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).     

Effect of solar chimney inclination angle on space flow pattern and ventilation rate

The solar chimney is a simple and practical idea that is applied to enhance space natural ventilation. The chimney could be vertical or inclined. The chimney inclination angle is an important parameter that greatly affects space flow pattern and ventilation rate.In the present study, the effect of chimney inclination angle on air change per hour and indoor flow pattern was numerically and analytically investigated. A numerical simulation using Ansys, a FEM-based code, was used to predict flow pattern. Then the results were compared with published experimental measurements. A FORTRAN program was developed to iteratively solve the mathematical model that was obtained through an overall energy balance on the solar chimney.The analytical results showed that an optimum air flow rate value was achieved when the chimney inclination is between 45° and 70° for latitude of 28.4°. The numerically predicted flow pattern inside the space supports this finding. Moreover, in the present study a correlation to predict the air change per hour was developed. The correlation was tested within a solar intensity greater than or equal to 500 W/m², and chimney width from 0.1 m to 0.35 m for different inclination angles with acceptable values.     

A study of solar chimney assisted wind tower system for natural ventilation in buildings

The concept of a solar chimney coupled with a wind tower to induce natural ventilation has been studied analytically in this paper. It is estimated that the effect of a solar chimney is relatively much higher for lower wind speeds. For ambient wind speed of 1.0 m/s, for example, the wind tower alone creates a mass flow rate of 0.75 kg/s only, while the solar chimney assisted system is able to create an air flow up to 1.4 kg/s at 700 W/m² incident solar radiation.     

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.     

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.     

Application of passive cooling systems in the hot and humid climate: The case study of solar chimney and wetted roof in Thailand

The thermal performance of two passive cooling systems under hot and humid climate condition is experimentally investigated. The experimental results were obtained from a test cell and a controlled cell with identical walls but different roof configurations. The passive cooling systems applied to the test cell are solar chimney and water spraying on roof. The experimental results obtained from the test cell are compared with the closed and no passive cooling controlled cell. In addition, the significant of solar-induced ventilation by using a solar chimney is realized by utilizing a wind shield to reduce the effect of wind-induced ventilation resulting in low measured air velocities to the solar chimney and low computed value of coefficient of discharge. The derived coefficient of discharge of 0.4 is used to compute Air Changes rates per Hour (ACH). The ACHs with application of solar chimney solely are found to be in the range of 0.16–1.98. The studies of air temperature differences between the room and the solar chimney suggest amount of air flow rates for different periods in a year. The derived relationships show that the air flow rate during February–March is higher than during June–October by 16.7–53.7%. The experimental results show that application of the solar chimney in the test cell could maintain the room temperature at 31.0–36.5 °C, accounting for 1.0–3.5 °C lower than the ambient air and 1.0–1.3 °C lower than the controlled cell. However, to make the test cell's room temperature much lower than the ambient temperature and increase the flow rate of air due to the buoyancy, the application of water spraying on roof is recommended together with solar chimney. The application of the two systems in the hot and humid climate are discovered to sustain the room temperature of the test cell to be lower than the ambient air by 2.0–6.2 °C and lower than the controlled cell by 1.4–3.0 °C.     

冲缝吸热板渗透型太阳能空气集热器性能研究

介绍了冲缝吸热板渗透型太阳能空气集热器的结构,建立了传热数学模型。采用Matlab程序对传热数学模型进行求解,模拟研究了结构参数、运行参数对集热器热性能的影响。集热器出口空气温度的实测结果与模拟结果的平均偏差为0.99K,证明传热数学模型准确可靠。集热量随吸热板外表面发射率增大而降低,随集热器出口空气流量、太阳辐射强度的增大而升高,随环境温度的增大先降低后升高。集热器出口空气温度随吸热板外表面发射率、集热器出口空气流量的增大而降低,随太阳辐射强度、环境温度的增大而升高。     

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.     

