Exhaust Vents Research Articles

The Impact of Exhaust Louvres and Emission Rates on The Effectiveness of Parking Lot Ventilation

Abstract This research investigated a couple of aspects of CO emissions from car vehicles. Firstly, it explored the influence of varying the number of vehicles in operation. Secondly, it analysed the significance of exhaust vents affecting the concentration of CO through parking space lots. The conducted analysis relied on simulation data obtained using ANSYS-Software, as opposed to experimental data. The accuracy of the natural ventilation model was validated. The impact of various running vehicles was examined, including those with half, partially, and fully-loaded. The objective was to determine the correlation between the number of running vehicles and the increase in CO concentration. In addition, several configurations of exhaust vents were examined for the fully loaded scenario. As a result, it was shown that the architectural layout has an impact on the natural ventilation system, which may not be suitable for human health, especially when dealing with greater car emission rates.

Energy consumption and thermal comfort assessment using CFD in a naturally ventilated indoor environment under different ventilations

The rising energy demands of modern buildings necessitate the proper balance between occupant comfort and energy efficiency. This study numerically evaluates the effect of different inlet and exhaust vent profiles on indoor IEQ and energy consumption in well-validated, occupied office buildings for a cold climate conditions. Using ANSYS products, the research evaluates the impact of different ventilation configurations on occupant comfort using different comfort parameters such as, PMV, PPD, air temperature, temperature gradient, fluid flow velocity. The study also analyze how different ventilation configurations affect the thermal load on the radiator for indoor thermal comfort. The findings reveal a significant effect of ventilation profiles on both IEQ and energy consumption. Inadequate ventilation configuration selection can lead to a significant increase in radiator heat load, potentially increase up to 117.3%. Conversely, the adoption of an optimized ventilation strategy can simultaneously reduce energy consumption and improve indoor occupant thermal comfort. Indoor occupant comfort with minimal radiator heat load can be achieved using vertically oriented, rectangular inlet and exhaust vents with a perimeter ratio of 0.611. This research contributes to the development of sustainable buildings and describes indoor comfort design for cold climate conditions.

Analysis of the airflow features and ventilation efficiency of an Ultra-Clean-Air operating theatre by qDNS simulations and experimental validation

Ultra-Clean-Air (UCA) operating theatres aim to minimise surgical instrument contamination and wound infection through high flow rates of ultra-clean air, reducing the presence of Microbe Carrying Particles (MCPs). This study investigates the airflow patterns and ventilation characteristics of a UCA operating theatre (OT) under standard ventilation system operating conditions, considering both empty and partially occupied scenarios. Utilising a precise computational model, quasi-Direct Numerical Simulations (qDNS) were conducted to delineate flow velocity profiles, energy spectra, distributions of turbulent kinetic energy, energy dissipation rate, local Kolmogorov scales, and pressure-based coherent structures. These results were also complemented by a tracer gas decay analysis following ASHRAE standard guidelines. Simulations showed that contrary to the intended laminar regime, the OT’s geometry inherently fosters a predominantly turbulent airflow, sustained until evacuation through the exhaust vents, and facilitating recirculation zones irrespective of occupancy level. Notably, the occupied scenario demonstrated superior ventilation efficiency, a phenomenon attributed to enhanced kinetic energy induced by the additional obstructions. The findings underscore the critical role of UCA-OT design in mitigating MCP dissemination, highlighting the potential to augment the design to optimise airflow across a broader theatre spectrum, thereby diminishing recirculation zones and consequently reducing the propensity for Surgical Site Infections (SSIs). The study advocates for design refinements to harness the turbulent dynamics beneficially, steering towards a safer surgical environment.

