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A COVID-19 outbreak occurred in May 2020 in a public housing building in Hong Kong - Luk Chuen House, located in Lek Yuen Estate. The horizontal cluster linked to the index case' flat (flat 812) remains to be explained. Computational fluid dynamics simulations were conducted to obtain the wind-pressure coefficients of each external opening on the eighth floor of the building. The data were then used in a multi-zone airflow model to estimate the airflow rate and aerosol concentration in the flats and corridors on that floor. Apart from flat 812 and corridors, the virus-laden aerosol concentrations in flats 811, 813, 815, 817 and 819 (opposite to flat 812, across the corridor) were the highest on the eighth floor. When the doors of flats 813 and 817 were opened by 20%, the hourly-averaged aerosol concentrations in these two flats were at least four times as high as those in flats 811, 815 and 819 during the index case's home hours or the suspected exposure period of secondary cases. Thus, the flats across the corridor that were immediately downstream from flat 812 were at the highest exposure risk under a prevailing easterly wind, especially when their doors or windows that connected to the corridor were open. Given that the floorplan and dimension of Luk Chuen House are similar to those of many hotels, our findings provide a probable explanation for COVID-19 outbreaks in quarantine hotels. Positive pressure and sufficient ventilation in the corridor would help to minimise such cross-corridor infections.

Warm and hot days account for most of the time in Hong Kong. Outdoor thermal comfort studies in Hong Kong should give its first consideration to warm and hot days. This study presents investigations about thermal comfort through 1600 human subject responses from the onsite survey with concurrent meteorological parameter measurements. Probit analysis was used for searching the thermal neutral range of Hong Kong residents in a year span. Logistic regression was used for locating the meteorological parameter ranges for thermal neutral and comfort conditions. It is shown that people had difficulties defining their actual thermal feelings near the thermal neutral status when being asked to use the nine-point thermal sensation scale. Obvious thermal adaptation effect for thermal neutral conditions were observed among Hong Kong residents over the seasons in a year. The transitional seasons had a wider thermal neutral range than that of winter and summer. Summer had the narrowest thermal neutral range. Wind and solar radiation had an interaction effect with air temperature in determining thermal sensation and thermal comfort. Wind can effectively offset the negative effect of solar radiation in summer when the air temperature was lower than 31 °C. The thermal comfort condition allowed a higher limit of solar radiation than the thermal neutral condition when the air temperature was lower than 31 °C. The investigations in this study provide some unique insights into the way to assess urban thermal comfort in the building design stage.

The appropriate selection of a turbulence model directly affects the prediction of pedestrian-level wind (PLW) around buildings. Delayed detached eddy simulation (DDES) model, has been reported to be able to predict airflow around a building as good as large eddy simulation (LES) does, but with a lower mesh requirement and much less computing time. This study aims to see if DDES model can perform similarly when simulating the wind flow around a building array. This hypothesis is tested by comparing wind velocities of DDES, LES, and a benchmark wind tunnel experiment. Sensitivity assessments of DDES model are conducted, including the mesh resolution and the choice of an unsteady Reynolds Averaged Navier-Stokes (URANS) model used in conjunction. The normalized minimal grid sizes (0.005 for the building array's windward side and 0.0025 for the lateral and leeward sides) and the unsteady k − ω shear stress transport (SST) model are the most economical and effective. Simulated results are further quantified using four validation indices. Specifically, the correlation coefficient R between the predicted mean velocities using DDES and LES is 0.90, which basically proves our hypothesis in the mean flow field; but DDES only takes 80.3% of the computing time using LES. The time histories and spectrums of instantaneous velocities are also analyzed, indicating that DDES performs the similar predictions as LES of the unsteady flow fluctuations, while it has the potential to save computing time and mesh numbers.

People's outdoor thermal sensation varies from that indoors. The highly asymmetric solar radiation and transient wind environment are the main causes. The University of California-Berkeley developed a multi-nodal human body thermal regulation model (the UCB model) to predict human thermal sensation and comfort in asymmetric and transient indoor environments. However, few studies compared its predictions with the survey responses outdoors. In this study, subjects' thermal sensations outdoors were surveyed and compared with the UCB model predictions. Meteorological parameters were monitored using a microclimate station, and over a thousand human subjects were surveyed. Results point out that subjects were highly sensitive to the changes in wind speed, especially under low-radiation conditions. However, the UCB model failed to predict such a high sensitivity. Besides, subjects had a higher tolerance to high air temperatures in outdoor environments when the solar radiation was acceptable, but the UCB model over-predicted the TSV (thermal sensation vote) in such conditions. Both the on-site results and the predictions by UCB model showed that subjects were more sensitive to wind speed in hotter environments while they were least sensitive to solar radiation in neutral thermal conditions. This study helps to reveal the potential of a multi-nodal thermal regulation model to address the asymmetric and transient features of outdoor environments and indicates the need to further refine the model for better quantitative prediction of outdoor thermal sensations.

