Experimental investigations on solar chimney for room ventilation

Experimental investigations on a small size solar chimney show that the rate of ventilation increases with increase of the ratio between height of absorber and gap between glass and absorber. This finding is in agreement with results of the steady-state mathematical model developed for analysis of such systems. Nine different combination of absorber height and air gap have been investigated on the experimental set-up. Highest rate of ventilation induced with the help of solar energy was found to be 5.6 air change per hour in a room of 27 m³, at solar radiation 700 W/m² on vertical surface with the stack height-air gap ratio of 2.83 for a 1 m high chimney.     

太阳能烟囱发电系统的CFD模拟研究

太阳能烟囱发电技术是一项综合应用温室效应技术、烟囱技术及风力涡轮发电技术于一体的太阳能发电新技术,是实现大规模开发和利用太阳能的一种新途径.采用计算流体动力学(CFD)方法对太阳能烟囱发电系统的速度场、压力场和温度场进行了数值模拟.结果表明:在其它条件不变的情况下,集热棚周边高度对系统的发电功率没有影响;太阳能烟囱直径存在一最佳值,使发电系统输出的发电功率最大.     

Experimental study for natural ventilation on a solar chimney

Thermal performance of a solar chimney for natural ventilation was experimentally investigated. The experimental model was implemented on full scale and real meteorological conditions, so that experimental results will be compared with the simulation results. The results show that for a maximum irradiance of 604 W/m², occurring around 13:00 h on September 15th, 2007, a maximum air temperature increment of 7 °C was obtained through the solar chimney. Also, a volumetric air flow rate ranging from 50 to 374 m³/h was measured on that day. Thus, an average air flow rate of 177 m³/h was achieved from 0:00 h to 24:00 h. The experimental solar chimney discharge coefficient, C_d, was 0.52. This coefficient is useful to determine the mass flow rate in the solar chimney design. It was observed that the air flow rate through the solar chimney is influenced by a pressure difference between input and output, caused by thermal gradients and wind velocity, mainly.     

Solar chimney and building ventilation

This study is concerned with the design of a solar chimney to induce ventilation in a building. CFD modelling techniques were used to assess the impacts of inclination angle, double glazing and low-emissivity finishes on the induced ventilation rate. It was found that for a south-facing chimney, an inclination angle of 67.5° from the horizontal was optimum for the location chosen, giving 11% greater efficiency than the vertical chimney, and that a 10% higher efficiency was obtained by using a low-emissivity wall surface.     

Experimental and simulation studies on the effect of suction opening orientation on solar vertical chimney

The zero energy building considered is a single storey building in Tiruchirappalli city retrofitted with various green features. This study investigated the effect of a suction opening orientation on a vertical solar chimney (VSC), integrated into a one-storey building. It was designed, manufactured and tested through selection of different suction openings for the entry of air, including right, left, front, back, both right and left and both front and back sides. Genetic algorithm (GA) calculates maximum air flow rate for a building with VSC for better suction opening, in Tiruchirappalli's dry, environmental conditions. GA is a useful technique for finding an improved suction opening specifically in the presence of a host of independent parameters which are large. The obtained results are related to fluid flow temperature distribution along the chimney, mass flow rate and air change per hour. The findings between the GA and the experimental results show sound agreement.     

Numerical study on mixed buoyancy-wind driving induced flow in a solar chimney for building ventilation

In a solar chimney, the buoyancy induced flow of air generates ventilation of the building where the chimney is attached. When atmospheric wind blows over the upper part of a solar chimney, a mixed buoyancy-wind driving induced flow appears, and then the thermal behaviour of the chimney changes drastically. Assuming that the chimney is devoid of any protective device at its upper part, numerical results for the pressure difference coefficients, average Nusselt number and the induced mass flow rate are obtained for values of Rayleigh number varying from 10⁷ to 10¹² (symmetrically, isothermal heating condition) and 10¹¹ to 10¹⁵ (symmetrically, uniform heat flux heating condition), with wind speeds from 0 to 10 m/s. A correlation for the non-dimensional mass flow rate is presented, which is valid for the complete range of relevant parameters regarded, with an average deviation about 6%.     

