Special Issue "Recent Advances in Urban Ventilation Assessment and Flow Modelling"

A special issue of Atmosphere (ISSN 2073-4433).

Deadline for manuscript submissions: closed (31 May 2018)

Special Issue Editors

Guest Editor
Dr. Riccardo Buccolieri

Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali (DiSTeBA), University of Salento, S.P. 6 Lecce-Monteroni, 73100 Lecce, Italy
Website | E-Mail
Interests: urban air quality and microclimate; experimental and computational fluid dynamics; turbulence and pollutant dispersion; city breathability and urban vegetation
Guest Editor
Dr. Jian Hang

Sun Yat-sen University, School of Atmospheric Sciences, Guangzhou, Guangdong province, P.R. China
Website | E-Mail
Interests: urban ventilation and turbulence modelling; urban pollutant dispersion and exposure assessment; urban heat island; experimental and computational fluid dynamics

Special Issue Information

Dear Colleagues,

We invite researchers to contribute original research articles, as well as review articles, dealing with all aspects of ventilation in urban areas. These contributions include recent experimental and modeling works, techniques and developments tailored to the assessment of urban ventilation and flow and pollutant dispersion in cities. We are also interested in reviews with possible future lines of investigations. Topics of interest include, but are not limited to:

  • ventilation efficiency and application/development of ventilation indices;

  • relation between indoor and outdoor ventilation;

  • effects of urban morphology and obstacles on ventilation;

  • data (meteorological and air quality) from new field campaigns in cities and wind tunnel experiments for the estimation of ventilation indices;

  • experimental and modeling application studies to real cities with attention to high density cities and high-rise buildings;

  • mitigation strategies of poor ventilation conditions and urban air pollution.

Dr. Riccardo Buccolieri
Dr. JianHang
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Atmosphere is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Ventilation efficiency
  • Urban morphology and obstacles
  • Field and wind tunnel experiments
  • Flow modelling
  • Mitigation strategies

Published Papers (21 papers)

