Outdoor Ventilation Research Articles

Performance analysis of particulate matter priority control algorithm for outdoor Air-Introduced ventilation Cleaner using prediction model

Growing concerns about health risks associated with poor indoor air quality, such as respiratory illnesses and allergies, highlight the need for improved management strategies. This study proposes a novel approach that combines an artificial neural network (ANN)-based indoor PM2.5 prediction model with a PM-priority control algorithm. This combined approach addresses the limitations of traditional methods by enabling proactive control measures based on predictive PM2.5 levels. With increased global attention to indoor air quality following the COVID-19 pandemic and the stringent 2021 WHO air quality guidelines, this research focuses on real-time management of PM2.5 and CO2 concentrations to maintain a healthy indoor environment. Two elementary school classrooms were equipped as living labs to analyze the performance of the developed system. The PM-priority control algorithm uses predictive data to dynamically regulate ventilation and air purification processes. Continuous retraining of the prediction model ensures adaptability to environmental changes by evaluating the algorithm’s efficiency in real time. The findings demonstrate that maintaining PM2.5 levels within comfortable ranges and reducing energy consumption can enhance the sustainability of buildings and improve the health and productivity of occupants. This approach provides a scalable solution applicable to schools and potentially other public buildings, emphasizing the preventive value of enhancing occupant health and productivity.

Impact of natural ventilation and outdoor environment on indoor air quality and occupant health in low-income tropical housing

Ventilation is pivotal in mitigating indoor pollutants and ensuring comfortable Indoor Air Quality (IAQ) levels globally. The outdoor environment and ventilation mechanisms significantly impact indoor air quality and occupant health. This research investigated the impact of natural ventilation (NV) and outdoor environment (OE) on indoor air quality (AQ) and occupant health (HI) in low-income housing in Kampala City, Uganda. The study followed a mixed methodology approach by employing self-administered questionnaires and statistical modeling using IBM® SPSS® Amos V24 to analyze the relationships between Natural Ventilation (NV), indoor Air Quality (AQ), Outdoor Environment (OE), and occupant health (HI). The research reveals a strong correlation (0.76) between NV and AQ. In contrast, correlations between AQ and OE (0.16) and NV and OE (0.08) are weak. Model comparative fit indices (CFI: 0.984, SRMR: 0.029, RMSEA: 0.053) indicate an excellent fit. Reliability is high with Cronbach's alpha (NV: 0.800, AQ: 0.862, OE: 0.782) and AVE values (NV: 0.832, AQ: 0.869, OE: 0.786). Significant positive relationships were found between NV and AQ and AQ and HI, highlighting the importance of natural ventilation in improving indoor air quality and occupant health. The study supports SDGs 3, 11, and 13, promoting sustainable building practices and promoting health, enhanced living conditions, and lower greenhouse gas emissions.

Using the Taguchi Method and Grey Relational Analysis to Optimize Ventilation Systems for Rural Outdoor Toilets in the Post-Pandemic Era

This study addresses the issue of poor air quality and thermal comfort in rural outdoor toilets by proposing a ventilation system powered by a building-applied photovoltaic (BAPV) roof. A numerical model is established and validated through comparison with the literature and experimental data. Based on a consensus, four influential variables, namely, inlet position, outlet height, supply air temperature, and ventilation rate, are selected for optimization to achieve multiple objectives: reduction in ammonia concentration, a predicted mean vote (PMV) value of 0, minimization of age of air, and energy consumption. The present study represents a pioneering effort in integrating the Taguchi method, computational fluid dynamics (CFD), and grey relational analysis to concurrently optimize the influential variables for outdoor toilet ventilation systems through design and simulation. The results indicate that all four variables exhibit nearly equal importance. Ventilation rate demonstrates a dominant effect on ammonia concentration and significantly impacts the age of air and energy consumption, while supply air temperature noticeably influences PMV. The optimal scheme features an inlet at center top position, an outlet height of 0.2 m, a supply air temperature of 12 °C and a ventilation rate of 20 times/h. This scheme improves ammonia concentration by 18.9%, PMV by 6.8%, and age of air by 30.0% at a height of 0.5 m, while achieving respective improvements by 18.9%, 5.5%, and 22.2% at a height of 1.5 m. The BAPV roof system generates an annual electricity output of 582.02 kWh, which covers the energy consumption of 358.1 kWh for toilet ventilation, achieving self-sufficiency. This study aims to develop a zero-carbon solution for outdoor toilets that provides a safe, comfortable, and sanitary environment.