Numerical Study on the Efficiency of the Point Smoke Exhaust System in V-shaped Urban Underground Road Tunnel

In order to study the exhaust effect of the point smoke exhaust system in V-shaped urban underground tunnel with different structures, effects of the slope differences on both sides of the slope changing point and the operating mode of the exhaust vent on the smoke spread distance, temperature at the height of 2 m above the road and the ceiling temperature were studied by the numerical method. The research results show that for the symmetric V-shaped tunnel, smoke can be controlled in the required range, but for asymmetric V-shaped tunnel with the slope difference on both sides, smoke cannot be easily controlled, ventilation supply is needed to improve the smoke exhaust efficiency. Point smoke exhaust system cannot effectively reduce the maximum temperature of the ceiling above the fire. When the fire source power is large, for the symmetrical V-shaped tunnel with a small slope, some fire prevention measures must be taken to protect the ceiling partition. For the asymmetric V-shaped tunnel, two exhaust vents opened on the small slope side and four opened on the large slope side are suggested for the occupant safe evacuation in tunnel.

Experimental investigation of impact of fire size on heat transfer and flame behavior of initial stage unsteady pool fires inside a cubical enclosure

The ventilation equipment for enclosed spaces or office rooms is specified according National Building Code of India published by the Bureau of Indian Standards. Natural ventilation peri-odically together with mechanical ventilation is recommended to remove pollutants. The need to study fire and smoke behavior inside a completely closed room with air intake and exhaust vents becomes important in case of low or no mechanical ventilation service. An experimental study on unsteady heptane pool fires of different sizes in their initial stages was conducted in a cubical fire test chamber of 27 m3 inside dimensions. The compartment was naturally ventilated with a typical configuration of a vertical intake on a side wall and an exhaust vent at the ceiling leading into a duct. Three circular pans of diameters 0.34, 0.47 and 0.61 m were employed to generate the fire with n-heptane as fuel on a bed of water. Temperatures, wall heat fluxes and mass loss rate were measured. The flame was visualized using a video camera through a tempered view glass. The total heat transfer to the ceiling and wall increased with the increase in fire size as the flames became taller in the initial stages (3-4 minutes) with sig-nificant increase in case of 500 kW fire. The smoke layer was observed at about mid height (1.5 m) above floor. The leaning behavior of flames was seen due to naturally induced air inflow. The wall heat flux of about 50 kW/m2 obtained indicate hazardous environment for further flame spread. A fourfold increase in mass loss rate was observed with just 2.5 times increase in fire size inside the ceiling vented compartment.

Deck level air extraction and its impact on trichloramine concentrations in an indoor swimming pool: A numerical study

Trichloramine (NCl3) is a disinfection by-product (DBP) that forms in swimming pool water due to water chlorination. It easily becomes airborne when water is agitated and can impair lung functions and cause illnesses such as asthma and bronchitis in workers and bathers, when inhaled. In indoor swimming pools, NCl3 must be removed from the breathing zones with mechanical ventilation. Since it tends to accumulate at the water surface, ASHRAE's recommendations are to add lower extraction vents to capture DBP. However, no guideline is found in literature on the number of vents, their position in the enclosure or their minimum airflow rate. This paper presents a numerical investigation of the impacts on NCl3 concentrations when adding extraction vents at deck level in a swimming pool hall in Montreal (Canada). The efficiency of four ventilation scenarios that include low extraction vents was determined numerically and compared to the reference case which does not have lower-level exhaust vents. Results show that the position of these vents affects the air movement above the water surface, causing either unwanted accumulation or reduction of NCl3. The most significant reduction was obtained when placing these vents on the side of the enclosure where low level air supplied grills are located. Finally, the NCl3 that is not extracted is sent upwards and diluted thanks to the nearby air delivery grills. The results demonstrate the importance of a numerical assessment of the airflow patterns in a pool enclosure and especially above the water and deck before planning the position of these deck level extraction vents.

Reconciling Airborne Disease Transmission Concerns with Energy Saving Requirements: The Potential of UV-C Pathogen Deactivation and Air Distribution Optimization

