Inhaled Air Quality Research Articles

Human body micro-environment: The benefits of controlling airflow interaction

This paper focuses on the micro-environment around a human body, and especially on its interaction with the surrounding environment. Research on the free convection flow generated by a human body (including the convective boundary layer around the body and the thermal plume above the body), its interaction with external invading flows and the resulting heat- and mass transfer, all of which are important for thermal comfort and inhaled air quality, is discussed. The benefit arising from control of the airflow interaction in the micro-environment, in terms of thermal comfort and inhaled air quality, is demonstrated by several methods that are applicable in practice.

Performance evaluation of an integrated Personalized Ventilation–Personalized Exhaust system in conjunction with two background ventilation systems

The inhaled air quality in the breathing zone is strongly influenced by flow interactions around occupants. Personalized Ventilation (PV) aims to supply conditioned outdoor air directly to the occupants' breathing zone and thus improves the inhaled air quality. In this research, a Personalized Exhaust (PE) system is developed, which has two local exhaust devices installed with the chair, just above the shoulder level. Such a system placed in front of a PV system will introduce more PV air into the breathing zone of a seated person as well as exhausting part of the exhaled air from the free convective flow. This study investigates how the performance of a PV system will be affected after being integrated with the PE system. Experiments were conducted in an environmental chamber in Mixing Ventilation or Displacement Ventilation mode for the background air-conditioning system. A breathing thermal manikin was placed in the PE integrated chair in front of the PV air terminal device (ATD) to simulate a seated person in an office environment. The manikin was moved longitudinally away from the PV ATD as well as in an arc to 12 different locations. The performance of the PV–PE system at the 12 different locations was tested with regard to its ability in pulling the PV air towards a seated person moving within a small area in front of the workstation. Findings imply that the use of the combined PV–PE system for a seated person could provide more outdoor air than a PV system alone.

“Conventional” and “Ceiling Mounted” Personalized Ventilation – The Dynamic Effects of a Moving Person on Personal Exposure Effectiveness

Ceiling mounted personalized ventilation (PV) aims to provide clean outdoor air into breathing zone of occupants directly without affecting indoor aesthetics. High momentum, at outlet of PV air terminal device (ATD), is utilized in order to avoid inducing more ambient air and let more personalized air come into breathing zone. In steady state, its performance depends much on the ceiling mounted ATD because supply air momentum, other than buoyancy effects and ambient air flow, is the major driving force in the micro-environment of occupied zone. In dynamic state, the movement of a person near PV ATD causes entrainment or detrainment effect, which can be regarded as another comparable factor influencing ceiling mounted PV performance. A typical office workplace consisting of either ceiling mounted PV ATD or conventional PV ATD and ambient air supply diffuser is simulated. One person is assumed to be seated and another moving person is simulated by dynamic meshes in computational fluid dynamics (CFD). Simulations at moving person velocities of 0.5, 1 and 1,5 m/s and distance between seated person and moving person of 0, 0.2, 0.4m are performed. A new index, computational personal exposure effectiveness, is utilized to assess the performance of the PV ATD in regard to inhaled air quality under the influence of moving person. According to numerical results, the stability of ceiling mounted PV, under dynamic environment with moving person, is better than that of conventional PV although the personal exposure effectiveness (PEE) is lower than that of conventional PV with the same personalized air flow rate in steady state.

Improved inhaled air quality at reduced ventilation rate by control of airflow interaction at the breathing zone with lobed jets

Inhaled air quality at a reduced supply of clean air was studied by controlling the airflow interaction at the breathing zone of a person using lobed jets as part of personalized ventilation (PV). Experiments were performed in a full-scale test room at 23°C (73.4°F) with a breathing thermal manikin seated at a workstation, with realistic free-convection flow around the body and a normal breathing cycle. The air in the room was mixed with tracer gas R134a. Clean air was supplied isothermally from three nozzles with circular, four-leafed clover, and six-edged star openings of 0.025 m (0.08 ft) equivalent diameter. The nozzles were positioned frontally at the face within the boundary layer and centered to the mouth. The enhancement of inhaled air quality by changing the initial velocity (0.2–0.6 m/s, 0.66–1.97 fps) and the distance from the mouth (0.02–0.06 m, 0.07–0.20 ft) was studied. The control over the interaction between the inserted jets and the free convection flow was efficient. Over 80% clean PV air was measured in inhalation. The worst performing nozzle was the four-leafed clover: its best performance yielded 23% clean air inhalation, at the shortest distance and the highest velocity. The other lobed nozzle, the six-edged star, performed similarly to the circular nozzle.

