There are a large number of airplanes currently being operated, in which the ventilation system needs to be improved to more effectively remove air contaminants. A potential approach is to adjust the ...supply air directions with the use of simple airflow deflectors. This study proposed a method for optimizing the supply air direction of ventilation in aircraft cabins based on the Re-field synergy index and Bayesian optimization. A validated numerical model was used to calculate the air distribution and air contaminant transport in a single-row single-aisle aircraft cabin to obtain the Re-field synergy values. The Bayesian optimization approach was used to identify the supply air direction which maximizes the Re-field synergy, namely, maximizes the mass transfer effectiveness. Finally, the air contaminant transport in a 7-row single-aisle aircraft cabin with the optimized supply air direction was evaluated to demonstrate the enhancement of ventilation performance. The results show that the proposed method based on the Re-field synergy index and Bayesian optimization can efficiently optimize the supply air direction in order to enhance the air contaminant removal in aircraft cabins. In the 7-row single-aisle aircraft cabin, the optimized supply air direction can reduce the average air contaminant concentration in the breathing zone of the passengers by up to 23 %.
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•A method for optimizing supply air direction in existing aircraft cabins was proposed.•The optimization method was based on Re-field synergy index and Bayesian optimization.•The optimized supply air direction can reduce air contaminant concentration in the cabin.
Natural ventilation in relatively enclosed underground spaces has aroused people’s interest due to the poor air quality and high energy consumption of mechanical ventilation. Small-scale experiments ...and numerical simulation are utilized to investigate the influence of thermal and wind conditions on the ventilation characteristics of underground corridors. The non-dimensional flow rate is calculated, which can be used to evaluate ventilation performance and predict airflow rate. The interaction of driving forces is quantitatively analyzed based on the Archimedes number and the critical non-dimensional flow rate. The results reveal that incoming wind counteracts buoyancy partly in shear ventilation, while the wind promotes buoyancy-driven ventilation in cross ventilation. The air change rate decreases under different driving force modes, from the purely buoyancy-driven to the combined-force-driven to the purely wind-driven, for shear ventilation with the wind speed of 1 ∼ 3 m/s. For cross ventilation, the descending order is the combined-force-driven, the purely wind-driven, and the purely buoyancy-driven. When driven by wind, non-dimensional flow rate remains constant with a value of 0.025 for shear ventilation and 0.68 for cross ventilation in the corridors with the opening ratio less than 12 %. When driven by combined force, Q* is not a constant value but rather varies with wind speed. Especially when the wind speed exceeds 1.5 m/s, the buoyancy can be ignored in cross ventilation. The findings of this study can serve as a basis for ventilation design and the prediction of ventilation rate in underground corridors.
Outdoor ventilation is very important for a healthy and livable urban environment. It is strongly influenced by wind speed and direction, which in turn are affected by urban morphology. This paper ...first provides a detailed review of the literature for CFD studies of outdoor ventilation for generic urban configurations. The review indicates that there is a clear lack of studies for urban configurations where not all parallel streets have equal street widths. Next, the paper presents Computational Fluid Dynamics (CFD) simulations of outdoor ventilation for generic configurations with parallel streets of equal and unequal street widths. The 3D steady RANS equations with the standard k- model and the passive scalar transport equation are used to calculate the effective local mean age of air at pedestrian level as an indicator of pollutant removal efficiency. The study is based on grid-convergence analysis and on validation with previously published wind-tunnel measurements. The influence of a central and wider main street on the wind-velocity pattern and on the effective local mean age of air of the surrounding area is analyzed for different wind directions. For wind directions oblique or perpendicular to the main street, the presence of this main street generally improves the ventilation efficiency because the main street acts as a sink of clean air. However, this is generally not the case for the parallel wind direction, where the higher flow rate through the main street reduces the flow rates through the parallel narrower streets, negatively affecting their ventilation efficiency.
Cross-ventilation using rooftop wind-catchers is very complex as it is influenced by a wide range of interrelated factors including aerodynamic characteristics of the wind catcher, approach-flow ...conditions and building geometry. Earlier studies on wind-driven cross-ventilation in buildings have shown the significant impact of the geometry and position of openings on the flow and ventilation performance. However, this has not yet been investigated for cross-ventilation using wind catchers. This paper, therefore, presents a detailed evaluation of the impact of the outlet openings on the ventilation performance of a single-zone isolated building with a wind catcher. The evaluation is based on three ventilation performance indicators: (i) induced airflow rate, (ii) age of air, and (iii) air change efficiency. High-resolution coupled 3D steady RANS CFD simulations of cross-ventilation are performed for different sizes and types of outlet openings. The CFD simulations are validated based on wind-tunnel measurements. The results show that using outlet openings very close to the wind catcher will not increase the induced airflow, while it leads to a considerable reduction in the indoor air quality. A combination of one-sided wind-catcher and window is superior, while the use of two-sided wind-catchers leads to the lowest indoor air quality and air change efficiency.
