stations, PM10 concentrations are higher at one station and lower at another, and SO2 concentrations are higher than in previous years (2015-2019). [ABSTRACT FROM AUTHOR]

The European initiatives for citizens' inclusion in the air quality monitoring process have impacted the participants' knowledge, and attitudes towards air pollution and have led to a higher sense of community toward activities and measures against air pollution. In the Republic of Serbia, an experiment with self-made sensor kits "Klimerko -- Air to the Citizens" started in 2018. In this paper, we have presented the level of agreement of the particulate matter (PM) readings from selected Klimerko devices to the PM readings of the reference equivalent PM monitors from the National Air Quality Monitoring Network in the cities of Bor and Belgrade. The Klimerko devices that we tested showed excellent stability and reliability during the comparison period. The conclusion of our investigation is that the properly calibrated Klimerko devices could be applied for indicative measurements of PM mass concentrations in the ambient air. [ABSTRACT FROM AUTHOR]

Kindergartens are probably the very first public buildings we actively use in our lives. Therefore, they can be considered as the physical structures that are providing for the very important educational and social function. Additionally, they can also be considered as the specific learning tool for future generations where they can encounter the ideas of green and energy-efficient buildings. One of the results of the research project "Energy efficiency in public buildings" has been formulated through the development of Serbian National Typology of Kindergartens which was conceived as a specific tool that can be used for improving this portion of building stock. The paper presents the methodology for identification of typical kindergarten buildings, covering various construction periods, building sizes and illustrates the type of analysis performed for model representatives. The potential for energy upgrades covering physical structure, installed technological systems, as well as expected impact on energy performance, has been estimated. The study presents results based on the analysis of the data derived from the National Typology, stressing out that energy retrofits of large and medium-sized kindergartens built during the 1970s and 1980s should be the primary focus of refurbishment activities. Accounting for almost 60% of total buildings and 69.59% of heated area, they are responsible for 75.97% of energy demands. Estimated energy savings of more than 60% indicate the effectiveness of their retrofit. The paper also presents the potential uses of National Typology as a retrofit tool on various scales, from single-building considerations to a strategic approach at the national level. [ABSTRACT FROM AUTHOR]

In this paper, a mathematical model for determining the reliability of ventilation plants was given and said ventilation plant was checked using a specific example for two types of fans operating in different modes due to the difference in the age of the fans. Within the framework of the paper, the principles of arrangement of ventilation systems of mines are stated, after which the mathematical model for determining the probability of reliability of ventilation systems is presented. For checking and proving the given mathematical model, coal mines in Serbia have been selected. The experimental part presents the basic characteristics of the main fan plants of active underground coal mines in Serbia, and based on the given mathematical model and collected data on downtime in the operation of the main fan plants at coal mines, the reliability of their operation is calculated. The paper confirms that the proposed method of determining the mathematical probability of reliability of ventilation systems can be used as an initial indicator of ventilation systems, where regular plant maintenance and application of this mathematical model could predict and prevent the operation of ventilation systems, and thus extend their lifespan. By processing the data on the operation of ventilation plants, the appropriate empirical dependence of the reliability parameters was obtained with the corresponding dependence, which enables application in practice. [ABSTRACT FROM AUTHOR]

Since the reduction of energy consumption and efficient energy use, particularly in the building stock, is the priority for contemporary societies, the ways of how to improve the existing buildings should be examined. Flat roofs, as a part of the existing building thermal envelope, are recognized as a field of intervention for improving efficient energy use for space cooling and heating. The topic of the paper is to determine to what extent different improved roof structures affect energy consumption intended to achieve thermal comfort. Comparative analysis of four roof structures was conducted for the building of Healthcare center Niš in Serbia, one improved non-walkable flat roof structure and three green roof systems. Urbancsape extensive green roof system was used in all tested green roof models: non-walkable extensive green roof, walkable extensive green roof, and extensive and intensive green roof systems within walkable terraces. DesignBuilder software was used for energy modelling. The obtained results indicate a slight decrease in energy consumption for building models with green roofs compared to the building model with the improved non-walkable roof structure, along the cooling period, by approximately 1.5%, which is correlated with previous studies in similar conditions. On the other hand, the reduction of energy consumption over the heating period was negligible (less than 1%). Considering the results and predominant usage of commercial Urbanscape extensive green roof system in all green roof models, being characterized by small thickness (10.64 cm) and light structure, and which is predicted to be installed over the already well-insulated roof, the system's role as an additional thermal mass was confirmed. [ABSTRACT FROM AUTHOR]

The article focuses on particulate matter (PM) research and management in Serbia. It discusses the impact of PM on human health, its various sizes and origins, including natural and anthropogenic sources, and the importance of improving outdoor and indoor air quality. It also highlights the WeBIOPATR conference platform, which aims to bridge the gap between research communities and air quality practitioners, facilitating dialogue and the incorporation of research into practice.

