Mixing Ventilation Research Articles

Optimisation of synergistic ventilation between dust and gas in a gas tunnel.

In view of the difficult problem of gas and dust exceeding the limit during the digging process of a gas tunnel in Guizhou Province, Southwest China, the CFD numerical simulation method was applied to study the gas tunnel airflow, dust and gas transport law during the digging process. A physical simulation experimental platform was established to verify the numerical simulation results, and research was carried out in terms of gas-containing gas-carrying dust disaster prevention and control, and ventilation optimization was carried out for this gas tunnel. The results showed that the maximum gas concentration in the tunnel face under press-in ventilation could be about 1%, and the local dust concentration can be up to 900 mg/m3. The gas mass fraction in localised areas of the tunnel exceeded 0.9% under mixed ventilation pressure-extraction ratios of 9:1 and 8:2. When the pressure to pumping ratio is 6:4, the dust was concentrated on the return side of the tunnel at a distance of 40-60 m from the head of the tunnel, and the highest local dust concentration reaches 700 mg/m3. When the pressure pumping ratio was 7:3, the dust pollution problem could be controlled more effectively, and at the same time, there was no higher concentration of gas gathering in the tunnel. A comprehensive analysis of the differences between dust and gas-enriched areas in gas tunnels could provide some guidance on the synergistic control of gas and dust in gas tunnels.

Comparing strategies for the mitigation of SARS-CoV-2 airborne infection risk in tiered auditorium venues

The COVID-19 pandemic demonstrated that reliable risk assessment of venues is still challenging and resulted in the indiscriminate closure of many venues worldwide. Therefore, this study used an experimental, numerical and analytical approach to investigate the airborne transmission risk potential of differently ventilated, sized and shaped venues. The data were used to assess the magnitude of effect of various mitigation measures and to develop recommendations. Here we show that, in general, positions in the near field of an emission source were at high risk, while the risk of infection from positions in the far field varied depending on the ventilation strategy. Occupancy, airflow rate, residence time, virus variants, activity level and face masks affected the individual and global infection risk in all venues. The global infection risk was lowest for the displacement ventilation case, making it the most effective ventilation strategy for keeping airborne transmission and the number of secondary cases low, compared to mixing or natural ventilation.

Computed tomography radiomics-based prognosis prediction of patients with chronic obstructive pulmonary disease

Objectivethe objective of this study was to develop a predictive model for pulmonary ventilation function in patients with chronic obstructive pulmonary disease (COPD) utilizing computed tomography (CT) and pulmonary function parameters. Material and methoda retrospective analysis was conducted on 90 patients with COPD from our hospital, who were divided into Group I (AG, normal pulmonary function), Group II (BG, mild ventilation dysfunction), Group III (CG, moderate ventilation dysfunction), Group IV (DG, severe ventilation dysfunction), Group V (EG, very severe restrictive ventilation dysfunction), and Group VI (FG, very severe mixed ventilation dysfunction) according to pulmonary function. The imaging and pulmonary function indicators of the subjects were analyzed. Resultas lung dysfunction worsened, structural changes in the lungs on CT images also progressively worsened, manifesting as an enlargement of emphysematous areas, a decrease in lung field homogeneity, changes in lung tissue density and structure, and a reduction in lung field volume. Maximal expiratory flow (MEF) when 75%, 50% of the forced vital capacity (FVC) remained in the lung, i.e. MEF75%, MEF50%, and maximum mid-expiratory flow (MMEF75%-25%) were most highly correlated with ventilation dysfunction. Conclusionthe severity of pulmonary ventilation dysfunction in patients with COPD can be better predicted by CT imaging and pulmonary function examination indicators.

Human exposure to respiratory aerosols: Impact of ventilation rates, mixing ventilation configuration, and breathing patterns

