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We used large-eddy simulation (LES) to numerically simulate two differently driven indoor airflows occurring in a multizone environment. In the first case, air flowed from one zone to another through a small hole driven by the total pressure difference. In the second case, unbalanced airflows arose from the buoyancy effect, which was generated by a heat source present in a specific location. To validate the LES prediction for the indoor flow analysis, we compared our simulation results with the chamber facility experimental results and other simulation results. Based on this validation, we confirmed that the LES reliably simulates indoor airflow. In addition, we discussed the flow characteristics and investigated the feasibility of modeling the flow rate through openings using an orifice formula. [ABSTRACT FROM AUTHOR]

In order to evaluate an indoor airflow, which may cause the spread of viruses, it is effective to measure the speed and direction of the airflow using several accurately evaluated anemometers. However, since calibration of anemometers is a time-consuming task, so the authors developed a compact wind tunnel that can evaluate the accuracy of anemometers in a short amount of time. The design concept and performance of the wind tunnel are described by several indices, including averaging time, settling time, spatial distribution, and blockage effect. These results demonstrate the capability of the wind tunnel to evaluate several anemometers in a short measurement time with sufficiently high precision. [ABSTRACT FROM AUTHOR]

Prediction of indoor airflow distribution often relies on high-fidelity, computationally intensive computational fluid dynamics (CFD) simulations. Artificial intelligence (AI) models trained by CFD data can be used for fast and accurate prediction of indoor airflow, but current methods have limitations, such as only predicting limited outputs rather than the entire flow field. Furthermore, conventional AI models are not always designed to predict different outputs based on a continuous input range, and instead make predictions for one or a few discrete inputs. This work addresses these gaps using a conditional generative adversarial network (CGAN) model approach, which is inspired by current state-of-the-art AI for synthetic image generation. We create a new Boundary Condition CGAN (BC-CGAN) model by extending the original CGAN model to generate 2D airflow distribution images based on a continuous input parameter, such as a boundary condition. Additionally, we design a novel feature-driven algorithm to strategically generate training data, with the goal of minimizing the amount of computationally expensive data while ensuring training quality of the AI model. The BC-CGAN model is evaluated for two benchmark airflow cases: an isothermal lid-driven cavity flow and a non-isothermal mixed convection flow with a heated box. We also investigate the performance of the BC-CGAN models when training is stopped based on different levels of validation error criteria. The results show that the trained BC-CGAN model can predict the 2D distribution of velocity and temperature with less than 5% relative error and up to about 75,000 times faster when compared to reference CFD simulations. The proposed feature-driven algorithm shows potential for reducing the amount of data and epochs required to train the AI models while maintaining prediction accuracy, particularly when the flow changes non-linearly with respect to an input. [ABSTRACT FROM AUTHOR]

Few studies have considered using artificial neural networks to predict the temperature distribution inside a room with a heat source, even though such an approach is potentially much faster than numerical analysis. In this study, a multilayer perceptron (MLP) model was developed and applied to predicting the temperature distribution in a room with a heat source, where the input variables were the x- and y-coordinates and the distances from the bottom of the wall to the airflow inlet and outlet. The MLP model was trained and evaluated to optimize the hyperparameters (i.e., batch size, node, learning rate, and number of layers) for the prediction accuracy. When compared with a computational fluid dynamics (CFD) simulation, the MLP model showed comparable prediction accuracy, but the computational time was about 11 s compared with 27 min for the CFD simulation. Thus, the MLP model can predict the temperature distribution in a room with an internal heat source with high accuracy and very low computational cost. [ABSTRACT FROM AUTHOR]

The COVID-19 pandemic has changed the way of living of many people across the planet. In the beginning of the pandemic, when the strict lockdown was implemented, numbers of individual were encouraged to work from home. In the city living, high rise living was apparent and became a global phenomenon. This paper evaluates natural ventilation performances of existing apartment units in Jakarta, Indonesia by measuring the indoor temperature, indoor airflow and relative humidity. This research studied three different apartment units in Jakarta in the form of single-sided ventilation or cross ventilation. This study conducted by field test measurement on three different apartment units across Jakarta with various natural ventilation strategy and room volume. Statistical analysis was carried out to investigate the relationship and influence between the results of field test measurement and external weather data collected from ERA5. The results of the analysis suggested that external weather influence the indoor air condition, especially indoor temperature where significant influence was apparent. Furthermore, the field test data measurement in this paper contributed to validation study in predicting indoor airflow. [ABSTRACT FROM AUTHOR]

