Measurements and numerical modeling of flow field and pollutant dispersion in areaway space

In residential building design, areaway can act as an open subsurface space to help improve the living environment in adjacent basement by natural ventilation. To study this particular ventilation phenomenon mainly driven by wind force, the first part of this paper presents an investigation of flow field and pollution dispersion inside areaway space based on a wind tunnel experiment. In the experiment, the measurement of mean velocity, turbulence and concentration as well as the flow visualization were carried out for a rectangular cavity-like areaway model with the width to height (w/h) ratio ranging from 0.3 to 1.0 and the influence of above-ground building has also been investigated. The experimental results reveal quite different airflow patterns characterized with unsteady vortex movement inside the areaway model, which indicates that the w/h ratio and the above-ground building are important factors for ventilating the areaway space. Furthermore, for the purpose of computational fluid dynamics (CFD) model validation, the experimental results of flow fields were compared with the simulation results. The areaway model of w/h = 1 was used for this study and the simulations were performed using large-eddy simulation (LES) and standard k-ε turbulence model. The numerical results show a good agreement with the experimental results when using LES with inflow turbulence. The further investigations with regard to the characteristics of flow field and pollutant removal as well as ventilation performance were also performed by LES.     

Wind-induced ventilation performances and airflow characteristics in an areaway-attached basement with a single-sided opening

In the present study, we performed both wind tunnel experiments and numerical simulations on a scale model with the focus on wind-driven natural ventilation in an areaway-attached basement with a single-sided opening. In the experiments, the mean value of the effective ventilation rate, purging flow rate (PFR) was measured for nine wind incidence angels based on the homogeneous emission rate method. The experimental results were used to validate two numerical approaches: Reynolds averaged Navier–Stokes (RANS) modeling and large-eddy simulation (LES). The influences of inflow turbulent fluctuations for LES modeling were also examined. The comparisons between the experiment and the numerical simulation indicate that LES can provide more accurate results than RANS and the inflow turbulent fluctuations should be taken into account for LES modeling. Based on LES with the inflow turbulent fluctuations, the mean airflow patterns within and around the areaway-attached basement were further studied for different wind incidence angles to investigate the influence of wind direction on ventilation performance in the areaway space. Furthermore, the relationships between the effective ventilation rate and the kinetic energy in the basement space were analyzed for three wind directions: 0°, 90° and 180°. A close correlation was found between the mean values, whereas the corresponding time variations showed large discrepancies. Finally, we compared the effective ventilation rate obtained using the homogeneous emission rate method and the airflow rates through the opening using two integration procedures. The effective ventilation rates were found lower than the airflow rates through the opening.     

城市住区室外通风与空气负离子浓度评测研究

选取合肥市东南区域典型居住区为研究对象,运用CFD数值模拟和室外实地观测相结合的研究方法,量化模拟了夏冬两季住区室外环境的风速图,并分析了其模拟通风状况;在此基础上得到了住区内不同环境的通风特征,包括建筑布局、空间形态、建筑密度、交通路网、植物绿化等对通风的影响;再根据模拟参数,在住区内选取样点实地观测了不同环境特征下的住区夏冬两季的空气负离子和风速、温度、相对湿度以及空气正离子等数据,探索了住区室外环境中空气负离子浓度与风速、温度、湿度和空气正离子之间的相关关系。同时进一步整理了近4万个有效数据应用于空气负离子和风速的时空分布研究,推导出夏季风速与空气负离子的线性回归方程,并运用偏相关分析,得出城市住区环境中空气负离子与风速呈极显著负相关,给出了线性回归方程Y=-0.001X-0.003。最后结合建筑布局的组合、开敞空间的设计和线性道路的组织等分析了空气负离子和风速的分布规律,用以说明评价住区室外环境通风状况的可行性,为今后城乡规划和建筑设计提供科学依据和设计思路。     

Heat release rate of accidental fire in a supertall building residential flat

Residential highrise building fire of height above 200 m is now a concern in the Far East. Long-term survey study on fire load density indicated that high amount of combustibles over the local upper limit of 1135 M Jm⁻² used to be stored in residential flats. Wind-induced air-flow rates through openings at upper levels of those tall buildings can be very high. Stack effect in areas with large indoor and outdoor temperature differences (such as 14 °C indoor and − 30 °C outdoor at Harbin, Heilongjiang, China) will also give high ventilation rate through leakage areas. Adequate oxygen is then supplied to burn up all stored combustibles to give a big fire. In applying performance-based design to determine the fire safety provisions, heat release rate of the design fire is the first parameter to decide. In this paper, stack effect and wind action on possible increase in the heat release rate for fires in supertall residential buildings will be explored. Air intake rates through openings to rooms at high levels due to stack effect and wind action are estimated by simple empirical formula. The maximum heat release rates for well-developed room fires in these tall buildings under different stack and wind conditions are determined by varying two parameters. Air flow rate through openings in an 800 m tall building induced by wind gust can be over 20 times the value at ground level. Consequently, heat release rate can be much higher, confirming experimental studies on building fires under wind action.     