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Research

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Open AccessArticle Application of GPU-Based Large Eddy Simulation in Urban Dispersion Studies
Atmosphere 2018, 9(11), 442; https://doi.org/10.3390/atmos9110442
Received: 20 September 2018 / Revised: 30 October 2018 / Accepted: 7 November 2018 / Published: 13 November 2018
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Abstract
While large eddy simulation has several advantages in microscale air pollutant dispersion modelling, the parametric investigation of geometries is not yet feasible because of its relatively high computational cost. By assuming an analogy between heat and mass transport processes, we utilize a Graphics
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While large eddy simulation has several advantages in microscale air pollutant dispersion modelling, the parametric investigation of geometries is not yet feasible because of its relatively high computational cost. By assuming an analogy between heat and mass transport processes, we utilize a Graphics Processing Unit based software—originally developed for mechanical engineering applications—to model urban dispersion. The software allows for the modification of the geometry as well as the visualization of the transient flow and concentration fields during the simulation, thus supporting the analysis and comparison of different design concepts. By placing passive turbulence generators near the inlet, a numerical wind tunnel was created, capable of producing the characteristic velocity and turbulence intensity profiles of the urban boundary layer. The model results show a satisfactory agreement with wind tunnel experiments examining single street canyons. The effect of low boundary walls placed in the middle of the road and adjacent to the walkways was investigated in a wide parameter range, along with the impact made by the roof slope angle. The presented approach can be beneficially used in the early phase of simulation driven urban design, by screening the concepts to be experimentally tested or simulated with high accuracy models. Full article
(This article belongs to the Special Issue Recent Advances in Urban Ventilation Assessment and Flow Modelling)
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Open AccessArticle Natural Ventilation of a Small-Scale Road Tunnel by Wind Catchers: A CFD Simulation Study
Atmosphere 2018, 9(10), 411; https://doi.org/10.3390/atmos9100411
Received: 29 July 2018 / Revised: 14 October 2018 / Accepted: 15 October 2018 / Published: 20 October 2018
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Abstract
Providing efficient ventilation in road tunnels is essential to prevent severe air pollution exposure for both drivers and pedestrians in such enclosed spaces with heavy vehicle emissions. Longitudinal ventilation methods like commercial jet fans have been widely applied and confirmed to be effective
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Providing efficient ventilation in road tunnels is essential to prevent severe air pollution exposure for both drivers and pedestrians in such enclosed spaces with heavy vehicle emissions. Longitudinal ventilation methods like commercial jet fans have been widely applied and confirmed to be effective for introducing external fresh air into road tunnels that are shorter than 3 km. However, operating tunnel jet fans is energy consuming. Therefore, for small-scale (~100 m–1 km) road tunnels, mechanical ventilation methods might be highly energetically expensive and unaffordable. Many studies have found that the use of wind catchers could improve buildings’ natural ventilation, but their effect on improving natural ventilation in small-scale road tunnels has, hitherto, rarely been studied. This paper, therefore, aims to quantify the influence of style and arrangement of one-sided flat-roof wind catchers on ventilation performance in a road tunnel. The concept of intake fraction (IF) is applied for ventilation and pollutant exposure assessment in the overall tunnel and for pedestrian regions. Computational fluid dynamics (CFD) methodology with a standard k-epsilon turbulence model is used to perform a three-dimensional (3D) turbulent flow simulation, and CFD results have been validated by wind-tunnel experiments for building cross ventilation. Results show that the introduction of wind catchers would significantly enhance wind speed at pedestrian level, but a negative velocity reduction effect and a near-catcher recirculation zone can also be found. A special downstream vortex extending along the downstream tunnel is found, helping remove the accumulated pollutants away from the low-level pedestrian sides. Both wind catcher style and arrangement would significantly influence the ventilation performance in the tunnel. Compared to long-catcher designs, short-catchers would be more effective for providing fresh air to pedestrian sides due to a weaker upstream velocity reduction effect and smaller near-catcher recirculation zone. In long-catcher cases, IF increases to 1.13 ppm when the wind catcher is positioned 240 m away from the tunnel entrance, which is almost twice that in short-catcher cases. For the effects of catcher arrangements, single, short-catcher, span-wise, shifting would not help dilute pollutants effectively. Generally, a design involving a double short-catcher in a parallel arrangement is the most recommended, with the smallest IF, i.e., 61% of that in the tunnel without wind catchers (0.36 ppm). Full article
(This article belongs to the Special Issue Recent Advances in Urban Ventilation Assessment and Flow Modelling)
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Open AccessArticle On Street-Canyon Flow Dynamics: Advanced Validation of LES by Time-Resolved PIV
Atmosphere 2018, 9(5), 161; https://doi.org/10.3390/atmos9050161
Received: 29 January 2018 / Revised: 19 April 2018 / Accepted: 21 April 2018 / Published: 25 April 2018
Cited by 1 | PDF Full-text (9624 KB) | HTML Full-text | XML Full-text
Abstract
The advanced statistical techniques for qualitative and quantitative validation of Large Eddy Simulation (LES) of turbulent flow within and above a two-dimensional street canyon are presented. Time-resolved data from 3D LES are compared with those obtained from time-resolved 2D Particle Image Velocimetry (PIV)
[...] Read more.
The advanced statistical techniques for qualitative and quantitative validation of Large Eddy Simulation (LES) of turbulent flow within and above a two-dimensional street canyon are presented. Time-resolved data from 3D LES are compared with those obtained from time-resolved 2D Particle Image Velocimetry (PIV) measurements. We have extended a standard validation approach based solely on time-mean statistics by a novel approach based on analyses of the intermittent flow dynamics. While the standard Hit rate validation metric indicates not so good agreement between compared values of both the streamwise and vertical velocity within the canyon canopy, the Fourier, quadrant and Proper Orthogonal Decomposition (POD) analyses demonstrate very good LES prediction of highly energetic and characteristic features in the flow. Using the quadrant analysis, we demonstrated similarity between the model and the experiment with respect to the typical shape of intensive sweep and ejection events and their frequency of appearance. These findings indicate that although the mean values predicted by the LES do not meet the criteria of all the standard validation metrics, the dominant coherent structures are simulated well. Full article
