Investigation and characterization of cross ventilating flows through openings in a school classroom

Abstract

Most Thai state schools use cross flow natural ventilation as a passive cooling system. Information on how window openings are able to provide good ventilation and comfort simultaneously is of great importance. The aim of this study is to investigate cross ventilating flows through the openings of a typical Thai state school classroom. Computational fluid dynamics technique was used as a tool in this simulation. The opening discharge coefficients of six different type windows and a door were determined. Wind, stack and combined effects through the openings were characterized and compared for a range of different wind speeds and surface wall temperatures. Results showed that sliding windows gave the highest C_d value among openings considered by stack effect. Casement and side hung (90°) windows appeared to provide high air exchange rates. Their discharge coefficients ranged between 0.63 and 0.83. As far as combined effects are concerned, buoyancy was found to be significant at low wind speed (0.25 m/s). Acceptable indoor airflow patterns and thermal distributions can be expected in the occupied zone. The findings from this investigation are useful to develop a plan for a natural ventilation strategy of classrooms to enhance thermal comfort levels.     

中学教室空调气流组织的数值模拟研究

针对相同室内条件、不同送回风口位置下的两种模型,运用暖通空调专用数值模拟软件Airpark,对室内速度场、温度场进行了数值模拟计算。并根据模拟结果分析不同送回风口位置下的空气品质和人体热舒适,为教室等人员密集区域空调室内的气流组织形式优化设计提供了研究依据。     

Comparison of performances of displacement and mixing ventilations. Part I: thermal comfort

A numerical simulation using a validated Computational Fluid Dynamics (CFD) model of several types of buildings was used to investigate the difference between mixing and displacement ventilation (DV). The comparison of performances of displacement and mixing ventilations (MV) will be reported in two parts, one on thermal comfort and the other one on indoor air quality. This paper, i.e., Part I, compares the performances of floor-supply DV systems with traditional MV systems for offices, classrooms, retail shops and industrial workshops under a wide range of Hong Kong thermal and flow boundary conditions, such as a very high cooling load. Through proper design, DV can maintain a thermally comfortable environment that has a low air velocity, a small temperature difference between the head and ankle level, and a low percentage of dissatisfied people.     

大学寝室空调气流组织数值模拟研究

针对相同室内条件(冬季工况),采用不同的送风口位置的两种模型,分别是上送上回和下送上回两种送回风方式,运用Airpak软件对室内温度场、速度场进行了数值模拟计算,并根据模拟结果分析两种送风形势下室内空气品质和人体舒适性,为寝室空调的室内气流组织形式优化设计提供了研究依据.     

Comparison of performances of displacement and mixing ventilations. Part II: indoor air quality

A numerical simulation using a validated computational fluid dynamics model is used to investigate and compare the performances of displacement and mixing ventilations (MVs), under different boundary conditions. A companion paper will report the results in terms of thermal comfort, while this paper investigates the indoor air quality (IAQ). The IAQ will be measured in terms of carbon monoxide, mean age of air and the three volatile organic compounds, toluene, benzene and formaldehyde, which are commonly found in indoor room furnishings. The case studies include offices, classrooms, retail shops and industrial workshops, under typical Hong Kong thermal boundary conditions. Compared with conventional MV, displacement ventilation may provide better IAQ in the occupied zone.     

自然通风作用下生态建筑热环境测试与数值模拟

以上海地区一实际生态建筑为例，进行一系列的实际测试，并以测试结果为边界条件，应用零方程模型进行了数值模拟。研究结果表明，利用数值模拟的方法能够很好地预测室内热环境，同时在过渡季节利用自然通风能有效地改善室内热环境，较好地满足舒适性要求。     

空调室内空气计算参数与建筑能耗

分析了空调室内空气计算参数对热舒适性和建筑能耗的影响，对实际建筑的模拟计算结果表明，在满足室内热舒适性的基础上，在一定的温度和湿度的范围内，可通过提高室内温度和相对湿度的途径来减少空调系统能耗。     

