Inhaled Air Quality Research Articles

Simulation study on the impact of heat source intensity on the inhaled air quality of an innovative personalized air supply method

Abstract To improve the local microenvironment of the human body in industrial buildings with strong heat sources, this paper proposes a new personalized air supply method based on the attachment effect. The numerical simulation method is used to study the influence of heat source intensity on the inhaled air quality in this paper. Studies have shown that when the air supply speed is less than or equal to 0.5 m/s, the fresh air ratio decreases as the Gr number of the heat source increases. When the air supply speed is greater than or equal to 0.7 m/s, the fresh air ratio increases as the Gr number of the heat source increases.

Bedroom ventilation performance in daycare centers under three typical ventilation strategies

With increasing reliance on daycare centers for early childhood development, ensuring healthy environments in semi-enclosed baby beds for napping is crucial, given infants' vulnerability to air pollutants and their inability to control surroundings. Despite concerns about indoor air quality, research on bed-level ventilation conditions remains scarce. This study investigates the performance of three ventilation strategies (mixing ventilation (MV), displacement ventilation (DV), and personalized ventilation (PV)) in enhancing air quality at bed level in daycare center bedrooms. Using a full-scale setup representing a typical Dutch daycare bedroom, ventilation performance was evaluated by examining CO2 dispersion and inhalation for 12 breathing thermal baby models sleeping in 12 beds, considering two sleep positions and ventilation rates. A total of 58 strategically located CO2 sensors enabled a thorough understanding of CO2 levels at inhalation and both the bed and room scales. The findings reveal the superior performance of PV, followed by DV and MV, with significantly different inhaled CO2 concentrations per baby: 1713 ppm (MV), 1104 ppm (DV), and 801 ppm (PV), though the mean in-bed values differed by less than 20 ppm among the modes. Thus, assessing ventilation performance of various ventilation strategies necessitates examining inhaled air quality. Sleep positions and ventilation rates significantly influenced MV and DV modes' performance. Importantly, PV demonstrated energy-saving potential by achieving comparable inhaled air quality at lower ventilation rates. These findings have practical implications for designing occupant-centric ventilation systems in daycare center bedrooms and effective CO2 monitoring in semi-enclosed spaces.

Experimental study on the supply air characteristics and thermal comfort of a novel personalized ventilation air terminal device

Personalized ventilation (PV) has a significant potential for improving thermal comfort, inhaled air quality and energy efficiency. A novel PV air terminal device (ATD) based on the function of bath showers was evaluated to determine discomfort related to thermal sensation, draughts, dry eyes and skin irritation. The supply air characteristics and thermal comfort were analyzed using objective and subjective experiments in an environmental chamber. Thirty college students participated in the subjective experiments. Results showed that the proposed PV ATD could provide uniform distributions of air velocity at the human head and chest. Compared with the conventional round-monitor panel ATD, the proposed PV ATD can provide an improved cooling effect, wherein overall thermal sensation was reduced by 0.56 scale, showing a potential for energy saving. Moreover, the proposed PV ATD could produce a highly uniform distribution of local thermal sensation (LTS). Compared with the conventional PV, the proposed PV ATD could reduce the standard deviation of distribution of LTS by 41.7% and reduce overall thermal discomfort by 45.5%. Fewer sick building syndrome symptoms at a lower supply airflow rate of 6.3 L/s was achieved. Consequently, the proposed PV ATD could improve the comfort performance with the usage of lower supply airflow rates.

Effect of source location on contaminant dispersion pattern and occupants inhaled air quality in lecture room under displacement ventilation

AbstractDisplacement 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.