(This article belongs to the Special Issue Recent Advances in Urban Ventilation Assessment and Flow Modelling)
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Open AccessArticle New Surrogate Model for Wind Pressure Coefficients in a Schematic Urban Environment with a Regular Pattern
Atmosphere 2018, 9(3), 113; https://doi.org/10.3390/atmos9030113
Received: 30 January 2018 / Revised: 11 March 2018 / Accepted: 16 March 2018 / Published: 19 March 2018
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Abstract
Natural ventilation and the use of fans are recognized as sustainable design strategies to reduce energy use while reaching thermal comfort. A big challenge for designers is to predict ventilation rates of buildings in dense urban areas. One significant factor for calculating the
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Natural ventilation and the use of fans are recognized as sustainable design strategies to reduce energy use while reaching thermal comfort. A big challenge for designers is to predict ventilation rates of buildings in dense urban areas. One significant factor for calculating the ventilation rate is the wind pressure coefficient (Cp). Cp values can be obtained at a high cost, via real measurements, wind tunnel experiments, or high computational effort via computational fluid dynamic (CFD) simulation. A fast surrogate model to predict Cp for a schematic urban environment is required for the integration in building performance simulations. There are well-known surrogate models for Cp. The average surface pressure coefficient model integrated in EnergyPlus considers only a box-shaped building, without surrounding buildings. CpCalc, a surrogate model for Cp, considers only one height of neighbouring buildings. The Toegepast Natuurwetenschappelijk Onderzoek (TNO) Cp Generator model was available via web interface, and could include several box-shaped buildings in the surrounding area. These models are complex for fast integration in a natural ventilation simulation. For optimization processes, with thousands of simulation runs, speed is even more essential. Our study proposes a new surrogate model for Cp estimation based on data obtained from the TNO CP Generator model. The new model considers the effect of different neighbouring buildings in a simplified urban configuration, with an orthogonal street pattern, box-shaped buildings, and repetitive dimensions. The developed surrogate model is fast, and can easily be integrated in a dynamic energy simulation tool like EnergyPlus for optimization of natural ventilation in the urban areas. Full article
(This article belongs to the Special Issue Recent Advances in Urban Ventilation Assessment and Flow Modelling)
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Open AccessArticle Optimisation of Heat Loss through Ventilation for Residential Buildings
Atmosphere 2018, 9(3), 95; https://doi.org/10.3390/atmos9030095
Received: 28 January 2018 / Revised: 5 March 2018 / Accepted: 6 March 2018 / Published: 8 March 2018
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Abstract
This study presents the results of research on heat loss from various types of residential buildings through ventilation systems. Experimental research was done to analyse the effectiveness of ventilation systems of different types and determine the parameters of air discharged via the ventilation
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This study presents the results of research on heat loss from various types of residential buildings through ventilation systems. Experimental research was done to analyse the effectiveness of ventilation systems of different types and determine the parameters of air discharged via the ventilation ducts. A model of heat loss from the discharge of exhaust air outside through air ducts has since been developed. Experiments were conducted on three experimental systems of building ventilation: gravitational, mechanical, and supply-exhaust ventilation systems with heat recovery. The proposed model dependencies were used to chart the daily fluctuations of the optimum multiplicity of air exchange for precise control of the parameters of mechanical ventilation systems in residential buildings. This study proves that natural ventilation in residential buildings fulfils its function only by increasing the air flow into the building, and that this incurs significant heat loss from buildings during the heating season. Full article
(This article belongs to the Special Issue Recent Advances in Urban Ventilation Assessment and Flow Modelling)
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Open AccessArticle On-Road Air Quality Associated with Traffic Composition and Street-Canyon Ventilation: Mobile Monitoring and CFD Modeling
Atmosphere 2018, 9(3), 92; https://doi.org/10.3390/atmos9030092
Received: 1 February 2018 / Revised: 24 February 2018 / Accepted: 24 February 2018 / Published: 2 March 2018
Cited by 2 | PDF Full-text (2908 KB) | HTML Full-text | XML Full-text
Abstract
Mobile monitoring and computational fluid dynamics (CFD) modeling are complementary methods to examine spatio-temporal variations of air pollutant concentrations at high resolutions in urban areas. We measured nitrogen oxides (NOx), black carbon (BC), particle-bound polycyclic aromatic hydrocarbons (pPAH), and particle number
[...] Read more.
Mobile monitoring and computational fluid dynamics (CFD) modeling are complementary methods to examine spatio-temporal variations of air pollutant concentrations at high resolutions in urban areas. We measured nitrogen oxides (NOx), black carbon (BC), particle-bound polycyclic aromatic hydrocarbons (pPAH), and particle number (PN) concentrations in a central business district using a mobile laboratory. The analysis of correlations between the measured concentrations and traffic volumes demonstrate that high emitting vehicles (HEVs) are deterministically responsible for poor air quality in the street canyon. The determination coefficient (R2) with the HEV traffic volume is the largest for the pPAH concentration (0.79). The measured NOx and pPAH concentrations at a signalized intersection are higher than those on a road between two intersections by 24% and 25%, respectively. The CFD modeling results reveal that the signalized intersection plays a role in increasing on-road concentrations due to accelerating and idling vehicles (i.e., emission process), but also plays a countervailing role in decreasing on-road concentrations due to lateral ventilation of emitted pollutants (i.e., dispersion process). It is suggested that the number of HEVs and street-canyon ventilation, especially near a signalized intersection, need to be controlled to mitigate poor air quality in a central business district of a megacity. Full article
