Personal Exposure in Displacement Ventilated Rooms (original) (raw)
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Exposure to aerosol and gaseous pollutants in a room ventilated with mixing air distribution
2016
The present study investigates the aerosol and gas dispersal in a mechanically ventilated room and the personal exposure to these contaminants. The study was performed in a full-scale climate chamber. The room was air conditioned via mixing total volume ventilation system. The room occupancy was simulated by a sitting dressed thermal manikin with realistic body shape. During the experiments monodisperse aerosols of three sizes and nitrous oxide tracer gas were generated simultaneously from one location in the room. The aerosol and gas concentrations in the bulk room air and in the breathing zone of the thermal manikin were measured. The results showed higher exposure to the contaminants measured at the breathing zone than at the ambient air. The behaviour of the tracer gas and the aerosols was similar. PRACTICAL IMPLICATIONS This research extends our knowledge of the effect of airflow distribution and local free convective currents around the human body on indoor exposure to different types of airborne contaminants, including aerosols and tracer gas. The results from the study can be used as input data for validating numerical and computational fluid dynamic models estimating personal exposure to indoor air pollutants.
Contaminant dispersion with personal displacement ventilation, Part I: Base case study
Building and Environment, 2009
Personal displacement ventilation (PDV) is a new ventilation concept that combines the positive features of displacement ventilation with those of task conditioning or personalized ventilation. PDV is expected to create a micro-environment around an occupant to control the environment individually. In this study, a base PDV case with a contaminant source at different locations was modeled for contaminant dispersion in a full-scale chamber. Computational fluid dynamics (CFD) was used to simulate the indoor airflow and pollutant transport, and the simulation results were validated against the experimental data. The contaminant concentration field for three different contaminant source locations was analyzed. Based on our results, it seems that this kind of PDV system cannot create the expected ''microenvironment'' to avoid the disturbance of the outside airflow. Further studies on how to improve the PDV performance are given in the companion paper.
Contaminant Dispersion in Personal Displacement Ventilation
2007
Personal displacement ventilation (PDV) is a new ventilation concept that intends to combine the positive features of displacement ventilation with those of task conditioning or personalized ventilation. PDV is expected to create a micro-environment around the occupant to control the environment individually. In this study, a PDV with a contaminant source at different locations was modeled for contaminant dispersion in a full scale chamber. Computational fluid dynamics (CFD) was used to simulate the indoor airflow and pollutant transport, and the simulation results were validated against the experimental data. The contaminant concentration field for three different contaminant source locations was analyzed. It seems that this kind of PDV system cannot create the expected "micro-environment" to avoid the disturbance of the outside airflow. Further studies are needed to examine the conditions where PDV could perform better.
Transport of gaseous pollutants around a human body in quiescent indoor environment
2014
Well-mixed" assumption often leads to inadequate prediction of the human exposure. In spaces that operate with a low air velocity, local airflows generated by occupants play predominant role for pollutant transport. The present study investigates the ability of a human convective boundary layer (CBL) to transport the pollution in quiescent indoor environment. A human body is resembled by a thermal manikin with a body shape and surface temperature distribution of a real person. The objective of the study is to examine the impact of the pollutant location around the human body on the pollution concentration levels in the breathing zone. The results show that the location of the pollution source has a considerable influence of the breathing zone concentrations. This is contributed to the human CBL, as it pulls the pollution emitted close to the human body and transports it to the breathing zone. For different pollutant location studied, the highest breathing zone concentrations are achieved when the pollution is located at the chest, while there is zero exposure for the pollutants emitted from the upper back or behind the chair. The results suggest that understanding of the air patterns around the human body should be recognized in ventilation design practice.
