Single-sided Ventilation Research Articles

CFD simulation of indoor-outdoor wind-driven ventilation and traffic pollutant dispersion at a T-shaped street intersection (ISHVAC 2023)

Traffic exhaust is considered a predominant pollutant source for buildings along streets. However, there are few studies on ventilation and pollution dispersion inside buildings and along streets in a T-shaped intersection. This study investigates the ventilation performance and pollutant dispersion inside and outside multi-unit buildings at T-shaped intersections in different wind directions. Different wind-driven ventilation modes have been compared, i.e. SS2 (single-sided ventilation with 2 openings) and CV (cross ventilation). The results show that multi-unit buildings have the potential to enhance SS2 ventilation performance. The diffusion of outdoor pollutants into indoor environments is more closely related to wind direction for SS2 than CV. However, at certain wind directions (θ = 135°), a significant increase in indoor pollutant concentrations is observed in CV, nearly tenfold higher than that in SS2 cases. The findings could contribute to the understanding of ventilation in multi-unit buildings at T-shaped street intersections.

Numerical Analysis of the Effects of Different Window-Opening Strategies on the Indoor Pollutant Dispersion in Street-Facing Buildings

The idling of automobiles at street intersections can lead to pollutant accumulation which impacts the health of residents in street-facing buildings. Previous research focused on pollutant dispersion within street canyons and did not consider the coupling of indoor and outdoor pollutants. This paper employs the computational fluid dynamics (CFD) method to simulate the dispersion characteristics of vehicle emission pollutants in street canyons, primarily investigating the indoor and outdoor pollutant dispersion patterns under various window opening configurations (single-sided ventilation, corner ventilation, and different positions of the glass under corner ventilation). Additionally, the study considers the impacts of the aspect ratio and ambient wind speed. Studies have shown that corner ventilation is effective in reducing indoor pollutant levels. When the two window glass positions are far away from the center of the intersection, the average CO mass fraction in the single-sided ventilation room is reduced by 87.1%. The average indoor CO mass fraction on the leeward side decreases with the increasing wind speed and aspect ratio. At a wind speed of 8 m/s, the average indoor CO mass fraction on the leeward side decreases to 2.45 × 10−8. At an aspect ratio of 2, the indoor CO mass fraction on the leeward side decreases with increasing floors before stabilizing at approximately 4.77 × 10−9. This study suggests optimal window opening strategies to reduce indoor pollutant levels in street-facing buildings at street intersections, offering guidance to indoor residents on window ventilation practices.

Characteristics of droplet dispersion and interpersonal exposure in indoor and outdoor dining areas of urban street: Elementary numerical investigations

Indoor and outdoor dining areas are special spaces where people generally sit close and talk face-to-face for a long time (∼hour). Semi-open dining area is of popularity among them, one of the reason is the thoughts that outdoor dining area have experienced small infectious risks, even though this opinion has not been thoroughly validated yet. As a novelty, this study conducts CFD simulations to investigate droplet dispersion and face-to-face exposure risk of customers in the indoor and outdoor dining areas of typical street canyons (H/W = 1) by coupling indoor/outdoor airflows. Different scenarios are considered including index patient locations, the setting of the desk isolation board (DIB, HDIB = 0.6 m or 1.2 m), and the outdoor semi-open street roof (SSR).Results show that indoor dining spaces with single-sided ventilation experience one-order poorer ventilation (net escape velocity NEV∼0.036 m/s) and subsequently 10–200 times higher face-to-face droplet trap fraction than those in outdoor dining areas (NEV∼0.407 m/s, TF∼3–102 ppm). Indoor desk isolation board can decrease face-to-face TF by 50 %, but in outdoors, TF without desk-isolation board is 6.5 ppm for 50 μm droplet and this value changes little or slightly increases as HDIB is 0.6 m (∼8.9 ppm) or 1.2 m (∼7.7 ppm), indicating DIB seems not helpful to reduce airborne exposure risk in outdoors. Moreover, the setting of an outdoor semi-open street roof (SSR) may reduce NEV in the indoor or outdoor dining area by half or 90 % respectively. Therefore, SSR may raise indoor and outdoor customers' face-to-face exposure risk (e.g. TF) by hundreds of times and seventy times respectively.

