CFD simulations of natural ventilation behaviour in high-rise buildings in regular and staggered arrangements at various spacings

Natural ventilation, which is in line with the concepts of sustainability and green energy, is widely acknowledged nowadays. Prevailing winds in urban areas are unavoidably modified by the increasing number of closely placed high-rise buildings that significantly modify the natural ventilation behaviour. This paper explores the effects of building interference on natural ventilation using computational fluid dynamics (CFD) techniques. The cross-ventilation rate (temporal-average volumetric airflow rate) of hypothetical apartments in a building cluster under isothermal conditions was examined using the standard two-equation k − ? turbulence model. The sensitivity of ventilation rate to wind direction, building separation and building disposition (building shift) was studied. Placing buildings farther away from one another substantially promoted the ventilation rate, cancelling the unfavourable interference eventually when the building separation was about five times the building width (the optimum separation). The characteristic flow pattern leading to this behaviour was revealed. With the adoption of building disposition, the optimum separation could be reduced to three times the building width. In addition, the airflow rates could be doubled with suitable shifts. Building disposition is therefore one of the feasible solutions to improve the natural ventilation performance in our crowded environment.     

A venturi-shaped roof for wind-induced natural ventilation of buildings: Wind tunnel and CFD evaluation of different design configurations

Wind tunnel experiments and Computational Fluid Dynamics (CFD) are used to analyse the flow conditions in a venturi-shaped roof, with focus on the underpressure in the narrowest roof section (contraction). This underpressure can be used to partly or completely drive the natural ventilation of the building zones. The wind tunnel experiments are performed in an atmospheric boundary layer wind tunnel at scale 1:100. The 3D CFD simulations are performed with steady RANS and the RNG k-? model. The purpose of this study is twofold: (1) to evaluate the accuracy of steady RANS and the RNG k-? model for this application and (2) to assess the magnitude of the underpressures generated with different design configurations of the venturi-shaped roof. The CFD simulations of mean wind speed and surface pressures inside the roof are generally in good agreement (10–20%) with the wind tunnel measurements. The study shows that for the configuration without guiding vanes, large negative pressure coefficients are obtained, down to −1.35, with reference to the free-stream wind speed at roof height. The comparison of design configurations with and without guiding vanes shows an – at least at first sight – counter-intuitive result: adding guiding vanes strongly decreases the absolute value of the underpressure. The reason is that the presence of the guiding vanes increases the flow resistance inside the roof and causes more wind to flow over and around the roof, and less wind through it (wind-blocking). As a result, the optimum configuration is the one without guiding vanes.     

Commonly encountered seismic design faults due to the architectural design of residential buildings in Turkey

The 17 August 1999 and 12 November 1999 earthquakes in Western Anatolia provided undesirable field evidence that most of the low story residential reinforced concrete buildings have very poor earthquake resistance. Architectural design faults negatively affect the structural behavior of buildings. In Turkey, earthquake-resistant design is considered to be exclusively within the field of responsibility of structural engineers. As a result, architects and especially students of architecture are not well informed about the effect of their design decisions on the seismic performance of the buildings. Structural damages in collapsed buildings demonstrate that most of the design faults that lead to destruction of buildings are due to architectural decisions. This paper intends to present the concept of earthquake-resistant design in a comprehensible format for the architects and builders, therefore aims to contribute to the efforts of creating a better awareness of earthquake resistant building design.     

Calculation of wind-driven cross ventilation in buildings with large openings

A simplified macroscopic method is commonly used for wind-driven ventilation analysis of buildings with small openings. Consequently, it is reasonable to question if and under what conditions will this method provide accurate results in predicting ventilation flow rates in buildings with large openings. We investigate a single-zone cubic building with two equal large openings using a computational fluid dynamics approach. We analyzed the driving forces and the ventilation flow rates due to wind as a function of the geometry, size and relative location of the two openings. The ventilation flow rates are found to be affected by both wind flows around and through the building when the two openings are relatively large. The simplified macroscopic method can provide reasonable engineering accuracy (i.e., less than 10% error) when the porosity of the building envelope does not exceed a critical value. This critical value is not a constant; instead it depends significantly on the degree of alignment between the wind direction and the character of the dominant stream tube associated with the flow through the room. We found that the simplified macroscopic method fails to provide acceptable accuracy when this stream tube is truly dominant and parallel to the wind direction. The effects of wall thickness and aspect ratio of openings are also investigated.     