基于太阳能热利用的生态建筑能源技术

本文介绍了几种基于太阳能热利用的生态建筑能源技术，涉及太阳能利用的建筑物自然通风，太阳能热水系统，太阳能地板采暖，太阳能热泵空调系统，太阳能热水驱动的吸收和吸附制冷系统。并以上海市生态建筑示范项目为例，介绍了其综合能源利用方案。     

Application of night cooling concept to social housing design in dry hot climate

A passive night cooling system was developed and implemented for a new project of social housing. The passive cooling system incorporates a solar chimney in combination with high thermal mass in the building construction. The natural ventilation is enhanced with the help of the solar chimney and night fresh air cools the building structure. The design of this concept was calculated by balancing energy using basic thermal equations for a summer reference day and evaluated using two simulation tools, TRNSYS and TAS. The building has been constructed and actually in process of monitoring.     

太阳能烟囱自然通风的一维稳态模型

太阳能烟囱是一种利用太阳能加热来强化自然通风的技术.在前人简化模型的基础上,考虑了玻璃盖板和集热墙的导热热阻的影响,建立了一个修正的太阳能烟囱自然通风的一维稳态数学模型.并利用此模型,对太阳能烟囱内的空气平均温度、集热墙温度、空气流量以及集热效率等进行了模拟计算和讨论.模型计算结果与相关实验数据及前人的简化模型进行了对...     

Low cost passive cooling system for social housing in dry hot climate

The low energy approach should be the key concept in any long-term strategy aiming to build sustainability. For Madrid climate, action should be taken to reduce energy demand for heating and cooling in residential buildings.The performance of a passive cooling system was developed as a part of design work for the project of a low cost residential building. The passive cooling systems incorporate a solar chimney and precool the air by using the sanitary area of the building. The natural ventilation is enhanced with the help of the solar chimney and fresh air is cooled down by circulation within the sanitary area. The application of this system to the living rooms of a low cost residential building was evaluated and implemented. This cooling system incorporated to a residential building is the third prototype developed since 1991 by the designers. A model was developed to allow to predict the temperature of the air in the living room. The performance of the passive cooling system was evaluated based on the energy balance for a typical summer day.To reduce the energy demand in winter, a new design and window orientation has been developed and evaluated using DOE-2 simulation tool. The building has been constructed and monitored during 2006-2007.     

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.     

Simulation of buoyancy-induced flow in open cavities for natural ventilation

Solar heated open cavities including solar chimneys and double façades were studied for enhancing natural ventilation of buildings. A commercial CFD package was used to predict buoyant air flow and flow rates in the cavities. The CFD model was validated against measured data from the literature and good agreement between the prediction and measurement was achieved. The effect of the cavity width of solar chimneys and double façades on the buoyancy-induced ventilation rate was investigated. It was found that there existed an optimum cavity width for maximising the buoyancy-induced flow rate and the optimum width was between 0.55 and 0.6 m for a solar chimney of 6 m high. The ventilation rate in a double façade of four-storeys high generally increased with cavity width but decreased with floor level from bottom to top. Integration of photovoltaics into a double façade increased the ventilation rate while reducing its variation from floor to floor.     

Performance analysis of sloped solar chimney power plants in the southwestern region of Iran

The sloped solar chimney power plant (SSCPP) has significant capability to fulfil a part of the forthcoming energy requirements of villages located in the southwestern region of Iran. This paper presents the performance analysis of SSCPP which was expected to fulfil the urgent need for electric power in the southwestern region of Iran. However, to investigate the SSCPP performance and power generation throughout the southwestern region of Iran, five different regions across the Persian Gulf were considered. A mathematical model was developed to estimate the power output of solar chimneys. The performances, such as rate of air mass flow, system efficiency and solar collector efficiency, of the SSCPP were studied. The obtained results show that SSCPPs can produce from 2.98 to 5.91?MW of electricity power in the selected regions during different months of the year.     

