Heat transfer modelling on windows and glazing under the exposure of solar radiation

Due to the effect of solar radiation on windows and glazing system the evaluation of heat flow is of primary importance in modeling the thermal performance within building interiors to account thermal comfort and overall energy consumption of a building. In this context the optical properties of window glazing are measured to determine the percentage absorption of incident solar radiation. An experimental study was performed in a room to measure the glazing surface temperature due to the global radiation on it. The corresponding window plane global radiation and horizontal global radiation were measured outside for simulation. Mathematical models have been developed to simulate the window plane solar radiation and corresponding glazing surface temperature aiming at validating the measured values. The thermal model is concerned with laminar heat transfer for natural and forced convection process according to the ambient conditions. The estimated errors between experimental and simulated values of window plane radiation and glazing temperature are shown to be within ±5%. Using the developed thermal model the heat flow inside the room through windows is determined. Thus overall heat transfer coefficient of glazing (U-factor) and the Solar Heat Gain (SHG) of building interior have been predicted from the simulation.     

基于自然通风原理的通风窗智能控制系统构造

针对建筑自然通风原理及特点,分析了电动开窗器的原理,讨论了风压和热压作用下的电动开窗控制系统流程,以及通风窗和电动开窗器的选型,并提出一种基于自然通风原理的楼宇智能通风窗控制系统,给出了构成要素,同时对系统底层、中间层、上层的特点加以讨论。     

自然通风建筑室内气流组织优化研究

通过fluent模拟软件对诸多因素中最为关键的风向、风速、开窗位置及面积等进行了优化模拟研究。结果表明:在西安地区,南向为最佳风向,室外风速在1.3～2.5 m/s之间,基本上都能满足自然通风要求,最佳风速为1.5 m/s;综合考虑采光和自然通风因素,窗户开在墙的中间为宜;北向面积适当减小有利于自然通风在室内形成较均匀的气流,在保证建筑节能标准的前提下,增大南向窗户面积有利于自然通风。     

Characteristics of airflow from open windows

In natural ventilation systems fresh air is often provided through opening of windows. However, the knowledge of the performance of windows is rather limited, especially with regard to their impact on thermal comfort and draught risk in the occupied zone. This paper describes and summarizes the results of a series of laboratory measurements that is performed on two different window types to determine the characteristics of the air flow in rooms. It is shown that the air flow can be described by traditional theory for jets and stratified flow and semi-empirical flow element models are developed for estimation of thermal comfort parameters in the occupied zone.     

住宅建筑夏季自然通风方式下热环境分析

文章采用模拟分析软件Dest，模拟乌鲁木齐地区某住宅建筑在采用三种不同的夜间通风模式的条件下，室温变化情况，分析了自然通风对室温的影响。同时指出白天关窗夜间开窗通风模式的室内热环境更适于人们居住，不但可以满足舒适度要求，还可以免去夏季开空调，节约能源。     

外窗开启方式对居住建筑自然通风影响研究

利用计算流体力学的分析方法,用平均空气龄和空气龄标准差对自然通风量的大小及其通风均匀性进行研究。对采用推拉窗、上悬窗、平开窗的板式居住建筑在N、NNW、WN风向下的自然通风状况进行对比分析。研究发现,对于自然通风的均匀性,平开窗开启方式优于推拉窗、上悬窗开启方式。对于建筑自然通风量,当风向为N及NNW风向时,推拉窗开启方式优于上悬窗、平开窗开启方式。当风向为WN风向时,平开窗开启方式优于推拉窗、上悬窗的开启方式。当同时考虑建筑自然通风量与自然通风均匀性时,平开窗开启方式具有明显的优势。     

自然通风环境下办公建筑中庭空间热舒适性模糊优化研究

：随着绿色建筑设计理念深入人心,办 公建筑的中庭空间因其特有空间特质受到越来 越多的关注。通常办公中庭空间中的节能性与热 舒适性是一对矛盾体,而自然通风作为被动节能 技术之一,不仅能够促进中庭空间的内外空气 循环,改善室内空气质量,而且降低能耗和提升 热舒适性,较好地解决这一矛盾。以江雅园办公 楼中庭空间为案例进行研究,从中庭屋顶形态、 中庭高度及进风口开启方式三个变量因素出发, 引用模糊评估方法寻找出中庭空间自然通风热 舒适性最佳方案,结论显示在多个组合方案中 斜屋顶形态+进风口全部开启的方案热舒适性最 佳,同时也证明屋顶形态与通风方式的变化对自 然通风舒适性的影响较大,而中庭空间高度的变化对自然通风舒适性影响较小。本研究希望建立一套以风速和温度为评价指标的模糊体系,为自 然通风的热舒适性的评价提供一种客观的评估手段,从而为方案阶段的中庭空间设计提供一种 有效的优化方法。     