Utilizing periodic boundary conditions to save computational resources for assessing building natural ventilation in urban areas

For the first time in literature, we innovatively conducted CFD simulations with periodic boundary conditions to predict coupled indoor-outdoor airflows for a full-scale 3D six-floor residential building unit in urban areas with uniformly building clusters. A few influencing parameters on building ventilation performance are comprehensively analyzed, including the impacts of the surrounding buildings, wind incident angle (θ), external opening designs, cross or single-sided ventilation modes, and indoor facilities. Ventilation evaluation is contingent on factors including air change rate per hour (ACH), the corresponding ACH of purging flow rate (ACHPFR), and age of air (τ).Results show that the efficiency of natural ventilation on each floor differs from previous research conclusions after considering the impacts of surrounding buildings. Single-sided ventilation is significantly less effective than cross-ventilation in all scenarios. Most cross-ventilation cases have one-order greater ACH and ACHPFR values compared to those with single-sided ventilation. The window-to-wall ratio on the windward and leeward sides can affect the natural ventilation rate of the corresponding rooms. A large leeward opening helps to increase the ventilation rate, especially for the rooms on the upper floor, but it decreases the ventilation for the rooms near the ground. Indoor furniture has an insignificant impact on outdoor airflow and natural ventilation efficiency.

Simulation-based suggestions for lockdown rules in dense urban areas considering indoor-outdoor droplet transmission under natural ventilation conditions

Lockdown rules have been arbitrarily applied to curtail respiratory disease outbreaks without being certain about indoor-outdoor droplet transmission mechanisms and associated infection risks, causing enormous economic losses and arousing social unrest. This study addressed these issues by proposing lockdown rules for dense urban areas using computational fluid dynamics (CFD) simulations of indoor-outdoor droplet dispersion originating from various source locations in single-sided and cross-ventilated spaces of a six-story building in idealized urban areas with plan area densities (λp) of 0.25, 0.44, 0.59, 0.69, and 0.82. The findings suggest issuing lockdown orders based on the relative locations of the patient and vulnerable persons. For example, droplets exhaled by a patient on the upper and middle floors can enter the apartments on one or two floors below under single-sided ventilation, while the droplets are transmitted to the same level downstream spaces by cross-ventilation. Although pedestrians and building occupants pose no infection risk to each other in urban areas with λp = 0.25, they are both exposed to high droplet concentrations in dense urban areas with λp = 0.69 and 0.82. Therefore, this study recommends area lockdowns for dense urban areas to protect residents and pedestrians from virus-laden droplets carried by indoor-outdoor droplet transmission.

CFD simulation of pumping ventilation with two asymmetrically arranged openings on the rear wall in a three-story isolated building

Pumping ventilation, driven by periodic vortex shedding, can effectively improve the ventilation rate of single-sided ventilation. Previous studies on pumping ventilation mainly considered symmetric opening conditions, while the asymmetric opening distribution has not been well studied. Therefore, this study investigates the pumping ventilation of an isolated three-story building with asymmetric opening conditions using computational fluid dynamics (CFD) simulations. Unsteady Reynolds-averaged Navier-Stokes (URANS) method with SST k-ω turbulent model is adopted to conduct the CFD simulations. The effects of horizontal translation distances, internal partitions, and inter-floor interference on time-averaged and fluctuating ventilation rates are investigated. The simulation results show that the mean ventilation rate is larger than the fluctuating ventilation rate. The mean ventilation rate increases while the fluctuating ventilation rate decreases with the increase of the horizontal translation distance. In addition, the internal partition decreases the pumping ventilation rate primarily by reducing the fluctuating ventilation rate rather than the mean ventilation rate. Furthermore, the ventilation rates of the 2nd floor are promoted by simultaneous pumping ventilation of the 1st and 3rd floors compared to the situation that only the 2nd floor is ventilated. The ventilation rates of the 1st floor are the largest, and of the 3rd floor are the lowest. The findings of this study benefit the deeper understanding of pumping ventilation and provide theoretical guidance on the opening designs of multi-story buildings for better ventilation efficiency.