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•Detailed evaluation of the impact of outlet openings on cross-ventilation using wind catchers.•Increasing the surface area of outlet openings enhances airflow rate and air change efficiency.•A combination of one-sided wind-catcher and window is superior.•The use of two-sided wind-catchers leads to the lowest value of air change efficiency.
The objective of this article is to review the scientific literature on airflow distribution systems and ventilation effectiveness to identify and assess the most suitable room air distribution ...methods for various spaces. In this study, different ventilation systems are classified according to specific requirements and assessment procedures. This study shows that eight ventilation methods have been employed in the built environment for different purposes and tasks. The investigation shows that numerous studies have been carried out on ventilation effectiveness but few studies have been done regarding other aspects of air distribution. Amongst existing types of ventilation systems, the performance of each ventilation methods varies from one case to another due to different usages of the ventilation system in a room and the different assessment indices used. This review shows that the assessment of ventilation effectiveness or efficiency should be determined according to each task of the ventilation system, such as removal of heat, removal of pollutant, supply fresh air to the breathing zone or protecting the occupant from cross infection. The analysis results form a basic framework regarding the application of airflow distribution for the benefit of designers, architects, engineers, installers and building owners.
•We review eight ventilation/airflow distribution methods regarding ventilation efficiency.•We find that five indices can be used to assess the performance of a ventilation system.•The review discovers that DV, PV, SV and POV have certain energy saving potentials from 20% to 75%.•POV has a potential to protect occupants from exposure to indoor contaminant.
Thorough investigations of urban-canopy drag primarily stemming from pressure drag on building surfaces are necessary given the turbulent flows within complex urban areas. Moreover, a gap persists ...regarding the relationships between canopy drag and breathability. Therefore, this work delves into the canopy-layer airflow dynamics for generic urban neighborhoods by performing three-dimensional Reynolds-Averaged Navier-Stokes simulations. A total of 32 subcases are examined, encompassing uniform- and varying-height and diverse plan area densities (λp, categorized into groups of sparse: 0.0625/0.067, medium: 0.23/0.25, and dense: 0.53/0.56). Results for the drag distribution highlight the windward-row shelter effect for the medium and the dense, local shelter by taller buildings, and distinct shapes of sectional drag forces (F⁎Z). Local velocity and mean age of air are found strongly positively and negatively correlated to F⁎Z, respectively, with distinct slopes in relation to λp. For the uniform-height, the normalized bulk drag (F⁎bulk, referred to as drag coefficient in literature) peaks for the medium with wake-interference regime; F⁎bulk demonstrates a maximum increase of over two times with height variation; moreover, F⁎bulk for varying-height groups exhibits a marked increase from the sparse to the medium, while remaining comparable values for the dense. The frontal area averaged drag (FAf,ave) exhibits a decreasing trend against λp across all cases. Further, FAf,ave exhibits strong correlations with λp and porosity, and with bulk ventilation indices such as spatially averaged velocity, air change rate, and normalized net escape velocity. Throughout the ‘suburban-urban-suburban’ canopy, medium neighborhoods exerting larger drag cause greater streamwise outdoor pressure drops and flow reductions compared to the sparse. However, dense neighborhoods with lower drag exhibit even larger pressure losses, which should be carefully scrutinized. The findings can inform urban planners in designing more aerodynamically efficient neighborhoods and guide strategies for improving air quality within urban environments.
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•Canopy drag and breathability are assessed by CFD simulation for 32 neighborhoods.•Windward and local shelter effects, and distinct sectional drag are revealed.•Linear models for sectional drag and velocity demonstrate the influence of λp.•Height variation increases the bulk drag force and changes its relation with λp.•The frontal area averaged drag exhibits strong correlations with ventilation indices.
•Ambient HCHO was studied in 30 Chinese cities.•A mail-based sampling device was developed.•Peak hours of 12pm-3pm were identified.•Median concentration in summer peak hour was 0.027 mg/m3.•Ambient ...HCHO pose high carcinogenic risk.
Formaldehyde is an important carcinogen commonly found indoors. Its indoor sources have been intensively investigated. But study on outdoor formaldehyde concentration, which is potentially an important source to indoors, remains scarce. This study attempts to characterize temporal and spatial distribution of the atmospheric formaldehyde concentration in Chinese cities. Diurnal variation of ambient formaldehyde was examined in 6 cities and peak hours were identified between 12:00 pm and 3:00 pm. Consequently, outdoor formaldehyde concentrations were measured in the peak hours in 30 cities during the summer months of Jul.-Aug., 2022. The formaldehyde concentrations in the peak hours fell into a range of 0.005–0.087 mg/m3 (median value is 0.027 mg/m3), 87.7% of which have exceeded the chronic reference exposure criteria of 0.009 mg/m3 set by Office of Environmental Health Hazard Assessment. Health risk analysis suggests that exposure to ambient formaldehyde could cause a median carcinogenic risk of 1.9 × 10−5 (3.17×10−6–6.13×10−5), higher than threshold limit of 10−6. Pearson correlation analysis of the 30 cities shows that ambient summertime atmospheric formaldehyde concentrations of the city are positively correlated with its Gross Domestic Product (r = 0.48). We also found that the outdoor formaldehyde concentrations in urban areas (median: 0.017 mg/m3) is slightly higher than those in suburban areas (median: 0.013 mg/m3). Results here prove that outdoor formaldehyde is ubiquitous in Chinese cities and reduces effectiveness of ventilation in dilution indoor concentrations. Neglecting it would underestimate air cleaner capacity needed by a factor of about two. It should be accounted for in health analysis and air quality engineering control design of built environment in the future.
