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Compared with the buoyancy-dominated upward spread, the interunit dispersion of pollutants in wind-dominated conditions is expected to be more complex and multiple. The aim of this study is to investigate the wind-induced airflow and interunit pollutant dispersion in typical multistory residential buildings using computational fluid dynamics. The mathematical model used is the nonstandard k-ε model incorporated with a two-layer near-wall modification, which is validated against experiments of previous investigators. Using tracer gas technique, the reentry of exhaust air from each distinct unit to other units on the same building, under different practical conditions, is quantified, and then, the possible dispersion routes are revealed. The units on the floor immediately below the source on the windward side, and vertically above it on the leeward side, where the reentry ratios are up to 4.8% and 14.9%, respectively, should be included on the high-infection list. It is also found that the presence of balconies results in a more turbulent near-wall flow field, which in turn significantly changes the reentry characteristics. Comparison of the dispersion characteristics of the slab-like building and the more complicated building in cross (#) floorplan concludes that distinctive infectious control measures should be implemented in these two types of buildings.

The thermal performance of building envelopes is the determinant factor of building energy consumption, and especially envelope retrofitting is an effective way of reducing energy consumptions in existing building. For different climates, there may exist different optimal retrofitting schemes. In this paper, two most popular retrofitting methods, namely thermal insulation and high-reflectivity coating on building walls in cooling dominate cities are investigated. Four cities with different climates are selected, and the impacts of internal versus external thermal insulation are investigated. Result indicates that in cooling-dominant cities employing both thermal insulation and high reflectivity coating could significantly reduce cooling load through building external wall. Also, performance of retrofitting on different wall surface varies with different orientations. In climates with little diurnal temperature change in the summer season, internal insulation performs better than external insulation in reducing air-conditioning load, which typically operates during part of a day, whereas in climates in which there is a free cooling period during the night, external insulation will perform better.

Re-ingestion of the contaminated exhaust air from the same building is a concern in high-rise residential buildings, and can be serious depending on wind conditions and contaminant source locations. In this paper, we aim to assess the prediction accuracy of three k-ɛ turbulence models, in numerically simulating the wind-induced pressure and indoor-originated air pollutant dispersion around a complex-shaped high-rise building, by comparing with our earlier wind tunnel test results. The building modeled is a typical, 33-story tower-like building consisting of 8-household units on each floor, and 4 semi-open, vertical re-entrant spaces are formed, with opposite household units facing each other in very close proximity. It was found that the predicted surface pressure distributions by the two revised k-ɛ models, namely the renormalized and realizable k-ɛ models agree reasonably with experimental data. However, with regard to the vertical pollutant concentration distribution in the windward re-entrance space, obvious differences were found between the three turbulence models, and the simulation result using the realizable k-ɛ model agreed the best with the experiment. On the other hand, with regard to the vertical pollutant concentration distribution in the re-entrant space oblique to the wind, all the three models gave acceptable predictions at the concentration level above the source location, but severely underestimated the downward dispersion. The effects of modifying the value of the turbulent Schmidt number in the realizable k-ɛ model were also examined for oblique-wind case. It was confirmed that the numerical results, especially the downward dispersion, are quite sensitive to the value of turbulent Schmidt number.

Complaints on thermal comfort and confusions on cooling load calculation are still two main issues for the design of stratified air distribution (STRAD) system. This paper investigated these two issues for STRAD systems applied in a large space lecture theatre. The simulation results revealed that best satisfied thermal environment was obtained when supplied air from floor level, terrace and desk-edge mounted grilles simultaneously. A new method for the calculation of the occupied zone cooling load, which is based on CFD (computational fluid dynamics) simulation was proposed and tried. The effective cooling load factor concept was further clarified, which can be conveniently used to calculate the occupied zone cooling load and then determine the supply airflow rate. The concepts of occupied zone cooling load reduction and the associated but different cooling coil load reduction were differentiated, and it was illustrated that cooling coil load reduction up to 16.5% of the space cooling load can be achieved with split location of return and exhaust grilles. These simulation works provide a good basis for full-scale experimental validation of the key energy saving features of a well-designed stratified air distribution system.

Microencapsulated phase change material (MPCM) slurry provides a good kind of medium for thermal energy storage due to its thermal properties, especially proper working temperature, which is appropriate for maximized utilizations of nature cooling sources. In this study, a novel MPCM slurry storage system is investigated by combining MPCM slurry storage with a nocturnal radiative cooling system. The cooling energy consumption and the effect of energy-free nocturnal radiation application were simulated using the energy simulation code ACCURACY and MATLAB model based on hour-by-hour calculations in five typical cities across China. It can be concluded that MPCM slurry appears to be a good medium for the combined application of passive cooling technology in air conditioning system. The results showed the energy saving potential in Lanzhou and Urumqi can reach 77% and 62% for low-rise buildings, which exhibits strong attractions for building energy conservation and emission reduction. Hong Kong has the weakest effect in the five typical cities under the same operating condition due to the hot and humid climate condition. The present hybrid system is recommended to be used in northern and central China cities where the weather is dry and the ambient temperature is low at night.