自然通风状态下围护结构性能对福州住宅室内热舒适性影响的研究

本文采用建筑热工模拟软件DeST-h和ePMV热舒适模型研究了自然通风下福州市住宅围护结构性能对室内热舒适性的影响。选择一栋11层高层住宅作为研究对象,计算分析了该建筑标准层7个不同朝向典型房间在自然通风环境下的逐月、全年热舒适状况,全面系统地研究了外墙、外窗、外遮阳、房间朝向等因素对改善自然通风下室内热舒适的效果和相关规律,并提出室内热舒适性改善的措施建议。     

冬季北方地区住宅建筑通风方式对比研究

随着住宅节能技术的广泛推行,对窗户的气密性要求越来越高,冬季冷风渗透远远不能满足室内人员对新风的最低需求。为了寻找节能、舒适的通风方式,本研究利用FLUENT对工程中较为常见的通风方式：自然通风方式、自然进机械排通风方式、带热交换的墙式通风器方式、带热交换的通风换气机组方式在气流组织、舒适性能、能耗特性及初投资方面进行了应用效果评价。最终得出：对于层高和装修标准较高的高级住宅中使用带热交换的通风换气机组,可以使通风系统在满足热舒适性和空气品质的基础上,更加节能,而对于一般住宅建筑,自然进机械排通风方式是相对最优选择。     

绿化和建筑布局对住宅小区的风热环境影响的数值模拟分析

良好的住宅小区风热环境可以加快室外热量的消散和污染物排放,保证居民的健康和舒适。影响小区风热环境的因素主要有小区布局、建筑形态及下垫面形式等。以青岛市一个实际小区为案例采用数值模拟的方法分析小区冬夏季行人高度的风场及温度场分布,评估设计的合理性,找出小区内风热环境不满足要求的区域。通过调整小区内建筑的布局和改变下垫面形式等方法改进小区的设计,并对改进后的方案进行模拟计算。通过模拟结果的对比发现:1合理布局建筑位置,在小区内形成风道可有效改善风环境;2改变下垫面热物性,提高地面材料的反射率,能够降低地面附近的空气温度和体感温度,改善小区热环境。     

窗户遮阳技术在节能住宅中的应用研究

外窗是建筑能耗的薄弱环节,同时还直接影响着室内的舒适性。结合上海地区的气候条件,分析了外窗热工性能对建筑能耗的影响,指出提高外窗遮阳性能的重要性。同时对比介绍了几种常用的遮阳技术及性能,并采用建筑能耗模拟分析软件DeST对3种外窗的遮阳效果进行了能耗模拟计算,结果表明,与普通中空窗相比,低遮阳系数的Low-E中空窗具有更好的节能效果。     

Energy-saving potential by changing window position and size in an isolated building

The physical comfort of a building completely depends on the airing in the building. The window plays a superior role in providing ventilation without burning artificial energy. The forced system releases high poisonous gases such as CFCs, HCFCs, and HFCs. This paper concentrates on improvement of natural ventilation which is freely available by changing the size of the window and the orientation of the building. The computational fluid approach is used to understand the physical mechanism of air circulating inside the building. The forces and moments of air created inside the building also measured to achieve healthier considerations of circulation. From the results, it is evident that the natural ventilation is not only dependent on the velocity of air but also the orientation and shape of windows, and implementing an optimised design can save up to 20% of energy in residential buildings.     

