Ventilation and supply air distribution play an important role in reducing exposure to airborne pathogens in hospital isolation rooms. Effective supply air distribution should dilute high concentrations readily close to the source and direct them away from the breathing zone of the occupants. In this study a healthcare worker (HCW) exposure to patient exhaled airborne contaminants was assessed with a typical total volume mixing ventilation (MV) and with a local downward ventilation (LDV) above the patient bed. The experiments were carried out in a full-scale isolation room mock-up with breathing thermal manikins simulating the HCW and the patient. Smoke visualisations and air speed measurements show that LDV increases air movement and enables more effective flushing of the patient's upper body compared to MV. Tracer gas measurements show that several factors, like HCW location, air exchange rate, and occupant movement, affect the HCW exposure and that LDV can reduce the exposure notably compared to MV, at least near the patient. Additionally, thermal comfort measurements indicate that LDV can produce adequate thermal conditions for the patient. These findings can be utilised when designing better ventilation solutions for hospital isolation and patient room environments.
Laboratory experiments were conducted to examine flow regimes in a room with a high-level opening and a doorway connected to the environment. Based on the neutral level concept, theoretical formulations for three distinct flow regimes (displacement, arrested outflow, and unbalanced exchange) are re-derived and validated against laboratory experiments. These models successfully predict both the stratified interface height and the neutral level position. This agreement demonstrates that the two-fluid model serves as an extension and complement to the classical hydraulic approach employed in previous studies. In the regimes of the displacement and arrested flows, the neutral level position is determined solely by the area ratio of the upper to lower openings for a fixed effective area. In the unbalanced exchange flow regime, increasing the doorway height or width is more effective in raising the interface height than increasing the upper opening area under a given effective area. This study is particularly significant for understanding and predicting the flow in a room with a high-level opening and a doorway, as well as for determining the geometry of the doorway at the preliminary architectural design stage.
With many existing Austrian school buildings to be renovated in the coming years, there are debates between stakeholders, about which ventilation strategy to pursue in existing schools. Therefore, different intervention strategies such as retrofitting mechanical ventilation systems, installing CO2-monitoring signals, or raising awareness among teachers and students should be evaluated. This paper presents the results from the project 'DIGIdat' based on air quality measurements conducted in the first quarter of 2023. The 'as-is' indoor air quality situation in 36 classrooms in western Austria is assessed by comparing results between different classrooms and ventilation types. To gather information on indoor air quality, measurements were performed using multiple low-cost air sensors per classroom that were programmed and maintained by the students under scientific supervision. The citizen science approach helped to overcome the spatial barrier between the scientists and the measurement sites, with students being 'responsible' for the continuous operation of their sensor kit. Altogether 15 sensor kits, distributed over three to four classrooms, were installed in each of the ten participating schools. The sensors measured CO2-, fine particulate matter (PM) and volatile organic compounds (VOC) concentration as well as temperature and humidity. The sensor kits were positioned and started recording after finishing the programming workshops, i.e. in January and February 2023 for most schools. Statistical analysis of the measured data (with varying sample size of approx. 10 to 20 thousand five-minute averages per category) was carried out utilising the Welch t-test and Mann-Whitney-U-test for differences between window airing and mechanical ventilation systems. Significantly higher CO2 and PM2.5 values were found with window airing compared to mechanical ventilation systems. Somewhat less significant, humidity was higher in classes with window airing than with mechanical ventilation. In addition to that, a correlation analysis showed a dependency between average CO2-levels in window-ventilated classrooms and average outside temperature, whereas this was not the case with classrooms equipped with mechanical ventilation systems. The same analysis comparing inside and outside PM2.5 concentrations showed also the mechanically ventilated classrooms have, probably due to the use of filters, lower ratios of fine particulate matter between inside and outside. Boxplots and correlation regression lines confirm graphically the data analysis results and highlight the conclusions.
