Ventilation Configurations Research Articles

Experimental study on the effect of mechanical ventilation on cable tray fires in compartments

This study deals with the effect of ventilation flow rate and the ventilation configuration on the behavior of a cable tray fire in a confined and mechanically ventilated enclosure. Results are based on large-scale fire tests performed within the framework of the OECD Nuclear Energy Agency (NEA) PRISME projects. The fire source, identical for all tests, consisted in five horizontal cable trays measuring 3 m in length, stacked vertically and filled with halogen-free flame retardant cable-type, non-powered cables. The installation consists of two rooms connected by an open doorway. Two ventilation configurations were considered with two different arrangements of the inlet and outlet branches. The analysis demonstrates the effects of ventilation flow rate and air intake position on the fire heat release rate (HRR). Decreasing the ventilation flow rate reduces the maximum HRR and delays combustion on the trays, which burn one after the other rather than simultaneously. This result is the consequence of oxygen vitiation near the cable trays, which reduces the horizontal flame spread on each cable tray. The analysis also discusses the phenomenon of low frequency oscillatory behavior of fire in a ventilated enclosure. The results highlight that the conditions of occurrence of oscillations combine two criteria: a low ventilation flow rate to favor the release of unburnt gases and an appropriate configuration of the ventilation air intake to generate ignition of premixed gases.

Efficient Ventilation Configurations for an Isolation Ward in View of Reducing the Potential Contamination of Its Occupants

The rise of respiratory infections, such as the SARS epidemic in 2003, and the H1N1 influenza epidemic in 2011, highlighted the importance of efficient ventilation in healthcare facilities. The novel SARS -Cov-2 disease has sparked many concerns over the ventilation performance of multi-bed isolation wards and their ability to suppress airborne infectious contamination. The study is primarily based on suggesting ventilation improvements for a locally acquired multi-bed intensive care isolation unit. The study via ANSYS -fluent incorporates a k-ε turbulent model that is used to analyze exhaled CO2 particle tracks of 4 human models. Three ventilation strategies, namely, Displacement, Stratum, and Curtain -Air-jet are initially considered and evaluated based on two indoor air quality indices (IAQs), namely, air change efficiency and contaminant removal effectiveness. Stratum ventilation comfortably exhibits unidirectional flow characteristics with an air change efficiency of 0.946, which was obtained through ANSYS -CFX while each suggested configuration is capable of achieving a contaminant removal effectiveness value greater than 1 which depicts that the contamination source is not in a perfect mixing zone. Results provided inconclusive evidence to draw correlations between the two IAQ indices and thus it is confirmed that these indices solely depend on the type of ventilation strategy. Contaminant concentration on health care worker breathing plane and exhaled particle tracking for 4 minutes in each analyzed configuration revealed that both Stratum and Curtain air-jet models improve the escaped particle efficiency by 25% and 29% respectively compared to the base model. These models are further compared against reference values specified by guidelines to evaluate their suitability for real-world operation. KEYWORDS: Ventilation, efficiency, ANSYS, isolation, airborne particles, Displacement, Stratum, Curtain -Air-jet

Air Quality Improvement in COVID-19 Pandemic: Numerical Study of ventilation system in a classroom

Air quality plays a significant role during the coronavirus pandemic. Air acts as a spreading media as well as a control measure for infection in polluted spaces. Insufficient ventilation around the building may lead to a rise of pollutants carrying the virus. One way to improve ventilation is by increasing the air change rate. This study investigates the air change rate effectiveness in reducing droplets spreading in a classroom. Cases with various layouts of inlet and outlet vents are considered, and the spread of droplets is studied. The airflow analysis shows the impact of the different ventilation layout configurations. The results show that the CFD model simulation indicates an optimum ventilation configuration to decrease the droplet spread. The discrete phase model results also determine the trajectory of droplets spread along the classroom. CFD results show that in the selected configuration, a significant number of droplets are expelled to the outside and reduce their concentration inside the classroom.