Buildings are significant energy consumers and provide a notable potential to reduce primary energy consumption and increase energy efficiency. Cost-effectiveness of energy efficiency projects is of crucial importance for their implementation. Cost-optimality of different packages of energy retrofit measures is studied across the EU, but Serbia mostly lacks such information. This paper analyzes cost-optimal solutions for Serbian residential buildings connected to district heating systems, considering three different scenarios related to the economic input parameters. Additionally, it considers the potential for primary energy savings beyond cost-optimality and associated costs. The optimal solutions, that correspond to minimal global cost or minimal primary energy consumption, are determined as the results of the combinatorial optimization problems. These problems are solved using the genetic algorithm and local search. The results are compared against the ones obtained with the sensitivity analysis. The global cost can be reduced by 8-43% in the cases of cost-optimal solutions, simultaneously saving 30-76% of primary energy. The potential to save primary energy is higher - it exceeds 70% in all the analyzed cases, but also requires higher global cost, sometimes larger than in the absence of the retrofit. The paper also emphasizes high dependencies of the results on very uncertain economic inputs. [ABSTRACT FROM AUTHOR]

Volatile energy prices in the past period, force countries and their market participants to find alternative and cheaper sources of electricity production, while respecting defined environmental principles. Serbia is one of the rare European countries that uses its reserves of dissolved gas in the heat and electricity production. Combined heat and power plants, although in an almost negligible amount, contribute to the diversification of Serbia's production mix. With the presence of organized markets and local power exchanges, sale of electricity from combined heat and power plants is guaranteed for all producers who do not meet the conditions for acquiring the right to feed-in tariffs. The aim of this paper is to analyze the most profitable sale on the power exchanges of the domestic market and the region, specifically the markets of Serbia, Croatia, Hungary, Romania, and Bulgaria. The calculation methodology itself implies the use of average monthly price value for the observed markets, in the period of the past three years and nine months. In addition to the aforementioned, the costs of cross-border capacities were considered. In order to have a clearer overview of the results and the possibility of applying the methodology, the amount for calculation is 1 MWh. Costs and revenues related to negative and positive balance energy deviations are excluded from the analysis. Results showed that sale of electricity is most profitable on Serbian power exchange. [ABSTRACT FROM AUTHOR]

The guarded hot plate (GHP) method is a widely used technique to measure thermal conductivity of thermal insulation specimens in steady-state conditions. In this paper, an advance of GHP has been developed in the Laboratory for Thermal Technique and Fire Protection in Institute IMS. The innovative GHP has been applied for measuring thermal conductivity using additional heat flux meters. The design of this GHP is similar to the design of the plate for GHP apparatus, however, it has different design: smaller width of thermal barrier, which is filled with insulation glue. Heaters inside hot and guard plates are built from wire for thermocouples, which is a unique type of heater. Geometry of heater has been optimized inside plates to achieve uniform temperature distribution along the specimen surface. Temperature uniformity of GHP and energy balance were experimentally determined. The verification and validation results of improved GHP have been shown. The test method was validated comparing test results of thermal conductivity with results of the round-robin test. Four national companies participated in the round-robin comparison on thermal conductivity measurement by GHP method. The measurement was performed on the same specimen of thermal insulation material (expanded polystyrene) according to SRPS EN 12667 at temperatures ranging between 10-40 °C. The measured thermal conductivity of all participants in the round-robin test was input data for statistical processing according to SRPS ISO 5725-2 and ISO 13528. To evaluate the performance of the participants, the "z " score has been used. Measurements were conducted successively for all participants. Since 2020, the Accreditation Body of Serbia also approved this test method. [ABSTRACT FROM AUTHOR]

The COVID-19 pandemic has begun in early 2020 and still continues to strongly affect the entire world delivering a significant global, shock, but varying across countries and commodity sectors. The Government of the Republic of Serbia has been adopting different measures to slow down the dissemination of the coronavirus, specifically nationwide lockdown in March and April 2020. Business activities have been reduced. The pandemic situation has changed the lifestyle as people are mostly staying home and working from home. This paper provides a review of unprecedented impacts of COVID-19 pandemic, with restrictions and lockdown in Serbia, on electricity sector at this stage of the crisis. The outcomes offer a contribution to the body of literature because limited research has been conducted on these relationships in case of Serbia. Sets of statistical indicators are used to analyze changes the electricity sector has been facing. Data visualization is used to compare developments during the pandemic with those of previous years. Our research and data-driven analysis of these impacts should improve the understanding of the techno-economic effects of unforeseen events, such as a pandemic, on the power system, scrutinizing if effects could be relatively short-lived or longer-lasting. [ABSTRACT FROM AUTHOR]

Greenhouse gases emission as well as total energy consumption in buildings of public importance, such as schools, municipal buildings, health care centers, can be significantly reduced by increasing buildings' energy efficiency. Buildings' energy consumption adds up to 37% of total energy consumption in the EU countries. In the Republic of Serbia this amount is significantly higher, about 50%. School buildings are considered as one of the most diverse structures from the point of energy-efficient design and construction. The main aim of this paper is to determine the most appropriate settings for possible improvements in energy efficiency and temperature comfort inside a typical primary school classroom in Serbia. The energy efficiency analysis was performed during the heating season for the naturally ventilated primary school classroom located in the eastern Serbia region. The analysis was performed using novel CFD model, suggested in this paper. The suggested model was used to solve two hypothetical scenarios. The first scenario simulates the temperature field in classroom with current energy characteristic envelope of the school building. The calculated numerical data from the first scenario were compared with in-situ measurements values of temperature and wall heat fluxes and showed satisfying accuracy. The second scenario was simulated to indicate possible improvements, which would allow energy consumption decrease and thermal quality enhancement. The analyzed results, calculated using the suggested numerical model under the second scenario conditions, showed that using appropriate set of measures, it is possible to obtain desired temperature comfort levels without need for increase in the building energy consumption. [ABSTRACT FROM AUTHOR]