(This article belongs to the Special Issue Recent Advances in Urban Ventilation Assessment and Flow Modelling)
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Open AccessArticle Impacts of Traffic Tidal Flow on Pollutant Dispersion in a Non-Uniform Urban Street Canyon
Atmosphere 2018, 9(3), 82; https://doi.org/10.3390/atmos9030082
Received: 5 January 2018 / Revised: 13 February 2018 / Accepted: 22 February 2018 / Published: 25 February 2018
Cited by 3 | PDF Full-text (4941 KB) | HTML Full-text | XML Full-text
Abstract
A three-dimensional geometrical model was established based on a section of street canyons in the 2nd Ring Road of Wuhan, China, and a mathematical model describing the fluid flow and pollutant dispersion characteristics in the street canyon was developed. The effect of traffic
[...] Read more.
A three-dimensional geometrical model was established based on a section of street canyons in the 2nd Ring Road of Wuhan, China, and a mathematical model describing the fluid flow and pollutant dispersion characteristics in the street canyon was developed. The effect of traffic tidal flow was investigated based on the measurement results of the passing vehicles as the pollution source of the CFD method and on the spatial distribution of pollutants under various ambient crosswinds. Numerical investigation results indicated that: (i) in this three-dimensional asymmetrical shallow street canyon, if the pollution source followed a non-uniform distribution due to the traffic tidal flow and the wind flow was perpendicular to the street, a leeward side source intensity stronger than the windward side intensity would cause an expansion of the pollution space even if the total source in the street is equal. When the ambient wind speed is 3 m/s, the pollutant source intensity near the leeward side that is stronger than that near the windward side (R = 2, R = 3, and R = 5) leads to an increased average concentration of CO at pedestrian breathing height by 26%, 37%, and 41%, respectively. (R is the ratio parameter of the left side pollution source and the right side pollution source); (ii) However, this feature will become less significant with increasing wind speeds and changes of wind direction; (iii) the pollution source intensity exerted a decisive influence on the pollutant level in the street canyon. With the decrease of the pollution source intensity, the pollutant concentration decreased proportionally. Full article
(This article belongs to the Special Issue Recent Advances in Urban Ventilation Assessment and Flow Modelling)
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Open AccessArticle Ventilation and Air Quality in City Blocks Using Large-Eddy Simulation—Urban Planning Perspective
Atmosphere 2018, 9(2), 65; https://doi.org/10.3390/atmos9020065
Received: 2 January 2018 / Revised: 9 February 2018 / Accepted: 11 February 2018 / Published: 13 February 2018
Cited by 3 | PDF Full-text (28890 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Buildings and vegetation alter the wind and pollutant transport in urban environments. This comparative study investigates the role of orientation and shape of perimeter blocks on the dispersion and ventilation of traffic-related air pollutants, and the street-level concentrations along a planned city boulevard.
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Buildings and vegetation alter the wind and pollutant transport in urban environments. This comparative study investigates the role of orientation and shape of perimeter blocks on the dispersion and ventilation of traffic-related air pollutants, and the street-level concentrations along a planned city boulevard. A large-eddy simulation (LES) model PALM is employed over a highly detailed representation of the urban domain including street trees and forested areas. Air pollutants are represented by massless and passive particles (non-reactive gases), which are released with traffic-related emission rates. High-resolution simulations for four different city-block-structures are conducted over a 8.2 km 2 domain under two contrasting inflow conditions with neutral and stable atmospheric stratification corresponding the general and wintry meteorological conditions. Variation in building height together with multiple cross streets along the boulevard improves ventilation, resulting in 7–9% lower mean concentrations at pedestrian level. The impact of smaller scale variability in building shape was negligible. Street trees further complicate the flow and dispersion. Notwithstanding the surface roughness, atmospheric stability controls the concentration levels with higher values under stably stratified inflow. Little traffic emissions are transported to courtyards. The results provide urban planners direct information to reduce air pollution by proper structural layout of perimeter blocks. Full article
(This article belongs to the Special Issue Recent Advances in Urban Ventilation Assessment and Flow Modelling)
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Open AccessArticle Prediction of Wind Environment and Indoor/Outdoor Relationships for PM2.5 in Different Building–Tree Grouping Patterns
Atmosphere 2018, 9(2), 39; https://doi.org/10.3390/atmos9020039
Received: 26 October 2017 / Revised: 9 January 2018 / Accepted: 22 January 2018 / Published: 24 January 2018
Cited by 4 | PDF Full-text (9532 KB) | HTML Full-text | XML Full-text
Abstract
Airflow behavior and indoor/outdoor PM2.5 dispersion in different building–tree grouping patterns depend significantly on the building–tree layouts and orientation towards the prevailing wind. By using a standard k-ε model and a revised generalized drift flux model, this study evaluated airflow fields and
[...] Read more.
Airflow behavior and indoor/outdoor PM2.5 dispersion in different building–tree grouping patterns depend significantly on the building–tree layouts and orientation towards the prevailing wind. By using a standard k-ε model and a revised generalized drift flux model, this study evaluated airflow fields and indoor/outdoor relationships for PM2.5 resulting from partly wind-induced natural ventilation in four hypothetical building–tree grouping patterns. Results showed that: (1) Patterns provide a variety of natural ventilation potential that relies on the wind influence, and buildings that deflect wind on the windward facade and separate airflow on the leeward facade have better ventilation potential; (2) Patterns where buildings and trees form a central space and a windward opening side towards the prevailing wind offer the best ventilation conditions; (3) Under the assumption that transported pollution sources are diluted through the inlet, the aerodynamics and deposition effects of trees cause the lower floors of a multi-storey building to be exposed to lower PM2.5 compared with upper floors, and lower indoor PM2.5 values were found close to the tree canopy; (4) Wind pressure differences across each flat showed a poor correlation (R2 = 0.059), with indoor PM2.5 concentrations; and (5) Patterns with the long facade of buildings and trees perpendicular to the prevailing wind have the lowest indoor PM2.5 concentrations. Full article