This study employs Computational Fluid Dynamics (CFD) to assess the impact of various ventilation configurations on respiratory droplet dispersion in a two-story restaurant building, aiming to reduce airborne infection transmission. A total of 24 scenarios, involving three ventilation configurations and eight individuals as potential droplet sources, are studied. The configurations— Case A , Case B , and Case C —are analyzed for their effectiveness in controlling droplet dispersion and improving air exchange effectiveness (AEE). Case B , with an outlet near occupants and an inlet above the zone separation, proved most effective in minimizing the droplet transmission between floors, reducing suspended airborne droplets on each floor, and preventing surface contamination, thereby enhancing indoor air quality. Despite the positioning inlet and outlet vents near crowded areas, Case A falls short in effectively removing droplets due to the intricate airflow patterns caused by air diffusers. Case C showed larger AEE but was less effective in droplet dispersion control, indicating a crucial balance between optimizing air circulation and limiting pathogen dispersion is needed. The findings underscore the importance of strategic ventilation design in mitigating airborne infection transmission in multi-level buildings. An optimal configuration, as demonstrated by Case B , combines efficient air distribution with strategic placement of ventilation components to create barriers against interzonal droplet transmission. This study highlights the potential of targeted ventilation strategies to significantly reduce the risk of airborne infection in enclosed, populated spaces. • Study evaluates interzonal droplets dispersion, AOA and AEE in two-story building. • 24 scenarios assesse various ventilation configurations and patient positions. • Case C has adverse effect on interzonal spread of droplets but increases AEE. • Case B excels in limiting interzonal droplets spread. • Case A negatively impacts both interzonal droplets dispersion and AEE. [ABSTRACT FROM AUTHOR]

The effects of walking speed, crowd density and human-to-source distance on pollutant dispersion in two scaled room models are investigated using simultaneous planar laser-induced fluorescence and particle-image velocimetry techniques. For a small 3 m high room, where the length-scales of the people and room are comparable, the walking motions significantly influenced the macro room mean flow patterns. This has a strong effect on the scalar dispersion properties as the magnitudes of the advective scalar fluxes are often comparable or larger than the turbulent scalar fluxes. As such, the scalar dispersion properties are case specific. For a large 9 m high room, the walking motion influenced only the local mean flow field. The increase in walking speed and crowd density improves the efficiency in which the scalar is transported and mixed with fresh ambient fluid out of the measurement plane (i.e. along the direction of the motion), leading to scalar-free zones observed on the opposite side of the room from the ventilation outlet. The area of the scalar-free zone increases with an increase in the walking speed and crowd density. The advective scalar fluxes are more sensitive to the human motion than the turbulent components, and as the mixing efficiency improves, the advective fluxes show a greater weakening with increased distance from source. The concentration PDFs in the near-source region can be described by the exponential function where the expected value at the 99% percentile can be derived as C 99 / c r m s ′ =4.61, which agreed well with the experimental measurements of 4.1 to 5.9. • Advective and turbulent scalar flux maps reveal underlying transport mechanism • Crowd effects can induce non-uniform and anisotropic scalar mixing • Scalar-free zone observed on the opposite side of the room from ventilation outlet • Dispersion patterns in small rooms are case specific due to non-linear interactions [ABSTRACT FROM AUTHOR]

This paper presents wind-tunnel experiments of cross-ventilative cooling in a generic isolated building with an interior heated side wall. Two different sizes of openings are considered: large and small openings. Particle image velocimetry (PIV) is used to determine velocities in the vertical centerplane. Air temperatures in the vertical centerplane are measured using negative temperature coefficient (NTC) sensors. Surface temperatures on the heated wall are measured using an infrared camera. Surface heat fluxes are obtained using heat flux sensors. In both cases the indoor airflow is dominated by the jet through the openings, with higher velocities in the building with large openings. The air temperatures measured with small openings are up to 7.5 % larger than those with large openings. The surface heat fluxes are up to 20 % higher in the building with large openings. The interior convective heat transfer coefficients vary considerably across the heated wall for both opening sizes and can be very different (up to 5 times higher) from those obtained by existing internal convective heat transfer coefficient correlations. The measurement results give insight into the complexity of ventilative cooling and can be used to validate computational fluid dynamics (CFD) simulations of cross-ventilative cooling. • Wind tunnel experiments on ventilative cooling in a building with heated wall. • The experiments are carried out for two different opening sizes (large and small). • Overall, larger temperatures are measured for case with small openings. • Heat flux varies considerably across the heated wall for both cases. • Comparison of CHTC from measurements with CHTC from correlations from literature. [ABSTRACT FROM AUTHOR]

After Covid-19, residential has become the main space for every activity, including work, education, and leisure. Therefore, comfort in residential space is crucial to the occupant. As researchers have found traces, that the virus is airborne, the air quality in the residence must be highlighted, especially for people who live in a centralized cooling system residence. When the cooling system is well maintained, there is no significant risk of viral transmission, but not all residential building has HEPA filters, nor a well-maintained system. This research focuses on the studio room apartment unit, as it has the smallest opening area compared to other room types. A small one-sided opening is not ideal for the wind to move throughout the room. A few design suggestion is simulated under three air-flow speed, to prove that natural ventilation is possible be adapted, to reach comfort while minimizing the risk of viral transmission. The result is, the indoor wind speed can be enhanced the most at the overall unit area by modifying the fixed window to an operable window, giving upper horizontal opening in the wall across the existing opening, and using gauze doors on both door openings. The furniture layout is proved to affect wind distribution in the room. This research can also serve as an alternative strategy to optimize the use of natural ventilation to decrease energy use for cooling in the tropic area, after the pandemic.

