Indoor Airflow Research Articles

Using trickle ventilators coupled to fan extractor to achieve a suitable airflow rate in an Australian apartment: A nodal network approach connected to a CFD approach

The level of airtightness is increasing in newly built Australian apartments. Due to the COVID-19 pandemic, restrictions have forced many people to work from home. An appropriate ventilation rate is needed to decrease virus transmission and provide occupants with a healthy environment. As occupants tend not to open windows, they need to be informed about the potential benefit of using trickle ventilators, in connection with exhaust systems, to ventilate their apartments. In 2022, a provision for lower rates of continuous ventilation (10 L.s−1 for the bathroom exhaust system and 12 L.s−1 for the kitchen exhaust system) was considered for inclusion in the National Construction Code of Australia. This provision was not adopted; however, this is still a valid reference for good practice. Based on this provision for continuous ventilation, our study aims to investigate the airflow velocity and the ventilation efficiency to remove the carbon dioxide (CO2) generated across winter and summer seasons in a Melbourne apartment occupied by two adults and a child over four hours.The study's objectives are 1) to connect two modelling approaches (Computational Fluid Dynamics and nodal networks), and 2) to investigate the potential benefits of using trickle ventilators across winter and summer seasons. The results show that wind conditions have limited effects (4% decrease in the extracted air flow rate) if the extraction network output is protected from the wind. Comparing winter and summer conditions, we found that indoor airflows differed, highly influenced by the temperature difference between outside and inside. We observed that the airflow patterns were more inclined to create “CO2 pockets” during winter, which could increase virus transmission due to ineffective ventilation in this area. However, in winter, ventilation performed better in reducing the CO2 concentration in the kitchen/living room area and the whole apartment than it did during summer.

The Numerical Simulation Study of Pumping Airflow Driven by Wind Pressure for Single- and Multi-Room Buildings

Pumping airflow occurs in single-sided natural ventilation buildings when the openings are located on the leeward side; the direction of airflow through the building then changes periodicity. In order to propose a calculation method of the ventilation rates for single-room buildings and analyze the pumping ventilation for multi-room buildings, the CFD method with an SST k-ω turbulence model was used to conduct numerical simulation in this study, which is verified by other experimental results. Firstly, the qualitative and quantitative characteristics of pumping ventilation were investigated for a single-room building with two openings. The results show that the steady-state method underestimates the ventilation flow rates, and the unsteady-state method captures the microstructures of the flow better. Secondly, the vortex-shedding and indoor airflow oscillation frequencies were analyzed based on transient simulation for a single-room building. It was found that both of them increase with air speed. Then, the factors affecting ventilation flow rates were analyzed. A calculation method for dimensionless ventilation rates is proposed. Finally, the pumping ventilation for a multi-room building was numerically simulated. The ventilation rate for a middle room is greater than that for a corner room, and the ventilation rate for any room in a multi-room building is greater than the single-room building given the same room size and the same incoming wind speed. The findings of this paper are helpful for the design and evaluation of natural ventilation.

Parametric Thermal Simulations of an Airflow-Screen Façade System

Energy-saving performance is required for building façades, and high-performance window systems, such as double-skin and airflow windows, are being considered as viable alternatives. However, those systems are costly owing to the increased number of glazing panes. Therefore, an airflow-screen façade system (AFS) that combines glazing, a blind, and a roller shade can be a viable solution. The design issues of AFS are the backflow to the indoor side and the effect of natural convection on indoor airflow when exhaust fans are not in use during holidays and at nighttime. However, only few studies exist on the annual thermal behavior of AFS. In this study, based on the thermal load calculation program NewHASP, a simulation model of AFS was built using a thermal node solar heat gain model and a ventilation network model. Sensitivity analysis of the maximum and annual thermal load were performed with the following parameters of the AFS: roller shade airtightness, glazing type, blind slat angle control system, window orientation, and exhaust fan air volume. The results of the sensitivity analysis indicate that the maximum and annual thermal loads were the most sensitive to were the direction the window faces and the airtightness of the roller shade.