Mitigating airborne viral transmission in enclosed public spaces, particularly acoustically sensitive conference rooms, remains a critical engineering challenge. While existing studies on radiant cooling predominantly focus on energy efficiency and thermal comfort, investigations into indoor air quality remain scarce. Specifically, the efficacy of combining Impinging Jet Ventilation (IJV) with radiant cooling to control aerosol transmission represents a critical knowledge gap. To address this, this study elucidates the aerosol dispersion dynamics within a hybrid airconditioning environment coupling Capillary Radiant Ceiling Panels (CRCP) with IJV. Integrating CFD with the Wells-Riley risk assessment model, we quantify the interplay between ventilation momentum, mask leakage aerodynamics, and infection probability. Results identify a pivotal flow regime transition: a high-momentum IJV strategy (Modified Archimedes number L-m approximate to 1.16) effectively suppresses thermal stratification 'lock-up,' significantly reducing aerosol residence time. Consequently, the spatial infection risk disparity between proximal and distal occupants is narrowed to a negligible 2.3%, demonstrating that high-momentum ventilation can effectively 'democratize' indoor safety. Furthermore, we uncover a critical aerodynamic trade-off in respiratory protection. While valveless N95 respirators achieve superior total containment efficiency (similar to 80%) compared to medical surgical masks (similar to 48%), their limited internal dead space induces high-velocity leakage jets (>15 m/s). Unlike the buoyant plumes typical of surgical masks, these jets entrain and project coarse droplets significantly further. These findings challenge the reliance on static concentration metrics, establishing that minimising exposure duration via optimised ventilation momentum is paramount for pandemic-resilient design.
In recent years, large public buildings have grown rapidly in China with high heating, ventilation and air conditioning energy consumption. Investigating its thermal stratification and maximising the use of thermal pressure ventilation are of much significance. A multi-zone model is established in EnergyPlus that the air is well-mixed in each zone. Field measurements were carried out on a 16 m high large Lab, and the simulated temperatures are verified by the measured ones. From point view of the acceptable indoor air temperature toc and the required minimum airflow rate mreq,min, an index is provided to assess the cooling potential of thermal pressure ventilation (CPTPV). Furthermore, a five-factor four-level orthogonal test is designed with four outdoor air temperatures, four building heights, four glazed materials, four occupant densities and four upper opening areas. The results show that the CPTPV are obtained under most cases; the combined scores are in range of 0.06 similar to 0.96 and differ in cases or weight assignments; the primary factor for comprehensive affect toc and m is the outdoor temperature, then the upper opening area, lastly the glazed material. This study provides a comprehensive reference for the CPTPV optimisation in large spaces in consideration of multiple factors.
Uneven blowing at the outlet of wall-mounted air conditioners is the key reason for the unreasonable air distribution and poor human draft sensation. To improve the situation, an asymmetrical diffusion panel is designed in this paper, and compared with the prototype scheme with a cyclone diffusion panel based on simulation and experimental verification. A full-scale 3D model is constructed to simulate the air distribution and thermal comfort in an air conditioner laboratory, with internal circulation boundary conditions adopted. The conclusion is as follows: The new scheme disperses the air well at an angle of 45 degrees with the ground, with a maximum diffusion angle of up to 80 degrees and a diffusion distance of 2.5 m. This effectively avoids direct cold air blowing and improves the user's blowing comfort. And it is found that in the new scheme, the temperature maximum range of the y plane at 20 min and 60 min has decreased by 0.59 and 1.71 degrees C, respectively, compared to the prototype scheme. At the same time, the new scheme effectively improved the phenomenon of cold air accumulating on the feet. Therefore, the asymmetric diffusion plate can provide a more uniform temperature distribution and a more comfortable indoor environment.
