Local Ventilation Research Articles

Heat stress, thermal comfort and control strategy in a warm-humid workplace.

The purpose of this study was to design a local ventilation system (LVS) to help reduce the moisture content of a Scalder hall, evaluate its comfort and thermal stress before and after implementation of LVS and introduce an appropriate index to evaluate warm and humid workplaces. The design of the LVS was performed according to the ACGIH standard (VS-30-01). Heat stress and thermal comfort assessment were performed before and after LVS using humidity index (Humidex), discomfort index (DI), heat index (HI), wet-bulb globe temperature (WBGT) and predicted mean vote index (PMV) indices and the results were compared with predicted mean vote index-predicted percentage of dissatisfied (PMV-PPD) subjective indices. The results of heat stress parameters showed that LVS was able to reduce relative humidity (RH) and wet temperature (tnw) by 47% and 7 ° C, respectively. This has caused subjects to feel the heat from hot and very RH hot to warm and the hot and percentage of dissatisfaction has dropped by more than 70%. Design and implementation of a LVS reduced the ambient tnw by decreasing RH. Results also showed in warm and humid workplaces, DI index are highly correlated with subjective evaluation of thermal comfort and this index can be used to evaluate the thermal conditions of the workplaces.

A novel measurement for evaluating the capture efficiency of local ventilation system using background oriented schlieren

In-situ measurement of the capture efficiency of local ventilation systems (CELV) is a challenge in field of indoor air quality control. This study introduced a novel method for assessing the capture efficiency using background oriented schlieren (BOS). A 1:4 model experimental platform was constructed to investigate the feasibility. The CELV was compared using both the BOS and the tracer gas method, and the optimization of BOS device parameters for better CELV results was investigated. The results showed that the CCD camera-BOS could detect thermal airflows with a temperature difference over 40 K. The best post-processing algorithm for CELV by BOS, which was combined density gradient variation-rate and gray-scale method (CE-DGR&GS), was closely matched the results of the tracer gas method (CE-SF6), with a correlation of 0.97. When the capture efficiency exceeded 90%, the deviation between the two methods was less than 10%. However, when the ventilation system captured poorly, the CELV by CE-DGR&GS was over-estimated. Higher NR of BOS image causes large deviation of the calculated capture efficiency, and CELV by BOS under the same flow can differ by as much as 40 % by various cameras. A high-pixel CCD camera with a long focal length lens (f ≥ 35 mm, ISO≤100, f# = 16) was recommended. The interrogation window size for cross-correlation algorithms could be 33%–66% of the collected image pixel resolution. To achieve sufficient optical sensitivity, the distance ratio Zd/Zb was suggested to be 1:2. This study provides a cost-effective and entrie flow-field measurement for assessing local ventilation capture efficiency.

Simulation-aided development of a compact local ventilation unit with the use of CFD analysis

Simulation-aided development of a compact local ventilation unit with the use of CFD analysis

Analysis on typical characteristics and causes of coal mine gas explosion accidents in China.

Large-scale coal mine gas explosion (CMGE) accidents have occurred occasionally and exerted a devastating effect on society. Therefore, it is essential to systematically identify the characteristics and association rules of causes of CMGE accidents through analysis on large-scale CMGE accident reports. In this study, 298 large-scale CMGE accidents in China from 2000 to 2021 were taken as the data sample, and mathematical statistical methods were adopted to analyze their general characteristics, coupling cross characteristics, and characteristics of gas accumulation and ignition sources. Moreover, the text mining technology and the Apriori algorithm were used for exploring the formation mechanism of CMGE accidents, during which 46 main causal factors were identified and 59 strong association rules were obtained. Furthermore, an accident causation network was constructed based on the co-occurrence matrix. The key causal items and sets of CMGE accidents were clarified through network centrality analysis. According to the research results, electrical equipment failure, cable short circuit, mine lamp misfire, hot-line work, and blasting spark are the key ignition sources of CMGE. Fan failure, airflow short circuit, and local ventilation fan damage are the main causes of gas accumulation. Besides, the confidence levels of two association rules of "static spark-fan failure" and "blasting spark-airflow short circuit" are higher than 70%, indicating that they are the two dominant risk-coupling paths of gas explosions. In addition, six causes appear frequently in the shortest risk paths of gas explosion and are closely related to other causes, i.e., fan failure, local ventilation fan damage, static sparks, electrical equipment failure, self-heating ignition, and friction impact sparks. This study provides a new perspective on identifying causes of accidents and their complex association mechanisms from accident report data for practical guidance in risk assessment and accident prevention.