Optimizing measurement schemes to improve indoor airflow and temperature CFD–EnKF joint simulation

An ensemble Kalman filter (EnKF) effectively rectifies simulation inaccuracies arising from uncertain flow field boundary conditions. In this methodology, measurement data plays a pivotal and indispensable role. This study investigated the requirements for observation data in joint EnKF and computational fluid dynamics (CFD) simulation models to correct errors. It established guiding principles for measurement schemes and validated them using numerical experiments on the airflow and temperature fields in a small chamber. The optimized scheme significantly reduced simulation errors, enhancing assimilation accuracy. In addition, the influence of measurement noise was considered, revealing a positive correlation between assimilation and measurement errors, thus highlighting the significance of high-precision instruments. Additionally, this study confirmed that the optimal number of measurement points corresponds to the number of uncertain boundary condition variables. Fewer measurement points hinder accurate estimation, whereas increasing their number does not significantly improve the data assimilation accuracy, regardless of measurement noise. Overall, this study provides guidelines for implementing EnKF data assimilation to ensure reliable and precise results.

Numerical simulation on air distribution and aerosol transportation in operating room with unidirectional flow system under operational condition

Surgical Site Infections (SSIs) is one of the common postoperative complications in hospitals. SSIs risk is positively correlated to the air contamination level in operating room. In order to explore the influence of different moving paths and different moving speeds of personnel on the ventilation efficiency under different air supply velocities in operating room, computational fluid dynamics simulation was performed with the dynamic mesh model. The air cleanliness level inside the surgical critical area was the best when the unidirectional air supply velocity was 0.35 m/s and when medical staff was standing still in the operating area. When medical staff was located in the peripheral area, particles generated from medical staff can be efficiently removed by the unidirectional airflow without transported into the surgical critical area. With the air supply velocity 0.35 m/s and the occupant's walking speed 1.0 m/s, the ventilation efficiency reached 53.8 %. It is found that the impact on the indoor airflow is the most significant when medical staff walks from the peripheral area to the surgical area. The numerical simulation method could be applied as an effective way to predict the performance of the air distribution in operating room under operational condition and to reduce the pollutant concentration in the critical surgical region.

Can windcatcher's natural ventilation beat the chill? A view from heat loss and thermal discomfort

Windcatchers provide effective low-energy ventilation and summer passive cooling in temperate climates. However, their use in winter is limited due to significant ventilation heat loss and potential discomfort. Limited research has been conducted on quantifying windcatcher heat loss in cold climates, particularly through field studies. This study aims to evaluate the applicability of windcatchers in low-temperature conditions, with a focus on ventilation heat loss and thermal discomfort. Field experiments were conducted in Nottingham, UK, during an icy period. A 3D-printed prototype windcatcher and a test room were built and tested in such weather conditions. A Computational Fluid Dynamics (CFD) model validated against the field experimental data was employed to investigate the windcatcher's performance in a typical UK primary school classroom. The field experimental results indicate that the indoor airflow patterns are dynamic and continuously change with varying external wind conditions. Using static boundary conditions for ventilation analysis is inadequate, as it may lead to inaccurate predictions due to observed fluctuations and irregular airflow patterns. CFD modelling revealed significant over-ventilation in the classroom at external wind speeds of 3 m/s, despite being previously deemed as “satisfactory”, “adequate”, or “sufficient” ventilation. At wind speeds of 3 m/s or higher, the over-ventilation can cause a minimum 941.4 W heat loss, adding 4.7 kWh heating load and £1.6 electricity cost for a typical-sized single classroom during a 5-h occupied period. The research findings highlighted that control strategies should be introduced to reduce over-ventilation. Integrating heat recovery or thermal storage can enhance winter thermal conditions.

Thermal environment optimization in a large space building for energy-saving

As the functionality of large space buildings becomes more sophisticated, to ensure that the interior of the building has a reasonable thermal environment when it is put to use, designers must consider the thermal comfort of the human body and the building's potential for energy-saving during the design stage. The Grand Canal Exhibition Center is used as the research object in this study. Its numerical simulation of two pre-design cases using CFD technique is carried out and it studies the indoor airflow organization and temperature field distribution. In addition, it considers the factors that affect the building's energy consumption and assesses the best case. The Grand Canal Exhibition Center's initial design is optimized using the ADPI index, which is also used to calculate the building's energy-saving and evaluate the whole area's thermal comfort uniformity. The results of the research show that case 2 has greater thermal comfort uniformity and energy-saving potential, with a ground floor ADPI value of 83.3% and uniform thermal comfort throughout the entire zone. The second floor's ADPI value is 85%, and the entire space has the best thermal comfort. The third floor's ADPI value is 79%, and the localized area's thermal comfort is poorer. The building of case 2 has a 5% increase in energy-saving over case 1 regardless of the season, and it still has a significant amount of energy to spare. The research in this paper will be an invaluable resource for architects to design large space buildings.