This study investigates airborne transmission dynamics between occupants in office rooms equipped with mixing ventilation (MV). The primary aim was to assess how different ventilation configurations, air change rates (ACH), breathing patterns, and supply air temperatures influence cross-exposure and infection risks. The experimental setup involved two thermal manikins simulating an infected and an exposed occupant within a climate chamber. The investigated parameters included four ACH levels (1.2, 2, 4 and 6.6 h⁻1, representing four EN 16798-1 ventilation categories), two MV configurations (near-ceiling and near-floor inlets), two breathing patterns (nose and mouth breathing), and two supply air temperatures (19°C and 21°C). Carbon dioxide (CO₂) was used as a tracer gas to simulate exhaled aerosols, enabling precise measurements of effectiveness (), intake fraction (IF), and infection probability (P). The findings indicate that higher ACH do not uniformly improve but are linked to reduced cross-exposure risk. The near-floor inlet MV configuration significantly outperformed the near-ceiling configuration in reducing IF and P by 15-41% under most investigated scenarios. Additionally, mouth breathing increased IF and P compared to nose breathing, especially at higher ACH (2, 4, and 6.6 h⁻1). The results also showed that lower supply temperatures do not always correlate with higher IF and P, as MV configuration and breathing patterns significantly influence outcomes. This research provides insights into optimizing ventilation strategies for safer indoor environments, emphasizing the importance of airflow dynamics, breathing patterns, and supply temperature in ventilation design.

The effects of ventilation layout on cough droplet dynamics relating to seasonal influenza

The primary aim of this paper is to investigate airborne virus transmission in a typical meeting room relating to the heating, ventilation, and air conditioning (A.C.) systems. While the installation of 4-way cassette A.C. systems in offices and meeting rooms has become increasingly common, their efficiency in mitigating short-range airborne virus spread remains poorly understood. Addressing this gap is critical in the post-pandemic era, where understanding the limitations of various ventilation systems is paramount for public health. We systematically compare the performance of the 4-way cassette A.C., various configurations of mixing and displacement ventilation systems, and natural ventilation in controlling the spread of respiratory viruses. Our research uniquely integrates evaporation models to accurately simulate cough clouds' multiphase behavior under both quiescent and thermally influenced conditions. The study benchmarks these systems against two widely recognized ventilation standards (i.e., 5 air changes per hour and 10 l/s per person), offering evidence-based insights applicable across diverse indoor settings. Our findings reveal significant thermal effects in the quiescent case, resulting in 32.3%, 54.3%, and 8.0% changes in the axial, vertical, and lateral spread of the virus-laden droplets, respectively. Notably, the 0.5 m/s 4-way cassette A.C. system demonstrated superior performance, reducing the axial spread by 29.6% compared to other mechanical ventilation configurations. Furthermore, the role of exhaust outlets or doors was found to be critical in shaping the spread pattern in natural ventilation scenarios. This work can offer practical guidance to office workers, engineers, and public health officials on enhancing indoor airborne infection control.

Experimental comparison of aerosol transmission in displacement ventilation and mixing ventilation in a meeting scenario

The performance of displacement ventilation (DV) and mixing ventilation (MV) in aerosol contamination control was compared. The considered contamination was an aerosol emitted from a person in meeting scenarios of two and four persons. The experiments were carried out in a full-scale room measuring 4.4 m × 5.2 m × 2.9 m. Particle counting was carried out at 41 measurement points in the room to assess the concentration field of particles in the room and in the inhalation zone. The influence of the supply airflow rate and the number of activated thermal mannequins on the contaminant removal effectiveness were examined. The main conclusion is that the DV system was superior to the MV system in reducing contamination. An enhanced contaminant removal effectiveness of displacement ventilation was observed for all supply air flow rates and increased with higher airflow rates. At lower airflow rates, contamination in the inhalation zone was reduced by 40% compared to mixing ventilation, while at higher flow rates, the reduction surpassed 50%. This study highlights the advantages of displacement ventilation in terms of contamination control, infection prevention and energy efficiency, emphasising the importance of ventilation system selection for indoor environments, particularly those where airborne transmission risks are prevalent.

The potential of local exhaust combined with mixing and displacement ventilation systems to mitigate COVID-19 transmission risks

The performance of two types of air diffusers, a perforated duct and a low-velocity unit coupled with local exhausts, on airborne transmission and cross-infection was investigated in a meeting room. The effect of air diffusers’ locations on airborne transmission was investigated. Six local exhausts were installed above six workstations at 2.0 m height. Respiratory-generated airborne pathogens were simulated using SF6 in the exhaled air of the manikin acting as an infected person. The SF6 concentration in the inhaled air of five susceptible persons remained steady with perforated duct located on the ceiling and at 1.7 m height attached to the corridor wall, but fluctuated greatly when perforated duct were located on the floor, although with a much lower concentration level. The perforated duct under the warm window showed the best potential for mitigating airborne transmission. The concentration in the inhaled air was varied with horizontally supplied low-velocity unit, but much steadier with low-velocity unit at 1.7 m attached to the wall. With an adjusted airflow pattern from low-velocity unit, the inhaled concentration was much lower and uniform among the five susceptible persons. The contaminant removal effectiveness (CRE) was 4.3 with perforated duct under a warm window on the floor. With an adjusted airflow pattern from low-velocity unit, the CRE was much more consistent and increased from 2.1 to 3.9 with an airflow rate from 61 l/s to 116 l/s. The infection probability was the lowest with the perforated duct on the floor and adjusted low-velocity unit.

