Summer-performance of inclined roof solar chimney for natural ventilation

Effect of inclination of absorber on the airflow rate has been investigated in a solar induced ventilation system using Roof Solar Chimney (RSC) concept. During summer months, due to the higher altitude of sun, absorber at small inclination with the horizontal plane captures more solar radiation, but suffers with reduction in the stack height. Results of the developed solution show that optimum absorber inclination varies from 40° to 60° depending upon the latitude of place. At Jaipur (India) 45° is found to be optimum for obtaining maximum rate of ventilation. At this inclination, the rate of ventilation is about 10% higher as compared to 60° and 30° inclinations. Experimental investigations show good agreement with the theoretical results. Roof Solar chimney of this size can easily be mounted on residential buildings for enhancing natural ventilation.     

太阳能强化烟囱技术在强化室内自然通风中的研究进展

详细阐述了研究背景、技术原理、研究进展以及研究意义。在总结国内外学者在该领域的主要研究方法和成果的基础上,指出了目前存在的问题。结合当前我国室内通风设计的现状,给出了富有建设性的意见。     

An analytical and numerical study of solar chimney use for room natural ventilation

The solar chimney concept used for improving room natural ventilation was analytically and numerically studied. The study considered some geometrical parameters such as chimney inlet size and width, which are believed to have a significant effect on space ventilation. The numerical analysis was intended to predict the flow pattern in the room as well as in the chimney. This would help optimizing design parameters. The results were compared with available published experimental and theoretical data. There was an acceptable trend match between the present analytical results and the published data for the room air change per hour, ACH. Further, it was noticed that the chimney width has a more significant effect on ACH compared to the chimney inlet size. The results showed that the absorber average temperature could be correlated to the intensity as: (T_w = 3.51I^0.461) with an accepted range of approximation error. In addition the average air exit velocity was found to vary with the intensity as (ν_ex = 0.013I^0.4).     

Enhancement of natural ventilation in buildings using a thermal chimney

A new module was developed for and implemented in the EnergyPlus program for the simulation and determination of the energy impact of thermal chimneys. This paper describes the basic concepts, assumptions, and algorithms implemented into the EnergyPlus program to predict the performance of a thermal chimney. Using the new module, the effects of the chimney height, solar absorptance of the absorber wall, solar transmittance of the glass cover and the air gap width are investigated under various conditions. Chimney height, solar absorptance and solar transmittance turned out to have more influence on the ventilation enhancement than the air gap width. The potential energy impacts of a thermal chimney under three different climate conditions are also investigated. It turned out that significant building cooling energy saving can be achieved by properly employing thermal chimneys and that they have more potential for cooling than for heating. In addition, the performance of a thermal chimney was heavily dependent on the climate of the location.     

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.     

外界风影响下高层建筑竖井自然排烟可行性

以高层建筑竖井自然排烟为研究对象,利用FDS软件对竖井自然排烟进行模拟,研究外界风对自然排烟的影响.模拟结果表明:当排烟口处于迎风面时,竖井自然排烟受到的影响最大;当竖井顶部四面开启排烟口时,自然排烟受室外风的影响最小.由模拟可见,通过合理设计竖井结构,高层建筑竖井自然排烟是可行的.     

太阳能烟囱结构对通风效果影响的数值研究

采用Realizable K-ε湍流模型和DO辐射模型对太阳能烟囱内部的流场和温度场进行了数值模拟,计算结果与文献中实验值吻合得较好。对太阳能烟囱高度和宽度等结构因素对通风效果的影响进行了模拟分析,结果表明,诱导风量随烟囱高度增大而增大,随宽度增大先增大后减小;Gr可作为设计太阳能烟囱高度时的参考;渐缩型通道能有效防止通道内回流的产生。     

双曲线钢筋混凝土冷却塔通风筒壁施工组织

结合具体工程实例，从施工准备、施工组织要点等方面，就双曲线钢筋混凝土冷却塔通风筒壁施工过程中的技术措施进行了介绍，提出了几点安全注意事项。     

Physical and numerical modelling of a solar chimney-based ventilation system for buildings

This paper describes an experimental and numerical study to analyse the thermal performance of a bio-climatic building prototype in Nigeria. The roof performs as a solar chimney, generating an air flow through the living space of the building to provide cooling. Experimental tests on a 1:12 small-scale model of the prototype are outlined, and the results, bith qualitative and quatitative, are used to validate a two-dimensional flow simulation model, in which the steady state conservation equations of mass, momentum and thermal energy are solved using a finite volume formulation.

