Improve Ventilation Efficiency Research Articles

Optimization principle and application of forced ventilation in railway tunnels based on improved TOPSIS theory and CFD simulations

The optimization of forced ventilation in tunnel construction becomes the key problem to improve the construction environment and energy saving. The influence of main factors on the flow field is considered for orthogonal experimental design and optimization, which includes the distance between the air duct outlet and the tunnel face, the bench length, the bench height, and the position of the air duct. Thus, the TOPSIS theory was adopted for the optimization method and improvement, and a series of CFD simulations were applied to analyze optimal solutions. The results show that the improved TOPSIS theory with entropy weight method and analytic hierarchy process could effectively solve the optimization problem of forced ventilation in tunnel construction. Based on this optimization principle, a case was analyzed, and the optimized ventilation parameters are obtained to improve ventilation efficiency and save energy. In the optimization scheme, the flow field in the tunnel is stable and the wind is strong enough to ventilate. Besides, there is none huge vortex, which might disrupt the stable flow field and reduce energy efficiency. It could improve the ventilation efficiency and stability, save time and cost, and bring considerable economic and social benefits to the tunnel construction.

Current Situation and Solutions to Advanced Ventilation Efficiency in Giap Khau Coal Mine Area, Hon Gai Coal Company of Viet Nam

Mine ventilation aims to dilute toxic gas concentrations, dilute dust concentrations, remove them from the mine and ensure pleasant microclimate conditions in the mine, especially at work sites. Currently, in underground coal mines in general and in Giap Khau mine area, Hon Gai coal company, in particular, is in the process of converting the mining area into deep, as well as increasing output. Therefore, it is important to ensure that ventilation is a top priority in long-term occupational safety and meets the plan to increase coal production. In this study, we have evaluated the current state of ventilation in Giap Khau mine area. From those research results, on the basis of computational research methods, we have come up with reasonable solutions to change and improve ventilation efficiency for the mine in the condition of complicated mining plan and technology characteristics are still limited compared to those in the world. Specific solutions solve 2 problems: First, ensure ventilation for the current mining operation stage; Secondly, we have researched and proposing suitable solutions for ventilation of Giap Khau area mine when it has to increase production and move down to an adjacent project at a deeper level.

Improving Prediction Accuracy Concerning the Thermal Environment of a Data Center by Using Design of Experiments

In data centers, heating, ventilation, and air-conditioning (HVAC) consumes 30–40% of total energy consumption. Of that portion, 26% is attributed to fan power, the ventilation efficiency of which should thus be improved. As an alternative method for experimentations, computational fluid dynamics (CFD) is used. In this study, “parameter tuning”—which aims to improve the prediction accuracy of CFD simulation—is implemented by using the method known as “design of experiments”. Moreover, it is attempted to improve the thermal environment by using a CFD model after parameter tuning. As a result of the parameter tuning, the difference between the result of experimental-measurement results and simulation results for average inlet temperature of information-technology equipment (ITE) installed in the ventilation room of a test data center was within 0.2 °C at maximum. After tuning, the CFD model was used to verify the effect of advanced insulation such as raised-floor fixed panels and show the possibility of reducing fan power by 26% while keeping the recirculation ratio constant. Improving heat-insulation performance is a different approach from the conventional approach (namely, segregating cold/hot airflow) to improving ventilation efficiency, and it is a possible solution to deal with excessive heat generated in data centers.

Windcatcher Louvers to Improve Ventilation Efficiency

Windcatcher louvers are designed to capture air flowing outside a building in order to increase its natural ventilation. There are no studies that have designed the shape of the louver to increase the natural ventilation efficiency of the building. This study aimed to conduct a computational fluid dynamics simulation and mock-up test of a Clark Y airfoil-type windcatcher louver designed to increase the natural ventilation in a building. The following test results were obtained. The optimal angle of attack of the airfoil was calculated via a numerical analysis, which demonstrated that the wind speed was at its highest when the angle of attack was 8°; further, flow separation occurred at angles exceeding 8°, at which point the wind speed began to decrease. The results of the mock-up test demonstrated that the time required to reduce the concentration of fine particles in the indoor air was 120 s shorter when the windcatcher was installed than when it was not, which indicating that the time to reduce particles represents a 37.5%reduction. These results can be seen as reducing the energy consumption of ventilation in the building because the natural ventilation efficiency is increased.