With the beginning of 2020, the Corona virus pandemic began, which negatively affected all of humanity, as medical and engineering research began to solve many problems faced by society during the era of the virus. Those who are exposed to this situation are among the medical staff responsible for treating and quarantining patients with the Corona virus. It has become the responsibility of engineers to develop solutions to the ventilation problem in order to limit the spread of this virus. Where the aim of this research paper was to study the effect of distance between patient and nurse and the effect of ventilation on the spread of the Corona virus. where a simulation model was created a room with real and 3D dimensions was studied with a patient lying down and the nurse treating him next to him. Where the room contains an air conditioner, two outlets for the airflow and an opening for the patient's mouth to simulate the exit of carbon dioxide gas from his mouth. Where the different and high speeds were studied to find out their effect on the spread of the virus abroad and its disposal. The result proves the best flow velocity of the ventilation system is 20 m/s, which led to a large limitation of the waiting for the Corona virus. The best place for the patient and the airway in the room should not be in the same airway, and the best place is between them. where these results serve as a reference for the engineering of medical rooms in terms of the effect of ventilation and distance of the pathogen on the spread of the Corona virus. [ABSTRACT FROM AUTHOR]

Conditioned airflows in mechanically ventilated rooms are characterized by a combination of complex features such as interaction or impingement with walls, buoyancy near a surface or a flow at a different temperature. The associated flow regimes can be either laminar, transient, or turbulent. Modeling these flows and the associated heat transfers at walls is therefore challenging, but is of the utmost importance for predicting building thermal behavior, thermal comfort, and ventilation efficiency. This study aims to evaluate the capacity of a Large-Eddy Simulation (LES) approach using the Lattice Boltzmann Method (LBM) with adapted wall modeling to simulate axisymmetric and thermal jets generated by an air diffuser of complex design and developing near the ceiling of a full-scale test room. Simulation results are compared with detailed experimental data for the cases of an isothermal jet, a hot jet, and a cold jet in terms of mean velocity, temperature, and turbulence intensity profiles. The jet turbulence distribution is further analyzed by means of anisotropic invariant mapping and vortex visualization. The results show good qualitative and quantitative agreement between simulation results and experimental data. In particular, the simulated velocity and temperature profiles within the jets are consistent with measurements, and the air temperature in the room's central occupancy region is correctly estimated. Also, the main turbulent mechanisms in the jets' development zone are well captured. Thus, the chosen approach enables detailed, high-fidelity simulations of airflow and heat transfer in ventilated rooms to be performed efficiently. • Lattice-Boltzmann-based Large-Eddy Simulation for indoor airflow applications. • Study of thermal jets developing near the ceiling of a full-scale test room. • Validation by comparing mean fields and turbulent quantities with measurements. • The LBM-LES model is able to predict airflow and heat transfer of the thermal jets. [ABSTRACT FROM AUTHOR]

The hypoxic environment at high altitudes causes various sleep disorders. Diffuse oxygen enrichment is an effective way to alleviate sleep disorders and improve the built environment in high altitude areas. In this study, a novel point source local diffuse oxygen supply method was proposed to improve the sleeping oxygen environment. The oxygen supply performance was investigated by the computational fluid dynamics (CFD) method including the oxygen concentration and air velocity distributions. A sleeping experiment was conducted on the plateau to validate the CFD model. The occupied zone including the inhalation zone and the active zone was defined. The results showed that the oxygen concentration showed a rapid rise, then decreased slowly, and finally tended to be stable. The oxygen concentration after stabilization was remarkably influenced by indoor ventilation rate. The sleeping environment's improvement was examined considering the oxygen enrichment efficiency, uniformity, stability and human comfort demand. The optimal strategies were recommended with a ventilation rate of 1 air change per hour, supplied oxygen concentration of 90%, and jet distance of 0.50 m. The study contributes to improving the oxygen environment and human sleep quality in an effective and energy-saving approach to the sustainable development of buildings in high altitude areas. [ABSTRACT FROM AUTHOR]

The heat radiation in a residential kitchen was simulated by CFD (Computational-fluid-dynamics) to evaluate the cooling by a radiant cooling ceiling panel and pollution dispersion by the range hood and the air extraction system. The kitchen has a 2-hobs stove and a fume hood for removing waste heat and fumes. The simulation was validated by measurements in a domestic kitchen in a home in Changsha, China, where summer temperature is generally about 33 °C and often over 35–42°C. The simulation results show that the pollutant concentration in the kitchen during cooking was much lower than the Chinese standard criteria of GB/T18883-2002. A standard turbulence model was used, which indicated satisfactory distribution of temperature and airflow in the kitchen. The indoor airflow velocity was low. The airflow temperature when both hobs were used was slightly higher by 3–4°C than when a single hob was used. The temperature in the kitchen during cooking was about 28 °C, which was a degree lower than the living-room temperature, thus maintaining a comfortable thermal and healthy environment. The radiant cooling in the ceiling was shown to be a significant contributing factor. The ring suction type range hood has a sufficient capacity to remove the kitchen fume contaminants. [ABSTRACT FROM AUTHOR]

