Complex Ventilation Systems Research Articles

Review of the experience in utilising waste heat from the metro

The exhaustibility of traditional fossil energy sources is leading to the increasing use of unconventional energy sources. One of the most promising areas of alternative energy is the use of low-potential ground energy to heat buildings and structures for various purposes using a heat pump. The subway generates a significant amount of heat, especially when trains are braking, stopping on platforms and picking up speed when they start moving from the station. Thus, to combat the rise in temperature in tunnels and stations, a complex ventilation system is designed, including shafts, fans, and under-platform exhaust. In modern Ukrainian subways, the ventilation system is designed to cope with the rising temperatures in tunnels and stations. This traditional approach results in high energy consumption for running fans and ignores the possibility of using the extracted heat above ground in buildings. Techniques such as lining underground railway tunnels with heat exchanger segments, installing a heat exchanger in a subway ventilation shaft, installing geothermal heat pumps next to a subway tunnel, installing energy piles, energy baffle walls, energy platforms, and introducing absorption pipes into tunnel segments can provide an alternative solution to cool tunnels and the surrounding ground, and transfer the resulting heat to neighbouring buildings for heating. This would also have the benefit of reducing energy consumption for tunnel ventilation. This article discusses the possibility of using waste heat from underground railway systems as a source of low-potential energy to provide heat to, for example, adjacent buildings. Various technologies for utilising waste heat from underground railway tunnels that have already been implemented or whose models are technically and economically feasible are presented.

Research on mine ventilation network solution and collaborative control technology

With the development of intelligent ventilation system in domestic coal mines, the demand for ventilation network solving software is becoming more and more intense. Aiming at the problem that the traditional ventilation network solution algorithm is difficult to meet the increasingly complex ventilation system solution needs of domestic mines, and the lack of functions of the collaborative control of ventilation equipment and facilities, this paper uses theoretical analysis combined with mine reality to study the relevant theories and algorithms in the field of ventilation network solution and collaborative control at home and abroad, and optimizes the network solution and collaborative control related algorithms such as iterative calculation of ventilation network, identification and stability analysis of angle-linked wind network, natural wind pressure calculation, local fan collaborative control, and collaborative control of damper and wind window. Provide theoretical guidance for future network solution software development.

Experimental simulation study on gas flow field in combined goaf during the transition period of coal pillar-free working face relocation

Regarding the gas disaster caused by the complex ventilation system and the changeable flow field in the combined goaf during the transition period of the coal pillar-free working face, the self-designed physical simulation test bench for the combined goaf of coal pillar-free mining was used to compare and analyze the distribution law of wind pressure, gas, and oxygen concentration field in the combined goaf during the moving period of the working face and the normal mining period. The results show that during the relocation period, the gas concentration in the stope will always be slightly higher than that in the normal mining period, and the existing air leakage channel will lead to complex air flow in the combined goaf, which is easy to cause gas explosion accidents. The formation conditions, judgment principles, and judgment methods of the dangerous area of gas explosion coupling disaster in goaf are analyzed. By changing the air distribution ratio of the main and auxiliary air intake roadways, it is concluded that the explosion area will form an “L”-shaped explosion zone in the goaf, and the area of gas explosion disaster area during the relocation period will be larger than that the normal mining period. According to the size of the gas explosion area, the optimal air distribution ratio of the main and auxiliary air intake roadway during the transition period of the working face relocation and the normal mining period is 2:1. Under this air distribution ratio, the gas explosion area is the smallest, which is 132 284 and 113 534 mm2, respectively. The research results are of great significance to reveal the mechanism of gas disaster induced by goaf during the transition period of coal pillar-free relocation.