(This article belongs to the Special Issue Recent Advances in Urban Ventilation Assessment and Flow Modelling)
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Open AccessArticle Source Apportionment and Data Assimilation in Urban Air Quality Modelling for NO2: The Lyon Case Study
Atmosphere 2018, 9(1), 8; https://doi.org/10.3390/atmos9010008
Received: 7 September 2017 / Revised: 17 December 2017 / Accepted: 18 December 2017 / Published: 1 January 2018
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Abstract
Developing effective strategies for reducing the atmospheric pollutant concentrations below regulatory threshold levels requires identifying the main origins/sources of air pollution. This can be achieved by implementing so called source apportionment methods in atmospheric dispersion models. This study presents the results of a
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Developing effective strategies for reducing the atmospheric pollutant concentrations below regulatory threshold levels requires identifying the main origins/sources of air pollution. This can be achieved by implementing so called source apportionment methods in atmospheric dispersion models. This study presents the results of a source apportionment module implemented in the SIRANE urban air-quality model. This module uses the tagged species approach and includes two methods, named SA-NO and SA-NOX, in order to evaluate the sources’ contributions to the NO 2 concentrations in air. We also present results of a data assimilation method, named SALS, that uses the source apportionment estimates to improve the accuracy of the SIRANE model results. The source apportionment module and the assimilation method have been tested on a real case study (the urban agglomeration of Lyon, France, for the year 2008) focusing on the NO 2 emissions and concentrations. Results of the source apportionment with the SA-NO and SA-NOX models are similar. Both models show that traffic is the main cause of NO 2 air pollution in the studied area. Results of the SALS data assimilation method highlights its ability in improving the predictions of an urban atmospheric models. Full article
(This article belongs to the Special Issue Recent Advances in Urban Ventilation Assessment and Flow Modelling)
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Open AccessArticle Inter-Building Effect and Its Relation with Highly Reflective Envelopes on Building Energy Use: Case Study for Cities of Japan
Atmosphere 2017, 8(11), 211; https://doi.org/10.3390/atmos8110211
Received: 19 September 2017 / Revised: 26 October 2017 / Accepted: 27 October 2017 / Published: 28 October 2017
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Abstract
The built environment with respect to building envelope designs and the surrounding micro-environment significantly affects building energy use. The influence of the inter-building effect (IBE) on building energy use cannot be ignored and thermal properties of building envelopes also largely affect building energy
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The built environment with respect to building envelope designs and the surrounding micro-environment significantly affects building energy use. The influence of the inter-building effect (IBE) on building energy use cannot be ignored and thermal properties of building envelopes also largely affect building energy use. In order to evaluate the influence of IBE and its relation with highly-reflective (HR) building envelopes on building energy use, the building energy use under three simulated scenarios was quantitatively analyzed using the building energy optimization software “BEopt” for five cities of Japan. Analysis indicated that when the simulated building is neighbored by other buildings, an envelope coated with HR material is more effective than lowly-reflective (LR) material to reduce building energy use. A simulated single building without surrounding buildings and a LR envelope has the highest building energy use among the three simulated scenarios. This study also showed the influence of IBE on building energy savings is stronger in cities with lower latitudes. Full article
(This article belongs to the Special Issue Recent Advances in Urban Ventilation Assessment and Flow Modelling)
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Open AccessArticle Assessment of Natural Ventilation Potential for Residential Buildings across Different Climate Zones in Australia
Atmosphere 2017, 8(9), 177; https://doi.org/10.3390/atmos8090177
Received: 3 September 2017 / Revised: 14 September 2017 / Accepted: 16 September 2017 / Published: 20 September 2017
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Abstract
In this study, the natural ventilation potential of residential buildings was numerically investigated based on a typical single-story house in the three most populous climate zones in Australia. Simulations using the commercial simulation software TRNSYS (Transient System Simulation Tool) were performed for all
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In this study, the natural ventilation potential of residential buildings was numerically investigated based on a typical single-story house in the three most populous climate zones in Australia. Simulations using the commercial simulation software TRNSYS (Transient System Simulation Tool) were performed for all seasons in three representative cities, i.e., Darwin for the hot humid summer and warm winter zone, Sydney for the mild temperate zone, and Melbourne for the cool temperate zone. A natural ventilation control strategy was generated by the rule-based decision-tree method based on the local climates. Natural ventilation hour (NVH) and satisfied natural ventilation hour (SNVH) were employed to evaluate the potential of natural ventilation in each city considering local climate and local indoor thermal comfort requirements, respectively. The numerical results revealed that natural ventilation potential was related to the local climate. The greatest natural ventilation potential for the case study building was observed in Darwin with an annual 4141 SNVH out of 4728 NVH, while the least natural ventilation potential was found in the Melbourne case. Moreover, summer and transition seasons (spring and autumn) were found to be the optimal periods to sustain indoor thermal comfort by utilising natural ventilation in Sydney and Melbourne. By contrast, natural ventilation was found applicable over the whole year in Darwin. In addition, the indoor operative temperature results demonstrated that indoor thermal comfort can be maintained only by utilising natural ventilation for all cases during the whole year, except for the non-natural ventilation periods in summer in Darwin and winter in Melbourne. These findings could improve the understanding of natural ventilation potential in different climates, and are beneficial for the climate-conscious design of residential buildings in Australia. Full article
