Ústav technických zařízení budov
Browse
Recent Submissions
Now showing 1 - 5 of 45
- ItemMould Risk in Technical Room in Four Underground Water Reservoirs(IOP Publishing, 2024-07-08) Nováková, Iva; Šikula, OndřejThis conference article analyses the indoor climate of a technical room in four underground water reservoirs. This indoor climate with minimal input energy is specific by high relative humidity and low air temperature, as shown in the experimental measurement. The unsteady 2D numerical simulation of the detail section (partly sub-terrain peripheral wall and floor) in software Calculation Area 4.0e calculates fluctuation of internal surface temperature and relative humidity. Finally, the empirical predictive Finnish VVT model predicts the seasonal mould risk on the internal surface of the peripheral wall.
- ItemAssessment of the Influence of Input Parameters in CFD Simulation of Ventilation in an Experimental Chamber(IOP Publishing, 2024-07-08) Kučírek, Pavel; Šikula, OndřejThe aim of this paper is to evaluate the impact of selected input parameters on the accuracy and usability of CFD simulations. This paper compares the achieved results of Computational Fluid Dynamics (hereinafter CFD) simulations of air age with the ventilation results of a specific experimental box. A total of 16 variants were simulated for different simulation settings, including various computational domains and meshes in OpenFOAM, Ansys Fluent, DesignBuilder, and BlueCFD-AIR software. The paper primarily focuses on the importance of meeting the suitability criterion for the yPlus parameter used in the wall function of turbulent models k- and k- SST, and the resulting air age. Simulation with the best yPlus parameter shows the best agreement in airflow velocity and air age with the experiment. Overall, this led to an improvement in accuracy by 41 % compared to original simulation and 56 % compared to the previous our best OpenFOAM simulation.
- ItemHybrid Roof Panels for Night Cooling and Solar Energy Utilization in Buildings(Elsevier, 2015-08-28) Šikula, Ondřej; Vojkůvková, Petra; Šíma, Jiří; Plášek, Josef; Gebauer, GünterThe aim of this contribution is to evaluate the usability of solar hybrid panels, which were originally optimized for heat load removal from buildings by radiation against the night sky, for water preheating. First we created a surrogate model based on CFD simulations defining performance of the panel dependent on changing boundary conditions. This model was then implemented to the water heating model created in TRNSYS software. Estimated hot water usage would suffice for operation of 2 restaurant facilities in a building of our interest. Subsequent simulations were carried out using reference year climate data for Brno (Central Europe). Results demonstrated that in the given conditions, the average annual efficiency of solar energy usage is 55%. The results also showed that the system is able to cover approximately 7% of the heat demand for water heating.
- ItemExperimental and numerical study of turbulent flow around a Fanwings profile(Taylor & Francis Group, 2019-07-20) BENFERHAT, Slimane; Tayeb, Yahiaoui; IMINE, Bachir; Ladjedel, Omar; Šikula, OndřejThe 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°<<+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.
- ItemHeat storage efficiency and effective thermal output: Indicators of thermal response and output of radiant heating and cooling systems(Elsevier, 2020-12-15) Krajčík, Michal; Šikula, OndřejAn alternative indicator of thermal response of radiant heating and cooling systems called heat storage efficiency (HSE) has been tested. The heat storage efficiency was compared with established indicators represented by the time constant tau(63), response time tau(95), and thermal energy stored (TES). The comparison was performed for three wall cooling systems with various combinations of pipe location, configuration of material layers, and materials of the thermal core. Considering the whole response curve (HSE) instead of focusing on one specific point on the curve (tau(63), tau(95)) allowed comparing the thermal response of complex systems by a single value. It also permitted predicting thermal response consistently regardless of the system and core material. Thermal energy stored predicted the thermal response of certain systems, but it may not be suitable for comparing the thermal response of radiant systems with different thermal admittance. Besides, a novel indicator of thermal output called effective thermal output (ETO) has been proposed. The effective thermal output considers both the steady-state thermal performance represented by the nominal thermal output and dynamic thermal performance represented by the heat storage efficiency. For thermally active building systems (TABS), effective thermal output was up to 57% lower than the nominal thermal output. (C) 2020 Elsevier B.V. All rights reserved.