Wind-induced ventilation rate of single-sided ventilation in a building with internal partition

Wind-induced single-sided ventilation is a prevalent form of natural ventilation extensively used in buildings. Nevertheless, prior experimental investigations predominantly focused on single-zone buildings, neglecting the multizone buildings with internal partitions which is representative of more common scenarios. This study addresses this gap by investigating the impact of internal partitions on single-sided ventilation, employing a combination of wind tunnel experiment and numerical analysis. Airflow rate (AFR) was measured with a split-fibre probe and purging flow rate (PFR) was assessed by the tracer gas methodology. The PFR exhibits greater sensitivity to internal partitions in unidirectional airflow compared to bidirectional flow. Large Eddy Simulation (LES) was conducted to elucidate the intricate airflow characteristics in single-sided ventilation. The ventilation efficiency (ratio of PFR and AFR) derived from LES ranges between 0.74 and 0.79, which means that <80% of the AFR actively contributes to the removal of contaminants. Notably, the investigation discerned that the AFR of a single room approximates that of the entire room, whereas the PFR of a single room is smaller than that of the whole room. The disparities in AFR and PFR were caused by the recirculating flow, which was elaborated by the theoretical analysis.

How much natural ventilation rate can suppress COVID-19 transmission in occupancy zones?

Previous research has emphasized the importance of efficient ventilation in suppressing COVID-19 transmission in indoor spaces, yet suitable ventilation rates have not been suggested. This study investigated the impacts of mechanical, natural, single-sided, cross-ventilation, and three mask types (homemade, surgical, N95) on COVID-19 spread across eight common indoor settings. Viral exposure was quantified using a mass balance calculation of inhaled viral particles, accounting for initial viral load, removal via ventilation, and mask filtration efficiency. Results demonstrated that natural cross-ventilation significantly reduced viral load, decreasing from 10,000 to 0 viruses over 15 minutes in a 100 m2 space by providing ~1325 m3/h of outdoor air via two 0.6 m2 openings at 1.5 m/s wind speed. In contrast, single-sided ventilation only halved viral load at best. Natural cross-ventilation with masks effectively suppressed airborne viruses, lowering potential infections and disease transmission. The study recommends suitable ventilation rates to reduce COVID-19 infection risks in indoor spaces.

Impact of architectural design strategies on the indoor natural ventilation of public residential buildings in Singapore

The architectural design pattern of the public residential buildings developed by Housing and Development Board (HDB) of Singapore has evolved gradually throughout the past decades. However, the fact is that although the new generations of HDB blocks built in recent years are designed to be modernized, the usage of air-conditioning has been increasing in comparison with the old generations. This study aims to investigate the ventilation performance of HDB blocks built in different generations from a historical view. By conducting computational fluid dynamics (CFD) simulations on five typical blocks built in different generations, the area-weighted wind velocities in various rooms of the target units were obtained. The effects of design factors on wind velocity ratio (VR) in corresponding spaces were analyzed and compared. The results show that the old generations with parallel plan layouts generally facilitate cross-ventilation while the new generations with centralized plan layouts usually generate single-sided ventilation which is more sensitive to incoming wind direction. Meanwhile, the window-to-wall ratio and shading depth of the studied facades were validated to have positive and negative relations to the VRs respectively. Though the correlations are insignificant, they show significant disparities between the scenarios under different incoming winds.

Experimental evaluation of airflow guiding components for wind-driven single-sided natural ventilation: A comparative study in a test chamber

Single-sided ventilation is a frequently employed ventilation strategy in contemporary structures, yet its effectiveness is often mediocre, underscoring the need for solutions to enhance its performance. To evaluate the effect of louvres and guide vanes on the effective ventilation rate, 21 different louvre configurations and four guide vane designs were compared with a plain opening for single-sided ventilation in a full-scale experimental test chamber under three different magnitudes of local wind velocity. Ventilation rates were measured using the tracer gas decay method with 12 NDIR CO2 sensors. The findings, obtained under specific test conditions, indicate that deeper openings result in a decline in ventilation rate performance. It was observed that wider guide vanes lead to higher ventilation rates, suggesting their potential to enhance SSV performance. The results reveal that, in most cases, louvres contribute to a decline in the system's performance. However, the ventilation rate is influenced by the angle and number of louvres, with optimal performance observed at specific angles and fewer louvres. These findings provide valuable insights for optimizing the design of airflow-guiding components in wind-driven single-sided ventilation systems, enabling the development of more efficient and customized solutions for natural ventilation in buildings.