Investigation on indoor airflow and contaminant dispersion of diffuse ceiling ventilation in heating and cooling modes

This paper systematically investigates the indoor airflow and contaminant dispersion of diffuse ceiling ventilation (DCV) for space heating and cooling. A numerical model of the office with DCV is built and validated. The indoor thermal comfort and air quality (IAQ) under different cases are analyzed. Simultaneously, different indices are employed to determine the influence of exhaust positions and air change rates on the system. The results indicate that DCV can provide a satisfying thermal environment both in heating and cooling modes, and there is no reverse flow from the room to the plenum. Besides, the visualizations of indoor airflow, temperature distributions, and mean age of air (MAA) show the different characteristics during heating and cooling. The ranges of contaminant removal effectiveness (CRE) and temperature effectiveness (TE) are 0.87–1.00 and 0.79–1.55 for heating, respectively. For cooling, they are 0.96–1.23 (CRE) and 0.92–1.06 (TE), respectively. Although the TE for heating is slightly higher than that of cooling, the CO2 concentrations and CRE manifest that DCV performs better for space cooling. Moreover, the results show that the exhaust positions influence TE more than CRE, especially for heating. Within the measured air change rates, it is found that the increase of air change per hour (ACH) can aid to the ventilation effectiveness of DCV. Meanwhile, the linear regression equations between ACHs and MAA are obtained. This research is helpful to reveal the flow mechanisms of DCV and guides the design and operation of the system.

CFD Analysis of Indoor Ventilation for Airborne Virus Infection

CFD Analysis of Indoor Ventilation for Airborne Virus Infection Indoor airflow patterns and air residence times significantly influence the spread of airborne infectious viruses, such as COVID-19. These factors can be quantified using computational fluid dynamics (CFD). In this study, CFD was utilized to assess the indoor airflow patterns and calculate air residence times in a typical restroom with high personnel flow and low ventilation efficiency. The results identified regions with high air residence times, indicating potential risk areas for airborne virus retention. Furthermore, the effects of different ventilation strategies on these high-risk areas were analyzed. Despite meeting air change standards, certain regions were found to potentially pose a higher risk due to prolonged air residence times. Based on these findings, recommendations for improving ventilation systems to reduce the risk of airborne virus infection were proposed. This study highlights the necessity of a more nuanced approach to indoor air assessment than simply calculating air changes per hour. It was concluded that (1) different ventilation strategies can greatly affect the air residence time in the room and (2) the variance of air residence time in the air circulation area are large in some locations, even with simple ventilation adjustments.

Impact of roof shape on indoor gaseous pollutant level for natural ventilation buildings in a street canyon: Numerical simulation

Introduction: Coupling the indoor and outdoor airflow of roadside buildings in a street canyon, the impact of flat and triangular roofs on indoor air pollutant concentration and ventilation rates of naturally ventilated buildings is studied using numerical simulation methods.
 Materials and methods: The flow and pollutant diffusion control equations are solved by using ANSYS Fluent. In simulation, RNG k-ε turbulence model is adopted. The numerical model is validated using the three-dimensional street canyon test data from the wind tunnel experiment at University of Karlsruhe.
 Results: The flow and pollutant concentration distributions under different roof shapes are obtained. The ventilation rates with different air flow resistances and pollution level indoors are provided.
 Conclusion: Ventilation direction through windows of roadside buildings determines the level of indoor air polluted by vehicle emissions in street canyon. When the building main height equals to the width of the street, flat roofs make the indoor concentration basically consistent with that near the external walls of the canyon. The higher the triangular roofs, the higher the ventilation rate and the lower the indoor concentration. The ventilation rate is influenced not only by roofs, but also by the floor location and indoor ventilation resistance.v

Impact of planar area ratio and opening positions on natural cross ventilation performance in sheltered high-rise buildings: A simulation study