The scalar dispersion from point sources in indoor spaces is experimentally investigated using simultaneous particle–image velocimetry and planar laser-induced fluorescence techniques in a 20:1 and a 60:1 full-to-model scale room model. The ventilation inlets dominate turbulence production, with magnitudes of the velocities and Reynolds stresses observed to increase with air changes per hour (ACH). Mean concentration maps show a dependence on the ACH and source location which is attributed to the flow field at the near-source region. The peak-to-mean concentration shows a weak dependence on the mean concentration and concentration variance maps, indicating risk for toxic chemicals may be underpredicted if based only on these information. The concentration PDFs are generally well-described by exponential distributions with C 99 / c r m s ′ values never exceeding 5.0. The magnitudes of the advective and turbulent scalar fluxes are strongly dependent on the ACH and source location, neither of which are able to dominate the other by more than an order of magnitude. The eddy diffusivity tensor was measured and a conditional-averaging based method is proposed to approximate it to an isotropic eddy diffusion coefficient, K. For real applications where K is used to estimate magnitudes of the turbulent scalar flux using the gradient transport model, the assumption of isotropic turbulence can introduce an uncertainty of around 17.8%. • Full 2D maps of the scalar fluxes and non-diagonal turbulent diffusivity tensor. • Scalar transport mechanism is dependent on the ACH and source locations. • Anisotropic turbulence contributes to turbulent diffusion coefficient uncertainties. • Implications of inconsistent 'turbulent diffusion coefficient' terminology. [ABSTRACT FROM AUTHOR]

Human activity is known to leave significant effects on indoor airflow patterns. These patterns are carefully designed for many facilities such as cleanrooms, pharmaceutical settings, and healthcare environments, where human‐induced wakes contribute to the transport of contaminants. Therefore, the knowledge about these wakes as it relates to indoor air quality is critical. As a result, a series of experiments were conducted in a controlled chamber to study the three‐dimensional effects of true human walking on airflow. Experiments were designed to capture the effect of human walking under three different flow conditions, and for two different walking schemes. The results show that the effect of walking on the airflow is not negligible and can sustain up to 10 seconds after the moving body has passed. Walking on a straight line creates significant change in the velocity normal to the walking path and vertical to the plane of walking movement. These changes were detectable till 1.0 m away from the walking track. Also, the similarity between airflow patterns of walking once and twice illustrated a promising opportunity of predicting the flow patterns of random walk from a set of base cases. [ABSTRACT FROM AUTHOR]

We present a probabilistic approach to designing an indoor sampler network for detecting an accidental or intentional chemical or biological release, and demonstrate it for a real building. In an earlier paper, Sohn and Lorenzetti(1) developed a proof of concept algorithm that assumed samplers could return measurements only slowly (on the order of hours). This led to optimal detect to treat architectures, which maximize the probability of detecting a release. This paper develops a more general approach, and applies it to samplers that can return measurements relatively quickly (in minutes). This leads to optimal detect to warn architectures, which minimize the expected time to detection. Using a model of a real, large, commercial building, we demonstrate the approach byoptimizing networks against uncertain release locations, source terms, and sampler characteristics. Finally, we speculate on rules of thumb for general sampler placement.

Indoor airflow patterns and the spreading of respiratory air were studied using the large-eddy simulation (LES) computational fluid dynamics (CFD) approach. A large model room with mixing ventilation was investigated. The model setup was motivated by super-spreading of the SARS-CoV-2 virus with a particular focus on a known choir practice setup where one singer infected all the other choir members. The room was heated with radiators at two opposite walls in the cold winter time. The singers produced further heat generating buoyancy in the room. The Reynolds number of the inflow air jets was set to R e = 2750 , corresponding to an air-changes-per-hour (ACH) value of approximately 3.5. The CFD solver was first validated after which a thorough grid convergence study was performed for the full numerical model room with heat sources. The simulations were then executed over a time of t = 20 min to account for slightly more than one air change timescale for three model cases: (1) full setup with heat sources (radiators+singers) in the winter scenario, (2) setup without radiators in a summer scenario, and (3) theoretical setup without buoyancy (uniform temperature). The main findings of the paper are as follows. First, the buoyant flow structures were noted to be significant. This was observed by comparing cases 1/2 with case 3. Second, the dispersion of the respiratory aerosol concentration, modeled as a passive scalar, was noted to be significantly affected by the buoyant flow structures in cases 1–2. In particular, the aerosol cloud was noted to either span the whole room (cases 1–2) or accumulate in the vicinity of the infected singer (case 3). Turbulence was clearly promoted by the interaction of the upward/downward moving warmer/cooler air currents which significantly affected the dispersion of the respiratory aerosols in the room. The study highlights the benefits of high-resolution, unsteady airflow modeling (e.g. LES) for interior design which may consequently also impact predictions on exposure to potentially infectious respiratory aerosols. • Airflow and virus super-spreading during a choir practice is investigated numerically. • Large-Eddy Simulation (LES) is used to capture the physics in high spatial resolution. • Flow structures and aerosol dispersion are compared between three model set-ups. • Respiratory aerosol dispersion is noted to be significantly affected by buoyancy. • Flow physics strongly impact the numerically predicted aerosol exposure. [ABSTRACT FROM AUTHOR]