Walking-induced particle resuspension in a commercial airliner cabin under different ventilation systems

The potential health risk posed by particle resuspension in the air of an airliner cabin is a concern for passengers. This study employed computational fluid dynamics (CFD) to analyze particle dispersion patterns under different ventilation systems, such as mixing ventilation (MV), underfloor air distribution (UFAD), and aisle displacement ventilation (ADV), within a twin-aisle cabin environment. To ensure the accuracy of the CFD model, the study validated the simulated air velocity distribution against experimental airflow patterns from a small-scale water model reported in existing literature. Additionally, the research included direct measurements of particle resuspension within the breathing zone of a full-scale, twin-aisle cabin mockup, which featured five rows of seats. These measurements were taken in response to the disturbance caused by a volunteer walking over an aviation carpet in the aisle. While the CFD simulation results generally aligned with the experimental data, some discrepancies were noted. Pinpointing the exact causes of these discrepancies proved challenging due to the numerous uncertainties and approximations inherent in the study. Nevertheless, the investigation revealed that the air in the upper region near the moving body was pushed forward, creating a strong airflow that enveloped the body. This dynamic resulted in the formation of a wake that lifted particles from the floor level to the upper cabin area. The study observed that particle concentration within the breathing zone increased in the direction of movement. The airflow patterns produced by the three ventilation systems were different. Despite the cabin's symmetrical design, some particles can still transfer from one side to the other, especially under the MV system. The peak particle concentration in the breathing zone was recorded at 20 s, after which it decreased to negligible levels by 120 s. Among the ventilation systems analyzed, the MV system exhibited the highest peak particle concentration, while the UFAD system showed the lowest peak. However, the UFAD system also presented the possibility of very high particle concentrations at certain seats.

Optimal operations of gaspers for minimizing the exposure risks of airborne disease transmission in an economy-class aircraft cabin

Overhead gaspers with adjustable open ratios and flow directions can alter the airflow pattern in aircraft cabins and consequently influence airborne infectious diseases transmission. To achieve the optimal operations of gaspers for minimizing the passengers’ exposure risks, this study developed a Bayesian optimization method based on computational fluid dynamics (CFD). A seven-row, single-aisle, fully occupied, economy-class aircraft cabin was used for the numerical investigation. Two air distribution systems, i.e., a mixing ventilation system and a personalized displacement ventilation system, were considered. First, the open ratios of all the gaspers were optimized by the CFD-based Bayesian optimization method. The optimal operations of gaspers were determined with only 20 trials calculated by CFD using the Bayesian optimization. With the optimal open ratios of all the gaspers, the number of relatively high-risk passengers (exposure index over 0.95) was effectively reduced by at least 55% and 86% under the mixing ventilation and the personalized displacement ventilation, respectively, when compared with the results with all the gaspers turned off. Next, the optimal open ratios and flow directions of the gaspers near the index passenger were also determined by the proposed method. With the optimized operations of gaspers, the number of relatively high-risk passengers was effectively reduced by at least 50% and 67% under the mixing ventilation and the personalized displacement ventilation, respectively.

Effects of exhalation modes and spatial distribution of an infected person on contaminant transmission in a classroom

Classrooms pose a huge risk from the cross-infection of respiratory infections. However, quantitative research on the combined effect of the location of the infected individual and exhalation activities on the diffusion and dissemination of contaminants in a classroom is lacking. We elucidated the effects of spatial distribution and exhalation modes of infected individuals, especially when they talk and breath nasally, on dissemination of contaminants under different ventilation modes: mixing (MV) and stratum ventilation (SV), using computational fluid dynamics, and calculated the contaminant removal efficiency (CRE) and personnel infection time (tin). Infected individuals’ exhalation modes and spatial distribution significantly affected indoor exposure risk. Under SV, risk was low (tin > 0.75 h) when infected individuals talk, but significantly higher (tin ≤ 0.75 h) during nasal exhalation. In MV, risk was lower (tin > 0.75 h) when infected individuals were near the outlet, but increased (tin ≤ 0.75 h) when they were further away. CRE revealed that MV was more sensitive to location changes (12.4- and 5.8-fold) than to exhalation mode changes (2.1- and 0.99-fold). Conversely, SV was more sensitive to exhalation mode changes (5.7- and 2.8-fold) than to location changes (3.7- and 1.8-fold), emphasizing the importance of the distribution of infected individuals and exhalation modes in classroom ventilation design.