Microplastics comparison of indoor and outdoor air and ventilation rate effect in outskirts of the Seoul metropolitan city

Microplastics in the air are becoming a concern, especially in indoor environments. Outdoor microplastics can travel from far spaces while indoor ones remain suspended and recirculate in the indoor environment. In this study, we collected air samples from the same buildings indoors and outdoors and observed the indoor microplastic concentration was 1.8 times higher than the outdoor. 24-hour sampling was performed with a mini-volume air sampler at the rate of 5 L/min. In this study, along with a comparison of indoor and outdoor concentrations, we also studied the microplastics' type size, and shape. We found that fiber-type microplastics account for nearly 90 % of the total and synthetic fibers. We also reported the 10 highest present microplastics are Polyethylene, Polyethersulfone, Polyamide, Polystyrene, Acrylic, Polyvinyl Chloride, Polytetrafluoroethylene, Alkyd, and Polyurethane. It is also observed the indoor ventilation rate plays a major role in the microplastic concentrations, long and periodic ventilation resulted in the lower concentration of the indoor microplastics. This study resulted in higher indoor air concentrations than outdoor and even in the outskirts of the metropolitan city which shows that indoor air concentrations are dependent on indoor sources and human activity.

City configurations to optimise pedestrian level ventilation and wind comfort

Mediterranean coastal cities encounter two conflicting urban environmental challenges. First, strong winds that pose a risk of pedestrian wind discomfort on coastal streets, and second, weak winds that lead to inadequate outdoor ventilation in inner urban fragments. This study aims to optimise pedestrian level ventilation and wind comfort in Izmir, a compact coastal city in the Mediterranean climate. Three hypothetical city configurations were created based on four morphological parameters: street layout, urban street canyon form, tower layout, and tower height variation. Computational fluid dynamics simulations of the city configurations were performed and validated by wind tunnel experiments. The weak, comfortable, and strong winds were determined and mapped at the pedestrian level to assess each city configuration's performance. The results show that using the strategy of a shifted coastal street layout with adding towers on second-row blocks results in a 20 % reduction of the maximum wind velocity ratio on coastal streets compared to a grid street layout without towers. Moreover, positioning step-up towers on step-up city blocks and shifted towers on step-down city blocks can increase pedestrian-level ventilation efficiency by up to 73 %. The research methodology and findings can be transferred to other climates and urban environments and guide urban designers.

Effectiveness of triethylene glycol disinfection on airborne MS2 bacteriophage under diverse building operational parameters

Research on triethylene glycol (TEG) use to disinfect airborne microorganisms have been conducted in non-realistic chamber settings. This study assesses how air temperature, humidity, HVAC settings, and filtration impact TEG's effectiveness in deactivating a common SARS-CoV-2 substitute, MS2 bacteriophage, in a simulated non-occupied office-sized chamber. The chamber was served by a dedicated HVAC system operating at 22.0, 23.5 and 25.0 °C, at 40, 55 and 70 % relative humidity, at 0, 3 and 6 air change per hour (ACH) recirculation, at 0.8, 2.5 and 5.0 ACH outdoor ventilation and at no, MERV8 and MERV14 filtration status. Airborne MS2 log10 reductions in the presence of TEG increased linearly over time and we noted a higher MS2 inactivation rate with higher TEG concentration. The estimated TEG concentration needed for a one-log inactivation of the MS2 within an hour was 0.44 mg/m3. The efficacy of TEG declined with the increase in temperature from 22.0 to 25.0 °C, peaked at 55 % RH, increased with higher recirculation rates but decreased with increasing ventilation rates and higher efficiency filters. The results of our study suggest that the optimum environmental and building conditions for TEG performance is at 22.0 or 23.5 °C air temperature, 55 % relative humidity, 0.8 ACH ventilation rate and 6 ACH recirculation rate. By conducting experiments in simulated office conditions, this study closes significant knowledge gaps in TEG performance application.