The control of indoor air quality and thermal comfort requires faster-than-real-time simulations of air distribution. One approach to achieve such simulations is to use coarse grid. This study developed two adaptive coarse grid generation methods by analysing the grid-related truncation errors in the solution of the Navier-Stokes equations by fast fluid dynamics (FFD). Method 1 generates a grid that is coarser than that for a grid-independent solution but can still provide accurate FFD predictions. Method 2 generates a very coarse grid that provides acceptable FFD predictions. This study assessed the performance of the developed methods by using them to simulate three typical indoor airflows. The assessment showed that the coarse grid generated by Method 1 accelerated the FFD simulation by at least two to five times, with similar computational accuracy. The coarse grid generated by Method 2 provided faster-than-real-time FFD simulations for the cases tested in this study. [ABSTRACT FROM AUTHOR]

The indoor air flow and mass exchange induced by the rotating motion of a hinged door separating two rooms is investigated. Experiments were conducted in a scale model based on Reynolds number matching. Flow visualisations show the transport mechanism associated with the open and close phases of the door motion. In the room into which the door is opened a large-scale vortex is formed during opening, which is advected along the walls. In the adjacent room, a volume of fluid spreads both longitudinally and transversely. Concentration measurements were carried out to quantify the mass exchange generated by these flow patterns. Results are presented in dimensionless form for the volume of fluid exchanged and are compared to earlier data. The effects of hold open time and door speed on the exchanged fluid volume are investigated. The exchange volume increases with hold open time, but it does not vary considerably with door speed for a constant hold open time. Further, three-dimensional velocity measurements were carried out near the doorway and the characteristics of the velocity field developed are also presented. [ABSTRACT FROM AUTHOR]

The CFD method is an essential approach to investigate the indoor airflow. In this paper the zero-equation turbulent model, the standard k- ɛ model and the PIV experiment are employed to calculate the flow field in a model room with three kinds of basic ventilation mode. The results show that the zero-equation model could capture the flow features of the flow field as well as k -ɛ model. The location of the large vortex compared with PIV experiment data is almost same by zero-equation model and standard k -ɛ model. The k -ɛ model could predict the values of velocity a little bit better than zero-equation model. However, the zero-equation which could give a well prediction on the flow pattern and velocity profiles in the model room also has a great advantage of fast and time-saving. [ABSTRACT FROM AUTHOR]

The inside and outside velocity distribution was highly related with contaminant transport of naturally ventilated buildings. The building sidewall openings have a large impact on the velocity distribution at wind-driven conditions, but were not comprehensively investigated in previous studies. To achieve knowledge on that, a laboratory experiment was conducted using a building model in a wind channel. A laser Doppler Anemometer (LDA) was applied for the velocity and turbulence measurements. Tracer gas method (using CO 2 as tracer) was applied to measure the air change rate. Eight configurations of the sidewall openings in varied sizes and locations in the sidewalls were investigated. Results showed that in the same outdoor wind conditions, the air change rate depended upon the inlet (windward opening) and outlet (leeward opening) sizes. The location of openings seems to have little impact on the air change rate. Even with the same size and location of inlet but different outlet, the velocity profiles ahead of building remain different. Inlet and indoor velocities with the same inlets were similar even in cases with varied outlet. The velocities at the outlet depended on the inlet sizes. The wake flow behind the building was highly depended on the size and location of inlet and outlet. It was recommended to consider the inlet and outlet size and location when investigate the contaminant transport from the inside of the building to the outside. [ABSTRACT FROM AUTHOR]

Inlet boundary conditions at the supply opening play an important role in the accuracy and reliability of computational fluid dynamics (CFD) simulations for indoor airflow. A non-exhaustive overview of past CFD simulations of ventilation flow in generic enclosures indicates that uniform hypotheses of inlet boundary conditions are commonly used. However, due to thermal effects and a complex air supply system geometry, constant values of inlet airflow quantities can be insufficient for an accurate simulation of non-isothermal ventilation flow. In addition, this can lead to biased conclusions on the performance of turbulence models and other computational settings. To assess this issue, a well-documented experiment on non-isothermal mechanical ventilation with detailed information of inlet conditions from the literature is used in this study. Different turbulence models and inlet boundary conditions are validated, including seven steady Reynolds-averaged Navier-Stokes (RANS) models, six methods of imposing inlet air velocity, three methods of specifying air temperature, and a wide range of turbulence quantities. The parametric study demonstrates that in this particular case, i.e., cold air supply from a single round nozzle diffuser close to the ceiling, ω-based turbulence models perform better than the ε-based turbulence models. The impacts of different methods to specify inlet air temperature profile and turbulence quantities on the simulation results are not significant. However, if the inlet airflow direction is not taken into account appropriately, significant deviations are observed between CFD simulations and experimental data. • Detailed analyses of influence of inlet boundary conditions in CFD simulations. • Validation of RANS CFD simulations with measurement data from the literature. • ω-based turbulence models perform better than the ε-based turbulence models. • The inlet flow conditions can have a very strong effect on overall flow pattern. • Care should be taken in validation studies when inlet conditions are not known. [ABSTRACT FROM AUTHOR]