Head-neck local ventilation mode for long-narrow mine working face

To improve the thermal health state of workers in mines facing heat hazards and enhance cooling capacity utilization efficiency of mine ventilation, this study proposes a suitable air distribution for mine workers’ local cooling, taking into account the characteristics of long-narrow underground space and workers. The suggested air distribution involves harnessing underground cold air jets along with the mine’s crossflow (mainstream ventilation) to create a localized safeguard airflow around the worker’s head-neck, known as jet ventilation in crossflow (JVIC). The flow visualization experiment identified five flow patterns within a confined space. The study explores the impact of the velocity ratio (R) and confinement scale (C) on the evolution of JVIC flow patterns and presents a parametric description of the resulting flow field. Drawing on the microclimate control scope around mine workers’ head-neck, the study defines the effective cooling zone and the ineffective cooling zone as the boundaries for controlling JVIC air distribution within confined mine spaces. This clarifies the applicability of the air distribution form and introduces an evaluation model for assessing the cooling effect and the efficiency of cooling capacity utilization to manage the non-uniform underground environment.

Analysing urban local cold air dynamics and climate functional zones using interpretable machine learning: A case study of Tianhe district, Guangzhou

Deterioration of the thermal environment in built-up areas poses a serious threat to human health, comfort, and urban infrastructure, while also increasing energy consumption and carbon emissions. This underscores the need to optimize wind environments as a key mitigation strategy for urban areas. This paper analyzed the effects of human activities and natural factors on local cold air in Tianhe District, Guangzhou, from the perspective of local ventilation systems. The KLAM_21 (Kaltluft Abfluss Modell) was used to simulate local cold air flow and delineate climate functional zones. A random forest model, interpreted with the SHapley Additive exPlanation (SHAP) method, assessed the impact of various factors on local cold air dynamics. The study found that: (1) The northern mountainous area is a crucial cold source; (2) Some open spaces in the built environment fail to function as effective local cold air corridors; (3) High-intensity urban development hinders local cold air transmission; (4) Water bodies are more effective than green spaces in collecting and transmitting local cold air. This study provided technical methods for identifying climate functional zones and understanding local cold air dynamics, as well as theoretical support for the construction of local ventilation systems in urban areas.

Exploring Systems Thinking and Systemic Design: Insights from a Summer School Experiment Addressing Urban Health Crises

This paper relates urban healthcare crises to the global challenges of overshoot and collapse and suggests systems thinking as an innovative approach towards addressing these amalgamated crisis situations. We begin by reviewing what systems are and how they are structured and behave, highlighting how systems thinking can identify high-leverage interventions and systemic design to achieve effective change. Subsequently, we illustrate how these system concepts were applied in an international, multidisciplinary summer school between European and Southeast Asian partners in collaboration with the World Health Organization’s (WHO) Technical Science for Health Network (Téchne). Examining how ventilation, temperature, humidity, and daylighting control strategies enhance Infection Prevention and Control (IPC), the initiative developed ideas and designs for a multiple disease treatment center that would provide isolation units and create a safe care environment for patients, families, and communities. The design process was informed through consultation with three physically and socio-economically diverse neighborhoods across the Bangkok Metropolitan Region to gain a richer understanding of the varied experiences and approaches in managing the COVID-19 disruption. Leveraging WHO guidelines, students adopted a systemic design approach to develop innovative solutions that could withstand natural hazards and used local materials and natural ventilation to prevent airborne infection and control indoor temperature. In conclusion, we propose a novel working model linking specific stages of systemic thinking and systemic design into a generalized, iterative urban and healthcare design framework that will be further refined as part of specific electives at the KU Leuven Faculty of Architecture and joint summer schools in 2023, 2024 and beyond.