With the development of the urban city, increasing attention has been paid to outdoor thermal comfort. In this paper, an analysis of the sensitivities of different factors, including the personal factors and physical parameters of the thermal environment was conducted. The results showed that there was a strong linear relationship between the Physiological Equivalent Temperature (PET) and operation temperature. When the operation temperature was lower than 32 °C, the effect of air velocity on the PET was positive. However, the effects of other factors, including relative humidity, clothing insulation, and metabolic rate, on the PET were insignificant. An exponential relationship was found between the UTCI and the operation temperature. The effect of air velocity change on the UTCI became weaker and weaker with the increase of operation temperature. Compared with the PET, the linear relationship between the UTCI and relative humidity was clearer. A field survey of thermal comfort carried out in Guangzhou University was used for the validation of the thermal comfort models. It was observed that the clothing insulation requirement increased with the decrease of air temperature in autumn. The variations in metabolic rate were also obvious, from 1met to 3.8 met. More than 70% of the people had been walking before they arrived at the survey locations. In addition, there were some differences in the neutral PET and UTCI temperature between the metabolic rates of 1.0–2.0 met and of 2.6 met. Meanwhile, models of MTSV against the PET and UTCI under different metabolic rates were established.

The growth of cities intensifies the urban heat island effect by obstructing and weakening the incoming wind and thus deteriorates thermal comfort in the pedestrian level. The elevated building design is believed to be able to create some localized comfort spots at precinct scale, but no researches on pedestrians' thermal perceptions in the area underneath an elevated building (UEB) have been reported. In this study, simultaneous on-site meteorological measurements and questionnaire surveys of 1107 human subjects were conducted in a university campus in Hong Kong. Three outdoor thermal comfort models, PET, UTCI and UC-Berkeley model, were compared. The survey results indicate that the UEB area is significantly (α = 0.05) more comfortable in hot weather without extra discomfort in cold weather. All three models outputs correlate well with the subjects' mean thermal sensation votes in linear regression (R2 ≈ 0.9). Yet, shifts in neutral indices (6.2 K, 5.8 K and 1.1 respectively for PET, UCTI and UC-Berkeley model) appeared when comparing the correlation results separately for the UEB areas and open areas, indicating that the impacts of solar radiation and wind or the lack of them on pedestrian's thermal comfort perceptions have not been well predicted by the three models. These investigations, on the one hand, characterize the benefits that elevated building designs have on the pedestrian-level microclimate and provide references and inspirations for urban planners to enhance pedestrian thermal comfort by altering building designs; on the other hand, indicate the need to refine the thermal comfort models for better outdoor thermal comfort assessment.

Wind flow turbulence is known to have a major influence on the pedestrian-level wind (PLW) environments, particularly around a building. The elevated design of a building, as a special feature, proved to improve pedestrian-level weak wind conditions in high-density cities. The present study aims to assess three turbulence models, the detached eddy simulation (DES), the steady-state RANS (SRANS), and the unsteady-state RANS (URANS), in their simulation of the PLW flow turbulence concerning wind gust. The simulated mean wind velocities around isolated buildings with and without an elevated design were compared with those obtained from a wind tunnel experiment. The effects of mesh resolution and inflow fluctuating algorithm on the performance of the DES model were thoroughly evaluated. The DES model can better reproduce the mean flow fields than the other two models. Finally, the unsteady fluctuations of wind flow around the buildings with and without the elevated design are analyzed in terms of instantaneous wind velocity, lift coefficient, energy spectral density, and turbulence intensity. The predicted lift coefficient and Strouhal number are approximately 0.01 and 0.09, respectively, which is consistent with what are reported in the literature. Modifications of the frequency of vortex shedding, periodical wind flow pattern, and the normalized wind gust flow fields around the two types of buildings are compared in detail. The work reveals that transient turbulent flow pattern can be reasonably obtained with the DES model, indicating the potential of using the DES for PLW gust assessments in urban planning.

City residents wish to have pleasant experience in outdoor space, which are often impeded by thermally uncomfortable conditions, particularly in hot and humid summer. Lift-up design can provide comfortable microclimate in summer but the effects of lift-up design on thermal comfort in a built-up environment have not been systematically studied. This paper aims to investigate the effects of lift-up design on outdoor thermal comfort comprehensively, as well as the effects on pedestrian level wind environment. The thermal comfort assessments are carried out by using a proposed integrated method, which combines wind tunnel tests and on-site monitoring to calculate Physiologically Equivalent Temperature (PET) values. The Hong Kong Polytechnic University (HKPolyU) campus is selected as study area. The investigation mainly focuses on summer and winter seasons. Four typical days in a year were chosen to carry out on-site monitoring for obtaining environmental parameters. This study demonstrates that the proposed integrated method can be used to predict outdoor thermal comfort. Results also show that lift-up design can effectively improve pedestrian level wind environment and thermal comfort. Moreover, lift-up design can provide a comfortable microclimate in summer while not cause strong cold stress in winter. These findings provide solid evidence bases to city planners and architects of available options for creating pleasant outdoor microclimate in precinct planning.

Owing to the void space at lower heights, lift-up buildings have high building permeability at ground level and subsequently improve the air circulation in congested urban areas. Despite this advantage, the lift-up design has been sparsely adopted for buildings in urban areas partly because of the lack of understanding of the combined effects of building dimensions and lift-up design on the surrounding pedestrian level wind (PLW) field. Therefore, this study aims to investigate the influence of lift-up buildings with different aspect ratios (height/width) on the surrounding PLW field and pedestrian wind comfort level. Five lift-up buildings with aspect ratios 4:1 to 0.5:1 were tested in a boundary layer wind tunnel and results were compared with those of five buildings with similar dimensions but without lift-up design. The results reveal a strong dependence of the maximum wind speed in lift-up areas with building height, which results subsequently a small area of acceptable wind conditions near tall and slender lift-up buildings. Lift-up designs adopted for short and wide buildings produce larger areas of pedestrian wind comfort. The central cores modified with corner modifications are effective in increasing the pedestrian wind comfort in the lift-up area of tall and slender buildings., Highlights • Tall and slender buildings generate high-speed wind flows in lift-up areas. • Modified corners of lift-up cores improve the pedestrian wind comfort. • Lift-up cores with modified corners are recommended for tall and slender buildings.

