不同送风速度下空调房间的气流组织数值模拟

以办公室空调房间为研究对象,运用计算流体力学(CFD)中Fluent软件数值模拟,对不同送风速度下空调房间的速度场、温度场进行三维数值模拟,对比分析不同送风速度对气流组织的影响。通过对几种不同工况下不同空间位置的速度云图、温度等值线图的分析,得到了不同送风速度对房间气流组织及热舒适性的影响。     

地板送风气流组织特性的研究

采用数值模拟方法,对一应用地板送风系统的开敞式办公环境的气流组织进行模拟计算。通过对模拟结果的速度场和温度场的分析,表明了地板送风能够提供具有较好热舒适性的室内环境。     

CFD模拟分析低温送风系统的热舒适性

采用低温送风时,用CFD模拟不同送风温度的气流组织,通过计算EDT和ADPI值分析模拟房间的热舒适性。     

空调送风角对办公室气流组织影响的数值研究

采用CFD方法对空调办公室内不同送风角度下气流组织进行三维数值模拟计算.在分析送风角度对房间内部流场和温度场影响的基础上,讨论了人员主要活动区的舒适性.结果表明:当空调送风角度处于120°时人员的舒适性最好.研究结果可以为其他类似结构房间空调送风角度的选择和气流组织研究提供参考.     

某建筑中庭气流组织的数值模拟

利用Fluent软件分别对冬、夏季工况下的球形喷口侧送风方案、条形风口侧送风方案和冬季工况下的条形风口侧送风+地板辐射供暖方案的气流组织进行了模拟,并对模拟结果进行了评价分析。结果表明条形风口侧送风+地板辐射供暖方案具有更好的舒适效果。     

低温送风室内气流组织模拟及热舒适评价

采用三维紊流k-ε模型,应用FLUENT软件对低温送风房间的气流组织和热环境进行了模拟。按照ISO7730标准,采用有效吹风感温度T_(ed),空气分布特性指标ADPI等指标对室内热舒适度进行评价。验证采用常规的送风末端和低温送风相结合的气流组织模式的可行性,同时为空调室内气流组织形式的优化设计及舒适性提供依据。     

孔板送风对壁挂式空调房间热舒适性的影响

为研究孔板送风方式对壁挂式空调房间热舒适性的影响,采用Airpak软件分别对在相同送风量和送风温度下采用传统射流送风和孔板送风的气流组织进行数值模拟,通过对温度场、速度场、PMV-PPD值的对比分析,评价两种送风方式下的室内热舒适性,并采用实验测试的方法,对模拟结果的准确性进行实验验证。结果表明:送风方式对室内热舒适性影响明显,孔板送风对室内气流组织的改进和热舒适性的提高有较显著效果,夏季工况采用孔板送风可以起到节省能耗的作用。     

某博物馆高大空间气流组织及节能设计研究

中庭处高大空间的气流组织及节能设计一直是众多暖通学者的研究焦点,中庭处的高大空间一般具有比较特殊的建筑构造,而且还是空调系统能耗高、热舒适性处理的难点.因此为选择出更为合适的方案,营造出更为合理的气流组织形式,就需要通过流体动力学计算模型对气流组织进行模拟.以上海市某博物馆中庭处的高大空间为例,通过计算得到送风参数后,利用CFD数值模拟的方法,分别对空调季地板和送风柱相结合的复合式送风方案与过渡季自然送风消除余热方案进行模拟仿真.模拟结果显示,空调季与过渡季的送风设计方案均可以满足室内需求并达到节能的效果,为今后该类建筑的气流组织和节能方案应用提供参考.     

地板送风系统气流组织及热舒适性研究

本文采用通风软件AirPak 3.0建立物卵模型和数学模型,模拟地板送风系统供冷运行和供热运行的室内空调环境研究不同送风温度和不同送风量对地板送风空调房间速度分布、温度分布、热舒适性和空气品质的影响。结果表明:供冷运行时房间设定温度为26℃,送风温度为18~19.5℃,热力分层良好,热舒适性适中,可作为空调系统运行的最佳工况;供热运行时,房间设定温度为18℃,送风温度为28~30℃时,温度分布趋势接近理想采暖要求,能够满足人体的热舒适需求。     

地板送风在乌克兰国家大剧院空调改造中应用

本文主要介绍乌克兰国家大剧院增加空调系统项目的设计思想,并结合该工程中地板送风的应用实例,对地板送风与置换通风的原理进行描述,说明了两者之间的差别.强调了置换通风的空调方式必须要有好的自控策略和控制系统来保证其运行效果.并用CFD技术对剧院观众厅的气流组织进行了数值模拟分析,证明地板送风的方式在剧院空调改造中具有很好的适用性,能很好地满足观众的舒适性要求.     