A number of radiant heating/cooling systems have been applied in Mainland China in recent years for its improved thermal comfort and inherent energy saving potential. Because the systems require relatively higher temperatures for cooling and lower temperatures for heating, many natural low-grade energy sources can be directly or indirectly used. However, because of a lack of information about prior practical projects, a number of difficulties in design, construction and management of the systems have been encountered, and energy efficiency is not necessarily achieved in all situations. This paper reviews the practical applications in four major projects involving different building types located in different climatic cities and presents the associated considerations in system design. Other factors affecting the energy efficiency of the systems are identified, such as the spatial convection and radiation heat transfer processes in indoor environments and the envelope thermal properties. Further studies are needed to achieve system optimization and to realize the full energy saving potentials of radiant systems by developing analytical design methods and monitoring the actual energy use of such systems in completed projects.

This paper adopts an Eulerian-Lagrangian approach to investigate the lock-up phenomenon (or trap phenomenon) of human exhaled droplets in a typical office room under displacement ventilation (DV). A particle-source-in-cell (PSI-C) scheme is used to correlate the concentration with the Lagrangian particle trajectories in computational cells. Respiratory droplets with sizes of 0.8 μm, 5 μm and 16 μm are released from a numerical thermal manikin (NTM). The influence factors including indoor temperature gradient, heat source configuration and exhalation modes are studied. It is found that large temperature gradient would result in trap phenomenon of small exhaled droplets (smaller than 5 μm). The intensive heat source near the NTM could help to transport the small droplets to the upper zone and decrease the concentration level in the trapped zone. Both nose-exhaled and mouth-exhaled small droplets would be trapped at the breathing height when temperature gradient is sufficiently high. However, the trap height of the droplets from mouth is a little bit higher. Because of large gravitational force, it is difficult for the thermal plume to carry 16 μm respiratory droplets to the upper zone.

Existed evidences show that airborne transmission of human respiratory droplets may be related with the spread of some infectious disease, such as severe acute respiratory syndrome (SARS) and H1N1 pandemic. Non-pharmaceutical approaches, including ventilation system and personal protection, are believed to have certain positive effects on the reduction of co-occupant's inhalation. This work then aims to numerically study the performances of mouth covering on co-occupant's exposure under mixing ventilation (MV), under-floor air distribution (UFAD) and displacement ventilation (DV) system, using drift-flux model. Desk partition, as one generally employed arrangement in plan office, is also investigated under MV. The dispersion of 1, 5 and 10 μm droplet residuals are numerically calculated and CO2 is used to represent tracer gas. The results show that using mouth covering by the infected person can reduce the co-occupant's inhalation greatly by interrupting direct spread of the expelled droplets, and best performance can be achieved under DV since the coughed air is mainly confined in the microenvironment of the infected person. The researches under MV show that the two interventions, mouth covering and desk partition, achieve almost the same inhalation for fine droplets while the inhalation of the co-occupant is lower when using mouth covering for large droplets.

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.

Energy-efficient retrofitting of existing building is a huge contribution to the sustainability of the society since building energy consumption takes more than one fourth of total energy consumption. The application of external shading system could block out unwanted radiant heat gain, thus reduces the cooling load of the air-conditioning system. During the assessment of energy-efficient retrofitting projects, apart from annual saving figures and economic payback time, energy and CO 2 emission payback periods should also be taken as indispensable references. In this paper, a methodology is described for analyzing the energy and CO 2 emission payback periods of external overhang shading in a university campus in Hong Kong. Result shows that due to requirements of structural strength under typhoon situation, although introducing overhang shading system could reduce almost half of the cooling load in the related area, the energy and CO 2 emission payback periods of the project are still unrealistically long. This case study presents an example of multi-disciplinary approach being not only important to the energy-efficient retrofitting but also necessary for policy making in different climatic and geographic regions.

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.

Prevention of supercooling is essential for phase change material (PCM) utilization. In this study, multi-wall carbon nano-tube (MWCNT) particles were dispersed in an organic liquid n-hexadecane used to decrease supercooling. Various surfactants were tested as additives to overcome the rapid aggregation and sedimentation of the nanoparticles in the organic liquid. Stable and homogenous dispersion was attained through surface modification of the MWCNT particles with strong acids H 2 SO 4 and HNO 3 , plus the addition of 1-decanol as a surfactant to the organic liquid. Thermal analysis of the n-hexadecane with well dispersed MWCNT particles at concentrations ranging from 0.1% to 10% w/w by differential scanning calorimeter (DSC) indicated that the supercooling of n-hexadecane was significantly decreased with the concentration of 0.1% and 0.5% but only slightly with the concentrations over 1.0%. It appears that well dispersed nanoparticles provided stable foreign nuclei of proper size to promote the heterogeneous nucleation process and accelerate crystallization process, thus the supercooling was significantly reduced. The obvious effects of MWCNT particles on the decrease of supercooling of n-hexadecane provide promising way of improving the performance of system energy efficiency in building cooling and heating applications.