The COVID-19 pandemic caused a paradigm shift in our way of using heating, ventilation, and air-conditioning (HVAC) systems in buildings. In the early stages of the pandemic, it was indeed advised to reduce the reuse and thus the recirculation of indoor air to minimize the risk of contamination through inhalation of virus-laden aerosol particles emitted by humans when coughing, sneezing, speaking, or breathing. However, such recommendations are not compatible with energy saving requirements stemming from climate change and energy price increase concerns, especially in winter and summer when the fraction of outdoor air supplied to the building needs to be significantly heated or cooled down. In this experimental study, we aim at providing low-cost and low-energy solutions to modify the ventilation strategies currently used in many buildings to reduce the risk of respiratory disease transmission. Measurements of the indoor air bacterial concentration in a typical office building reveal that ultraviolet germicidal irradiation (UVGI) modules added to the HVAC system are very efficient at inactivating pathogens present in aerosols, leading to indoor concentrations as low as outdoor concentrations, even with significant indoor air recirculation. Moreover, measurements of the CO2 and aerosol air concentration reveal that, with air supply vents placed in the ceiling, placing the air exhaust vents near the floor instead of on the ceiling can improve the ventilation capacity in terms of effective flow rate, with significant consequences in terms of energy savings.

Temporal and Spatial Distribution of SARS-CoV-2 Aerosols in a Large-Scale Fangcang Shelter Hospital in Shanghai, China

The coronavirus disease 2019 (COVID-19) pandemic caused by frequently mutating severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has had a worldwide impact. However, detailed data on the potential aerosol transmission of SARS-CoV-2 in real-world and controlled laboratory settings remain sparse. During the COVID-19 pandemic in Shanghai, China in 2022, samples were collected in a Fangcang shelter hospital, a large-scale temporary hospital rapidly built by converting the existing National Exhibition and Convention Center (Shanghai) into a health care facility. Aerosol samples at different sites and intervals around patients and in public areas, surface samples, and pharyngeal swab samples from corresponding patients were included. Samples were tested for SARS-CoV-2 using real-time quantitative polymerase chain reaction (RT-qPCR) assays, followed by sequencing if the cycle threshold (Ct) value was < 30. The positivity rate for SARS-CoV-2 in aerosol samples was high in contaminated zones (37.5%, 104/277), especially around the bed (41.2%, 68/165) and near ventilation inlets (45.2%, 14/31). The prevalence of SARS-CoV-2 around the bed, public areas, and air inlets of exhaust vents fluctuated and was closely related to the positivity rate among patients at corresponding sampling sites. Some surface samples of different personal protective equipment from medical staff had high positivity rates. Sixty sequences of joined ORF1ab and spike genes obtained from sixty samples represented two main clusters of Omicron SARS-CoV-2. There was consistency in virus sequences from the same patient and their environment, and the detected virus sequences matched those of virus strains in circulation during the collection periods, which indicated a high likelihood of cross-contamination in the Fangcang shelter hospital. In summary, the results provide a quantitative and real landscape of the aerosol transmission of SARS-CoV-2 and a patient-centered view of contamination in large and enclosed spaces and offer a useful guide for taking targeted measures to avoid nosocomial infections during the management of SARS-CoV-2 or other respiratory virus diseases in a Fangcang shelter hospital.

Optimal sensor placement for personal inhalation exposure detection in static and dynamic office environments

Modern health and productivity concerns related to air pollutant exposure in buildings have sparked the need for occupant-centric monitoring and ventilation control. The existing personal exposure monitoring is often restricted to stationary air quality sensors and static occupancy. This study aims to identify optimal stationary sensor placement that best represents exposure to CO2, PM2.5, and PM10 under static and dynamic office occupancies. A total of 48 controlled chamber experiments were executed in four office layouts with variation of occupant numbers (2, 4, 6 or 8), activities (sitting/standing and static/dynamic), ventilation strategies (mixing/displacement) and air change rates (0.5–0.7 h−1, 2.4–2.6 h−1, and 3.8–4.2 h−1). The breathing zone concentration of a reference occupant was monitored with concurrent measurements at seven stationary locations: front edge of the desk, sides of two desks, two sidewalls, and two exhaust vents. The proximity of sensors to the reference occupant and ventilation rate/strategy were important determinants of personal exposure detection. Regression analyses showed that the wall- and desk-mounted CO2 sensors near the occupant (<1 m) best captured CO2 exposure under dynamic–standing activities (R2∼0.4). The wall immediately behind the seated occupant and the ceiling-mounted exhaust near the standing occupant (<1–1.5 m) were the best sensor placements for capturing exposure to particles (R2=0.8–0.9). Separating static from dynamic occupancy activities resulted in improved exposure prediction by 1.4-6.1× . This study is a step towards provision of practical guidelines on stationary air quality sensor placement indoors with the consideration of dynamic occupancy profiles.