Ventilation performance study of a high-speed train cabin based on displacement ventilation and mixed ventilation

Indoor ventilation systems play an important role in controlling energy consumption, thermal comfort, and airborne pollutants. This work is concerned with whether the combination of displacement and mixed ventilation can overcome these systems' respective shortcomings to improve the ventilation performance of high-speed train cabins. This work is based on computational fluid dynamics. The results show that when more fresh airflow enters the compartment from the top vents, the flow field is mainly driven by mechanical forces, and two vortices are formed. When more fresh airflow enters the compartment from the bottom vents, the flow field is mainly driven by thermal buoyancy. Meanwhile, the airflow mainly spreads upward, with lower cooling energy consumption, lower wind speed, higher ventilation efficiency, and smaller longitudinal diffusion of pollutants, but increased temperature difference. When the ratio of top and bottom supply air flow is 75%/25%, thermal comfort can be improved, while balancing energy consumption and air quality. If there was a disease outbreak, the flow rate of the bottom air supply could be increased appropriately. To further improve the ventilation performance, on the one hand, it is necessary to appropriately increase the temperature of the bottom air supply, and on the other hand, it is necessary to avoid short-circuiting of the airflow, due to the lack of synergy between thermal buoyancy and mechanical force. The results of the study can provide a reference for safeguarding passengers and improving the ventilation design of high-speed trains.

Experimental Device to Evaluate Aerosol Dispersion in Venues

The COVID-19 pandemic has focused attention on the importance of understanding and mitigating the airborne transmission of pathogens in indoor environments. This study investigated the aerosol distribution in different indoor venues with varying ventilation concepts, including displacement, mixed, and natural ventilation. A measurement system was developed to investigate venue-specific aerosol distribution patterns using a sodium chloride solution as a tracer. To analyse the spatial dispersion of aerosols, Computational Fluid Dynamics (CFD) simulations were conducted in addition to experimental investigations. The investigations indicated the lowest aerosol load for the venue with displacement ventilation and the highest for the naturally ventilated venue. The measurement system developed in this study provides a useful tool for assessing the effectiveness of ventilation measures in reducing airborne transmission of pathogens in indoor environments. It also proved its wide range of applications, as it can be used in variously sized and shaped indoor environments, with or without an audience.

A numerical study on transport of dust particles accompanied by air gouging process and energy consumption in a circulating ventilation workshop

A modified circulating layered ventilation system is proposed to address the issue of particulate pollutants in the casting cleaning workshop, taking into account the characteristics of end treatment and production processes. By combining Reynolds Average Navier-Stokes (RANS) turbulence model and Discrete Phase Model (DPM), the particle transport law in the coupled flow process of thermal plumes generated by purified circulating airflow and heat source was explored, and ventilation energy consumption was evaluated from the perspective of particle removal energy efficiency ratio. Comparing three ventilation modes: mixed ventilation (MV), wall-based attachment ventilation (WAV), and wall-based attachment ventilation with deflector (WAV-D), it was found that the large vortex region formed by the change in airflow direction during WAV played a key role in particle transport. Placing deflector helped to reduce the impact of vortex recirculation zones generated by the intersection of airflow and plumes on particles. A higher fresh air rate will weaken the diffusion effect of particles in the horizontal air lake region. Continuously increasing the air supply volume to a certain level has little effect on the transportation of low-inertia particles, yet it still manages to effectively enhance the removal efficiency of medium-inertia particles. However, for high-inertia particles, an increase in air supply can easily lead to excessive particle concentration in local areas. When the particle removal efficiency reaches a certain level, higher supply air volume and fresh air rate may lead to a significant decrease in energy efficiency ratio.