(This article belongs to the Special Issue Recent Advances in Urban Ventilation Assessment and Flow Modelling)
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Open AccessArticle Impacts of Urban Layouts and Open Space on Urban Ventilation Evaluated by Concentration Decay Method
Atmosphere 2017, 8(9), 169; https://doi.org/10.3390/atmos8090169
Received: 20 August 2017 / Revised: 6 September 2017 / Accepted: 6 September 2017 / Published: 11 September 2017
Cited by 3 | PDF Full-text (30672 KB) | HTML Full-text | XML Full-text
Abstract
Previous researchers calculated air change rate per hour (ACH) in the urban canopy layers (UCL) by integrating the normal component of air mean velocity (convection) and fluctuation velocity (turbulent diffusions) across UCL boundaries. However they are usually greater than the actual
[...] Read more.
Previous researchers calculated air change rate per hour (ACH) in the urban canopy layers (UCL) by integrating the normal component of air mean velocity (convection) and fluctuation velocity (turbulent diffusions) across UCL boundaries. However they are usually greater than the actual ACH induced by flow rates flushing UCL and never returning again. As a novelty, this paper aims to verify the exponential concentration decay history occurring in UCL models and applies the concentration decay method to assess the actual UCL ACH and predict the urban age of air at various points. Computational fluid dynamic (CFD) simulations with the standard k-ε models are successfully validated by wind tunnel data. The typical street-scale UCL models are studied under neutral atmospheric conditions. Larger urban size attains smaller ACH. For square overall urban form (Lx = Ly = 390 m), the parallel wind (θ = 0°) attains greater ACH than non-parallel wind (θ = 15°, 30°, 45°), but it experiences smaller ACH than the rectangular urban form (Lx = 570 m, Ly = 270 m) under most wind directions (θ = 30° to 90°). Open space increases ACH more effectively under oblique wind (θ = 15°, 30°, 45°) than parallel wind. Although further investigations are still required, this paper provides an effective approach to quantify the actual ACH in urban-like geometries. Full article
(This article belongs to the Special Issue Recent Advances in Urban Ventilation Assessment and Flow Modelling)
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Open AccessArticle Effects of Unstable Stratification on Ventilation in Hong Kong
Atmosphere 2017, 8(9), 168; https://doi.org/10.3390/atmos8090168
Received: 3 August 2017 / Revised: 24 August 2017 / Accepted: 6 September 2017 / Published: 8 September 2017
Cited by 4 | PDF Full-text (1408 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Ventilation in cities is crucial for the well being of their inhabitants. Therefore, local governments require air ventilation assessments (AVAs) prior to the construction of new buildings. In a standard AVA, however, only neutral stratification is considered, although diabatic and particularly unstable conditions
[...] Read more.
Ventilation in cities is crucial for the well being of their inhabitants. Therefore, local governments require air ventilation assessments (AVAs) prior to the construction of new buildings. In a standard AVA, however, only neutral stratification is considered, although diabatic and particularly unstable conditions may be observed more frequently in nature. The results presented here indicate significant changes in ventilation within most of the area of Kowloon City, Hong Kong, included in the study. A new definition for calculating ventilation was introduced, and used to compare the influence of buildings on ventilation under conditions of neutral and unstable stratification. The overall ventilation increased due to enhanced vertical mixing. In the vicinity of exposed buildings, however, ventilation was weaker for unstable stratification than for neutral stratification. The influence on ventilation by building parameters, such as the plan area index, was altered when unstable stratification was considered. Consequently, differences in stratification were shown to have marked effects on ventilation estimates, which should be taken into consideration in future AVAs. Full article
(This article belongs to the Special Issue Recent Advances in Urban Ventilation Assessment and Flow Modelling)
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Open AccessArticle Numerical Study on the Urban Ventilation in Regulating Microclimate and Pollutant Dispersion in Urban Street Canyon: A Case Study of Nanjing New Region, China
Atmosphere 2017, 8(9), 164; https://doi.org/10.3390/atmos8090164
Received: 30 July 2017 / Revised: 26 August 2017 / Accepted: 26 August 2017 / Published: 29 August 2017
Cited by 2 | PDF Full-text (4466 KB) | HTML Full-text | XML Full-text
Abstract
Urban ventilation plays an important role in regulating city climate and air quality. A numerical study was conducted to explore the ventilation effectiveness on the microclimate and pollutant removal in the urban street canyon based on the rebuilt Southern New Town region in
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Urban ventilation plays an important role in regulating city climate and air quality. A numerical study was conducted to explore the ventilation effectiveness on the microclimate and pollutant removal in the urban street canyon based on the rebuilt Southern New Town region in Nanjing, China. The RNG k ε turbulence model in the computational fluid dynamics (CFD) was employed to study the street canyon under parallel and perpendicular wind directions, respectively. Velocity inside of the street canyon and temperature on the building envelopes were obtained. A novel pressure coefficient was defined, and three methods were applied to evaluate the urban ventilation effectiveness. Results revealed that there was little comfort difference for the human body under two ventilation patterns in the street canyon. Air stagnation occurred easily in dense building clusters, especially under the perpendicular wind direction. In addition, large pressure coefficients ( C P > 1 ) appeared at the windward region, contributing to promising ventilation. The air age was introduced to evaluate the “freshness” of the air in the street canyon and illustrated the ventilation effectiveness on the pollutant removal. It was found that the young air distributed where the corresponding ventilation was favorable and the wind speed was large. The results from this study can be useful in further city renovation for the street canyon construction and municipal planning. Full article