绿化和建筑布局对住宅小区的风热环境影响的数值模拟分析

良好的住宅小区风热环境可以加快室外热量的消散和污染物排放,保证居民的健康和舒适。影响小区风热环境的因素主要有小区布局、建筑形态及下垫面形式等。以青岛市一个实际小区为案例采用数值模拟的方法分析小区冬夏季行人高度的风场及温度场分布,评估设计的合理性,找出小区内风热环境不满足要求的区域。通过调整小区内建筑的布局和改变下垫面形式等方法改进小区的设计,并对改进后的方案进行模拟计算。通过模拟结果的对比发现:1合理布局建筑位置,在小区内形成风道可有效改善风环境;2改变下垫面热物性,提高地面材料的反射率,能够降低地面附近的空气温度和体感温度,改善小区热环境。     

厦门地区住宅自然通风节能设计初探

自然通风设计是结合气候的建筑设计,是实现建筑节能,创造健康人居环境的有效方法。厦门地区夏季炎热漫长且潮湿,本文在分析研究可借鉴厦门地区传统建筑自然通风设计经验等基础上,总结适应厦门地区住宅自然通风的技术措施。利用厦门地区亚热带湿润型季风气候特点,在住宅设计中充分考虑利用海风自然通风的优越性,以自然通风为主,空调设计为辅的原则,以期对厦门地区住宅自然通风节能设计提供参考。     

Prediction of wind environment in different grouping patterns of housing blocks

The idea of utilising natural ventilation for passive cooling has increasingly attracted the attention of researchers. In urban areas, this is intended to improve the outdoor and indoor thermal conditions without compromising the principles of sustainable building design. This study investigates the effect of building grouping pattern on the resulting wind environment in the outdoor spaces and the resulting ventilation potential of these buildings. A parametric three-dimensional modelling study has been carried out using computational fluid dynamics (CFD). Several configurations of housing blocks exposed to different wind directions have been modelled and compared considering the hot climate of Gaza. It has been found that grouping pattern of buildings as well as their orientation with respect to wind has a dramatic effect on the resulting airflow behaviour and pressure fields. Configurations that contain a central space articulated by buildings and oriented towards the prevailing wind can offer better exposure to air currents and better containment of wind. Such configurations are recommended for better wind-driven ventilation, where the main design objective is passive cooling.     

Investigation of indoor air pollutant dispersion and cross-contamination around a typical high-rise residential building: Wind tunnel tests

The dispersion of air pollutant in complex building environment has become of great concern as more and more people live in large and crowded cities. The present work is aimed at investigating the indoor air pollutant dispersion and possible cross-unit contamination with typical high-rise residential building design in Hong Kong. Experiments were performed in a boundary layer wind tunnel for a 1:30 scale model that represented a 10-story residential building in prototype. Tracer gas, simulating exhausted room air, was continuously released from three different floor levels, and its concentrations on the adjacent and opposite envelope surfaces were measured using fast flame ionization detectors, while the pressure distributions along building facade were also measured and examined under a typical incoming wind profile. By analyzing the pressure and concentration distribution, the risk of air cross-contamination was evaluated under two wind directions. The experiment results illustrated that, in the so-called re-entrance spaces, the pollutant can spread in both vertical directions, not only in the upward direction that was found under buoyancy effect, but also in the downward direction. Furthermore, dispersion can also occur in the horizontal direction, indicating a potential risk of cross-contamination in the horizontal adjacent flats could not be overlooked as well. The study on this physical process is directly useful for the purpose of prevention and control of infectious diseases outbreak in the residential environment. In the long run, the wind tunnel test data will serve to develop computational tools to assist natural ventilation design for high-rise buildings.     

茂名地区住宅建筑通风节能设计

茂名地区地处于夏热冬暖地带,在利用自然通风对改善住宅建筑室内热环境上有着重要作用一文章通过对住宅建筑的体量、栋间、地形、绿化及门窗部品等设计时,充分渗入了自然通风要素作了分析：既达到了建筑节能的要求,也提高了室内的通风质量,对人与自然的和谐环境有着积极意义。     

Predicting integrated thermal and acoustic performance in naturally ventilated high-rise buildings using CFD and FEM simulation