Evaluation of ventilation and indoor air quality inside bedrooms of an elderly care centre

Ventilation and indoor air quality are important factors that affect the health of the elderly. The purpose of this study was to find effective ventilation design measures for improving ventilation and air quality in typical two-bed bedrooms in elderly care centres (ECCs). Mixing ventilation (MV), displacement ventilation (DV), zone ventilation (ZV) and stratum ventilation (SV) were analysed with twelve scenarios to find the most effective ventilation design solutions including six scenarios with curtains between the beds and six scenarios without curtains between the beds. Airflow distribution, CO2 concentration, ventilation efficiency and health risk assessment were adopted for discussion. SV was found to be an effective method for improving air quality in the ECC bedroom while also taking into account the needs and rights of elderly residents, such as privacy. Comparing scenarios with and without curtains between beds under same types of ventilation, scenarios without curtains showed a slight (≤8%) decrease in CO2 concentration in the pillow area. However, this could increase virus transmission risk and compromise elderly privacy, so it is not recommended. Regarding the scenarios with curtains between the beds, the contaminant removal efficiency (CRE) of scenarios using SV was increased by 2.58, 3.22 and 2.12 times compared to the scenarios using MV, DV, and ZV respectively. Additionally, the health ratio (HR) of SV was reduced by 46.3 %, 53.7 %, and 41.7 %. Hence, it is recommended to install curtains between the beds and apply SV in ECC bedrooms. This study can be used as a guide for systematically designing ventilation systems in ECC bedrooms. Furthermore, collaboration among environmental engineers, designers, policymakers, and the wider community is essential to develop sustainable indoor environments for the elderly.

Updated national guidelines for spirometry. Part 2. An Approach to Interpreting Spirometry

The second part of the article discusses the spirometry interpretation using the latest international and national recommendations. Different systems of predicted values were considered, attention was paid to the GLI‑2012 reference equations advantages and the z-score assessment. The severity classification, obstructive disorders, extrathoracic and intrathoracic airway obstruction and possible spirometry indications of restrictive and mixed ventilation disorders were considered. The algorithm for spirometry evaluation was also presented, and the most common errors in the spirometry interpretation were discussed.

Experimental evaluation of alternative ceiling-based ventilation systems for long-range passenger aircraft

Alternative ventilation technology bricks, such as ceiling-based, sidewall-based or floor-based ventilation, are of high interest in terms of manufacturing and customization benefits for passenger aircraft. Two novel ventilation systems and state-of-the-art Mixing Ventilation (MV) were experimentally investigated under static conditions in a ground-based research facility. In case of Micro-Jet Ventilation, a perforated ceiling brings the air into the cabin as localized micro-jets with high momentum. Further, Low-Momentum Ceiling Ventilation characterized by a low-momentum air supply through planar and large-surface inlets is investigated. The measurement techniques and the test matrix were designed in order to quantify and evaluate thermal comfort, local air quality and energy efficiency of the ventilation concept. The results proved that there is not one single ventilation concept which optimizes all challenges: air quality, thermal comfort and energy efficiency. Both advantages and disadvantages were found for each ventilation system. In terms of technology bricks, the following main results were found: The average local age-of-air was between 5 and 14%, depending on the boundary conditions. It was lower for the ceiling-based concepts compared to state-of-the-art MV. At the same time the average CO2 concentration decreased by 7–14% for the ceiling-based concepts compared to MV. The local velocities in the vicinity of the passengers were similar for cruise conditions, whereas they decreased by up to 38% in case of hot-day-on-ground conditions for ceiling-based ventilation compared to MV. On the other hand, the heat removal efficiency was low for all concepts and the temperature stratification increased in case of ceiling-based ventilation.

An Experimental Study on the Efficacy of Local Exhaust Systems for the Mitigation of Exhaled Contaminants in a Meeting Room

In industrial applications, local exhaust systems have been used extensively for capturing and confining contaminants at their source. The present study investigates the efficacy of these systems in mitigating the spread of exhaled pollutants by combining them with mixing and displacement ventilation. Experiments were conducted in a simulated meeting room with six closely situated workstations, featuring five exposed persons (simulated with heated dummies) and one infected person (simulated with a breathing manikin). Six overhead local exhaust units, merged with panels, corresponding to workstations, were installed using a lowered false ceiling. Additionally, a table plenum setting for air inlets was introduced to enhance displacement ventilation effectiveness along with local exhaust systems. Results from 16 experimental cases are presented, using the local air quality index and ventilation effectiveness in the breathing zone. The local exhaust system improved the local air quality at the measuring locations closest to the infector in almost all test scenarios. The improvement, particularly significant with displacement ventilation, marked a maximum 35% increase in the local air quality index adjacent to the infector and 25% in the entire breathing zone of the tested meeting room. Moreover, the table plenum settings, coupled with displacement ventilation, further enhanced conditions in the breathing zone. Under the specific conditions of this investigation, the number of operational local exhausts had a marginal impact on mixing ventilation but a significant one on displacement ventilation tests. The efficacy of local exhaust systems was also influenced by the levels of heat gains present in the room. Overall, the study aims to contribute to ongoing efforts to identify sustainable solutions to mitigate indoor airborne diseases with a combination of supply and local exhaust units.

