Wind-Thermal Environmental Characteristic of Multi-Variable Passive Enhanced Natural Ventilation System for High and Large Space Building

Natural ventilation effects in high and large space buildings of tropical areas greatlya ffect the air conditioning energy consumption.Aiming at nearly zero energy building design,thisp aper mainly contributes to provide theoretical basis and reference for thermal comfortable air conditioning system design of high and large space buildings.Taking a theatre in Hainan as study object,a newly composite enhanced natural ventilation system is proposed by integrating theu nderground tunnel-based earth to air heat exchange system and the solar chimney.Ventilationq uantity,air velocity and air temperature field,human vertical temperature gradient differenceu nder24simulation working conditions are considered and analyzed by using ANSYS Fluent.Fort he underground tunnel,results show that Group Two with double underground tunnels and side airs upply location shows its advantages in cooling effects and air supply uniformity.Then for the solar chimney,results show that the solar radiation intensity contributes to larger difference int ransmission power and leads to different cooling effects.On the whole,the system under workingc ondition No.7with120m long,side air supply,double underground tunnel and20m high,1mw ide,0.6°absorber plate angle solar chimney shows its priority in better comprehensive performance.

Prediction Analysis on the Transport Distance of Supply Air in Warm Air Heating Room with Impinging Jet Ventilation Systems

To overcome the disadvantages of displacement ventilation( DV) and traditional mixing ventilation( MV) system,a new ventilation system known as impinging jet ventilation system( IJVS)has been developing. The warm air can be supplied with impinging jet ventilation( IJV), while the DV is only used for cooling.However,the flow and temperature field of IJV under heating scenario has had few references. The paper is mainly focused on computational fluid dynamics( CFD) and developing an adequate correlation between the distance L that warm air can reach and different parameters in the warm IJVS by using response surface methodology( RSM). The results indicate that L decreases as the supply velocity υ decreases but increases as the supply temperature difference ΔT or the discharge height h decreases. In the variable air volume( VAV) system, it is necessary to determine supply parameters both under the maximum-heat-load condition and the small-heat-load condition. Unlike the VAV system,the constant air volume( CAV) system has no need to study the small-heat-load condition. Draught discomfort near the nozzle becomes the issue of concern in IJVS, thus the suitable discharge height is of great importance in design and can be calculated based on the predictive model.

Numerical simulation to evaluate gas diffusion of turbulent flow in mine ventilation system

Tracer gas technique is a method to analyze the airflow path, measure the airflow quantity, and detect any recirculation or leakages in underground mine. In addition, it is also possible to evaluate the axial gas diffusion of gas in turbulent bulk flow by utilizing the tracer gas data. This paper discussed about the measurement using tracer gas technique in Cibaliung Underground Mine, Indonesia and the evaluation of effective axial diffusion coefficient, E, by numerical simulation. In addition, a scheme to treat network flow in mine ventilation system was also proposed. The effective axial diffusion coefficient for each airway was evaluated based on Taylor's theoretical equation. It is found that the evaluated diffusion coefficient agrees well with Taylor's equation by considering that the wall friction factor, f, is higher than those for smooth pipe flow. It also shows that the value of effective diffusion coefficient can be inherently determined and the value is constant when matching with other measurements. Furthermore, there are possibilities to utilize the tracer gas measurement data to evaluate the airway friction factors.

Study of the Temperature Distribution in a Road Tunnel Under the Effect of Two Ventilation Systems

This paper proposes numerical investigations carried out on a small scale tunnel model airing to study the fire-induced smoke control by longitudinal and longitudinal-natural ventilation systems. We studied the effect of two ventilation systems on the temperature distribution and stratification of the pollutant to estimate the efficiency of ventilation systems. The flow is characterized by the temperature fields, temperature profiles and the Froude number. The numerical tool used is FDS (version 4.0). This numerical study requires validation with an experience of literature. Good agreement with experimental results confirms the possibility of using this code in the problem.