Role of Fluid Dynamics in Infectious Disease Transmission: Insights from COVID-19 and Other Pathogens

The spread of infectious diseases such as COVID-19 depends on complex fluid dynamics interactions between pathogens and fluid phases, including individual droplets and multiphase clouds. Understanding these interactions is crucial for predicting and controlling disease spread. This applies to human and animal exhalations, such as coughs and sneezes, as well as bursting bubbles that create micron-sized droplets in various indoor and outdoor environments. By exploring case studies in this regard, this study examines the emerging field of fluid dynamics in disease transmission, focusing on multiphase flows, interfacial flows, turbulence, pathogens, human traffic, aerosol transmission, ventilation, and breathing microenvironments. These results indicate that increased ventilation rates and local ventilation methods can effectively reduce the concentration of SARS-CoV-2-laden aerosols in the immediate breathing spaces between individuals. In a displacement-ventilated room, both neutral and unstable conditions were more effective in removing breathed SARS-CoV-2-laden aerosols from the air, regardless of the presence of test subjects. However, stable conditions may increase the risk of infection in individuals living in confined spaces. Thus, the findings of this study are useful for providing practical guidance for managing the spread of airborne infections. HIGHLIGHTS Fluid dynamics affect the transmission of infectious diseases such as COVID-19 This study explored multiphase fluid flow, aerosol dispersion, and respiratory zones Increased ventilation and local methods reduce SARS-CoV-2 aerosol concentration Displacement ventilation eliminates SARS-CoV-2 aerosols under unstable conditions Cramped and damp living environments can increase the risk of transmission of infection GRAPHICAL ABSTRACT

Net escape velocity, transfer probability, and travel time distributions within a cross-ventilated room model sheltered by urban-like block array

Natural ventilation offers significant advantages, especially in terms of energy conservation. However, most published articles have focused on the ventilation flow rate to determine the average contaminant concentration, while few have examined local ventilation distributions. Therefore, isothermal steady-state Reynolds-averaged Navier–Stokes simulations were conducted to analyze the airflow and scalar concentration fields of a cross-ventilation model sheltered by buildings. Based on these fields, we generated the spatial distributions of ventilation indices, namely, the net escape velocity (NEV), point-to-point indices transfer probability (TP), and travel time (TT), to discuss the dispersion of scalars emitted from local points in a room with natural ventilation. The NEV, which indicates the direction of the scalar discharge from each cell, exhibited a distribution distinct from the advection velocity because of concentration gradient effect. Higher TPs were observed when evaluated from a contaminant source to a target point following the NEV streamlines. Meanwhile, lower TTs were observed when evaluated in a point near the source and also from a contaminant source to a target point following the NEV streamlines. Although TP and TT are independent ventilation indices, a negative correlation between them was observed. Instead of the ventilation flow rate, the detailed structure of scalar dispersion can now be described by simultaneously analyzing the ventilation efficiency indices, which provide information on the general contaminant transport direction, and the probability and duration of transfer from a source to a target point. This potentially helps in the design of ventilation system especially in room lay-out to avoid cross-contamination.

Improved aerodynamic performance of the exhaust hood with triple-faced flange

For a local exhaust ventilation system to trap contaminants effectively, it is highly important to minimize its energy consumption without forgoing efficiency. Energy savings can be achieved by reducing the aerodynamic drag of non-straight elements of local ventilation systems. Goal of the study is to minimize the drag of an exhaust with a triple-faced flange by varying shelves lengths and tilt angles by the method of coordinated descent. Study conducted numerically and experimentally. For the first time a pattern of changes in LDC value depending on the size of the shelves was revealed. The minimum value of LDC is reached when the length of the first shelf adjacent to the exhaust channel is 0.5l (l -half width of the slot or radius of round exhaust hood), the angle of its inclination is 30°; the length of the second shelf is 0.7l with an angle of inclination of 90°; the length of the third shelf is 0.2l with an angle of inclination of 120°. The found velocity distribution shows the effectiveness of the exhaust hood capture. The reduction of the LDC, when compared with the typical exhaust hood with the flange inclined on 90° was 76 %, and compared with a real industrial exhaust hood from the welding table – 65.7 %. The outline of vortex zones at the entrance to the exhaust hood was determined by different methods. The findings can be used for the design and development of energy-saving slotted and round exhaust hoods.

