Ventilation Scenarios Research Articles

Ultrassonografia da Veia Cava Inferior na Avaliação do Volume Intravascular e Fluido-Responsividade em Pacientes Críticos: Uma Revisão Sistemática

Background: The assessment of intravascular volume and fluid responsiveness is challenging in the management of critically ill patients. Diagnostic methods of hemodynamic monitoring must be safe, reproducible, and practical. Objective: To describe the applicability of ultrasound indices of the inferior vena cava in the assessment of intravascular volume and prediction of fluid responsiveness in critically ill patients. Method: A systematic review performed of the PubMed®, Latin American and Caribbean Health Sciences Literature, and Scientific Electronic Library Online databases for articles published in the previous five years. The descriptors used were “inferior vena cava,” “ultrasonography,” “fluid responsiveness,” and “volume status.” Results: The search identified 13 relevant articles. The collapsibility index of the inferior vena cava was 25%–50% as the cutoff point for defining hypovolemia and showed applicability in predicting fluid responsiveness in patients breathing spontaneously with cutoff points of 25%–57%. In mechanical ventilation scenarios, the distensibility index of the inferior vena cava was more effective at predicting fluid responsiveness than the other measurements with variation of 10.2%–20.5%. The inferior vena cava/aorta diameter index was especially useful in the pediatric population for defining intravascular volume; however, in adults, there were many divergences in its applicability. Conclusion: The assessment of intravascular volume and fluid responsiveness through ultrasound indices of the inferior vena cava is applicable and safe for diagnosing and monitoring hemodynamic instability. However, studies of value standardization are necessary due to divergences in the cutoff points used in each index.

Improving the thermal comfort in hot region through the design of walls made of compressed earth blocks: An experimental investigation

There is growing need for new buildings to support the urbanization and demographic boom in developing countries. These buildings should be environmentally friendly, economically accessible and, most importantly, thermally efficient. The latter aspect is particularly important when dealing with naturally ventilated buildings in hot-dry regions. For this purpose, the thermal design of walls based on compressed earth blocks (CEB) need to be studied in order to achieve optimal use of this material. The present study aimed at experimentally analysing the thermal performance of a test building which has three different design (wall layers) of external wall and two scenario of ventilation. Thermal sensors was used on the test building in order to determine the indoor and outdoor air temperature as well as the surface temperature of the walls. The results show that the location of wall layers influences the indoor climate. When CEBs layer is placed inside, it leads to the highest reduction of the indoor temperature fluctuations. When CEBs layer is placed outside, it presents the best opportunity to prevent overheating in building spaces mainly occupied at night. Regardless of the wall design, nocturnal ventilation is the most suitable strategy which leads to improving the indoor climate compared to continuous ventilation. It is highlighted that the occupancy pattern of the buildings’ spaces as well as the addition of the insulation layer to the CEBs walls are important factor to consider for the design of external walls.

An Experimentally Validated Analytical Model for Aerosol Number Concentration Reduction in Classrooms

To predict the aerosol number concentration decay in modern classrooms, this study derived an analytical model that addresses various indoor factors, viz., the filtration efficiency of air ventilation systems, effects of indoor air cleaners, particle deposition on walls, and particle emission from occupants. We also conducted experimental measurements to determine the wall-loss coefficient and the occupants’ particle generation rate, and the modeling results agreed with the experimental data reasonably well. Additionally, we investigated the behavior of the particle concentration decay in different ventilation scenarios. The model has been incorporated into web-based software that is freely available to the public. © The Author(s).

Heart-Lung Interactions During Mechanical Ventilation: Analysis via a Cardiopulmonary Simulation Model.