Dimensionless Study on Secretion Clearance of a Pressure Controlled Mechanical Ventilation System with Double Lungs

A pressure controlled mechanical ventilator with an automatic secretion clearance function can improve secretion clearance safely and efficiently.Studies on secretion clearance by pressure controlled systems show that these are suited for clinical applications.However,these studies are based on a single lung electric model and neglect the coupling between the two lungs.The research methods applied are too complex for the analysis of a multi-parameter system.In order to understand the functioning of the human respiratory system,this paper develops a dimensionless mathematical model of doublelung mechanical ventilation system with a secretion clearance function.An experiment is designed to verify the mathematical model through comparison of dimensionless experimental data and dimensionless simulation data.Finally,the coupling between the two lungs is studied,and an orthogonal experiment designed to identify the impact of each parameter on the system.

The Research of Performance Comparison of Displacement and Mixing Ventilation System in Catering Kitchen

A commercial kitchen is a complicated environment where multiple components of a ventilation system including hood exhaust, conditioned air supply, and makeup air systems work together but not always in unison. And the application of an appropriate ventilation system is extremely vital to keep the catering kitchen comfortable, which consequently promotes the productivity and gains. Application of two systems (traditional mixing ventilation system and thermal displacement ventilation system) is compared in a typical kitchen environment using computational fluid dynamics modeling which was used to investigate the difference between mixing and displacement ventilation (DV). It was reported in two parts, one on thermal comfort and the other one on indoor air quality. The results show that DV can maintain a thermally comfortable environment that has a low air velocity, a small temperature difference between the head and ankle level, and a low percentage of dissatisfied people, and may provide better IAQ in the occupied zone. So it was persuasive that using thermal displacement ventilation in kitchen environment allows for a reduction in space temperature without increasing the air-conditioning system capacity.

The Research of Performance Comparison of Displacement and Mixing Ventilation System in Catering Kitchen

A commercial kitchen is a complicated environment where multiple components of a ventilation system including hood exhaust, conditioned air supply, and makeup air systems work together but not always in unison. And the application of an appropriate ventilation system is extremely vital to keep the catering kitchen comfortable, which consequently promotes the productivity and gains. Application of two systems (traditional mixing ventilation system and thermal displacement ventilation system) is compared in a typical kitchen environment using computational fluid dynamics modeling which was used to investigate the difference between mixing and displacement ventilation (DV). It was reported in two parts, one on thermal comfort and the other one on indoor air quality. The results show that DV can maintain a thermally comfortable environment that has a low air velocity, a small temperature difference between the head and ankle level, and a low percentage of dissatisfied people, and may provide better IAQ in the occupied zone. So it was persuasive that using thermal displacement ventilation in kitchen environment allows for a reduction in space temperature without increasing the air-conditioning system capacity.

Modelling and Simulation of Pressure Controlled Mechanical Ventilation System

A mathematical model of mechanical ventilator describes its behavior during artificial ventilation. This paper purposes to create and simulate Mathematical Model (MM) of Pressure Controlled Ventilator (PCV) signal. This MM represents the respiratory activities and an important controlled parameter during mechanical ventilation—Positive End Expiration Pressure (PEEP). The MM is expressed and modelled using periodic functions with inequalities to control the beginning of inspiration and expiration durations. The created MM of PCV signal is combined with an existing multi compartmental model of respiratory system that is modified and developed in the internal parameters—compliances (C) to test created MM. The created MM and model of respiratory system are constructed and simulated using Simulink package in MATLAB platform. The obtained simulator of mechnical ventilation system could potentially represent the pressure signal of PVC as a complete respiratory cycle and continuance waveform. This simulator is also able to reflect a respiratory mechanic by changing some input variables such as inspiration pressure (IP), PEEP and C, which are monitored in volume, flow, pressure and PV loop waveforms. The obtained simulator has provided a simple environment for testing and monitoring PCV signal and other parameters (volume, flow and dynamic compliance) during artificial ventilation. Furthermore, the simulator may be used for studying in the laboratory and training ventilator’s operators.