Predicting thermal and energy performance of mixed-mode ventilation using an integrated simulation approach

Mixed-mode ventilation can effectively reduce energy consumption in buildings, as well as improve thermal comfort and productivity of occupants. This study predicts thermal and energy performance of mixed-mode ventilation by integrating computational fluid dynamics (CFD) with energy simulation. In the simulation of change-over mixed-mode ventilation, it is critical to determine whether outdoor conditions are suitable for natural ventilation at each time step. This study uses CFD simulations to search for the outdoor temperature thresholds when natural ventilation alone is adequate for thermal comfort. The temperature thresholds for wind-driven natural ventilation are identified by a heat balance model, in which air change rate (ACH) is explicitly computed by CFD considering the influence of the surrounding buildings. In buoyancy-driven natural ventilation, the outdoor temperature thresholds are obtained directly from CFD-based parametric analysis. The integrated approach takes advantage of both the CFD algorithm and energy simulation while maintaining low levels of complexity, enabling building designers to utilize this method for early-stage decisionmaking. This paper first describes the workflow of the proposed integrated approach, followed by two case studies, which are presented using a three-floor office building in an urban context. The results are compared with those using an energy simulation program with built-in multizone modules for natural ventilation. Additionally, adaptive thermal comfort models are applied in these case studies, which shows the possibility of further reducing the electricity used for cooling.     

Numerical simulation of rooftop ventilator flow

Rotating rooftop turbine ventilators are cost effective environmental friendly natural ventilation devices, which are used to extract airflow from a building to improve air quality and comfort. A CFD study using the standard k-? turbulence model with multiple reference frame (MRF) meshing technique was employed to explore the suitability of numerical approach in modelling various features of a ventilator flow. The initial CFD results were validated against wind tunnel data obtained for a commercial ventilator on a simulated inclined rooftop configuration conducted at the aerodynamic laboratory of University of New South Wales. The numerical studies were then extended to examine both the internal and the external flows associated with the ventilator at different wind speeds and to quantify the performance of a rotating ventilator in terms of air extraction rate. The trend observed appeared to be in good agreement with published data suggesting that application of numerical simulation is feasible as a cost effective tool in the future design, development and performance analysis of rotating wind driven ventilation device.     

Experimental and numerical investigation on the distribution characteristics of wind pressure coefficient of airflow around enclosed and open-window buildings

In the present paper, the distribution characteristics of the wind pressure coefficient of the air flow around enclosed and open-window buildings were studied by using wind tunnel model tests and numerical analyses. A typical high-rise building model was designed and wind tunnel tests were performed for the airflow around the building for an enclosed and an open-window condition. The experimental findings were complemented by the numerical analysis. This study shows that the opening windows of a building has little influence on the wind pressure coefficients in the area around the window of adjacent area from window edge; the wind pressure coefficient increases slightly after opening the windows of the buildings. Opening the windows in the rooms adjacent to this window decreases the ventilation efficiency of the room although the influence is small. The time-average value of the wind pressure coefficient can effectively represent the magnitude of the instantaneous wind pressure coefficient. The wind pressure coefficient is independent of the wind velocity of inflow. Furthermore, this study also proposed the distribution characteristics of wind pressure coefficients with different incident angles of wind.     

A study on terraced apartments and their natural ventilation performance in hot and humid regions

Terraced apartments as a typology of the buildings are new approaches to meet energy conservation targets. This principle in the form of interactive spaces contributes to an incorporation of interior and exterior, daylight addition and exploitation of natural ventilation. This study mainly investigates the natural ventilation exploitation of a terraced apartment in the hot and humid region. One solid block and 4 porous apartments with different terrace depths (TD) are evaluated using computational fluid dynamics (CFD) analysis. The k-ε turbulence model was adapted to simulate airflow in and around a mid-rise building with 42 residential blocks. CFD analysis compares the effect of permeability in the form of terraces on wind behaviour and natural ventilation efficiency in a mid-rise building. Ventilation assessment parameters such as mean air velocity and mean age of air are measured to compare the natural ventilation performance. The simulation results clearly indicate that the implementation of permeability in the form of terraces can enhance building natural ventilation performance significantly. However, it is proved that some physical configurations such as terrace depth can influence this performance greatly. According to the results, increasing the terrace depth up to 1.2 meters will enhance the mean wind velocity 40%–88% inside the room, 10.61%–12.29% near the window and 63.44% on the openings. Velocity diagram follows a descending process after TD 1.2. The mean wind speed decreases to 25.53% inside the room, 15.09% inside terraces and 1.09% near the window. The average wind velocity on the openings is revealed to be 1.54 to 1.64 times larger in the porous models than the solid one. On the other hand, porous cases indicate lower values for the mean age of air compared to the solid model. This study provides proper guidelines to predict ventilation performance and to improve the design of naturally ventilated mid-rise buildings in hot and humid regions.     