Modeling of dispersion of aerosolized airborne pathogens exhaled in indoor spaces

Since the beginning of the COVID19 pandemic, there has been a lack of data to quantify the role played by breathing-out of pathogens in the spread of SARS-Cov-2 despite sufficient indication of its culpability. This work aims to establish the role of aerosol dispersion of SARS-Cov-2 virus and similar airborne pathogens on the spread of the disease in enclosed spaces. A steady-state fluid solver is used to simulate the air flow field, which is then used to compute the dispersion of SARS-Cov-2 and spatial probability distribution of infection inside two representative classrooms. In particular, the dependence of the turbulent diffusivity of the passive scalar on the air changes per hour and the number of inlet ducts has been given due consideration. By mimicking the presence of several humans in an enclosed space with a time-periodic inhalation–exhalation cycle, this study firmly establishes breathing as a major contributor in the spread of the pathogen, especially by superspreaders. Second, a spatial gradient of pathogen concentration is established inside the domain, which strongly refutes the well-mixed theory. Furthermore, higher ventilation rates and proximity of the infected person to the inlet and exhaust vents play an important role in determining the spread of the pathogen. In the case of classrooms, a ventilation rate equivalent to 9 air changes or more is recommended. The simulations show that the “one-meter distance rule” between the occupants can significantly reduce the risk of spreading infection by a high-emitter.

Evaluating Natural Gas Emissions from Pneumatic Controllers from Upstream Oil and Gas Facilities in West Virginia.

In April of 2018, an optical gas imaging (OGI) and full flow sampler (FFS) emissions measurement study of pneumatic controllers (PCs) was conducted at 15 oil and natural gas production sites in West Virginia. The objective of the study was to identify and characterize PC systems with excessive emissions caused by maintenance issues or nonoptimized process conditions. A total of 391 PC systems were found on the sites and all were classified by the operator as snap-acting (on/off) intermittent venting PCs (IPCs) that should exhibit little gas release while the PC is closed between actuation events. The population was comprised of two groups, 259 infrequently actuating, lower emitting (LE) IPCs and 132 gas processing unit (GPU) liquid level IPCs and associated dump valve actuators that vent more frequently and have larger emission volumes. Using a PC-specific OGI inspection protocol with an assumed whole gas OGI detection threshold of 2.0 scfh, only 2 out of 259 LE-IPCs exhibited OGI detectable emissions indicating good inspection and maintenance practices for this category. Due to combined (ganged) GPU exhaust vents, the OGI inspection of the GPU liquid level IPCs was comparatively less informative and determination of single component IPC emissions by the FFS was more difficult. The time resolved FFS measurements of GPU IPCs defined three categories of operation: one that indicated proper function and two associated with higher emissions that may result from an IPC maintenance or process issues. The overall GPU IPC emission distribution was heavy tailed, with a median value of 12.8 scfh, similar to the 13.5 scfh whole gas IPC emission factor (EF). Total emissions were dominated by non-optimal temporal profile high-emitter IPC cases with the top 20% of IPC systems accounting for between 51.3% and 70.7% of GPU liquid level IPC emissions by volume. The uncertainty in the estimate was due to the ganged nature of the GPU exhaust vents. The highest GPU IPC emission came from a single malfunctioning unit with a measured whole gas value of 157 scfh. Up to six IPCs exceeded 100 scfh. An analysis of FFS emission measurements compared to liquids production per IPC unit employed indicated that production sites operating at a high level of liquids production test the limits of the site engineering, likely resulting in higher IPC emissions. Overall, this study found that the LE-IPCs with OGI-verified low closed bleed rates may emit well below the IPC EF while GPU liquid level IPC systems are likely well represented by the current IPC EF. IPCs that are experiencing a maintenance or process issue or that are operating at sites with a very high product throughput per IPC employed can emit at rates exceeding ten times IPC EF.