The ongoing Covid-19 pandemic, and its associated public health and socioeconomic burden, has reaffirmed the necessity for a comprehensive understanding of flow-mediated infection transmission in occupied indoor spaces. This is an inherently multiscale problem, and suitable investigation approaches that can enable evidence-based decision-making for infection control strategies, interventions, and policies; will need to account for flow physics, and occupant behavior. Here, we present a mesoscale infection transmission model for human occupied indoor spaces, by integrating an agent-based human interaction model with a flow physics model for respiratory droplet dynamics and transport. We outline the mathematical and algorithmic details of the modeling framework, and demonstrate its validity using two simple simulation scenarios that verify each of the major sub-models. We then present a detailed case-study of infection transmission in a model indoor space with 60 human occupants; using a systematic set of simulations representing various flow scenarios. Data from the simulations illustrate the utility and efficacy of the devised mesoscale model in resolving flow-mediated infection transmission; and elucidate key trends in infection transmission dynamics amongst the human occupants. [ABSTRACT FROM AUTHOR]

3-D Lagrangian Particle Tracking (3DLPT) is becoming widely used to characterize the convective indoor air movements in large scale spaces. The need to implement a robust algorithm led us to develop a multi-scale based approach to detect features (Helium filled soap bubbles). On the other hand, the particle tracking is another challenging problem. To this end, a new tracking algorithm based on fuzzy Kalman filtering is proposed in this paper. The Kalman filter is used to optimally estimate the new position of the particles based on their actual position. In our approach, the initial particle positions are represented with multivariate fuzzy sets. [ABSTRACT FROM AUTHOR]

The natural ventilation is an easy way to exchange the indoor polluted warm air with outdoor fresh air. The wind power injects outdoor fresh air into the building. A good indoor air current and subsequently a proper exhaust depend on the openings’ conditions and their situations. A serious architectural question is under what conditions of the openings the wind-cross ventilation can be effective, and the required indoor air current in the enclosure is established. The purpose of this article is analyzing the conditions of indoor airflow in an analytical architectural model to upgrade the natural ventilation by focusing on opposite opening’s conditions. This research considers some wind driven ventilation manner with respect to openings circumstances in an assumed cubic model. The research method includes a numerical simulation using a validated computational fluid dynamics (CFD) model. It investigates and compares the performances of different models of airflow currents in a natural ventilation process and subsequently the indoor airflow paths, under the different conditions of the openings in a fixed boundary condition model; the simulations are performed in an assumed model (a 6×6×6m cubic building with just 2 opposite openings in stationary walls as boundaries of the model) by using Gambit and Fluent software. With an analytical method (using Fluent) the gathered data would be analyzed. Finally the results are presented and generalized: the results demonstrate that whatever the wind speed is, the indoor airflow condition depends on the situations of the openings. It means that the quality of wind-driven cross ventilation and its path is not depended on the wind speed. Besides for establishing proper natural ventilation, the opposite windows must not be installed in front of each other, or in the same level. [ABSTRACT FROM AUTHOR]

A critically important quantity of energy is required nowadays to heat and ventilate our buildings. In order to reduce this energy demand, we need to characterize the convective indoor air movements in large scale spaces like building rooms. 3D Lagrangian Particle Tracking is used here; hence a feedback schema has been designed, it applies multi-view information to correct uncertainties in particle positioning. Moreover, a multi-scale based approach has been developed and tested with experimental and synthetic datasets. The method shows good robustness and efficiency against different kinds of noise and allows a generally applicable algorithm thanks to the use of automatic scale selection. On the other hand, the particle tracking is another challenging problem. Therefore, a new tracking algorithm based on fuzzy Kalman filtering is proposed. The Kalman filter is used to optimally estimate the new position of the particles based on their actual position. A quantitative comparison of the performances of this technique and other commonly used tracking algorithms allows validating the method. [ABSTRACT FROM AUTHOR]

Computational fluid dynamics (CFD) provides a suitable means to predict the air distribution characteristics in indoor spaces. This paper evaluates the performance of two turbulence models in predicting an indoor airflow: the RAST (Rahman-Agarwal-Siikonen-Taghinia) sub-grid scale model (SGS) and SST-SAS (Shear Stress Transport with Scale-Adaptive Simulation) k- ω model of hybrid RANS-LES type. These two models are applied to investigate the airflows for three ventilation scenarios: (a) forced convection, (b) mixed (natural+forced) convection and (c) isothermal impinging jet in a room. The predictions are compared with the available experimental data in the literature. However, both models produce good results but comparisons show that RAST model predictions are in better agreement with experiments due to its sensitivity toward both the resolved strain rate and vorticity parameters. [ABSTRACT FROM AUTHOR]