Sine ventilation in lung injury models: a new perspective for lung protective ventilation

Mechanical ventilation is associated with the risk of ventilator induced lung injury. For reducing lung injury in mechanically ventilated patients, the application of small tidal volumes and positive end-expiratory pressures has become clinical standard. Recently, an approach based on linear airway pressure decline and decelerated expiratory flow during expiration implied lung protective capacities. We assumed that ventilation with a smoothed, i.e. sinusoidal airway pressure profile may further improve ventilation efficiency and lung protection. We compared the effects of mechanical ventilation with sinusoidal airway pressure profile (SINE) regarding gas exchange, respiratory system compliance and histology to conventional volume and pressure controlled ventilation (VCV and PCV) and to VCV with flow-controlled expiration (FLEX) in two rat models of lung injury, tween induced surfactant depletion and high tidal volume mechanical ventilation. In both lung injury models ventilation with SINE showed more efficient CO2 elimination and blood oxygenation, improved respiratory system compliance and resulted in lower alveolar wall thickness, compared to VCV, PCV and FLEX. Optimization of the airway pressure profile may provide a novel means of lung protective mechanical ventilation.

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.

A Discussion on the Effective Ventilation Distance in Dead-End Tunnels

Forcing ventilation is the most widely used system to remove noxious gases from a working face during tunnel construction. This system creates a region near the face (dead zone), in which ventilation takes place by natural diffusion, rather than being directly swept by the air current. Despite the extensive use of this system, there is still a lack of parametrical studies discerning the main parameters affecting its formation as well as a correlation indicating their interrelation. With this aim in mind, computational fluid dynamics (CFDs) models were used to define the dead zone based on the airflow field patterns. The formation of counter vortices, which although maintain the movement of air hinder its renewal, allowed us to discuss the old paradigm of defining the dead zone as a very low air velocity zone. Moreover, further simulations using a model of air mixed with NO2 offered an idea of NO2 concentrations over time and distance to the face, allowing us to derive at a more realistic equation for the effective distance. The results given here confirm the degree of conservativism of present-day regulations and may assist engineers to improve ventilation efficiency in tunnels by modifying the duct end-to-face distance.

Implementation of an algorithm for determining the effectiveness of ventilation and energy efficiency in industrial ventilation systems

The requirements for good indoor air quality and energy efficiency have often been considered to conflict with each other, however, buildings with low energy consumption in Europe seem to have also a lower rate of building related health symptoms. The paper aims to develop a succession of necessary operations, an algorithm, for the determination of ventilation efficiency and energy efficiency in industrial ventilation systems, starting from a general model that will be developed according to the particularities of the industrial ventilation system. These systems are important as they are related both to energy cost and indoor climate management as well as to the health of the occupants. The stages of algorithm development will include: source control and efficient removal of contaminants, proper location of fresh air intakes, cleaning of intake air, efficient air distribution in rooms with improved ventilation efficiency, heat recovery from exhaust air, night time ventilation cooling, ventilation rates control by air quality, correct balancing of air flows and controlling the indoor climate locally.

Improving Ventilation Efficiency for a Highly Energy Efficient Indoor Swimming Pool Using CFD Simulations

The operation of a typical indoor swimming pool is very energy intensive. Previous studies have shown that high quality thermal building envelopes, i.e., with high levels of insulation and airtightness, make it possible to rethink conventional ventilation concepts. Due to the reduced condensation risk in and on envelopes of high thermal quality, ventilation design can be optimized for indoor air quality rather than for averting condensation on the facade. This work investigates different air distribution concepts for an existing swimming pool via computational fluid dynamics (CFD) simulations to evaluate their ventilation efficiency. To reduce modelling and computational resources, the velocity and turbulence fields produced by the swirl-diffusers are determined in a set of separate CFD simulations and incorporated into the swimming pool models. The results show that the ventilation efficiency in the examined swimming pool could potentially be improved with various alternative air distribution concepts, therefore improving the indoor air quality. Although the results seem plausible and compare well with the limited measurement data of air humidity, a more formal experimental validation is still needed before generalizing recommendations.

