Natural gas is used for the production of almost 20% of total energy today. The natural gas security of the Republic of Serbia is an urgent strategic, political and security issue. Serbia is one of the most vulnerable countries in Southeast Europe, because it only has one supply route. This study is a contribution to efforts to better understand the factors affecting energy security through the implementation of a new methodology based on the fuzzy–AHP synthesis model for measuring energy security. This new methodology was used to identify the energy, economic, environmental, social and technical indicators that accompany energy security analysis. The fuzzy–AHP synthesis model uses the asymmetric fuzzy inference approach for an outcome finding with the asymmetric position of fuzzy sets. The most important characteristic of the proposed model is its ability to operate with numerical and linguistic data and universality of application. The result of the proposed model shows a quantified assessment of energy security and its trend in the future of the natural gas sector. It indicates an unacceptably low level of present energy security and a gas system very vulnerable to supply cuts if the current gas infrastructure remains as it is in the future.

The integration of wastewater heat pumps (using purified water) in district heating systems is analyzed in this paper. The simulation procedure is proposed to analyze the impacts of stochasticity of purified water temperature and flow to heat pump integration and operation. The analysis includes calculation of the daily and seasonal coefficient of performance, as well as fossil fuel savings and CO2 emission reduction due to wastewater heat pump use. The proposed procedure is implemented for the case study in the city of Šabac (Serbia) and obtained results are discussed and evaluated. The historical data for two heating seasons was used for simulation. It was shown that the wastewater heat pump could provide 27-28% savings in fuel consumption, and 3.6-4.1% GHG emissions reduction, while the seasonal COP could be 4.2 - 4.3. Simulation based approach shows approximately 40% less savings of fuel consumption, compared to the approach based on the average values of heat pump input parameters.

Due to its complexity and heterogeneity, the household sector represents an essential point in energy transition policies. In the European Union, household energy consumption accounts for about 26% of final energy consumption, while in Serbia, this sector has the largest share in final consumption, accounting for about one-third of final consumption. By implementing energy efficiency measures, significant energy savings can be achieved, which, together with the reduction and substitution of the use of fossil fuels, contribute to a lesser impact on climate change and significant reduction in air pollution. The package of legislative measures "Clean Energy for All Europeans" is a comprehensive set of laws defining European climate and energy policy after 2020. This package encompasses and links a series of topics related to the household sector. Through this package, member states are required to set high goals for energy efficiency and decarbonisation in the construction and revitalization of residential buildings, while simultaneously implementing measures concerning households affected by energy poverty. The Directive on the Energy Performance of Buildings, the Energy Efficiency Directive, the Renewable Energy Directive, the Regulation on the Governance of the Energy Union and Climate Action, and the Regulation on the Establishment of a Framework for Achieving Climate Neutrality cover the main issues related to energy transition policy in households in the European Union. As a member of the Energy Community and a candidate for membership in the European Union, Serbia has committed to harmonizing its energy policy and legislation, accepting technical assistance and support in implementing reforms to adapt the national energy system to European standards. The aim of this paper is to present the regulatory and strategic framework "Clean Energy for All Europeans" in the part related to the household sector and to analyse its transposition into key legal provisions dealing with this topic in the Republic of Serbia