Computational fluid dynamics study and evaluation of different personalized exhaust devices

This article investigates the performance of three different types of personalized exhaust devices. A top-personalized exhaust, which is a round device just above the human head; a shoulder-personalized exhaust, which consists of two local exhaust devices installed at the chair just above shoulder level; and a chair-personalized exhaust, which is at the upper part of a chair just behind the human head, were simulated, evaluated, and compared numerically using the computational fluid dynamics method. Two seated occupants representing healthy and infected manikins equipped with two types of personalized ventilation devices in a simulated consulting room in a healthcare center were modeled. Two indices—personalized exposure effectiveness and inhaled fraction—were introduced to evaluate the improvement of general inhaled air quality after adding different types of personalized exhaust devices and to compare the performance of different kinds of personalized exhaust devices with respect to the healthy manikin's exposure to exhaled contaminated air. The computational fluid dynamics models were validated with a set of experiments conducted in an environmental chamber. The results indicate that all the three personalized exhaust devices might be able to reduce the transmission of exhaled air between occupants. The lowest inhaled fraction was achieved by the combination of a vertical desk grill and a top-personalized exhaust. However, only the shoulder-personalized exhaust device has the potential to improve the amount of personalized ventilation air in the inhaled air.

Performance evaluation of personalized ventilation system with two types of air terminal devices coupled with displacement ventilation in a mock-up office

This article presents a study on the performance of personalized ventilation (PV) with the displacement ventilation (DV) system in a mock-up office space. It is an advantage to leverage on the benefits of personalized and displacement ventilations to bring better air quality to the breathing zone with personalized control and improved thermal comfort respectively. A series of experiments were carried out to determine the performance of two types of PV air terminal devices (ATDs), round movable panel (RMP) and a pair of desktop PV ATDs (DATDs), in terms of pollutant transportation characteristics and thermal comfort of the breathing thermal manikin in a room served by a DV system. It was found that the performance of the two PV ATDs is different in terms of inhaled air quality and thermal comfort. RMP was found to provide a wider range of protection and cooling as compared to DATD, which is more localized but more effective in both protection and cooling. In addition, computational fluid dymanics simulations were performed to have an in-depth understanding on the effect of PV air temperature on the performance of the PV-DV coupled system. It was found that the simulated data correlates well with the measured data. Simulated data shows that the optimum airflow rate for RMP is around 10 L/s. On the whole, the PV supply air temperature and flow rate do affect the local air quality. The PV system coupled with DV system can have a reduction of pollutant's exposure of up to 86% at the nose level when the polluting source is on the table as compared to DV only.

Experimental investigation on reduced exposure to pollutants indoors by applying wearable personalized ventilation

A wearable personalized ventilation unit able to improve inhaled air quality and reduce risk from airborne disease contamination is reported. The performance of the personalized ventilation device relies on control over the flow interaction near the face of a person by inserting a reduced amount of clean air into the breathing zone. Experiments at 23°C (73.4°F) were performed in a full-scale test room with a breathing thermal manikin resembling a seated occupant in a state of thermal comfort, with a realistic free convection flow around the body and breathing cycle. The room air was mixed with tracer gas. The personalized ventilation supplied isothermally clean air from circular or elliptical nozzles of different diameters (equivalent diameter: 0.025–0.035 m [0.08–0.12 ft]) positioned near the mouth of the manikin. The enhancement of inhaled air quality was studied by varying the initial velocity (0.2–0.6 m/s [0.66– 1.97 fps]), the distance between the nozzles and the mouth (0.02–0.06 m [0.07–0.2 ft]), or the direction of the jet (front, side, or below). The personalized ventilation made it possible to increase up to 94% the portion of clean air into the air inhaled. A wearable personalized ventilation unit can significantly reduce (more than six times) the number of secondarily infected occupants compared to mixing ventilation.

Interaction of dynamic indoor environment with moving person and performance of ceiling mounted personalized ventilation system

Ceiling mounted personalized ventilation (PV) aims to provide clean outdoor air into human breathing zone without affecting indoor aesthetics in energy-efficient manner. In steady state, its performance depends much on the ceiling mounted air terminal device (ATD) because supply air momentum, other than human body thermal plume and ambient air flow, is the major driving force in the micro-environment of occupied zone. A typical office workplace consisting of ceiling mounted PV ATD and ambient air supply diffusers was simulated. One person was seated and another moving person was simulated by dynamic meshes in computational fluid dynamics (CFDs). A new index, computational personal exposure effectiveness (PEEc), was utilized to assess the performance of ceiling mounted PV system in regard to inhaled air quality under influence of moving person. Meanwhile, influence of evenly distributed ceiling mounted PV ATDs on inhaled air quality was also studied. According to numerical results, stability of ceiling mounted PV under dynamic environment with moving person was acceptable with minor changes of PEEc and inhaled air quality could be improved over larger occupied area for both seated person and moving person.