The objective of this paper is to raise awareness of the risk of boiling liquid expanding vapor explosions (steam explosions) in heating systems in Serbia caused by a combination of the following factors: solid fuel burning, older boiler design, closed systems, and non-installation of heat dissipation devices. The practice is in accordance with neither Standard SRPS EN 303-5:2012 nor subject literature, which both demand that this type of heating be installed in open systems. Explosions do occur; there was one in 2014 in Futog, Serbia, with fatal consequences. The main protection element, safety valve, is designed for temperatures up to 110 °C. Its operation above 110 °C is unknown. The experiment physically simulated the worst case scenario, where there is no circulation in the heating system. It used a 90 L water-filled vessel with six 3 kW electric heaters installed and safety valves attached. This paper presents the first results for the case where the set pressure of the safety valve was 1.5 bar and one heater of 3 kW was in operation. The results showed that the safety valve did not prevent boiling. The recorded pressure peaks were at 2.2 bar and the lows were at 0.8 bar, so its operation intensified boiling. Therefore, the system cannot be considered safe even with a brand new safety valve and at low overheating rates. Better air removal in the system is to be solved in future experiments. Tests will be done with different safety valves and overheating rates. [ABSTRACT FROM AUTHOR]

Paper gives a review of the most important results of extensive and wide-ranging research program on R&D of fluidized bed combustion technology in the Laboratory for Thermal Engineering and Energy of the VINCA Institute of Nuclear Sciences. Paper presents detailed overview of R&D activities from the beginning in the second half of the 1970's up to present days. These activities encompass applied research achievements in the field of characterization of limestones and bed agglomeration and sintering and modeling of overall processes during fluidized bed combustion, all of which have facilitated the R&D of the fluidized bed combustion technology. Attention is also given to steady-state combustion testing of a wide-range of fuels (coals, liquid fuels, biomass, waste solid and liquid materials, etc.) in our fluidized bed combustor and development of original methodology for testing the suitability of fuels for fluidized bed combustion, as well as specific achievements in the area of technology application in Serbia. [ABSTRACT FROM AUTHOR]

Energy certification of buildings in Serbia was introduced in 2011 and energy label depends on energy need for heating per unit floor area of heated space, calculated by the fully prescribed monthly quasi-steady-state method defined by ISO 13790. In the Republic of Serbia, most of families live in single-family houses built before the energy certification of buildings was introduced. Therefore, the estimation of energy performance of the existing buildings is important for labeling, and evaluation of energy saving measures and energy strategies to be implemented. This paper examines the applicability of monthly method defined by National legislation on the existing buildings stock in Serbia, by comparing it to the more accurate dynamic simulation method. Typical singlefamily houses are taken as a test case, since they are responsible for about 76% of energy consumption for heating. The results show that the dynamic simulation method estimates 21% to 54% higher energy need for heating, compared to the monthly method. Also, the monthly method estimates up to 13% higher savings by typical building envelope energy saving measures, compared to the dynamic simulation. This paper recommends improvement in procedures for calculation of building energy performance index to better assess energy consumption, effects of energy saving measures, and create solid background for developing and implementing of energy saving strategies. [ABSTRACT FROM AUTHOR]

The ability of flying continuously over prolonged periods of time has become target of numerous research studies performed in recent years in both the fields of civil aviation and unmanned drones. High altitude platform stations are aircrafts that can operate for an extended period of time at altitudes 17 km above sea level and higher. The aim of this paper is to design and optimize a wing for such platforms and computationally investigate its aerodynamic performance. For that purpose, two-objective genetic algorithm, class shape transformation and panel method were combined and used to define different airfoils with the highest lift-to-drag ratio and maximal lift coefficient. Once the most suitable airfoil was chosen, polyhedral halfwing was modeled and its aerodynamic performances were estimated using the CFD approach. Flow simulations of transitional flow at various angles-of-attack were realized in ANSYS FLUENT and various quantitative and qualitative results are presented, such as aerodynamic coefficient curves and flow visualizations. In the end, daily mission of the aircraft is simulated and its energy requirement is estimated. In order to be able to cruise above Serbia in July, an aircraft weighing 150 kg must accumulate 17 kWh of solar energy per day. [ABSTRACT FROM AUTHOR]

Homogeneity of the flue gas-flow through the chamber of an electrostatic precipitator is one of the basic influencing parameter on dedusting efficiency. This paper presents results of a multiobjective optimization study of the flue gas controlling devices of electrostatic precipitator of 324 MWe lignite fired Unit A4 of TPP "Nikola Tesla" in Serbia. The aim was to achieve better flow homogeneity in the cross-section of the precipitator compared to the original design. Additional constraints were to maintain the minimum as possible overall weight of the proposed design as well as pressure drop through the precipitator. Numerical simulations based on CFD were used to investigate dependence of the velocity distribution in the ducts and precipitator's chamber with respect to the geometrical parameters of tested concepts of turning blades. A series of 22 detailed full-scale numerical models of the precipitator with different concepts of turning vanes designs were developed. Assessment of the flow field uniformity for each tested design was performed based on the analysis of several homogeneity parameters calculated for selected vertical cross-sections of the precipitator. After the reconstruction according to optimized design, results of measurements confirmed significant improvements of the velocity distribution in the vertical cross-sections of the precipitator, increase of dedusting efficiency and reduction of PM emission. [ABSTRACT FROM AUTHOR]