G‘UJUMSOY KONI HAVO UZATISH STVOLIDA HAVO OQIMINI BOSHQARISH SAMARADORLIGINI OSHIRISHDA HAVO PARDASINI QOʻLLASH

On the extraction of gold-bearing ores in mines, the amount of air in the ventilation network of mines increases in proportion to increases in the length of excavations and deepening of the mines. The article deals with issues of managing the air flows into mines, the use of air curtains to reduce external and internal losses to the mine, and aerodynamic resistance. The work describes the use of the main fan and an optimal ventilation scheme in order to increase the efficiency of ventilation in mines with complex ventilation systems, with the view to reducing outdoor air losses in the ventilation duct and ventilation network by determining the optimal values for air flow, air flow rates, and pressure changes with ventilation parameters to ensure ways of effective control and distribution of the air flow.

Propagation of SARS-CoV-2 in a Closed Cell Culture Device: Potential GMP Compatible Production Platform for Live-Attenuated Vaccine Candidates under BSL-3 Conditions?

Live-attenuated SARS-CoV-2 vaccines present themselves as a promising approach for the induction of broad mucosal immunity. However, for initial safety assessment in clinical trials, virus production requires conditions meeting Good Manufacturing Practice (GMP) standards while maintaining biosafety level 3 (BSL-3) requirements. Since facilities providing the necessary complex ventilation systems to meet both requirements are rare, we here describe a possibility to reproducibly propagate SARS-CoV-2 in the automated, closed cell culture device CliniMACS Prodigy® in a common BSL-3 laboratory. In this proof-of-concept study, we observed an approximately 300-fold amplification of SARS-CoV-2 under serum-free conditions with high lot-to-lot consistency in the infectious titers obtained. With the possibility to increase production capacity to up to 3000 doses per run, this study outlines a potential fast-track approach for the production of live-attenuated vaccine candidates based on highly pathogenic viruses under GMP-like conditions that may contribute to pandemic preparedness.

Study on hydrogen dispersion in confined space with complex air supply and exhaust system

The safety issue involving unplanned H2 leakage has retarded promotion of Hydrogen fuel cell vehicles (HFCVs). When an accidental leakage occurs in a relatively closed space, H2 tends to accumulate. It is necessary to obtain a better understanding of the H2 dispersion characteristics in a relatively closed space. Most studies focus on the dispersion features in a small garage, whereas few consider large underground garages with complex ventilation systems. Herein, H2 released from a pressurized tank in a real large underground garage was investigated by a two-stage computational fluid dynamics (CFD) study. An isentropic expansion model with a real gas equation of state was employed in stage (1) to estimate the source strength which can be used as inlet boundary conditions for stage (2), the dispersion stage. The CFD models were validated against the experimental results. The concentration field and flammability envelope were focused. This study provides a feasible method for assessing the risks associated with HFCVs.

Interaction between the Standard and the Measurement Instrument during the Flow Velocity Sensor Calibration Process

The complex ventilation system development process is associated with the stages of modelling, design, execution, and testing. Each of these steps requires the use of measuring equipment that is capable of determining the basic parameters of the flow. In the process of calibrating instruments for measuring flow velocity, one of the limitations is the size of the calibrated devices positioned in the test section of the wind tunnel. This is related to the change in the flow condition within the vicinity of the calibrated anemometers, which is caused by the blockage effect. Instruments with significant dimensions in relation to the cross-sectional area of the wind tunnel test section may have an impact on the reference velocity as indicated by the standard. In such cases, the calibration results may be affected by additional systematic error. This article presents a study of this effect using a real case of a calibration laboratory and commonly used sensors. The influence of different types of air velocity sensors on velocity profiles in the measurement standard area is also investigated. Additionally, the area of the blockage effect is described. The obtained results indicate the possibility of a proper placement for the measuring standard due to minimization of the flow-blocking effect.