Influence of the ventilation strategy on the respiratory droplets dispersion inside a coach bus: CFD approach

The airborne transmission of the COVID-19 virus was considered the main cause of infection. The increasing concern about the virus spread in confined spaces, characterized by high crowding indexes and an often-inadequate air exchange system, pushes the scientific community to the design of many studies aimed at improving indoor air quality. The risk of transmission depends on several factors such as droplet properties, virus characteristics, and indoor airflow patterns. The main transmission route of the SARS-CoV-2 virus to humans is the respiratory route through small (<100 μm) and large droplets. In an indoor environment, the air exchange plays a fundamental role on the dispersion of the droplets. In this study, an integrated approach was developed to evaluate the influence of the ventilation strategy on the dispersion of respiratory droplets emitted inside a coach bus. There are no specific guidelines and standards on the air exchange rate (AER) values to be respected in indoor environments such as coach buses. The aim of this work is to analyse the influence of ventilation strategy on the respiratory droplet concentration and distribution emitted in a coach bus. Ansys FLUENT was used to numerically solve the well-known transient Navier-Stokes equations (URANS equations), the energy equation and using the Lagrangian Discrete Phase Model (DPM) approach to construct the droplet trajectories. The geometry is representative of an intercity bus, a vehicle constructed exclusively for the carriage of seated passengers. The 3D CAD model represented a coach bus with an HVAC system, within which an infected subject was present. The positions of exhaust vents and air-conditioning vents were chosen to ensure complete air circulation throughout the bus. The infected subject emitted droplets with a well-defined size distribution and mass through the mouth. The air exchange is provided in two different ways: general ventilation (from air intakes positioned along the bus windows and top side of central corridor) and personal ventilation (with air intakes for each passenger). For the general ventilation a single AER value was set (0.3 m3 s−1). The first results obtained showed a slight particle dispersion in the computational domain due to the airflow rate entered through the HVAC system, but a still elevated level of particle concentration tended to accumulate on the area near to infected subject. Additional analysis was executed to evaluate the beneficial effects linked to further addition of airflow through personal air-conditioning vents placed above every passenger’s head. The results show the importance of the use of the ventilation system inside a coach bus, highlighting how the contribution linked to of the personal air exchange rate can lead to a significant reduction of droplet concentration exposure and consequently a reduction of the risk of infection from airborne diseases.

Enhancing crop growth in rooftop farms by repurposing CO2 from human respiration inside buildings

Integrating cities with the surrounding environment by incorporating green spaces in creative ways would help counter climate change. We propose a rooftop farm system called BIG GRO where air enriched with carbon dioxide (CO2) produced through respiration from indoor spaces is applied through existing ventilation systems to produce a fertilization effect and increased plant growth. CO2 measurements were taken inside 20 classrooms and at two exhaust vents on a rooftop at Boston University in Boston, MA. Exhausted air was directed toward spinach and corn and plant biomass and leaf number were analyzed. High concentrations of CO2 persisted inside classrooms and at rooftop exhaust vents in correlation with expected human occupancy. CO2 levels averaged 1,070 and 830 parts per million (ppm), reaching a maximum of 4,470 and 1,300 ppm CO2 indoors and at exhaust vents, respectively. The biomass of spinach grown next to exhaust air increased fourfold compared to plants grown next to a control fan applying atmospheric air. High wind speed from fans decreased growth by approximately twofold. The biomass of corn, a C4 plant, experienced a two to threefold increase, indicating that alternative environmental factors, such as temperature, likely contribute to growth enhancement. Enhancing growth in rooftop farms using indoor air would help increase yield and help crops survive harsh conditions, which would make their installation in cities more feasible.

Numerical study on the smoke movement in office rooms with various exhaust vents settings

The ventilation system is essential to maintain a high level of the smoke layer to improve visibility during a building fire. The high level of the smoke layer allows the nearby exits can be easily located, and the fire sources can be identified during the building fire and rescue. Hence, the study of smoke movement in building fires with exhaust vent settings is essential to improve fire safety in the building. In this study, the smoke movement in real-scale offices is numerically investigated by utilising the Large Eddy Simulation (LES) computational model. Six scenarios with various exhaust vents settings are considered. The temperature distribution and the smoke layer height in the four office rooms and lobby area are analysed for all the cases. Results confirmed that the temperature distribution and the layer height have no significant difference by increasing exhaust vent size. However, the upper wall-mounted exhaust vents provide an effective smoke exhaust system, significantly increasing the smoke layer height in all office rooms.