The experimental and numerical results, expressed in terms of temperature and velocity fields, for two different window geometries are critically evaluated and compared with good agreement.     

Control of natural ventilation for aerodynamic high-rise buildings

The aim of the paper is to present a framework for the optimal control of natural ventilation. To account for the significant crossflow between zones, the notion of ASHRAE-equivalent airflow is proposed which is used to evaluate the quality of ventilation provided to different zones within a building. A model-based predictive control approach is developed which is used to simulate different ventilation strategies and select the most appropriate strategy. To this end, the rationale behind choosing an objective function that captures the goals of a ventilation system is described, and candidate objective functions are discussed. Finally, an illustrative example with an elliptical cross-section building is discussed in detail. The framework for model-predictive control developed in this paper is applicable beyond natural ventilation and high-rise buildings.     

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。     

Thermodynamical analysis of dry cooling tower and solar chimney power plant combination

Solar chimney power plant is one of the rather new technologies that can produce power from solar energy. Its high stack is one of the important parts of the system in which the differential density of air among its top and bottom sections causes air-flow. Dry cooling towers are used in industries for cooling condensing water by utilising this concept and generating air-flow. The structural and conceptual similarity between these two systems cause the feasibility of their combination and usage of waste energy in industries. In this article, a simple and useful analytical thermodynamic model is improved in order to estimate the thermodynamic flow properties for combining both systems. Results show that the stack height and diameter are effective parameters in recovery of power. Moreover, the results show that the collector area does not remarkably affect the system performance.     

Experimental study on natural ventilation performance of one-sided wind catcher

Hydrodynamic performance of a one-sided wind catcher was investigated by experimental wind tunnel and smoke visualization testing. Wind catchers or what is called Baud-Geers in Persian language was a main component of buildings in central region of Iran and the neighboring countries. A Baud-Geer is a tower used to capture wind from external air stream and induce it into the building in order to provide natural ventilation and passive cooling. Due to geographical coordinates of the region, wind power and the direction of blowing wind, wind catchers are employed in different heights, cross sections of the air passages and the places and the number of the openings. The one-sided wind catcher has only one channel as a passage of induced air and is often related to the areas where there is prevailing wind. These Baud-Geers are employed to catch the wind blowing at higher elevations and direct it to the building, causing it to leave through windows, doors or other exhausted segments. In this study a 1:40 scale model of Kharmani's School Baud-Geer was employed and the induced air flow rate into the test room and the pressure coefficients around all surfaces of its channel were measured for different values of approaching air incident angles. Using measured pressure coefficients, the theoretical values of ventilation air flow were estimated to evaluate ability of simplified models in natural ventilation studies. Due to placing of urban full-scale wind catchers in the boundary layer of atmospheric winds, the effect of this phenomenon was also examined. The experiments were conducted when the wind catcher model with adjoining house was placed in the wake of upstream objects, resembling neighboring buildings. It was found that for an isolated wind catcher model, the maximum efficiency is achieved at zero air incident angle. Also it was concluded that the angle of incidence of the wind, the presence of an upstream building around the structure and blowing of atmospheric wind influence the pressure coefficients, the rate and the direction of ventilation air flow.     

Structural stability of concrete wind turbines and solar chimney towers exposed to dynamic wind action

Apart from burning classical fossil resources or generating nuclear power, alternatives have been developed, like the classical ways to capture energy from wind, water and sun, or the innovative solar chimney concept.The paper presents some structural aspects of classical wind energy turbines, like their high-cycle dynamic loading and reaction as well as their fatigue behaviour. Actual research results concerning pre-stressed concrete tower constructions for wind turbines will be focused on. For the solar chimney concept the structural challenges concerning wind action, eigenfrequencies, stiffening and shape optimization with special focus on the inlet guide vanes will be discussed. Both classical wind turbines and the innovative solar chimney concept may successfully contribute to the future energy supply in Southern Africa.     

建筑自然通风模拟技术的回顾和应用

介绍了现有的自然通风模拟软件,分析了其共性和差异.以国家游泳中心为例,详细介绍了自然通风模拟技术的应用.国家游泳中心采用机械辅助自然通风方式,在节能设计中利用了建筑环境集成模拟软件Visualesp-r,以建筑物综合能耗为目标函数,模拟确定了最优通风模式.模拟预测的结果与现场实测结果非常吻合.     