This study investigates a novel ventilation technology called vertical single-row inclined slit ventilation (VSISV). Numerical simulations were employed to analyse the effects of slit quantity, supply air flow and flow distribution strategies on indoor environment. Results show that increasing slit number improves vertical jet flow continuity but has limited effect on horizontal reach and overall temperature distribution. The VSISV system performs inadequately at low supply air flow rates, but as the supply flow increases, its performance gradually approaches that of the impinging jet ventilation (IJV) system. At high supply flow rates, its unique airflow circulation characteristics contribute to a more concentrated high-temperature distribution. By adjusting the thermal buoyancy length scale (lm) of the flow from the lowest slit to match that of the IJV system, an independent air supply flow distribution strategy for the slits in the VSISV system is proposed. This strategy significantly enhances the horizontal spread of the jet, thereby enhancing temperature uniformity, energy efficiency and indoor air quality. However, at high air supply rates, caution should be taken to prevent potential localised discomfort in the room's front zone, such as increased draft rate (DR) and predicted mean vote (PMV) issues.
Incompressible air is often used to study the tunnel flow field when the train movement at low speed. However, with the increase of train speed, the effect of air properties on tunnel flow field is increasingly serious. In this paper, the influence of compressible effect of air on tunnel flow field is studied deeply. Based on the different train speed, the compressible air model and the incompressible air model are established respectively for comparative study. The influence of different models on tunnel flow field is discussed, including piston wind, tunnel pressure, air density and temperature. The results show that the increase of train speed leads to the significant change of air density, which also makes the compressible effect of air more important for some parameters, such as maximum piston wind velocity and air pressure. By comparing the change of tunnel pressure after the train stops and the temperature distribution under fire conditions, it is found that the compressible effect of air at low speed also has research significance. This study reveals the influence of air properties on tunnel flow field with the increase of train speed. It provides support and reference for the detailed study of high-speed metro tunnel.
In response to the dust control requirements during the blasting construction period of long tunnels, this study investigates the dust reduction characteristics under the synergistic effect of electrostatic precipitator technology and ventilation system. Based on the similarity theory, a scaled down physical model of the tunnel is constructed. By adjusting parameters such as return air velocity, electrostatic voltage, and adsorption plate length, multiple sets of working condition experiments are conducted to systematically analyse the dust settling law and dust removal efficiency. The results showed that increasing the return air velocity significantly reduced the dust concentration in the palm area and shortened the time required for dust reduction; Increasing the electrostatic voltage has a promoting effect on dust deposition in the near palm area, but the improvement is relatively limited; Increasing the length of the adsorption plate can improve the dust reduction efficiency in the near working area, while having a smaller impact on the distant area. Research has shown that the return air velocity has the most significant impact on dust control, and electrostatic precipitators have good applicability in the near working face area. The ventilation electrostatic synergy can effectively improve the dust control effect during tunnel construction.
To address the challenge of controlling high-temperature fume pollution in rubber vulcanisation workshops, this work proposes an optimised push-pull ventilation system aimed at enhancing pollutant capture efficiency while reducing ventilation energy consumption. By integrating a scaled-down experimental platform constructed based on similarity theory with computational fluid dynamics simulations, the direct capture efficiency (DCE) is introduced as a performance evaluation metric, overcoming the overestimation issue inherent in traditional capture efficiency definitions due to pollutant recirculation. Orthogonal experiments were employed to analyse the sensitivity of air-curtain and exhaust-hood parameters on the system's capture performance. The results indicate that the exhaust flow rate has the most significant impact on DCE. The optimal parameter combination was determined as follows: a hood inclination angle of 15 degrees, a hood height of 0.75 m, a supply air velocity of 6 m/s, an outlet width of 50 mm, and an exhaust flow rate of 6000 m3/h, achieving a DCE of 90.3%. The study further reveals that the push-pull system exhibits comparable capture capability for particulate matter with diameters up to 10 mu m as for gaseous pollutants, whereas a decrease in emission temperature weakens the buoyancy of the fume plume, leading to a reduction in DCE.