Experimental study on temperature decay and smoke control in tunnel fires with combination of multi-point smoke exhaust and longitudinal ventilation

This paper investigates the longitudinal temperature distribution characteristics beneath the ceiling and smoke control of the tunnel with combination of multi-point smoke exhaust and longitudinal ventilation. Experiments are carried out in a model tunnel with dimensions of 60 m × 1.3 m × 0.67 m. The longitudinal wind speed is set to 0–0.5 m/s, the exhaust air volume to 0.34–1.09 m³/s and the fire heat release rates (HRR) are 30.7 kW and 61.4 kW. The results show that the tunnel fire with combination of multi-point smoke exhaust system and longitudinal ventilation mode (the exhaust fan is installed on the upstream side of the tunnel) causes the offset of flame, and the maximum temperature point beneath the tunnel ceiling appears in the upstream direction from the fire source. The large smoke exhaust air volume will cause smoke layering plug-holing at the smoke exhaust vents, and the temperature of the vents where plug-holing occurs is lower. Longitudinal ventilation combined with the top multi-point smoke exhaust system has a better smoke control effect, but the longitudinal wind speed cannot be greater than 0.5 m/s. The temperature decay beneath the tunnel ceiling is in accordance with the exponential attenuation law in a tunnel with combination of multi-point smoke exhaust system and longitudinal ventilation mode (the exhaust fan is installed on the upstream side of the tunnel), and the longitudinal temperature decay rate of the side close to the exhaust fan is smaller than that of the other side.

Facilities for Reducing Infections

Features| August 2022 Facilities for Reducing Infections Uday Jain, BSEE, MD, PhD, FASA Uday Jain, BSEE, MD, PhD, FASA Search for other works by this author on: This Site PubMed Google Scholar ASA Monitor August 2022, Vol. 86, 24. https://doi.org/10.1097/01.ASM.0000855672.04435.c2 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Facebook Twitter LinkedIn MailTo Cite Icon Cite Get Permissions Search Site Citation Uday Jain; Facilities for Reducing Infections. ASA Monitor 2022; 86:24 doi: https://doi.org/10.1097/01.ASM.0000855672.04435.c2 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll PublicationsASA Monitor Search Advanced Search Topics: infections Toxic plumes, the contents of which include viruses, aerosols, and volatile organic compounds, are produced by vaporization of tissue by electrocautery or laser surgery (Dermatol 2021;62:37-40). Inhalation carries infectious, respiratory, and cardiovascular risks. Surgical masks provide some protection, but N95 respirators are even more protective (J Hosp Infect 2006;64:278-81). OR air should be filtered through a high-efficiency particulate air filtration (HEPA) system. An air suction/scavenging system reduces exposure to viruses and other toxic elements of the plume. Air drawn through the scavenging system should be filtered either through a HEPA filter (99.97 efficacy at 0.3 μm) or (preferably) an ultra-low penetration air filter (99.9995% efficacy at 0.12 μm). Toxic volatile gases readily pass through HEPA or ULPA filters but can be removed with activated carbon filters. ORs should be maintained at pressures below atmospheric to ensure that the toxic fumes leave through exhaust vents and not... You do not currently have access to this content.

Numerical study on the critical criterion for predicting the plug-holing under lateral mechanical exhaust in tunnel fires: Considering the effect of smoke flow in longitudinal direction