Coupling of thermal mass and natural ventilation in buildings

The coupling of thermal mass and natural ventilation is important to passive building design. Thermal mass can be classified as external thermal mass and internal thermal mass. Due to great diurnal variation of ambient air temperature and solar radiation intensity, heat transfer through building envelopes, which is called external thermal mass, is a complex and unsteady process. Indoor furniture are internal thermal mass, affecting the indoor air temperature through the process of absorbing and releasing heat. In this paper, a heat balance model coupling the external and internal thermal mass, natural ventilation rate and indoor air temperature for naturally ventilated building is developed. In this model, the inner surface temperature of building envelopes is obtained based on the harmonic response method. The effect of external and internal thermal mass on indoor air temperature for six external walls is discussed of different configurations including lightweight and heavy structures with and without external/internal insulation. Based on this model, a simple tool is developed to estimate the indoor air temperature for certain external and internal thermal mass and to determine the internal thermal mass needed to maintain required indoor air temperature for certain external wall for naturally ventilated building.     

The fluid mechanics of natural ventilation—displacement ventilation by buoyancy-driven flows assisted by wind

This paper describes the fluid mechanics of natural ventilation by the combined effects of buoyancy and wind. Attention is restricted to transient draining flows in a space containing buoyant fluid, when the wind and buoyancy forces reinforce one another. The flows have been studied theoretically and the results compared with small-scale laboratory experiments. Connections between the enclosure and the surrounding fluid are with high-level and low-level openings on both windward and leeward faces. Dense fluid enters through windward openings at low levels and displaces the lighter fluid within the enclosure through high-level, leeward openings. A strong, stable stratification develops in this case and a displacement flow is maintained for a range of Froude numbers. The rate at which the enclosure drains increases as the wind-induced pressure drop between the inlet and outlet is increased and as the density difference between the exterior and interior environment is increased. A major result of this work is the identification of the form of the nonlinear relationship between the buoyancy and wind effects. It is shown that there is a Pythagorean relationship between the combined buoyancy and wind-driven velocity and the velocities which are produced by buoyancy and wind forces acting in isolation. This study has particular relevance to understanding and predicting the air flow in a building which is night cooled by natural ventilation, and to the flushing of gas from a building after a leak.     

深圳居住建筑夏季自然通风降温实验研究

以深圳市六种布局不同、楼层不同的居住建筑为对象，调查了夏季室内热环境，测试了不同通风工况下围护结构内表面以及室内外温湿度，分析了居住建筑在夏季采用自然通风降温的可行性，比较了持续自然通风与间歇自然通风的优劣以及不同遮阳方式的遮阳效果，提出了采用自然通风降温方式的条件及建筑设计中应改进之处。     

Natural ventilation performance of a double-skin façade with a solar chimney

Double-skin façade is getting more and more attention as it provides many possibilities for energy conservation and at the same time creates good indoor environment. In this paper, natural ventilation performance of a double-skin façade is highlighted. A prototype building is proposed, which is thought to be an eight-storey office building with an atrium space in the north side. The south façade of the building is a double-skin façade and a thermal storage space called solar chimney is considered above the double-skin space. Actually, the double-skin space is connected with the chimney channel. Reduced scale model experiments and computational fluid dynamics (CFD) analysis are carried out in this research to evaluate the natural ventilation performance of the prototype building.     

Computational modeling of natural ventilation in low-rise non-rectangular floor-plan buildings

Natural ventilation (NV) is a relevant passive strategy for the design of buildings in seek of energy savings and the improvement of the indoor air quality and the thermal comfort. The main aim of this work is to present a comprehensive NV modeling study of a non-rectangular floor-plan dwelling. Given the arbitrary shape of the building, recourse is made to computational fluid dynamics (CFD) to determine the surface-averaged pressure coefficients (\(\overline {{C_p}} \)). The CFD model was calibrated to match experimental data from an extensive wind tunnel database for low-rise buildings. Then, \(\overline {{C_p}} \) computation via CFD is used to feed the building performance simulation software EnergyPlus, in replacement of the built-in Swami and Chandra parametric model that is only valid for estimating \(\overline {{C_p}} \) in rectangular floor-plan buildings. This computational tool is used to investigate the effect of NV on the thermal performance and the airflow rate in a social housing located in the Argentine Littoral region. Simulation results of the considered building show that NV enables to reduce even more than 65% of the cooling degree-hours. Furthermore, regarding to the \(\overline {{C_p}} \) source (either CFD or Swami and Chandra’s), it is also found that this data has a considerable effect on the airflow rates, but a little effect on the thermal performance.