亲子乐园空调送风方式的数值模拟研究

大型综合室内亲子乐园属于高大空间,设有游乐设施和游戏的特殊性使得对空间的舒适性要求一致,但是送风气流遇阻严重,室内存在较多气流死角,影响室内空气质量和儿童健康。因此其空调设计不仅需要考虑温度、风速的空间均匀度,还要考虑各点的空气龄和PMV-PPD指标。以天津某亲子乐园为研究对象,利用scSTREAM软件对适用于该房间的辐射供冷加新风、置换通风、混合通风三种空调方式的送风效果进行数值模拟分析,从流场的均匀性、人员的热舒适性等方面对模拟结果进行探讨,研究结果表明辐射供冷加新风方式的空间均匀性和PMV指标最佳,混合通风方式的空气龄最小。     

办公建筑自然通风节能效果模拟

Esp—r实现了热模拟与多区域网络通风模拟的耦合计算,可以较为准确地模拟自然通风建筑的气流组织及室内热环境。本文用Esp—r对上海某一办公建筑标准层的自然通风进行模拟,对过渡季节典型周内开窗和不开窗条件下的室内温度进行了比较,并统计了建筑全年不开窗和过渡季节开窗通风两种工况下的全年建筑冷、热负荷,结果表明过渡季节自然通风可以较好地满足室内温度及换气次数需求,并大大地降低了全年空调运行时间和建筑能耗。     

风环境风洞模拟研究及其舒适性判断

某些建筑布局会引起很强的局部风,带来不舒适的风环境问题,通过风洞模拟实验研究可以解决这一问题.从大气边界层模拟、建筑模型风洞试验、风统计特性、风环境舒适性判断等方面介绍了几种风环境风洞模拟研究方法.     

重庆某高校学生宿舍冬季空调工况热环境研究

以重庆大学学生宿舍为研究对象,实地调研安装分体式空调器后学生宿舍冬季室内热环境状况。通过采用现场测试与问卷调查相结合的方法,从主观和客观2方面分析冬季空调房间内的热环境。主要调查某一特定温度及风速下不同位置室内人员的热舒适度,分析问卷调查个体差异产生的原因,通过进一步分析比较数值模拟与实测结果之间存在的偏差,提出改善宿舍热环境建议措施,以提高冬季空调工况下学生宿舍的舒适度。     

火车站候车厅夏季热舒适性研究

对西安火车站候车厅室内热环境舒适度进行了现场调查和分析。结果表明,候车厅内平均空气温度较高,人们的热感觉普遍偏热。夏季实测热中性温度27.1℃,期望温度27.68℃,80％可接受的热舒适温度范围为24.45～30.6℃,比ASHRAE标准规定的舒适区温度范围要宽的多。分析得到的热中性温度和热舒适温度范围可为火车站改扩建在暖通空调系统的节能设计方面提供一定的参考。     

甘肃某博物馆中庭热环境数值模拟与分析

以甘肃一拟建博物馆中庭为例，采用CFD数值方法对建筑中庭温度场进行模拟，计算不同负荷下中庭高度方向和人员活动范围内的温度分布，分析各种建筑因素对中庭内温度分布的影响。研究结果表明，良好的中庭建筑和通风设计能有效改善室内热环境，满足人体的热舒适要求。     

基于分离涡方法的台北101大厦流固耦合风致响应分析

以台北101大楼为研究对象,应用一种新的湍流脉动流场产生方法(DSRFG)模拟了台北101大厦周围风场的湍流入口边界条件,采用分离涡方法对该建筑进行数值风洞模拟。根据大厦外形特征,建立了几何模型,用于大厦风荷载的数值模拟;基于大厦振动监测系统得到的结构模态、自振频率等数据,建立了大厦的结构模型,用于气弹响应分析。将计算结果与现场实测以及风洞测力试验的相应数据进行了对比,以验证数值风洞的有效性。对是否考虑流固耦合的大厦数值模型的等效风荷载及风致响应进行对比分析,并探讨了流固耦合效应对大厦周围风流场的影响。对该对象的研究结果表明,在顺风向上,建筑物的风致响应不易受流固耦合效应影响,而在横风向上,考虑了双向流固耦合的有限元模型,其等效静风荷载及加速度与位移响应均小于未考虑流固耦合的有限元模型。在流场上,流固耦合效应减小了建筑两侧的涡量,但会产生较大的脱落涡旋,可能会对下游建筑风环境造成不利影响。     