Numerical simulation on supply air of high sidewall grille with retrofitted energy recovery ventilator system for thermal comfort in the tropics

Energy recovery ventilator (ERV) is capable of being integrated into buildings to cut down energy usage for ventilation. However, retrofitting an ERV system into existing occupiable space with mixed ventilation presents drawback to the supply air considering the existing air distribution equipment on the ceiling is limiting the options for ventilation supply. The indoor airflow conditions from supply air of high sidewall grille with obstruction imposed by retrofitted ERV system were investigated for thermal comfort. Three cases of discharged angles of 0° horizontal blades, 45° upward blades and 45° downward blades at high sidewall grille in a studied classroom with tropical outdoor conditions were analyzed numerically. The investigation revealed that the obstruction imposed by ceiling-mounted supply duct in the ERV system can decrease comfort due to improper air mixing into the occupied zone. The results provided useful insight and practical implementation to ensure acceptable thermal comfort for the occupants in retrofitting an ERV in the context of mixed ventilation, which represents the most common design for air distribution in most existing buildings.

Concept and ventilation performance demonstration of graded ventilation

Advanced air distribution is essential for the energy-efficient provision of thermal comfort and indoor air quality. This study proposes a novel advanced air distribution, i.e., graded ventilation. The airflow pattern of graded ventilation is characterized by a bimodal distribution of vertical air velocity and a unimodal distribution of vertical air temperature. Graded ventilation possesses four mechanisms for high energy-efficient provision of thermal comfort and indoor air quality. First, graded ventilation has a high conditioned air supply efficiency into the occupied zone, particularly the head level, for both thermal comfort and indoor air quality, due to the push-down and pull-down forces of the internal airflow recycling. Second, graded ventilation decouples outdoor fresh air and return air, with high outdoor fresh air supply efficiency for indoor air quality. Third, graded ventilation utilizes higher-quality conditioned air for the zone, which is more critical to thermal comfort and indoor air quality. Fourth, graded ventilation only handles the cooling load of the outdoor fresh air without handling the cooling load of the return air. Case studies demonstrate that compared with mixing ventilation, Type-I stratum ventilation, Type-II stratum ventilation, and interactive cascade ventilation, graded ventilation improves energy efficiency by 49.7%–55.4%, 24.8%–29.1%, 16.3%–23.3%, and 8.4%–12.3% respectively for thermal comfort and indoor air quality. Therefore, this study advances air distribution for low-carbon, thermally comfortable, and healthy buildings.

The influence of displacement ventilation on indoor carbon dioxide exposure and ventilation efficiency in a living laboratory open-plan office

Good indoor air quality in office environments is essential for occupant health and productivity. In open-plan offices, displacement ventilation has been recognized for its higher efficiency compared to mixing ventilation. This study evaluates the performance of displacement ventilation in an open-plan office under cooling and heating conditions, considering various supply ventilation rates, supply air temperatures, and occupancy levels. Field measurements were conducted over three months in a living laboratory office in a high-performance building. The indoor environment was controlled by an independent variable air volume (VAV) air conditioning system. The supply ventilation rate ranged from 6 to 12 h−1. Real-time measurements of carbon dioxide (CO2) concentrations in the supply air, return air, and breathing zone of the office were conducted to assess occupants’ exposure to CO2 and ventilation efficiency. The results show that the supply ventilation rate plays an important role in shaping the air distribution and overall effectiveness of the mechanical ventilation system. Higher supply ventilation rates can enhance air distribution robustness, improving ventilation efficiency and reducing CO2 exposure under both cooling and heating conditions. These findings also suggest the need for an optimized control logic that differs from the conventional control logic used in VAV systems. Specifically, during the heating condition of displacement ventilation, it is recommended to maintain the supply ventilation rate at a higher level to effectively mitigate the impact of occupant behavior on air quality, minimize CO2 exposure risks, and ensure a more robust and reliable indoor air distribution.