Investigation on thermal performance of the wall-mounted attached ventilation for night cooling under hot summer conditions

In Hot Summer and Cold Winter Climate Zone, the cooling potential of natural/passive night ventilation is limited during summer due to the insignificant difference between the outdoor and indoor temperatures. Therefore, a novel mechanical ventilation strategy, the wall-mounted attached ventilation (WAV) system, is proposed in the present paper to improve ventilation efficiency of night cooling. The idea is that WAV can produce a downward airflow over the internal wall surface that is somewhat similar to a sidewall jet, so as to achieve enhanced heat transfer in the room. This paper starts with a series of experiments in a test chamber, and continues with thermal analysis of the heat transfer characteristics and heat removal performance of WAV. The performance of night ventilation with WAV is further evaluated in terms of ventilation efficiency index and energy performance index. It is shown that the overall average value of the convective heat transfer coefficient at the internal wall surface with WAV is 10.79 W m−2 °C−1. With WAV, the amount of heat removed from the ventilated wall is about five times that in the natural night ventilation case, and the total amount of heat removed from the whole chamber is twice as much. The average value of the surface cooling effectiveness of WAV is 1.48, and the overall coefficient of performance (COP) of WAV turns out to be 26.8. As a night ventilation strategy, WAV is capable to achieve good cooling performance under hot summer conditions.

Variable ventilation decreases airway responsiveness and improves ventilation efficiency in a rat model of asthma

The optimal ventilation strategy in patients receiving mechanical ventilation for severe asthma remains unclear. The effect of conventional ventilation (with constant tidal volume and respiratory rate) and variable ventilation (with the same average but variable tidal volume and respiratory rate) on peak airway pressure and airway exacerbation induced by increasing doses of methacholine was compared in a rat model of asthma. The respiratory rate and tidal volume data were obtained from a spontaneously breathing intact rat during immobility using a whole-body plethysmograph. Peak airway pressure and airway responsiveness to cumulative doses of methacholine were significantly affected by ventilation mode and they were lower in variable ventilation group than in the conventional ventilation group. Also, variable ventilation improved oxygen saturation compared to conventional ventilation. Our results indicate that variable ventilation decreases airway responsiveness and enhances ventilation efficiency in a rat model of asthma. We suggest further investigations on beneficial effects of variable ventilation strategy in mechanically ventilated patients with severe asthma.

Bias flow rate and ventilation efficiency during adult high-frequency oscillatory ventilation: a lung model study

BackgroundBias flow (BF) is essential to maintain mean airway pressure (MAP) and to washout carbon dioxide (CO2) from the oscillator circuit during high-frequency oscillatory ventilation (HFOV). If the BF rate is inadequate, substantial CO2 rebreathing could occur and ventilation efficiency could worsen. With lower ventilation efficiency, the required stroke volume (SV) would increase in order to obtain the same alveolar ventilation with constant frequency. The aim of this study was to assess the effect of BF rate on ventilation efficiency during adult HFOV.MethodsThe R100 oscillator (Metran, Japan) was connected to an original lung model internally equipped with a simulated bronchial tree. The actual SV was measured with a flow sensor placed at the Y-piece. Carbon dioxide (CO2) was continuously insufflated into the lung model ( dot{mathrm{V}} CO2), and the partial pressure of CO2 (PCO2) in the lung model was monitored. Alveolar ventilation ( dot{mathrm{V}} A) was estimated as dot{mathrm{V}} CO2 divided by the stabilized value of PCO2. dot{mathrm{V}} A was evaluated by setting SV from 80 to 180 mL (10 mL increments, n = 5) at a frequency of 8 Hz, a MAP of 25 cmH2O, and a BF of 10, 20, 30, and 40 L/min (study 1). Ventilation efficiency was calculated as dot{mathrm{V}} A divided by the actual minute volume. The experiment was also performed with an actual SV of 80, 100, and 120 mL and a BF from 10 to 60 L/min (10 L/min increments: study 2).ResultsStudy 1: With the same setting SV, the dot{mathrm{V}} A with a BF of 20 L/min or more was significantly higher than that with a BF of 10 L/min. Study 2: With the same actual SV, the dot{mathrm{V}} A and the ventilation efficiency with a BF of 30 L/min or more were significantly higher than those with a BF of 10 or 20 L/min.ConclusionsIncreasing BF up to 30 L/min or more improved ventilation efficiency in the R100 oscillator.

Computational fluid dynamics evaluation of the furniture arrangement for ventilation efficiency

People spend most of their time indoors; therefore, maintaining a good indoor air quality and meeting the requirements of comfort and energy efficiency are essential. One of the most widespread strategies to achieve this objective is improving ventilation efficiency; therefore, the main aim of this study was to show an optimization of the ventilation efficiency, in a specific room, considering 47 variations (case studies) in the furniture arrangement. For this purpose, a numerical analysis using computational fluid dynamics techniques, validated by the tracer gas decay technique, was used to assess the distribution of the age of air within the space. The concept of “age of air” was implemented in the computational fluid dynamics code through user-defined functions, using the steady-state method based on the resolution of a transport equation for an additional scalar. Variations up to 5.75% in the ventilation efficiency between the cases studied have been achieved. It is concluded that an improvement up to 1.65% can be obtained when the elements of the study are introduced in a way that facilitates the air movement towards the exhaust; therefore, improvement of the ventilation efficiency through specific furniture distributions is possible, although not significant, according to the outcomes.