Removal of contaminants released from room surfaces by displacement and mixing ventilation: modeling and validation

This paper presents the experimental and numerical modeling of contaminant dispersion in a full-scale environmental chamber with different room air distribution systems. For the experimental modeling, an area source with uniform emissions of a hypothetical contaminant (SF6) from the entire floor surface is designed and constructed. Two different types of ventilation are studied: displacement and mixing ventilation. A computer model for predicting the contaminant dispersion in indoor spaces was validated with experimental data. The validated model is used to study the effects of airflow and the area-source location on contaminant dispersion. Results show that the global airflow pattern has a strong impact on the distribution of the contaminants. In general, the personal exposure could be estimated by analyzing the relative source positions in the airflow pattern. Accordingly, the location of an exhaust diffuser may not greatly affect the airflow pattern, but can significantly affect the exposure level in the room. PRACTICAL IMPLICATIONS: When designing ventilation in addition to bringing fresh air to occupants, it is important to consider the removal of contaminants released in the off-gassing of building materials. Typical indoor off-gassing examples are emissions of volatile organic compounds from building enclosure surfaces such as flooring and painted walls. In this study, we conducted experimental and numerical modeling of different area sources in a mock-up office setup, with displacement or mixing ventilation. Displacement ventilation was as successful as mixing ventilation in removing the contaminant source from the floor area. Actually, the most important consideration in the removal of these contaminants is the relative position of the area source to the main airflow pattern and the occupied zone.     

Effect of internal partitions on the performance of under floor air supply ventilation in a typical office environment

This paper presents a case to investigate the effect of partitions in an office on the performance of under floor air supply ventilation system via computational fluid dynamics. The assessment is in terms of thermal comfort and indoor air quality with the use of a validated computer model. The results indicate that the partitions may significantly affect airflow and performance of a under floor air supply ventilation system. In particular, the presence of a gap above the partition wall is able to improve air distribution owing to less air re-circulation in the upper zone. Its effect on thermal comfort and indoor air quality indicators are evaluated.     

Approaches for improving airflow uniformity in unidirectional flow cleanrooms

Airflow behavior inside a cleanroom with vertical unidirectional flow has been investigated. The design parameters, such as porosity and height of raised floor, width of cleanroom and inlet velocity profile, which affect the uniformity of air velocity distribution inside the cleanroom have been studied computationally. The Reynolds-averaged Navier–Stokes equations governing the flow are solved using a finite-volume code STAR-CD. The standard k-ε turbulence model has been used. Approaches for improving airflow uniformity have been proposed and quantitatively examined based on intensive case studies. The present results show that the uniformity increases along with the height of raised floor. Alternatively, better airflow uniformity can also be achieved through a proper allocation of floor porosity or by controlling the distribution of inlet velocity profile. Suggestions on how to design unidirectional cleanrooms with desired airflow uniformity under practical constraints have been given.     

Airflow distribution through perforated tiles in raised-floor data centers

Raised-floor data centers are the most commonly used facilities for housing computer and telecommunication equipment. To adequately cool this equipment, the cooling air through perforated tiles must be distributed properly. The airflow distribution depends on the pressure distribution or the flow field in the space under the raised floor (plenum); it is a complex function of a large number of variables, including the size of the plenum, the open area of the perforated tiles, the locations and flow rates of the computer room air conditioner (CRAC) units, and the size and location of the under-floor obstructions like cables and pipes. In this article, the effect of these parameters on the airflow distribution is studied using an idealized one-dimensional computational model. Within the one-dimensional framework, the airflow distribution is governed by two dimensionless parameters: one related to the pressure variation in the plenum and the other to the frictional resistance. Results, in terms of distributions of pressure in the plenum and flow rates through the perforated tiles, are presented over a range of values of these two parameters. These results provide an understanding of the fundamental fluid mechanical processes controlling the airflow distribution through the perforated tiles. The one-dimensional model is used to calculate flow rates for two possible arrangements of the CRAC units, and these results are compared with those given by a three-dimensional model.     