Modern megacities are teeming with closely-spaced tall buildings, which limit air circulation at the pedestrian level. The resultant lack of air circulation creates poorly ventilated areas with accumulated air pollutants and thermal discomfort in the summer. To improve air circulation at the pedestrian level, buildings may be designed to have a ‘lift-up’ shape, in which the main structure is supported by a central core, columns or shear walls. However, a lack of knowledge on the influence of the ‘lift-up’ design on the surrounding wind environment limits the use of ‘lift-up’ buildings. This study aims to investigate the influence of ‘lift-up’ buildings and their dimensions on the pedestrian-level wind environments using wind tunnel tests. A parametric study was undertaken by using 9 ‘lift-up’ building models with different core heights and widths. The results were compared with the surrounding wind environment of a control building with similar dimensions. The results reveal that the ‘lift-up’ core height is the most influential parameter and governs the area and magnitude of high and low wind speed zones around such buildings. Based on wind tunnel test results and a selected comfort criterion, appropriate core dimensions could be selected to have acceptable wind conditions near lift-up buildings., Highlights • The effects of ‘lift-up’ buildings and their dimensions on the surrounding wind environments are studied. • The ‘lift-up’ core height is the most important parameter of a ‘lift-up’ design. • Appropriate lift-up dimensions are selected by combining wind speed data with a predetermined wind comfort criterion.

The pedestrian level wind environment is seriously deteriorated by moderated local wind flow in a densely built-up subtropical city like Hong Kong. In order to improve the weak wind condition, the lift-up design has been used for some time. However, there is a lack of understanding and quantitative assessment of its modification on the pedestrian level wind comfort around different building configurations under different wind directions. This paper aims to study the effects of lift-up design in four common building configurations on the wind comfort via computational fluid dynamics (CFD) simulations. The turbulence model and numerical method are firstly validated by comparing the simulated wind flow data with the wind tunnel test results. The validated model is then utilized to simulate the four building configurations, including the “─”, “L”, “U” and “□” shaped buildings. The mean wind velocity ratio ( MVR ) and mean wind velocity change ratio ( Δ MVR ) are employed to identify the wind comfort and to quantitatively evaluate the improvements due to the lift-up design. Results show that the lift-up design can improve the wind comfort in building surroundings and its influence is highly dependent on the incident wind direction. Specifically, the wind comfort is better under the oblique wind direction than the other two wind directions. These findings can provide us a better understanding of the lift-up design and will be helpful in better precinct planning.

This study aims at further investigating the respiratory infectious diseases transmission in typical high-rise residential (HRR) environments, and at developing reliable CFD modeling method. The inter-building dispersion under wind effect was focused on and the cross-infection risk was assessed. The URANS model and DES model were compared, and the representation of surroundings was evaluated to improve the prediction of airflow and pollutant dispersion among a group of buildings. The DES model can better reproduce unsteady fluctuations of airflow around the buildings, and can accurately predict the frequency of vortex shedding. The predicted Strouhal number is approximately 0.15, which is consistent with the reported value in literature, whereas the URANS model fails to reproduce the whole features of unsteady airflow and significantly under-estimates the vortex shedding frequency. Ignoring the surrounding buildings in the simulation will significantly over-estimate the downward dispersion and over-estimate the risks in lower heights. The tracer gas concentrations near the downstream buildings are four orders lower than the concentration in the index/source unit, but only one order lower than the concentration in the leeward side and on the roof of the index building, and therefore the risk is comparable to that of intra-building dispersion within the index building. The tracer gas can diffuse to a long distance with slow concentration decay in empty areas. The cross-infection risk of inter-building dispersion should not be overlooked, especially when a super infector with high pathogen generation rate exists.

The utilization of outdoor spaces is affected by its thermal environment, and wind, which determines the convective heat loss from the human body, is one of the most influencing factors of thermal comfort. There is a lack of study of the correlation between the convective heat loss and the wind turbulence at the pedestrian height. In this study, we measured the wind speed and turbulence characteristics within the first 2-m above ground level at three city green-spaces surrounded by buildings of different heights and densities. To accurately calculate the turbulence intensity from the time-series of wind velocity data, the synoptic trend was removed, otherwise it may cause over-estimation of the 10-min average turbulence intensity by 30–60%. The present onsite wind measurements show that the average turbulence intensity ranges from 22 to 48%, and the turbulence scale is within 1.2–12.0 m. Since wind effect on convective heat transfer is mediated through its impact on the convective heat transfer coefficient, which is often obtained experimentally in a controlled environment, the onsite wind data from this study provides a reference for the design of the experimental conditions.