浅谈自然通风原理与建筑设计

对自然通风进行了介绍,通过对风压通风和热压通风的原理进行分析,明确了自然通风原理,并进一步结合建筑设计实例进行了解析,为今后建筑设计中的自然通风设计提供了良好的技术支撑.     

Low energy architecture for a severe US climate: Design and evaluation of a hybrid ventilation strategy

Natural ventilation, relying on openings in the façade, is applicable to a limited range of climates, sites and building types. Advanced naturally ventilated buildings, such as those using stacks to encourage buoyancy driven airflow, or hybrid buildings, which integrate both natural and mechanical systems, can extend the range of buildings and climate within which natural ventilation might be used.     

高大空间建筑的自然通风模拟案例研究

针对大空间玻璃幕墙建筑,将多区域流体网络计算软件Contamw与热流及热平衡计算的Matlab程序相结合,以实现其自然通风与热的耦合计算,同时,利用建筑性能模拟软件Ecotect计算玻璃幕墙的入射辐射量,以实现精确的室内热流计算。     

Optimising the ventilation configuration of naturally ventilated livestock buildings for improved indoor environmental homogeneity

Due to the geometrical structure and ventilation configuration of naturally ventilated livestock buildings the animal occupied zone can experience large heterogeneities in ventilation efficiency. Ensuring a homogeneous indoor environment is important when designing naturally livestock buildings as producers should be confident that all animals are receiving the same environmental conditions, at least for the prevailing climate. Moreover, by including climate homogeneity in the building design process, the occurrence of high airspeeds in specific regions of a building can be reduced during windy outdoor conditions, thereby reducing the cold-stressing of animals in these regions. Therefore, it is desirable to know how to alter the geometrical features of a building in order to promote homogeneity in the indoor environment. In the present study, response surface methodology and computational fluid dynamics were used to develop predictive models that described the homogeneity of the indoor environment of a naturally ventilated livestock building as a function of its geometry and ventilation configuration. Three different eave opening conditions were chosen in order to improve the applicability of the developed response surfaces to practical situations encountered in Ireland. Results showed that for high to medium porosity eave opening conditions the environmental homogeneity was most sensitive to the building's roof pitch. However, when low porosity eave opening conditions were used the homogeneity was found to be highly sensitive to the sidewall height. Overall, this study found that modifying the building geometry has the greatest effect on environmental heterogeneity when the most restrictive eave opening condition was employed. It is also hoped that with the developed equations, a designer can subsequently select the best combination of design variables in order to achieve good uniformity in a naturally ventilated calf building.     

Impact of adaptive thermal comfort on climatic suitability of natural ventilation in office buildings

In earlier work [1], NIST developed a climate suitability analysis method to evaluate the potential of a given location for direct ventilative cooling and nighttime ventilative cooling. The direct ventilative cooling may be provided by either a natural ventilation system or a fan-powered economizer system. The climate suitability analysis is based on a general single-zone thermal model of a building configured to make optimal use of direct and/or nighttime ventilative cooling. This paper describes a new tool implementing this climate suitability methodology and its capability to consider an adaptive thermal comfort option and presents results from its application to analyze a variety of U.S. climates. The adaptive thermal comfort option has the potential to substantially increase the effectiveness of natural ventilation cooling for many U.S. cities. However, this impact is very dependent on the acceptable humidity range. If a dewpoint limit is used, the increase is significant for a dry climate such as Phoenix but much smaller for humid climates such as Miami. While ASHRAE Standard 55 does not impose a limit on humidity when using the adaptive thermal comfort option, the necessity of limiting humidity for other reasons needs to be considered.     