Proposed Procedure to Design an Optimum Ventilation System for Chemical Laboratory

The safe environmental condition of biological and chemical laboratories at universities in Sudan is a real and tangible problem that needs to be properly addressed due to the increased number of universities which grew up to 25 State-Level Universities. This could sum up to 200 students per academic year. One of the significant problems is the proper ventilation inside the laboratories. This paper aims to provide a proposal for design of an optimum ventilation system for: 1) Good and safe environment;2) Comfortable workplace for laboratories occupants;3) Ensure the health of the surrounding environment while minimizing the energy consumption. Five chemicals are selected for this study as the most consumed and the most hazardous (permissible exposure limits) inside the laboratories of the department of chemistry faculty of science, Al-Neelain university;formaldehyde, nitric acid, acetic acid, xylene and ethanol. Concentration level of materials in laboratory is calculated in correlation with air exchange rate, vapor pressure and area of laboratory. Results concluded to that up 15 ACH the concentration of formaldehyde and nitric acid is still high. Recommendations are given with the limitation of using the suggested mathematical model, regarding laboratory conditions, severity of the material hazardousness, number of people.

A state-of-the-art review on shallow geothermal ventilation systems with thermal performance enhancement-system classifications,advanced technologies and applications

Geothermal energy with abundance and large quantity can partially cover building heating/cooling loads and promote the carbon-neutrality transitions.Shallow geothermal ventilation(SGV)system,with a little initial in-vestment cost,is one of promising technologies to partly replace the conventional air-conditioning system for air pre-cooling/pre-heating.This paper reviews applications of SGV system for improving thermal performance over latest two decades,which mainly includes the reclassification of SGV system,coupling with other advanced energy-saving technologies,application potentials for building cooling/heating under various weather conditions.Heat transfer mechanism and mathematical modelling techniques have been reviewed,together with in-depth analysis on current research trends,existing limitations,and recommendations of SGV system.Phase change materials,with considerable latent energy density,can stabilize the thermal performance with high reliability.The review identifies that optimization designs and advanced approaches need to be investigated to address the existing urgent issues of SGV system(e.g.,large land occupation,difficulty in centralized collection of condensate water timely for horizontal buried pipe,bacteria growth,polluted supply air,and high construction cost for ver-tical buried pipe).A plenty of studies show that the SGV system could greatly expand the application scope and improve system energy efficiency by combining with other energy-saving technologies.This paper will provide some guidelines for the scientific researchers and engineers to keep track on recent advancements and research trends of SGV system for the building thermal performance enhancement and pave path for future research works.

CFD simulations of a semi-transverse ventilation system in a long tunnel

In the present work,a semi-transverse ventilation system in a long tunnel with a length of 4.9 km,as a complex case study,is numer-ically studied by performing a set of three-dimensional steady incompressible computational fluid dynamics(CFD)simulations.The ven-tilation system consisted of a ceiling duct connected to two axial fans at the ending portals,and a series of jet fans in the main tunnel for supporting airflow in the desired direction.To focus on what can and cannot be achieved in commissioning tests,the ventilation system’s performance in various scenarios is numerically evaluated with two different tunnel states;empty tunnel and complete traffic congestion with 1176 stationary vehicles–which is almost impossible to evaluate during a commissioning test.By considering two hypothetical loca-tions for the extraction zone from the main tunnel(in a distance of 450 and 1000 m from one portal),it is shown that the required number of jet fans in a traffic condition drops from 57 for the first extraction location to 43(25%decrease)when the ventilation system extracts from the second zone.We show that if only the close axial fan to the extraction zone is activated,the required number of jet fans reduces by 56%and 72%for the first and second extraction locations,respectively.This finding can provide a cheaper and easier controlling scenario for emergency ventilation.