Assessment of Thermal Comfort and Air Quality of Room Conditions by Impinging Jet Ventilation Integrated with Ductless Personalized Ventilation

Advanced ventilation methods are responsible for creating an appropriate temperature environment with satisfactory inhaled air quality. The ductless personalized ventilation system integrated with impinging jet ventilation shows the good ventilation performance. In order to investigate the effect of using such an integrated system on thermal comfort and air quality improvement. Twenty subjects participated in a chamber test at 25 °C, 27 °C, and 29 °C, respectively, with operating DPV devices at three modes (no flow, pre-set flow, and user control flow). Votes on thermal comfort, thermal sensation, thermal acceptability, and perceived air quality were collected from the them. The results showed that overall thermal sensation votes with DPV running at the user control flow mode were close to neutral (0.1, 0.4, and 0.5, respectively, at 25 °C, 27 °C, and 29 °C). Thermal comfort and perceived air quality were improved at all three temperatures studied in the user control DPV flow mode, with 90% of occupants reporting that the thermal environments were acceptable. An integrated system of this type could raise the acceptable HVAC temperature setpoint to 29 °C, resulting in an average energy savings of 34% over the neutral condition at 25 °C. Hence, occupants are advised to use the DPV’s user-control mode. Lastly, it is concluded that the integrated system could greatly improve thermal comfort, perceived air quality, and save HVAC energy, despite some issues with dry eyes at 29 °C.

Numerical Investigation of Covid-19 Infection Spread Expelled from Cough in an Isolation Ward Under Different Air Distribution Strategies

COVID-19 is a severe and rapidly spreading respiratory disease that can be transmitted through airborne particles, emitted from cough. This study investigated the influence of underfloor air distribution (UFAD) and overhead air distribution on the diffusion of the coughed particles emitted from two infected patients in an isolation ward. Additionally, the study examined the performance of mounting retractable covers around the exhausts on minimizing the dispersion of the particles. A coupled Eulerian-Lagrangian approach is adopted by using a discrete random walk model. The effect of Brownian force, drag force with Cunningham slip correction factor, turbulence dispersion, Rosin-Rammler, and the breakup is considered in the respiratory airborne coughed particles simulation. The model has a good agreement with the experimental data. The results show that overhead air distribution (case 1) disperses the particles faster to the occupied zone due to the strong mixing between downward inlet airflow and indoor air accompanied by infectious particles. The usage of retractable covers (case 2) significantly minimized the diffusion of the particles inside the ward and their residence time. The particles quantity drops by 53, 98.62, and 99.94 % at 2.0, 10.0, and 120.0 s, respectively, compared to case 1. Case 2 shows the best efficient protection and inhaled air quality for the HCW in all the walking areas inside the room. The upward inlet air in underfloor air distribution (case 3) keeps particles floating for a while at a higher level near the ceiling exhausts, enhancing removal efficiency. Also, it has a slower lateral dispersion of the particles than in case 1. Underfloor air distribution minimized the number of particles by 30.0 % at 120.0 s, compared to overhead air distribution. Inlet air location significantly affects the diffusion of infectious particles in the indoor environment.

Investigation of the Upper Respiratory Tract of a Male Smoker with Laryngeal Cancer by Inhaling Air Associated with Various Physical Activity Levels

Smokers are at a higher risk of laryngeal cancer, which is a type of head and neck cancer in which cancer cells proliferate and can metastasize to other tissues after a tumor has formed. Cigarette smoke greatly reduces the inhaled air quality and can also lead to laryngeal cancer. In this study, the upper airway of a 70-year-old smoker with laryngeal cancer was reconstructed by taking a CT scan using Mimics software. To solve the governing equations, computational fluid dynamics (CFD) with a pressure base approach was used with the help of Ansys 2021 R1 software. As a result, the maximum turbulence intensity occurred in the larynx. At 13 L/min, 55 L/min, and 100 L/min, the maximum turbulence intensity was 1.1, 3.5, and 6.1, respectively. The turbulence intensity in the respiratory system is crucial because it demonstrates the ability to transfer energy. The maximum wall shear stress (WSS) also occurred in the larynx. At 13 L/min, 55 L/min, and 100 L/min, the maximum WSS was 0.62 Pa, 5.4 Pa, and 12.4 Pa, respectively. The WSS index cannot be calculated in vivo and should be calculated in vitro. Excessive WSS in the epiglottis is inappropriate and can lead to an airway obstruction. Furthermore, real mathematical modeling outcomes provide an approach for future prevention, treatment, and management planning by forecasting the zones prone to an acceleration of disease progression. In this regard, accurate computational modeling leads to pre-visualization in surgical planning to define the best reformative techniques to determine the most probable patient condition consequences.