自然通风室内热舒适均匀度ADPl研究

《绿色建筑评价标准》中对自然通风时外窗的室内外风压差提出了要求,但并未考虑室内热舒适均匀度的问题.通过结合空气分布特性指标(ADPI)对天津地区过渡季自然通风室内热舒适区的确定,对不同外窗风压、房间进深及门窗组织形式进行了数值模拟计算,发现室内热舒适均匀度与室外风压、房间进深均存在比例关系,室内热舒适均匀度随室外风压的上升而下降,并给出了ADPI在不同房间进深、风压及门窗组织形式下的预测图表,供建筑师参考.     

Building performance assessment of user behaviour as a post occupancy evaluation indicator: Case study on youth housing in Egypt

Youth housing prototypes are widely spread all over Egypt as a cheap economic housing for youth which are designed in a number of different shapes. A post occupancy evaluation (POE) has been conducted to one of these prototypes to assess some modifications spontaneously done by users to the original design for the sake of enhancing building performance, e.g., creating new openings to improve lighting and natural ventilation thermal comfort, and making sunshades to control direct sunlight and thermal radiation. These assessments have been validated using simulation techniques i.e. CFD, thermal and daylight simulations, to compare natural ventilation, thermal comfort, and daylight energy efficiency in the original designs to that in the user modified. A wind tunnel test has been conducted to validate the standard k–epsilon turbulence CFD simulation in addition to daylighting in-situ measurements to validate natural lighting. The outcome of this research could be widely used as an important feedback tool in the future designs of the same prototype to evaluate user behaviour role in building performance efficiency. The research showed that some of these behaviours has improved thermal comfort by 60% to 87% from the original design while daylight efficiency has been improved by 31.8% to 41.4% while sensible cooling loads’ improvement ranges from 27.4% to 77.2% for the northern zone and 29.9% to 91.6% for the southern one, and thus, it could be used as a reliable POE feedback tool.     

Passive cooling in hot,arid regions in developing countries by employing domed roofs and reducing the temperature of internal surfaces

Natural ventilation due to wind effects through buildings employing domed roofs was estimated by a flow network analysis. The dome was assumed to have an opening at its crown. When compared with flat roofs, the domed roofs always increase the air flow rate through the building. The increase in natural ventilation becomes significant in buildings with doors and windows all in one wall, or whenever the wind effects on the building envelope do not produce large pressure differences at the openings.The large air flow rate in the buildings with domed roofs may be utilized to store night air coolness in the structure more effectively and keep the mean radiant temperature of the interior surfaces low for thermal comfort in summer. The lowest internal surface temperatures can be obtained when the surfaces are kept moist and evaporatively cooled.Through a one-dimensional energy analysis the inside surface temperature of a horizontal slab was estimated for various slab materials and thicknesses and external and internal conditions. The inside surface temperature was compared with the case of employing a roof pond. It was found that lower temperatures can be obtained by evaporatively-cooled moist internal surfaces than that which can be obtained by unshaded roof ponds: For a building whose internal surfaces (walls and ceiling) are kept moist a large ventilation rate is needed to prevent water vapor build-up in the space. A domed roof with a hole in its crown can produce the necessary ventilation for such a building.     

Winter indoor air quality,thermal comfort and acoustic performance of newly built secondary schools in England

Previous studies have found that classrooms are often inadequately ventilated, with the resultant increased risk of negative impacts on the pupils. This paper describes a series of field measurements that investigated the indoor air quality, thermal comfort and acoustic performance of nine recently built secondary schools in England. The most significant conclusion is that the complex interaction between ventilation, thermal comfort and acoustics presents considerable challenges for designers. The study showed that while the acoustic standards are demanding it was possible to achieve natural ventilation designs that met the criteria for indoor ambient noise levels when external noise levels were not excessive. Most classrooms in the sample met the requirement of limiting the daily average CO₂ concentration to below 1500 ppm but just a few met the need to readily provide 8 l/s per person of fresh air under the easy control of the occupants. It would seem that the basic requirement of 1500 ppm of CO₂ is achieved as a consequence of the window areas being just sufficient to provide the minimum of 3 l/s per person at low and intermittent occupancy. Thermal comfort in the monitored classrooms was mostly acceptable but temperatures tended to be much higher in practice than the design assumed.