太阳能烟囱通风效果的实验研究与数值模拟

实际测量华东地区某实验建筑中的太阳能烟囱通风量,所得结果与理论计算、数值模拟相比较,结果显示实际测量通风量普遍低于理论值。测量当日9∶15~13∶15时间段内太阳能烟囱垂直面上太阳总辐射强度为5~600 W/m2,实测风口的通风速率为0.02~0.45 m/s。通过数据分析得到实际工程中太阳能烟囱的流量系数Cd推荐值0.51。通过数值模拟研讨了太阳能烟囱结构尺寸对其产生自然通风量的影响,结果表明太阳能烟囱的高度与宽度均与太阳能烟囱通风量大小呈正相关,对于竖直式太阳能烟囱存在最佳高宽比0.3~0.4使其达到最大通风量。     

重庆过渡季节太阳辐射对太阳能烟囱性能影响研究

通过对重庆城区气象要素分析,使用数值模拟的手段研究太阳能烟囱通风性能随太阳辐射强度的变化规律,指出烟囱通风量随太阳辐射强度的变化趋势在一定范围内为二项式分布,辐射强度越大,通风量也越大,但是变化幅度并不明显;烟囱出口布置在烟囱顶部比布置在侧面能更有效利用太阳辐射加强自然通风。     

地道风与太阳能烟囱通风复合系统适应性研究

通过建立地道风与太阳能烟囱通风复合系统三维稳态模型,采用正交模拟试验研究了系统在地道长度、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因素影响下的适应范围。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,面积比为0.8时,通风量最大;地道长度和太阳能烟囱高度是影响室内温度的主要因素,烟囱高度为2~3 m时,降温效果最佳,可降低约4.6℃,地道长度保持在1倍房间长度以上,该复合系统的降温效果最佳,可适应的室外温度最高限值约为32.6℃。     

太阳能烟囱辅助教室混合通风的温度分布特征研究

由于教室人员密集,通风非常重要,自然通风与机械通风相结合的混合通风是一种适合于教室的通风方式,而太阳能烟囱可以提高自然通风的热压作用。本文对太阳能烟囱辅助教室混合通风进行了研究,采用模型实验和数值模拟的方法对室内热源强度、机械送风口位置、机械送风速度和太阳能烟囱辐射强度对教室内空气温度的影响进行了讨论,分析了太阳能辅助教室混合通风的室内空气温度分布特征。     

太阳能烟囱结合自然通风建筑开口的数值研究

自然通风是实施绿色建筑中常用的一项技术措施。随着节能减排的大力倡导,自然通风技术引起了人们的普遍关注。目前,人们已通过不同的措施与手段来最大程度地利用自然通风以满足舒适度要求,其中太阳能烟囱作为一种利用热压来强化自然通风的有效技术也被广泛采用。太阳能烟囱的通风效果除与烟囱尺寸及当地太阳辐射强度密切相关外,也与其自然通风建筑特性有关。采用FLUENT软件对太阳能烟囱结合不同建筑开口形式及不同开口尺寸的自然通风模型进行了三维稳态数值模拟。研究了在不同方案下,不同开口形式对通风量的影响,分析了通风量随进风口尺寸的变化情况。模拟结果表明,在相同热流密度情况下,单开口建筑下的太阳能烟囱诱导的通风量大于双开口建筑,且当进出风口面积比A1/A2=2.5~4时,竖直集热板屋顶式太阳能烟囱能诱导更多的空气。     

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。     

太阳能烟囱强化通风对室内热环境影响研究——以天津地区办公建筑为例

办公建筑能耗大、人员集中,节能潜力巨大,而太阳能烟囱强化通风技术是改善室内环境、实现建筑节能减排的有效途径。从通风原理、类型、材料组成方面分析了太阳能烟囱在办公建筑中的应用情况;以天津地区为例,结合现行标准规范建立了带有太阳能烟囱的办公建筑模型,采用Fluent软件对模型的室内热环境进行了模拟分析,并提出了太阳能烟囱在办公建筑通风设计中的应用策略。模拟结果表明:太阳能烟囱强化通风使室内热环境得到改善,建筑进风口风速、室内通风量及室内温度在13:00达到最大值,与南向太阳辐射强度最大值出现的时间相比延迟1 h,可利用延时特性降低建筑的峰值冷负荷,改善室内热环境;室内温度随楼层增高逐渐上升,太阳能烟囱在多、高层建筑中应用时宜分层设置,每组太阳能烟囱不宜负担过多楼层。     

