Distributions of respiratory contaminants from a patient with different postures and exhaling modes in a single-bed inpatient room
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Displacement ventilation
Supine position
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The characteristics and advantages of displacement ventilation were presented by comparing displacement ventilation and mixing ventilation.The superiority of energy-saving of displacement ventilation on aircraft cabin by energy-saving analysis was given,using the way of the HVAC to design displacement ventilation,standards such as ISO7730-2005,ASHRAE62-1989,and relevant standards about aircraft cabin ventilation.
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Elevated concentration of indoor particulate matter (PM) has been linked to adverse effects on human health. To explore how particles from cigarette smoke affect the indoor PM 2.5 concentration and whether such circumstance is harmful to people, distribution characteristics of indoor particulate matter in a typical residence with a smoker were numerically studied under different ventilation strategies. The indoor PM 2.5 concentration without forced ventilation was shown to far exceed the air quality standard of 75 µg/m 3 as recommended by the World Health Organization. In this study, we numerically investigated the performances of the mixing and displacement ventilation strategies in reducing indoor particle levels. Different airflow patterns could significantly influence the movement and deposition of particles in ventilated rooms, even with the same air change rate and particle characteristics. When comparing with the mixing ventilation strategy, the displacement ventilation strategy was shown to have a lower deposition mass and a larger portion of particles leaving the room. Thus, the average indoor PM 2.5 concentration in the displacement ventilation strategy was shown to be higher than the mixing ventilation strategy. In spite of this, low particle concentration in the personnel’s breathing zone was shown by our measurement. Displacement ventilation strategy could provide a cleaner ambient air than the mixing one.
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Abstract Displacement ventilation (DV) is considered an energy saving air conditioning system and is especially recommended for classrooms for providing cool clean air in the occupied zone. However, in the current pandemic situation, ventilation systems should be assessed in terms of infection‐spread prevention as well. Hence, this study aims at assessing the efficiency of displacement ventilation in minimizing infection spread in lecture halls through investigating the effect of source position on the contaminant concentration distribution. The settings of a mid‐size DV lecture hall in Osaka University, Japan was chosen as a case‐study. Ten single‐contaminant‐source cases were simulated using CFD software. The cases were analyzed in terms of temperature distribution, contaminant diffusion pattern and vertical distribution, and breathing air quality using indices, such as local air quality index and scale of ventilation efficiency. The results demonstrated a considerable variation between cases in terms of contaminant distribution pattern, number of occupants affected, average inhaled‐air quality, and diffusion radius. Accordingly, given the ventilation system design, best and worst case‐scenarios were pointed out and factors affecting the variation were highlighted and further investigated to conclude the impact of each factor.
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Natural Ventilation
Room air distribution
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Mixing ventilation and displacement ventilation were compared in an intervention study in classrooms. Particles, cat allergen and CO2, were measured in classroom air at different levels above the floor, during regular lessons. With mixing ventilation, the particle concentration tended to decrease with height, with a stronger gradient occurring for larger particles. With displacement ventilation, the particle concentration increased with height, except for particles >25 µm. The displacement system thus tended to have a slight upward displacement effect on most of the particles. Significant correlations were found between concentrations of cat allergen and particles in the size fraction 1–10 µm. The particle and cat allergen concentration at breathing height did not, however, differ significantly between the two ventilation systems. CO2 was about 10% lower with displacement ventilation. A fairly high level of physical activity of the pupils is believed to have had significant dispersing effect on the airborne contaminants.
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Particle (ecology)
Jet ventilation
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Displacement ventilation
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Energy recovery ventilation
Natural Ventilation
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The numerical simulations of air distribution in a displacement ventilation room usually usehigh-Reynolds number K-e turbulent model,but the results hard display the phenomena of buoyant airflow andlow-Reynolds number airflow.This paper utilizes a LB low-Reynolds number K-e model,to simulate air distribution ofthree-dimension airflow in a displacement ventilation room,and the velocity field and the temperature field of airflow areobtained.Finallv by analvsing and summing simulate results (?)
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Based on big data simulation, three ventilation systems including mixing ventilation, displacement ventilation and diffuse ceiling ventilation are numerically simulated and compared in an office room. Ventilation performances of these three ventilation systems are obtained through analysing indoor air velocity distribution, temperature distribution, PMV, age of air and ventilation efficiency. Results show that the vertical temperature gradient of diffuse ceiling ventilation is 0.30 °C/m. Compared with displacement ventilation and mixing ventilation, the indoor vertical temperature gradient of diffuse ceiling ventilation is reduced by 3.95°C/m and 1.22°C/m, respectively. The indoor temperature distribution is relatively uniform, and there is no local thermal discomfort in the occupied zone. In addition, the indoor air velocity gradient of diffuse ceiling ventilation is very small, and there is no cold air draught even when the supplied air has high momentum. The indoor PMV is also within the requirement of regulations, and the thermal comfort can be greatly improved. The indoor air age of diffuse ceiling ventilation is 539 s, with the ventilation efficiency close to 1.0. Although it is less than that of displacement ventilation, the effects of ventilation and heat rejection are still excellent. This study can provide technical basis for the application of diffuse ceiling ventilation in practical projects.
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Displacement ventilation
Stratum
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The physical and mathematical model for an assembly room with displacement ventilation system or mixed ventilation system is established.The velocity field and temperature field in the room are simulated by the software AirPak.The thermal comforts of room are analyzed between displacement ventilation and mixed ventilation.
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