对建筑自然通风设计的探讨

介绍了自然通风在生态建筑中的应用,并对自然通风的研究方法及研究工具做了简单介绍,分析了建筑设计对自然通风的影响,通过对国内外著名生态建筑中采用的自然通风技术的例子,提出了一些对于风能利用的处理方法。     

Forcing biological sciences into architectural design: On conceptual confusions in the field of biomimetic architecture

Certain confusion may be observed in the field of biomimetic architecture, as it emerges at the crossroad of two disciplinary domains: architectural design and biological sciences. If biomimetics is defined as a science, once it is applied to architecture, biomimetic architecture should logically be defined as a science too. This assertion collides with the nature of architectural design, which may rather be defined as a technology: its aim is to transform the world, not to explain it. On the one hand, there is no obvious relationship between architecture and life sciences. On the other hand, the biomimetic approach tends to redefine the concept of science itself by seeking to avoid the excesses of scientism. Moreover, existing applications of biomimetic design show that it is difficult to observe a genuine biomimetic architecture; most cases are closer to engineering component or urban planning and sometimes they involve little or no life sciences. The aim of this paper is to describe this conceptual confusion through two movements called “forcings”, occurring between design and science. These forcings are conceptualised as shifts between constructed scientific objects and given empirical objects. Models, used in biology as in architecture, allow these shifts by virtue of their double function. They are both tools for knowledge and for design, thus they may be conceptually forced into what they are not supposed to be, particularly in the field of biomimetic architecture where design process and scientific knowledge are said to meet.     

Development of a computational tool to quantify architectural-design effects on thermal comfort in naturally ventilated rural houses

In the present study, the effect of the opening size and building direction on night hours thermal comfort in a naturally ventilated rural house is investigated. Initially, the airflow in and around the building is simulated using a validated computational fluid dynamics (CFD) model. Local climate night-time data (wind velocity and direction, temperature and relative humidity) are recorded in a weather station and the prevailing conditions are imposed in the CFD model as inlet boundary conditions. The produced airflow patterns are then used to evaluate indoor thermal comfort. For this reason, special thermal comfort indices, i.e. the well-known predicted mean vote (PMV) index and its modifications especially for natural ventilation, are calculated with respect to various residential activities. Mean values of these indices (output variables) within the occupied zone are calculated for different combinations of opening sizes and building directions (input variables), to generate a database of input–output pairs. Finally, the database is used to train and validate Radial Basis Function Artificial Neural Network (RBF ANN) input–output “meta-models”. It is demonstrated that the proposed methodology leads to reliable thermal comfort predictions, while the optimum design variables are easily recognized.     

Experimental and numerical study on natural ventilation performance of various multi-opening wind catchers

Wind catcher as a natural ventilation system is increasingly used in modern buildings to minimize the consumption of non-renewable energy and reduce the harmful emissions. Height, cross section of the air passages and also place and the number of openings are the main factors which affect the ventilation performance of a wind catcher structure. In this study, experimental wind tunnel, smoke visualization testing and computational fluid dynamic (CFD) modeling were conducted to investigate ventilation performance of wind catchers with different number of openings to find how the number of opening affects hydrodynamic behavior of wind catchers. To achieve this particular aim, five cylindrical models with same cross section areas and same heights were employed. The cross sections of all these wind catchers were divided internally into various segments to get two-sided, three-sided, four-sided, six-sided and twelve-sided wind catchers. The experimental investigations were conducted in an open circuit subsonic wind tunnel. For all these five shapes, the ventilated air flow rate into the test room was measured at different air incident angles. Numerical solutions were used for all these five configurations to validate the proposed measuring techniques and the corresponding wind tunnel results. The results show that the number of openings is a main factor in performance of wind catcher systems. It also shows that the sensitivity of the performance of different wind catchers related to the wind angle decreases by increasing the number of openings. Moreover, comparing with a circular wind catcher a rectangular system provides a higher efficiency.     

Effect of volumetric heat sources on hysteresis phenomena in natural and mixed-mode ventilation

The summer-time cooling efficiency of hybrid buildings depends critically upon exploiting multiple environmental resources to dispose of waste heat. To this end, many previous studies have explored the role of wind, which exerts different static pressures on a building's windward and leeward facades. Here, we consider how this methodology may be extended to the converse problem of winter-time heating wherein hot, buoyant air is purposefully supplied to the interior space using a coupled ventilation scheme. A “blocked” flow regime is desired such that cold air inflow is impeded; to avoid interstitial condensation, the pressure distribution within the building must favor outflow through designated extraction vents. For the idealized geometry considered here, blocked conditions represent a unique solution to the flow equations in well-defined regions of parameter space. The likelihood of blocking may be increased through prudent choice of extraction vent size/orientation depending on the external forcing conditions. A discussion of the inherent tradeoffs associated with multi-season design of hybrid buildings is also presented.     