Improving wind environment design based on assessing spatial distribution of ventilation efficiency in regional space

This paper discusses the influence of design variations on spatial distribution of Ventilation Efficiency (VE) in idealized residential building groups. Series of design cases referring building length and spacing changing are investigated using Computational Fluid Dynamics (CFD) simulation method. Air change rate (ACH) and purging flow rate (PFR) are adopted as evaluation indices of ventilation efficiency. Simulation results indicate that these design changes have evident effects on distribution of spatial ventilation efficiency. Widening building spacing could improve ventilation efficiency of different spaces. However, the benefit is not linear improved as spacing distance increases. When the distance is higher than 15m, improving extent of spatial ventilation efficiency decreases evidently. Variations of building length also has effect on distribution of spatial ventilation efficiency. As building length increase, less wind could reach into space between south and north buildings, which lead to the decrease of wind ventilation for middle residential-unit. Preliminary study indicates that building length should be restricted within 5 residential-unit.

Cardiopulmonary Exercise Test as a Tool to Choose Therapy in Heart Failure.

Heart failure treatment depends on several drugs, all providing improvement in outcome, but that cannot be realistically used all together in the same patient. It would be useful to have a tool that allows the arrangement of the most appropriate therapy cocktail for each patient. The aim of this article is to show the main differences in the effects of several drugs on cardiopulmonary function in patients with heart failure, both while resting and during exercise, and to discuss how these differences can be taken into account when choosing the most appropriate therapeutic protocol. In summary, angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers act synergistically to increase exercise capacity and peak oxygen uptake, but through different mechanisms: the former improving lung diffusion and exercise ventilatory efficiency, an action that is counteracted by concomitant aspirin therapy, and the latter probably by improving muscle perfusion. As for β-blockers, nonselective compounds, such as carvedilol, improve ventilation efficiency on the one hand, but interfere with lung diffusion on the other, and they are probably less tolerated under hypoxic conditions. On the contrary, β1-selective compounds, such as bisoprolol or nebivolol, have a neutral effect on both lung diffusion and ventilation efficiency. These observations could be the basis for the choice of pharmacological therapy in patients with heart failure.

A Study on the Ventilation Efficiency Improved by Airflow Characteristics of the Axial Fan Installed in Parallel at the Side Wall of the Narrow Exhaust Tower

A numerical study has been conducted to simulate airflow and ventilation characteristics in the exhaust tower installed to ventilation of the multi-story underground parking lot. It is the objective of the present study to identify ventilation problems and to suggest the flow direction modifications of the ventilation system with the axial fan to improve ventilation efficiency in the low-rise section of the exhaust tower. Numerical results on SVE4 (scale of ventilation efficiency NO.4) and local mean age of exhaust ports are presented along with the location of axial fan on the direction of swirl flow and the dimension of exhaust tower. Ventilation system modifications on the direction of swirl flow have been suggested from the numerical results in order to prevent the flow interference by airflow discharged from the adjacent stories. The overall ventilation efficiency according to the rotational condition of the axial fans are compared quantitatively using the concept of SVE4 calculated by means of tracer gas pulse method to investigate distribution characteristics of the air discharged from each story among the exhausted air to the two exhaust ports in the narrow exhaust tower.

Heated humidified high-flow nasal cannula therapy in children.

Heated humidified high-flow nasal cannula therapy (HHHFNC) was originally described as a mode of respiratory support in premature neonates and is now increasingly used in the management of acute respiratory failure in older infants and children. Heating and humidification of gas mixtures allow comfortable delivery of flow rates that match or exceed the patient's inspiratory flow rate. Emerging evidence from observational studies suggests that the use of HHHFNC therapy may be associated with reduced work of breathing, improved ventilation efficiency and a decreased need for intubation in children with respiratory insufficiency. There are several proposed mechanisms of action, and the potential for provision of unpredictable positive distending pressure has caused concern. Randomised controlled trial evidence comparing clinical outcomes with those achieved using other forms of respiratory support is, however, awaited. We review the proposed mechanisms of actions, indications, advantages and complications of HHHFNC therapy in children and describe our approach to its use in the paediatric ward environment.