微型客车热环境计算机模拟与优化

应用计算流体动力学方法（CFD）对微车车室几种进出风口位置的温度场、速度场进行了计算机模拟,并对这几种温度场、速度场进行了比较,得到使热环境最优的计算结果,达到车室热环境优化的目的。证明计算流体动力学方法是进行车室热环境优化的有效方法。     

办公建筑空调室内设计参数选取的研究

文章以PMV-PPD指标作为衡量室内热舒适的指标,以广州地区某办公建筑为例,分析了温度、相对湿度、空气流速对空调能耗的影响。研究表明：在相同人体热舒适条件下,相对湿度大、温度低的室内设计参数组合需要的空调能耗比相对湿度小、温度高的室内设计参数组合需要的空调能耗小。根据研究结果,文章提出了在相同人体热舒适条件下,室内设计参数选取的方法,可供工程设计人员参考。     

某办公楼中庭空调系统末端形式的对比分析

在某办公楼中庭采用常规全空气空调系统和温湿度独立控制空调系统(THIC)2种方案时,对室内的空调冷负荷及对应的送、回风参数进行计算和对比,进而对室内气流组织的差异进行模拟分析,并从热舒适性、空气品质等角度对模拟结果进行讨论。结果显示,采用THIC空调方式比常规全空气空调系统的室内气流速度场、温度场更加均匀,人员活动区域的热舒适、空气品质更好,而且可以显著降低高大空间的空调区域,相对于常规全空气空调系统,可降低空调冷负荷25%左右。     

太阳能空气集热耦合地板蓄热系统热特性实验研究

提出了一种适用于被动式太阳能空气供暖的混凝土地板蓄热系统,并对该蓄热系统在寒冷地区农村住宅中的应用进行了热特性及其影响因素实验研究。讨论了该蓄热系统对室内热环境的作用,不同集热器朝向、热气流湿度及供风速度作用下地板蓄热系统的蓄放热特性。实验结果表明,太阳能空气集热耦合混凝土地板蓄热系统充分利用建筑本体结构蓄热,有效提高了太阳能供暖房间的室内温度及其稳定性。     

西安市办公楼冬季热舒适研究分析

随着人们对室内热环境认识的不断加深,其越来越受到人们的重视,但就目前的资料与文献来看,人们更多的注重于住宅环境,办公建筑很少有人问津.本文就西安气候条件下的办公建筑进行测试及分析,来对办公建筑的室内热舒适性给出客观性的展示及合理性的建议.     

Experimental investigation of the effects of airflow nonuniformity on performance of a fin-and-tube heat exchanger

The effects of airflow nonuniformity on the thermal–hydraulic performance of a fin-and-tube heat exchanger were investigated experimentally. The test subject was a four-depth-row fin-and-tube heat exchanger with face split tube circuitry. Nonuniform inlet air distribution was generated by partially blocking the heat exchanger entrance cross-section. It was found that airflow nonuniformity causes thermal effectiveness deterioration and pressure drop increase. The size of effectiveness deterioration and pressure drop increase depend on the degree of airflow nonuniformity as well as on the orientation between airflow nonuniformity and tube-side fluid circuitry. For most of the observed nonuniform airflow profiles, which had low or moderate degrees of airflow nonuniformity, the effectiveness deterioration was between 5% and 10%, while the pressure drop increase was between 10% and 20%. For severely nonuniform airflow profiles the effectiveness deterioration was up to 30% and the pressure drop increase was up to 90%.