In numerical modeling of swirl diffusers, simplifying the diffuser geometry can substantially reduce simulation costs. This study describes the development and performance evaluation of simplified computational fluid dynamics (CFD) models of a swirl diffuser by using 2D particle image velocimetry (PIV). Two simplified models were created by replacing the diffuser with simple supply openings, where momentums were prescribed. The first model defined momentums solely based on geometric rules. In the second, it was demonstrated how the accuracy of the first, geometry-based model, can be improved by adjusting the momentums using results from a detailed CFD model. The effect of using the Reynolds stress model or the SST k-ω turbulence model on the accuracy of the CFD model and computation time was investigated. The simplified models were benchmarked against both the detailed CFD model and the PIV measurements. The corrected simplified geometry combined with the SST k-ω turbulence model achieved a favorable balance between reliability and computational efficiency. Although the two-dimensional nature of the PIV measurements presented challenges for three-dimensional CFD validation, they proved valuable for developing and assessing the simplified models.

Large low-rise industrial halls offer extensive roof areas for adding vegetated roof assemblies (VRAs) as part of reconstruction. However, existing structures often require lightweight VRAs to avoid overloading. To assess the wind resistance of such lightweight systems, atmospheric boundary layer simulations were conducted in OpenFOAM using Reynolds-Averaged Navier-Stokes approach for a cuboid industrial hall in a low-density built environment, representative of many industrial facilities worldwide. Additional roof geometries and adjoining-building cases were analysed to cover configurations not addressed in prior studies. Compared with a simple cuboid, a combined cuboid-bevel geometry experienced notably higher roof underpressure. The presence of an adjoining building further intensified corner-zone suction, increasing peak local suction from-608 Pa to-830 Pa (37%). For an extreme air velocity of 43.1 m/s recorded at the Brno (Czech Republic) meteorological station, the computed pressures were compared with the European standard for wind actions on structures. The peak suction reached approximately-4 kPa at the roof corner for a 45 degrees wind direction, about twice the allowable limit for components with effective area <= 1 m2, indicating that perpendicular-wind (0 degrees) analyses may underestimate the risk for modular systems. The results have implications for the long-term green-roof performance, because wind-induced uplift or substrate displacement can alter VRA thermal behaviour; maintaining aerodynamic stability is therefore essential to sustain the intended thermal performance. The findings highlight potential failure mechanisms, particularly in unanchored lightweight VRAs, and support more resilient green-roof design and standards for industrial buildings.

This article assesses the indoor environment and thermal comfort in a kindergarten. It is a case study involving experimental measurements and a simulation analysis. During the winter period, experimental measurements were conducted in one of the kindergarten classrooms, collecting data such as indoor air temperature, relative humidity, and carbon dioxide concentration. Based on these data and operational records of the classroom during the measurement period, a model was developed in the DesignBuilder software. This model was utilized to perform an energy simulation followed by a Computational Fluid Dynamics (CFD) simulation. The model was calibrated to closely match the measured data. The output is a qualitative spatial distribution of thermal comfort parameters. The simulations and experiments conducted reveal an unfavourable indoor environment in terms of the thermal comfort and may serve as a basis for designing a more suitable method of room ventilation.

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-epsilon 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.

This conference article aims at the indoor climate in the technical room of an underground water reservoir. This indoor climate is specific by high relative humidity (average 75.2% r.h.) and low air temperature (average 13.6 °C). Therefore, this research study focuses on surface condensation and mould risk on the partly underground wall in the technical room. The experimental research combines long-term monitoring (22 months). Long-term of indoor climate and thermal numerical simulation. The experimental measurement shows condensation risk on the indoor wall surface, and the unsteady 2D numerical simulation in software Calculation Area 4.0e shows temperature fluctuation on indoor wall surfaces. Finally, the empirical VVT model predicts mould risk on the indoor wall surface for the over-terrain part in autumn and summer for the under-terrain part.