Evaluation of Manual and Automatic Manually Triggered Ventilation Performance and Ergonomics Using a Simulation Model

In the absence of endotracheal intubation, the manual bag-valve-mask (BVM) is the most frequently used ventilation technique during resuscitation. The efficiency of other devices has been poorly studied. The bench-test study described here was designed to evaluate the effectiveness of an automatic, manually triggered system, and to compare it with manual BVM ventilation. A respiratory system bench model was assembled using a lung simulator connected to a manikin to simulate a patient with unprotected airways. Fifty health-care providers from different professional groups (emergency physicians, residents, advanced paramedics, nurses, and paramedics; n = 10 per group) evaluated manual BVM ventilation, and compared it with an automatic manually triggered device (EasyCPR). Three pathological situations were simulated (restrictive, obstructive, normal). Standard ventilation parameters were recorded; the ergonomics of the system were assessed by the health-care professionals using a standard numerical scale once the recordings were completed. The tidal volume fell within the standard range (400-600 mL) for 25.6% of breaths (0.6-45 breaths) using manual BVM ventilation, and for 28.6% of breaths (0.3-80 breaths) using the automatic manually triggered device (EasyCPR) (P < .0002). Peak inspiratory airway pressure was lower using the automatic manually triggered device (EasyCPR) (10.6 ± 5 vs 15.9 ± 10 cm H2O, P < .001). The ventilation rate fell consistently within the guidelines, in the case of the automatic manually triggered device (EasyCPR) only (10.3 ± 2 vs 17.6 ± 6, P < .001). Significant pulmonary overdistention was observed when using the manual BVM device during the normal and obstructive sequences. The nurses and paramedics considered the ergonomics of the automatic manually triggered device (EasyCPR) to be better than those of the manual device. The use of an automatic manually triggered device may improve ventilation efficiency and decrease the risk of pulmonary overdistention, while decreasing the ventilation rate.

Hospital‐based supervised aerobic training effectively improves ventilation efficiency and cardiac output power in patients with systolic heart failure

This study investigated the effects of hospital‐based supervised aerobic training on ventilation efficiency and cardiac output power in patients with systolic heart failure (SHF). Thirty‐three patients with SHF who completed hospital‐based supervised aerobic training for 36 sessions were retrospectively collected. The former 18 sessions and the latter 18 sessions were performed at moderate continuous training (constant 60%VO2peak) and aerobic interval ntraining (3‐minute intervals at 40% and 80%VO2peak) for 45 minutes, respectively. Thirty‐three SHF patients who only received community‐based exercise program education were gathered as control group. The results showed that hospital‐based supervised aerobic training 1) increased work‐rate and VO2 at ventilation threshold and peak exercise, 2) reduced the value of VE/VO2 during submaximal exercise, 3) enhanced cardiac output power at peak exercise, and 4) lowered the score of Minnesota Living with Heart Failure Questionnaire (MLHFQ). Despite modestly lowered MLHFQ score, no significant changes in ventilatory/hemodynamic responses to exercise were observed in control group. Hence, we conclude that hospital‐based supervised aerobic training in patients with SHF effectively improves ventilation efficiency and cardiac output power at submaximal and peak workloads, respectively.

Effects of Slow Deep Breathing at High Altitude on Oxygen Saturation, Pulmonary and Systemic Hemodynamics

Slow deep breathing improves blood oxygenation (SpO2) and affects hemodynamics in hypoxic patients. We investigated the ventilatory and hemodynamic effects of slow deep breathing in normal subjects at high altitude. We collected data in healthy lowlanders staying either at 4559 m for 2–3 days (Study A; N = 39) or at 5400 m for 12–16 days (Study B; N = 28). Study variables, including SpO2 and systemic and pulmonary arterial pressure, were assessed before, during and after 15 minutes of breathing at 6 breaths/min. At the end of slow breathing, an increase in SpO2 (Study A: from 80.2±7.7% to 89.5±8.2%; Study B: from 81.0±4.2% to 88.6±4.5; both p<0.001) and significant reductions in systemic and pulmonary arterial pressure occurred. This was associated with increased tidal volume and no changes in minute ventilation or pulmonary CO diffusion. Slow deep breathing improves ventilation efficiency for oxygen as shown by blood oxygenation increase, and it reduces systemic and pulmonary blood pressure at high altitude but does not change pulmonary gas diffusion.