Human re-inhalation ratio under typical conditions

Inhaled air quality is directly related to occupants’ health and quality of life. In this study, a numerical breathing thermal manikin was employed, who breathed following a sinusoidal function, with 10 breathing cycles per minute. Each cycle was composed of three phases: 2.5 s inhalation, 2.5 s exhalation, and 1 s pause. The influence of pulmonary ventilation rate, breathing mode and breathing cycle period on the re-inhalation ratio were studied by computational fluid dynamics (CFD) technology in combination with the species transport model. It was found that increasing the pulmonary ventilation rate led to a lower re-inhalation ratio. The re-inhalation ratio is the largest with the value of 0.91%, when exhaled through the mouth and inhaled through the nose. The re-inhalation ratio was up to 23.9 % lower with a pause of 1 s in the breathing cycle than without pause. When the pulmonary ventilation rate increased from 6 L/min to 8 L/min, the re-inhalation ratio decreased from 0.91% to 0.71%. This information would be an important basis for the development of the human microenvironment control and technologies, including intelligent, personalized air supply devices, local air supply and exhaust methods, and other advanced ventilation and airflow technologies.

Effect of individually controlled personalized ventilation on cross-contamination due to respiratory activities

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.

Could the ductless personalized ventilation be an alternative to the regular ducted personalized ventilation?

This study investigates the performance of two systems: personalized ventilation (PV) and ductless personalized ventilation (DPV). Even though the literature indicates a compelling performance of PV, it is not often used in practice due to its impracticality. Therefore, the present study assesses the possibility of replacing the inflexible PV with DPV in office rooms equipped with displacement ventilation (DV) in the summer season. Numerical simulations were utilized to evaluate the inhaled concentration of pollutants when PV and DPV are used. The systems were compared in a simulated office with two occupants: a susceptible occupant and a source occupant. Three types of pollution were simulated: exhaled infectious air, dermally emitted contamination, and room contamination from a passive source. Results indicated that PV improved the inhaled air quality regardless of the location of the pollution source; a higher PV supply flow rate positively impacted the inhaled air quality. Contrarily, the performance of DPV was highly sensitive to the source location and the personalized flow rate. A higher DPV flow rate tends to decrease the inhaled air quality due to increased mixing of pollutants in the room. Moreover, both systems achieved better results when the personalized system of the source occupant was switched off.

Multi-parameter performance optimization for whole year operation of stratum ventilation in offices

Stratum ventilation with proper operation can provide thermal comfort and good inhaled air quality with energy efficiency. Previous studies mainly focused on stratum ventilation for cooling or heating in separate seasons, while little attention on stratum ventilation for whole year operation. Proper year-round operation of stratum ventilation is more complicated, with multiple ventilation operation parameters (i.e., the supply vane angle, supply air velocity, supply air temperature, and air outlet position) non-linearly affecting multiple mutually conflicting criteria of the ventilation performance (i.e., thermal comfort, air quality and energy efficiency). This study optimized the whole year operation of stratum ventilation by using a multi-parameter fitting technology. An experiment on stratum ventilation for both heating and cooling a typical office is conducted. Based on experimentally validated Computational Fluid Dynamics (CFD) simulations, the stratum ventilation performance is investigated. Ventilation effectiveness (Et) and air distribution performance index (ADPI) are introduced to be as the evaluation indicators to assess the performance of stratum ventilation. Results demonstrate that the mentioned factors play different roles in the thermal performance of stratum ventilation, and exist interactions among each other. The economic-comfort ratio is proposed to assess the indoor comfort and energy consumption simultaneously. Combining with building energy simulation technology and Marquardt method, the optimal year-round parameters of stratum ventilation under four air outlet positions in different climate zones can be determined. This study provides a comprehensive guide for stratum ventilation in practical application.