竖直式太阳能烟囱优化及其通风性能研究

介绍了一种基于风压和热压耦合作用的竖直式太阳能烟囱优化结构,通过三维数值模拟,研究外筒高度h、通道Ⅱ宽度w、室外风速v和太阳辐射强度I对其通风性能的影响。结果表明:在相同工况下,优化结构的太阳能烟囱的通风性能优于传统的竖直式太阳能烟囱;风压和热压对通风量均为增益作用;通风量随外筒高度h的增加而持续增大;当增加通道Ⅱ宽度w时,通风量先增后减再增,在w=50 mm附近通风量达到最大值。     

Induced flow for ventilation and cooling by a solar chimney

An experimental and numerical model of a solar chimney was proposed in order to predict its performance under varying geometrical features in Iraqi environmental conditions. Steady, two dimensional, turbulent flow was developed by natural convection inside an inclined solar chimney. This flow was investigated numerically at inclination angles 15° to 60°, solar heat flux 150–750 W/m² and chimney thickness (50, 100 and 150) mm. The experimental study was conducted using a single solar chimney installed on the roof of a single room with a volume of 12 m³. The chimney was 2 m long; 2 m wide has three gap thicknesses namely: 50, 100 and 150 mm. The performance of the solar chimney was evaluated by measuring the temperature of its glass cover, the absorbing wall and the temperature and velocity of induced air. The results of numerical model showed that; the optimum chimney inclination angle was 60° to obtain the maximum rate of ventilation. At this inclination angle, the rate of ventilation was about 20% higher than 45°. Highest rate of ventilation induced with the help of solar energy was found to be 30 air changes per hour in a room of 12 m³ volumes, at a solar radiation of 750 W/m², inclined surface angle of 60°, aspect ratio of 13.3 and chimney length of 2 m. The maximum air velocity was 0.8 m/s for a radiation intensity of 750 W/m² at an air gap of 50 mm thickness. No reverse air flow circulation was observed even at the largest gap of 150 mm. The induced air stream by solar chimney can be used for ventilation and cooling in a natural way (passive), without any mechanical assistance.     

Dynamic simulation and parametric sensitivity studies on a flat-plate solar collector

A dynamic simulation program for a flat-plate solar collector has been developed and used for a parametric sensitivity study of the collector. A computer simulation language, C.S.M.P., was used for the simultaneous solution of the differential equations describing the system. The program is developed from basic principles and defined parameters, so that the effect of each element of the collector on its efficiency and outlet fluid temperature can be analyzed. The dynamic simulation program was validated by comparing calculated with actual test results on a commercial flat-plate solar collector; the agreement between the results was found to be very good.Sensitivity studies were carried out to determine the effect of the following parameters on the performance of a single-glazed solar collector: heat transfer coefficient between absorber plate and fluid transport tubes; fluid flow rate through the collector; plate absorptivity; plate emissivity and insulation thickness. Sensitivity studies were also performed on a double-glazed solar collector but for only the last three of the above listed parameters. The results of these sensitivity studies are analyzed in the text.The transient behavior of the solar collector, viz. the response of the outlet fluid temperature to a step change in insolation rate, has also been studied.     

太阳能烟囱发电装置的CFD模拟

用Fluent软件对太阳能烟囱发电装置内的气流进行了数值模拟，获得了太阳能烟囱发电装置内气流流速、温度等分布，并将温度场模拟计算值和试验检测值进行了比较。结果表明：气流在集热棚中从四周向中部汇流是一个加速的过程；从地面到烟囱，随着高度的增加温度呈递减分布。温度分布模拟与试验检测结果的规律基本相似。但由于进行了稳态假设，也存在一定差别。数值模拟结果以集热棚中心呈对称分布。然而，由于集热棚南部接收的太阳辐射大于北部，在试验检测中南边的温度明显高于北边的温度，温度的峰值向南边偏移，呈不对称分布。     