Current ventilation strategies in Greenlandic dwellings

The Arctic winters are long and cold. When temperatures drop deep below freezing point, the occupants of Arctic dwellings become hesitant to opening windows in order to avoid cold draught. Natural vents are typically sealed. Mechanical ventilation is either not existing or comprises of bathroom fan and range hood. Air tightening of the building envelope to prevent draught results in a lack of makeup air for the extraction fans. This leads to further reduction of air change in majority of the dwellings. One consequence is poor indoor air quality. The other may be moisture levels high enough to damage the construction. The current Greenlandic building code does not require use of complex ventilation systems. Lack of experience and requirements together with higher construction costs will typically cause ruling the complex mechanical ventilation systems out of the projects and replacing them by bare minimum. In this project we mapped, three ventilation solutions. Two renovations and one new home. The measurements have shown that the IAQ (evaluated based on CO2 and humidity measurements and occupant interviews) had improved significantly with use of balanced mechanical ventilation with heat recovery. The occupants have reported increase in their comfort. The systems were capable of continuous operation throughout the Arctic winter. Installation of the mechanical ventilation had proved to be an efficient solution to IAQ problem in Greenland.

Simulation of spectators’ aerodynamic drag using porous models approximation

Evaluation of the thermal comfort is essential for complex ventilation systems design. Assessment of thermal indices requires representative velocity and pressure fields' values. When simulating the air flow in large facilities such as stadium, the effect of crowds' geometrical features needs to be captured. Using porous models approximations to simulate the aerodynamic effect of detailed spectators' geometry reduces the required mesh size and associated processing time. This paper investigates the use of different porous media models approximations for capturing the effect of large crowds inside complex building systems, such as stadiums. Their efficiency of capturing the effect of spectators on the air flow were compared to the simulation of the exact spectators' geometry. The exact spectators' geometrical model was of a stadium tiers section with 28 spectators. Using a wind tunnel, the exact spectator's model results were validated against a 1:10 scaled physical model. The experiments included PIV and hot-wire velocity measurements. The results of the pressure drop were used to obtain the coefficients needed to utilize the porous models. Compared to the exact spectators' case, the three-dimensional porous volume model approximation yielded an average absolute error of 24.5% in velocity, while the two-dimensional porous jump model yielded results with an average error of 1.5%. In comparison to the exact model cooling load, the results yielded a difference of 6% for the 2D porous jump and 6.5% for the 3D porous volume. Nevertheless, both models yielded more representative results than the case of simulation of empty bleachers.

The Sows productivity and annual dynamics of piglet growth depending on the design features of the microclimate system

This article studied the dependence of the reproductive qualities of sows and the intensity of Danish suckling piglets growth on the seasons and the structural features of the microclimate system in the gender. It was found that sows kept in rooms with a geothermal ventilation system had better retention rates, weights of 1 head at weaning, masses of piglets at weaning, fewer and proportion of still-born pigs compared to analogues that were kept during this period in the classical system of support the climate. At the same time, there are no significant differences in the number of piglets at birth and their number when weaned. The estimated index for a limited number of reproductive traits and the breeding index of sows were also found higher in 1,01% and 1,09%, respectively, as for sows whose suckers were subjected to geothermal ventilation. There is no significant difference between the absolute, average and relative growth rates of piglets maintained under different microclimate systems throughout the year. This is due to the weak influence of the ventilation type factor on the growth rate within 7,71 – 10,20%. The intensity of growth of suckling pigs in the conditions of the both industrial complex ventilation systems of pigsties increased in winter and spring and decreased in summer and autumn. It was caused by a significant strong influence of the factor of season influence on the absolute, average and relative growths, which characterize it within 21,83 to 23,54%. Due to the identified dependence of the reproductive qualities of sows and the intensity of suckling pigsgrowth on the type of ventilation and the time of year, it should be noted that further studies of these factors influence are important to continue. Key words: sow, piglet, type of ventilation, multiple pregnancy, weight of the nest of piglets, safety, season of the year.