A laboratory experiment on natural ventilation through a roof cavity for reduction of solar heat gain

The study targets the reduction of roof solar heat gain through the use of natural ventilation in a roof cavity. This study is mainly concerned with factory buildings. Experimental outcomes were obtained from an inclined cavity model which was heated on the upper surface to mimic solar radiation on a roof. The dimensions of the cavity were 4882 mm× 400 mm × 78 mm. The two opposing smallest sides were allotted as the inlet and outlet, and narrowed to simulate resistance of the air flow in practical applications. Temperature and velocity measuring facilities were prepared in the experimental model. A number of measurements were carried out by varying the combinations of different heat production, inclination angles, and opening ratios. It was found that resistance to heat and air flow in the cavity was strongly influenced by the opening size. When the Reynolds number was examined, it showed that the flow belonged to the laminar region. The average velocity reached to 0.25 m/s at the highest in the examined cases. In other words, the cavity air was turned over 184 times in an hour. Natural ventilation in the roof cavity seemed to be effectively applicable to solar incidence discharges in factory buildings.     

建筑户型对自然通风效果的影响

从自然通风的基本原理入手,采用计算流体力学方法对典型户型的自然通风效果进行了研究,模拟发现不同户型对自然通风的效果影响很大,提出了改进自然通风效果的建议,对今后的建筑设计给出了很好的参考和改进依据。     

A study on a porous residential building model in hot and humid regions: Part 1—the natural ventilation performance and the cooling load reduction effect of the building model

This study targets environmental load reduction in hot and humid regions. It reveals the effects that porous residential buildings have on the natural ventilation performance and, consequently, the cooling load reduction. Two residential building models, namely a model with a void ratio of 0% and a model with a void ratio of 50%, are evaluated using computational fluid dynamics (CFD) analysis and thermal and airflow network analysis. The analysis on components of the heat load indicates that improvements in the natural ventilation performance would significantly reduce the cooling load.     

住宅建筑设计的常见问题

指出住宅设计应当贯彻“适用、经济、安全、美观”的建设方针和“以人为本”的指导思想,分析了住宅建筑设计中的常见问题,以更新住宅设计观念,提高住宅设计水平,设计出更适合消费者的住宅;     

Modelling of cowl performance in building simulation tools using experimental data and computational fluid dynamics

Exhaust cowls are used in conjunction with hybrid ventilation systems to efficiently convert wind energy into negative pressure and thus minimize the electrical energy required by the extract fan. Yet the fact that cowl performance is largely dictated by operating conditions imposes particularly stringent demands on modelling. This paper demonstrates, by way of a concrete example, the need for and potential benefits of a new methodological approach to the modelling of cowls. The study focuses on a specific modelling strategy, applied within a building simulation program, for a cowl used in a hybrid ventilation system. The method is progressively simplified to produce four variants, which chiefly vary according to their level of detail and, hence, the associated modelling effort. Wind pressure coefficients at facade, above roof and in the cowl are needed for all model variants. Some of the investigated variants rely on CFD computations of airflow around the building to determine these values. This study uses the example of a single-family house (SFH) to identify those criteria requiring particular attention in the performance of CFD numerical flow analyses. All four variants are examined on the basis of this example to determine which simplifications to the model are appropriate and permissible without unduly compromising the accuracy of the results.     

A numerical investigation into the effect of Windvent louvre external angle on passive stack ventilation performance

The Windvent is a commercially available passive ventilation device. The device is constructed from sheet metal and works on the principle of pressure differential. Whereby warm air rises, creating a low pressure in the receiving room, which then draws in the fresh air. This paper investigates the effect of altering the external angle of the Windvent louvres against the internal pressure and velocity within the device and the microclimate velocity. Numerical analysis is carried out using a commercial Computational Fluid Dynamics (CFD) code, to investigate the effect of various louvre angles (range 10–45°) on pressure and velocity to optimise the device performance. The results show that the louvre performance mimics that of thin airfoil from aerodynamic theory. The relationship between trailing-edge stall and delivery velocity is established. The optimum louvre angle with a prevailing wind velocity of 4.5 m/s is shown to be 35° with a stall angle of 40° illustrated. The external, performance enhancing louvre angle, determined through this investigation is subject to UK patent number 0809311.4.