Heart-lung interaction mechanisms are generally not well understood. Mechanical ventilation, for example, accentuates such interactions and could compromise cardiac activity. Thereby, assessment of ventilation-induced changes in cardiac function is considered an unmet clinical need. We believe that mathematical models of the human cardiopulmonary system can provide invaluable insights into such cardiorespiratory interactions. In this article, we aim to use a mathematical model to explain heart-lung interaction phenomena and provide physiologic hypotheses to certain contradictory experimental observations during mechanical ventilation. To accomplish this task, we highlight three model components that play a crucial role in heart-lung interactions: 1) pericardial membrane, 2) interventricular septum, and 3) pulmonary circulation that enables pulmonary capillary compression due to lung inflation. Evaluation of the model’s response under simulated ventilation scenarios shows good agreement with experimental data from the literature. A sensitivity analysis is also presented to evaluate the relative impact of the model’s highlighted components on the cyclic ventilation-induced changes in cardiac function.

Performance evaluation of three attached ventilation scenarios for tiny sleeping spaces

The indoor ventilation environment has restricted the development of tiny sleeping spaces, such as capsule hotels, sleeping boxes and soft sleeper compartments, that play an increasingly important role in urban life. Thus, it is imperative to determine a ventilation method that can create comfortable sleeping environments in tiny spaces. In this study, three attached ventilation scenarios were proposed, and numerical simulations and experimental validations were conducted to investigate the airflow characteristics. The draught rate, facial-area speed ratio, predicted mean vote, CO2 concentration, ventilation effectiveness, and mean age of air were used to evaluate the performance of three ventilation scenarios. In Scenario 1, the velocity in the occupied zone was between 0.1 and 0.24 m/s, which could achieve the most comfortable facial speed distribution; the PMV also met the criteria for category B (−0.5 < PMV < +0.5), as defined in ISO 7730. Scenario 2 had a more uniform temperature distribution and minimum air age; however, the local velocity was too high (more than 0.5 m/s), and CO2 cannot be discharged from the occupied zone in time. The DR in Scenario 3 was in the range of 2.5%–5.3%, which was highly beneficial in avoiding draught. Finally, the overall performance of the three ventilation scenarios was as follows: Scenario 1 was superior to Scenario 3, which in turn, was superior to Scenario 2. The results showed that the attached ventilation could solve the problem of supply air momentum not being able to diffuse in a reasonable time in restricted spaces.

Evaluation of airflow pattern and thermal behavior of the arched greenhouses with designed roof ventilation scenarios using CFD simulation.

Natural ventilation is an effective energy-saving strategy conducive to promoting sustainable agricultural production. A comprehensive numerical simulation is performed to predict the airflow pattern and thermal behavior in different arched greenhouses. The defined arc chord angle and position angle are employed to examine the natural ventilation process and corresponding roof vent scenarios. The numerical simulation is compared with the experimental data and good agreements are observed. Various configurations of ventilated structures, wind conditions and ventilation layouts are simulated on a high-resolution polyhedral grid based on a grid sensitivity analysis, which is beneficial to the optimization of greenhouse cooling combined with the water circulation heat collection system. The cooling effect in summer is analyzed by estimating the ventilation flow rate and microclimate inhomogeneity. The results demonstrate that the position angle of 85° of the arched greenhouses is an optimum ventilation direction and its impact on the microclimate is marginally affected by the change of the ventilation structure. The designed ventilation scheme has perfect air exchange capacity and cooling effect because the average air temperature can be reduced by 1.5°C more than the existing greenhouse in 10 minutes of ventilation. Likewise, the results show that the temperature and velocity inhomogeneities are approximately decreased by 33.3% and 11.89%, respectively. The practical value of the research is expected to provide basic quantitative conclusions for evaluating the natural ventilation performance.

Continuous aldehydes monitoring in primary schools in France: Evaluation of emission sources and ventilation practices over 5 weeks

