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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 CO emission reduction, which are attained by the use of a hybrid system, are shown in 2 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.

The systematically varying properties and generally coherent and predictable behavior of rare earth elements (REE) make them potential tracers for studying water/rock interaction and weathering processes. In this work, a compilation and analysis of REE data in mineral and thermal waters were performed, focusing on their content and distributions in different hydrogeological systems, to quantify the natural REE variability and to discuss the controlling factors of REE concentrations. Quantitative challenges presented by multiply censored data were addressed with nonparametric and multivariate statistical methods. Considering a regional character of the research the application of Q and R mode Hierarchical Cluster Analysis with spatial analysis was an important approach for meaningful interpretation of large data set. An efficient approach to analyze differences between obtained HCA groups (clusters) was using a plot of reference-normalized concentrations. The results showed that REE data along with anomalies of Ce and Eu and inter-element ratios were good indicators of the aquifer lithology (hydrogeological systems formed in granitoid and volcanic rocks of various age, two main types of hydrogeological basins, and carbonate aquifers). The important mechanisms controlling REE migration in water were hydrochemical conditions in aquifers. The significance of the applied statistical analyses was represented by defining specific hydrochemical fingerprints of identified hydrogeological systems with distinct geochemical characteristics where REE showed the necessity of understanding of complex geological and hydrogeological settings, geodynamic evolution, and hydrogeochemical processes in fluid flow systems.

The objective of this paper was to determine background values (BV) and anomalous values (AV) of U and Th in groundwater and to establish hydrogeochemical conditions which lead to the elevated concentrations of these elements in groundwater. The methodology included planning and collecting of water samples, laboratory work, and assessment of BV and AV concentrations in accordance with the dataset distribution, based on consideration of hydrogeochemical conditions in the hydrogeological system. Groundwater sampling included 144 occurrences of mineral and thermal water from Serbian territory, belonging to different hydrogeological systems. Field parameters were measured for temperature (T), pH, electrical conductivity (EC), oxidation–reduction potential (ORP), dissolved oxygen (DO), and carbon dioxide (CO2). Standard laboratory measurements were applied for the determination of major chemical components (Ca, Mg, Na, K, Cl, HCO3, and SO4) and U and Th concentrations were measured by ICP-MS. The first step for obtaining U and Th threshold values was based on non-parametric statistical analysis on the data sets. Further analysis of threshold values enabled establishing hydrogeochemical conditions influencing elevated concentrations of U and Th and setting up the logistic regression (LR) model. Differences in the hydrochemical properties of U and Th can be observed based on predictor variables from LR models. Physico-chemical parameters Eh and pH, groundwater type, and geochemical environment (cretaceous igneous rocks) were significant predictors for elevated uranium concentrations, while significant predictors in the thorium LR model were the pH value, the concentration of SO4 in the solution, and the water-bearing rocks (tertiary igneous rocks).

This paper presents a new laboratory set-up for the air-conditioning operation analysis in the Laboratory for Automatic Control at the Faculty of Mechanical Engineering, University of Belgrade. The new HVAC laboratory is designed to investigate different complex HVAC system working regimes and to provide desired space comfort. The emphasis is specially given to an impact on energy consumption. The laboratory set-up is designed to operate in the complex, dynamic regimes, when indoor environment parameters are intensively changed, together with a change of outdoor conditions. In order to minimize energy consumption, a new software and various automatic control algorithms are designed for automatic control of the air handlig unit.

The paper presents an experimental analysis of the relationship between local thermal comfort and productivity loss in classrooms. The experimental investigation was performed in a real university classroom during the winter semester in city of Belgrade. Measurements were taken for four scenarios, with different indoor comfort conditions. Variations were made by setting the central heating system on/off, adding an additional heat source to provoke higher indoor temperatures, and measuring the radiant asymmetry impact. Innovative questionnaires were developed especially for the research, in order to investigate students’ subjective feelings about local thermal comfort and indoor environmental quality. Local predicted mean vote and predicted percentage dissatisfied indices were calculated using data measured in situ. The results were compared to existing models recommended in literature and European and ASHRAE standards. Student productivity was evaluated using novel tests, designed to fit the purposes of the research. Surveys were conducted for 19 days under different thermal conditions, during lectures in a real classroom, using a sample of 240 productivity test results in total. Using the measured data, new correlations between the predicted mean vote, CO2, personal factor and productivity loss were developed. The research findings imply that local thermal comfort is an important factor that can impact productivity, but the impact of the personal factor is of tremendous importance, together with CO2 concentration in the classroom. [Projects of the Serbian Ministry of Education, Science and Technological Development, Grant no. 33047 and Grant no. III 42008]

The paper deals with a comprehensive, three-dimensional numerical CFD analysis of temperature fields in Trombe wall and in the adjacent room for several days of a typical meteorological year (TMY) for a moderate continental climate. Construction of the Trombe wall is optimized, using different types of glassing on the outside of the wall. For summer day, the glass is considered to be covered with PV stripes during the daylight in order to prevent overheating. The central concrete core of the wall is covered with a layer of dark paint, on the outside, to improve absorptivity of the wall. The Trombe wall is oriented on south side of the house, and designed with openings with flaps in concrete core. Those openings are simulated in opened and closed positions. The U-values of the house envelope are considered according to passive house standards. Temperature fields in concrete core and in the room with Trombe wall are simulated, as well as velocity fields. According to these results, analysis of energy savings potential is performed.

This paper analyses the influence of time-predicted night ventilation applied during the summer season on the total energy consumption of airconditioning system. Analysis has been made on the basis of a computer program for dynamic simulation of air-conditioned rooms thermal behavior. The program was developed at the Department for Thermal Engineering at the Faculty of Mechanical Engineering, University of Belgrade. Air-conditioning operating modes without and with application of night ventilation, and different periods of night ventilation are analyzed. Cooling loads, fan energy consumption and overall energy consumption for summer conditions for Belgrade for the whole cooling season are given. The obtained results were compared, and hereupon a review is given of the energy savings for the whole cooling season.

Multivariate statistical analyses are used for reducing large datasets to a smaller number of variables, which explain main hydrogeochemical processes that control water geochemistry. Factor analysis (FA) allows discovering intercorrelations inside the data matrix and grouping of similar variables, i.e. chemical parameters. In this way new variables are extracted, which are called factors, and each factor is explained by some hydrogeochemical process. Applying FA to a dataset that consists of 15 chemical parameters measured on 40 groundwater samples from Serbia, four factors were extracted, which explain 73.9% of total variance in the analyzed dataset. Interpretation of obtained factors indicated several hydrogeochemical processes: the impact of sea water intrusions and volatiles in previous geological periods, solutes diffusion from the marine clay, cation exchange and dissolution of carbonate and silicate minerals. [Projekat Ministarstva nauke Republike Srbije, br. 43004]