A study of the air quality in the breathing zone in a room with displacement ventilation
Building and Environment, 2001
This paper is concerned with the di erence in the air quality that is perceived by the occupants (breathing zone) and that existing in the occupied zone as a whole. An environmental chamber with displacement ventilation system has been used to carry out the measurements with the presence of a heated mannequin and other heat sources. Measurements of the age of air distribution, the air exchange index and the ventilation e ectiveness were carried out at di erent points in the chamber for di erent room thermal loads. CFD simulations were also carried out for the purpose of ow visualisation as well as the calculation of air velocity, temperature and age of air distribution. In addition, CFD simulations were carried out to study the e ect of changing the air ow rate to the chamber and the position of air inlet to extend the range of parameters. The results from the CFD simulations were compared with those from measurements and good agreement was obtained in most cases.
Indoor Air, 2015
The effects of the human convective boundary layer (CBL), room airflow patterns, and their velocities on personal exposure are examined. Two pollutants are studied which simulate particles released from the feet and generated at distances of 2 and 3 m by a human cough. A thermal manikin whose body shape, size, and surface temperatures correspond to those of an average person is used to simulate the CBL. The findings of the study reveal that for accurate predictions of personal exposure, the CBL needs to be considered, as it can transport the pollution around the human body. The best way to control and reduce personal exposure when the pollution originates at the feet is to employ transverse flow from in front and from the side, relative to the exposed occupant. The flow from the above opposing the CBL create the most unfavorable velocity field that can increase personal exposure by 85%, which demonstrates a nonlinear dependence between the supplied flow rate and personal exposure. In the current ventilation design, it is commonly accepted that an increased amount of air supplied to the rooms reduces the exposure. The results of this study suggest that the understanding of air patterns should be prioritized.
Building and Environment, 2021
While personalized ventilation (PV) has been integrated to enhance inhaled air quality, some studies showed that it can contribute to contaminants' transport indoors. This work investigates the effect of the individual preferences of PV users on potential cross-contamination in an office. Two occupants were using PV, sitting either face to face or back to face (i.e. in tandem). One of the occupants was infecting the office space through two respiratory activities: coughing and breathing. The PV flowrate control ranged between 0 and 13 l/s, ensuring thermal comfort. A 3-D computational fluid dynamics model was developed and experimentally validated in a climatic chamber equipped with one thermal manikin representing the infected person and a heated dummy representing the healthy person. The cross-contamination was assessed using the inhaled intake fraction (iF) index, which is the ratio of the contaminants' mass inhaled by the healthy person to that exhaled by the infected person. It was found that minimal exposure levels were reached when the infected person used low PV (in the range of 0-4 l/s) for the tandem seating and high PV(in the range of 9-13 l/s) for the face-to-face seating. Furthermore, the average iF for face-to-face seating was 31% lower than that of tandem seating for coughing and 86% for breathing for all possible PV ventilation cases.
The contaminant distribution in a ventilated room with different air terminal devices
The room ventilation is investigated for three different air terminal devices under isothermal conditions. Velocity distribution in the occupied zone is measured for each air terminal device at different air exchange rates. The maximum air exchange rate is determined on the base of both the throw of the jets and the comfort requirements applied to measured air velocities in the occupied zone.
HVAC&R Research, 2014
It is essential to investigate person-to-person contaminant transport in mechanically ventilated spaces to improve air distribution design and reduce the infection risk from airborne infectious diseases. This paper provides a systematic study of the effects of ventilation mode, ventilation rate, and person-to-person distance on person-to-person contaminant transport. This study first collected available cases of person-to-person contaminant transport from the literature to create a database. Then this investigation identified the limitations of the existing data and added a number of cases to complete the database. The additional cases were generated by using a RANS-Eulerian model that was validated by experimental data from an occupied office with under-floor air-distribution (UFAD) systems. The database shows that the overall performance of displacement ventilation and the UFAD systems was better than that of mixing ventilation. A higher ventilation rate was beneficial in reducing person-to-person contaminant transport to some extent. Person-to-person contaminant exposure increased rapidly with a decrease in personto-person distance when the distance was smaller than 1.1 m. Generally speaking, person-toperson distance is an important parameter when compared with ventilation mode and ventilation rate.