Airborne migration behaviour of SARS-CoV-2 coupled with varied air distribution systems in a ventilated space

Air distribution system could critically affect SARS-CoV-2 transmission in indoor space; therefore, this study aims at demonstrating numerical characteristics of SARS-CoV-2 migration with varied air distribution system configurations. Seven cases were investigated regarding three major aspects: how fast suspended particles can be removed from the ventilated space or changed into deposited particles; how much particles are attached to various object surfaces which leads to an infection by touching fomite. All cases were analyzed through computational fluid dynamics (CFD). Both different shapes (round or linear diffusers) and installation locations (ceiling or floor) of inlet and outlet diffusers were investigated. Results showed that different air distribution system would lead to different dispersion profiles of infectious particles and different deposition pattern of particles on interior surfaces. With the same air flow rate, linear-diffuser would perform better for CO2 extraction while requiring less time to remove or collide the same magnitude of suspended droplets compared to round-diffuser. However, how quickly removed or suspended droplets collide is not proportional to how less the number of total particles are remained. Two additional cases with double sized space possessing best ventilation configuration were also examined to explore potential application of the best-ventilated configuration to various spatial expansion cases.

The Trade-Off between Airborne Pandemic Control and Energy Consumption Using Air Ventilation Solutions.

Airborne diseases cause high mortality and adverse socioeconomic consequences. Due to urbanization, more people spend more time indoors. According to recent research, air ventilation reduces long-range airborne transmission in indoor settings. However, air ventilation solutions often incur significant energy costs and ecological footprints. The trade-offs between energy consumption and pandemic control indoors have not yet been thoroughly analyzed. In this work, we use advanced sensors to monitor the energy consumption and pandemic control capabilities of an air-conditioning system, a pedestal fan, and an open window in hospital rooms, classrooms, and conference rooms. A simulation of an indoor airborne pandemic spread of Coronavirus (COVID-19) is used to analyze the Pareto front. For the three examined room types, the Pareto front consists of all three air ventilation solutions, with some ventilation configurations demonstrating significant inefficiencies. Specifically, air-conditioning is found to be efficient only at a very high energy cost and fans seem to pose a reasonable alternative. To conclude, a more informed ventilation policy can bring about a more desirable compromise between energy consumption and pandemic spread control.

Study of a novel front-roof-back natural ventilation system for Chinese solar greenhouses.

A Chinese solar greenhouse (CSG) is a highly efficient and energy-saving horticultural facility. Ventilation is significantly important for crop production in the greenhouse, and the vent configuration is the basis of the greenhouse design. Current CSG ventilation structures mostly include front bottom vents and top vents to create a suitable temperature environment for the normal development of crops. However, the ventilation capacity and efficiency are limited. In the present study, we proposed a comprehensive front bottom + top + back roof (FTB) ventilation configuration. The greenhouse ventilation was investigated during the summer season by means of field testing and simulation, and the performance of three ventilation structures-front bottom + top (FT), front bottom + back roof (FB) and FTB-was compared. The results showed that FTB stabilized the greenhouse temperature for 20 s less time than FT and FB. The cooling rate of FTB showed a 24.84% and 5.52% improvement over FT and FB, respectively, and the average temperature showed a 13.81% and 3.65% decrease, respectively. Moreover, the ventilation performance of the side walls was investigated in order to determine if they might serve as auxiliary structures for FTB ventilation. Nevertheless, the improvements of cooling rate, wind speed and average temperature were only 0.52%, 2.09% and 0.11%, respectively. The results demonstrated that the novel FTB ventilation proposed in the present study significantly improved ventilation efficiency and uniformity compared with conventional ventilation structures. The results presented herein provide theoretical support for the use and design of greenhouses suitable for China's special climate.

Validation of a numerical model for hot-spot detection on the surface of a rotor pole using a scale model of a hydroelectric generator