The study of ventilation windows for both natural ventilation and noise mitigation has drawn significant attention recently. This paper presents the numerical approaches to analyse the integrated thermal and acoustical performance of ventilation windows, for a residential building in tropical climate which employs double-layer noise mitigation window for natural ventilation. Given a set of outdoor wind conditions, the distributions of indoor flow and temperature fields are simulated using Computational Fluid Dynamics (CFD) model. The thermal comfort is evaluated using statistical Predicted Mean Vote (PMV) method. For the acoustic performance, noise radiation from road traffic is assumed as the noise source, and the sound insulation of building façade is simulated using Finite Element Method (FEM). From the simulation results, it is found that the thermal satisfaction response is closely related to the inlet wind temperature and speed, and the window opening size greatly affects the ventilation performance. From the case study in Singapore, during certain season, day/night time and with sufficient wind flow, the ventilation window can provide enough fresh air, maintain adequate thermal comfort and quiet acoustic environment for the occupants. The numerical approaches presented in this paper are applicable to general window design studies, and the simulation findings can be incorporated into green building planning. The advantages of using simulation approaches are highlighted and their limitations are discussed.     

Sensitivity of air change rates in a naturally ventilated atrium space subject to variations in external wind speed and direction

Design guidelines for natural ventilation (NV) in buildings focus on the potential hourly air change (ACH) rates based on the building space parameters. Critically, external airflow data is often assumed on the basis of a single mean wind speed and an associated prevailing wind direction. This can result in significant variation in ventilation rates and comfort conditions when non-design external wind conditions prevail. This paper describes a CFD study aimed at examining the influence of variations in external wind speed and direction on the air change rate for the atrium space of a two-storey naturally ventilated building. The building atrium is ventilated by a series of entry vents on one wall of the building in conjunction with roof vents. External wind speeds from 25 to 250% of the mean site wind speed (5.7 m/s) were examined and found to result in an almost linear increase in the ACH rate. For a single wind speed, the relationship between wind direction and the ACH rate was also found to be approximately linear for wind directions between 0° and 90° (orthogonal and parallel) to the wall vent openings, but non-linear for other wind directions (90–135°). More generally, the significant variation in the atrium ACH rate with changes in external wind conditions, evident in this particular building model, illustrates the importance of considering non-design wind conditions when designing NV buildings.     

Energy efficiency optimization of combined ventilation systems in livestock buildings

Good ventilation system in livestock buildings is necessary for removing excess moisture and heat and for improving building environment in general. Natural ventilation does not require energy consumption and on the other hand, animals would not be affected by electrical power failures. Because natural ventilation depends largely on temperature difference between inside and outside air and wind velocity and direction it is very important in early stages of building design to provide orientation and accurate opening areas. Numerical simulation of natural ventilation and computation of fluid dynamics in livestock buildings can be usefully integrated in whole ventilation system optimization and related energy consumption decrease. Even in mechanical system ventilation, from flow field obtained in numerical simulation it is possible to optimize these systems. CFD analysis is generally restricted to the study of buildings’ environment flows and space study, and the designer must supply boundary conditions in the form of external and internal buildings’ envelope/wall surface conditions. Finally, the needs for further research and engineering development are outlined.     

Airflow assessment in cross-ventilated buildings with operable façade elements

This paper presents an experimental study of basic cross-ventilation flow characteristics that are essential inputs for accurate natural ventilation modelling and design. The study focuses on a generic single-zone building model tested in a wind tunnel under isothermal flow conditions (wind-driven ventilation). An advanced experimental method based on particle image velocimetry (PIV) was developed to investigate the air velocity field in buildings with cross-ventilation. It was found that airflow patterns in rooms with cross-ventilation are complex and cannot be predicted by simplified macroscopic models such as the orifice equation. Inlet-to-outlet ratio and relative location of openings on a building façade are important parameters to be considered, in addition to the wall porosity. This study provides new insights that enable improved design and control of operable façade elements to enhance space cooling using natural ventilation.     

自然通风环境下办公建筑中庭空间热舒适性模糊优化研究

：随着绿色建筑设计理念深入人心,办 公建筑的中庭空间因其特有空间特质受到越来 越多的关注。通常办公中庭空间中的节能性与热 舒适性是一对矛盾体,而自然通风作为被动节能 技术之一,不仅能够促进中庭空间的内外空气 循环,改善室内空气质量,而且降低能耗和提升 热舒适性,较好地解决这一矛盾。以江雅园办公 楼中庭空间为案例进行研究,从中庭屋顶形态、 中庭高度及进风口开启方式三个变量因素出发, 引用模糊评估方法寻找出中庭空间自然通风热 舒适性最佳方案,结论显示在多个组合方案中 斜屋顶形态+进风口全部开启的方案热舒适性最 佳,同时也证明屋顶形态与通风方式的变化对自 然通风舒适性的影响较大,而中庭空间高度的变化对自然通风舒适性影响较小。本研究希望建立一套以风速和温度为评价指标的模糊体系,为自 然通风的热舒适性的评价提供一种客观的评估手段,从而为方案阶段的中庭空间设计提供一种 有效的优化方法。     