Investigation of particle transport in offices equipped with ceiling-mounted personalized ventilators

The performance of ceiling-mounted personalized ventilators (PV) in reducing particle migration between office stations was assessed. The PV nozzles were integrated with peripheral diffusers that were able to form a canopy of conditioned air around the occupant. A numerical CFD model was developed to simulate the flow, temperature and particle concentration fields. Validation against experimental measurements and published experimental data was performed. The canopy was effective in reducing the migration of particles from the macroclimate to the microclimate region and low intake fractions of 1.90 × 10−4 and 5.9 × 10−4 were achieved for particle sizes of 1 μm and 0.01 μm, respectively. The PV jet was capable of maintaining an intake fraction of 3.6 × 10−4 for fine particle sizes (1 μm) and 2.95 × 10−4 for ultrafine particles (0.01 μm) when the particle-emitting source is in the proximity of the occupant. However, in spite of the good inhaled air quality achieved by the PV nozzle, the particle deposition rate on solid surfaces that are easily reached by the occupant is high when the source is placed in the microclimate.

Research on Flow Behavior, Ventilation Efficiencies and Inhaled Air Quality in a Truck Cabin with Cooling Mode

Research on Flow Behavior, Ventilation Efficiencies and Inhaled Air Quality in a Truck Cabin with Cooling Mode

Co-occupant's exposure to exhaled pollutants with two types of personalized ventilation strategies under mixing and displacement ventilation systems

Personalized ventilation (PV) system in conjunction with total ventilation system can provide cleaner inhaled air for the user. Concerns still exist about whether the normally protecting PV device, on the other hand, facilitates the dispersion of infectious agents generated by its user. In this article, two types of PV systems with upward supplied fresh air, namely a chair-based PV and one kind of desk-mounted PV systems, when combined with mixing ventilation (MV) and displacement ventilation (DV) systems, are investigated using simulation method with regard to their impacts on co-occupant's exposure to the exhaled droplet nuclei generated by the infected PV user. Simulation results of tracer gas and particles with aerodynamic diameter of 1, 5, and 10 μm from exhaled air show that, when only the infected person uses a PV, the different PV air supplying directions present very different impacts on the co-occupant's intake under DV, while no apparent differences can be observed under MV. The findings demonstrate that better inhaled air quality can always be achieved under DV when the adopted PV system can deliver conditioned fresh air in the same direction with the mainly upward airflow patterns of DV.

Evaluation of an improved air distribution system for aircraft cabin

An improved air distribution system for aircraft cabin was proposed in this paper. Personalized outlets were introduced and placed at the bottom of the baggage hold. Its ratio of fresh air to recirculation air and the conditioned temperature of different types of inlets were also designed carefully to meet the goals of high air quality, thermal comfort and energy saving. Some experiments were conducted to evaluate and compare its performances with two other systems. First the Flow Visualization with Green Laser (FVGL) technology was used to analyze the air flow. The top-in-side bottom-out pattern may have the disadvantages of an indirect path to deliver fresh air to passengers, a low fresh air utilization ratio and the potential to widely spreading airborne infectious diseases. The bottom-in-top-out pattern can overcome these disadvantages very well, but it also faces the stratification of contaminated air above the head of the passengers. The improved pattern may overcome the above challenges quite well while also delivering good ventilation performance. The modified Personal Exposure Effectiveness (PEE) was measured to compare their performances with regard to inhaled air quality. The measured results suggest that personalized inlet should be designed to adjust its supply air angle according to the height of the passenger's face to provide a higher fresh air utilization effectiveness and better air quality for passengers in the improved pattern. Some simulations revealed that the improved pattern had the potential to save energy by decreasing the amount of fresh air without significantly affecting air quality and thermal comfort.