Viable aerosols in the airflow may increase the risk of occupants contracting diseases. Natural ventilation is common in buildings and is accompanied by re-entry airflow during the ventilation process. If the re-entry airflow contains toxic or infectious species, it may cause potential harm to residents. One of the Covid-19 outbreaks occurred in a public residential building at Luk Chuen House (LC-House) in Hong Kong. It is highly suspected that the outbreak of the disease is related to the re-entry airflow. The study attempts to explain and discuss possible causes of the outbreak. In order to understand the impact of airflow on the outbreak, a public residential building similar to LC-House was used in the study. Two measurements M − I and M − II with the same settings were conducted for a sampling unit in the corridor under low and strong wind conditions respectively. The sampling unit and the tracer gas carbon dioxide (CO2) were used to simulate the index unit and infectious contaminated airflow respectively. The CO2 concentrations of the unit and corridor were measured simultaneously. Two models of Traditional Single-zone model (TSZ-model) and New Dual-zone model (NDZ-model) were used in the analysis. By comparing the ACH values obtained from the two models, it is indicated that the re-entry airflow of the unit is related to the corridor wind speeds and this provides a reasonable explanation for the outbreak in LC-House, and believes that the results can help understand the recent frequent cluster outbreaks in other residential buildings.

Taking into account outdoor thermal comfort in the urban design stage can potentially enhance the livability of a city. This study aims to demonstrate an outdoor thermal comfort prediction method using measured thermal parameters and simulated wind velocities. This is done by first comparing the CFD simulation results of wind velocities around a single building with and without elevated design with those obtained from a wind tunnel experiment, and two turbulence models, the Delayed Detached Eddy Simulation (DDES) and the RNG k-e model, were assessed. The mean velocity field obtained using DDES model has better agreement with the wind tunnel measurements, especially in the wake region and at the open space beneath the elevated building. It is shown that the building elevation modified the mean flow pattern around a building. Then the potential impact on pedestrian thermal comfort was assessed using a simplified method by combining the predicted wind velocity and the on-site monitored radiant and air temperatures and air humidity on two summer days. It is revealed that the elevated design improves the thermal comfort only in the limited neighboring area, but that the open space underneath the elevated building provides much better thermal comfort in the summer conditions. The work demonstrates that CFD simulation of wind conditions can be used to assess outdoor thermal comfort in the planning stage without being coupled with thermal simulation.

Single-sided natural ventilation is an energy efficient ventilation strategy that could provide satisfactory indoor air quality and thermal comfort. However, one of its possible negative influences is the cross-infection between households due to the two-way airflow. The present study aims at assessing the efficacy of mechanical exhaust (ME) devices to eliminate this possible cross-infection. CFD method was employed to simulate the buoyancy driven single-sided natural ventilation and the cross-contamination. Different occupant behaviour scenarios, such as ME-on centrally or ME-on individually, were compared with the no-ME case. It is found that mechanical exhaust could reduce the outflow of indoor air and increase the inflow of fresh air. However, the weakened outflow tends to be more attached to the facade and the re-entry risk may be increased. As the exhaust rate is large enough, the two-way airflow will turn into one-way inflow, and accordingly the vertical cross-household infection can be avoided. With ME-on in both floors, a low exhaust rate of 5 h −1 could reduce the presence of the tracer from the lower floor in the upper floor by an order of magnitude. But if the ME is on only in one of the two floors, the re-entry of outflow to the upper floor may be aggravated at some specific exhaust rate. Therefore, in epidemic seasons, appealing residents to switch on their individual exhaust fans, or alternatively switching on a central exhaust system is recommended. The results will contribute to the control of airborne transmission infectious diseases in high-rise residential buildings.

The choice of proper turbulence models in computational fluid dynamics is still a challenging issue for accurately predicting outdoor microclimate and thermal comfort conditions in urban planning. This study compared the performances of the Steady Reynolds Averaged Navier–Stokes (SRANS) RNG k-e , Large Eddy Simulation (LES) and Detached Eddy Simulation (DES) modeling approaches in simulating the wind flow around an isolated building (with a 1:1:2 shape). The effects of the computational parameters were analyzed, including the grid resolution for all cases, and the discretization time step ( Δt ) and non-dimensional sampling time ( t * ) for the LES and DES cases. The results of the LES and DES simulations were affected by the gradual decrease in Δt and increase in t * until the two parameters reached 0.005 s and 288, respectively. The mean velocity fields on the windward side of the building predicted by the three models were in good agreement with the wind tunnel results. However, the results of the LES and DES cases were in better agreement with the experimental results for the leeward and lateral regions in both vertical and horizontal planes. The DDES (Delayed Detached Eddy Simulation) and LES models predicted similar results in the wake region, but the DDES has a lower overall mesh requirement. It is encouraging that the DDES model provides not only the mean flow field, but also the instantaneous wind characteristics, which can be useful for more accurate analysis of outdoor wind and thermal comfort.

Urban residents are increasingly encouraged to go outside for recreational and relaxing purposes, which may improve personal health and reduce building energy consumption. Therefore, it is important to understand the heat transfer between human body and surrounding urban outdoor environments. This study aims to predict the convective heat loss from a human body subject to urban outdoor wind environments. Firstly, the effects of the wind velocity and turbulent conditions on the convective heat loss from human body are investigated through a computational thermal manikin model, which is validated against published experimental data. Subsequently, wind data from onsite measurements in the city of Sydney, Australia is used to predict human body's convective heat loss using numerically obtained empirical correlations. The present result shows that the convective heat loss of most body segments increases with increasing wind velocity and turbulent intensity and decreasing turbulence length scale. Empirical correlations for predicting the convective heat transfer coefficients as a function of the wind velocity, turbulent intensity and turbulence length scale are derived based on simple-geometry assumptions. It is found that, at a given wind velocity with the ranges of the turbulence conditions from the field measurements, the variations between the high and low values of the convective heat transfer coefficient can be up to 67%. The results of this study demonstrate the significance of capturing the turbulent wind conditions for accurately predicting heat loss for outdoor thermal comfort studies.