The effect of geometry and location of balconies on single-sided natural ventilation in high-rise buildings

The demand for housing and the expansion of urbanization have increased the price of land and vertical growth of buildings, resulting in converting the courtyard and porch to balconies. Nowadays, semi-open spaces, which play a critical role in providing optimal indoor air and thermal conditions, are neglected. In addition, the area of such spaces is regarded as limited and sometimes even the balcony is eliminated, leading to improper thermal behavior and increased energy consumption, while such elements can be used for better natural ventilation of spaces and utilization of natural energy, resulting in reducing energy consumption in addition to controlling the pressure created by the wind in the case of correct design. The purpose of the current paper is to evaluate the performance of balconies on the high-rise buildings using single-sided ventilation in the harsh hot-arid climate of Hamdan in Iran, which there has not been studied already A general basic model is presented according to field studies and criteria. Field survey indicates that most of the high-rise buildings in Hamedan have single-sided natural ventilation, as well as are located on the south side, have a rectangular shape, are enclosed on three sides, and have recessed balconies. Based on the climate data of Hamedan, July is considered the hottest month of the year, during which natural ventilation should be applied. Simulation is conducted by computational fluid dynamics (CFD) method and ANSYS software. Based on the results, 4.5 m width and 1.5 m depth are regarded as the best geometry of the balcony for Hamedan providing a mass flow rate up to 1.38 kg/s. In addition, the position of the balcony in the wall of the building should not be symmetrical. The usage of a balcony in the middle of the façade could provide higher ventilation rate and reduce cooling energy up to 7% compared with the base case. Through a meticulous balcony design, wind could path through the larger spaces then it is led towards the opposite window, and finally exits the building in a single-sided ventilation mode. This causes the air to flow in most of the interior spaces, leading to better ventilation than other methods.

Experimental investigation of buoyancy-driven natural ventilation in a building with an atrium using particle image velocimetry (PIV) method

ABSTRACT Natural ventilation is one of the main passive ways to reduce energy needs by delivering fresh air into the building without the help of mechanical systems. In this perspective, using the water bath model and particle image velocimetry, an experimental study of the relationship between fluid velocity caused by buoyancy-driven natural ventilation in a building with single-sided and cross ventilation has been conducted. A case study building with a jointed atrium has been considered for the six initial conditions tests. In the test model which has two low-level inlet openings, fluid velocity in single-sided ventilation mode was meaningfully higher than in cross-ventilation mode, ranging from 18% to 32%. In contrast, by changing the position of the windows to higher levels, cross ventilation creates a flow with 28% higher velocity. Analyzing velocity data demonstrates that, in all tests, the air change rate caused by buoyancy force in cross ventilation mode is more than in single-sided one. Furthermore, in the tests with two high-level openings acting as outlet openings, by opening both sides’ windows in the building, the air change rate increases significantly by 71.75%.

Inter-room pollutant transmission routes in naturally ventilated street canyon buildings

Airborne transmission of pollutants is a significant concern in urban areas, especially since the recent pandemic. While previous studies have explored inter-room pollutant crossflow in highrise buildings and isolated scenarios, the ventilation characteristics within street canyon configurations have not received enough attention. Understanding ventilation characteristics in this layout will help limit the spread of pollutants along the street. This study investigates the wind-driven transmission characteristics of pollutants between the indoor rooms situated adjacent to a street canyon, subjected to perpendicular approach flow. Numerical simulations were performed using the 3D steady Reynolds-Averaged Navier-Stokes approach and validated against surface pressure measurements inside a wind tunnel. The impacts of seven building ventilation strategies were compared, each representing a window opening combination on the two buildings. Based on the set environmental conditions, the results indicate that the inter-room transmission is dependent on both the ventilation efficiency and the specific location of the room. Increasing the ventilation rate decreases the cross transmission between the rooms, while rooms at the centre of the canyon have an increased susceptibility of being contaminated. For instance, switching from cross to single-sided ventilation decreased the average air change rate from 42.3h-1 to 1.4h-1, coinciding with a rise in pollutant concentration by 114-fold and 12-fold at the canyon's centre and side, respectively. Rooms at the edge of the canyon were more contagious and could contaminate other rooms located further inside the street, albeit in small doses. Our findings present new insights within the domain of indoor-outdoor air interaction, shedding light on the interplay between room location and potential inter-unit pollutant transmission. In addition, the pressure measurement results from the wind tunnel experiment provide a valuable resource for other researchers aiming to validate numerical simulations for building engineering applications.

