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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, CO 2 , 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 CO 2 concentration in the classroom.

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More than one third of the world’s primary energy demand refers to residential sector. Heating is considered as one of the main part of the energy consumption in buildings. In this study, a thermodynamic sustainability assessment analysis of different energy sources for heating of residential building, with net floor heated area of 162 m2, for Belgrade weather data, was presented. Five options of energy sources were studied, namely: coal, natural gas, electricity, district heating and air-water heat pump. Energy and exergy analyses were conducted and appropriate efficiencies were determined. Energy and exergy flows in boundaries of the building and in the whole chain from primary to final values were analyzed. The environmental impact factor and exergetic sustainability index were determined for all considered energy sources. The exergy efficiency is very low in all analyzed cases, which further implies poor thermodynamic compatibility of energy quality from the supplied side and the energy used for building heating. It was shown that the highest exergy efficiency is for the case of heat pump utilization (about 6%), due to the energy used from environment. The minimum environmental impact factor (15.37) and maximum exergetic sustainability index (0.065) were found for the case of heat pump utilization.

На основу података Енергетског биланаса Републике Србије за 2017. годину, потрошња финалне енергије је процењена на 8429 Mtoe, од чега је 48% укупне потрошње у сектору домаћинства, пољопривреда и јавно-комуналне делатности. У укупној структури коришћења финалне енргије, обновљиви извори енергије (само геотермална енергија и биомаса заједно) учествују са 12%. Осим квантитативне (енергијске) анализе, за потпуно разумевање свих важних аспеката коришћења енергије и успостављања одговарајуће енергетске политике, потребно је извршити и квалитативну (ексергијску) анализу, као и анализу утицаја коришћења различитих енергената на животну средину. Цене енергената треба да одражавају вредност искористивог дела, односно квалитет, њихове енергије, тј. ексергије. У раду је приказана термодинамичка и економска анализа коришћења различитих енергената у стамбеној згради грејане површине око 160 m 2 , за климатско подручје Београда. Поређени су различити енергенти за грејање и припрему санитарне топле воде: електрична енергија, природни гас, даљинско грејање, угаљ и обновљиви извори енергије. Дат је упоредни приказ потребне примарне енергије, емисије угљен-диоксида, ексергије, као и цена енергије и ексергије за различите енергенте. Кључне речи: Енергија; ексергија; цене енергената; обновљиви извори енергије; емисија CO2 According to the energy balance for Republic of Serbia for 2017, the total final energy needs for 2017 for Republic of Serbia are estimated as 8429 Mtoe, with a share of 48% estimated for households, agricultural, public and commercial sectors. In the structure of final energy consumption by fuel for 2017 in Serbia, the renewable energy sources are participating with a share of 12% (only geothermal energy and biomass). In order to provide better understanding of all important aspects of energy usage, beside the quantitative (energetic) analysis, it is necessary to perform also qualitative (exergetic) analysis, together with the analysis of different fuels usage impact on environment. Fuel costs should take into a consideration the value of usable part, with other words the quality of their energy, namely exergy. The paper presents thermodynamic and economic analysis of different fuels usage, for residential building, with net heated area cca 160 m 2 , for Belgrade weather data. Results are presented as a comparison between different fuels used for heating and domestic hot water preparation, such as: electricity, natural gas, district heating, coal and renewable energy sources. The comparison is shown for primary energy consumption, CO2 emission, exergy consumption and energy and exergy costs for different fuels.