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.

Highlights ► We examine unsteady characteristics of cross-contamination in high-rise building. ► The values of concentration fluctuation intensity were greater than 1 and can be up to 10. ► The intermittency factor and peak-to-mean ratio can be up to 0.8 and 70, respectively. ► The concentration fluctuation is increased under open-window conditions. ► Instantaneous peak infection risk is below 0.1% under open-window condition., This article presents experimental results that illustrate the unsteady characteristics of gas dispersion around a complex-shaped high-rise building for different incident wind directions. A series of wind tunnel experiments were conducted using a 1:30 scale model that represented the real structures under study. The objective of this paper is to study the behaviour of concentration fluctuations through transient analysis. Tracer gas was continuously released from a point source located at different positions, and a time series of fluctuating concentrations were recorded at a large number of points using fast flame ionization detectors. The experimental data were analysed to provide a comprehensive data set including variances and associated statistical quantities. Both the unsteady characteristics of the system and their potential practical impact are presented and discussed. Under crowd living conditions, the air pollutant exhausted from one household could probably re-enter into the neighbouring households, traveling with ambient airflow. Such pollutant dispersion process is defined as air cross-contamination in this study. The results indicate that the wind-induced cross-contamination around the studied type of high-rise building should not be overlooked, and the fluctuating concentrations should be paid attention to particularly during the evaluation of a potential contamination risk. This study can help deepen our understanding of the mechanisms of air cross-contamination, and will be useful for implementing optimization strategies to improve the built environments in metropolitan cities such as Hong Kong.

This article presents a numerical study of ventilation performance of balconies using computational fluid dynamics. The pressure coefficients distributed on the opposite walls of a five-storey building model, both with and without balconies, were studied under variation of the wind direction, balcony dimensions and building height. The effect of balconies on the capacity for wind-induced natural ventilation is discussed. The numerical results show good agreement with the experiments of Chand et al. They also indicate that a balcony enhances the cross-ventilation of intermediate floors but weakens that of the ground and top floors, by significantly changing the pressure distribution on the windward wall. Finally, the ventilation performance of a balcony is not greatly affected by variations in its size but is slightly weakened as the height of the building increases. Practical application: This study provides information and guidance in how best to incorporate the use of a balcony in building development at the design stage.

Chand et al. conducted experiments in a low speed wind tunnel to study the effect of balconies on the ventilative force on low-rise buildings without openings. Using their model, this study intends to investigate indoor ventilation performance by examining mass flow rate and average velocity on the working plane using computational fluid dynamics. Simulations were validated against their experiments. The numerical results indicate that, for single-sided ventilation, the provision of balconies increases mass flow rate and reduces average velocity on the working plane in most rooms, but for cross ventilation, this provision has no significant effect under normally or obliquely incident wind conditions. After the addition of balconies, the worst ventilation circumstances on the windward side under single-sided ventilation conditions were found on the intermediate floor. The simulation results also showed that, in many cases, wind flows into and out of the rooms through the left or right side of the opening rather than through the bottom and top of the opening, especially in the case of buildings that are obliquely oriented to the air stream. This phenomenon demonstrates that predictions of single-sided ventilative force using data relating to the bottom and top parts of the opening are not accurate enough.

The presence of the parapet and floor of a balcony is expected to have a range of effects on a building’s environmental behaviour, in terms of aspects, such as natural ventilation, thermal comfort, pollutant transportation and shading and daylighting. The authors have previously reported that the presence of a balcony can significantly increase the air flow rate of most rooms in a naturally ventilated building. In this study, the CFD technique and Fanger and Toftum’s extended PMV—PPD model are combined to investigate numerically the effect of a balcony on thermal comfort for naturally ventilated buildings in tropical-humid regions. The results show that although a balcony reduces the indoor average velocity for most rooms, and in turn increases the PMVnv value in both the seated and standing positions, it does not change the indoor thermal comfort level. However, the presence of a balcony improves comfort by increasing the uniformity of indoor air distribution. PMVnv is also shown to be less sensitive to velocity than PMV, allowing for a wider thermal comfort range for naturally ventilated buildings. Practical application: This study will help designers and engineers who are considering the use of a balcony at the design stage to have a better understanding of its effect on thermal comfort in naturally ventilated buildings.

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.