Airflow field measurement plays a significant role in creating a thermally comfortable indoor environment, by providing adequate quantitative information of indoor air distribution and local air velocity. In recent years, the Particle Tracking Velocimetry (PTV) technique has gradually become a promising and powerful tool for indoor airflow field measurement. This paper firstly gives an overview of the equipments and methods involved in typical PTV applications to indoor environments, and then introduces related applications of PTV for measuring indoor airflow fields. The Particle Streak Velocimetry (PSV) technique for indoor airflow measurement is also introduced. This paper shows how the quantitative and detailed turbulent flow information obtained by PTV measurement is critical for analyzing turbulent properties and developing numerical simulations. The limitations and future developments of PTV and PSV techniques are also discussed. [ABSTRACT FROM AUTHOR]

The paper presents a strategy to develop a fully transient numerical model of a heat transfer in building, using a transient CFD model of indoor air and a thermal envelope model, running in a co-simulation. The strategy relies on the utilization of RANS with a high-Returbulence model and a wall function, which enables to use a coarse computational mesh limiting the computational time. Since wall functions give invalid heat transfer coefficients in thermally developing indoor air regions and the exact location of these regions is not known in indoor spaces, a new air-wall heat transfer calibration procedure is adopted in the co-simulation. It is assumed that there is a uniform surface-averaged and time-dependent heat transfer coefficient per surface, extracted from the CFD solution. The calibration procedure is based on the near-wall mesh density adjustment to obtain surface-average heat transfer coefficients close to those calculated from empirical relationships for natural and forced convection. No local heat transfer coefficients are checked and no dimensionless wall distancesy+are monitored during the simulation. Due to the calibration it is ensured that the average air-wall heat transfer rate is accurate despite the use of wall functions. The capabilities of the model developed based on the strategy are presented in the case study: the analysis of the influence of wall thermal capacitance on indoor environment in a single well-ventilated room. [ABSTRACT FROM AUTHOR]

The objective of this work is to evaluate the quality of the zonal airflow predictions compared to those provided by computational fluid dynamics (CFD) tools for an isothermal airflow induced in a room by a linear ceiling diffuser. This comparative analysis was conducted for a typical rectangular office designed for two people, considering two different arrangements of obstacles within the room volume. The ventilation was provided by a four-way ceiling diffuser type with large aspect ratio slots, the outlet integrated into it, operating in a three-way mode with slot Reynolds number of 2700. As a result, the airflow was transitional or weakly turbulent. The airflow patterns obtained with the zonal models were first compared qualitatively with the CFD computations. A quantitative comparison based on the mean velocities at the interface of the zonal grid was then carried out. The characteristic features of the zonal predictions are shown and the limitations of the zonal and CFD approaches are discussed. [ABSTRACT FROM AUTHOR]

Low-dimensional discrete linear ventilation models have been studied by literature. In the present study, we investigate the validity and applicability of linear ventilation models for heavy-gas dispersion by employing Reynolds-averaged Navier-Stokes (RANS) simulations. A simple benchmark ventilation case is considered under isothermal condition. Considering large density differences from pollutant gas and fresh air, the effect of buoyancy force has been taken into account in turbulent production term to obtain correct diffusion behaviour. A low- Re k-ε model has been selected and the generalised gradient diffusion hypothesis is used for buoyancy source term. It is concluded that the flow equations decouple from the concentration equation when the ratio α of air mass-flow rate to pollutant mass-flow rate is larger than 10, which is 10 times higher than the range without density differences ( α>10). The dependence of the coupling on Richardson number Ri is also studied. It is found that the higher the Richardson number, the larger the α should be to decouple equations. [ABSTRACT FROM AUTHOR]

Providing welfare status for personnel of industrial plants is necessary and also emphasized in all standards. Preparing fresh, cool and clean air especially in warm seasons is one of the most important duties of plant owners to keep workers safe and healthy. Although in many workshops some cooling and air-conditioning systems (commonly mixing ventilation systems) were installed, most of them have economical problems and may not be energy efficient as the entire room volume gets cooled. The purpose of this article is presenting an executive improved solution in architecture to upgrade existing Mixing Ventilation Systems (MVS) by intervening in architectural variables. The new solution is compared with a traditional MVS taking into account technical and economic performances. The study was carried out resorting to experimental measurements on a single-diffuser pilot installation of the existing MVS in an actual industrial facility. The research method is experimental: the thermometry tests and interviews with workers which were carried out after initial observations and the case study selection. After that some interventions in architecture were impelled and the testes were repeated. To confirm the results, after interventions, a questionnaire was given to the operators, and their answers were registered. A comparison was fulfilled with respect to energy consumption and also the consumed power was checked before and after the interventions. The results demonstrate that architectural alterations based on this research can improve the quality of existing MVS (Satisfactions of the workers approved the interventions) and reduce the energy consumptions. It could be generalized. [ABSTRACT FROM AUTHOR]