Unsteady thermal performance analysis of a room with serial and parallel duct radiant floor heating system using hot airflow

In this study, the unsteady thermal performance of a test room heated by circulating hot airflow under the floor was analyzed with a developed mathematical model based on heat transfer equilibrium among the air flow, the floor and the indoor air. The time variations in the indoor air temperature for the serial duct floor heating system were investigated theoretically and experimentally. The time variations in the floor surface and the indoor air temperatures were predicted theoretically for the parallel duct floor heating system. Experiments on the time variations of the dimensionless numbers such as Nu for the airflow in duct and the indoor air, Gr for the indoor air and the heat ratios of convection and radiation to total heat for the serial duct floor heating system were performed. The theoretical and experimental results showed a good agreement.     

末端装置特性对置换通风工作区速度场与温度梯度的影响

阐述了稍低于室温的空气经靠墙散流器低速进入后，下沉于地面及扩放的概念。介绍了贴地冷气流层速度分布的一般特性，分析了风口特性对地面气流速度场及工作区空气温度梯度的影响。     

Simulation-based feasibility study of improved air conditioning systems for hospital operating room

The goal of the air distribution inside a hospital operating room (OR) is to protect the patient and staff from cross-infection while maintaining occupant comfort and not affecting the facilitation of surgical tasks. In ORs, HEPA-filtered air and vertical (downward) laminar airflow are often used to achieve a unidirectional flow of fresh air from ceiling, washing over the patient and flowing out of exhaust vents on the side walls, near the floor. However, previous research has shown that this method does not necessarily achieve the desired unidirectional flow pattern or adequately achieve optimal air asepsis. The results from this study show that maximizing the area of the laminar flow diffusers remedies this issue and provides very low contamination levels. The use of air curtains as specified by manufacturers of commercial products may not provide satisfactory results, with noticeable contamination levels at the wound site.     

Determination of particle concentration in the breathing zone for four different types of office ventilation systems

Many factors affect the airflow patterns, thermal comfort, contaminant removal efficiency and indoor air quality at individual workstations in office buildings. In this study, four ventilation systems were used in a test chamber designed to represent an area of a typical office building floor and reproduce the real characteristics of a modern office space. Measurements of particle concentration and thermal parameters (temperature and velocity) were carried out for each of the following types of ventilation systems: (a) conventional air distribution system with ceiling supply and return; (b) conventional air distribution system with ceiling supply and return near the floor; (c) underfloor air distribution system; and (d) split system. The measurements aimed to analyse the particle removal efficiency in the breathing zone and the impact of particle concentration on an individual at the workstation. The efficiency of the ventilation system was analysed by measuring particle size and concentration, ventilation effectiveness and the indoor/outdoor ratio. Each ventilation system showed different airflow patterns and the efficiency of each ventilation system in the removal of the particles in the breathing zone showed no correlation with particle size and the various methods of analyses used.     

Air Change Effectiveness and Pollutant Removal Efficiency during Adverse Mixing Conditions

Abstract The air change effectiveness (ACE), an indicator of the indoor airflow pattern, was measured in twenty-six laboratory experiments. Ventilation air was supplied through induction-type diffusers located in the ceiling and removed through a ceiling mounted return grille. The tracer-gas step-up measurement procedure was employed. In five of the experiments, pollutant removal efficiencies were also measured for simulated pollutant emissions from the floor covering and for simulated emissions from occupants. In experiments with heated supply air, supply airflow rates typical of the minimum supply flow rates of VAV ventilation systems, and 100% outside air, the ACE ranged from 0.69 to 0.89. These results indicate that significant short-circuiting of ventilation air between the supply air diffuser and return air grille does occur under these adverse conditions. Mechanical recirculation of air, so that the supply air contained approximately 50% outside air, increased the ACE by about 0.05. When the supply air was cooled, the ACE ranged from 0.99 to 1.15, adding to existing evidence that short-circuiting is rarely a problem when the building is being cooled. The pollutant removal efficiency for simulated pollutant emissions from the floor covering (PRE_floor) was strongly correlated with ACE (R²= 0.98) and the values of PRE_floor were within approximately 0.1 of the values of ACE. The pollutant removal efficiency for simulated pollutant emissions by occupants varied between workstations and was not as well correlated with the ACE.