This paper studies the impact of planar area ratio (λP) and opening positions on natural cross ventilation performance of a sheltered three-level high-rise building through numerical simulations. Three building clusters of different λP and five different opening configurations each were assessed. To improve the accuracy of the numerical simulations, a novel calibration method utilizing 2k full-factorial design of experiment (DoE) approach was proposed to determine the closure coefficients of the Standard k−ε (SKE) turbulence model. Various parameters such as velocity profile (U/UH), pressure difference (ΔCp), turbulence kinetic energy (TKE), dimensionless flow rate (DFR), age of air (AOA) and air exchange efficiency (AEE) were examined. On level 1, distinct variations in DFR, AEE and AOA were observed for different λP values. Maximum DFR and AEE and maximum AOA are achieved when λP=0.25 for all opening configurations. Conversely, the impact of λP is minor for levels 2 and 3. Specific opening configurations, such as top-bottom and top-top on levels 1 and 2, and center-center and bottom-top on level 3, demonstrate favorable AEE of about 45–50%. The trade-off between AEE and DFR suggests that the bottom-bottom configuration performs best on level 1, while top-top and top-bottom configurations work best on level 2, and the center-center configuration is the best on level 3. The presence or absence of openings on levels 1 and 3 do not significantly affect the indoor airflow on level 2. The insights and recommendations derived from this study have practical implications for sustainable high-rise building design.

Quantifying natural cross-ventilation flow of a two-layered model used for terraced houses in tropical zones by particle image velocimetry

Wind-induced natural ventilation is a sustainable approach for improving the indoor thermal comfort, air quality, and energy consumption. Although numerous ventilation studies have addressed generic ventilation models, the cross-ventilation flow of a multilayered model (widely ingrained in a tropical climate zone such as Malaysia as a typical terraced house with a deep-plan layout) has not been studied well. Therefore, this study aims to investigate the flow patterns inside a simplified two-layered model separated by a second floor at the middle height with an opening using wind tunnel experiments. Two cases are considered based on the positions of the inlet and outlet openings on each floor. Two velocity components are measured using particle image velocimetry (PIV) and hot-wire anemometry (HWA). This study provides high-quality experimental datasets, which enables us to understand turbulent characteristics of indoor airflow, obtained using PIV and HWA for a generic two-layered cross-ventilation model. In addition, the results show that the ventilation performance of two-layered stratified buildings is significantly affected by the inlet opening positions. Moreover, the indoor flow direction is considerably changed owing to the multi-zoning of the indoor space. Although we employed only a generic two-layered model, this study clearly highlights the importance of considering multi-layered buildings for a better understanding of the ventilation performance.

Effect of outdoor wind on the hybrid natural ventilation performance of monitor roofs

The monitor roof of a building has a raised structure running along the gable ridge, with its smaller roof parallel to the lower main roof. As a common building ventilation design, monitor roofs are expected to induce indoor airflow through thermal buoyancy and/or wind; however, studies on the design details and the induced natural ventilation performance are limited. In this study, how outdoor wind affects the efficiency of induced hybrid natural ventilation of monitor roofs was analyzed through computational fluid dynamics (CFD). Based on engineering practice and weather conditions, the Grashof number (Gr) was 2.11x1011-5.67x1011, and the Reynolds number (Re) was 2.5x105-1.7x106. The results indicated that for a larger monitor roof (width = 3 m, height = 1.2 m), the presence of outdoor wind combined with thermal buoyancy increased the ventilation rate to 1.5–3.5 times that found when only buoyancy was present. For a smaller monitor roof (width = 1.2 m, height = 0.3 m), Gr/Re2 = 0.45–3.2 was the transition range over which the presence of outdoor wind decreased the ventilation rate below that found when only buoyancy was present. Therefore, attention should be given to this disadvantage in ventilation design.