《进气道布局对屋顶太阳能烟囱性能影响的实验和数值分析》

屋顶太阳能烟囱系统,是一种利用太阳能使热气流上升的技术,太阳能在系统通道内产生风力流——有足够的驱动力产生烟囱效应。通过实验和数值模拟研究了太阳能集热器气流入口形状对太阳能烟囱性能的影响。为空气入口四种布局形式建模,并应用ANSYS FLUENT软件进行模拟,使入口区域周围的二维热流场可视化。通过设置屋顶太阳能烟囱对四种入口布局进行实验测量,以验证模拟结果,并评估和比较每个入口配置的系统性能。实验模型中,有两份完全相同的透明覆盖材料安装在模拟房间的屋顶上方,开口在房间顶部方便空气从两侧流向烟囱管道。结果发现,当进气口设有垂直截面时,烟囱空气流速和质量流量比其他三种进气口结构高,因此性能最好。当进气口的横截面为水平设置时,集热器性能比进气口为垂直设置时在下午1:00减少了84%。有趣的是,CFD分析表明,集热器中大部分气流从进口的上部区域被导入,仅少量气流从进口的底部流动。这证明了进气口布局为水平取向设置的太阳能空气集热器的能效非常低的原因。结果揭示了减少太阳能烟囱热气流发电系统透明罩面积,并将外部区域转换成开放的顶部吸收器的可能性。     

屋顶式太阳能烟囱对厂房气流组织的影响

本文采用计算流体力学(CFD)方法对太阳能烟囱加强厂房自然通风的过程进行数值模拟研究。先采用Realizable k-ε湍流模型及DO辐射模型对传统厂房自然通风过程进行了数值计算,其计算结果与文献中实验值的对比吻合良好。在该基础上,进一步将传统厂房结构与4种不同形式的太阳能烟囱结合起来进行模拟及对比分析,结果表明:太阳能烟囱对厂房自然通风效果有不同程度的促进作用。在本文中采用的优化形式中SC-I型与SC-III型在不同应用条件下有相对较好的工程前景。     

阳台对低层建筑风压作用下自然通风影响的数值研究

本文将通风量和工作平面平均风速作为衡量房间通风效果的指标,采用计算流体力学方法,分析了阳台对低层建筑风压作用下自然通风的影响.首先通过实验数据验证了数学模型的可靠性,数值模拟结果与实验结果具有良好的一致性.而后,通过模拟得到以下结论:对于单侧通风建筑,阳台能够极大地提高建筑中部及下部房间的通风性能;对于双侧通风建筑,阳台对室内通风性能的影响较小;阳台可以诱导空气进入房间更深的区域,在工作平面形成更为均匀的风环境.     

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.     

Modeling of window-sized solar chimneys for ventilation

The mathematical model for predicting airflow velocity in a solar chimney has been developed through predicting temperature of the absorber, air in flow channel and glass cover. Experimental validation of the model has been done using a solar chimney having less than a 1-m-high absorber. Investigations have been carried out with three different combinations of air gap and size of the inlet opening for entry of air in the chimney. Good agreement between observed and calculated results has been obtained. The small size of the analyzed solar chimney has opened possibilities of utilizing windows as solar chimneys since the flow velocity upto 0.24 m/s has been experimentally recorded.     

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.     

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.     

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.     

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.     

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.     

Free-running temperature and potential for free cooling by ventilation: A case study

Free-cooling by ventilation is one of the most energy efficient techniques for cooling. When ventilation is used for cooling, variable airflow rates should to be used in order to achieve comfortable room temperatures and to minimize the energy demand for mechanical ventilation. Thus, free-cooling, requires, obviously, the existence of a potential for cooling and needs control mechanisms for the airflow. In this study, the free cooling potential by ventilation for office buildings is evaluated by the free-running temperature. The free-running temperature approach is based on the energy balance of heat gains and losses. It is adapted to evaluate the potential for free cooling by ventilation of office buildings for which the gains through the walls are negligible as compared to the internal and solar gains. The free-running temperature of each office room considers solar and internal heat gains, outdoor temperature, indoor temperatures and ventilation air flow rates. The approach is applied to 14 office rooms in a passively cooled office building in Germany and is used to estimate the potential and to evaluate the total energy saving by free cooling by ventilation. The good fit between monitoring data and calculation procedure proves that the free cooling potential can be accurately estimated by using the difference between the comfort limits, i.e. the target value of the indoor temperature, and the free-running temperature.     

Correlation between minimum airflow and discharge air temperature

Airflow and discharge air temperature can be varied to maintain room temperature setpoint according to heating load. Increasing discharge air temperature and the decreasing airflow can save energy, but it causes reduced air circulation as supply air temperature rises above the space temperature. On the other hand, increasing airflow can improve air circulation; however, it may waste energy. The objective of this study is to identify the correlation between the minimum airflow and discharge air temperature that will maintain room thermal comfort. Near-optimal room airflow and discharge air temperature were analyzed, and the impact of room airflow and discharge air temperature on thermal stratification was evaluated and potential energy savings was estimated. Its performance was conducted through field experiment.