To meet the ever-increasing demand for electricity, Hydro-Québec is investigating the viability of running its existing hydroelectric generators at higher power levels than their current operating limits. To assist in this investigation, numerical models capable of simulating the conjugate turbulent air flow and heat transfer phenomena in these generators were formulated and then validated, by using them to predict these phenomena within a scale model of a hydroelectric generator available at Hydro-Québec’s Research Institute and comparing the results to complementary experimental data. Reynolds-averaged governing equations were used, with turbulent stresses and heat fluxes approximated using eddy-viscosity and eddy-diffusivity approaches, in conjunction with the standard k − ɛ and a k − ω shear-stress-transport models, constant turbulent Prandtl number, and specialized treatments of the near-wall regions. Variable- and constant-fluid-property formulations (with coupled and decoupled solutions of the fluid flow and heat transfer) were assessed. The discretization of the complex geometry and the governing equations, and solutions of the discretized equations, were done using commercial codes. These numerical models gave favorable and comparable results, with predictions of global flow quantities (such as windage losses and overall mass flow rates) lying within 4%, and average and maximum temperatures of the pole surface within 5 °C and 3 °C, respectively, of the corresponding experimental data when using the constant-property, coupled, standard k − ɛ model with specialized wall functions. However, the equivalent decoupled model, which was the least computationally intensive, was also adequate for the task at hand. Numerical assessments of two alternate ventilation configurations in the scale model were also undertaken. They showed that increasing the surface area of the spider arms reduced the maximum temperature of the pole by 2.6 °C; and restricting the rotor inlet area reduced the windage losses and the maximum temperature of the pole by 4.7% and 1.5 °C, respectively. • 3D Conjugate heat transfer simulations of a hydroelectric generator scale model. • Validation of flow and temperature distributions by way of experimental measurements. • In contrast with design assumptions, flow across the rotor rim ducts is non-uniform. • Numerical predictions of hot-spots on the scale model’s rotor to within 2.7 °C. • Proposed modifications to the rotor design to reduce rotor pole hot-spot temperatures.

Numerical investigation on the thermal management of lithium-ion battery system and cooling effect optimization

The widespread application of lithium-ion batteries as the practice facility of energy storage has come alongside much unforeseen fire safety and thermal runaway issues that leads to increasing research interests. A comprehensive understanding of the thermal features of battery packs and the heat exchange process of energy storage systems is imperative. In this paper, a three-dimensional thermo-electrochemical model has been developed to simulate the detailed temperature distribution of battery packs. The numerical analysis of the cooling effect with both natural and forced air ventilation configurations are compared as well. Moreover, the artificial neural network (ANN) model was coupled with the computational fluid dynamics (CFD) simulation results to perform an optimization of a specific configuration battery system considering configuration dimensions and operating conditions simultaneously. The ANN model builds a relationship between battery spacing and ambient cooling properties. It was found that the changing of ambient pressure creates a larger temperature drop under the forced air cooling than that under natural ventilation. The optimum design for the battery pack can decrease the maximum temperature and the temperature difference by 1.94% and 17%, respectively. Overall, the present modelling framework presents an innovative approach to utilising high-fidelity CFD numerical results as inputs for establishing ANN training dataset, potentially enhancing the state-of-art thermal management of lithium-ion battery systems reducing the risks of thermal runaway and fire outbreak.

Large-Eddy Simulations of Wind-Driven Cross Ventilation, Part 2: Comparison of Ventilation Performance Under Different Ventilation Configurations

Natural ventilation can contribute to a sustainable and healthy built environment, but the flow can be highly dependent on the ventilation configuration and the outdoor turbulent wind conditions. As a result, quantifying natural ventilation flow rates can be a challenging task. Wind tunnel experiments offer one approach for studying natural ventilation, but measurements are often restricted to a few points or planes in the building, and the data can have limitations due to the intrusive nature of measurement techniques or due to challenges with optical access. Large-eddy simulations (LES) can offer an effective alternative for analyzing natural ventilation flow, since they can provide a precise prediction of turbulent flow at any point in the computational domain and enable accurate estimates of different ventilation measures. The objective of this study is to use a validated LES set-up to investigate the effect of the opening size, opening location and wind direction on the ventilation flow through an isolated building. The effects are quantified in terms of time-averaged and instantaneous ventilation flow rates, age of air, and ventilation efficiency. The LES results indicate that, for this isolated building case, the effect of the wind direction is more pronounced than the effect of the size and position of the ventilation openings. Importantly, when ventilation is primarily driven by turbulent fluctuations, e.g. for the 90° wind direction, an accurate estimation of the ventilation rate requires knowledge of the instantaneous velocity field.

Numerical Simulation of Airborne Disease Spread in Cage-Free Hen Housing with Multiple Ventilation Options.