Ice storage is currently the dominant cooling energy storage method. To more effectively utilize natural, renewable cooling sources, such as evaporative cooling and sky-radiative cooling, diurnal storage media operated on a daily basis at the temperate range between 10 and 20 °C are the most desirable. This paper will present the experimental investigation of microencapsulated paraffin slurry as cooling storage media for building cooling applications. The water slurry of microencapsulated n-hexadecane with a melting temperature of 18 °C was cooled to 5 °C and heated to 25 °C cyclically in a storage tank of 230 l, and it was observed that full latent heat storage can only be realized at around 7 °C due to supercooling, and the effective cooling storage capacity at the cooling temperature range between 5 and 18 °C are obtained, which can be used to realistically estimate cooling storage capacity with various natural cooling schemes.

Due to its large apparent specific heat during the phase change period, microencapsulated phase change material slurry (MPCMS) has been suggested as a medium for heat transfer. In this paper, the convective heat transfer characteristics of MPCMS flowing in a circular tube were experimentally and numerically investigated. The enhanced convective heat transfer mechanism of MPCMS, especially in the thermal fully developed range, was analyzed by using the enthalpy model. Three kinds of fluid–pure water, micro-particle slurry and MPCMS were numerically investigated. The results show that in the phase change heat transfer region the Ste number and the Mr number are the most important parameters influencing the Nusselt number fluctuation profile and the dimensionless wall temperature. Reb, dp and c also influence the Nusselt number profile and the dimensionless wall temperature, but they are independent of phase change process.

The main objectives were to (1) calculate the total volatile organic compounds (TVOCs) inhalation dose, (2) analyze the proportions of human’s inhaled contaminant dose from different sources, and (3) present a newly defined ratio of relative inhalation dose level (RIDL) to assess indoor air quality (IAQ). A user defined function based on CFD (computational fluid dynamics) was developed, which integrated human motion model with TVOCs emission model in a high sidewall air supply ventilation mode. Based on simulation results of 10 cases, it is shown that the spatial concentration distribution of TVOCs is affected by human motion. TVOCs diffusion characteristic of building material is the most effective way to impact the TVOCs inhalation dose. From the RIDL index, case A-2 has the most serious IAQ problem, while case D-1 is of the best IAQ.

Microencapsulated phase change material (MPCM) slurry is advantageous for thermal storage systems to use as a heat transfer and storage medium. In this paper, a new design of air-conditioning system is proposed, which is a combination of CC and a MPCM slurry storage tank. The mathematical model of the combined system is provided and used to predict the system performance of an office room under Hong Kong weather condition using hour-by-hour calculations. A feasibility analysis for the combined system was also made with computer calculations. The results indicate that a small MPCM slurry storage tank is able to shift the part of cooling load from the daytime to nighttime. It is also revealed that the proposed combined system is an energy saving and economy-favorable air-conditioning system.

The dispersion characteristics of respiratory droplets are important in controlling transmission of airborne diseases indoors. This study investigates the spatial concentration distribution and temporal evolution of exhaled and sneezed/coughed droplets within the range of 1.0 − 10.0μm in an office room with three air distribution methods, specifically mixing ventilation (MV), displacement ventilation (DV), and under-floor air distribution (UFAD). The diffusion, gravitational settling and deposition mechanism of particulate matter were accounted by using an Eulerian modeling approach with one-way coupling. The simulation results indicate that exhaled droplets up to 10μm in diameter from normal human respiration are uniformly distributed in MV. However, they become trapped in the breathing zone by thermal stratifications in DV and UFAD, resulting in a higher droplet concentration and an increased exposure risk to other room occupants. Sneezed/coughed droplets are more slowly diluted in DV/UFAD than in MV. Low air speed in the breathing zone in DV/UFAD can lead to prolonged human exposure to droplets in the breathing zone.

By contrast with the conventional heat transfer fluid (water), the microencapsulated phase change material (MPCM) suspension, with a small temperature difference between storing and releasing heat, is of much larger apparent specific heat and much higher thermal energy storage capacity. It has been suggested to serve as a dual-functional medium for thermal energy transport and/or storage. The heat transfer characteristics of a kind of MPCM suspension, formed by microencapsulating industrial-grade 1-bromohexadecane (C16H33Br) as phase change material, were experimentally studied for laminar flow in a circular tube under constant heat flux. A new expression of Ste is put forward in the paper, according to the physical definition of Stefan number. The results in the experiments show: (a) the dimensionless internal wall temperature of the MPCM suspension is lower than pure water, and the decrease can be up to 30% of that of water; (b) the heat transfer enhancement ratio can be 1.42 times of that of water at x+ = 4.2 × 10−2 for 15.8 wt% MPCM suspension, which is not as much as in some references; and (c) the pump consumption of the MPCM suspension system decrease greatly for the larger heat transfer rate compared with water, due to phase change, the decrease can be up to 67.5% of that of water at q = 750 W (15.8 wt%). The kind of MPCM suspension has good application feasibility in practice.

