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This study is focused on the feasibility of using energy performance contracting (EPC) for the retrofit of two apartment buildings constructed using precast concrete technologies in Slovakia decades ago. The retrofit packages were defined, and their suitability for EPC was evaluated through discounted payback. The uncertainties in the profitability calculations were covered by designing five possible economic developments and defining input ranges instead of just single inputs. The measures in the technical systems were shown to be more feasible than the retrofit of the building envelopes. The potential to finance the selected measures for technical systems through EPC was further evaluated. It was shown that, for at least one of the two buildings studied, the EPC was recommended only for the economic developments with a notable increase in energy prices compared to the baseline that referred to the situation before the Covid-19 pandemic. In the best case, the payback was four years for one building and seven years for the other; thus, both were potentially suitable for EPC. However, for a complex retrofit, the EPC must be combined with a different funding source to also finance other retrofit measures.

A current trend is to reduce the energy performance of buildings by using alternative sources for heating and cooling. One of the most promising, and so far unprecedented sources of heating and cooling, is the use of energy from the earth using the thermally-activated foundation piles of a building, the so-called energy piles. The paper deals with an overview and comparison of computer-aided analytical models of energy piles. The individual analytical models are compared (categorized) from the point of view of their physical complexity, computational costs, and thus their usability for the purpose of optimizing energy-pile equipment or assessing the long-term energy efficiency of an energy pile field. Selected mathematical models were algorithmized, and the results obtained were compared with a more robust numerical solution performed using CalA 4 software.

The topic of the contribution can be included in computer modeling of the thermal behavior of radiators for heating of buildings. Control of heaters leads to dynamic phenomena affecting the final thermal state of the heated room and heating energy consumption. The paper focuses on modeling of radiator quantitative control method using thermostatic valve. The objective of the paper is to show a quality of controlling and to compare an energy consumption when various thermostatic radiator valves time delay are set. The models of control, radiator, and a room are implemented in software TRNSYS. The results show significant differences in energy consumption.

ABSTRACTThe main objective of this paper is an experimental and numerical study of airflow on a propulsive wing also called ventilated wing or FANWING, which is a drone operating at low speed. To optimize the aerodynamic shape of the Fanwing, two different configurations of NACA4415 rectangular wing profile were realized. The first one is a wing where the Cross-Flow Fan is fitted directly to the leading edge with a classic niche. For the second one, we truncated the extension of the niche to create a profile without nose. Two flow velocities with constant fan rotation were used and observed in the range of −16° < α < +30°. A lift coefficient generated by the profiles increases and the drag coefficient decreases, while the distribution of the pressure coefficient on the upper surface increases abruptly because of the flow recirculation. The experiment was performed in a subsonic wind tunnel TE44 and numerical simulations in software Fluent 6.3.2.6. Both approaches are in good agreement. The visualization showed that the recirculation phenomenon occurs right after the discharge of the cross-flow fan. It reveals that the jet coming out of the fan causes a strong wake behind the profile and suppresses the boundary layer separation.

During the cooking process, pollutant fumes are released into the ambient air by the convection plumes. These convective plumes - thermal plumes – are generated above hot surfaces and they need to be efficiently and ecologically ventilated in order to achieve appropriate internal climate. Calculation method for determination of volume flow rate of rising convective plumes is described in German standard DIN 18869 [1]. This article focuses on study of thermal plumes using numerical model in software Ansys Fluent, determinates volume flow rate of rising air and compares the simulation results with the results from known computational relations.