This paper details the use of a simplified CFD model to predict the flow patterns around a computer simulated person in a displacement ventilated room. The use of CFD is a valuable tool for indoor airflow analysis and the level of complexity of the model being investigated is often critical to the accuracy of predictions. The closer the computational geometry is to the real geometry of interest, the more accurate the corresponding results are expected to be. High complexity meshes enable elaborated geometries to be resolved. The drawback is, however, their increased computational cost. The Fire Dynamics Simulator (FDS) model (Version 5) enabled to investigate the effects of geometry and computational grid simplification on the accuracy of numerical predictions. The FDS model is based on a three-dimensional Cartesian coordinate system and all solid obstructions are forced to conform to the underlying numerical grid which is a potential limitation when dealing with complex geometries such as those of a human body. Nevertheless, the developed computational model was based exclusively on a three-dimensional rectangular geometry. At the same time, in order to limit the total number of grid cells, a relatively coarser grid than those used for similar simulations was adopted in the investigation. The developed model was then assessed in terms of its capability of reproducing benchmark temperature and air velocity distributions. The extent to which numerical results depend on different simulation settings was detailed and different boundary conditions are discussed in order to provide some guidance on the parameters that resulted to affect the accuracy of the predicted results. The comparison between numerical results and measurements showed that a simplified CFD model can be used to capture the airflow characteristics of the investigated scenario with predictions showing a favourable agreement with experimental data at least in the qualitative features of the flow (the detailed investigation of the local airflow field near the occupant can not be probably conducted apart from considering the real human geometry). Significant influence of simulator geometry and of boundary conditions was found. [ABSTRACT FROM AUTHOR]

The spread of respiratory diseases via aerosol particles in indoor settings is of significant concern. The SARS-CoV-2 virus has been found to spread widely in confined enclosures like hotels, hospitals, cruise ships, prisons, and churches. Particles exhaled from a person indoors can remain suspended long enough for increasing the opportunity for particles to spread spatially. Careful consideration of the ventilation system is essential to minimise the spread of particles containing infectious pathogens. Previous studies have shown that indoor airflow induced by opened windows would minimise the spread of particles. However, how outdoor airflow through an open window influences the indoor airflow has not been considered. The aim of this study is to provide a clear understanding of the indoor particle spread across multiple rooms, in a situation similar to what is found in quarantine hotels and cruise ships, using a combination of HVAC (Heating, Ventilation and Air-Conditioning) ventilation and an opening window. Using a previously validated mathematical model, we used 3D CFD (computational fluid dynamics) simulations to investigate to what extent different indoor airflow scenarios contribute to the transport of a single injection of particles ( 1 . 3 μ m ) in a basic 3D multi-room indoor environment. Although this study is limited to short times, we demonstrate that in certain conditions approximately 80% of the particles move from one room to the corridor and over 60% move to the nearby room within 5 to 15 s. Our results provide additional information to help identifying relevant recommendations to limit particles from spreading in enclosures., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2022 Turkish National Committee for Air Pollution Research and Control. Production and hosting by Elsevier B.V. All rights reserved.)

• The computational accuracy and efficiency of four pressure-velocity decoupling algorithms are evaluated. • The fractional-step method significantly reduces the computational cost while maintaining satisfactory accuracy. • The fast flow dynamics method can reduce computational cost significantly and is more suitable for large-scale simulations. • The time-periodic air supply can provide periodic disturbance to eliminate stagnation zones. Simulations of indoor airflow can effectively assist in the design of a built environment. However, the intensive computational cost of current computational fluid dynamics (CFD) techniques restricts their efficient deployment, especially in transient airflow simulations. The fast fluid dynamics (FFD) method and fractional-step (FS) method have demonstrated their potential to reduce computational cost by reforming conventional pressure-velocity decoupling algorithms. Thus, this study evaluated the computational accuracy and computational efficiency of four promising schemes, which were chosen and developed from the FFD and FS methods, by applying them to lid-driven cavity flow and forced convection flow. All cases were simulated under constant boundary conditions and periodic boundary conditions with different time step sizes. The results showed that the FS method can achieve similar computational accuracy as the pressure-implicit with splitting operators (PISO) algorithm with approximately half the computational cost. The accuracy of one scheme of the FS method decrease rapidly with increasing time step size. The FFD method can reduce computational cost significantly because it is stable with a large time step size and is more suitable for large-scale numerical simulations. Simulation results of ventilation cases employing these methods also proved that time-periodic boundary conditions induced periodic changes in indoor airflow patterns that could facilitate the dispersion of air pollutants, especially in airflow stagnation areas. [ABSTRACT FROM AUTHOR]

In the present study, the relevance of the airflow to the response time of the smoke detector has been investigated regarding the different air purifier locations by Fire Dynamics Simulator (FDS). Particular attention has been devoted to the impact on the smoke detector response with different device types, i.e., top-discharge and front-discharge air purifiers. Additionally, the response delay rate regarding the fire sizes (200 kW and 550 kW) was also evaluated with the top-discharge type purifier. The obscuration plots suggest that the response delay rate generally increases when the air purifier and the smoke detector are in a straight line. The change in the delay rate of the detector was distinct for the top-discharge type device due to the formation of a current barrier by the ceiling jet flow, and a nearby physical barrier (e.g., wall) can further suppress the flow diffusion during a fire event. The delay rate tends to decrease with the increment of the fire intensity. [ABSTRACT FROM AUTHOR]