The subject of this paper is utilization of corn cobs as a fuel in small residential heating appliances in Serbia. The objective was to investigate the profitability of the three cob forms: whole, crushed, and pellets. Thereby, construction and reconstruction option of a heating system that uses corn cobs were compared with woody and fossil fuel forms. Net present values of generated costs in the first option, as well as net present value of savings, payback period, and internal rate or return in the second, were analyzed. Assessment was conducted using BIOMASAPRO calculator with integrated approach for energy facility investments. Only utilization of whole cobs were profitable, comparing with wood logs, coal, and natural gas. In option construction, around 8700 €, 7000 €, and more than 4100 € could be thus saved after the appliance lifespan, respectively. The savings could be 7800 €, 5500 €, and more than 3600 € in option reconstruction, with payback period less than two years compared with wood logs and coal, and around 2.5 years with natural gas. Sensitivity analysis showed that utilization of whole cobs could be profitable with up to three times higher purchase price. With bank loan as a financing option for economically weaker biomass users, the scenarios though remain profitable. Subsidy of more than 40% for a heating appliance that uses crushed cobs would allow for profitable investment in comparison with wood chips. Future investigation should comprise assessment including social and environmental aspects, to conclude if corn cobs are a sustainable fuel in Serbia. [ABSTRACT FROM AUTHOR]

Application of Innovative methodology for risk assessment and inspection methods is the result of a long-term work in the field of Risk-Based Inspection. As such, it was successfully applied on oil and gas facilities in the Middle East. As an example of its versatility, application will be shown on small experimental biomass gasifi- cation plant utilized for the purpose of combined heat and power generation, built in Serbia in the middle of the past decade. Throughout the analysis both active and passive damage mechanisms will be identified as well as barriers thus enabling the creation of a system that documents the dynamics of the damage mechanisms and installed barriers. [ABSTRACT FROM AUTHOR]

An emergency caused by the COVID-19 pandemic affected the rethinking of existing healthcare systems. The increased need for hospital beds appeared short after the outbreak of the pandemic and the solution was to adapt the existing buildings, primarily public ones. Among all, sports buildings, i.e. sports halls were successfully used around the globe for conversion into hospitals. Topic of the paper was to investigate whether sports halls in Serbia, which were also used as temporary hospitals, are suitable for conversion in terms of energy consumption needed for achieving thermal comfort. Two case studies were analysed. The energy simulations were done using the DesingBuilder software. The results of thermal comfort summary and energy consumption led to the conclusion that this building type in Serbia could be successfully used for hospital purposes. Although the multiple increase in energy consumption was noted during the heating period, the results were within the limits required by both national and international standards. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to research the ways of integrating sustainable development into study programs of engineering faculties in an international context, as well as to analyse the current state of engineering education for sustainable development at the universities of the Republic of Serbia. Therefore, a desktop research, as well as an analysis of the engineering education curricula, have been conducted. The results of the research indicated to two possible approaches to the integration of sustainable development into the engineering curricula – in the form of special subjects dedicated to the problems of sustainable development in the engineering, or as an integrative approach which implies that sustainable development becomes an integral part of the entire curriculum. Subjects dedicated to sustainable development have been identified at all universities, but not at all faculties where engineers are educated in the Republic of Serbia, they are present at all levels of study (undergraduate, master, doctoral), as well as within applied, integrated and specialist studies, and by status they are most often elective. The results confirm that the engineering curricula open up towards the questions of sustainable development both in international context, and in higher education of the Republic of Serbia and as such, they can serve to the relevant ministries of education and science, universities and engineering faculties as a recommendation in which way to plan and design higher education of engineers in the future in order to provide overall support in the integration of sustainability into the engineering. [ABSTRACT FROM AUTHOR]

Sustainable development indicators mainly provide information that can link the observed energy system with sustainable development. This paper considers building energy indicators in order to provide monitoring and measurement of energy performance of buildings. The results of measurement which are considered were obtained in school buildings in Serbia. The aim of this paper is to select, define, and calculate energy indicators as criteria for evaluating the quality of public buildings, with regard to sustainable development. The criteria for assessing sustainability are quantified by certain defined sets of economic, social and environmental indicators. The analyse and synthesis parameters under information deficiency method of multi-criteria analysis is also described and mathematically presented. This method is based on the synthesis technique of fuzzy sets and the sustainability of the school buildings was based on their assessment as complex energy systems. [ABSTRACT FROM AUTHOR]

This paper analyzes the effects of coal grindability and its characteristics on the grinding capacity and power consumption for beater wheel mill during exploitation in thermal power plant TENT B in Obrenovac, Serbia. For this purpose, experiments were made on the mill, before and after its reconstruction. Experiments included the determination of grinding capacity, mill power consumption, and laboratory analysis of coal characteristics and Hardgrove grindability index (HGI). The analysis of experimental results found that the grinding capacity has a negative correlation with the ash content in coal. Moisture content in analysis sample of coal has a positive correlation with the consumption of electricity and grinding capacity. Between the grinding capacity and the value of HGI exists a negative correlation. Analysis of the influence of grindability of coal and coal characteristics on grinding capacity and energy consumption was carried out. Based on coal characteristics and values of HGI, mathematical expressions were derived for the calculation of grinding capacity and electric energy consumption. In addition, ability to predict specific power consumption of the mill on the basis of HGI values, were carried out. Specific power consumption obtained from HGI values showed good agreement with the experimentally determined specific power consumption of the mill. [ABSTRACT FROM AUTHOR]

The paper presents the results on the study of the possible application of the Canadian Forest Fire Weather Index and the Modified Angstrom Index in forest fire risk assessments. The daily values of these indices for the period 2005-2015 were related to the forest fire database. It was found that there is a relatively weak to moderate correlation between forest fires and the values of the Canadian Forest Fire Weather Index. In order to improve the wildfire risk assessments (including forest fires), the index was modified. The modified index has a significantly greater correlation with the actual events of forest fires and consequently a much wider application in southern Serbia. The modified index can be of great importance in the future concepts of forest fire risk management. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editor discusses various reports within the issue on topics including scientific achievements in Serbian scientific institutions, 55th Anniversary of Mechanical Engineering Faculty in University of Nis, Serbia and problems related to engineering.