Evaporative cooling is able to generate the cooling medium at a temperature approaching to the ambient wet bulb temperature. In this paper, a low-energy air-conditioning strategy is proposed, which is a combination of cooled ceiling (CC), microencapsulated phase change material (MPCM) slurry storage and evaporative cooling technologies. The assessment of evaporative cooling availability and utilization is done for five representative climatic cities, including Hong Kong, Shanghai, Beijing, Lanzhou and Urumqi in China, and the energy saving potential of the proposed air-conditioning system is analyzed by using a well validated building simulation code. The results indicate that the new system offers energy saving potential up to 80% under northwestern Chinese climate and up to 10% under southeastern Chinese climate. The optimal design method of the slurry storage tank is also proposed based on the slurry cooling storage behaviors and cooling demand variations of the ceiling panels.

UNLABELLED In the worldwide spread of Severe Acute Respiratory Syndrome (SARS) in 2003, cluster of cases occurred in a number of large high-rise residential building blocks, especially in Hong Kong. In this study, we examined one of the most likely virus-spread mechanisms, which is related to the inter-flat or inter-zonal airflow through open-windows caused by buoyancy effects. Dual tracer gases of CO2 and SF6 are employed simultaneously to quantify the amount of the exhaust air coming out of the upper part of the window of a floor that re-enters the lower part of the open-window at the immediate upper floor. It was found that the room air could contain up to 7% of the exhaust air from the lower floor, and this occurs at low wind conditions with a combination of indoor-outdoor temperature difference. The results can well explain the earlier governmental finding that DNA strings of SARS Corono-Virus were detected within the sampled deposits on the window sills of the upper floors of the two index patients' flats. The preliminary and yet alarming conclusion may be that, in high-rise buildings, windows flush with a flat facade can be a major route for the vertical spread of pathogen-containing aerosols. PRACTICAL IMPLICATIONS The confirmation of the transmission route can have a number of implications to both building design and infectious disease control. With respect to the former, considerations should be given to minimize the inter-flat airflow via windows flush with facade for high-rise buildings with natural ventilation; and with respect to the latter, more targeted and earlier intervention can be implemented in case of any highly infectious disease outbreaks.

Larger window openings in the walls of a building may provide better natural ventilation. However, it also increases the penetration of direct solar radiation into indoor environment. The use of wing wall, one of the green features, is an alternative to create effective natural ventilation. Givoni conducted experiments in a wind tunnel to study the ventilation performance of wing walls. This paper presents a numerical study of the ventilation performance of wing walls using computational fluid dynamics (CFD). Two-dimensional and three-dimensional simulations are compared with the results of the experiments of Givoni. The results indicate that wing wall can promote natural ventilation by increasing the air change per hour and the mean indoor air speed relative to wind speed at various wind speeds and wind directions. The best performance of wing wall is at the wind angle of around 45°. The study also shows that 3D CFD simulation produces similar trend to the experimental results though there are some discrepancies.

The flow and convective heat transfer behaviors of microencapsulated phase change material (MPCM) slurries in a horizontal circular tube have been experimentally investigated. The slurry consisted of microencapsulated 1-bromohexadecane (C16H33Br) and water, with the mass fractions of MPCM varying from 5% to 27.6%. The pressure drop and local heat transfer coefficients were measured, and the influences of capsule fractions, heating rates, and flow structures on heat transfer performance were also studied. Heat transfer coefficients measured for MPCM slurry are significantly higher than for those for single-phase fluid flow in laminar flow conditions, but exhibit more complicated phenomena at low turbulent conditions. Moreover, a new simple heat transfer correlation equation was proposed that accurately predicts the local heat transfer coefficients of laminar MPCM slurry flow in a horizontal circular tube.

Particle dispersion and deposition in man-made enclosed environments are closely related to the well-being of occupants. The present study developed a three-dimensional drift-flux model for particle movements in turbulent indoor airflows, and combined it into Eulerian approaches. To account for the process of particle deposition at solid boundaries, a semi-empirical deposition model was adopted in which the size-dependent deposition characteristics were well resolved. After validation against the experimental data in a scaled isothermal chamber and in a full-scale non-isothermal environmental chamber, the drift-flux model was used to investigate the deposition rates and human exposures to particles from two different sources with three typical ventilation systems: mixing ventilation (MV), displacement ventilation (DV), and under-floor air distribution (UFAD). For particles originating from the supply air, a V-shaped curve of the deposition velocity variation as a function of particle size was observed. The minimum deposition appeared at 0.1– 0.5 μ m . For supermicron particles, the ventilation type and air exchange rate had an ignorable effect on the deposition rate. The movements of submicron particles were like tracer gases while the gravitational settling effect should be taken into account for particles larger than 2.5 μ m . The temporal increment of human exposure to a step-up particle release in the supply air was determined, among many factors, by the distance between the occupant and air outlet. The larger the particle size, the lower the human exposure. For particles released from an internal heat source, the concentration stratification of small particles (diameter 10 μ m ) in the vertical direction appeared with DV and UFAD, and it was found the advantageous principle for gaseous pollutants that a relatively less-polluted occupied zone existed in DV and UFAD was also applicable to small particles.