(This article belongs to the Special Issue Recent Advances in Urban Ventilation Assessment and Flow Modelling)
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Open AccessArticle Pedestrian-Level Urban Wind Flow Enhancement with Wind Catchers
Atmosphere 2017, 8(9), 159; https://doi.org/10.3390/atmos8090159
Received: 10 July 2017 / Revised: 3 August 2017 / Accepted: 22 August 2017 / Published: 25 August 2017
Cited by 5 | PDF Full-text (4072 KB) | HTML Full-text | XML Full-text
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Dense urban areas restrict air movement, causing airflow in urban street canyons to be much lower than the flow above buildings. Boosting near-ground wind speed can enhance thermal comfort in warm climates by increasing skin convective heat transfer. We explored the potential of
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Dense urban areas restrict air movement, causing airflow in urban street canyons to be much lower than the flow above buildings. Boosting near-ground wind speed can enhance thermal comfort in warm climates by increasing skin convective heat transfer. We explored the potential of a wind catcher to direct atmospheric wind into urban street canyons. We arranged scaled-down models of buildings with a wind catcher prototype in a water channel to simulate flow across two-dimensional urban street canyons. Velocity profiles were measured with Acoustic Doppler Velocimeters. Experiments showed that a wind catcher enhances pedestrian-level wind speed in the target canyon by 2.5 times. The flow enhancement is local to the target canyon with little effect in other canyons. With reversed flow direction, a “reversed wind catcher” has no effect in the target canyon but reduces the flow in the immediate downstream canyon. The reversed wind catcher exhibits a similar blockage effect of a tall building amid an array of lower buildings. Next, we validated Computational Fluid Dynamics (CFD) simulations of all cases with experiments and extended the study to reveal impacts on three-dimensional ensembles of buildings. A wind catcher with closed sidewalls enhances maximum pedestrian-level wind speed in three-dimensional canyons by four times. Our results encourage better designs of wind catchers to increase wind speed in targeted areas. Full article
(This article belongs to the Special Issue Recent Advances in Urban Ventilation Assessment and Flow Modelling)
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Open AccessArticle The Impact of Planting Trees on NOx Concentrations: The Case of the Plaza de la Cruz Neighborhood in Pamplona (Spain)
Atmosphere 2017, 8(7), 131; https://doi.org/10.3390/atmos8070131
Received: 4 May 2017 / Revised: 19 July 2017 / Accepted: 20 July 2017 / Published: 22 July 2017
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Abstract
In this paper, the role of trees on airborne pollutant dispersion in a real neighborhood in Pamplona (Spain) is discussed. A Computational Fluid Dynamics (CFD) model is employed and evaluated against concentrations measured during the last part of winter season at a monitoring
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In this paper, the role of trees on airborne pollutant dispersion in a real neighborhood in Pamplona (Spain) is discussed. A Computational Fluid Dynamics (CFD) model is employed and evaluated against concentrations measured during the last part of winter season at a monitoring station located in the study area. Aerodynamic and deposition effects of trees are jointly considered, which has only been done in few recent studies. Specifically, the impact on NOx concentration of: (a) tree-foliage; and (b) introducing new vegetation in a tree-free street is analyzed considering several deposition velocities and Leaf Area Densities (LAD) to model deciduous and evergreen vegetation. Results show that the higher the LAD, the higher the deposition (concentration reduction) and the blocking aerodynamic effect (concentration increase). Regardless of foliage or deposition rates, results suggest the predominance of aerodynamic effects which induce concentration increases up to a maximum of 7.2%, while deposition induces concentration decreases up to a maximum of 6.9%. The inclusion of new trees in one street modifies the distribution of pollutant, not only in that street, but also in nearby locations with concentration increase or decrease. This finding suggests that planting trees in street with traffic as an air pollution reduction strategy seems to be not appropriate in general, highlighting the necessity of ad hoc studies for each particular case to select the suitable location of new vegetation. Full article
(This article belongs to the Special Issue Recent Advances in Urban Ventilation Assessment and Flow Modelling)
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Open AccessArticle Street-Level Ventilation in Hypothetical Urban Areas
Atmosphere 2017, 8(7), 124; https://doi.org/10.3390/atmos8070124
Received: 11 May 2017 / Revised: 5 July 2017 / Accepted: 10 July 2017 / Published: 16 July 2017
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Abstract
Street-level ventilation is often weakened by the surrounding high-rise buildings. A thorough understanding of the flows and turbulence over urban areas assists in improving urban air quality as well as effectuating environmental management. In this paper, reduced-scale physical modeling in a wind tunnel
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Street-level ventilation is often weakened by the surrounding high-rise buildings. A thorough understanding of the flows and turbulence over urban areas assists in improving urban air quality as well as effectuating environmental management. In this paper, reduced-scale physical modeling in a wind tunnel is employed to examine the dynamics in hypothetical urban areas in the form of identical surface-mounted ribs in crossflows (two-dimensional scenarios) to enrich our fundamental understanding of the street-level ventilation mechanism. We critically compare the flow behaviors over rough surfaces with different aerodynamic resistance. It is found that the friction velocity u τ is appropriate for scaling the dynamics in the near-wall region but not the outer layer. The different freestream wind speeds ( U ) over rough surfaces suggest that the drag coefficient C d (= 2 u τ 2 / U 2 ) is able to characterize the turbulent transport processes over hypothetical urban areas. Linear regression shows that street-level ventilation, which is dominated by the turbulent component of the air change rate (ACH), is proportional to the square root of drag coefficient ACH C d 1 / 2 . This conceptual framework is then extended to formulate a new indicator, the vertical fluctuating velocity scale in the roughness sublayer (RSL) w ^ RSL , for breathability assessment over urban areas with diversified building height. Quadrant analyses and frequency spectra demonstrate that the turbulence is more inhomogeneous and the scales of vertical turbulence intensity w w ¯ 1 / 2 are larger over rougher surfaces, resulting in more efficient street-level ventilation. Full article