居住小区健康生活空间的营造探析

通过对多个住宅小区工程的建筑设计,从现状环境分析,指导思想与设计理念、设计原则、阳光、风、水、视觉、景观配置、建筑材料及人车分流等几个方面进行了深入分析,针对居住小区健康生活空间的设计进行了总结,为营造和谐健康的空间提供指导。     

A study of natural ventilation in a refuge floor

Under the Building Codes of Hong Kong Special Administration Region, the provision of refuge floors has been an indispensable element in high-rise building design since 1996. Wind-induced cross natural ventilation is an important design criterion of a refuge floor since it helps to prevent any smoke entering to become persistent state remained (logging) on the refuge floor. This paper reports a study of refuge floor natural ventilation induced by wind flow around a high-rise building with a refuge floor arriving from different wind incidence angles. The study is based on CFD simulations which are validated by wind tunnel measurements. The refuge floor under investigation has a main services core at the centre and support walls flush with the building walls along two opposite sides. The results reveal that at all wind angles, wind is able to enter the refuge space from the windward side and escape from the leeward side. At some wind angles, wind is found to re-enter the refuge space from the leeward opening and accumulate behind the main services core. Based on the results, we suggest that stairs connecting to the refuge space should be located inside the side corridors formed by the internal and external side walls.     

基于热环境模拟分析的滨河住区建筑布局研究

城市河流对住区热环境具有显著的改善作用。以深圳气候条件为参考,探讨河流与建筑布局对滨河住区热环境的影响,对改进滨河住区布局,提高住区热环境舒适性有重要作用。研究运用CFD模拟技术方法,分析在不同建筑布局模式下,基于河流影响的住区温度、相对湿度和风速的变化情况;以标准有效温度SET*为评价标准,探讨滨河住区建筑布局与热舒适的关系;基于河流产生的良好微环境气候效应,对住区建筑布局提出优化方法,为营造生态、舒适的滨河住区环境起到重要作用。研究表明,减小建筑面向盛行风的垂直投影面积、创造利于河流风向的通风降温廊道、以及营造相应的住区开敞空间等,是改善滨河住区热环境舒适性的主要建筑布局方法。     

Numerical study of the influences of different patterns of the building and green space on micro-scale outdoor thermal comfort and indoor natural ventilation

Citizens could enjoy a healthy and comfortable living environment if outdoor thermal comfort and sufficient natural ventilation are available in their dwellings. In this paper, numerical studies were performed with the Simulation Platform for Outdoor Thermal Environment (SPOTE) to investigate: (1) the thermal environment and pedestrian thermal comfort of the occupants in the open space with different patterns of the building and green space; (2) the wind pressures on the building facades and the natural ventilation rate of these buildings. The conclusions are summarized as follows: (1) it has been observed that the long facades of building and green space, which are parallel to the prevailing wind direction, can accelerate horizontal vortex airflow at the edges where such airflow could strengthen the convective exchange efficiency of hot air in low altitude and cold air in high altitude, and can obtain thermal comfort and sufficient natural ventilation at the pedestrian level; (2) after a series of simulations and comparisons, the configuration in which buildings are grouped in staggered layout with a centralized green space can provide better ventilation conditions and suitable air movement as a result of attenuated revised standard effective temperature (SET*). This configuration is regarded as the optimum pattern of the building and green space.     

Computational analysis of wind driven natural ventilation in buildings

The design of natural ventilation in buildings is often performed by means of computational fluid dynamics (CFD) techniques, whose application is gaining popularity. In the present study, Reynolds averaged Navier–Stokes equation (RANS) approach is applied to wind driven natural ventilation in a cubic building. Two different models are considered, namely the two-equation k–ɛ model and the Renormalization Group (RNG) theory. The velocity and pressure distribution inside and around the building are determined, as well as the ventilation rate, for three different configurations: cross ventilation, single-sided ventilation with an opening on the windward wall and single-sided ventilation with an opening on the leeward wall. The numerical results are compared with experimental data, showing a good agreement, particularly when using RNG. The discrepancy in the determination of the ventilation rate is reasonable and the flow distribution inside the building is properly described when RNG model is used. However, the k–ɛ model fails to determine the correct velocity components near the horizontal surfaces. According to these results, the RNG model can be considered a useful tool for the study of wind driven natural ventilation, especially for the assessment of the ventilation rate and of the air distribution inside a room.     

夏热冬冷地区生态节能农宅设计研究

以作者的获奖农宅设计方案为例,探讨福建夏热冬冷地区,从规划选址与平面设计、围护结构与体型设计、风能利用与通风设计、太阳能与沼气利用、建筑遮阳与庭院绿化等方面,如何使用低技术、低能耗,建造绿色、生态、节能的新型农村住宅。