Simulation modelling of heat and mass transfer processes is conducted in the case of a special type of a building integrated photovoltaic (BiPV) façade system with latent thermal energy storage (LTES) based on a phase change material (PCM). Experimental and simulation models are developed as part of the ventilated façade system for it to analyze and verify the adequacy of the available simulation tools. The key aspect of a BiPV/PCM façade concept is focused on reducing the peak operating temperatures of the PV modules and affecting action-reaction processes involving heat and mass transfer changes inside the façade elements. Experimental measurements were performed using an outdoor test cell to verify and validate numerical models. A comparative investigation of two façade concepts (BiPV, BiPV/PCM) is conducted using two simulation domains: the BES method (EnergyPlus) and the numerical CFD method (Ansys). The heat transfer rate through all façade elements is influenced by the high thermal inertia of the PCM differently in the diurnal/nocturnal period. The dynamic thermal response function of this façade system changes concerning the climate conditions at a small timescale (reactivity). The experimental measurements and simulation results are compared for it to provide an insight into consistency between the theoretical results and the experimental data. However, this indicates several limitations that need to be properly identified for further design.

A numerical study was carried out for heat transfer in flow past four cylinders in in-line square arrangement with a pitch-to-diameter ratio L/D = 4.2. Computational fluid dynamics (CFD) computations were performed for Reynolds numbers of 9300 and 20,000 to investigate passive control using a rectangular splitter plate placed on the rear side of the cylinders. Three different configurations were considered: the first one contains only smooth cylinders, the second uses cylinders equipped with splitter plate in the upstream row, and the third configuration where all cylinders have a splitter plate. The steady-state Reynolds-averaged Navier-Stokes equations were solved using a finite volume method, where the k-ω SST turbulence model was used to produce a closed system of solvable equations. Results of the simulations in terms of temperature and Nusselt number distributions for all cylinders are presented and compared. The effect of new configurations on the heat transfer is well demonstrated, where a drop of about 7.92% in Nusselt number is reported using the splitter plate.

Ventilated building-integrated photovoltaic (BiPV)/phase-change material (PCM) facades have been applied and validated in building energy simulations; however, the dynamic thermal response of these facades has not been investigated. Notably, performance predictions and simulations for systems featur-ing natural airflows in the facade cavity are important for guiding the decision-making for energy-efficient buildings. To address this challenge in literature, in this work, numerical analyses were con-ducted, focusing on the climate adaptive reactions of a BiPV facade system coupled with a latent thermal energy storage system, based on a PCM. Numerical methods for determining the PCM heat transfer were evaluated, including their limitations. The thermodynamic reactions of two BiPV facade concepts were comparatively studied using two simulation domains: building energy simulations and computational fluid dynamics. The reliability of the theoretical methods was also evaluated. Good agreement between the simulation results and experimental data was noted through dynamic outdoor tests, empirically val-idating the study; standard statistical indicators were calculated and employed to assess the consistency between the experimental and simulation results. The used numerical approach can reliably predict the thermo-responsive capabilities of PCM-based BiPV facades with respect to the overall tendencies. The parameter variation techniques revealed modifications in the overall thermal and energy performance of the facade system. The most undesirable instance of overheating was predicted when using RT27; therefore, the PCM is considered inappropriate in this case. (c) 2022 Elsevier B.V. All rights reserved.

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.

This paper presents the results of an investigation on the effects of wavy cylindrical tubes on the turbulent cross-flow in a staggered tube bundle arrangement with transverse and longitudinal pitch-to-diameter ratios of 3.8 and 2.1, respectively. Two models of staggered tube bundles equipped with wavy cylinders are tested; the Model-A having a wavelength ratio (λ/DSUBm/SUB= 2) corresponding to a wave steepness (a/λ = 0.1) and the Model-B having (λ/DSUBm/SUB= 1) corresponding to (a/λ= 0.2).Experimental measurements were performed using a subsonic wind tunnel to study and compare the flow characteristics of the new configuration of cylindrical tubes with that of a similar arrangement with smooth cylinders for Reynolds numbers ranging from 0.5×10⁴ to 2×10⁴ based on the mean tube diameter and the free stream velocity. Experimental results show that the circumferential minimum pressure coefficients for wavy tube bundles are greater than at the bundle with smooth cylinders. As a result, the lift forces of wavy tube bundles are suppressed and a significant drag reduction is observed up to 20% for both wavy models. This continuous reduction of the drag force becomes larger with the increase of Reynolds number.