An Experimental Study on the Efficacy of Local Exhaust Systems for the Mitigation of Exhaled Contaminants in a Meeting Room

In industrial applications, local exhaust systems have been used extensively for capturing and confining contaminants at their source. The present study investigates the efficacy of these systems in mitigating the spread of exhaled pollutants by combining them with mixing and displacement ventilation. Experiments were conducted in a simulated meeting room with six closely situated workstations, featuring five exposed persons (simulated with heated dummies) and one infected person (simulated with a breathing manikin). Six overhead local exhaust units, merged with panels, corresponding to workstations, were installed using a lowered false ceiling. Additionally, a table plenum setting for air inlets was introduced to enhance displacement ventilation effectiveness along with local exhaust systems. Results from 16 experimental cases are presented, using the local air quality index and ventilation effectiveness in the breathing zone. The local exhaust system improved the local air quality at the measuring locations closest to the infector in almost all test scenarios. The improvement, particularly significant with displacement ventilation, marked a maximum 35% increase in the local air quality index adjacent to the infector and 25% in the entire breathing zone of the tested meeting room. Moreover, the table plenum settings, coupled with displacement ventilation, further enhanced conditions in the breathing zone. Under the specific conditions of this investigation, the number of operational local exhausts had a marginal impact on mixing ventilation but a significant one on displacement ventilation tests. The efficacy of local exhaust systems was also influenced by the levels of heat gains present in the room. Overall, the study aims to contribute to ongoing efforts to identify sustainable solutions to mitigate indoor airborne diseases with a combination of supply and local exhaust units.

Linkages between urban growth and land surface temperature variations in the Seoul metropolitan area: A spatial first-order difference approach

This study investigates the effects of urban development and expansion on Land Surface Temperature (LST) changes from 2000 to 2018, using the Seoul Metropolitan area (SMA) as a case study area. Along with descriptive analysis, this study uses a spatial first-order difference model to statistically analyze the longitudinal relationship between land use features and LST, including impervious surface (IS), enhanced vegetation index (EVI), anthropogenic factors, and urban spatial and topographical factors as well as urban development types as influential factors on LST variations. Our findings support prior research indicating the cooling effects of vegetation and warming effects of imperviousness. We also found a positive association between detached housing units, manufacturing activities and LST changes and a negative relationship between apartment units, urban parks, service activities and LST changes. More importantly, substantial LST reduction was found in the large-scale high-rise apartment complexes redeveloped from the low-rise, detached housing sites in inner-city infill areas, contrasting with significant LST rise in the suburban new town development. We suggest redevelopment of inner-city low-rise compact areas into high-rise but greener blocks as a LST mitigation strategy, equipped with cooling strategies such as green infrastructure and climate-sensitive design considering local microclimate and natural ventilation.

(882) - Comparison of Local Ventilation in Patients Very Early After Bilateral Lung Transplantation and Healthy Subjects Using Magnetic Resonance Imaging

(882) - Comparison of Local Ventilation in Patients Very Early After Bilateral Lung Transplantation and Healthy Subjects Using Magnetic Resonance Imaging

Performance of local supply-exhaust ventilation around stove with numerical simulation in a residential kitchen

A large number of fine particulate matters (PM2.5) are generated during cooking, which have negative impacts on kitchen environment. This study proposed a novel ventilation strategy of local supply-exhaust ventilation around stove (LSEVAS) for improving air quality in a residential kitchen during cooking. Five factors affecting the performance of LSEVAS were explored with orthogonal design and computational fluid dynamics (CFD). Evaluation indexes including PM2.5 mass concentration in breathing zone (CB), capture efficiency (CE) of fume exhaust device and intake fraction (IF) of occupant were also analyzed. The performance of LSEVAS was also identified without air supply condition in kitchen in terms of these above evaluation indexes. Results show that the emission rate and exhaust air volume were the most significant factors, followed by the upside air supply angle, upside air supply speed and downside air supply speed. The CB in LSEVAS was reduced by 83%, 60% and 66% than without air supply condition under low, medium and high emission rates, respectively. The CE was improved by 1.8%, 13.9% and 14.5%, respectively. The IF value was decreased by one order of magnitude. Furthermore, with increasing of upside and downside air supply speed, the ability of air supply airflow in preventing the escape of PM2.5 became stronger, while the core concentration distribution of PM2.5 was gradually closer to breathing zone of occupant. It means that the novel local ventilation strategy proposed in this study is effective in improving cooking environment in the residential kitchen.