Brain protective effect of dexmedetomidine vs propofol for sedation during prolonged mechanical ventilation in non-brain injured patients

BACKGROUND Dexmedetomidine and propofol are two sedatives used for long-term sedation.It remains unclear whether dexmedetomidine provides superior cerebral protection for patients undergoing long-term mechanical ventilation.AIM To compare the neuroprotective effects of dexmedetomidine and propofol for sedation during prolonged mechanical ventilation in patients without brain injury.METHODS Patients who underwent mechanical ventilation for>72 h were randomly assigned to receive sedation with dexmedetomidine or propofol.The Richmond Agitation and Sedation Scale(RASS)was used to evaluate sedation effects,with a target range of-3 to 0.The primary outcomes were serum levels of S100-βand neuron-specific enolase(NSE)every 24 h.The secondary outcomes were remifentanil dosage,the proportion of patients requiring rescue sedation,and the time and frequency of RASS scores within the target range.RESULTS A total of 52 and 63 patients were allocated to the dexmedetomidine group and propofol group,respectively.Baseline data were comparable between groups.No significant differences were identified between groups within the median duration of study drug infusion[52.0(IQR:36.0-73.5)h vs 53.0(IQR:37.0-72.0)h,P=0.958],the median dose of remifentanil[4.5(IQR:4.0-5.0)μg/kg/h vs 4.6(IQR:4.0-5.0)μg/kg/h,P=0.395],the median percentage of time in the target RASS range without rescue sedation[85.6%(IQR:65.8%-96.6%)vs 86.7%(IQR:72.3%-95.3),P=0.592],and the median frequency within the target RASS range without rescue sedation[72.2%(60.8%-91.7%)vs 73.3%(60.0%-100.0%),P=0.880].The proportion of patients in the dexmedetomidine group who required rescue sedation was higher than in the propofol group with statistical significance(69.2%vs 50.8%,P=0.045).Serum S100-βand NSE levels in the propofol group were higher than in the dexmedetomidine group with statistical significance during the first six and five days of mechanical ventilation,respectively(all P<0.05).CONCLUSION Dexmedetomidine demonstrated stronger protective effects on the brain compared to propofol for long-term mechanical ventilation in patients without brain injury.

Effects of unilateral superimposed high-frequency jet ventilation on porcine hemodynamics and gas exchange during one-lung flooding

BACKGROUND Superimposed high-frequency jet ventilation(SHFJV)is suitable for respiratory motion reduction and essential for effective lung tumor ablation.Fluid filling of the target lung wing one-lung flooding(OLF)is necessary for therapeutic ultrasound applications.However,whether unilateral SHFJV allows adequate hemodynamics and gas exchange is unclear.AIM To compared SHFJV with pressure-controlled ventilation(PCV)during OLF by assessing hemodynamics and gas exchange in different animal positions.METHODS SHFJV or PCV was used alternatingly to ventilate the non-flooded lungs of the 12 anesthetized pigs during OLF.The animal positions were changed from left lateral position to supine position(SP)to right lateral position(RLP)every 30 min.In each position,ventilation was maintained for 15 min in both modalities.Hemodynamic variables and arterial blood gas levels were repeatedly measured.RESULTS Unilateral SHFJV led to lower carbon dioxide removal than PCV without abnormally elevated carbon dioxide levels.SHFJV slightly decreased oxygenation in SP and RLP compared with PCV;the lowest values of PaO_(2) and PaO_(2)/FiO_(2) ratio were found in SP[13.0;interquartile range(IQR):12.6-5.6 and 32.5(IQR:31.5-38.9)kPa].Conversely,during SHFJV,the shunt fraction was higher in all animal positions(highest in the RLP:0.30).CONCLUSION In porcine model,unilateral SHFJV may provide adequate ventilation in different animal positions during OLF.Lower oxygenation and CO_(2) removal rates compared to PCV did not lead to hypoxia or hypercapnia.SHFJV can be safely used for lung tumor ablation to minimize ventilation-induced lung motion.

Driving pressure in mechanical ventilation:A review

Driving pressure(ΔP)is a core therapeutic component of mechanical ventilation(MV).Varying levels ofΔP have been employed during MV depending on the type of underlying pathology and severity of injury.However,ΔP levels have also been shown to closely impact hard endpoints such as mortality.Considering this,conducting an in-depth review ofΔP as a unique,outcome-impacting therapeutic modality is extremely important.There is a need to understand the subtleties involved in making sureΔP levels are optimized to enhance outcomes and minimize harm.We performed this narrative review to further explore the various uses ofΔP,the different parameters that can affect its use,and how outcomes vary in different patient populations at different pressure levels.To better utilizeΔP in MV-requiring patients,additional large-scale clinical studies are needed.