Long-term prediction of dynamic distribution of passive contaminant in complex recirculating ventilation system

Recirculating ventilation systems may act as carriers of hazardous substances. The long-term prediction of the dynamic distribution of contaminants in this type of system is crucial for the evaluation of pollution and further design of more efficient ventilation systems. However, few convenient methods can predict the dynamic distribution of contaminants, because the dynamic supply air concentrations resulting from air recirculation are unknown, especially over long time periods, such as months or years. In this study, a novel method is proposed to predict the dynamic distribution of contaminants over a long time period in a complex recirculating ventilation system, where an algebraic expression based on the indices of the response coefficient is applied to account for the relationship between the contaminant distribution inside the room and various boundary conditions. The method is established by obtaining comprehensive mathematical descriptions of the relationships between concentrations of contaminants in the air handling units, supply air inlets, return air outlets, and fresh air. Hourly supply air concentrations can be easily obtained by solving a matrix, and the dynamic distribution of contaminants is then calculated using an expression based on the response coefficient. The reliability of the proposed method is analyzed by both experimental and numerical methods. A simplified method is suggested to accelerate the time-consuming calculation of the response coefficient. The proposed method is beneficial for predicting three-dimensional dynamic distribution of contaminants in complex ventilation systems with an acceptable accuracy and time cost.

Predicting gas dispersion in large scale underground ventilation: A particle tracking approach

The present work highlights the gas dispersion evaluation in large underground tunnel ventilation by means of tracer gas measurement and numerical simulation using particle tracking method. Ventilation system is a tool to control pollutants and/or hazardous gas spreading. The use of grid-based numerical method is limited by the spatial dimension of ventilation network. Therefore, the applicability of such technique for large ventilation network is constrained. A Lagrangian based Particle Tracking method is proposed to evaluate the dispersion of tracer gas from a releasing point to the downstream position in a complex ventilation system. This method simulates mass transport by discretizing mass concentration into numbers of particles. Rather to solving the transport equation in grid system to obtain the mass concentration, this technique simulates mass concentration by counting number of particles at any specified position within the ventilation network. In this research, the network splitting scheme was used to simulate particles' transition in junctions. Further, it was found that by setting effective diffusion coefficient to 47 times larger than those for common underground airway and with velocity correction factor of α = 0.59, a good agreement between particle tracking result and tracer gas measurement data can be achieved. This results suggests that the analytical approach in evaluating gas (or pollutant) dispersion and residence time in large ventilation system by the means of conventional ventilation network analysis have to consider both mechanical dispersion and the effect of delay due to trapping mechanism of gas.

The design of thermal tunnel energy segments for Crossrail, UK

Significant heat is generated by underground trains, particularly when braking, stopping at platforms and accelerating away from stations. A complex ventilation system including shaft, fans and under-platform extraction thus has to be designed to manage the rising temperature in tunnels and stations. This conventional approach results in high energy consumption for running the fans and neglects the possibility to use the extracted heat above ground in buildings. Lining underground rail tunnels with heat-exchange segments can provide an alternative solution to cool the tunnels and surrounding ground, and transfer the harvested heat to adjacent buildings for heating. It will also bring benefits in terms of reduction of energy consumption for tunnel ventilation operations. This paper reports on the work carried out in designing thermal energy segments for use on the tunnelled sections of the Crossrail project in London, UK.

A theoretical model to calculate the distribution of air age in general ventilation system

Air age is a widely used concept to evaluate indoor air quality. Available models of air age distribution apply only to simple ventilation systems with one room or one air handling unit (AHU). Furthermore, these models would be computationally intensive for complex ventilation systems since a large number of computational fluid dynamics (CFD) simulations or iterations would be required. This study presents a theoretical model which is capable of calculating the air age distribution in a wide variety of ventilation systems with recirculation. The model was validated by combining tracer gas experiments and CFD simulation and demonstrated by a case study using a recirculation ventilation system with multiple AHUs and rooms. A comparison between the model and the conventional iterative method indicated that for complex ventilation systems the model has a potential to significantly reduce the CPU-time requirements and allows additional new scenarios to be tested without further CFD simulations. Practical applications: The theoretical model presented can be used to obtain the distribution of air age in a wide variety of ventilation systems with recirculation and much more computationally efficient than the conventional iterative method. The model can be a useful tool to evaluate and improve a wide range of indoor environments, which are ventilated by a variety of practical ventilation systems that utilise fresh and return air mixing.