Effect of cubicle hood system on methane concentrations around the lying area in cold climate dairy cattle buildings

There is scarcity of data on methane (CH4) concentration levels and other gas compositions around animals in commercial cattle barns, especially for developing technology for gaseous CH4 treatment. Consequently, use of biofiltration and catalytic combustion strategies as alternative enteric CH4 mitigation techniques remain concepts yet to be validated in real cattle barns. One of the major barriers to implementing these techniques is that they require close buildings, which is not the case for most cattle barns. Open cattle barns are frequently associated with excessive ventilation, resulting in low CH4 concentrations, which can reduce the cost effectiveness of CH4 treatment techniques. With the development of low-cost, low-CH4-concentration enrichment technologies still in their infancy, developing local ventilation systems at the animal level capable of collecting breath CH4 from cows prior to air mixing could be an option. Therefore, the effect of a cubicle hood system (CHS) with different air extraction techniques on increasing CH4 concentrations at the lying area were evaluated in natural and mechanically ventilated dairy cattle buildings during the winter in Norway. In both barns, the use of CHS increased CH4 concentrations under the hood at the lying area by 14-25 % compared to without CHS. The results obtained depended on the height of the CHS from the floor and effect of outdoor temperature on air exchange rate in the barns. In the naturally ventilated barn, the hourly mean CH4 concentrations under the cubicle hood ranged from 14-225 ppm, and 31-322 ppm in the mechanically ventilated building.

ANALISIS KONSENTRASI PARTIKEL MIKRO AMBIENT PADA FUNGSI PARU POPULASI URBAN JAKARTA

Introduction: The potential impact on lung function due to high exposure to ambient microparticles in cities such as Jakarta has not been comprehensively studied. The background of this research is based on the lack of studies regarding the impact of high micro-particle exposure in major cities like Jakarta on lung function. Research Objective: The purpose of this study is to investigate the relationship between the dominant levels of ambient micro-particle concentration in urban areas of Jakarta and changes in spirometry indices among its residents. Method: A cross-sectional approach was used to determine the relationship between ambient micro-particle concentration and irregularities in spirometry indices among the urban population of Jakarta. This study involved 187 adults, aged between 20 to 65 years, mostly from the busy urban sectors of Jakarta. Statistical techniques of association and logistic regression were used for the assessment of the collected data. Results: The average exposure to ambient micro-particles was 315 µg/m³. Aberrations in spirometry indices were detected in 41.2% of participants. A significant relationship was found between high micro-particle concentrations and anomalies in spirometry readings among urban residents of Jakarta. This correlation remained significant after considering confounding factors such as gender, duration of exposure, local ventilation quality, smoking habits, and prevailing humidity. Conclusion: The results of this analysis suggest that the dominant levels of ambient micro-particles in the urban areas of Jakarta may play an important role in causing variations in spirometry results among its inhabitants..