This paper presents a field campaign conducted in two French elementary schools for 5 weeks aiming at identifying effects of occupation and ventilation practices on indoor aldehyde concentrations and discriminating aldehyde emission from building materials and furniture. The investigated classrooms were first empty and not occupied whereas the furniture was added the following week. Normal school activities were restarted for the last three weeks under various ventilation practices.C2–C7 aldehydes concentrations were monitored with the conventional method based on DNPH derivatization using active sampling followed by off-line HPLC/UV analysis. Acetaldehyde (AA) and hexanal (HA) were the two main aldehydes present if formaldehyde is not considered. The weekly mean values of acetaldehyde concentrations were found in the range 9.5–13.1 μg m−3 (School 1), 9.4–17.6 μg m−3 (School 2) and equal to 5.3 μg m−3 (School 3). In Schools 2 and 3, weekly hexanal concentrations ranged between 3.3 and 5.4 μg m−3 but increased up to 40.1 μg m−3 in school 1 where painting work was performed during the week 2. Smaller amount of propionaldehyde (PA) and benzaldehyde (BA) were always detected, their weekly average concentrations being in the range 0.4–4.0 μg m−3 and 0.9–2.7 μg m−3 for PA and BA, respectively. The results supported by Student's tests show that building materials and furniture contribute to aldehyde emissions while ventilation significantly improves indoor air quality without being able to privilege one of the three ventilation scenarios tested.

A novel method for pre-ventilation of shipping containers.

Numerous shipping containers arrive with high levels of hazardous volatile chemicals in the interior air. This may constitute a health risk during inspection and unstuffing. The problem remains largely unaddressed due to ignorance, lack of suitable field instruments for chemical identification, and lack of easy to use, effective ventilation methods. Here, we present a novel ventilation approach based on extraction of air from the closed container via the existing top corner ventilators. A suction plate was developed to fit tightly over the corner ventilator and connected with a flexible hose to an extraction fan. Air flow rates and vacuum under the plate were measured in the lab with five different types of extraction fans. The vacuum produced under the suction plate held it securely in place. Washout of air contaminants under different configurations and ventilation scenarios was studied in an experimental 20-ft container stuffed with acetone emitting cardboard boxes and in the field with containers stuffed with commercial goods. Volatiles in container air were continuously recorded with logging photoionization detectors in various positions before, during and after ventilation. A maximum air flow through the ventilator of 186m3/h was achieved. At 100m3/h, the initial acetone levels were reduced to 11% and 4.9% in the tightly stuffed and to 6.0% and 3.1% in the loosely stuffed (pallets) experimental container after 1h and 4h, respectively, as measured inside the closed door (mean values). As expected, the washout was somewhat slower in nine 40-ft field containers and reached 22% and 11%, respectively. In both experimental and field containers the concentration rose quickly when ventilation ceased. In conclusion, the new ventilation method allows for convenient, safe and efficient ventilation of risk containers. The container should be continuously ventilated until it is opened, or rapid re-accumulation of volatiles will occur.

An Innovative Finite Tube Method for Coupling of Mine Ventilation Network and Gob Flow Field: Methodology and Application in Risk Analysis

Explosions and fires originated from longwall gob due to the formation of methane-air mixture have been a severe threat to coal miner’s lives. Many numerical studies on coal mine fire and explosion hazards have focused on the airflow in roadways and mine gobs. However, most of these studies isolate the gob from its surrounding roadways, and the network analysis and the CFD method are applied independently to model the two classes of airflows. This approach greatly limits the ability of simulating mine ventilation flow, especially unable to consider the effects of gob boundary conditions on air exchange between the gob and the surrounding airways. An innovative finite tube method (FTM) is developed to couple the one-dimensional mine ventilation network (MVN) and the 2D/3D gob flow field (GFF). In FTM, GFF is discretized into a finite number of flow tubes each of which is formed by any two adjacent stream lines. These tubes, representing the gob’s field flow, connect the MVN into a new coupling network. To solve the coupling model between MVN and GFF, an iterative solution technique is developed in which the MVN analysis is used to evaluate the boundary pressures for GFF simulation and in turn the FTM feeds the GFF results back to the coupling network. Based on the FTM approach, a model for gas migration in gob has been established for delineating the hazard zones of explosive methane concentration and spontaneous combustion. A computer program is developed to implement the FTM simulation. An illustrative example with five flow tubes representing the GFF is created to verify the stability and convergence of the FTM solution process. A simulation example also indicates that the accuracy of FTM is improved by 12% compared with previous method. Results of an application case show that the program is capable of quantitatively evaluating the gob’s risk zones prone for spontaneous combustion and gas explosion as well as performing risk analysis for various ventilation scenarios.