Performance evaluation of ductless personalized ventilation in comparison with desk fans using numerical simulations.

The performance of ductless personalized ventilation (DPV) was compared to the performance of a typical desk fan since they are both stand-alone systems that allow the users to personalize their indoor environment. The two systems were evaluated using a validated computational fluid dynamics (CFD) model of an office room occupied by two users. To investigate the impact of DPV and the fan on the inhaled air quality, two types of contamination sources were modeled in the domain: an active source and a passive source. Additionally, the influence of the compared systems on thermal comfort was assessed using the coupling of CFD with the comfort model developed by the University of California, Berkeley (UCB model). Results indicated that DPV performed generally better than the desk fan. It provided better thermal comfort and showed a superior performance in removing the exhaled contaminants. However, the desk fan performed better in removing the contaminants emitted from a passive source near the floor level. This indicates that the performance of DPV and desk fans depends highly on the location of the contamination source. Moreover, the simulations showed that both systems increased the spread of exhaled contamination when used by the source occupant.

The effect of human breathing on the effectiveness of intermittent personalized ventilation coupled with mixing ventilation

The aim of this work is to study the interaction of human breathing and the intermittent personalized ventilation (IPV) jet and investigate its effectiveness in supplying clean breathable air when operating in relaxed background contaminants’ concentration condition. A transient 3-D computational fluid dynamics (CFD) model of a breathing occupant in an office space equipped with an IPV combined with mixed ventilation system was developed. Two breathing modes were considered: nose breathing and mouth breathing. Tracer gas method was used to evaluate the breathable air quality of the IPV user at different IPV operating frequencies. The flow field resulting from interaction of IPV jet and nose breathing was experimentally validated in a climatic chamber equipped using a breathing thermal manikin. The validated CFD model was used to assess the inhaled air quality at different IPV frequencies in both nose and mouth breathing modes, while comparing it to no-breathing case.It was found that maximum ventilation effectiveness εV ranges during inhalation were obtained at an IPV frequency of 0.5 Hz ranging from 36.75% to 86.6% for nose breathing mode, 49.6%–87.3% for mouth breathing mode and 42.42–86.93% when breathing was not considered. The nose breathing mode gave the lowest εV while the mouth breathing mode gave better εV due to the stronger dilution offered by the horizontally exhaled air. The average εV for the nose and mouth breathing were fairly close to the case of no-breathing and provided satisfactory air quality at the BZ.

Carbon nanotube bundles assembled flexible hierarchical framework based phase change material composites for thermal energy harvesting and thermotherapy

Conventional single thermal nature of phase change materials (PCMs) seriously obstructs their frontier applications. Herein, we designed advanced carbon nanotube (CNT) bundles assembled flexible hierarchical framework based phase change material composites for high-performance thermotherapy of allergic rhinitis. Hierarchically interconnected 3D freestanding flexible CNT sponge was constructed via a facile organic solvent-free route using table salt as a sacrificial template. The resulting hierarchical CNT sponge serves as an ideal compatible supporting host and polyethylene glycol (PEG) serves as an excellent thermal energy guest. Subsequently, we designed advanced portable integrated functional mask consisting of outer air purification layer and inner thermal regulation layer for the thermotherapy of allergic rhinitis, in which pristine CNT sponge serves as an excellent particulate matter capturer and PEG-infiltrated CNT sponge serves as a superior thermal regulator. Strikingly, our uniquely constructed flexible CNT sponge-involved composite PCMs assisted by polyvinylidene fluoride (PVDF) harvest high-performance thermotherapy (~33 ​min of the plateau at ~43.5 ​°C). The corresponding medical results (HE staining and Wrights staining) further indicate that our designed thermotherapy mask can significantly reduce the inflammatory injury of nasal mucosa. Additionally, pristine hierarchical CNT sponge guarantees the inhaled air quality and enhances the thermotherapy effect. This synthetic strategy can be scaled up for large-scale production. This novel functional host-guest strategy creates an innovative platform for developing advanced multifunctional PCMs with multiple fascinating peculiarities and desired functional properties and teaches an old dog new tricks.