Wind tower is a traditional zero-energy natural ventilation device, which is capable of reducing building energy consumption and improving indoor environment. Many studies were conducted for its performance evaluation and design optimization, but most of them are more like underground applications. This paper aims to integrate the wind tower with single-sided natural ventilated house to arrange more desirable indoor air distribution. The ventilation behavior of the wind tower in a low-rise house was firstly compared with a common underground application. Then, effects of combining with different window configurations were investigated. CFD simulations were conducted using well validated numerical models. The results show that local wind environment must be well reproduced to accurately predict indoor airflow. Under the same incoming wind speed, the ventilation effectiveness of the wind tower in the low-rise house is 15%–40% lower than the underground application due to the effect of the separating flow above the roof. Optimizing the roof structure and slope to change the local flow field may improve the ventilation capability of the wind tower. When combining wind tower with different window configurations, setting a window on the windward wall is a more promising solution to improve cross-ventilation, since that the wind tower is in the negative pressure region above the roof. When the indoor temperature is higher than the outdoor, the exhaust wind tower will perform better due to the stack effect. The findings can provide practical implications for the performance evaluation and application of wind tower in contemporary house design.

The psychometric tool known as the thermal sensation scale has been extensively used in outdoor thermal comfort research. However, this one-dimensional descriptive scale was originally developed for indoor assessments and therefore has certain shortcomings in outdoor settings. The scale contains no affective information such as pleasure and it overlooks the dynamic wind and solar radiation fluxes outdoors. Accordingly, this study develops a six-dimensional semantic framework for outdoor thermal comfort assessments comprising four descriptive - ‘thermal sensation’, ‘humidity’, ‘wind’ and ‘solar radiation,’ plus two affective - ‘thermal pleasure’ and ‘thermal intensity’ dimensions. In Phase 1 an online questionnaire recruited 135 native English-speakers to place 76 climatic adjectives into this six-dimensional semantic space. Phase 2 launched a field study with another 22 subjects locating real-time outdoor thermal experiences in the same semantic space. They were then asked to select from a subset of the 76 climatic adjectives those that best described their right here-right-now thermal experience. Validation was then performed by comparing coordinates of the 31 most frequently chosen adjectives in Phase 2 with those assigned to them in Phase 1. Good correlations (R2 > 0.65) of adjectives' coordinates between the two research phases indicate consistency regarding which adjectives best describe specific scenarios, regardless of seasons, locations, or current exposures. The results emphasise that the thermal sensation scale inadequately characterises outdoor thermal comfort experiences. This study initiates the transition of biometeorological comfort research from crude unidimensional descriptive thermal sensation scale, towards a more nuanced, multi-dimensional descriptions of subjective thermal state.

The growing need for planning eco-cities is calling on a tool that can give better prediction of the thermal comfort conditions for a specific microclimate. A multi-nodal thermal regulation model can potentially factor in the impacts of the transient and asymmetric thermal conditions on human subjects. In this study, Human subjects were invited to experience various kinds of urban open spaces and to express their thermal feelings, while skin temperatures of 17 local body segments were measured. We tested the multi-nodal thermal regulation model developed by UC Berkeley by comparing its predictions of human body skin temperature, thermal sensation vote (TSV), and thermal comfort vote (TCV) with our onsite human subject measurements and questionnaire survey, in order to identify the causes of the errors between the prediction and measurements. Corresponding to the thermal neutral status, the field-measured data recorded wider local skin temperature ranges than the simulated ones. We proposed using a “null zone” instead of “set-point” in the thermal comfort model to accommodate the possible adaptation of human subjects to the highly fluctuating wind environment in open spaces. It was proposed that the forehead was counted as one of the dominant local body parts when defining the overall thermal sensation. The correlation coefficient R 2 between the prediction and the field measured TSV improved to 93.7% for the revised model from 76.2% of the original model.

Ongoing urbanization and urban densification are leading to an increasing number of tall buildings, giving rise to an increasingly complex urban morphology which, in turn, is complicating the pedestrian-level wind environment of urban areas. As a key climatic element determining pedestrian outdoor thermal comfort, wind is represented in most of the existing outdoor comfort models, but its effects have been oversimplified to date. This study aims to examine how wind velocity and turbulence intensity affect convective heat loss over a human body. A wind tunnel with a turbulence-grid is used to simulate outdoor wind flow with turbulence intensity ranging from 13% to 36%, and wind velocity from 0.7 m/s to 6.7 m/s. Forced convective heat loss for individual body segments have been measured on a thermal manikin using a constant skin temperature regulation mode. Results for unit effect confirm that convective heat loss increases with turbulence intensity, which prompts us to make explicit the turbulence intensity when calculating the heat loss from human body. Ignoring turbulence causes the impact of wind on pedestrian thermal sensation to be underestimated by up to 50%. Based on the present data, regression formula derived from regular geometry for predicting convective heat transfer coefficients has been expanded to serve individual body segments. Accounting for the effect of both wind velocity and turbulence intensity, the accuracy of convective heat loss calculations in outdoor thermal comfort research would be improved.