Building envelopes are usually comprised of several different layers of building materials, which may alternatively act as VOC sources or sinks depending on their emission and sorption potentials and the indoor environmental conditions as well. In this research, a whole room IAQ model consisting of multi-phase emission/sorption model for wall materials and room volume mass balance model catering for practical ventilation schemes was developed. The interactions of VOC and building materials composing different building components can be modeled based on fundamental mass transfer theories. The effects of various construction materials and ventilation strategies on the emission characteristics were investigated. Results show that measures like pre-occupancy flush-out, lead-time ventilation, etc. have substantial impacts on indoor VOC concentration and the model can successfully handle different building scenarios. Although more rigorous validation, in particular more experimental verification, is needed, the proposed model has proven to be valuable in handling different building scenarios. It is useful in analyzing the levels of contaminant buildup that would occur during no ventilation period for intermittent ventilation situations and in determining the amount of outdoor air and the lead-time period required to flush out the contaminants prior to occupancy. It is likely to be a simple routine tool for building owners, designers and operators to attain acceptable indoor VOC concentration level.

In this paper, we investigated the pollutant exposure reduction and thermal comfort that can be achieved with personalised ventilation (PV) design when a PV system is combined with two types of background air conditioning systems. For the investigation of inhaled air quality, pollutants emitted from building materials are the targeted pollutants; and for the investigation of thermal comfort, local discomfort associated with nonuniform thermal environment is focused upon. These investigations were performed by combining CFD simulation of the 3D air flow and a multi-nodal humanbody thermo-regulation model. The results reveal some new characteristics of the three typical air distribution designs, i.e. mixed ventilation, displacement ventilation and PV, and provide insight into the possible optimisation of system combinations.

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.

There have been few recent studies demonstrating a definitive association between the transmission of airborne infections and the ventilation of buildings. The severe acute respiratory syndrome (SARS) epidemic in 2003 and current concerns about the risk of an avian influenza (H5N1) pandemic, have made a review of this area timely. We searched the major literature databases between 1960 and 2005, and then screened titles and abstracts, and finally selected 40 original studies based on a set of criteria. We established a review panel comprising medical and engineering experts in the fields of microbiology, medicine, epidemiology, indoor air quality, building ventilation, etc. Most panel members had experience with research into the 2003 SARS epidemic. The panel systematically assessed 40 original studies through both individual assessment and a 2-day face-to-face consensus meeting. Ten of 40 studies reviewed were considered to be conclusive with regard to the association between building ventilation and the transmission of airborne infection. There is strong and sufficient evidence to demonstrate the association between ventilation, air movements in buildings and the transmission/spread of infectious diseases such as measles, tuberculosis, chickenpox, influenza, smallpox and SARS. There is insufficient data to specify and quantify the minimum ventilation requirements in hospitals, schools, offices, homes and isolation rooms in relation to spread of infectious diseases via the airborne route. PRACTICAL IMPLICATION: The strong and sufficient evidence of the association between ventilation, the control of airflow direction in buildings, and the transmission and spread of infectious diseases supports the use of negatively pressurized isolation rooms for patients with these diseases in hospitals, in addition to the use of other engineering control methods. However, the lack of sufficient data on the specification and quantification of the minimum ventilation requirements in hospitals, schools and offices in relation to the spread of airborne infectious diseases, suggest the existence of a knowledge gap. Our study reveals a strong need for a multidisciplinary study in investigating disease outbreaks, and the impact of indoor air environments on the spread of airborne infectious diseases.

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.

WOS:000346951400031; International audience; This paper reports a numerical and analytical study of time dependent storage of energy by melting a phase change material in a cylindrical tank. In the first part of the study the heater was a vertical spiral tube positioned coaxially with the tank. In the second part, the heater consisted of two coaxial spirals positioned on the same axis as the cylinder. In accord with the philosophy of constructal design, the heat and fluid flow configuration was endowed with degrees of freedom in order to morph toward better overall performance for a fixed amount of heating material. The paper documents the effect of the geometrical features such as helix diameter and pitch on the overall performance. (C) 2014 Elsevier Ltd. All rights reserved.

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.