Characteristic studies of heat sources and performance analysis of free-cooling assisted air conditioning and ventilation systems for working faces of mineral mines

High temperature heat hazard at mineral mine becomes more and more serious as the increase of mining depth.Heat sources at working faces of mineral mines are complex and are of different characteristics,presenting new challenges for air conditioning systems.In this paper,heat sources at four types of working faces are summarized and their characteristics are investigated.Based on this,simplified equations,which are linear with length of working faces,are proposed to calculate heat dissipation rates.So that the main heat sources of different working faces can be found,and cooling load of air conditioning systems can be calculated.Then,considering main heat sources of coal mines,a typical working face is designed to investigate performances of different ventilation systems and air conditioning systems.Simulation results show that segmented ventilation systems(SC)and heat shield assisted centralized ventilation systems(CCHS)can realize much better temperature distributions at working faces.However,cooling load can be greatly reduced for CCHS,when untreated air is supplied to the coal seam side.Based on this,free cooling assisted air conditioning systems are designed,and annual average energy efficiency ratio(EERann)of the systems are investigated and compared between direct evaporate cooling and indirect evaporate cooling(IEC).For SC,as compared with scenarios without free-cooling,IEC can increase EERann by 15%-23%and 22%-32%under Benxi and Datong ambient conditions,respectively.Besides,to ensure high EERann,CCHS is preferred and it is essential to increase thermal insulation of air ducts.

Localization and characterization of intermittent pollutant source in buildings with ventilation systems:Development and validation of an inverse model

Terrorist attacks through building ventilation systems are becoming an increasing concern.In case pollutants are intentionally released in a building with mechanical ventilation systems,it is critical to localize the source and characterize its releasing curve.Previous inverse modeling studies have adopted the adjoint probability method to identify the source location and used the Tikhonov regularization method to determine the source releasing profile,but the selection of the prediction model and determination of the regularization parameter remain challenging.These limitations can affect the identification accuracy and prolong the computational time required.To address the difficulties in solving the inverse problems,this work proposed a Markov-chain-oriented inverse approach to identify the temporal release rate and location of a pollutant source in buildings with ventilation systems and validated it in an experimental chamber.In the modified Markov chain,the source term was discrete by each time step,and the pollutant distribution was directly calculated with no iterations.The forward Markov chain was reversed to characterize the intermittently releasing profile by introducing the Tikhonov regularization method,while the regularized parameter was determined by an automatic iterative discrepancy method.The source location was further estimated by adopting the Bayes inference.With chamber experiments,the effectiveness of the proposed inverse model was validated,and the impact of the sensor performance,quantity and placement,as well as pollutant releasing curves on the identification accuracy of the source intensity was explicitly discussed.Results showed that the inverse model can identify the intermittent releasing rate efficiently and promptly,and the identification error for pollutant releasing curves with complex waveforms is about 20%.

Monitoring and evaluation of building ventilation system fans operation using performance curves

Ventilation fans are an important component of any mechanically ventilated building.Poor fan performance could significantly affect the whole building performance metrics.There are several issues such as dirty blades,mechanical wear,aging of fans could impact the fan’s performance.In present work,a novel,indirect and data-driven methodology is introduced to monitor the ventilation fan unit performance.The proposed method is able to perform continuous monitoring of ventilation fan unit in real-time.The real-time performance of 3 Air handling unit(AHU)fans is examined in an academic building.Expected fan performance is modeled with the help of manufacturer data and compared against the real-time performance.Two data-driven models are developed and implemented.The first model is used to compute expected total fan pressure at a given airflow rate while second is a Support Vector Regression(SVR)model,to predict the fan efficiency.The performance monitoring of the ventilation fan unit is determined in terms of expected and actual fan energy consumption.Findings indicated a significant performance gap in three ventilation fan unit in a case building known as OU44,located in city Odense,Denmark.The advantage of this method comprises simplicity,no direct human intervention and scalability to the series of ventilation units.