Residents wish to have outdoor spaces to enjoy walking, cycling, and other recreational activities, which are often hindered by the unfavorable thermal comfort conditions, especially in the summer. High building densities lower the average wind speed and this intensifies the urban heat island effects at city scale. The conscientious use of building morphology to create local thermal comfort zone at selected spots in a large precinct is becoming a pressing issue for sustainable urbanization. This paper is a proof of concept study via continuous monitoring of the pedestrian level winds and thermal parameters at two sample days in summer, which include instantaneous air temperature, globe temperature, wind speed and humidity. Three outdoor locations at an university campus are chosen and daytime thermal perceptions at the three sites were evaluated using PET (Physiological equivalent temperature). A PET based new index was defined, which is called the thermally-perceivable environmental parameter difference. By analyzing the simultaneous differences of radiant temperature, wind speed and air temperature between the monitored spots, it is shown that it was the wind speed and radiant temperature differences that were making significant differences in thermal comfort. This pilot study clearly indicates that wind amplification combined with shading effects can generate thermally comfortable conditions in the open ground floor beneath an elevated building, even on a sunny, hot summer day in a subtropical city. This finding helps to alert city planners of additional options available in precinct planning to encourage outdoor activities.

This study investigates the capability and accuracy of three Reynolds-Averaged Navier–Stokes (RANS) turbulence models, i.e. a Reynolds stress model (RSM), a RNG k-e model, and an SST k-ω model in the prediction of particle deposition in vertical and horizontal turbulent channel flows. The particle movement was simulated using a Lagrangian-based discrete random walk (DRW) model. The performances of the three RANS turbulence models with and without near-wall turbulence corrections were evaluated. A new modification method for turbulence kinetic energy was proposed for the RNG k-e model and the SST k-ω model. The results were compared with previous experimental data, empirical equation as well as simulation outcomes. It is found that the isotropic SST k-ω model and the RSM model can successfully predict the transition from the diffusion region to the inertia-moderated region. The RNG k-e model with near-wall modifications can also reflect the V-shape deposition curve although without modifications it greatly over-predicts the deposition velocity and shows an almost straight deposition line. For all of the three turbulence models, application of near-wall corrections is able to improve the simulation results to different extents.

Thermal comfort may be achieved more energy-efficiently in non-uniform thermal environments than in uniform ones, and such environments are also frequently transient, so developing a thermal comfort model to evaluate thermal comfort asymmetrical environments or transient conditions has being an hotspot of recent study. This paper first reviews several thermal comfort models that address local thermal sensations and attempts to distinguish these models by their advantages, limitations and suitable ranges of applications. Then, two typical thermal comfort models, the simple ISO 14505 standard method and the comprehensive UC Berkeley thermal comfort model (UCB model), were coupled to computational fluid dynamic (CFD) numerical simulation with different process to evaluate thermal environment of a small office. The results indicated that compared with the UCB model, the ISO 14505 index could be applied with caution as a convenient method to evaluate thermal comfort in non-uniform, overall thermally neutral environments.

The windcatcher system is a green architectural feature that uses natural ventilation to induce external airflow into residential buildings. This paper presents different configuration and ventilation strategies for the windcatcher to evaluate the performance of the system in relation to ventilation and indoor particle dispersion. A commercial computational fluid dynamic (CFD) code is used to evaluate the windcatcher’s performance using different numbers of louvers and louver lengths. The effects of buoyancy and window positions on the system’s performance are considered. The flow rate of air induced into the windcatcher is found to increase with the number of louver layers and the highest ventilation rate is reached when the louver length equates with the reference length. With respect to the buoyancy effect, the results show that the system performs well in stimulating airflow and removing contaminants when a window is positioned on the leeward side. A uniform and low particle concentration is created when a window is positioned on the leeward side. However, due to the high air velocity below the windcatcher, the general airflow distribution of the system is not uniform. A damper or egg crated grill should be installed at the terminal of the system, especially when the external wind is strong.

This paper investigated the transmission of respiratory droplets between two seated occupants equipped with one type of personalized ventilation (PV) device using round movable panel (RMP) in an office room. The office was ventilated by three different total volume (TV) ventilation strategies, i.e. mixing ventilation (MV), displacement ventilation (DV), and under-floor air distribution (UFAD) system respectively as background ventilation methods. Concentrations of particles with aerodynamic diameters of 0.8 μm, 5 μm, and 16 μm as well as tracer gas were numerically studied in the Eulerian frame. Two indexes, i.e. intake fraction (IF) and concentration uniformity index RC were introduced to evaluate the performance of ventilation systems. It was found that without PV, DV performed best concern protecting the exposed manikin from the pollutants exhaled by the polluting manikin. In MV when the exposed manikin opened RMP the inhaled air quality could always be improved. In DV and UFAD application of RMP might sometimes, depending on the personalized airflow rate, increase the exposure of the others to the exhaled droplets of tracer gas, 0.8 μm particles, and 5 μm particles from the infected occupants. Application of PV could reduce RC for all the three TV systems of 0.8 μm and 5 μm particles. PV enhanced mixing degree of particles under DV and UFAD based conditions much stronger than under MV based ones. PV could increase the average concentration in the occupied zone of the exposed manikin as well as provide clean personalized airflow. Whether inhaled air quality could be improved depended on the balance of pros and cons of PV.