(This article belongs to the Special Issue Recent Advances in Urban Ventilation Assessment and Flow Modelling)
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Open AccessArticle Improving Residential Wind Environments by Understanding the Relationship between Building Arrangements and Outdoor Regional Ventilation
Atmosphere 2017, 8(6), 102; https://doi.org/10.3390/atmos8060102
Received: 23 April 2017 / Revised: 5 June 2017 / Accepted: 6 June 2017 / Published: 9 June 2017
Cited by 3 | PDF Full-text (9854 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
This paper explores the method of assessing regional spatial ventilation performance for the design of residential building arrangements at an operational level. Three ventilation efficiency (VE) indices, Net Escape Velocity (NEV), Visitation Frequency (VF) and spatial-mean Velocity Magnitude (VM), are adopted to quantify
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This paper explores the method of assessing regional spatial ventilation performance for the design of residential building arrangements at an operational level. Three ventilation efficiency (VE) indices, Net Escape Velocity (NEV), Visitation Frequency (VF) and spatial-mean Velocity Magnitude (VM), are adopted to quantify the influence of design variation on VE within different regional spaces. Computational Fluid Dynamics (CFD) method is applied to calculate VE indices mentioned above. Several residential building arrangement cases are set to discuss the effect of different building length, lateral spacing and layouts on four typical space patterns under wind directions oblique or perpendicular to the main (long) building facade. The simulation results prove that NEV, VF and VM are useful VE indices, which can reflect different features of flow pattern in studied regional domains. Preliminary parametric studies indicate that wind direction might be the most important factor for improving spatial ventilation. When the angle between main building facade and wind direction is more than 30°, ventilation of different exterior spaces could improve evidently. When wind direction is perpendicular to main building façade, decreasing building length can increase NEV of the middle space by 50%, while decreasing lateral spacing would decrease NEV of the intersection space by 35%. Full article
(This article belongs to the Special Issue Recent Advances in Urban Ventilation Assessment and Flow Modelling)
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Open AccessArticle Seasonal Changing Effect on Airflow and Pollutant Dispersion Characteristics in Urban Street Canyons
Atmosphere 2017, 8(3), 43; https://doi.org/10.3390/atmos8030043
Received: 8 January 2017 / Revised: 17 February 2017 / Accepted: 17 February 2017 / Published: 23 February 2017
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Abstract
In this study, the effect of seasonal variation on air flow and pollutant dispersion characteristics was numerically investigated. A three-dimensional urban canopy model with unit aspect ratio (H/D = 1) was used to calculate surface temperature distribution in the street
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In this study, the effect of seasonal variation on air flow and pollutant dispersion characteristics was numerically investigated. A three-dimensional urban canopy model with unit aspect ratio (H/D = 1) was used to calculate surface temperature distribution in the street canyon. Four representative time events (1000 LST, 1300 LST, 1600 LST and 2000 LST) during typical clear summer and winter days were selected to examine the air flow diurnal variation. The results revealed the seasonal variation significantly altered the street canyon microclimate. Compared with the street canyon surface temperature distribution in summer, the winter case showed a more evenly distributed surface temperature. In addition, the summer case showed greater daily temperature fluctuation than that of the winter case. Consequently, distinct pollutant dispersion patterns were observed between summer and winter scenarios, especially for the afternoon (1600 LST) and night (2000 LST) events. Among all studied time events, the pollutant removal performance of the morning (1000 LST) and the night (2000 LST) events were more sensitive to the seasonal variation. Lastly, limited natural ventilation performance was found during the summer morning and the winter night, which induced relatively high pollutant concentration along the pedestrian height level. Full article
(This article belongs to the Special Issue Recent Advances in Urban Ventilation Assessment and Flow Modelling)
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Open AccessReview Assessment of Indoor-Outdoor Particulate Matter Air Pollution: A Review
Atmosphere 2017, 8(8), 136; https://doi.org/10.3390/atmos8080136
Received: 9 June 2017 / Revised: 12 July 2017 / Accepted: 20 July 2017 / Published: 26 July 2017
Cited by 9 | PDF Full-text (1773 KB) | HTML Full-text | XML Full-text
Abstract
Background: Air pollution is a major global environmental risk factor. Since people spend most of their time indoors, the sole measure of outdoor concentrations is not sufficient to assess total exposure to air pollution. Therefore, the arising interest by the international community to
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Background: Air pollution is a major global environmental risk factor. Since people spend most of their time indoors, the sole measure of outdoor concentrations is not sufficient to assess total exposure to air pollution. Therefore, the arising interest by the international community to indoor-outdoor relationships has led to the development of various techniques for the study of emission and exchange parameters among ambient and non-ambient pollutants. However, a standardised method is still lacking due to the complex release and dispersion of pollutants and the site conditions among studies. Methods: This review attempts to fill this gap to some extent by focusing on the analysis of the variety of site-specific approaches for the assessment of particulate matter in work and life environments. Results: First, the main analogies and differences between indoor and outdoor particles emerging from several studies are briefly described. Commonly-used indicators, sampling methods, and other approaches are compared. Second, recommendations for further studies based on recent results in order to improve the assessment and management of those issues are provided. Conclusions: This review is a step towards a comprehensive understanding of indoor and outdoor exposures which may stimulate the development of innovative tools for further epidemiological and multidisciplinary research. Full article
(This article belongs to the Special Issue Recent Advances in Urban Ventilation Assessment and Flow Modelling)
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