The walking of clustered pedestrians strongly influences the indoor flow field structure in transportation hub with high passenger flows. This study analyzes the wake characteristics of passengers in clusters walking in long and narrow channels by combining the proper orthogonal decomposition (POD) method with the dynamic mesh technique. The large eddy simulation (LES) is used to simulate the wake distribution of full-scale human motion. The snapshot POD method is used to decompose the instantaneous velocity field to obtain different modes energy and temporal coefficients. POD results show that the first mode contributes approximately 84-87% of the total energy, indicating that a small number of modes can accurately reconstruct the primary flow structures. The influences of the wake-core region and wake-interference region are studied by analysing the wake velocity field and vorticity field in different regions, revealing multi-scale vortex interactions and the evolution of secondary vortices in clustered pedestrian wakes. The proposed approach establishes a reduced-order analysis framework for understanding clustered pedestrian wake dynamics and provides a physical and methodological foundation for future flow field prediction and ventilation optimisation in crowded indoor environments.
Understanding the influence of thermal plumes on pollutant dispersion in urban environments is crucial for effective pollution management. This study investigates the impact of thermal plumes on pollutant dispersion around a cubic building using Large Eddy Simulation (LES) for temperatures ranging from 300K to 380K. The results show that higher pollutant temperatures, particularly at 360K and 380K, significantly increase temperature increments near the pollutant source, leading to stronger buoyancy forces and enhanced vertical and lateral dispersion. For example, at the pollutant source, temperature increments are 18K, 30K, 50K, and 70K for 320K, 340K, 360K, and 380K. The thermal plume effect diminishes with height, with pollutants at temperatures below 360K showing limited dispersion, while at 380K, both vertical and backward dispersion are significantly enhanced. In the backflow region, higher temperatures increase buoyant forces due to a greater density contrast, accelerating dispersion and resulting in elevated convective and turbulent fluxes. Specifically, the normal turbulent flux for 380K is 0.25, compared to 0.05, 0.2, 0.15, and 0.12 for lower temperatures. Additionally, peak spanwise turbulent flux are 2.5 and 2.25 for 360K and 380K, respectively, indicating stronger mixing and dispersion. These findings emphasise the key role of pollutant temperature in influencing dispersion dynamics.
This study investigates the effectiveness of wing walls in enhancing natural ventilation in typical Philippine residential units with single-sided openings. Wind tunnel experiments were conducted to evaluate the impact of wing wall geometry and wind direction on airflow distribution and air change rate (ACH). The results indicate a significant improvement in ACH, with airflow increasing by 297% at a 45 degrees wind angle compared to the baseline configuration without wing walls. The wing wall configuration with a length equal to the window width achieved a 95.44% increase in ACH. While wind speed was identified as the primary driver of ventilation, the presence of wing walls rendered ACH more responsive to variations in wind direction. The R2 values for the wing wall configurations ranged from 0.3648 to 0.5092, in contrast to 0.2366 for the no-wing-wall case, highlighting the influence of wing walls on airflow predictability. The results show that diagonal wind angles (22.5 degrees and 45 degrees) provided optimal performance for Cases 2, 3 and 4, while perpendicular wind angles (67.5 degrees and 90 degrees) favoured Case 5. Additionally, the study examined both inlet and outlet airflow patterns, revealing that wing walls generate significant pressure differences, which enhance inlet velocity but also induce rapid air exit through the outlet, limiting internal circulation. These findings quantitatively demonstrate that wing walls, particularly those matching the window width, can substantially improve natural ventilation and airflow efficiency in tropical residential buildings.
Moxibustion clinics suffer from smoke pollution due to the combustion of moxa sticks, which poses a serious health hazard to indoor occupants. It is widely recognised that effective ventilation strategies are essential to reduce indoor pollution. This study aims to systematically evaluate the effectiveness of displacement ventilation (DV) and mixing ventilation (MV) in controlling particulate matter (PM) concentration and to investigate effective ventilation strategies for PM control in moxibustion environments. The results show that the DV system can significantly reduce the PM concentration in the personnel breathing zone (0.8-1.8 m) by thermal stratification compared with the MV system, and air supply (Qv) and the ceiling height (H) have a synergistic effect on PM concentration control in the DV system. In the DV system, the PM concentration is initially reduced significantly with the increase of the Qv, and as Qv continues to increase, the higher the H, the earlier the PM concentration reaches a terminal value, and the stronger the stratification effect. It is recommended to apply the DV system with H >= 3 m and hti >= 1.8 m for Qv >= 80 L/s in a moxibustion environment. This study may be helpful for designing ventilation systems in moxibustion environments.