Personalized ventilation is expected to improve the quality of inhaled air and accommodate individual thermal preferences. In this paper, a chair-based personalized ventilation system is proposed that can potentially be applied in theatres, cinemas, lecture halls, aircrafts, and even offices. Air quality, thermal comfort, and the human response to this ventilation method were investigated by experiments. By comparing eight different air terminal devices (ATDs) it was found that up to 80% of the inhaled air could be composed of fresh personalized air with a supply flow rate of less than 3.0 l/s. Perceived air quality improved greatly by serving cool air directly to the breathing zone. Feelings of irritation and local drafts could be eliminated by proper designs. Personalized air with a temperature below that of room air was able to bring “a cool head” and increased thermal comfort in comparison with mixing ventilation. Massive applications of this chair-based personalized ventilation system can be envisaged in the future.

Airborne transmission is a main spread mode of respiratory infectious diseases, whose frequent epidemic has brought serious social burden. Identifying possible routes of the airborne transmission and predicting the potential infection risk are meaningful for infectious disease control. In the present study, an internal spread route between horizontal adjacent flats induced by air infiltration was investigated. On-site measurements were conducted, and tracer gas technique was employed. Two measurement scenarios, closed window mode and open window mode, were compared. Using the calculated air change rate and mass fraction, the cross-infection risk was estimated using the Wells–Riley model. It found that tracer gas concentrations in receptor rooms are one order lower than the source room, and the infection risks are also one order lower. Opening windows results in larger air change rate on the one hand, but higher mass fraction on the other hand. Higher mass fraction not necessarily results in higher infection risk as the pathogen concentration in the source room is reduced by the higher air change rate. In the present study, opening windows could significantly reduce the infection risk of the index room but slightly reduce the risks in receptor rooms. The mass fraction of air originated from the index room to the receptor units could be 0.28 and the relative cross-infection risk through the internal transmission route could be 9%, which are higher than the external spread through single-sided window flush. The study implicates that the horizontal transmission route induced by air infiltration should not be underestimated., Highlights • On-site measurements were carried out to explore possible airborne transmission route. • A spread route between horizontal adjacent units induced by air infiltration was verified. • The relative cross-infection risk was assessed using the Wells–Riley model. • The risk of the verified route may be higher than that due to single-side open window plume.

Paints are widely used in residential and commercial buildings. The surface areas covered by this kind of coatings are usually very large. The volatile organic compounds (VOCs) emissions from such kind of materials will affect indoor air quality decisively. A relatively simple but physically-based model was developed to simulate VOCs emissions from paints. The model parameters have distinct physical meanings and thus the model is easy to scale up. The field and laboratory emission cell (FLEC) was used to investigate the VOCs emissions from commercially available water-based emulsion paint. Totally 23 individual VOCs were detected and quantified, the most abundant VOC was 1-ethyl-3-methylbenzene. Test data were used to obtain model parameters and to validate the proposed model. Good agreements between experimental data and model predictions were evidenced. Paints applied on two different substrates aluminium and particle board were simulated. Results indicated that real substrates like particle board would act like a ‘sponge’, which lowers the peak concentration but prolongs the presence of VOCs from the applied paint.

The diffusion and partition coefficients of eight volatile organic compounds (VOCs) in cement slabs were experimentally determined using a field and laboratory emission cell (FLEC) system based on the method developed in a previous study on the water vapor diffusion. A cement slab planted with a mixture of eight VOCs was placed in an one-FLEC system to undergo the mass diffusion in the slab and the emission to air flowing through the FLEC. The concentration of each VOC in the air flowing out of the FLEC was measured according to the EPA Method TO-17 using sorbent tube-automatic thermal desorption (ATD) and the gas chromatography-mass spectrum detector (GC-MSD) system. The diffusion and partition coefficients were then obtained by solving the inverse problem of the one-dimensional unsteady mass diffusion equations in the cement slab. And, the partition coefficient was also obtained from the total mass transfer estimated from the VOC concentration measurements and air flowrate, which was equivalent to the headspace concentration-weighting method.

An analytic model describing the one-dimensional transient VOC diffusion in the building material slab was selected. An inverse analysis was applied to estimate the volatile organic compounds (VOCs) constant diffusion coefficient (D) and partition coefficient (K) in the building material. The present parameter estimation problem was solved with Levenberg–Marquardt's method of minimization of the ordinary least-squares norm. The effects of the number and the time step of measurements, errors involved in the initial concentration data in the building material, random errors involved in the measured VOCs concentration data in the chamber air and errors involved in the calculation of the mean convective mass transfer coefficient on the accuracy of estimates were studied. The first two factors were found to have significant effects on the accuracy of the estimates, while the effect of the third factor was insignificant. The results also indicate that D is insensitive to the errors involved in the mean convective mass transfer coefficient. The present study would be useful for obtaining material properties and helpful for designing and improving experiments.

