R134a is currently the most widely used refrigerant, whose problem is the high value of the global warming potential, and which will have to be replaced in the near future. Thus far, R1234ze(E) has proven to be the most suitable alternative, but it is slightly flammable. Recently, R1336mzz(E) has emerged as a possible alternative. During the research, the mentioned refrigerants were compared with simulations using the Aspen Plus software package in the case of using groundwater as a heat source. It was found that R1336mzz(E) could be a suitable alternative to R134a since the highest value of coefficient of performance was obtained using it. However, it must be superheated with an internal heat exchanger. The problem with using an internal heat exchanger is that the superheating of the refrigerant vapors affects the isentropic efficiency of the heat pump compressor negatively and, consequently, lowers the COP value of the heat pump. It has been shown that a one percent decrease in isentropic efficiency results in a one percent decrease in the COP value.

This paper presents the conceptual design of a technological solution for the efficient conversion of food waste into heat and power. The distribution and composition of food loss and waste at different stages of the food supply chain in Slovenia and their potential for biogas production were determined. It was found that more than 50% of food waste comes from households. Therefore, a small plant was designed to convert food waste into biogas, which was innovatively coupled with a combined heat and power (CHP) unit and a heat pump. This doubles the amount of heat generated compared to conventional cogeneration. Based on the capacity of a micro commercial CHP unit, 3330 households (about 8000 residents) would supply food waste. The heat generated could replace 5% of the natural gas used for domestic water heating. The payback period would be 7.2 years at a heat price of about 80 EUR/MWh, however, for municipalities with more than 40,000 inhabitants the payback period would be reduced to less than 3 years. The cost price of the heat generated by this system would be about 25 EUR/MWh, taking into account the government subsidy for the operation of the CHP unit.

Food self-sufficiency is increasingly relevant to national food-system resilience, but higher domestic production can create competing economic, environmental, and resource trade-offs. This study develops an integrated optimization framework to evaluate product-specific self-sufficiency targets at the national agri-food-system level. The framework was applied to the Slovenian agri-food system by extending a national linear programming model with explicit self-sufficiency constraints and embedding the Agricultural Circularity and Sustainability (ACS) Index as a multidimensional objective function. Simultaneous and individual product-specific scenarios were analyzed, followed by Pareto analysis of the trade-off between aggregate food self-sufficiency and ACS performance. Product-specific responses differed markedly: vegetables provided the most favorable response in terms of ACS and net economic balance, potatoes showed smaller positive effects, wheat yielded only marginal ACS gains, and higher pork self-sufficiency reduced both ACS and economic performance. The Pareto frontier revealed increasing ACS losses as self-sufficiency approached its maximum feasible level, with a balanced compromise identified at 94.5% aggregate self-sufficiency. Alternative Pareto-efficient solutions required substantially different land use, livestock, feed, and trade configurations. The framework supports decision makers in evaluating self-sufficiency targets together with their broader system-wide consequences.

This study develops the Agriculture Circularity and Sustainability (ACS) Index, a composite framework for assessing and monitoring circularity and sustainability of agricultural systems at the national level. The framework integrates environmental, societal, economic, and food waste categories and enables systematic comparison across EU Member States using publicly available Eurostat and FAOSTAT data. Indicators were selected based on relevance to the Farm to Fork Strategy, data availability, and cross-country comparability. The analysis covers the period 2020-2023, with overall data completeness exceeding 97 %.The results revealed substantial differences among EU agricultural systems. Higher ACS Index values were primarily associated with balanced performance across multiple sustainability categories rather than strong performance in a single category. Spain, Austria, and Slovenia achieved the highest overall scores, whereas several intensive and export-oriented systems showed trade-offs between economic performance and environmental or food waste outcomes. Countries with stronger food self-sufficiency generally achieved higher societal sustainability scores, while smaller and import-dependent systems were constrained by limited domestic production capacity and greater dependence on external food supply.Temporal analysis showed that the highest- and lowest-performing country groups remained relatively stable over the study period. Sensitivity analysis further confirmed that alternative weighting and indicator-selection assumptions influenced some ranking positions, particularly among mid-ranked countries, but did not alter the overall interpretation of country performance. The ACS Index provides a transparent, reproducible, and sensitivity-tested framework for comparative assessment and monitoring of circularity and sustainability transitions in EU agri-food systems.