This study compared the particle removal performance of an existing general exhaust system with a newly installed local exhaust system in a hospital endoscopy room. Overall, the local system reduced particle concentrations by 56%, showing greater effectiveness for smaller particles. For 0.3 mu m particles, reductions during procedures such as Bronchoscopy, Esophagogastroduodenoscopy, and Upper endoscopy reached 70%, 73%, and 78%, respectively. The local exhaust system demonstrated superior particle control and showed potential to reduce the risk of infection in the evaluated environment.
With the development of extra-long tunnels, the single ventilation mode can no longer meet the needs of the whole construction stage. In order to solve the problems of long ventilation distance and serious secondary pollution in extra-long tunnels. By optimising the original ventilation scheme of Wushan tunnel, an extra-long wind chamber was set up in the horizontal guide non-operation section. Through on-site real-time monitoring and comprehensive comparative analysis, the pollutant concentration, environmental parameters and dust concentration near the working face in special positions such as construction section, main tunnel section and parallel crossing tunnel before and after the adoption of extra-long wind chamber in the tunnel are analysed, and verified by Fluent software. The results show that after the tunnel adopts the extra-long wind chamber, the dilution efficiency of CO concentration and dust concentration can be increased by 10%-30% and 5%-25% respectively. The use of extra-long wind chamber can significantly improve the air quality and reasonably use the existing space, which can prolong the construction limit ventilation distance of long tunnel and reduce the wind energy loss. Not only can the working environment in the tunnel be improved, but also it has high economic benefits.
We compared two IAQ standards-EN 16798-1:2019 and ASHRAE 62.1-and four infection control documents: ASHRAE Standard 241, and guidelines from REHVA, WHO, and the Lancet COVID-19 Commission. The objective was to estimate exposure and infection risk for exhaled contaminants across various occupancy levels in classrooms, restaurants, and offices using simplified steady-state mass balance models. Ventilation design methods in these documents rely on five basic principles: occupancy, floor area, air change rates, and formulas considering occupant numbers and room volume. We assessed exposure risk through metrics like Delta CO2 (indoor CO2 above outdoor levels), infection risk probability (P), event reproduction number (R), and quanta independent metrics relative risk reduction (r), and maximum absolute difference (Delta P-abs.max). The latter two metrics address variability in virus emission. The infection risk was calculated using SARS-CoV-2 data. We also assessed the methods based on specific fan energy consumption. The latter two metrics address variability in virus emission. Using SARS-CoV-2 data, we calculated infection risk. We also calculated specific fan energy consumption. Our analysis revealed inconsistencies across metrics, with some methods showing no change in infection risk, specific fan energy consumption, triangle CO2 , or risk reduction (r) despite varying occupancy levels. To improve protection, we also proposed two alternative calculation approaches that maintain a constant reproduction number (R) and (Delta P-abs.max) regardless of occupancy density.
Achieving better energy efficiency requires dwellings to face a delicate equilibrium, balancing thermal comfort and indoor air quality. This longitudinal study uses crowdsourced data collected over a year from 14 residences in Santiago, Chile, to examine the relationship between these two parameters. Results highlight considerable variability in PM2.5 and PM10 concentrations and thermal comfort across the sample. PM concentrations are below the global medians, but the maximum values exceed them. Chronic harm from exposure to these concentrations is 1271 and 683 (DALYs/105 person/year) for PM2.5 and PM10, respectively. Moreover, the annual WHO 2021 recommendations are not met, and the daily mean is met by 25% and 72% of the measured days for PM2.5 and PM10, respectively. Determinants of these variations may include geographical location and construction materials, which will be included in future research. The indoor environment does not provide the hygrothermal conditions to achieve acceptable thermal comfort, which is only reached during 56% of the measured time. This research advocates for a regulatory approach to optimise energy efficiency and prioritise occupant well-being. Insights from this study contribute to a better understanding of competing objectives in residential architecture, informing strategic decision-making and interventions.