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•An empirical formula for obtaining the capture efficiency of local ventilation.•A fast method to find optimal flow rates for general and local ventilations.•The method ensures IAQ and thermal ...comfort at lowest cost.•The method showed energy consumption reduction of 16% in case study.
The manufacturing industry consumes a large quantity of energy for ventilation to remove pollutants and heat generated during production processes. Both general and local ventilation systems have been widely used in industrial buildings for a healthy and comfortable indoor environment. However, in most industrial buildings, general and local ventilation systems were designed individually, and this will produce excessive ventilation and energy waste. Therefore, this investigation put forward a novel and fast method for simultaneously determining the optimal flow rates for general and local ventilation systems. To facilitate the calculations in this method, an empirical formula for predicting the capture efficiency of local ventilation was developed and validated. Next, based on heat and mass conservation, an empirical formula was developed to calculate the required flow rates of general and local ventilation systems. Based on the two empirical formulas above, a novel empirical formula was derived for quickly predicting the optimal flow rate. The novel ventilation design method was applied in an actual manufacturing plant to obtain the best combination of flow rates. The results predicted for the factory by our fast method were validated by computational fluid dynamics (CFD) and building energy simulation (BES). Compared to two common conditions of traditional ventilation design method, optimal combination of general and local ventilation systems consumed 15% and 20% less energy, while ensuring thermal comfort and indoor air quality. This study offers a novel method for fast and comprehensive design of general and local ventilation systems in an industrial plant.
Wind-induced natural ventilation is a sustainable approach for improving the indoor thermal comfort, air quality, and energy consumption. Although numerous ventilation studies have addressed generic ...ventilation models, the cross-ventilation flow of a multilayered model (widely ingrained in a tropical climate zone such as Malaysia as a typical terraced house with a deep-plan layout) has not been studied well. Therefore, this study aims to investigate the flow patterns inside a simplified two-layered model separated by a second floor at the middle height with an opening using wind tunnel experiments. Two cases are considered based on the positions of the inlet and outlet openings on each floor. Two velocity components are measured using particle image velocimetry (PIV) and hot-wire anemometry (HWA). This study provides high-quality experimental datasets, which enables us to understand turbulent characteristics of indoor airflow, obtained using PIV and HWA for a generic two-layered cross-ventilation model. In addition, the results show that the ventilation performance of two-layered stratified buildings is significantly affected by the inlet opening positions. Moreover, the indoor flow direction is considerably changed owing to the multi-zoning of the indoor space. Although we employed only a generic two-layered model, this study clearly highlights the importance of considering multi-layered buildings for a better understanding of the ventilation performance.
•Cross-ventilation flow patterns were measured for a generic two-layered model.•Flow directions were considerably changed owing to the multi-zone indoor space.•High-quality experimental datasets of cross ventilation were provided by PIV and HWA.
The main objective of this study is to investigate the airflow patterns in single-sided ventilation of isolated buildings in which the ventilation rate can not be easily predicted by the conventional ...Orifice equation. The research focuses on buildings with two openings located either at the front or back external wall, with building aspect ratios of 1:1 and 1:2.The study utilizes Large Eddy Simulation (LES) with the particle tracking technique validated by velocity data obtained from a wind tunnel experiment. Ventilation performance is evaluated by Airflow Rate (AFR) and Purging Flow Rate (PFR). AFR was obtained based on the instantaneous velocity over the openings, and PFR was determined by the tracer gas method. The results show that the influence of pulsation flow and eddy penetration both exist in single-sided ventilation. The comparison of AFR and PFR indicates part of the airflow through the opening does not contribute to effectively removing the indoor contaminants, which is quantitively evaluated by ventilation efficiency (εv) defined as the ratio of PFR and AFR. In order to explicitly observe and depict the airflow, the massless particles were emitted at the opening, and the trajectories were analysed. The Probability Density Function (PDF) of indoor residence and indoor travel distance was calculated. The high probability of short indoor travel distance and the residence time, which is mainly caused by the eddy at the openings and time-variant pulsation flow, can explain the difference between AFR and PFR.
•The airflow characteristics of single-sided ventilation are analysed by LES simulation.•The particle tracking method is used to interpret the unsteady airflow of single-sided ventilation.•The impact of opening locations and building aspect ratio on AFR and PFR of single-sided ventilation was investigated.•The mixing theory and pulsation theory of single-sided ventilation are illustrated by numerical simulation results.
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