Dynamic simulation and parametric sensitivity studies on a central solar domestic hot water system

A computer simulation program for a central solar domestic heat water (DHW) system has been developed and validated by comparing it with the actual performance data obtained from a real-life system. A computer simulation language, CSMP, was used for the simultaneous solution of the differential equations describing the system. The program was developed from basic principles and defined parameters. It was utilized to study the dynamic behavior of the system and to perform parametric studies to determine the effects of various system parameters on its performance.Parametric sensitivity studies were carried out to determine the response of the central solar DHW system performance to the following parameters: flow rate of heat-exchange fluid in the solar collector loop, consumption rate in the consumer loop, start-up time (i.e., activation of the collector loop circulation pump), and storage tank capacity.The concept of consumption management is analyzed and discussed in order to emphasize the fact that solar loop productivity, both qualitative and quantitative, is not independent of load. As a corollary, we show that it is possible, when the situation allows, to maximize solar loop productivity by controlling the consumer loop consumption schedule.     

Modeling and numerical simulation of solar chimney power plants

The solar chimney power plant is a simple solar thermal power plant that is capable of converting solar energy into thermal energy in the solar collector. In the second stage, the generated thermal energy is converted into kinetic energy in the chimney and ultimately into electric energy using a combination of a wind turbine and a generator. The purpose of this study is to conduct a more detailed numerical analysis of a solar chimney power plant. A mathematical model based on the Navier-Stokes, continuity and energy equations was developed to describe the solar chimney power plant mechanism in detail. Two different numerical simulations were performed for the geometry of the prototype in Manzanares, Spain. First, the governing equations were solved numerically using an iterative technique. Then, the numerical simulation was performed using the CFD software FLUENT that can simulate a two-dimensional axisymmetric model of a solar chimney power plant with the standard k-epsilon turbulence model. Both the predictions were compared with the available experimental data to assess the validity of the model. The temperature, velocity and pressure distributions in the solar collector are illustrated for three different solar radiations. Reasonably good quantitative agreement was obtained between the experimental data of the Manzanares prototype and both the numerical results.     

太阳能烟囱的通风效应及应用研究

对太阳能烟囱自然通风模型进行了理论分析和数值计算，得出了通风量与烟囱高度、宽度及太阳辐射强度之间的关系。最后提出了太阳能烟囱在应用中应注意的几个问题。     

地道与太阳能烟囱复合通风系统影响因素及优化设计研究

同时利用地热能和太阳能来调节室内温度和室内空气品质,可实现可再生能源在建筑领域的优化利用。文章通过建立地道与太阳能烟囱复合通风系统模型,研究了地道长度、地道宽度、太阳能烟囱高度、地道进风口与太阳能烟囱出风口面积比等参数对房间通风量和室内温度的影响。研究结果表明:地道进风口与太阳能烟囱出风口面积比是影响房间通风量的主要因素;地道长度、地道进风口与烟囱出风口面积比是影响室内温度的主要因素;在复合通风系统的设计过程中,首先应优先考虑将地道长度增加至房间宽度的3倍以上,这样可提高复合通风系统的供冷能力,其次应保证地道进风口面积大于太阳能烟囱出风口面积,这样可降低地道的通风阻力,增加由地道进入到室内的风量,保证该复合通风系统能够较好地满足室内环境的热舒适性要求。     

A numerical study of solar chimney for natural ventilation of buildings with heat recovery

The performance of a glazed solar chimney for heat recovery in naturally-ventilated buildings was investigated using the CFD technique. The CFD program was validated against experimental data from the literature and good agreement between the prediction and measurement was achieved. The predicted ventilation rate increased with the chimney wall temperature. The effects of solar heat gain and glazing type were investigated. It was shown that in order to maximise the ventilation rate in a cold winter, double or even triple glazing should be used. Installing heat pipes in the chimney for heat recovery not only increased the flow resistance but also decreased the thermal buoyancy effect. To achieve the required air flow rates in naturally-ventilated buildings with heat recovery, use should be made of wind forces.     