A numerical method to determine the steady state distribution of passive contaminant in generic ventilation systems

Ventilation system with air recirculation is designed to conserve energy, yet at the same time may result in transporting hazardous substance among different rooms in the same building, which is a concern in indoor air quality control. There is a lack of effective methods to predict indoor contaminant distribution primarily because of uncertainty of the contaminant concentration in supply air which in turn due to the mixing ratio of fresh and recirculation air. In this paper, a versatile numerical method to determine the pollutant distribution of ventilation system with recirculation at steady state is proposed based on typical ventilation systems with accessibility of supply air (ASA) and accessibility of contaminant source (ACS). The relationship is established between contaminant concentrations of supply air and return air in a ventilated room or zone. The concentrations of supply air and contaminant distribution in each room can be determined using such parameters as ASA and ACS. The proposed method is validated by both experimental data and numerical simulation result. The computing speed of the proposed method is compared with the iteration method. The comparisons between the proposed method and the lumped parameter model are also conducted. The advantages of the proposed method in terms of accuracy, speed and versatility make it advantageous to be applied in air quality control of complex ventilation systems with recirculation.

Numerical and Experimental Investigation of a Mechanically Ventilated Room: The Impact of Inlet Boundary Conditions on CFD Modelling of the Ventilation System

Among the tools which serve to predict heat and mass transfer in a mechanically ventilated room, CFD is increasingly used. However, this type of tool needs a correct description of the boundary conditions, especially concerning the air inlet. The ventilation inlet is often geometrically complex and many models exist in order to simplify their equivalent boundary conditions included in CFD codes. Nevertheless, none of these simplified models can predict the correct behaviour of flows issuing, for example, from a T-pipe, a bend or a more complex ventilation system. The main idea is then to model a part of the ventilation system with the help of CFD and to impose boundary conditions on a fully developed flow section situated far from the inlet. The validation of this approach consists of the comparison of experimental and numerical data obtained for a mechanically ventilated room with and without thermal effects. This model has also been tested with more complex diffusers to show its broader scope.

A GENERALIZED ALGORITHM FOR SIMULATING CONTAMINANT DISTRIBUTION IN COMPLEX VENTILATION SYSTEMS WITH RECIRCULATION

In complex ventilation systems with air recirculation, the contaminant concentration at the supply inlets is generally unknown, which limits the application of computational fluid dynamics (CFD) tools to simulate the indoor contaminant distribution. In this article, we develop a new algorithm that can deal with different ventilation scenarios while it requires minimum computing time. This algorithm divides indoor contaminant distribution into two parts: the contribution from inlets and the contribution from sources. The former can be obtained with the concentrations at inlets and volume fraction for each inlet, which is defined as the relative concentration when the boundary concentrations are 1 for the inlet and 0 for other inlets. The latter is calculated by setting the concentrations at all inlets as 0. By combining the contaminant transportation characteristics in rooms and system ducts, the algorithm does not require iteration to solve the contaminant distribution in actual ventilation systems. The demonstration results of two case studies show the great influence of duct configuration on indoor contaminant distribution.

Shelter and indoor air.

Improvements in outdoor air quality that were achieved through the implementation of the Clean Air Act accentuate the quality of the indoor air as an important, if not dominant, factor in the determination of the total population exposure to air contaminants. A number of developments are adding important new determinants of indoor air quality. Energy conservation strategies require reductions in infiltration of outdoor air into buildings. New materials introduced in the construction and in the maintenance of buildings are contributing new air contaminants into the building atmosphere. Larger buildings require more and more complex ventilation systems that are less and less under the individual control of the occupants. All of these factors contribute to the current reality that indoor air contains more pollutants, and often at higher concentrations, than outdoor air. Especially in the larger buildings, it will be necessary to assure that an adequate quantity of fresh air of acceptable quality is provided to each individual space, and that no new sources of pollutants are added to a space or a whole building without appropriate adjustments in the supply of fresh air.