Assessment of year-round wind-driven ventilation by an integrated ventilation model

This study integrates a physical model for cross ventilation and empirical formulae for single-sided ventilation to predict wind-driven ventilation of buildings. The prediction model uses reduction factors to account for the different effects of wind direction, window type, nearby buildings, and building length. The predicted ventilation rates are validated by the results of wind tunnel experiments, a CFD model, and the airflow network model in the EnergyPlus model. The integrated model is then utilized to realistically assess the natural ventilation of a residential building under varying wind speeds and directions throughout a year. The simulation results demonstrate that double-sided cross-ventilation can achieve a ventilation rate roughly 20 times larger than single-sided ventilation under the same wind speed and opening area. In addition, the EnergyPlus model underestimates the annual average ventilation rate by neglecting the shear-induced ventilation when the prevailing wind direction is parallel to the building openings. The change of prevailing wind direction in different seasons can have a substantial effect on the ventilation rate, especially when the external openings of the building are limited to certain sides. Thus, the assessment of natural ventilation of a building must take into account the building orientation and seasonal variation of natural wind conditions.

Impact of building density on natural ventilation potential and cooling energy saving across Chinese climate zones

Natural ventilation is an energy-efficient approach to reduce the need for mechanical ventilation and air conditioning in buildings. However, traditionally weather data for building energy simulation are obtained from rural areas, which do not reflect the urban micrometeorological conditions. This study combines the Surface Urban Energy and Water Balance Scheme (SUEWS) and EnergyPlus to predict natural ventilation potential (NVP) and cooling energy saving in three idealised urban neighbourhoods with different urban densities in five Chinese cities of different climate zones. SUEWS downscales the meteorological inputs required by EnergyPlus, including air temperature, relative humidity, and wind speed profiles. The findings indicate that NVP and cooling energy saving differences between urban and rural areas are climate- and season-dependent. During summer, the urban-rural differences in natural ventilation hours are −43% to 10% (cf. rural) across all climates, while in spring/autumn, they range from −7% to 36%. The study also suggests that single-sided ventilation can be as effective as cross ventilation for buildings in dense urban areas. Our findings highlight the importance of considering local or neighbourhood-scale climate when evaluating NVP. We demonstrate a method to enhance NVP prediction accuracy in urban regions using EnergyPlus, which can contribute to achieving low-carbon building design.

Wind tunnel experiment of wind-induced single-sided ventilation under generic sheltered urban area

Natural ventilation is an important ventilation method due to its potential to improve indoor air quality and provide an acceptable thermal environment without energy consumption. In the urban area, the ventilation performance of the natural ventilation is very sensitive to surrounding building density. This paper presents a wind tunnel experiment to assess the influence of urban density on the ventilation rate of single-sided ventilation. Spacing density, wind direction, and the number of openings were factors that were investigated in this experiment. The ventilation rate is evaluated by a continuous dose method of the tracer gas technique. The wind pressure coefficient at openings of the sealed model without openings was measured by pressure transducers. The streamwise velocity at the street canyon was measured by a split-film probe with a constant temperature anemometer unit. The ventilation rate, wind pressure coefficient fluctuations and velocity of an isolated building are compared to those of a building with two layers of surrounding buildings with the spacing of 0.5H (H is building height), 1H and 1.5H. A higher building density decreases the ventilation performance of windward opening cases and increases the ventilation performance of the leeward opening cases. The simplified ventilation rate prediction methods for wind-induced ventilation are presented.

The Effect of Window Placement on Natural Ventilation Capability in a Jakarta High-Rise Building Unit

The purpose of this study was to investigate the natural ventilation potential in an apartment unit in a high-rise building. A corner unit of a two-bedroom apartment was selected for this study, where single-sided and cross ventilation occurred in the unit. This study employed a CFD simulation to model the indoor airflow of an apartment unit in West Jakarta. The units were modelled and simulated using CFD with a RANS k-ε turbulence model. The results were validated with the readings from the field measurements that had been conducted. Based on CFD results, the window position influences indoor airflow. In the case of cross ventilation, a windward opening is more beneficial, while in single-sided ventilation, a leeward opening creates more indoor airflow. Therefore, it is recommended that the characteristic of window design be considered in the early design stage not only to improve indoor air quality but also to maintain privacy and safety measures.