Personalized ventilation has great potential to improve inhaled air quality and to accommodate individual thermal preferences. In order to quantify these perceived benefits, a numerical method has been developed. In this method, a numerical thermal manikin (NTM), with the real geometry of a human body, is obtained by employing a laser scanning technique. When placed in a virtual environment, the thermal interactions with the environment are calculated using computational fluid dynamics (CFD). By iteration, the calculated air velocity near the body surface is fed into a sophisticated thermoregulation model developed at the University of California, Berkeley, so that the local thermal comfort in a non-uniform environment created by personalized air (PA) is rigorously investigated. In this paper, the performances of three different PV systems are investigated, namely, the desk-edge-based PV, PV using a movable panel (MP), and chair-based PV. The results exhibit reasonable agreement with the experimental meas...

As compared with the mixing system, indoor air temperature stratification in the under-floor air distribution (UFAD) system offers an opportunity for cooling load reduction in the occupied zone. This stratification is a major feature that offers the energy saving potential, but it has not been thoroughly taken into account in most energy simulation programs. In this article, a numerical procedure, based on coupling two types of modeling, i.e., CFD (computational fluid dynamic) simulation and dynamic cooling load simulation, is proposed to predict annual energy consumption. The dimensionless temperature coefficient is first defined in the UFAD system and obtained from CFD simulation, based on the boundary conditions from a cooling load program ACCURACY. According to this coefficient, temperature stratification input to ACCURACY is then revised to calculate the updated supply and exhaust air temperatures for final annual energy prediction. To demonstrate the method, a small office room is investigated using Hong Kong weather data. With the constant air volume (CAV) supply in the UFAD system, it is found that the dimensionless temperature coefficient is almost a constant, when the locations of heat sources are fixed. As compared with the mixing system, the UFAD system derives its energy saving potential from the following three factors: an extended free cooling time, a reduced ventilation load, and increased coefficients of performance (COP) for chillers.

This article presents numerical results of convective heat transfer from two identical square cylinders (TISC) arranged at close proximity in a uniform cross flow of air (Pr = 0.71) at the particular Reynolds number of 250. The proximity arrangement of the TISC is defined by longitudinal spacing ranging from zero to unity, with the transverse spacing ranging from 0.125 to unity. Results are obtained by the finite-difference method for 25 cases, divided into five groups for convenience of discussion. It is found that the time-averaged or mean convective heat transfer rates from the TISC reach their maxima when the transverse spacing value is about 0.3 from the view of the group averaging at a given transverse spacing. The heat transfer rates from inner faces of the TISC are generally greater than those of the outer sides, by a factor of about 2 to 3. Depending on the TISC arrangement, a bifurcation sometimes occurs, with the bifurcated lower St value corresponding to the shedding from the outer shear layer...

Building-related health complaints and sick building syndrome (SBS) represent significant health problems. Personalized ventilation (PV) is able to provide better inhaled air quality since the fresh air is supplied directly to the breathing zone “gently.” In this paper, after the numerical methods are validated by experiments, a seated computational thermal manikin (CTM) with geometry of a real human body is used to carry out the parameters study of PV. The modeling outcome shows that in a stagnant environment the human body is enclosed by the thermal plume, whose intensity is affected by the room air temperature. Warm rising airflow around the human body will entrain room air into inhalation and thus decreases the fraction of personalized air in the inhaled air. A uniform invading airflow in the horizontal level with the speed of 0.2 m/s (40 ft/min) is strong enough to tear away the thermal plume at the windward side of the human body. Its effect on the performance of PV is dependent on the flow directio...

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.

Indoor radon concentration is mainly associated with the radon production rate of building material, ventilation rate, and the outdoor radon concentrations. Radon production rate of a room is defined as the sum of the products of the radon emanation rates and the exposed areas of the materials. Since the selection of the building materials and the exposed areas are different from room to room, it makes the radon production rate of homes fall in a wide range. Here, the radon production rate of a room is suggested to be quantified by a sealing method, in which the systematic radon growth curve is obtained. The radon production rate of the room can be determined from the initial slope of the growth curve. Three rooms at different homes in Hong Kong were selected in the study for verifying the methodology. The uncertainty characterized by data scatter arisen from the coupling effect of the leakage rate and outdoor radon was also included in the discussion. During the measurements, no occupant was allowed into the home. No mechanical ventilation was involved in the measurement. The indoor and outdoor radon concentrations of the sampled homes were monitored simultaneously and lasted for more than three days. The radon production rates and the uncertainties of three rooms at Homes 1, 2, and 3 were found to be 232.8, 46.0, 414.6, and 20.3, 9.4, 59.2 Bq h - 1 , respectively. The approach is valid when the air leakage rate of the room is controlled below 0.1 h - 1 .

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.