Simple SummaryAirborne diseases, such as highly pathogenic avian influenza, are among the deadliest threats to the egg industry and can easily cause devastating losses of poultry when severe outbreak events occur. During the ongoing transition to cage-free production, uncertainty regarding ventilation designs for cage-free facilities also exposes vulnerability with respect to disease control within facilities. To address ventilation system design and the capability of restraining internal airborne disease spread, this study was conducted to model and compare indoor airborne virus dispersal for a commercial cage-free hen house within four different ventilation schemes. A one-eighth length, full-scale, floor-raised hen house with commercial bird density was modeled to simulate the environmental conditions and disease spread under steady-state conditions inside the barn during cold weather. Analyses of the dispersion of virus particles coupled with airflow patterns were performed by visualizing contours of virus particles and air velocities at critical locations. In addition, the virus mass fraction at bird level was of particular interest when comparing and evaluating the performance of various ventilation schemes. The simulation results demonstrated that the internal dispersion of airborne virus particles was determined by indoor airflow patterns and implied the role of ventilation configuration in reducing disease spread in a poultry barn. Furthermore, valuable insights are provided for further investigations of ventilation options for cage-free hen housing.The current ventilation designs of poultry barns have been present deficiencies with respect to the capacity to protect against disease exposure, especially during epidemic events. An evolution of ventilation options is needed in the egg industry to keep pace with the advancing transition to cage-free production. In this study, we analyzed the performances of four ventilation schemes for constraining airborne disease spread in a commercial cage-free hen house using computational fluid dynamics (CFD) modeling. In total, four three-dimensional models were developed to compare a standard ventilation configuration (top-wall inlet sidewall exhaust, TISE) with three alternative designs, all with mid-wall inlet and a central vertical exhaust. A one-eighth scale commercial floor-raised hen house with 2365 hens served as the model. Each ventilation configuration simulated airflow and surrogate airborne virus particle spread, assuming the initial virus was introduced from upwind inlets. Simulation outputs predicted the MICE and MIAE models maintained a reduced average bird level at 47% and 24%, respectively, of the standard TISE model, although the MIRE model predicted comparable virus mass fraction levels with TISE. These numerical differences unveiled the critical role of centrally located vertical exhaust in removing contaminated, virus-laden air from the birds housing environment. Moreover, the auxiliary attic space in the MIAE model was beneficial for keeping virus particles above the bird-occupied floor area.

Optimized mechanism for fast removal of infectious pathogen-laden aerosols in the negative-pressure unit

It has been frequently emphasized that highly contagious respiratory disease pathogens (such as SARS-CoV-2) are transmitted to the other hosts in the form of micro-sized aerosols (< 5 μm) in the air without physical contacts. Hospital environments such as negative-pressure unit are considered being consistently exposed to pathogens, so it is essential to quickly discharge them through the effective ventilation system. To achieve that, in the present study, we propose the optimized ventilation mechanism and design for the fastest removal of pathogen-laden aerosol using numerical simulations. We quantitatively evaluated the aerosol removal performance of various ventilation configurations (combinations of air exhaust and supply ducts), and found that the key mechanism is to form the coherent (preferentially upward) airflow structure to surround the respiratory flow containing the aerosol cluster. We believe that the present findings will play a critical role in developing the high-efficiency negative-pressure facility irrespective of its size and environments.

Computational Study of Thermal Comfort and Reduction of CO2 Levels inside a Classroom.

Due to the current COVID-19 pandemic, guaranteeing thermal comfort and low CO2 levels in classrooms through efficient ventilation has become vitally important. This study presents three-dimensional simulations based on computational fluid dynamics of airflow inside an air-conditioned classroom located in Veracruz, Mexico. The analysis included various positions of an air extractor, Reynolds numbers up to 3.5 × 104, four different concentrations of pollutant sources, and three different times of the day. The simulations produced velocity, air temperature, and CO2 concentrations fields, and we calculated average air temperatures, average CO2 concentrations, and overall ventilation effectiveness. Our results revealed an optimal extractor position and Reynolds number conducive to thermal comfort and low CO2 levels due to an adequate ventilation configuration. At high pollutant concentrations, it is necessary to reduce the number of students in the classroom to achieve safe CO2 levels.

Aerosol transmission in passenger car cabins: Effects of ventilation configuration and driving speed.

