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The worldwide spread of COVID-19 viruses induced many people to pay attention to indoor air quality. In this study, multiple air cleaners were installed in a four-bed ward equipped with a ventilation system to enhance indoor air quality by finding optimal air cleaner operation combinations. The age of air was used as an index to assess indoor air quality. The age of air distribution in the room was obtained through particle number concentration measurement experiment and flow simulation. The cases of operating multiple air cleaners were considered depending on whether the ventilation system and curtains were used. When two air cleaners were operated, their effects were identified by varying their positions. When only two air cleaners were used, the local age of air significantly varied by 18.3 % at maximum depending on the combination of operating positions. When all four air cleaners were operated, the age of air was lowered by 51.1 % at maximum compared to the cases of operating two air cleaners, regardless of operating the ventilation system and using the curtains. The results of this study are expected to be used for determining the optimal operating positions to improve indoor air quality when using multiple air cleaners in various indoor spaces. [ABSTRACT FROM AUTHOR]

In developed countries, presence at home varies between 60% and 90% of the day, sleeping supposes 30%. Therefore, it is essential to ensure good indoor air quality that enhances health and benefits rest and recovery. In this context, it is necessary to achieve a balance between energy efficiency and air distribution parameters; thus, the influence exerted by the furniture of a bedroom on the air exchange efficiency, in the breathing zone during sleep, is assessed in this study. Computational fluid dynamics techniques, experimentally validated by the tracer gas (SF6) concentration decay method, are used to analyze 52 case studies corresponding to the same space, but varying both the number and the arrangement of the furniture inside. It is concluded that, in order to achieve a significant improvement in the air exchange efficiency, the number of elements included in the bedroom is not relevant, but the position of them. The highest increase in the ventilation efficiency in breathing zone is observed when the furniture is located avoiding the airflow obstruction in the area near the inlet and creating an unfilled volume of air in the area close to the outlet. [ABSTRACT FROM AUTHOR]

Cross-ventilation using rooftop wind-catchers is very complex as it is influenced by a wide range of interrelated factors including aerodynamic characteristics of the wind catcher, approach-flow conditions and building geometry. Earlier studies on wind-driven cross-ventilation in buildings have shown the significant impact of the geometry and position of openings on the flow and ventilation performance. However, this has not yet been investigated for cross-ventilation using wind catchers. This paper, therefore, presents a detailed evaluation of the impact of the outlet openings on the ventilation performance of a single-zone isolated building with a wind catcher. The evaluation is based on three ventilation performance indicators: (i) induced airflow rate, (ii) age of air, and (iii) air change efficiency. High-resolution coupled 3D steady RANS CFD simulations of cross-ventilation are performed for different sizes and types of outlet openings. The CFD simulations are validated based on wind-tunnel measurements. The results show that using outlet openings very close to the wind catcher will not increase the induced airflow, while it leads to a considerable reduction in the indoor air quality. A combination of one-sided wind-catcher and window is superior, while the use of two-sided wind-catchers leads to the lowest indoor air quality and air change efficiency. [ABSTRACT FROM AUTHOR]

Most people spend approximately 90% of their lives indoors. Thus, designing effective ventilation systems is essential to mitigating problems with indoor air quality. The measures of mechanical ventilation design performance considered in this study are age of air, air residual life time, air residence time, and ventilation effectiveness. This paper presents two different methods to help quantify these measures. The first method is based on transport equations, where a continuous representation of these quantities are calculated. The second method is based on Markov matrices, where a discrete representation of these quantities are calculated. We show 1) how both the continuous and discrete methods are related and 2) that the age of air and residual life time are adjoints. A new transport equation for residual life time along with methods for these quantities using Markov matrices are established. The two approaches are validated and compared using previously established experimental data. The results show that both approaches provide similar results. Using these techniques allows for the quantities of residual life time and residence time to be integrated into the design processes. This paper provides a simple framework that enables designers to get a comprehensive picture of the ventilation systems they design. [ABSTRACT FROM AUTHOR]

Abstract: A ventilation system of sufficient performance is the basic condition for comfort and health risk free environment in enclosed aircraft cabin spaces. The airflow pattern and spreading of fresh air into the cabin space mainly depend on the type of the air distribution system and location of heat sources/sinks. The present study deals with the investigation of the dependency between the type of the air distribution system and indoor air quality in a cabin of a small transport aircraft. The mock-up interior geometry of a small aircraft cabin for nine passengers was adopted for the investigation. Three types of the air distribution system were investigated: a typical mixing ventilation system, a modified mixing ventilation system and an under-aisle displacement ventilation system. The quality of ventilation was assessed based on the local mean age of air using CFD software Star-CCM+. At first, the CFD model of a typical mixing ventilation was validated against the experimental data of airflow in the mock-up of the small aircraft cabin. The validated model was then used for the evaluation of the three distribution systems under cold, mild and hot ambient environment conditions from the point of their performance for several typical aircraft operational conditions. Results of the study show a strong dependence of the air distribution systems performance on the ambient conditions. The most stable air distribution was reached with the modified mixing air distribution system. Other types of ventilation systems failed to provide sufficient ventilation and cooling under hot ambient conditions. [Copyright &y& Elsevier]

[Display omitted] • Experimental and CFD studies were performed to investigate a novel DIV system. • The developed CFD model accurately predicted air quality and airflow in DIV. • Stratified air distributions were created by DIV in both cooling and heating. • The thermal comfort in a room with DIV met ASHRAE requirements. • The novel DIV system effectively remedied limitation of traditional DV. Traditional displacement ventilation (DV) creates high indoor air quality in occupied zone in cooling season due to thermal plume created by heat sources which then effectively purge contaminants out of the breathing zone, but tend to be challenged when high cooling loads are present. In addition, traditional DV, when supplying heated air via its diffusers has low ventilation effectiveness in heating season. This study investigated a novel wall-mounted displacement induction ventilation (DIV) system in comparison to traditional DV system. The investigation used an environmental chamber to mimic a typical classroom and measured the distributions of air velocity, air temperature, and contaminant concentration for validating the subsequent computational fluid dynamics (CFD) model developed across an array of operational modes. Then the CFD model was employed to evaluate the performance of DIV system in terms of ventilation effectiveness, mean age of air and vertical temperature gradient as it relates to thermal comfort. Each DIV unit receives 100% outdoor (or primary) air to its plenum chamber. As the primary air pressurizes the chamber, it exits a series of nozzles, creating a low pressure which then induces room air across the integral hydronic coil. A room is typically supplied with multiple DIV units, which allows for individual control operation during both cooling and heating modes. Results showed that stratified air distribution was achieved in both cooling and heating modes with DIV system, which remedied the current limitation of traditional DV. [ABSTRACT FROM AUTHOR]