Feasibility study of an off-grid container unit for industrial construction

This article presents solutions for improved energy efficiency by adapting a shipping container building in Shanghai for off-grid operation. While this prototype is based on a single unit, larger buildings made from multiple units constructed at factories is the ultimate goal. Previous studies of container buildings have revealed gaps concerning the quality of construction and thermal comfort. In this study, the heat transfer resistance of a typical container building wall has been improved from 1.0 m2K/W to around 3.7 m2K/W by installing Vacuum Insulation Panels (VIP), verified through measurements. VIPs reduce the temperature dependence of the heating need and the thermal bridges from the steel beams. Through validated building performance simulation using the software IDA ICE, the energy use and indoor air quality were examined for different ventilation scenarios and indoor temperature setpoints in Shanghai. A wider range of heating and cooling setpoints outside operation hours, lowering the heating setpoint at night and upgrading to triple glazed windows were found to be the most economic energy saving measures. Combined with roof rainwater harvesting, the possibility of achieving near self-sufficiency of water and electricity in the suburbs of Shanghai shows promise in the quest for a higher degree sustainable living.

Aerosolization During Common Ventilation Scenarios.

Otolaryngologists are at increased risk for exposure to suspected aerosol-generating procedures during the ongoing coronavirus disease 2019 (COVID-19) pandemic. In the present study, we sought to quantify differences in aerosol generation during common ventilation scenarios. We performed a series of 30-second ventilation experiments on porcine larynx-trachea-lung specimens. We used an optical particle sizer to quantify the number of 1- to 10-µm particles observed per 30-second period (PP30). No significant aerosols were observed with ventilation of intubated specimens (10.8 ± 2.4 PP30 vs background 9.5 ± 2.1, P = 1.0000). Simulated coughing through a tracheostomy produced 53.5 ± 25.2 PP30, significantly more than background (P = .0121) and ventilation of an intubated specimen (P = .0401). These data suggest that undisturbed ventilation and thus intubation without stimulation or coughing may be safer than believed. Coughing increases aerosol production, particularly via tracheostomy. Otolaryngologists who frequently manage patient airways and perform tracheostomy are at increased risk for aerosol exposure and require appropriate personal protective equipment, especially during the ongoing COVID-19 pandemic.

Effects of combined central air conditioning diffusers and window-integrated ventilation system on indoor air quality and thermal comfort in an office

Despite the advantages of building enclosure systems for improving ventilation efficiency and reducing energy consumption, there is a large difference in performance from the central heating, ventilating, and air-conditioning (HVAC) system. This study investigated the performance of a smart window-integrated ventilation (SWV) system in conjunction with a centralized HVAC system for enhancing indoor air quality (IAQ) and thermal comfort in a typical single-occupancy office. To evaluate the performance of two coupled systems, IAQ and thermal comfort in an office were analyzed for satisfying seasonally optimal ventilation scenarios using computational fluid dynamics simulations. A set of scenarios for case study was determined by outdoor temperature, supply airflow rate and temperature, and operation strategy of the two systems. Numerical results showed that using the SWV system as an aid to the HVAC system was more effective in winter than in summer for improving IAQ and thermal comfort. Only in the summer, the SWV led to poor IAQ. In spring and autumn, there were scenarios in which the SWV system performed similar to the HVAC system. Therefore, depending on indoor and outdoor conditions, the SWV system can be a good choice as an auxiliary means of the HVAC system or for single operation.

