Exposure assessment involving entrainment during human motion in the indoor environment (original) (raw)
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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.
Personal Exposure in Displacement Ventilated Rooms
Indoor Air, 1996
l'crsonal exposure in a displacement ventilated room is examined. The stratified flow and the considerable concentration gradients necessitate an improvement of the widely used fully mixing compartmental approach. The exposure of a seated and a standing person in proportion to the stratification height is examined by means of fullscale measurements. A breathing thermal manikin is used to simulate a person. It is found that the flow in the boundary layer around a person is able to a great extent to entrain and transport air from below the hrcathing zone. In the case of non-passive, heated contaminant sources, this entrainment improves the indoor air quality. Measurements of exposure due to a passive contaminant source show a significant dependence on the flow field as well as on the contaminant source location. Poor system performance is found in the case of a passive contaminant released in the lower part of the room close to the occupant. A personal exposure model for displacement ventilated rooms is proposed. The model takes the influence of gradients and the human thermal boundary layer into account. Two new quantities describing the interaction between a person and the ventilation are defined.
Human convective boundary layer and its interaction with room ventilation flow
Indoor Air, 2014
This study investigates the interaction between the human convective boundary layer (CBL) and uniform airflow with different velocity and from different directions. Human body is resembled by a thermal manikin with complex body shape and surface temperature distribution as the skin temperature of an average person. Particle image velocimetry (PIV) and pseudocolor visualization (PCV) are applied to identify the flow around the manikin's body. The findings show that the direction and magnitude of the surrounding airflows considerably influence the airflow distribution around the human body. Downward flow with velocity of 0.175 m/s does not influence the convective flow in the breathing zone, while flow at 0.30 m/s collides with the CBL at the nose level reducing the peak velocity from 0.185 to 0.10 m/s. Transverse horizontal flow disturbs the CBL at the breathing zone even at 0.175 m/s. A sitting manikin exposed to airflow from below with velocity of 0.30 and 0.425 m/s assisting the CBL reduces the peak velocity in the breathing zone and changes the flow pattern around the body, compared to the assisting flow of 0.175 m/s or quiescent conditions. In this case, the airflow interaction is strongly affected by the presence of the chair.
Energy and Buildings, 2019
This study characterized the interaction between human thermal plume and breathing air flow while people are sitting in a quiescent indoor environment. A sitting breathing thermal manikin was developed to mimic a real human, and data from real human subjects was collected to verify the breathing thermal manikin. In this study the velocity and temperature were measured in front of and above the breathing thermal manikin with and without breathing. In addition, the breathing modes through mouth and nose were studied to investigate the influence of breathing mode on the development of thermal plume, respectively. The ambient temperature was set at 23 ± 0.5 °C, and the surface temperature of manikin varied between 33-34 °C. Without breathing, a maximum value of 0.19 m/s was reached at around 35 cm height above the head which was similar with the mouth-breathing case (0.19 m/s) and higher than the nose breathing case (0.17 m/s). However, the two breathing mode would mitigate the thermal gradient and lower the maximum velocity and had little influence on the height of maximum velocity. Above the manikin's head, non-breathing thermal manikin can produce very similar velocity distribution compared to the breathing modes. But the velocity above the head in the non-breathing case reported the highest maximum value and developed faster to reach the maximum velocity. Breathing through the nose had much more impact on thermal plumes around manikin than breathing through the mouth, even change the flow direction.
Analysis of the Interaction of Thermal Plumes Within Office Environment Using a Thermal Manikin
The present work focus on the study of the interaction of the thermal plume generated by one person, engaged on sedentary activities, with furniture and with other buoyancy driven flow generated by other heat source typical of an office environment. The measurements took place in a climate chamber, using a thermal manikin seated on an office desk with a common desktop PC. The velocity and temperature profiles were obtained with 15 omni direction probes, spanning two normal axes. To cover the volume above the manikin, the desk and the personal computer, the measurements were made by means of an automatic traversing mechanism.
Assessing thermal comfort of active people in transitional spaces in presence of Air Movement
The aim of this study is to develop a modeling methodology to assess thermal comfort and sensation of active people in transitional spaces and consider how comfort can be achieved by air movement while changing upper body clothing properties. The modeling is based on a bioheat model, capable of predicting segmental skin and core temperature from locally ventilated clothed body parts. The bioheat model is integrated with thermal comfort and sensation models to predict comfort in presence of air movement. The model accuracy in predicting comfort was validated by and agreed with the results of a survey administered to subjects wearing typical clothing at different activity levels to record their overall and local thermal sensation and comfort in a transitional space at Beirut summer climate. The transitional space temperature monitored during the experiments ranged between 27 ◦ C and 30 ◦ C. A parametric study is performed to assess thermal comfort in transitional spaces for different air move- ment levels and for three clothing designs. The high permeable clothing at 1.5 m/s and indoor temperature of 30 ◦ C improved the Predicted Mean Vote to values less than 0.5 compared to 1.01 attained with typical low permeable clothing. © 2011 Elsevier B.V. All rights reserved.
Analysis of thermal plumes generated by a seated person, a thermal manikin and a dummy
In this work, the main features of the mean velocity and temperature fields developed above different kinds of stationary heat sources, in quiet and isothermal surroundings, are presented and discussed. The major objective of the present contribution concerns the analysis of the modeling capabilities of thermal manikins and heated dummies, as compared to the case of real occupants, engaged on sedentary activities, typical of office work. As it might be expected, the buoyancy driven flow promoted by a thermal manikin (nude or dressed) provides a more sound reproduction of what may be generated by a human being, here restricted to the case of a seated person, normally dressed with common winter clothing. Consideration of the axial decay of mean velocities and temperatures clearly suggest that the development of an axisymmetric turbulent plume originating at a point source is not fully attained. Instead, the flow field seems to be better described by a shear free heated wake, a situation that calls for further analysis.
PIV measurement of human thermal convection flow in a simplified vehicle cabin
Building and Environment, 2018
Understanding of human thermal convection is important in designing an energy-saving ventilation system for a comfortable environment in vehicle cabins. In this study, the thermal convection flow around a passenger inside a small simplified cabin chamber was measured via a 2D particle image velocimetry (PIV) system to provide validation data for numerical simulations and to reveal the development process of human thermal convection flow. The rising convection flow from the legs merged with the convective boundary layer of the trunk at a height of Y = 0.8 m. The rising flow then ascended along the back of the head and reached a maximum velocity of 0.179 m/s at a height of 0.068 m above the head, as limited by the small vehicle cabin. The convective boundary layers were close to the manikin's surface, with thicknesses of 0.042 m and 0.032 m in the front and back of the manikin, respectively. The overall convection flow in front of the manikin (0.220 m) was thicker than that in the back (0.090 m), adding the width of the manikin, which totally resulted in a 0.498 m coverage width in the sagittal direction. The human thermal convection flow exhibited strong unsteady behavior, indicated by the intermittent rising of plumes one after another and the high standard deviation of the instantaneous velocity. The vortexes of the thermal convection flow were identified by the λ ci criterion, which indicated increasing size and intensity in the region alongside the rising plumes.