Simulation Study on Natural Ventilation Performance in a Low-Carbon Large-Space Public Building in Hot-Summer and Cold-Winter Region of China

Recently, climate governance has entered a new phase of accelerating decarbonization. In order to achieve low-carbon buildings, natural ventilation has been widely used as it requires no fan power. However, there are great challenges for achieving effective natural ventilation in large-space public buildings especially in areas characterized by hot-summer and cold-winter climatic regions, due to empirically unsuitable ambient temperatures and theoretically complex joint effect of wind pressure and thermal buoyancy. Therefore, this numerical study was conducted on the performance of a natural ventilation strategy in a large-space public building in a hot-summer and cold-winter region by using computational fluid dynamics (CFD) methods. Simulations were performed by applying FLUENT software for obtaining airflow distributions within and around a typical low-carbon public building. The temperature distribution in the atrium of the building was simulated particularly for analyzing the natural ventilation performance in a large-space area. Results demonstrated that thermal pressure was dominant for the large-space building in the case study. The average indoor airflow velocities on different floors ranged from 0.43 m/s to 0.47 m/s on the windward side which met indoor ventilation requirements. Most areas of wind velocities could meet ventilation requirements. The natural ventilation performance could be improved by increasing the relative height difference between the air inlets and air outlets. These findings could help provide references and solutions for realizing natural ventilation in low-carbon large-space public buildings in hot-summer and cold-winter regions.

Assessing the impact of architectural and behavioral interventions for controlling indoor COVID-19 infection risk: An agent-based approach

The COVID-19 pandemic changed our lives, forcing us to reconsider our built environment. In some buildings with high traffic flow, infected individuals release viral particles during movement. The complex interactions between humans, building, and viruses make it difficult to predict indoor infection risk by traditional computational fluid dynamics methods. The paper developed a spatially-explicit agent-based model to simulate indoor respiratory pathogen transmission for buildings with frequent movement of people. The social force model simulating pedestrian movement and a simple forcing method simulating indoor airflow were coupled in an agent-based modeling environment. The impact of architectural and behavioral interventions on the indoor infection risk was then compared by simulating a supermarket case. We found that wearing a mask was the most effective single intervention, with all people wearing masks reducing the percentage of infections to 0.08%. Among the combined interventions, the combination of customer control is the most effective and can reduce the percentage of infections to 0.04%. In addition, the extremely strict combination of all the interventions makes the supermarket free of new infections during its 8-hour operation. The approach can help architects, managers, or the government better understand the effect of nonpharmaceutical interventions to reduce the infection risk and improve the level of indoor safety.

Coughed droplets dispersion pattern in two-bed ward under different heating strategies

This study aims to compare the dispersion of coughed droplets with different diameters under two heating strategies of hospital ward in winter. An experimentally verified computational fluid dynamics (CFD) method has been used to simulate the evaporation and diffusion of droplets with five different diameters in a two-bed ward with air conditioning strategy (MV) and floor radiant heating strategy (FH). Results show that in the boundary of the human body, indoor air flow, human expiratory airflow and thermal plume play an important role in the dispersion of coughed droplets. Small and medium-sized droplets suspension in the ward for a longer time, while large droplets deposit rapidly. The removal ratio of 50 μm droplets under MV strategies is the highest. The 100 μm droplets in the two heating strategies are completely removed within 30 s. There is an obvious difference of droplets deposition ratio on each surface in the ward.

CFD modeling of room airflow effects on inactivation of aerosol SARS-CoV-2 by an upper-room ultraviolet germicidal irradiation (UVGI) system

Ultraviolet germicidal irradiation (UVGI) systems inactivate microorganisms indoors. Upper-room UVGI systems use wall- or ceiling-mounted fixtures to create an air disinfection zone above the occupied zone. The performance of upper-room UVGI systems varies with indoor airflow patterns induced by mechanical ventilation and thermal plumes from indoor heat sources. Little information is available on the effects of ventilation strategies on upper-room UVGI system performance for the control of viral aerosols in occupied spaces. This study simulated the effects of ventilation system characteristics in an office space on the ability of an upper-room UVGI system to inactivate viral aerosols with UV-C susceptibility representative of coronaviruses. UVGI reduced viral aerosol concentration by two orders of magnitude relative to the concentration without UVGI. Air change rates and air distribution strategy (mixing vs. displacement) had notable effects on the effectiveness of the UVGI system. For mixing ventilation, as the recirculation airflow rate increased from 0 to 5.3 h−1 for a room volume of 108 m3 with a fixed outdoor air change rate of 0.7 h−1, UVGI inactivation increased by 96.7%. Mixing ventilation with 100% outdoor air of 0.7 h−1 yielded airborne virus inactivation that was double that of displacement ventilation, due to enhanced air mixing.