The application of radiant heating and cooling systems in building retrofit could facilitate the use of renewable energy sources in existing buildings. This research focused on adapting the design of a ceiling and wall system with pipes underneath the surface and a wall system with the pipe embedded in a bricklayer. These systems are suitable for installation in retrofitted rooms, but the findings are also applicable to new buildings. Heat transfer was computed using a validated numerical model. With a conductive core, insulation thickness of up to 3 cm was appropriate for an internal wall. With an insulating core, insulation was not necessary even if the core was only 15 cm thin. The increase in output per 1 cm of pipe spacing was maximal at 6 cm. Spacing below 3 cm was inefficient. A dense spacing maximized the system output per energy input by creating a uniform surface temperature, while also shortening the response time. Attaching a metal fin to a pipe in plaster increased the output by as much as reducing the pipe spacing from 10 to 6 cm (14 M-2, i.e. 20%). Attaching a metal fin to a pipe embedded in insulation for a compact design led to the highest output of all cases studied. Placing the pipe in a brick layer added to a conductive wall did not increase the heat storage capacity of the wall. (C) 2022 Elsevier B.V. All rights reserved.

AbstraktSúčasným trendom je znižovanie energetickej náročnosti budov využívaním alternatívnych zdrojov vykurovania a chladenia.Jedným z najperspektívnejších a zdrojov vykurovania a chladenia je využitie energie zeme pomocou tepelne aktivovaných základových pilót budovy, takzvaných energetických pilót.Príspevok sa zaoberá prehľadom a porovnaním analytických modelov energetických pilót.Jednotlivé analytické modely sú porovnávané

Thermal baths in Slovakia produce waste pool water, which is most often discharged to the water recipient. Cooling of waste pool water is ensured by means of cooling ponds or canals. However, cooling the water from the pool is not sufficient. Therefore, thermal bath operators face sanctions for environmental pollution. The possibility of ensuring the maximum temperature of waste pool water is by means of a heat recovery system, which will be presented in the article. If it is not possible to apply a heat recovery system, it is necessary to ensure sufficient cooling of the water in another way. Another possibility of increasing the cooling of wastewater is to ensure a sufficient evaporate area which has a great effect on water cooling. Another crucial parameter that affects the cooling of wastewater is the speed of air flow above the water surface. The article is focused on influence of air flow rate and evaporation surface on cooling of waste pool water produced by thermal baths and briefly introduces another wastewater cooling option, which is a heat recovery system. The results presented in the article indicate a significant impact of the evaporation area on the heat flow through the evaporation.

Steam jet ejector chillers (SJECs) can be a suitable cooling technology in buildings where solar heat gains constitute a significant part of the cooling load. In this study, an SJEC was combined with a radiant chilled ceiling (CC) instead of traditionally used convective cooling terminals in an effort to increase the coefficient of performance (COP) by increasing the supply water temperature to the terminal (T-water,T-sup) and thus the evaporation temperature. Experiments were used to verify a mathematical model of SJEC. The model was combined with T-water,T- sup obtained from heat transfer calculations in three types of CC performed by a verified software. The COP of the ejector cooling system was 0.25 and 0.38 for R718 (water) and R1233zd, respectively, at a generation temperature of 130 degrees C and T-water,T- sup of 7 degrees C, assuming a fancoil. Increasing T-water,T- sup to 9 degrees C, which was considered to be the lowest T-water,T- sup theoretically possible for CC involving pipes underneath the surface, improved COP by up to 14% while providing a maximum cooling capacity of about 80 W per m(2) of room area. Further increasing T-water,T- sup to 15 degrees C improved the COP by 50% compared to the fancoil, while covering cooling loads of at least 40 W per m(2). The estimated reduction in generation temperatures due to increased COP was up to 12% (T-water,T- sup = 9 degrees C) and 37% (T-water,T- sup = 15 degrees C). This means a lower energy input needed for the cooling machine, which allows a smaller solar collector area.

This study reviews water-based wall systems for space heating and cooling and thermal barriers (TB) for the reduction of buildings' thermal load. The review gives a general overview of the research and groups it into subtopics that are discussed in detail. For space heating and cooling, the subtopics entail thermal performance, thermal comfort, renewable energy sources, use for building retrofit, and combination with phase change materials (PCM). For TB, especially the working principle, types and designs, and performance are discussed. A classification system is proposed separately for wall heating and cooling systems and TB based on the designs found in scientific literature. Benefits and drawbacks are summarized, and design recommendations are provided for the wall systems. It was shown that in certain cases, radiant wall systems can be preferable to radiant floors and ceilings, but further comparisons would be useful to provide conclusive evidence. For TB, the studies uniformly declare that TB reduce buildings' thermal loads and energy demands. Few studies focused on the economic and environmental aspects of using TB. Most of the studies about TB are based on calculations. Measurements to quantify the benefits of TB under real operation and refine the conditions under which various types of TB are feasible are lacking. Enhancing the wall performance by PCM in the active layer, application of the wall systems in building retrofit, and alternating between the functions of heating, cooling, and TB present the biggest research opportunities and challenges. (c) 2021 Elsevier B.V. All rights reserved.