Identifying the potential routes of airborne transmission during transportation is of critical importance to limit the spread of the SARS-CoV-2 virus. Here, we numerically solve the Reynolds-averaged Navier–Stokes equations along with the transport equation for a passive scalar in order to study aerosol transmission inside the passenger cabin of an automobile. Extending the previous work on this topic, we explore several driving scenarios including the effects of having the windows fully open, half-open, and one-quarter open, the effect of opening a moon roof, and the scaling of the aerosol transport as a function of vehicle speed. The flow in the passenger cabin is largely driven by the external surface pressure distribution on the vehicle, and the relative concentration of aerosols in the cabin scales inversely with vehicle speed. For the simplified geometry studied here, we find that the half-open windows configuration has almost the same ventilation effectively as the one with the windows fully open. The utility of the moonroof as an effective exit vent for removing the aerosols generated within the cabin space is discussed. Using our results, we propose a “speed–time” map, which gives guidance regarding the relative risk of transmission between driver and passenger as a function of trip duration and vehicle speed. A few strategies for the removal of airborne contaminants during low-speed driving, or in a situation where the vehicle is stuck in traffic, are suggested.

Influence of the Height in a Colombian Multi-Tunnel Greenhouse on Natural Ventilation and Thermal Behavior: Modeling Approach

The dimensions of a passive greenhouse are one of the decisions made by producers or builders based on characteristics of the available land and the economic cost of building the structure per unit of covered area. In few cases, the design criteria are reviewed and the dimensions are established based on the type of crop and local climate conditions. One of the dimensions that is generally exposed to greater manipulation is the height above the gutter and the general height of the structure, since a greenhouse with a lower height has a lower economic cost. This has led some countries in the tropical region to build greenhouses that, due to their architectural characteristics, have inadequate microclimatic conditions for agricultural production. The objective of this study was to analyze the effect on air flows and thermal distribution generated by the increase of the height over gutter of a Colombian multi-tunnel greenhouse using a successfully two-dimensional computational fluid dynamics (CFD) model. The simulated numerical results showed that increasing the height of the greenhouse allows obtaining temperature reductions from 0.1 to 11.7 °C depending on the ventilation configuration used and the external wind speed. Likewise, it was identified that the combined side and roof ventilation configuration (RS) allows obtaining higher renovation indexes (RI) in values between 144 and 449% with respect to the side ventilation (S) and roof ventilation (R) configurations. Finally, the numerical results were successfully fitted within the surface regression models responses.

Behavior of cough droplets emitted from Covid-19 patient in hospital isolation room with different ventilation configurations

The world is now facing the Covid-19 pandemic and the control of Covid-19 spread in health care facilities is a serious concern. The ventilation system in hospital isolation rooms with infectious patients plays a significant role in minimizing the spread of viruses and the risk of infection in hospital. In this study, computational fluid dynamics (CFD) simulation is applied to investigate the important factors on transport and evaporation of multi-component cough droplets in the isolation room with different ventilation configurations. We analyzed the effects of various air outlet positions on the removal efficiency of infectious droplets in isolation room and proposed the optimum location of exhaust vent in hospital isolation room to maximize the droplet removal efficiencies. We found that the evaporation rate of droplets is strongly dependent on the relative humidity (RH) and, at low RH, the large-sized droplets with Covid-19 virus can evaporate quickly and become small-sized aerosols to stay in air for a long time and the Covid-19 can propagate more easily through the respiratory organs during breathing. It also explains why the Covid-19 can propagate faster in winter with low humidity than in summer with high humidity.

ANALYSIS AND EVALUATION OF THE THERMOPHYSICAL PROPERTIES OF VENTILATED FAÇADE TYPOLOGIES

&amp;lt;jats:p&amp;gt;The energy efficiency of the construction sector is denoted by the European energy and environmental policies, by international standards and national legislation. Ventilated facades can contribute towards more efficient buildings, hence this paper focuses on the evaluation of ventilated fa&amp;ccedil;ade construction typologies and the impact of thermal radiance exposure. The selected scenarios were evaluated in terms of thermophysical analysis and laboratory measurements, and based on the results useful conclusions can be derived. Nevertheless, there is need of further investigation towards alternative configurations of the facades, such as implementing alternative ventilation configurations and patterns as well as more innovative and technical efficient construction materials.&amp;lt;/jats:p&amp;gt;

Experimental study on the effect of mechanical ventilation conditions and fire dynamics on the pressure evolution in an air-tight compartment