Validation of CFD simulation for flat plate solar energy collector

The problem of flat plate solar energy collector with water flow is simulated and analyzed using computational fluid dynamics (CFD) software. The considered case includes the CFD modeling of solar irradiation and the modes of mixed convection and radiation heat transfer between tube surface, glass cover, side walls, and insulating base of the collector as well as the mixed convective heat transfer in the circulating water inside the tube and conduction between the base and tube material. The collector performance, after obtaining 3-D temperature distribution over the volume of the body of the collector, was studied with and without circulating water flow. An experimental model was built and experiments were performed to validate the CFD model. The outlet temperature of water is compared with experimental results and there is a good agreement.     

Experimental investigation of solar tower with chimney effect installed in CRTEn,Tunisia

This paper studies the performance of a solar tower power plant (STPP) with chimney effect based on renewable energy proposed for electricity production. That's way, a solar tower prototype was constructed and tested in the Research and Technology Centre of Energy (CRTEn), Borj Cédria, northern Tunisia.The design involves heating air using solar energy and the chimney effect to raise the hot air up the chimney stack. The hot air velocity increases by the use of a convergent nozzle to reach a suitable velocity which can run the wind turbine. The kinetic energy of the hot air is then converted to electricity by the wind turbine.During this study, the influence of the climatic conditions of Borj Cédria site (insulation, ambient temperature) as well as the chimney height and the collector diameter on the amount of electricity production were investigated.The distribution and the evolution of the temperature at different positions of the prototype as well as the electrical energy produced were determined.The results reveal that when the temperatures reach 45 °C, the electric power reaches an average value of about 0.3 W/m² for a solar tower prototype with 8 m of diameter and 2 m of height chimney.     

Enhancement of natural ventilation in a solar house with a solar chimney and a solid adsorption cooling cavity

This paper presents a parametric analytical study on the enhancement of natural ventilation in a solar house induced by a solar chimney and a solid adsorption cooling cavity. Some details on sizing such a system are also provided. Theoretical analyses are carried out to investigate the ventilation in the solar house with solar chimney alone, cooling cavity alone or with combined solar chimney and solar adsorption cooling cavity, without considering the wind effects. It is found that on a typical day, the solar house comprising of a 2.5 m² solar chimney, is able to create an airflow rate of more than 150 kg/h for the studied house. In addition, the ventilation rate at night is also increased by about 20% with the solar adsorption cooling cavity. It is expected that the proposed concept is useful to be incorporated with a stand-alone building or with a cluster of buildings for some favorable climates.     

Experimental and simulation studies on the no-load performance assessment of a domestic solar dryer

Solar dryers have been tested with various simple and complex design modifications for better efficiencies. This article attempts to investigate the effect of a very simple design modification on the no-load performance of a natural convection domestic solar dryer (NCDSD). A direct-type domestic solar dryer has been developed with an air cavity surrounding the drying chamber. To compare the effect of air cavity, a domestic solar dryer without air cavity has also been developed and both the dryers were tested simultaneously under the climate of Hisar, India. The values of thermal efficiency were calculated along with convective heat transfer coefficient from absorber plate to the drying air. Both the dryers were also analyzed by developing finite element models in COMSOL multiphysics computer software. The no-load thermal efficiency for the domestic solar dryer without and with air cavity was found to be 22.68% and 34.08%, respectively. The values of coefficient of correlation for modeled and actual drying tray temperatures for dryer without and with air cavity were 0.980466 and 0.9833917, respectively. The proposed finite element model would be helpful in the design and development of NCDSDs.     

Experimental studies on double-effect solar distillers

Application of the multiple-effect concept to the direct utilization of solar energy in atmospheric distillation of saline water has been investigated experimentally. Considerable improvements in productivity are obtained because of re-use of latent heat, especially for high levels of insolation. It is found that a double-effect solar still (with two glass covers on the top. liquid feed as coolant and preheated on the outside surface of the bottom plate) may yield high productivity.