A Review of CFD Analysis Methods for Personalized Ventilation (PV) in Indoor Built Environments

Computational fluid dynamics (CFD) is an effective analysis method of personalized ventilation (PV) in indoor built environments. As an increasingly important supplement to experimental and theoretical methods, the quality of CFD simulations must be maintained through an adequately controlled numerical modeling process. CFD numerical data can explain PV performance in terms of inhaled air quality, occupants’ thermal comfort, and building energy savings. Therefore, this paper presents state-of-the-art CFD analyses of PV systems in indoor built environments. The results emphasize the importance of accurate thermal boundary conditions for computational thermal manikins (CTMs) to properly analyze the heat exchange between human body and the microenvironment, including both convective and radiative heat exchange. CFD modeling performance is examined in terms of effectiveness of computational grids, convergence criteria, and validation methods. Additionally, indices of PV performance are suggested as system-performance evaluation criteria. A specific utilization of realistic PV air supply diffuser configurations remains a challenging task for further study. Overall, the adaptable airflow characteristics of a PV air supply provide an opportunity to achieve better thermal comfort with lower energy use based on CFD numerical analyses.

Experimental study of local thermal comfort and ventilation performance for mixing, displacement and stratum ventilation in an office

Satisfactory thermal comfort and efficient removals of airborne contaminants are crucial to the work efficiency and health of occupants. Different air distributions can generate distinct airflow patterns, thus affecting thermal comfort and ventilation performance. The experiments were conducted to study the performances of three air distribution methods (i.e. mixing ventilation (MV), displacement ventilation (DV) and stratum ventilation (SV)). Local thermal comfort was evaluated for the three air distribution methods with their individual thermally neutral temperatures. Three gaseous point pollutant sources located at the desktop, floor and manikin armpit respectively were applied to study the impact of the pollutant source locations on their ventilation performances. The distributions of air velocity, air temperature and contaminant concentration were measured. Results showed that a vertical air temperature difference of above 3 °C between the head and ankle levels appeared with DV, but the draught ratings (DR) under SV were higher than those under both MV and DV. Pollutant source locations exerted different effects on contaminant dispersion and contaminant removal effectiveness (CRE) for the three air distribution methods. SV always removed the contaminants effectively with all the three pollutant source locations to maintain good inhaled air quality, which was superior to MV and DV.

Impacts of airflow interactions with thermal boundary layer on performance of personalized ventilation

The flow interactions between the personalized air and the thermal boundary layer (TBL) may play an important role to the inhaled air quality and energy efficiency performance of a personalized ventilation (PV) system. This paper aims to investigate these interactions and their impacts on the performance of a PV system. Schlieren imaging technique, Laser Doppler Anemometry (LDA) and tracer gas measurements are employed to identify the airflow patterns in the breathing zone (BZ) and the effect of the interactions on ventilation effectiveness. Although it has always been considered that it is difficult for a PV jet of low flow rate to penetrate the TBL, it is found in this study that the TBL is penetrable even at invading velocities lower than the normally recognized value of 0.3 m/s. The advantage of the reduced blockage effect allows for a more effective delivery of fresh air to the BZ. It is also shown that the airflow interactions alter the airflow distributions in the BZ and affect the inhaled air quality. This interaction depends on the positioning and direction of the non-uniform invading flow from the nozzle, which should be carefully considered for optimal ventilation design to enhance the effectiveness of ventilation at relatively low energy consumptions.