It is known that the person-to-person spreading of certain infectious diseases is related with the transmission of human exhaled air in the indoor environments, and this is suspected to be the case with the severe acute respiratory syndrome (SARS) outbreak. This paper presents the numerical analysis of the human respiration process and the transport of exhaled air by breathing, sneezing, and coughing and their potential impact on the adjacent person in a modeled room with displacement ventilation. In order to account for the influence of the thermal plume around the human body, a three-dimensional computational thermal manikin (CTM) with an accurate description of body geometry was applied. Some of the results were compared with those from former simulations and experiments. It was found that personal exposure to the exhaled air from the normal respiration process of other persons is very low in a modeled room with displacement ventilation. Personal exposure to pollution caused by sneezing or coughing is highly directional. When two occupants face each other the cross-infection may happen due to the long transport distance of the exhalation.

A seated computational thermal manikin (CTM) with geometry of a real human body is used to study the micro-environment around human body with and without personalized ventilation (PV) system. Two novel evaluation indices, pollutant exposure reduction and personalized air utilization efficiency, are introduced. In the range of the personalized airflow rate from 0.0 to 3.0 l/s , the best inhaled air quality is achieved at the airflow rate of 0.8 l/s in the numerical simulation, whereas in our earlier experiments this occurred at the maximum flow rate 3.0 l/s . Through detailed analysis of interaction between thermal plume around human body and personalized airflow, the mechanism of inhalation process becomes more perspicuous. Results from computational fluid dynamics (CFD) and experiment are compared and improvements of CFD simulation accuracy are recommended.

Building envelopes are usually comprised of several layers with different materials, which can significantly affect volatile organic compounds (VOCs) concentrations in indoor environments. These layers may act as source and sink alternatively depending on the different sorption and diffusion potentials. The model proposed here is a single zone one and it considers the different emission properties of building components, namely, the different sorption and diffusion characteristics of the side walls, the floor and the ceiling. In addition, each component comprises of several layers, which represents different construction materials. Two VOCs, ethyl acetate and n-octane, representing polar and nonpolar compounds respectively, are modeled to study the emission profiles in a room with several building materials. The effects of various construction materials, and the different convective mass transfer coefficients between room air and different building components, on the emission characteristics are investigated.

Solvent-based interior coating materials have long been recognized as a major source of volatile organic compounds (VOCs) in the indoor environment. In the emission process, substrate acts as a secondary source. The sink effects are studied with a detailed mass transfer model considering convective mass transfer in air streams, the VOCs diffusions in painting film, and the sorption and diffusions of VOCs in substrate. The model is proposed and validated by the emission profiles of a water-based emulsion paint in a standard field and laboratory emission cell. The focus is on the role the substrate plays in the emission process. The effects of the substrate parameters, such as the substrate diffusivity and sorption characteristics, on the emission profiles are investigated. This is helpful in exposure control through both selecting healthy materials and proper ventilations.

Radiant cooling with independent air dehumidification/ventilation is a complementary cooling and ventilation technology that has the potential to provide better thermal comfort, air quality and energy consumption than conventional all-air systems. However, in hot and humid regions, fears for the risk of condensation on ceiling panels limit its market penetration. To address this problem, in this paper, indoor humidity behaviors associated with decoupled cooling in hot and humid climates are investigated. Room mean temperature, mean humidity, maximum RH on the ceiling panel surfaces, annual condensation hours and annual primary energy consumptions are predicted with systems combining chilled ceiling with various air dehumidification and ventilation strategies, using a building energy simulation code ACCURACY. The effects of night air infiltration rates and the ratios of air flow rates of return air to those of fresh air on the indoor humidity performance and annual condensation hours are discussed. The results indicate that dehumidification and ventilation prior to cooling panels operation is required to reduce condensation risks in hot and humid climates. It is also revealed that a 1 h in advance dehumidification/ventilation in summer could completely eliminate the condensation problems.

By using thermal dynamics simulation and CFD (computational fluid dynamics) techniques, thermal comfort and indoor contaminant distributions are analysed for a room with: (1) a conventional displacement ventilation system, (2) a cooled ceiling with displacement ventilation system, and (3) a cooled ceiling with ceiling air supply system. The numerical simulation results indicate that a cooled ceiling reduces the vertical temperature gradients while still maintaining the ventilation effectiveness much higher than one at a load of nearly 50 W/m2 floor area. By comparison, maximum cooling capacities of the three systems are discussed, specifically in respect to their thermal comfort performances.

Airborne transmission of infectious respiratory diseases in indoor environments has drawn our attention for decades, and this issue is revitalized with the outbreak of severe acute respiratory syndrome (SARS). One of the concerns is that there may be multiple transmission routes across households in high-rise residential buildings, one of which is the natural ventilative airflow through open windows between flats, caused by buoyancy effects. Our early on-site measurement using tracer gases confirmed qualitatively and quantitatively that the re-entry of the exhaust-polluted air from the window of the lower floor into the adjacent upper floor is a fact. This study presents the modeling of this cascade effect using computational fluid dynamics (CFD) technique. It is found that the presence of the pollutants generated in the lower floor is generally lower in the immediate upper floor by two orders of magnitude, but the risk of infection calculated by the Wells–Riley equation is only around one order of magnitude lower. It is found that, with single-side open-window conditions, wind blowing perpendicularly to the building may either reinforce or suppress the upward transport, depending on the wind speed. High-speed winds can restrain the convective transfer of heat and mass between flats, functioning like an air curtain. Despite the complexities of the air flow involved, it is clear that this transmission route should be taken into account in infection control.