Quality of inhaled air in displacement ventilation systems assisted by personalized ventilation

The air quality in spaces conditioned by displacement ventilation (DV) aided with personalized ventilation (PV) is assessed on the basis of the average CO2 concentration levels. The interaction between the displacement ventilation flow, upward flow of the rising occupant plume, exhalation flow, and personalized airflow is modeled in order to predict the CO2 transport inside the space and the inhalation zone of occupants to monitor the air quality. The contribution of PV in lowering the CO2 concentration of the inhaled air is evaluated by computing the personal exposure effectiveness in terms of the CO2 concentrations in PV air and inhaled air with and without PV. The developed model was validated by comparing model results of CO2 concentrations with results obtained from 3D simulations using commercial software and with published experimental data for different PV distances from the occupant, flow rates, and temperatures of PV jets. For DV supply temperature of 18°C (64.4°F) and PV air supply temperature range of 18°C to 22°C (64.4°F to 71.6°F), it was found that PV at flows ranging from 4 L/s to 10 L/s (8.48 cfm to 21.19 cfm) could improve the inhaled air quality up to 20% in the breathing zone.

Thermal comfort and indoor air quality in rooms with integrated personalized ventilation and under-floor air distribution systems

A comprehensive study comprising physical measurements and human subject experiments was conducted to explore the potential for improving occupants’ thermal comfort and indoor air quality (IAQ) using a personalized ventilation (PV) system combined with an under-floor air distribution(UFAD) system. The integrated PV-UFAD system, when operated at relatively high temperature of the air supplied from the UFAD system, provided comfortable cooling of the facial region, improved inhaled air quality, and decreased the risk of “cold feet,” which is often reported in rooms with UFAD alone. This article explores associations between the physical measurements and human responses in a room served with a PV-UFAD system. The experiments were conducted in a field environmental chamber served by two dedicated systems—a primary air-handling unit (AHU) for 100% outdoor air that is supplied through the PV air terminal devices and a secondary AHU for 100% recirculated air that is supplied through UFAD outlets. Velocity and temperature distribution in the chamber were measured. A breathing thermal manikin was used to measure the heat loss from 26 body segments and to determine the equivalent temperature. The responses of 30 human subjects were collected. The experiments were performed at various combinations of room air and PV air temperatures. The results reveal improved overall thermal sensation and decrease of cold feet complaints, as well as improved inhaled air quality (including perceived air quality) with PV-UFAD in comparison with the reference case of UFAD alone or mixing ventilation with a ceiling supply diffuser. Increase of predicted draft rating with the decrease of the local thermal sensation at the feet was identified. The manikin-based equivalent temperature determined for the face was positively correlated with thermal sensation at the face region. The measured inhaled air quality indices (personalized exposure effectiveness and personalized exposure index) were improved by decreasing PV supply air temperature. The perceived inhaled air freshness increased with the decrease of the inhaled air temperature and increase of facial velocity.

Seat headrest-incorporated personalized ventilation: Thermal comfort and inhaled air quality

The performance of personalized ventilation with seat headrest-mounted air supply terminal devices (ATD), named seat headrest personalized ventilation (SHPV), was studied. Physical measurements using a breathing thermal manikin were taken to identify its ability to provide clean air to inhalation depending on design, shape, size and positioning of the ATD, flow rate and temperature of personalized air, room temperature, clothing thermal insulation of the manikin, etc. Tracer gas was mixed with the room air. The air supplied by the SHPV was free of tracer gas. Tracer gas concentration in the air inhaled by the manikin was measured and used to assess the clean air supply efficiency of the SHPV. The response of 35 subjects was collected to examine thermal comfort with the SHPV. The subjects participated in 3 experiments at personalized air temperature and room air temperature of 22/20 °C, 23/23 °C and 26/26 °C, respectively. Questionnaires were used to collect human responses. Personal exposure effectiveness (the portion of the clean personalized air in inhalation) of up to 99% was measured during the manikin experiments. The results suggest a dramatic improvement of inhaled air quality and a decreased risk of airborne cross-infection when SHPV is used. Subjects assessed the air movement and the cooling provided by the SHPV as acceptable. Acceptability was unchanged over in time and increased with the increase of the air temperature. No draught was reported. The SHPV can be used in spaces where occupants are seated most of the time, e.g. theatres, vehicle compartments, etc.

The impact of temperature on mean local air age and thermal comfort in a stratum ventilated office

The influence of the supply air temperature on the mean local air age and thermal comfort of a typical individual office under stratum ventilation is investigated by a numerical method, which is validated by an experiment carried out by the authors. The results show that for an office, when the supply air temperature is increased from 19 °C to 21 °C, the corresponding mean occupied zone temperature rises from 24.5 °C to 26.5 °C. The inhaled air quality for the occupant is improved when supply air temperature rises from 19 °C to 21 °C. Also, the thermal comfort indices (predicted mean vote or PMV, predicted percentage of dissatisfied or PPD and predicted dissatisfied or PD) fulfill the requirements of ISO 7730 and CR 175 1998. For summer cooling operation, stratum ventilation may offer a feasible solution to elevated indoor temperatures, which are recommended by several governments in East Asia.