The influence of school bus ventilation scenarios over in-cabin PM number concentration and air exchange rates

School students are exposed to the increased particulate (PM) number concentration inside the school bus on daily basis while commuting on urban road networks. However, the potential effect of different ventilation over in-cabin pollutants is still unclear in many aspects. The present paper investigates the influence of varying ventilation scenarios over in-cabin particle number concentration (PNC) and air exchange rates (AERs) inside idle and moving (unoccupied (SBu) and occupied (SBo)) school bus. The in-cabin total PNC sharply increased by a factor of 1.53, 1.57 and 1.14 for SBp, SBu, and SBo respectively under windows open (WO) from windows closed (WC) scenarios. In-vehicle student activity and ventilation scenarios were positively correlated with the change in in-cabin PNC. For SBp, the average estimated AERs are 9.19 h−1 and 3.30 h−1 under WO and WC scenarios respectively whereas, total PNC deposition rate under natural convection condition varied between 2.52 to 6.89 h−1. In the present study, inside-outside measurements were recorded for 10 km long road segment under realistic driving conditions. The average AERs value of SBu and SBo are highest for WO (42.40 h−1 and 14.46 h−1) compared to WC (10.91 h−1 and 10.94 h−1) scenarios. A Generalized estimating model (GEE) model was developed and the model suggested that vehicle age, mileage, and speed are the factors positively associated with the AERs estimated for WO and WC scenarios under realistic driving conditions.

Rapid field measurement of ventilation rate using a quartz-enhanced photoacoustic SF6 gas sensor

We reported the development of a quartz-enhanced photoacoustic sulfur hexafluoride (SF6) sensor for ventilation studies using a continuous-wave distributed-feedback quantum cascade laser (QCL) at 10.5 µm. The SF6 sensor was developed by detecting the gas-absorption induced acoustic wave using a tiny quartz tuning fork that is enclosed in a gas cell with a sample volume of 2.5 ml. By locking the QCL wavelength at the absorption peak of SF6, we obtained a recording time interval of 0.4 s and a detection limit of 4.6 ppb. The sensor response time (t90) was found to be 2.8 s at a flow rate of 550 ml min−1. The sensor was then implemented in measuring air exchange rates in a laboratory room using the standard tracer gas concentration decay method. Our measurements are in good agreement with a commercial analyzer when studying two typical passive ventilation scenarios of infiltration and natural ventilation. Additionally, the developed photoacoustic gas sensor is fast enough to capture the transient variations of the SF6 concentration during natural ventilation. This study provides a promising method of studying transient contaminant transport that remains a major challenge in air quality research.

Assessing the Energy Demand Reduction in a Surgical Suite by Optimizing the HVAC Operation During Off-Use Periods

Hospital surgical suites are high consumers of energy due to the strict indoor air quality (IAQ) conditions. However, by varying the ventilation strategies, the potential for energy savings is great, particularly during periods without activity. In addition, there is no international consensus on the ventilation and hygrothermal requirements for surgical areas. In this work, a dynamic energy model of a surgical suite of a Spanish hospital is developed. This energy model is calibrated and validated with experimental data collected during real operation. The model is used to simulate the yearly energy performance of the surgical suite under different ventilation scenarios. The common issue in the studied ventilation strategies is that the hygrothermal conditions ranges are extended during off-use hours. The maximum savings obtained are around 70% of the energy demand without compromising the safety and health of patients and medical staff, as the study complies with current heating, ventilation and air conditioning (HVAC) regulations.

The Impacts of Air Leakage Paths and Airtightness Levels on Air Change Rates

Southern European countries have milder climatic conditions that differ from their colder northern counterparts, which greatly influence indoor ventilation strategies. The relation between a building’s airtightness and the air change rates remains a topic to be fully tackled in these countries, since natural ventilation is very frequent. In this work, the ventilation and airtightness of a case study were analyzed in-depth to support a discussion on this topic. CO2 concentration decay and blower-door measurements were used to characterize the infiltration and ventilation conditions of the case study. The case study represents a common Portuguese situation, with highly permeable envelopes, combined with highly variable air change rates. Transient simulations were carried out for the comparison of scenarios where different configurations of possible air paths were analyzed. The simulations included both natural and mechanical ventilation scenarios. An air sweeping effect from bedroom to bathroom only occurred when the mechanical extraction ventilation (MEV) was on. Different air leakage path configurations resulted in substantial offsets, up to 63%, of the air change rate (ACH) due to natural occurring forces. The results confirmed that the relation between airtightness and air change rates should be carefully analyzed in southern European countries, as indoor air quality, comfort of occupants, and energy efficiency are highly influenced by the considered variables.