Regression analysis is used to develop models for minimal daily pavement surface temperature, using minimal daily air temperature, day of the year, wind speed and solar radiation as predictors, based on data from Awbari, Libya. Results were compared with the existing SHRP and LTPP models. This paper also presents the models to predict surface pavement temperature depending on the days of the year using neural networks. Four annual periods are defined and new models are formulated for each period. Models using neural networks are formed on the basis of data gathered on the territory of the Republic of Serbia and are valid for that territory. [ABSTRACT FROM AUTHOR]

The paper introduces basic information on the geographical location, climate and solar radiation in Serbia. It focuses particularly on the air pollution in Serbia and its influence on the solar cells energy efficiency. Moreover, detailed information on the development of solar energy in Serbia and the examples of the application of the low, medium and high temperature and photovoltaic conversion of solar radiation is provided. The paper also gives an overview of the installed greater capacity solar power stations related to the electricity network and the smaller capacity solar power stations as the independent sources of electricity in Serbia. In conclusion, the paper stresses Serbia's favourite climate and other conditions for the prospective successful development of solar energy. [ABSTRACT FROM AUTHOR]

Following the guidance set by the Directive on the energy performance of buildings (recast) (EPBD2), current regulations in Serbia which refer to the issue of energy efficiency and energy certification of buildings provides an opportunity of certification of selected unit of a building, such as a dwelling. This measure was set in order to make it possible for owners or tenants of the building or the building unit to assess and compare its energy performance. From the user's perspective this measure is very important since, apart from reviewing the quality or the deficiencies of space in which they live, it would be an important parameter of economic evaluation of the apartment in the future. As energy performance of the apartment is not a priori identical to that of the whole building, the paper will analyze and compare these values for different positions in a horizontal and vertical plan of the same apartment within the building. Comparison of the results obtained for individual dwellings and for a building as a whole, will provide insight into the extent to which the disposition and the orientation of the apartment affect its energy performance. [ABSTRACT FROM AUTHOR]

This paper presents a study of a free convection flow around the walls of a ventilation mill of the Thermal Power Plant "Kostolac B", Kostolac, Serbia. A combined method consists of thermography and software post-processing, PATS. The PATS is specially developed for recognition of turbulence zones by the custom processing of large input data sets from thermal videos. The calculations determine maximum temperature fluctuation i.e. peak-to-peak fluctuation at every spot during the recording time. Three thermal videos of the walls were analyzed. Maximum temperature fluctuation occurred in the zones close to the obstacles, which are thus recognized as one of the main sources of turbulence. Besides, PATS has recognized fine camera oscillations and mechanical movements of a flexible material near the dozer wall. The detected zones of turbulence correspond to the previous studies and to the theory. The method shows good potential in the field of free convective flow research through the improvement of testing efficiency and cost savings. State-of-the-art thermograph cameras and updated software are recommended. [ABSTRACT FROM AUTHOR]

This paper deals with the techno-economic analysis of gas turbine-based combined heat and power production, within a current local legislation frame for the promotion of such production of energy in the Republic of Serbia. Since the legislation includes plants with electric power below 10 MW, an overview of the relevant technical characteristics for a number of appropriate gas turbines was prepared. The relevant thermodynamic parameters are calculated in order to estimate the economic feasibility of combined heat and power production using these plants. The production cost of useful heat is determined by taking into account the incomes from the sale of electricity to the electric grid under a feed-in tariff. It is compared with the production cost from an equivalent boiler for the separate production of the heat. One of the main objectives is to determine the effectiveness of the implemented legislative measures in the promotion of combined production of heat and power. Clear conclusions were drawn based on the results obtained. [ABSTRACT FROM AUTHOR]

There is a range of modern approaches and models in literature for the evaluation and determination of energy security, which are based on different parameters and indicators. For most of them, a common characteristic is emphasizing the availability of energy, as an important dimension for ensuring energy security. In this paper, concise overview of Serbian energy sectors is given and appropriate energy indicators are defined and determined. Selected indicators provide insight into the main components that characterize availability - security of supply, self-sufficiency, diversification of energy sources, the level of renewable energy use, and technological maturity. Besides calculation of energy indicators, the aim is to investigate and establish the relationships among components of availability of energy in Republic of Serbia, and to provide some recommendations for the policy makers to develop efficacious measures for enhancing energy security. Therefore, analytic hierarchy process methodology is applied to analyse collected data, to reveal cause - effect relationships, and to prioritize components of availability mutually. Conclusion is that the main activities in Serbian energy sector should be directed to improvement of energy efficiency, increase the use of renewable energy sources and diversification of energy sources and energy imports directions. [ABSTRACT FROM AUTHOR]

The technical analysis of a hybrid wind-photovoltaic energy system with hydrogen gas storage was studied. The market for the distributed power generation based on renewable energy is increasing, particularly for the standalone minigrid applications. The main design components of photovoltaic/wind hybrid system are the photovoltaic panels, the wind turbine and an alkaline electrolyzer with tank. The technical analysis is based on the transient system simulation program TRNSYS 16. The study is realized using the meteorological data for a Typical Metrological Year for region of Novi Sad, Belgrade cities, and Kopaonik national park in Serbia. The purpose of the study is to design a realistic energy system that maximizes the use of renewable energy and minimizes the use of fossil fuels. The reduction in the CO2 emissions is also analyzed in the paper. [ABSTRACT FROM AUTHOR]