The effect of airflow guiding components on effective ventilation rates in single-sided ventilation applications

Wind-driven single-sided ventilation (SSV) is present in many existing buildings across Europe, and with new near-zero energy building (NZEB) regulations for the refurbishment of the existing building stock, its attractiveness as a noninvasive, low-energy solution is set to continue. As a strategy, however, in addition to its air change rate capacity, the distribution of fresh air is an important evaluation criterion for its performance. Airflow guiding components located in the external opening that enhance the effectiveness of the wind-driven flow in ventilating the occupied zone could improve the quality of indoor environments. To our knowledge, the literature is sparse on the practical implications for ventilation when adopting guiding components such as louvres, an increasingly popular approach. In the present study, the performance of wind-dominant SSV was simulated using RNG and RSM CFD models, with and without louvres at three building orientations, for example, windward, parallel and leeward. The purpose of this study was to investigate whether louvres installed in the opening would improve both the effective ventilation rate and the penetration depth of the flow into the indoor space. The performance of SSV was evaluated using the age of air and interpreting the secondary air circulation inside the room affected by louvres. As a result of these investigations, a newly configured airflow guiding component was designed and compared to the other cases. Results show louvres can play a crucial role in controlling the secondary air circulation inside the room, and they could either improve or worsen the performance of SSV in terms of air-exchange efficiency. It was shown that in most cases, if louvres were the cause of incremental changes in turbulent intensity within the indoor space, then they are effective as an air-exchange efficiency improvement strategy.

Analysis of single-sided ventilation flows of a generic isolated building using particle tracking method in LES simulation

The main objective of this study is to investigate the airflow patterns in single-sided ventilation of isolated buildings in which the ventilation rate can not be easily predicted by the conventional Orifice equation. The research focuses on buildings with two openings located either at the front or back external wall, with building aspect ratios of 1:1 and 1:2.The study utilizes Large Eddy Simulation (LES) with the particle tracking technique validated by velocity data obtained from a wind tunnel experiment. Ventilation performance is evaluated by Airflow Rate (AFR) and Purging Flow Rate (PFR). AFR was obtained based on the instantaneous velocity over the openings, and PFR was determined by the tracer gas method. The results show that the influence of pulsation flow and eddy penetration both exist in single-sided ventilation. The comparison of AFR and PFR indicates part of the airflow through the opening does not contribute to effectively removing the indoor contaminants, which is quantitively evaluated by ventilation efficiency (εv) defined as the ratio of PFR and AFR. In order to explicitly observe and depict the airflow, the massless particles were emitted at the opening, and the trajectories were analysed. The Probability Density Function (PDF) of indoor residence and indoor travel distance was calculated. The high probability of short indoor travel distance and the residence time, which is mainly caused by the eddy at the openings and time-variant pulsation flow, can explain the difference between AFR and PFR.

The role of near-façade flow in wind-dominant single-sided natural ventilation for an isolated three-storey building: An LES study

Wind-driven single-sided ventilation is present in many existing buildings globally, and its performance can be unreliable and challenging to improve. To address these performance challenges, a better understanding of the interconnected relationship between the external and internal flows is required. Therefore, a detailed assessment of this type of natural ventilation is vital. A detailed CFD analysis of wind-dominant single-sided natural ventilation is presented by adopting the Large Eddy Simulation method, validated using previous wind tunnel studies. An isolated cube, representing a three-storey building, was used to investigate four case studies with different opening positions on the building façade. The presence of parallel flow near the building façade and the effect this has, both on the structure of the flow at the opening and the internal secondary flow, is investigated. Results demonstrate that a mixing layer jet of air is the main structure of the flow at the opening. The flow characteristics of this jet are a function of how the external near-façade flow interacts with the building. It can be deflected or attenuated by the near-façade fluctuating pressure and vortex structures close to the opening. Tracer gas decay results show that only 3/5 of the flow at the opening contributes to effective ventilation in this type of natural ventilation. Comparisons between the ventilation rates for openings at different positions on the building façade demonstrate the importance of the pressure role at the opening in single-sided natural ventilation.