The use of green features in building design not only improves the environmental quality, but also reduces the consumption of non-renewable energy used in active control of indoor environment. Larger window openings in the walls of a building may provide better natural ventilation. However, it also increases the penetration of direct solar radiation into indoor environment. The use of wing wall, one of the green features, is an alternative to create effective natural ventilation. This paper presents a preliminary numerical study of its ventilation performance using Computational Fluid Dynamics (CFD). The results of the CFD analysis show that the wing wall is a useful green feature added onto the south-facing wall with window openings to increase single-sided ventilation rate. Its performances under different wind directions and speeds and wing sizes are also examined.

A model for the prediction of emission of volatile organic compounds (VOCs) from dry building material was developed based on mass transfer theory. The model considers both diffusion and convective mass transfer. In addition, it does not neglect the fact that, in most cases, the initial distribution of VOCs within the material is non-uniform. Under the condition that the initial amount of VOCs contained in the building material is the same, six different types of initial VOC distributions were studied in order to show their effects on the characteristics of emission. The results show that, for short-term predictions, the effects are significant and thus cannot be neglected. Based on the fact that the initial distribution of VOCs is very difficult to directly determine, a conjugate gradient method with an adjoint problem for estimating functions was developed, which can be used to inversely estimate the initial distribution of VOCs within the material without a priori information on the functional form of the unknown function. Simulated measurements with and without measurement errors were used to validate the algorithm. This powerful method successfully recovered all of the aforementioned six different types of initial VOC distributions. A deviation between the exact and predicted initial condition near the bottom of the material was noticed, and a twin chamber method is proposed to obtain more accurate results. With accurate knowledge of the initial distribution of VOCs, source models will be able to yield more accurate predictions.

A mass transfer theory based model describing volatile organic compounds (VOCs) diffusion in dry building material was presented. Effects of some key parameters on the model output were theoretically studied. An inverse method was developed to estimate the diffusion coefficient (D) and partition coefficient (K) of VOC/material combination by utilizing dynamic chamber emission data. The present inverse parameter estimation problem was solved with Levenberg–Marquardt method of minimization of the ordinary least-squares norm. Sensitivity analysis showed the feasibility of simultaneous estimation of D and K. The present inverse method was first validated by a theoretical case. Measurements with different error levels were used to show their effects on the accuracy of the estimates. Results indicate that the present inverse method can be used to accurately estimate both D and K with the additional information of measured VOC concentration in chamber. Then experimental data of styrene/carpet combination obtained from standard field and laboratory emission cell emission test were used to determine D and K using the validated inverse method. Reliable results were obtained.

Computational fluid dynamics (CFD) simulations of thermal manikins can provide detailed information which it is impossible to obtain from experiments. In this review several issues from CFD studies of thermal manikins are discussed, such as geometric complexity of computational thermal manikins (CTMs), selection of turbulence models, grid generation and boundary conditions. Calculation of CTMs with simple geometry requires less computational resource but a more anthropomorphic geometry can provide more accurate results. In the simulations using complex geometric representations of the human body the computational domain is discretised by body-fitted co-ordinates or unstructured grids. The total number of cells can reach the quantitative magnitude of 1 million. The simulation results about airflow field, radiative and convective heat transfer and contaminant distribution from different researchers are compared. Further developments in the use of these simulations are proposed.

A methodology has been established to quantify the ozone emission rate from electronic air cleaners, as well as the ozone decay parameter. Three different portable ionisation-type air cleaners were used in the experiments. A stainless steel environmental chamber with volume size 6.4m3 (1.6×2×2m) was employed in the study. The leakage rate of the chamber was measured to be 0.0042h-1 by a tracer decay gas test. The ozone growth curve within the chamber was used to quantify the ozone emission rate of the air cleaner and the ozone decay parameter. The emission rate and the decay parameter were determined by the initial slope and the equilibrium state of the growth curve simultaneously, and the technique of least squares fitting was introduced in the data analysis. The ozone emission rates and the decay parameters of Air Cleaner I, II, and III were found to be 119.4±15.6, 77.6±5.4, and 1092.3±112.5ppbh−1 and 2.59×10−1±0.03, 1.68×10−2± 0.001 and 9.48×10−2±0.01h−1, respectively. The wide range of the emission rates was believed to relate to the individual designs of the air cleaners. The variation in decay parameters obtained from the measurements was tentatively associated with the level of VOCs in the sampling environment.

Almost in all the major cities in Asian countries, residential buildings are characterized with high-rise and high density. Under this circumstance, achieving comfortable and healthy indoor environment with minimized energy consumption becomes a very challenging engineering and societal issue. While the wide use of air-conditioning helped to improve thermal comfort, health problems associated with poor indoor air qualities have appeared more frequently. The increased energy consumption is also a great concern in view of its impact on the energy economics of the region. Drawn from some of the onsite measurements and survey, and also the author’s personal observation, some of the key issues are discussed in this paper. © 2004 Elsevier B.V. All rights reserved.