In this paper we have examined the effect of variable frequency electromagnetic field generated with a homemade device on deposit formation in installations with geothermal water from Sijarinjska spa. The frequency alteration of the electromagnetic field in time was made by means of the sinusoidal and saw-tooth function. In laboratory conditions, with the flow of geothermal water at 0.015 l/s and temperature of 60 °C for 6 hours through a zig-zag glass pipe, a multiple decrease of total deposit has been achieved. By applying the saw-tooth and sinusoidal function, the decrease in contents of calcium and deposit has been achieved by 8 and 6 times, respectively. A device was also used on geothermal water installation in Sijarinjska Spa (Serbia), with the water flow through a 1"diameter non-magnetic prochrome pipe at 0.15 l/s and temperature of 75 °C in a ten-day period. A significant decrease in total deposit and calcium in the deposit has also been achieved. [ABSTRACT FROM AUTHOR]

The paper presents results of the research in wood fuels consumption for household needs in Serbia. Research was performed during the period from October 2010 until April 2011, i. e. in the period of heating season in order to get the ac-tual situation regarding the presence of certain fuel types in the consumption of households with special highlight on types and amounts of wood fuels. For this purpose, an adequate methodological concept was defined with the aim to pri-marily get relevant and reliable data on wood fuels consumption and afterwards, by using FAO WISDOM methodology and adequate GIS software packages to perform their analysis, mapping, and graphic representation. One of the most significant elements of the adopted methodological concept was field research-questionnaire of households which was conducted on the sample of 36.946 households out of which 20.725 urban and 16.221 rural in 22 municipalities in Serbia, which was 1.46% of the total number of households in Serbia. Results of the survey showed that 23.2% of the total number of households in Serbia used district heating system (based on conventional fossil fuels as dominant), 25.3% used electricity, and 10.6% used gas for heating purposes. Most households (40.9%) used solid fuels such as fuelwood, coal, briquettes, pellets, agricultural residues and combinations of solid and other fuels. [ABSTRACT FROM AUTHOR]

Thermal power plants in the Republic of Serbia are making considerable efforts and even more considerable investments, not only to maintain electricity production at maximum design levels, but even to additionally increase the power output of existing generating units. Capacities of mills used in pulverized coal preparation are identified as one of the main constraints to achieving maximum mill plant capacity, while coal grindability is seen as one of the factors that directly affect capacities of the coal mills utilized in thermal power plants. The paper presents results of experimental investigation conducted for the purpose of determining Hardgrove grindability index of coal. The investigation was conducted in accordance with ISO 5074 and included analysis of approximately 70 coal samples taken from the open pit mine of Kolubara coal basin. Research results obtained indicate that coal rich in mineral matter and thus, of lower heating value is characterized by higher grindability index. Therefore, analyses presented in the paper suggest that characteristics of solid fuels analyzed in the research investigation conducted are such that the use coals less rich in mineral matter i. e. coals characterized by lower grindability index will cause coal mills to operate at reduced capacity. This fact should be taken into account when considering a potential for electricity production increase. [ABSTRACT FROM AUTHOR]

Implementation of co-generation of thermal and electrical energy in district heating systems often results with higher overall energy efficiency of the systems, primary energy savings and environmental benefits. Financial results depend on number of parameters, some of which are very difficult to predict. After introduction of feed-in tariffs for generation of electrical energy in Serbia, better conditions for implementation of co-generation are created, although in district heating systems barriers are still present. In this paper, possibilities and effects of implementation of natural gas fired co-generation engines are examined and presented for the boiler house that is a part of the district heating system owned and operated by the Faculty of Mechanical Engineering in Niš. At the moment, in this boiler house only thermal energy is produced. The boilers are natural gas fired and often operate in low part load regimes. The plant is working only during the heating season. For estimation of effects of implementation of co-generation, referent values are taken from literature or are based on the results of measurements performed on site. Results are presented in the form of primary energy savings and greenhouse gasses emission reduction potentials. Financial aspects are also considered and triangle of costs is shown. [ABSTRACT FROM AUTHOR]

This paper presents a methodology development and the results achieved in the process of establishing energy management system in the city of Kragujevac (Serbia) and in its public services. The paper is an overview of influential factors in the field of energy management, analyzing their impact on raising the energy efficiency of individual utility service and the city of Kragujevac, as a whole. The paper also presents the most interesting scientific and research projects realized in the co-operation of several actors which were co-ordinated by Regional Euro Energy Efficiency Center Kragujevac. The municipal companies together with the city administration are the direct beneficiaries of the results realized in the following areas: - Development of energy management in municipalities and the establishment of energy planning at the local level; - Improvement of municipal services by applying energy efficiency measures in public enterprises: "Energetika" (heating), "Cistoca" (communal waste management), and "Vodovod i kanalizacija" (water and waste water management). [ABSTRACT FROM AUTHOR]

