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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]

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]

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]

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 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]

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]

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]

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 article, Sohn and Lorenzetti 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 that maximize the probability of detecting a release. This article 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 that minimize the expected time to detection. Using a model of a real, large, commercial building, we demonstrate the approach by optimizing networks against uncertain release locations, source terms, and sampler characteristics. Finally, we speculate on rules of thumb for general sampler placement. [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]

This article presents a numerical study of indoor airflows and contaminant particle transportation in three ventilated rooms. The realizable k - ε model is employed to model the air-phase turbulence, while the Lagrangian particle tracking model is utilized for the particle-phase simulation. The predicted air-phase velocities and contaminant particle concentrations are validated against the experimental data obtained from the literature. In the first case, the realizable k - ε model successfully captures the flow trend and reasonably predicts the airflow velocity. The realizable k - ε model under-predicts the vertical air velocities along the vertical inlet jet axis by 11% at x = 0.219 m, which is slightly better than the standard k - ε model error of 17%. In a two-zone room case, the realizable k - ε model, combined with a Lagrangian particle tracking model, predicts the particle concentration decay with the highest normalized difference being 24%. In the third case, the influence of particle size, location of particle resource, and particle-wall collision on the particle concentrations is investigated by the realizable k - ε model and the Lagrangian model. It is found that for relatively small particles (diameter ≤ 10 μm), the particle concentration may be insensitive to the particle diameter. In addition it has been observed that the particle-collision model may have considerable effect on the particle concentration prediction. [ABSTRACT FROM AUTHOR]

We describe a probabilistic approach to siting samplers for detecting accidental or intentional releases of biological material. In the face of uncertainty and variability in the release conditions, we place samplers in order to maximize the probability of detecting a release from among a suite of realistic scenarios. The scenarios may differ in any unknown, for example, the release size or location, weather, mode of building operation, etc. In an illustrative example, we apply the algorithm to a hypothetical 24-room commercial building, finding optimal networks for a variety of assumed sampler types. The results show how sampler characteristics, most importantly the detection limit, affect the network performance. This suggests using the probabilistic approach to guide the priorities of sampler designers, as well as to site samplers in specific buildings. [ABSTRACT FROM AUTHOR]

The ventilation system of an operating theatre (OT) in a hospital needs to provide a comfortable and healthy surgical environment, particularly to minimise the risk of airborne infection. Engineering standards are available to outline specialised ventilation design and installation requirements based on knowledge accumulated from quality research and day-to-day practices. In this paper, the integrated effect of a reduction in supply air velocity and changed medical lamp positions on the ultra-clean ventilation performance of a standard OT environment is reported. The dispersion of infectious particles from both the surgical team and the patient were examined through computational fluid dynamic analysis. It was observed that variations in supply velocity and medical lamp configuration will only slightly affect the thermal comfort environment. However, they could have a serious effect on the movement of infectious particles and hence increase the cross infection risk. [ABSTRACT FROM AUTHOR]