Applying Natural Ventilation for Commercial Buildings With Atrium: Indoor Environment Prediction and Outdoor Pollutant Impact

Abstract The use of natural ventilation for commercial buildings becomes ever attractive due to the potential for economic savings and increased occupant satisfaction. However, it has proven to be particularly challenging to predict the indoor air temperature and airflow distribution from natural ventilation in more complex building geometries such as those with an atrium. This study used the energy-simulation-coupled computational fluid dynamics (CFD) method to predict the indoor temperatures of a typical multi-story, open-floorplan office building with a central atrium. The prediction accuracy using CFD was slightly improved for the periods with extreme outdoor conditions, where large temperature disparities often occur between simulation and experiment. For the tested cases, adjustment of window opening sizes seems to have marginal impacts on the simulation results. This paper further explores the impacts of outdoor gas-phase pollutants on indoor air quality of such a naturally ventilated commercial building with an atrium. A few architectural features such as window blockers and double skin façade (DSF) designs were numerically investigated for their performance to lower the indoor pollution levels while still maintaining adequate building ventilation rates. The results reveal that the features affecting the wind patterns around and above the building have a strong influence on the contamination rates on each floor of the building. DSF can not only reduce indoor pollution levels but also reduce the ventilation rate. When a pollutant source is not close to the building, a conventional central atrium design is preferred for better ventilation rates.

Experimental research on the cross-infection control performance of different ventilation strategies

Sustained pandemics have awakened the growing need to select appropriate indoor ventilation strategies to create a healthy environment. Hence, this study experimentally evaluated the cross-infection control performance of different ventilation strategies, namely mixing ventilation with outlets installed in the bottom of the side wall (MV-BR) and at ceilings (MV-CR), stratum ventilation with outlets installed in the side wall (SV-SR) and at ceilings (SV-CR), interactive cascade ventilation with outlets installed in the side wall (ICV-SR) and at ceilings (ICV-CR). The supply air flow rate of the studied ventilation strategies remains the same (6.51 h−1) for fair comparison. The infection risk and maximum cumulative exposure are introduced as the evaluation indicators. The research results show that the mean infection risk in the respiratory zone of susceptible individuals who are standing in the sidewind directions of the infected people under ICV-SR has the lowest potential infection risk (Pi) value of 0.012, which is consistently lower than ICV-CR by 8.3%, MV-CR by 42%, MV-BR by 45%, SV-CR by 50%, and SV-SR by 55%, respectively. And the average max long-term exposure of MV-BR is 15.2% lower than MV-CR. Compared with SV-CR and ICV-CR, SV-SR and ICV-SR can also realize to reduce the max long-term exposure by 21.3% and 25%, respectively. The integrated scenario index calculation results demonstrate that ICV presents excellent cross-infection control performance than SV and MV, obtaining 53.5% and 61.2% lower cross-infection risk. The conclusions got from this study can provide guide for the design of indoor airflow organization with the epidemic normalizing.

Dispersion of sneeze droplets in a meat facility indoor environment – Without partitions

Spreading patterns of the coronavirus disease (COVID-19) showed that infected and asymptotic carriers both played critical role in escalating transmission of virus leading to global pandemic. Indoor environments of restaurants, classrooms, hospitals, offices, large assemblies, and industrial installations are susceptible to virus outbreak. Industrial facilities such as fabrication rooms of meat processing plants, which are laden with moisture and fat in indoor air are the most sensitive spaces. Fabrication room workers standing next to each other are exposed to the risk of long-range viral droplets transmission within the facility. An asymptomatic carrier may transmit the virus unintentionally to fellow workers through sporadic sneezing leading to community spread. A novel Computational Fluid Dynamics (CFD) model of a fabrication room with typical interior (stationary objects) was prepared and investigated. Study was conducted to identify indoor airflow patterns, droplets spreading patterns, leading droplets removal mechanism, locations causing maximum spread of droplets, and infection index for workers along with stationary objects in reference to seven sneeze locations covering the entire room. The role of condensers, exhaust fans and leakage of indoor air through large and small openings to other rooms was investigated. This comprehensive study presents flow scenarios in the facility and helps identify locations that are potentially at lower or higher risk for exposure to COVID-19. The results presented in this study are suitable for future engineering analyses aimed at redesigning public spaces and common areas to minimize the spread of aerosols and droplets that may contain pathogens.