Solar chimney—A passive strategy for natural ventilation

Passive ventilation systems are being increasingly proposed as an alternate to mechanical ventilation systems because of their potential benefits in terms of operational cost, energy requirement and carbon dioxide emission. Solar chimney is an excellent passive ventilation system which relies on natural driving force, that is, the energy from the sun. A significant amount of research work has been done on solar chimney since the 1990s. This article presents an overview of solar chimney research that has taken place in the last two decades. The review focuses on two main areas of research - the effects of geometry and inclination angle on the ventilation performance of a solar chimney. The experimental investigations of solar chimney have dominated the existing literature. However, numerical modelling of solar chimney using computational fluid dynamics (CFD) technique has attracted increasing attention. Moreover, this review found that solar chimney as a passive ventilation strategy has not been fully understood.     

Simulation of air flow in the IEA Annex 20 test room—validation of a simplified model for the nozzle diffuser in isothermal test cases

The modeling of air supply devices has been identified from the International Energy Agency (IEA) Annex 20 project as one of the most important problems in applying computational fluid dynamics (CFD) to predict air flow pattern and air distribution in buildings, and the complicated HESCO nozzle diffuser used in the IEA Annex 20 test room has been proved to be particularly difficult to model. In a previous study, a simplified model for this diffuser was developed and validated against experimental data. It has been shown that this model can yield good prediction for the wall jet flow issued from the diffuser, but whether this model is capable of correctly predicting the global flow pattern in the whole test room was not known. In this paper, the benchmark data of the IEA Annex 20 Test Cases B2 and B3 were used to evaluate the performance of the model for the prediction of the global air flow pattern in the test room. It was demonstrated that this model can predict the air flow pattern in the whole test room for both the Test Cases B2 and B3 with reasonable accuracy. The significance of a velocity correction when comparing the numerical prediction with experimental data obtained using omni-directional anemometers was also discussed.     

Characteristic parameters of a hypocaust construction

Hypocaust, an ancient Roman concept for keeping the inside of buildings warm, has been explained with a survey of a few modern buildings based on these concepts and using solar heat employing a number of design variations. Results expressed in terms of energy requirements per m² of floor area per degree day comes out to be minimum (15.4 kJ m⁻² per DD per annum) for a solar chimney and maximum for solar air collectors (128.4 kJ m⁻² per DD per annum). The basic parameters that determine the performance of a hypocaust construction are size of the cavity determining the heat transfer between the flowing fluid and the building component and the storage capacity of the hypocaust element. The optimum width of the cavity comes out to be between 50 mm and 100 mm. Heat storage capacity of the building element used as hypocaust corresponds to 0.125°K temperature rise per hour in relation to the building heat load.     

Experimental study and simulation of a solar dryer for spearmint leaves (Mentha spicata)

An indirect forced convection solar dryer consisting of an air flat plate collector and a drying cabin was designed and fabricated to investigate its performance under the climate of Algiers. Drying experiments have been performed for spearmint leaves at different air flow rates in order to determine the drying velocity, the characteristic drying curve, the effective diffusion coefficient and the activation energy. A mathematical model based on thermal and mass balances over the component of the solar collector and the cabinet dryer was developed. Simulations are carried out for meteorological data of Algiers (Algeria). We analyse the effect of air mass flow rate, air temperature, products mass, collector area, air recycling rate on the drying time, the solar fraction and the efficiency of the dryer.     

Numerical simulation of the performance of an air heating solar collector

The effects of the thermal and hydrodynamics entry length for both laminar and turbulent flow regimes within an air-heating solar collector have been studied using a numerical procedure. Two internal arrangements were considered: (1) air passing on both sides of the absorber (parallel flow), and (2) use of finned and other augmented surfaces.

Results of the analysis showed that the temperatures of the cover plates for the parallel flow collector were lower than if the air had passed on only one side of the absorber plate (single flow). Consequently, the heat losses were reduced and the efficiency of the parallel flow collector was increased. Also the pumping power per unit energy gained by the collector for parallel flow mode was less than that for the single flow mode. By using a finned surface, the temperatures of the cover plates were lower than for single and parallel flow and consequently the heat losses were reduced and the efficiency of the finned surface collector was increased. But in this case, the pumping power per unit energy gained by the collector and operating costs also increased.