Regarding to the structure of final energy consumption in buildings and National Action Plans, the paper gives a short overview of energy consumption in buildings in Serbia, showing that the greatest potential for achieving savings lies in the implementation of measures which improve energy efficiency. Considering that over 60% of energy requirements for buildings is related to thermal energy, particular attention should be paid to the centralized heating systems, both during the design of a new system, and in the reconstruction of the existing one. Further discussed are the heat sources for the heating systems. The seasonal heat load duration curve for winter conditions in accordance to the Typical Meteorological Year for Belgrade is constructed and displayed. The analysis of the conventional system with a fossil fuel source, as well as the analysis of a hybrid heat source are conducted. The savings achieved in the primary energy, heating bills and CO2 emission reduction, which are attained by the use of a hybrid system, are shown in comparison with the conventional systems. Collecting data on investment costs, as well as the prices of energy and fuels in Serbian market, enabled calculation of the payback period when replacing the conventional system by the new hybrid one. [ABSTRACT FROM AUTHOR]

Wood chips are often used as solid fuel in modern biomass boilers. Experiments were conducted on 22 boilers located in Serbia burning wood chips as fuel. The influence of wood chips characteristics is analyzed in relation to the flue gas losses and the thermal efficiency of the boiler. Measured useful heat output of the tested boilers was 460-2585 kW. Moisture content of the wood chips was 19.21-38.23% with a net calorific value of 10177-14139 kJ/kg and ash content of 0.84-3.59%. Thermal efficiency of the boilers was 88.78-94.06%, flue gas losses 5.84-11.13% and flue gas temperature 121.83-188.44 °C. Experimental research and analysis of the results showed that an increase in moisture content of wood chips lead to a decrease of net calorific value i.e., decrease in flue gas temperature. Moisture content of wood chips has an influence on both useful heat output and boiler thermal efficiency. The experimental results showed that for a given boiler construction, this impact is not negative. Based on regression analysis, mathematical expressions were derived for the calculation of thermal efficiency and flue gas losses. Throughout the experiments, pollutant emissions were measured, NOx, CO, and particulate matter. [ABSTRACT FROM AUTHOR]

The Urgent Care Center of the Clinical Center of Vojvodina in city of Novi Sad, Republic od Serbia, as a specific medical facility with very demanding conditions of work and functioning, has an extensive and constant energy demands. The building is new, set into operation in 2010. The state-of-the-art concept and the equipment installed create conditions for using advanced solutions in the framework of supervisory and control systems, increasing energy efficiency and reducing operating costs in the Urgent Center. The aim of this paper is the assessment of additional possibilities for increasing energy efficiency in the building using a number of control techniques available today. According to a source of energy, the most utilized is the electric power, which is consumed for air conditioning, compressed air, and lighting. Thermal energy is used for space heating in winter and the preparation of hot water. The first step in increasing energy efficiency was the continuous monitoring and recording of consumption. The next step was the analysis of the energy consumption and the discovery of critical areas of consumption. The final step was related to the plans and algorithms for the energy reduction. To this goal, the energy consumption in the period March 2014-February 2016 was measured and recorded. According to that measuring and data analysis, an expert system based on the methods of computational intelligence that combines all the developed actions and algorithms for increasing energy efficiency in one unit was implemented. [ABSTRACT FROM AUTHOR]

Serbia is dependent on imports of crude-oil and natural gas, but is endowed by reserves of lignite and the potential of renewable energy sources. Serbia has a strategy to reduce greenhouse gas emissions in the energy sector and to increase the share of renewable in gross final energy production 27% by 2020. Serbia's total estimated technically usable potential of renewable energy sources is 5.65 Mtoe per year. Biomass has the highest potential for use in Serbia (3.448 Mtoe), followed by hydro power (1.679 Mtoe), solar energy (0.240 Mtoe), geothermal energy (0.180 Mtoe), and wind energy (0.103 Mtoe). This paper presents the potential of renewable energy sources available in Serbia, with current status of their use and prospects for further exploitation. [ABSTRACT FROM AUTHOR]

The buildings are among major energy consumers, whose energy efficiency is rather low. Clerestory windows are responsible for a large portion of energy losses from the buildings. The energy efficiency of buildings can greatly be improved by upgrading clerestory and other windows. This paper focuses on the theoretical and experimental investigations on how this can be performed in an old school building in the town of Bor in eastern part of Serbia. For that purpose a modern measuring technique has been applied to identify the existing status, and to compare theoretical and actual conditions. [ABSTRACT FROM AUTHOR]

The paper presents the analysis of possible potentials for the production of forest biomass in Serbia taking into consideration the condition of forests, present organizational and technical capacities as well as the needs and situation on the firewood market. Starting point for the estimation of production potentials for forest biomass is the condition of forests which is analyzed based on the available planning documents on all levels. Potentials for biomass production and use refer to initial periods in the production and use of forest biomass in Serbia. [ABSTRACT FROM AUTHOR]

Global discussion on climate change and strengthening environmental protection has been launched, especially in the last three decades. As climate change is a result of greenhouse gas emissions, different mechanisms were introduced in order to reduce this impact, surely the most significant was set by the Kyoto Protocol. The Republic of Serbia considers a proper policy on environmental protection as one of its priorities. As the switch from traditional to renewable energy sources carries valuable improvements in environmental protection and economic efficacy, the Government encourages the use of renewable energy sources for the production of energy. This paper provides analysis of the potential of renewable energy sources in Serbia, carbon potential and their possible role in mitigation of climate changes. Results presented in the paper can be useful for the improvement of the strategic planning on the national level with the final aim to contribute to the increase in importance of use of renewable energy sources in that planning. [ABSTRACT FROM AUTHOR]