Numerical investigation of different building configurations for improving outdoor spatial ventilation conditions in strip-type residential neighbourhoods

Understanding the influence of building configurations on spatial wind flows is essential for architects to optimize urban ventilation in the design process. However, the design changes in urban form are abundant and many detailed design variations were not examined. This study aims to explore the potential of spatial forms to improve wind conditions in strip-type residential neighbourhoods. Several specific building design variations were investigated using computational fluid dynamic (CFD) simulations. The ventilation performance indicators including spatial averaged wind velocity (<V>), purging flow rate (PFR), and net escape velocity (NEV) were adopted to quantify the effects of design changes on spatial ventilation efficiency of overall and local residential spaces. The results show that the buildings with staggers of residential units could have a noticeable impact on the overall residential space, especially when the wind direction is inclined or parallel to the corridor space between the strip buildings. The PFR and < V > values of the residential space can be reduced by 19% and 18%. Building length variation and square setting can be beneficial to the ventilation conditions of the local residential spaces.

Wind Flow Characteristics on a Vertical Farm with Potential Use of Energy Harvesting

The response to the climate emergency requires solutions that address multiple sustainability targets, which could be conducted by merging scientific research from areas that have traditionally evolved separately. This investigation presents advances in that direction by studying a building prototype designated for vertical farming, which enables the wind energy potential across built-up areas to be explored, in this case through the implementation of micro-wind turbines on the surface of the prototype. The study includes a parametric analysis consisting of varying locations of wind turbines across the building envelope, and the width of ventilation corridors. The effects of different widths of outdoor ventilation corridors, various locations, and additional wind angles on the capacity to harvest wind resources were investigated. The results showed that the 5 m wide outdoor corridor has the best ventilation effect, and the wind turbine placed on the roof has the best wind energy potential. The efficiency of wind turbines decreases significantly when multiple devices are placed at the same height on the façades, although overall, the potential for energy harvesting seems incremental.

Estimation of children's CO2 generation rates in naturally ventilated educational buildings

Indoor CO2 concentration serves as an indicator of indoor air quality, which is mainly influenced by occupants' CO2 generation rate, outdoor ventilation rate and outdoor CO2 levels. Determining the CO2 generation rate is fundamental to design effective ventilation systems that ensure good indoor air quality. The ASTM D6245 standard offers a method to estimate human CO2 generation based on sex, age, body mass, and activity level. However, due to the limited number of studies on CO2 generation rate for children and adolescents in daily scholarly activities, accurated values are difficult to estimate. This research uses a stochastic grey box modelling approach to estimate CO2 generation rates in naturally ventilated schools and compares it with the standard approach. This method can address the complexities and variations in real educational environments. The proposed model was verified through an experimental campaign including 32 classrooms with students aged 4, 10, 13 and 16 years. The model provided a detailed description of the indoor CO2 dynamics in 72% of the studied cases. Estimated CO2 generation rates were found to be in line with the expected standard value of between 1.0 MET to 2.0 MET activity levels (7.07–12.65 L/h for a 4-year-old, 9.63–13.29 L/h for a 10-year-old, 14.54–19.32 L/h for a 13-year-old, and 12.11–20.53 L/h for a 16-year-old). These findings not only bridge the gap in children's CO2 generation rates but also introduce a novel approach to assess human CO2 generation rates under uncontrolled conditions.

Data-mining framework for in-depth quantitative study of influences on low-wind-velocity area from morphological parameters of cuboid-form buildings