Uniformity and energy evaluation of equal cross-section ventilation system(ECVS)for long tunnel in underground buildings

Uniform ventilation is important for the safety of long tunnel in underground buildings,it is difficult to install the large size air duct to ensure the centerline of each cross-section of the traditional variable cross-section ventila-tion system(VCVS)superimposed on the same horizontal axis,which is significant to the ventilation uniformity,energy consumption and installation convenience of the VCVS.On the contrary,each cross-section of the Equal Cross-section Ventilation System(ECVS)has the same horizontal axis,therefore,it is more convenient to manu-facture and install the large size air duct in the underground long tunnel and achieve uniform ventilation.This study proposes an ECVS,using computational fluid dynamics(CFD)numerical simulation analyzed the influences of main duct velocity,aspect ratio,and outlet numbers on uniformity and energy consumption per unit air vol-ume(ECPV).It revealed that when each ventilation equalizer’s valve Angle𝛽is given,uniformity of air supply decreases slightly with an increase in the inlet velocity.When the air supply main duct aspect ratio increases,the outlet velocity standard deviation range is from 0.22 to 0.34.When outlet numbers N=7~12 and𝛽are constant,air supply uniformity and resistance coefficient𝜉also decrease with the decrease of outlet numbers.The outlet number has a significant influence on the uniformity of system air supply,main duct velocity,and aspect ratio are relatively small.ECPV is positively correlated with the main duct velocity and outlet number,and is negatively correlated with aspect ratio.

Experimental study on the flow field and economic characteristics of parallel push-pull ventilation system

Push-pull ventilation systems provide excellent control of contaminants and harmful gases.However,since both a push inlet and a pull outlet are used in the push-pull ventilation system,the flow rate required by the system is large.In that case,the energy consumption of the system is large.The purpose of this paper is to study the flow field and economic characteristics of a parallel push-pull ventilation system by reducing the flow rate of the exhaust outlet,which will be achieved by reducing the size of the exhaust hood.The three commonly used push-pull ventilation systems were analyzed:a high velocity push-pull system with high air supply velocity,a low velocity push-pull system with wide airflow and small velocity,and a parallel push-pull system with wide airflow and uniform air supply velocity.Results showed that the parallel push-pull ventilation system was the only one in which the flow rate of the exhaust outlet could be reduced,reducing the overall energy consumption.Under conditions of the parallel air supply jet,the diffusion range of contaminants in the push-pull flow field was the smallest and reducing the exhaust air flow rate did not affect the capture efficiency of pollutants.These results may be useful in guiding the design of push-pull ventilation system and optimize economic constraints.

Cooling System Design Optimization of an Enclosed PM Traction Motor for Subway Propulsion Systems

This paper presents the design optimization of a self-circulated ventilation system for an enclosed permanent magnet(PM)traction motor utilized in the propulsion systems for subway trains.In order to analyze accurately the machine's inherent cooling capacity when the train is running,the ambient airflow and the related heat transfer coefficient(HTC)are numerically investigated considering synchronously the bogie installation structure.The machine is preliminary cooled with air ducts set on the motor shell,and the fluidic-thermal field distributions with only the shell air duct cooling are numerically calculated.During simulations,the HTC obtained in the former steps is applied to the external surface of the machine to model the inherent cooling characteristic caused by the train movement.To reduce the temperature rise and thus guarantee the motor's working reliability,an internal self-circulated air cooling system is proposed according to the machine temperature distribution.The air enclosed in the end-caps is driven by the blades mounted on both sides of the rotor core and forms two air circuits to bring the excessive power losses generated in the heating components to cool regions.The fluid flow and temperature rise distributions of the cooling system's structural parameters are further improved by the Taguchi method in order to confirm the efficacy of the internal air cooling system.