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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.

In this paper, a new configuration of a horizontal axis wind turbine with three blades for domestic electricity production on farms was numerically simulated. Three configurations were tested numerically: a standard single-blade wind turbine (STWT), a single wind turbine (SWT), and a tandem three-blade wind turbine (TWT) for rural use. For the tandem wind turbine, the effects of pitch angle and the distance between the blades were also investigated. The Gambit and Fluent 19.2 codes were, respectively, used to generate different meshes and determine various parameters. The resolution of the averaged Navier–Stokes equations (RANS) using a finite volume method was conducted. The k–ε realizable two-equation model was chosen for turbulence calculation. The obtained results showed that the maximum power coefficient (Cp) was 0.444 for one of the tandem configurations (TWT), compared to the conventional blade (STWT). The maximum Cp obtained in this study is slightly greater than the experimental results found in the literature. It has also been observed that the flow on these new turbines exhibits a complex phenomenon on both surfaces. [ABSTRACT FROM AUTHOR]