The paper presents a comprehensive set of experiments on the effect of mechanical ventilation conditions and fire dynamics on temporal pressure evolution in a reduced-scale, air-tight and mechanically-ventilated enclosure.A square propane burner with flow controller imposes a quadratic fire growth followed by a steady-state (0.1 or 0.2 g/s) and then a quadratic decay phase. Eight tests are discussed with different ventilation conditions in terms of flow resistances and initial ventilation flow rates ranging from 12 to 40 m3/h, corresponding to air renewal rates of 6.4–21.3 h−1.The pressure evolution is characterized by an over-pressure peak (up to 900 Pa) followed by a quasi-steady state and then, an under-pressure peak (up to −760 Pa). The pressure variation is due to the mechanical effect (i.e., ventilation configurations), while also influenced by thermal effects. The pressure amplitudes increase with ventilation resistances. Both the total network resistance and individual resistances in admission and extraction ducts are important for the pressure variation. The enhancement and reduction of ventilation flow rates depend on both the fire-induced pressure and ventilation resistances. Experimental results show that the mechanical effect does not strongly affect gas temperatures.

Indoor Air Quality in Naturally Ventilated Classrooms. Lessons Learned from a Case Study in a COVID-19 Scenario

This paper describes the implementation of a series of ventilation strategies in a nursery and primary school from September 2020, when the government decided to resume the students’ face-to-face activity in the middle of a COVID scenario. Air quality and hygrothermal comfort conditions were analysed before the pandemic and compared for different ventilation configurations in a post-COVID scenario. Ventilation strategies included the protocols issued by the Public Administration, while others were developed based on the typological configuration and use of the school. Results revealed that it is advisable to implement certain strategies that reduce the risk of infection among the occupants of the spaces, without a significant decrease in hygrothermal comfort. Given the importance of maintaining better IAQ in the future within classrooms, and regarding the pre-COVID situation, these strategies may be extended beyond this pandemic period, through a simple protocol and necessary didactic package to be assumed by both teachers and students of the centre.

Performance of Asbestos Enclosure Ventilation: Laboratory Evaluation of Complex Configuration.

The aim of the study was to find out good practices for effective air distribution inside a complex shaped asbestos enclosure and for control of pressure differences between the enclosure and the surroundings. In addition, sufficient pressure difference for asbestos containment was tested. The effect of air distribution was studied in laboratory conditions by constructing an L-shaped asbestos enclosure and connecting it to a negative pressure unit. The efficiency of six different ventilation configurations was compared using a tracer decay method and the local air change indexes as the performance indicator. The sufficient negative pressure for containment was assessed by simulating person traffic to and from the enclosure and recording the pressure difference continuously. The effect of a pressure controller unit in maintaining the target pressure difference was also tested by simulating filter loadings of the negative pressure unit causing changes in the air flow rate. The results showed that high nominal air change rates alone do not guarantee good air distribution. Effective air distribution within an asbestos enclosure can be arranged by locating additional air supply openings far away from the air exhaustion point, using recirculation air with a pressure controller, or extending the exhaust location to the poorly ventilated areas. A pressure difference of at least −10 Pa is recommended to ensure a sufficient margin of safety in practical situations.

Full-scale CFD simulation of commercial pig building and comparison with porous media approximation of animal occupied zone

Many CFD simulation studies substitute Animal Occupied Zone (AOZ) as porous media to reduce computation time and resources. With the improved computational capacity, it is now possible to include realistic geometric models of individual animals and partition walls. This study presents a CFD model of a large commercial-sized, hybrid ventilated pig building with 1,360 animals. It compares the developed full-scale model (that includes pigs and partition walls) with a simplified model that substitutes AOZ with a porous media approximation. We find that the simplified model with porous media approximation predicts the airflow rates and overall flow characteristics in the building as good as the full-scale model. Full-scale simulations with animals and partition walls give a snapshot of a particular situation in the building and the environmental conditions in the AOZ level; for example, we found that even in a well-ventilated pig building temperatures in the AOZ were, on average, 3 °C - 5 °C higher than at a height 0.5 m above the AOZ. Including the realistic shape of animals and the partition walls is overkill if the aim is to study ventilation configurations’ effects. However, porous media models are not good enough to describe the conditions in the AOZ.