Integrated analysis of numerical weather prediction and computational fluid dynamics for estimating cross-ventilation effects on inhaled air quality inside a factory

Mechanical and passive ventilation strategies directly impact indoor air quality. Passive ventilation has recently become widespread owing to its ability to reduce energy demand in buildings, such as the case of natural or cross ventilation. To understand the effect of natural ventilation on indoor environmental quality, outdoor–indoor flow paths need to be analyzed as functions of urban atmospheric conditions, topology of the built environment, and indoor conditions. Wind-driven natural ventilation (e.g., cross ventilation) can be calculated through the wind pressure coefficient distributions of outdoor wall surfaces and openings of a building, allowing the study of indoor air parameters and airborne contaminant concentrations. Variations in outside parameters will directly impact indoor air quality and residents’ health. Numerical modeling can contribute to comprehend these various parameters because it allows full control of boundary conditions and sampling points. In this study, numerical weather prediction modeling was used to calculate wind profiles/distributions at the atmospheric scale, and computational fluid dynamics was used to model detailed urban and indoor flows, which were then integrated into a dynamic downscaling analysis to predict specific urban wind parameters from the atmospheric to built-environment scale. Wind velocity and contaminant concentration distributions inside a factory building were analyzed to assess the quality of the human working environment by using a computer simulated person. The impact of cross ventilation flows and its variations on local average contaminant concentration around a factory worker, and inhaled contaminant dose, were then discussed.

Numerical investigation of height impact of local exhaust combined with an office work station on energy saving and indoor environment

A healthy and comfortable working environment is very important for improving its occupants' productivity. In this study, the evaluation of the height impact for the proposed local exhaust ventilation system on the indoor thermal comfort, inhaled air quality and energy savings was explored numerically. In the proposed system, the exhaust opening was combined with the office workstation in a single unit. The intention was to help extract the warmed and contaminated air locally before it disperses across the room. The performance of the new system at three different heights of the combined system (1.4 m, 1.6 m and 2.0 m) above floor level was investigated numerically with a validated CFD model in a room with and without inclusion of the novel local exhaust ventilation system. The performance of using this system was evaluated using the main evaluation indices for any ventilation system such as energy saving, occupant thermal comfort, draught risk and the quality of the indoor air. The results showed that by selecting a suitable height for the combined system, a significant improvement on energy savings (up to 22.56%) and inhaled air quality can be realised with an acceptable level of the indoor thermal comfort. It was found that in comparison to cases 2 (1.4 m) and 4 (2.0 m), case 3 (1.6 m) was considered to be the best height at which optimal performance could be achieved from the LEVO system.

Energy saving and indoor thermal comfort evaluation using a novel local exhaust ventilation system for office rooms

Energy saving, indoor thermal comfort and inhaled air quality in an office are strongly affected by the flow interaction in the micro-environment around the occupants. The local exhaust ventilation system, which aims to control the transmission of contaminant and extract contaminant air locally, is widely used in industrial applications. In this study, the concept of the local exhaust ventilation system is developed for use in office applications. Consequently, a novel local exhaust ventilation system for offices was combined with an office work station in one unit. Energy saving, thermal comfort and inhaled air quality were used to evaluate the performance of the new system. Experimental data from published work are used to validate the computational fluid dynamic model of this study. The performance of the new system for three different amounts of recirculated air (35%, 50%, and 65% of the total mass flow rate) was investigated numerically in an office room with and without using the new system to show its impact on energy saving, thermal comfort and inhaled air quality. The result shows that the new local exhaust ventilation system can reduce the energy consumption by up to 30%, compared with an office not using this system. Furthermore, this system was able to reduce the contaminant concentration in a micro-environment area by up to 61% and improve the human thermal comfort in the occupied zone. It can be concluded that using the local exhaust ventilation concept can make significant improvements to the quality of inhaled air and produce extra energy saving with an acceptable thermal comfort.