The aim of this paper is to analyze and explore the most suitable energy policy instruments for energy efficiency improvement in Serbia. The analysis has been carried out with a focus on energy indicators for Serbia and EU27. It encompasses a period of twenty-two years and is directed towards the consideration of amendments that need to be made in the National Energy Efficiency Policy. Despite constant attempts to improve and increase energy efficiency and to expand utilization of renewable energy sources, it seems that accomplished results are still very modest. The comparative analysis of the situation in the area of energy efficiency in Serbia and in the EU takes into consideration deficiencies in the energy policy in Serbia and proposed measures for overcoming them. The Multiple Criteria Decision Analysis method is used for analyzing the extent of key influences on success in the implementation of energy efficiency policy in Serbia and also for the interpretation of results. The analysis shows that identified energy policy instruments are such that the success in their implementation will depend on a reformed institutional approach. This method can be applied in any other country. [ABSTRACT FROM AUTHOR]

The paper presents a theoretical analysis of the cooling system of a 110 MW coal-fired power plant located in central Serbia, where eight evaporative towers cool down the plant. An updated research on the evaporative tower cooling system has been carried out to show the theoretical analysis of the tower heat and mass balance, taking into account the sensible and latent heat exchanged during the processes which occur inside these towers. Power plants which are using wet cooling towers for cooling condenser cooling water have higher design temperature of cooling water, thus the designed condensing pressure is higher compared to plants with a once-through cooling system. Daily and seasonal changes further deteriorate energy efficiency of these plants, so it can be concluded that these plants have up to 5% less efficiency compared to systems with once-through cooling. The whole analysis permitted to evaluate the optimal conditions, as far as the operation of the towers is concerned, and to suggest an improvement of the plant. Since plant energy efficiency improvement has become a quite common issue today, the evaluation of the cooling system operation was conducted under the hypothesis of an increase in the plant overall energy efficiency due to low cost improvement in cooling tower system. [ABSTRACT FROM AUTHOR]

Data assessment and potential use of concentrating solar power plants in Serbia and the Republic of Srpska, B&H, are given in the paper. Besides, concentrating solar power plants schematics and manner of their functioning are described. Then follows geographical position and the results of PVGIS calculation of the yearly average values of the solar irradiation on horizontal, vertical and optimally inclined plane, optimal inclination, linke turbidity, ratio of diffuse to global solar irradiation, average daytime temperature, and 24 hours average of temperature for some locations in Europe where concentrating solar power plants are installed or are in construction, and in some cities in Serbia and the Republic of Srpska. The paper also gives comparative surveys of the solar irradiation on horizontal plane and ratio of diffuse to global solar irradiation on some locations in Europe with installed and concentrating solar power plants in construction, and in some cities in Serbia and the Republic of Srpska. Data for direct normal irradiance for locations in Europe with installed or concentrating solar power plants under construction, and for some other cities in Serbia and the Republic of Srpska are also given. Data for direct normal irradiance were obtained by means of SWERA. In the light of the obtained results it was concluded that Serbia and the Republic of Srpska have favorable climatic and geographical conditions for the installation of the experimental concentrating solar power plants, and the area of Trebinje in the Republic of Srpska has favorable conditions for commercial concentrating solar power plants installation. [ABSTRACT FROM AUTHOR]

The main objective of this paper is to present the advantages of using Cost-Benefit analysis in energy efficiency projects implemented in public buildings, and to prove the hypothesis that Cost-Benefit analysis boosts the effectiveness and efficiency of the said type of projects. The paper offers theoretical and practical explanation of the implementation of Cost-Benefit analysis in the relevant area. Since energy efficiency projects in public buildings usually represent a part of a broader portfolio of similar projects and their implementation demands allocation of substantial financial resources, communities are often be interested in achieving maximal economic and non-economic benefits. This paper aims to demonstrate that Cost-Benefit analysis can represent an excellent contribution when attempting to select the projects for implementation within a broader portfolio of energy efficiency projects in public buildings. This hypothesis was demonstrated by putting a greater emphasis on non-economic benefits and the costs arising from implementation of the aforementioned types of projects. In addition, a practical test of this hypothesis was performed through the implementation of an energy efficiency portfolio in public buildings, worth several tens of millions of dollars - the Serbian Energy Efficiency Project. The paper concludes that the use of Cost-Benefit analysis can help us to effectively evaluate and manage projects of this type aimed at achieving maximum benefits for the community in question. [ABSTRACT FROM AUTHOR]

The revised Intergovernmental Panel on Climate Change guidelines for national greenhouse gas inventories recommends that more comprehensive and thus more reliable characteristics of the local fossil fuels should be used for the national greenhouse gas inventory calculations. This paper deal with the carbon emission characteristics of low-calorific lignite recovered from the Kolubara open-pit mine. The samples of coal were carefully selected in order to cover the net calorific value, ash and water content of the broad spectrum of the quality of the raw lignite supplied to the Serbian thermal power plants. Correlation analysis of the laboratory analysis data gave a linear dependency of the net calorific value on the combustible content in the coal samples. Also, linear correlation between the carbon content and the net calorific value was found. The regression analysis of experimentally determined coal characteristics implies that the carbon emission factor is dependent on the net calorific value. For the subset of raw lignite samples with the net calorific value Qdr = 6-10 MJ/kg, that is most representative for current and near future use for power generation in Serbian thermal power plants, the linear dependency CEFr (tC/TJ) = 34.407 - 0.5891. Qdr MJ/kg was proposed. Regarding the net calorific ranges of samples examined, the raw Kolubara lignite carbon emission factor is considerably higher than those recommended by Intergovernmental Panel on Climate Change Tier 1 method of 27.6 tC/TJ. [ABSTRACT FROM AUTHOR]