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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.

In the following years and decades the increase in cooling capacity will put tremendous pressure on the energy infrastructure and severely increase the environmental impacts. In a moderate climate and well thermally insulated buildings like, e.g., in Europe, installation of low-exergy radiant systems could help alleviate these negative effects. Wall systems may be especially suitable for installation in existing buildings, however, their possible applications in buildings retrofit have not been fully explored. We therefore investigate the possible applications of wall cooling in existing buildings by numerical simulations of two-dimension heat flow through a wall fragment. Three wall systems are proposed and compared in terms of thermal response and heat transfer. The effect of various parameters is investigated to facilitate the design of the wall systems.

Radiant systems are being increasingly used for space heating and cooling of buildings. The contemporary research of radiant systems addresses mainly floor and ceiling structures. Research regarding the possibilities of their incorporation in wall structures is lacking, despite their potential advantages. This study addresses a radiant wall system manufactured according to a patent. The patented design involves panels that consist of pipes arranged in milled channels in thermal insulation. The potential advantage of this system is the fact that the thermally active panels can be attached to the facades of existing buildings as a part of their retrofit. Thereby, only minor interventions on the interior side of the retrofitted buildings are needed. To test and improve the design of the wall system, laboratory measurements and computer simulations were performed on a wall fragment for its operation under summer conditions. The results indicate a significant potential for improvement of the patented design by addressing the imperfections in the contact between pipe and wall. Inserting a metal fin between pipe and wall enhanced the cool distribution within the wall fragment considerably. From the three materials of the metal fin considered, using copper led to highest values of the cooling output, followed by aluminium. For these two metals the effect of increasing the thickness of the fin on the cooling output was small. On the contrary, the fin made of steel was the least efficient in terms of cool distribution. In this case the cooling output was most sensitive to the thickness of the fin.

The analyzed topic belongs to the field of design and operation of HVAC systems, focusing mainly on mixing chambers. The paper deals with problems of condensation and freezing of water vapour on walls of mixing chambers in a special case, when the partial pressure of the final resulting state of the mixture of warm moist air and colder air is located above the saturation limit. Experimental in situ methods and computer computational fluid dynamics (CFD) modelling method were used for processing. The main contribution of this work is the finding that partial condensation and freezing of water vapour may occur in local parts of the mixing chamber. It causes problems in terms of hygienic safety and service life of these devices. In particular it has been found that condensation and freezing of water vapour may occur even if relative humidity of the resulting mixture is about 70 %.

This paper presents and discusses the results of the transient numerical simulation carried out for an isolated main rotor model and a helicopter in vertical descent autorotation by developing the 6-degree of freedom, rigid-body equations of helicopter motion. The Unsteady Reynolds Averaged Navier-Stokes model is used to simulate the unsteady flow field surrounding four-bladed BO-105 isolated main rotor and complete helicopter which includes the fuselage and the tail rotor. The principal autorotation characteristics for the helicopter such as induced velocity, rate of descent, main rotor angular speed, thrust and torque have been calculated. The simulation results show the creation of a spanwise flow on the upper surface of the blade, and moving fluid in the direction of the blade tip in a region downstream and beneath the leading edge vortex. The aerodynamic characteristics on the complete helicopter are similar to the ones attained for the isolated rotor simulation. [ABSTRACT FROM AUTHOR]

This paper is divided into two parts; the first describes a CFD analysis of a gland packing labyrinth seals in 20 MW steam turbine in LNG plant using ANSYS CFX code as an isothermal simulation in fluid domain. The results of two turbulence models k-ε and k-ω SST are compared and validated against experimental data. It is shown that the labyrinth seal leakage is proportional to the clearance cube so any variation in clearance can have a significant impact on the steam leakage. This clearance between the shaft and the labyrinth seal vary as a function of operating temperature due to the different rates of thermal expansion of the materials for these two components. Likewise the fluid temperature has a direct effect on fluid dynamic behavior. For that; the second part of the paper investigates the effect of fluid thermal conditions of the labyrinth seal via the heat transfer and Nusselt number variation in the stator and the rotor, for different cases of inlet temperature (400 °C, 200 °C, 100 °C, 50 °C) and pressure ratio (2.5, 4.5, 6.5) for an ideal gas. Also it is important to know the temperature distribution across tooth and cavities of the labyrinth seal, and finally the Influence of Inlet total temperature on fluid pressure drop in the labyrinth seal will be treated for improving and readjusting the steam turbine sealing system. [ABSTRACT FROM AUTHOR]

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]