The impact of dynamic traffic and wind conditions on green infrastructure performance to improve local air quality

Road traffic represents the dominant source of air pollution in urban street canyons. Local wind conditions greatly impacts the dispersion of these pollutants, yet street trees complicate ventilation in such settings. This case study adopts a novel modelling framework to account for dynamic traffic and wind conditions to identify the optimal street tree configuration that prevents a deterioration in air quality. Measurement data from a shallow to moderately deep street canyon (average 0.5 H/W aspect ratio and four lanes of 1-way traffic) in Dublin, Ireland was used for model calibration. The computational fluid dynamics (CFD) models were used to examine scenarios of dynamic traffic flows within each traffic lane with respect to its impact on local PM2.5 concentrations on adjacent footpaths, segmenting air quality monitoring results based on different wind conditions for model calibration. The monitoring campaign identified higher PM2.5 concentrations on the leeward (north) footpath, with average differences of 14.1 % (2.15 μg/m3) for early evening peaks. The modelling results demonstrated how street trees negatively impacted air quality on the windward footpath in parallel wind conditions regardless of leaf area density (LAD) or tree spacing, with mixed results observed on the leeward footpath in varying traffic flows and wind speeds. Perpendicular wind direction models and high wind speed exacerbated poor air quality on the windward footpath for all tree spacing models, while improving the air quality on the leeward footpath. The findings advise against planting high-LAD trees in this type of street, with a minimum of 20 m spacing for low-LAD trees to balance reducing local air pollution and ventilation capacity in the street. This study highlights the complexities of those in key decision-marking roles and demonstrates the need to adopt a transparent framework to ensure adequate modelling evidence can inform tree planting in city streets.

Potential of a bed ventilation system in reducing the risk of exposure to contaminants in infectious wards

A proposed bed ventilation system named Hospital Bed Integrated Ventilation Cleansing Unit (HBIVCU) has shown its great potential in reducing the risk of airborne cross-infection. However, the key operating parameters are still unclear, restricting its practical application. This study numerically investigated the performance of the HBIVCU under various operating parameters (supply and exhaust airflow rates increased from 0 L/s to 5 L/s and 0 L/s to 40 L/s, respectively) in a four-bed infectious ward with different background ventilation rates. Both tracer gas CO2, (simulating aerosols smaller than 5 μm) and particles (mean diameter of 80 μm) in the exhaled by one of the patients were considered. Compared to the ward without the HBIVCU, the concentration of CO2 at the bed microenvironment and breathing height of standing and sitting persons are reduced by more than half when the HBIVCU operates with supply and exhaust airflow rates of 5 L/s and 40 L/s, respectively. For this case, the highest draught risk of 13% at the patients’ head region is obtained. Increasing the supply and exhaust airflow rates of the HBIVCU are both helpful for removing the exhaled gaseous contaminants from the room due to increased induction effect of the local bed ventilation flow. The removal efficiency is around twice higher when the HBIVCU is operating at background ventilation at 6 air changes per hour (ACH) when compared to when it is not operating at background ventilation of 12 ACH. Finally, the HBIVCU can efficiently remove the exhaled gaseous contaminants, though it has no discernible effect on the removal of coughing droplets. The HBIVCU has great potential to reduce the risk of cross-infection and save energy by lowering the background ventilation rate.

Multi-scale analysis of respiratory droplets transport within the breathing cloud

Infectious diseases are transmitted primarily through pathogen laden droplets commonly exhaled during respiratory events such as breathing, coughing, or sneezing. The transport and evaporation of droplets are governed by the fundamental laws of fluid mechanics and convection-diffusion. From these, analytical models can be created helping in better understanding pathogens transmission from a mechanical perspective. The droplet transport within the humid air breath cloud and the local ventilation are crucial for accurately predicting the droplet fate. Different levels of complexity are possible for modelling the breath cloud, from simple 1D models to complex unsteady 3D simulations including discrete phase models for the droplets simulation. The former are too simple to capture the fluid dynamics of intermittent jets in detail, while the latter are too computationally expensive. The current work presents a novel multi-scale approach where an analytical model of the droplet transport and evaporation is coupled to unsteady CFD simulations of warm humid puffs of exhaled air. The proposed model has the advantage of the accuracy of an analytical model and the computational cost of a relatively standard unsteady CFD simulation, and can be used to predict the trajectory of the exhaled droplets for a variety of respiratory events.

Development of a Local Ventilation and Purification System with Integrated Supply and Exhaust Air for Healthcare Workers’ Protection in Infectious Disease Isolation Rooms

Development of a Local Ventilation and Purification System with Integrated Supply and Exhaust Air for Healthcare Workers’ Protection in Infectious Disease Isolation Rooms