CFD study of exhaled droplet transmission between occupants under different ventilation strategies in a typical office room

This paper investigated the transmission of respiratory droplets between two seated occupants equipped with one type of personalized ventilation (PV) device using round movable panel (RMP) in an office room. The office was ventilated by three different total volume (TV) ventilation strategies, i.e. mixing ventilation (MV), displacement ventilation (DV), and under-floor air distribution (UFAD) system respectively as background ventilation methods. Concentrations of particles with aerodynamic diameters of 0.8 μm, 5 μm, and 16 μm as well as tracer gas were numerically studied in the Eulerian frame. Two indexes, i.e. intake fraction (IF) and concentration uniformity index R C were introduced to evaluate the performance of ventilation systems. It was found that without PV, DV performed best concern protecting the exposed manikin from the pollutants exhaled by the polluting manikin. In MV when the exposed manikin opened RMP the inhaled air quality could always be improved. In DV and UFAD application of RMP might sometimes, depending on the personalized airflow rate, increase the exposure of the others to the exhaled droplets of tracer gas, 0.8 μm particles, and 5 μm particles from the infected occupants. Application of PV could reduce R C for all the three TV systems of 0.8 μm and 5 μm particles. PV enhanced mixing degree of particles under DV and UFAD based conditions much stronger than under MV based ones. PV could increase the average concentration in the occupied zone of the exposed manikin as well as provide clean personalized airflow. Whether inhaled air quality could be improved depended on the balance of pros and cons of PV.

Control of the Free Convective Flow around the Human Body for Enhanced Inhaled Air Quality: Application to a Seat-Incorporated Personalized Ventilation Unit

This paper reports on methods for control of the free convective flow around the human body, with the aim of improving inhaled air quality. The methods were studied with sea-incorporated personalized ventilation (PV)—two PV nozzles placed sideways at the head level of a seated occupant supplied the clean air. Another pair of control nozzles below the PV nozzles, the height of the shoulders, either provided an additional amount of clean PV air or exhausted part of the air from the free convective flow. The effectiveness of the methods for enhancing the quality of the inhaled air was studied in full-scale room experiments. A thermal manikin with a realistic free convective flow was used to resemble an occupant in a state of thermal neutrality at a sedentary activity level. Numerous experiments comprising different combinations of nozzle sizes, supply and exhaust flow rates, and direction of the supplied PV flows and of the control flows, etc., were performed under isothermal conditions at 20°C (68°F) and 26°C (78.8°F). The methods of control proved to be efficient and made it possible to increase the amount of clean air into inhalation at reduced personalized flow rate and to reduce the risk of draft.

ASSESSMENT OF CONFLUENT JETS FOR IMPROVED PERFORMANCE OF PERSONALIZED VENTILATION MOUNTED ON THE DESK

A unique method for inhaled air quality improvement by personalized ventilation by control of the free convection flow and its interaction with the clean air based on confluent jets was studied. The confluent upward jets were generated close to the front of the human body by openings at the front edge of a desk board pressed against the abdominal area. The inner jet supplied clean air, while the assisting outer jet supplied polluted room air. Comprehensive experiments were performed under isothermal conditions (26°C) in a full-scale room with a thermal manikin simulating realistically human body shape and the generated free convection flow. Tracer gas measurements were performed to identify the impact of the control method on inhaled air quality. Results showed the use of confluent jet of polluted air improved the inhaled air quality compared to the single jet application.

Energy analysis of the personalized ventilation system in hot and humid climates

Personalized ventilation (PV) is an individually controlled air distribution system aimed at improving the quality of inhaled air and the thermal comfort of each occupant. Numerous studies have shown that PV in comparison with traditional mechanical ventilation systems may improve occupants’ health, inhaled air quality, thermal comfort, and self-estimated productivity. Little is known about its energy performance. In this study, the energy consumption of a personalized ventilation system introduced in an office building located in a hot and humid climate (Singapore) has been investigated by means of simulations with the empirically tested IDA-ICE software. The results reveal that the use of PV may reduce the energy consumption substantially (up to 51%) compared to mixing ventilation when the following control strategies are applied: (a) reducing the airflow rate due to the higher ventilation effectiveness of PV; (b) increasing the maximum allowed room air temperature due to PV capacity to control the microclimate; (c) supplying the outdoor air only when the occupant is at the desk. The strategy to control the supply air temperature does not affect the energy consumption in a hot and humid climate.