Wind environment is important in architectural sustainable design, as existing studies show that it can be considerably influenced by building morphologies. This study aimed to develop a data-mining framework to quantitatively evaluate and compare influences on Low-Wind-Velocity Area (LWVA) of common cuboid-form buildings with typical morphological parameters. The data-mining framework was originally developed by integrating multiple computational methods for rapid in-depth iterative analyses, including the generation of building models using parametric modelling, the big data generation based on hybrid model, and the statistical metric analysis method. The hybrid model was created by combining the CFD model and machine learning model. The accuracy and efficiency of the framework were fully demonstrated through the comprehensive validation and analyses of different models. The data of more than fifty thousand building cases with different morphological parameters and relevant wind conditions were generated and analyzed. Influences on LWVA of morphological parameters of cuboid-form building was comprehensively evaluated, including the visualization of multiple parameters, calculation and comparison of several correlation coefficients. It suggested that the reduction of height and width on the windward side would significantly decrease the LWVA and promote the outdoor ventilation. The change of depth would have relatively limited influence on the LWVA. Multivariate regression model-fit and variance analyses were further implemented, and it was found that there was a relatively significant linear correlation between the LWVA and morphological parameters. The equation of multivariate regression model was provided for extra rapid prediction. The study outcome could contribute to efficient evaluation of LWVA and provide useful information for sustainable design.

Assessment of urban ventilation in typical Egyptian housing layouts from four eras using a multi-directional CFD analysis

ABSTRACTAir pollution is globally rising, especially in low- and middle-income countries, due to rapid urbanization. In hot arid environments like Egypt, adequate outdoor ventilation is required to aid in the removal of heat and pollutants and provide healthy living environments. In this context, the current research analyses the urban ventilation of typical Egyptian housing layouts using a simulated multi-directional approach. It is significant because few studies on evaluating urban ventilation of housing prototypes were undertaken in Egypt, and the approaches used were employed in nearly no relevant research in the region. Linear parallel, clustered, dot, and clustered-shifted patterns were investigated. Eight wind directions were analyzed to assess five parameters: 1) wind velocity, 2) age of air (aoa), 3) airflow, 4) pressure coefficient (cp) and 5) comfort index. An automated toolkit that enables the simultaneous simulation of several wind directions was employed. It consists of Eddy3D, a validated Grasshopper tool that uses OpenFOAM’s RANS models. The results showed that best velocities were found in the linear-parallel-unaligned and clustered layouts, directions NNE and N. The latter exhibited favorable airflow within its courtyards. In addition, wind directions had little influence on aoa, as did the layout pattern. Uncomfortable wind was greater in the clustered layout and lowest in the clustered-shifted layout. Except for ENE direction, cp was in opposition with ventilation, since W and WNW directions witnessed the greatest cross-ventilation potential. While linear-parallel-unaligned and clustered layouts created optimum ventilation and allowed outdoor activities, they require more research to increase cp and reduce uncomfortable winds.

Performance Comparison of Indoor Humidity Modeling: A Novel Hybrid Model vs. the Simplified Calculation Model by EN ISO 13788

Ventilation is essential for maintaining indoor air quality and human comfort, particularly in buildings with mechanical ventilation systems. However, modeling the complex relationship between ventilation rate and measurable indoor environmental parameters, such as humidity, poses significant challenges. Current methods for modeling this relationship are often inefficient. For example, data-driven models frequently require sufficient information on ventilation, which may not be available for constant air volume (CAV) systems. On the other hand, simulation programs can be time-consuming and require expert engagement. In this study, we present two simplified calculation models, including a hybrid model developed by the authors, and a well-known model introduced by EN ISO 13788. We compare their performance in evaluating the impact of ventilation rate on indoor humidity. The hybrid model uses a novel analytical method to upgrade a single-input regression model (which considers only outdoor humidity as input) to enable the evaluation of indoor humidity based on both outdoor humidity and ventilation rate. We used the commercial TRNSYS program to model two scenarios: increasing the reference ventilation rate and decreasing the reference ventilation rate. The results showed that both models matched TRNSYS simulations with satisfactory accuracies, but the hybrid model demonstrated superior performance to the EN ISO 13788 model in both scenarios. The hybrid model’s higher accuracy and hybrid features make it better suited for big data analysis and field studies.