A radiant wall heating and cooling system with pipes attached to thermally insulating bricks was tested using climate chambers and a hotbox. This system is especially suitable for building retrofit due to its affordability and ease of installation but can be also applied in new buildings. Besides walls, the design tested can be also used for ceilings. Thermal output and response, wall surface and cross-section temperature, and water temperature were measured under a range of thermal loads. The thermal response was fast despite the coupling of the pipe with the bricks; the time constant tau(63) was 0.5 h. The low conductivity core substantially reduced thermal losses meaning that the system can properly function even without thermal insulation. These qualities may present an advantage compared to systems with pipes coupled to a conductive core which require insulation and have longer response times. The difference between water and average surface temperature was small, up to 7.0 degrees C at the peak output of 100 W/m(2), which benefits the energy source efficiency. However, the surface temperature was nonuniform, which should be considered to prevent local condensation. Numerical simulations at room level showed that locating the system at one wall leads to a non-homogeneous thermal environment. Installation at multiple walls can be preferable to attain more uniform conditions. (C) 2021 Elsevier B.V. All rights reserved.

Holistic comparisons of radiant heating systems that would help make an informed decision on the selection of the most convenient system for the specific application are lacking. The applicability of six representative radiant floor, wall, and ceiling heating systems was therefore compared in terms of thermal output and surface area required, controllability, short-term and long-term heat storage, suitability for building retrofit, and investments. Temperature and heat flux distribution in the structure, time constant τ63, response time τ90, and the number of operating cycles were computed by a custom-made and verified software tool using the finite volume method. Thermal energy stored was used to determine the ability of energy storage, whereas investment costs indicated affordability. Wall heating with pipes attached to a thermally insulating core had the highest thermal output, was easy to control, suitable for building retrofit, and most affordable while providing limited thermal storage. The performance of the wall system was retained when locating the pipes in plasterboard separated from the core by an air gap. Floor heating performed consistently in all the aspects evaluated. It was demonstrated that inserting a metal fin between pipes and the concrete spread layer improved thermal output, controllability, and storage capacity of the floor system with minor effect on investments. Ceiling with pipes insulated from the core performed well when thermal storage was not required. Ceiling with pipes embedded in the core was only feasible when long-term heat storage was needed.

Equipping the foundation piles with a liquid circuit pipeline makes it possible to use the advantageous ther-mal capacity of the soil for heating and cooling buildings at low cost. The energy performance of the energy-pile in a soil is a transient phenomenon dependent on many parameters, which could be investigate by a computational model. The contribution deals with the description and verification of a new numerical computational software based on a simplified 2D and 2D rotational symmetrical heat conduction model being developed for energy-piles modeling.

Polycarbonate panels are a specific type of transparent insulation material that can be usefully integrated in building envelope structures. As the applications for such systems are increasing, it was necessary to analyse in detail data for materials which are already available to improve their thermal performance. In this paper the experimental campaign was based on the detailed characterization of the equivalent thermal conductivity parameters of several representative polycarbonate panels. The dependence of the equivalent thermal conductivity on the temperature and different angles of inclination are analyzed. Increasing the angle of the investigated polycarbonate panels changed the thermal conductivity parameters to a very minor degree. On the other hand, the effect of temperature on the thermal properties is proved to be significant and the conversion temperature coefficient is provided in this regard. The computational fluid dynamics (CFD) numerical analysis is employed to validate three-dimensional CFD models and simulate the thermal performance of low-e panels for it to theoretically improve their overall thermal parameters. When applying low-e functionality, depending on the type of polycarbonate panel, the equivalent thermal conductivity was found to range from 0.03750 W/(m.K) to 0.04172 W/(m.K), representing a reduction ranging from 43% to 24%.

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.