This paper has analyzed the phenomenon of plug-holing under lateral mechanical exhaust in tunnel fires by conducting large eddy simulations (LES) with Fire Dynamics Simulator (FDS). The lateral mechanical smoke exhaust is a method of smoke controlling in tunnel fires with exhaust vents set in the tunnel sidewall. The results show that the phenomenon of plug-holing occurs at the lateral exhaust vent as the exhaust rate increases. The occurrence of plug-holing will lead more fresh air discharged through the vent, thereby reducing the smoke exhaust efficiency. The smoke layer thickness and temperature downstream the vent in the tunnel are analyzed to evaluate the exhaust effectiveness of lateral mechanical exhaust. When the plug-holing does not occur, increasing exhaust rate can effectively reduce the smoke layer thickness. While the plug-holing occurs, the increasing exhaust rate will increase the smoke layer thickness on the contrary. In terms of reducing smoke temperature in the tunnel, increasing exhaust rate has very limited effect in this study. Therefore, it is not the case that the higher the exhaust rate, the better the smoke exhaust efficiency and effectiveness. There is a critical exhaust rate under which the plug-holing can be avoided. Furthermore, considering the horizontal and vertical inertial forces of the smoke beneath the vent, a critical criterion (Ri'critical) for predicting the occurrence of plug-holing of lateral mechanical exhausting is proposed. Based on the results of different exhaust rates, heat release rates and vent sizes, the critical criterion (Ri'critical) that corresponds to the occurrence of plug-holing can be determined as 0.6.

Total Methane and CO2 Emissions from Liquefied Natural Gas Carrier Ships: The First Primary Measurements.

Mitigating methane emissions is vital in meeting global climate targets, but there is a lack of understanding of emissions and abatement opportunities to enable this. The natural gas supply chain is a key emission source, where methane emissions from liquefied natural gas (LNG) shipping have until now not been directly measured. This study provides the first measurement and modeling of total methane and CO2 emissions from an LNG carrier on a round trip voyage from the USA to Belgium and back, including loading, laden voyage, unloading, and ballast voyage, measuring emissions from exhaust stacks, vents, and fugitives. Venting and fugitive emissions were extremely low, contributing less than 0.1% of total greenhouse gas emissions. CO2 emissions from fuel usage were also lower than previous estimates due to improved efficiencies in modern engines and ship design. However, methane slip through the engines were higher than those in prior studies, averaging 3.8% across all engines: equating to 0.1% of delivered LNG. Generator engines are not typically included in emissions analyses but were the key cause of methane emissions. Engines exhibited higher methane slip rates at low loads, and optimized operation could reduce slip rates by half. More measurement studies are now needed to better understand fleet emissions and enable cost-effective mitigation strategies.

Dynamic Performance Analysis and Design of Vortex Array Grippers

In this study, the performance of a vortex array gripper was numerically investigated based on the pressure distribution on the surface of a gripped object and the resulting suction force. An analysis of the suction force generated by a single-vortex gripper was performed to determine the geometric parameters for providing a good suction force and subsequently, for the vortex array gripper configuration. Array grippers consisting of two- and four-vortex grippers were studied. For dual-vortex grippers, the generated suction forces of various inlet air configurations with different vortex gripper distances are illustrated. The pros and cons of all types of air supply and the influence of positive pressure formed by outlet airflow interaction were examined. The analysis of quad-vortex grippers also revealed that the suction force could be increased by reducing the outlet flow interaction between the grippers using the placement of exhaust vents. Thus, the installation of array grippers can be arranged in a more compact form to increase the total suction force per unit operation area with uniformity.

Digital Twin Evaluation of Environment and Health of Public Toilet Ventilation Design Based on Building Information Modeling

Poor indoor air quality reduces the comfort experienced in the environment and can also harm our physical health. Mechanical ventilation design plays an important role in improving the indoor environment and the safety of public toilets. Therefore, in this study, we aimed to evaluate public toilet ventilation design schemes through a digital twin to determine the most effective scheme for reducing indoor pollutant concentrations. In this study, we used Autodesk Revit to create a digital twin BIM of different ventilation systems. We simulated the diffusion of pollutants in these models using computational fluid dynamics (CFD)-based methods, and we used DesignBuilder to simulate building energy consumption. From the perspective of architectural design, we determined measures important for reducing the concentration of air pollutants by increasing the number and volume of air exchanges and controlling the installation height of exhaust vents. The results show that the ventilation design of an all-air air conditioning system with an exhaust height of 400 mm can remarkably improve the indoor environmental health and ventilation efficiency of public toilets, while consuming 20.4% less energy and reducing carbon emissions by 30,681 kg CO2.