Experimental Study of Indoor Air Quality in Educational Buildings: A Spanish Case Study

Ensuring good indoor air quality in the spaces within educational centres is essential for the health and academic performance of students. In this sense, studying the evolution of health pollutants and their relationship with the environmental parameters of indoor humidity and temperature presents a challenge for the design of more efficient and comfortable buildings with a lower risk of virus infection. In this work, the relationship between pollution levels and SARS-CoV-2 virus infections in the academic year 2021/22 is shown, comparing the pollution values measured on-site with the value of the official measuring stations of the Community of Madrid. In addition, the impact of ventilation measures implemented during this period is assessed, aiming to establish guidelines for ensuring a safer and healthier school environment. It was found that during winter months, when there is less outdoor ventilation, pollution levels exceeded the recommended limits, according to reference regulations. This highlights the need for interior conditioning strategies in educational spaces. Thus, this multidimensional approach, considering both airborne pollutants and weather conditions, provides a comprehensive perspective on indoor air quality in school buildings in the central area of a metropolitan city, such as the Community of Madrid.

Large eddy simulation of sneeze plumes and particles in a poorly ventilated outdoor air condition: A case study of the University of Houston main campus

Since the outbreak of the COVID-19 pandemic, many previous studies using computational fluid dynamics (CFD) have focused on the dynamics of air masses, which are believed to be the carriers of respiratory diseases, in enclosed indoor environments. Although outdoor air may seem to provide smaller exposure risks, it may not necessarily offer adequate ventilation that varies with different micro-climate settings. To comprehensively assess the fluid dynamics in outdoor environments and the efficiency of outdoor ventilation, we simulated the outdoor transmission of a sneeze plume in “hot spots” or areas in which the air is not quickly ventilated. We began by simulating the airflow over buildings at the University of Houston using an OpenFOAM computational fluid dynamics solver that utilized the 2019 seasonal atmospheric velocity profile from an on-site station. Next, we calculated the length of time an existing fluid is replaced by new fresh air in the domain by defining a new variable and selecting the hot spots. Finally, we conducted a large-eddy simulation of a sneeze in outdoor conditions and then simulated a sneeze plume and particles in a hot spot. The results show that fresh incoming air takes as long as 1000 s to ventilate the hot spot area in some specific regions on campus. We also found that even the slightest upward wind causes a sneeze plume to dissipate almost instantaneously at lower elevations. However, downward wind provides a stable condition for the plume, and forward wind can carry a plume even beyond six feet, the recommended social distance for preventing infection. Additionally, the simulation of sneeze droplets shows that the majority of the particles adhered to the ground or body immediately, and airborne particles can be transported more than six feet, even in a minimal amount of ambient air.

Assessment of Outdoor Pedestrian Ventilation Performance While Controlling Building Array Scale and Density

In hot and humid regions of China, people experience great discomfort. Good ventilation improves human comfort by facilitating the discharge of heat in a region. None of the previous studies considered which scale is appropriate for the outdoor ventilation of building arrays, and the ventilation performance differs with the array size. Moreover, the building density has an upper limit in Chinese cities, and many studies overestimate this density. Based on these considerations, the neighborhood block is proposed to represent the scale of building arrays with the combination of the urban planning scale and climatic scale. Using this scale, the building density and representative building array configurations for hot and humid regions of China were determined. The outdoor ventilation of these building arrays at the pedestrian height was then studied via computational fluid dynamics simulations. The results show that, in the neighborhood block, an increase in the building height and length is beneficial for the mean velocity, whereas an increase in the building distance is not, and a staggered layout has a negative effect on ventilation. Furthermore, the semi-enclosed layouts are no better than the enclosed layouts in terms of ventilation and sunlight. Some contributions contradict the existing studies because of the selection of different array scales and densities, which prove their significance.

CFD prediction of urban outdoor ventilation around a building group: impact of high-rise building’s height and distance variation

CFD prediction of urban outdoor ventilation around a building group: impact of high-rise building’s height and distance variation

Outdoor environmental comfort evaluation for retail planning in a tropical business district using Integrated Environmental Modeller.