Quantifying the impact of housing interventions on indoor air quality and energy consumption using coupled simulation models.

While residential energy and ventilation standards aim to improve the energy performance and indoor air quality (IAQ) of homes, their combined impact across diverse residential activities and housing environments has not been well-established. This study demonstrates the insights that a recently-developed, freely-available coupled IAQ-energy modeling platform can provide regarding the energy and IAQ trade-offs of weatherization (i.e., sealing and insulation) and ventilation retrofits in multifamily housing across varied indoor occupant activity and mechanical ventilation scenarios in Boston, MA. Overall, it was found that combined weatherization and improved ventilation recommended by design standards could lead to both energy savings and IAQ-related benefits; however, ventilation standards may not be sufficient to protect against IAQ disbenefits for residents exposed to strong indoor sources (e.g., heavy cooking or smoking) and could lead to net increases in energy costs (e.g. due to addition of continuous outdoor air ventilation). The modeling platform employed in this study is flexible and can be applied to a wide range of building typologies, retrofits, climates, and indoor occupant activities; therefore, it stands as a valuable tool for identifying cost-effective interventions that meet both energy efficiency and ventilation standards and improve IAQ across diverse housing populations.

Efficiency of night ventilation in limiting the overheating of passive sports hall

It is especially difficult to provide optimal microclimatic conditions in sports facilities during summer time. The internal heat gains and an airtight building insulation, combined with high external temperature can easily lead to overheating and upsetting of the body's thermal balance. This article focuses primarily on the effect of natural night ventilation on the thermal comfort in a passive sports hall building. Based on experimental studies of thermal conditions in the hall, a simulation model was made using the Design Builder program. Through simulation analysis, the program considered thermal conditions that arise in various scenarios of natural and mechanical ventilation. Results presented in this article show that the natural ventilation at night in a large volume building is the most effective and the easiest way to reduce overheating in summer.

Indoor Air Quality Assessment: Comparison of Ventilation Scenarios for Retrofitting Classrooms in a Hot Climate

Current energy efficiency policies in buildings foster the promotion of energy retrofitting of the existing stock. In southern Spain, the most extensive public sector is that of educational buildings, which is especially subject to significant internal loads due to high occupancy. A large fraction of the energy retrofit strategies conducted to date have focused on energy aspects and indoor thermal comfort, repeatedly disregarding indoor air quality criteria. This research assesses indoor air quality in a school located in the Mediterranean area, with the objective of promoting different ventilation scenarios, based on occupancy patterns and carbon dioxide levels monitored on site. Results show that manual ventilation cannot guarantee minimum indoor quality levels following current standards. A constant ventilation based on CO2 levels allows 15% more thermal comfort hours a year to be reached, compared to CO2-based optimized demand-controlled ventilation. Nevertheless, the latter ensures 35% annual energy savings, compared to a constant CO2-based ventilation, and 37% more annual energy savings over that of a constant ventilation rate of outdoor air per person.

Analysis of distribution of toxic species of a fired train in ventilated tunnel

A procedure is established and the distribution of products of a fired passenger train, (such as CO, and NOx) in a tunnel is simulated by fire dynamics simulator (FDS). Materials of a real train wagon are estimated and their fire products are calculated under both complete and incomplete combustion. A big urban railway tunnel with 4 lines in Tehran is considered and the effects of some parameters such as delay in emergency ventilation and tunnel separation wall on distribution of fire products are analyzed. Results show that delay in emergency ventilation causes to dispersion of fire products in tunnel and threats the passengers in an unsafe escape path at fire upstream after operation. The simulations show that the maximum time for rescue of passengers due to the fired train in tunnel is about 430 sec which is limited with accumulation of HCN as a first pollutant over critical health value. It is shown that the presence of separation wall may create a good escape path in the opposite lines of the tunnel for passengers in delay time duration. The results can be used for reaching to an optimized emergency ventilation scenario in tunnels due to rescue of passengers from dangers.