This research proposes a simulation-based assessment of outdoor thermal and acoustic comfort for a planned business urban district in Singapore for retail planning using a customized OpenFOAM-centric multi-physics environmental simulation platform called the Integrated Environmental Modeller (IEM). IEM was employed to simulate the coupled impacts of solar radiation on wind and air temperature and wind and air temperature effects on traffic noise propagation in the district on the equinox and solstice day of the hottest period. Using IEM simulation results, we computed the thermal and acoustic comfort acceptability indicators derived from local field studies' results. The spatial distribution of environmental comfort acceptability indicators in the worst-case scenario can be used to distinguish the zones exposed to thermal or noise influence. The noise-affected zones are near the main roads and overlap a part of the thermal-affected area. The thermal-affected area is almost everywhere in the studied sites in the worst-case scenario. Having outdoor retail spaces with both poor thermal and acoustic comfort is not recommended if the thermal and acoustic comfort cannot be improved simultaneously. For the high-level retail planning, a simplified parametric analysis considering solar irradiance blockage and wind speed enhancements, is provided. Considering the worst-case scenario, ≥50% thermal acceptability can be achieved by blocking 54%-68% solar irradiance among the pedestrian thoroughfares and the retail spaces. Coupled together, blocking the solar irradiance and enhancing the wind speed can further improve thermal comfort locally. These results can guide the retail mix (e.g., al fresco restaurants, pop-up kiosks etc.) near high footfall areas and provide reference for future plans combining landscape and infrastructure, (e.g., trees with shelter walkaways, green walls with outdoor ventilation fans etc.) taking into account the environmental acceptability of people working in or visiting the tropical urban district.

Characteristics of outdoor pollutants intrusion and ventilation control in sentry buildings with normal openings

Characteristics of outdoor pollutants intrusion and ventilation control in sentry buildings with normal openings

Outdoor ventilation evaluation and optimization based on spatial morphology analysis in Macau

Owing to Macau's high urban development intensity, outdoor ventilation is important to enhance human comfort. In this study, four morphological indices as frontal area index (FAI), site coverage (SC), building height (BH) and floor area ratio (FAR) were mapped and analyzed by establishing a refined three-dimensional urban digital model. Then indicator analysis, numerical simulation and LST retrieval were comprehensively used to assess the present outdoor ventilation conditions of Macau. The results showed that Macau's overall spatial morphology was not conducive to ventilation. In hot season, the cool sea breeze was obstructed by high-rise buildings in coastal area of the northern peninsula and difficult to infiltrate into the inner city. In cold season, the high pedestrian level wind speed of urban blocks in coastal areas of southern island was not good for wind protection. In Macau's northern peninsula, three potential wind corridors that connecting several existing open spaces are suggested. In southern island, a clustered urban development mode is proposed to create a wind corridor network. In addition, the existing heat islands in the windward side of wind corridors can be reduced by optimizing land surface. For pedestrian-level ventilation, the wind speed of traditional neighborhoods can be enhanced by reducing site coverage and introducing high-rise buildings during urban renewal. Wind protection methods should be considered in existing coastal urban areas, and low-rise high-density development mode is recommended for coastal new town planning in southern island. This research presents an opportunity to assist urban planners and researchers in developing a comprehensive understanding of Macau's ventilation condition, and provides theoretical support for planning practices for Macau and cities with comparable conditions.

Developing Urban Heat Mitigation Strategies for a Historic Area Using a High-Fidelity Parametric Numerical Simulation: A Case Study in Singapore

The coexistence of developed areas and historic buildings is an important topic in urban planning. Our study focuses on this topic from the perspective of urban microclimate. A multi-physics CFD simulation is applied to model urban microclimate with anthropogenic heat and buoyancy effects. First, we clarified the impact of new development, i.e., high-rises on pedestrian-level air flow by comparing city structures in Case A (the past, 1960s) and Case B (the current, 2020s). The results showed an average wind speed decrease of 43% over time. Second, we assessed air temperature increments from anthropogenic heat emitted from Case C (high-rises), Case D (historic buildings), and Case E (both). We found that the mean air temperature increased by 0.16 °C for Case C, 0.52 °C for Case D, and 0.87 °C for Case E, respectively. Third, we developed heat mitigation strategies based on the assessment results in the previous steps. The integration of open spaces and building porosity, which create wind corridors together, can promote outdoor ventilation and heat dispersion in the study area. Compared with Case E, the three mitigation cases improve outdoor thermal environment, with mean temperature reductions of 33%, 25%, and 21%, respectively. Finally, we developed new mitigation strategies by considering the constraints in this special region, where modernity and history coexist. Our practical mitigation strategies will aid urban planning and support conservation efforts not only in Singapore, but also in other tropical and subtropical cities.