Thermal comparison between ceiling diffusers and fabric ductwork diffusers for green buildings

Continuously increasing energy standards have driven the need for increasing the efficiency of buildings. Most enhancements to building efficiency have been a result of changes to the heating/cooling systems, improvements in construction materials, or building design code improvements. These approaches neglect the way in which air is dispersed into individual rooms or in a building – i.e., the ducting system. This opens up the possibility of significant energy savings by making ductwork systems lighter and better insulating while ensuring cost effectiveness.The current study explores this idea by comparing the performance of conventional ductwork with recent advancements in fabric-based ductwork. We focus on the transient behavior of an on/off control system, as well as the steady state behavior of the two ductwork systems. Transient, fully three dimensional validated computational (CFD) simulations are performed to determine flow patterns and thermal evolution in rooms containing either conventional or fabric ductwork. This analysis is used to construct metrics on efficiency. A number of different flow rates are examined to determine the performance over a range of operating conditions. Transient finite volume simulations consisted of over 13 million degrees of freedom for over 10,000 time steps. The simulations utilized HPC (High Performance Computing) for the large scale analysis.The results conclusively show that fabric ducting systems are superior to the conventional systems in terms of efficiency. Observations from the data show that fabric ducting systems heat the room faster, more uniformly, and more efficiently. The increase in performance demonstrates the potential benefits of moving away from conventional systems to fabric systems for the construction of green buildings: particularly in conjunction with adaptive control systems.     

Gas transfer from air diffusers

The bubble and surface volumetric mass transfer coefficients for oxygen, k(L)a(b) and k(L)a(s), are separately determined for 179 aeration tests, with diffuser depths ranging from 2.25 to 32 m, using the DeMoyer et al. 12003. Impact of bubble and free surface oxygen transfer on diffused aeration systems. Water Res 37, 1890-1904] mass transfer model. Two empirical characterization equations are developed for k(L)a(b) and k(L)a(s), correlating the coefficients to air flow, Qa, diffuser depth, hd, cross-sectional area, Acs, and volume, V. The characterization equations indicate that the bubble transfer coefficient, k(L)a(b), increases with increasing gas flow rate and depth, and decreases with increasing water volume. For fine bubble diffusers, k(L)a(b) is approximately six times greater than k(L)a(b) for coarse bubble diffusers. The surface transfer coefficient, k(L)A(s), increases with increasing gas flow rate and diffuser depth. The characterization equations make it possible to predict the gas transfer that will occur across bubble interfaces and across the free surface with a bubble plume at depths up to 32 m and with variable air discharge in deep tanks and reservoirs.     

Fine-pore aeration diffusers: accelerated membrane ageing studies

Polymeric membranes are widely used in aeration systems for biological treatment. These membranes may degrade over time and are sensitive to fouling and scaling. Membrane degradation is reflected in a decline in operating performance and higher headloss, resulting in increased energy costs. Mechanical property parameters, such as membrane hardness, Young's modulus, and orifice creep, were used to characterize the performance of membranes over time in operation and to predict their failure. Used diffusers from municipal wastewater treatment plants were collected and tested for efficiency and headloss, and then dissected to facilitate measurements of Young's modulus, hardness, and orifice creep. Higher degree of membrane fouling corresponded consistently with larger orifice creep. A lab-scale membrane ageing simulation was performed with polyurethane and four different ethylene-propylene-diene (EPDM) membrane diffusers by subjecting them to chemical ageing cycles and periodic testing. The results confirmed full-scale plant results and showed the superiority of orifice creep over Young's modulus and hardness in predicting diffuser deterioration.     

Air flow characteristics of a room with square cone diffusers

A computational fluid dynamics model with radiant exchange between surfaces is developed to examine the air flow characteristics of a room with square cone diffusers. As an input to the full-scale 3-D room model, a 2-D diffuser model that supplies direction and magnitude of air flow into the room is developed and evaluated using infrared visualization. The room air flow model is assessed using several previously documented problems with various geometries and boundary conditions. Simulations are conducted for heating and cooling of the room with one or two supply air diffusers. The results show that the offset and lips of the diffuser work together to determine the discharge air angles, which play an important role in determining the room air flow patterns. For a certain discharge angle in the heating case, the air flows along the ceiling. The results indicate that, for the same supply air flow, operating only a single diffuser initiates more mixing of the room air flow, which results in enhanced temperature uniformity compared to that for two diffusers. Radiant exchange between the exterior window and interior surfaces causes a significant change in the window temperature.     

低温送风条件下风口结露实验研究

对3种普通风口在低温送风条件下的结露特性进行了实验研究,针对实验现象分析了各种风口的结露机理,为普通风口在低温送风条件下的使用制定了软启动控制策略,认为若无软启动措施,低温送风系统宜采用专用风口。     

国产旋流风口用于低温送风系统的试验研究

针对低温送风系统应用时容易产生的问题,对国产旋流风口用于低温送风系统的可行性进行了试验研究和理论分析。结果表明,只要选择正确、设计合理,具有高诱导比的旋流风口也可用于低温送风系统。     

Effects of plume spacing and flowrate on destratification efficiency of air diffusers

This study adopts techniques of computational fluid dynamics (CFD) to analyze the combined effect of adjacent plumes of an air-diffuser system on its destratification efficiency. Lab experiments were carried out to calibrate and verify the CFD models in thermally stratified freshwater. The CFD simulation and lab experiment results were analyzed to relate destratification efficiency with four non-dimensional variables. The results indicate that destratification number, D(N), has the best relationship that includes air flowrate, stratification frequency, water depth, and bubble slip velocity. Since plume spacing and air flowrate are the major control variables of the system, especially in the field, two charts showing the relationships between destratification efficiency, plume spacing, and destratification number are developed for guiding their control in its design and operation.     

散流器平送气流组织计算方法的优化

介绍了气流组织的基本要求,结合设计手册中推荐的散流器送风设计计算方法,提出了优化的散流器平送气流组织设计计算方法,并通过实例证明,优化后的方法避免了现有设计方法需要查表的不便。     

几何的神秘主义

几何的神秘主义意味着理性几何形式之外的耐人寻味、琢磨不定,以及与宇宙、人的精神世界或神的世界沟通的向往.建筑几何的神秘主义最早体现于希腊神话中人类第一位建筑师代达罗斯(Daedalus)建造的历史上第一座迷宫.迷宫作为神话中建筑的起源,意指建筑天生包含着有序与无序、理性与感性、光与影、有限与无限的关系.代达罗斯的另外两件历史最早的作品在建筑理论中也是意味深长:第一座露天剧场和第一对能飞翔的人造翅膀.在中世纪的教堂中,迷宫图案象征着走向耶路撒冷的艰辛而喜悦的朝圣之旅,与此同时,长着翅膀的天使成为神界与人界交流的信使.剧场在文艺复兴的建筑理论中演变为建筑的戏剧性(theatricality)本质,而迷宫被看作这个本质的“基础”性象征[参考维特鲁威《建筑十书》的第一个意大利语版本中关于“宇宙剧场”(Theatrum Mundi)的插图:Cesare Cesariano,Vitruvius,1521].     

An easy-to-use turbulent inlet boundary condition for large-eddy simulation of radial diffusers

When applying time-accurate computational fluid dynamics, large-eddy simulation (CFD LES) to room ventilation, a common problem is that the supply jets do not model properly if there is no realistic turbulence in the inflow boundary. In this paper we introduce a novel, easy-to-use method of generating a turbulent inlet boundary condition for simulating a radial diffuser. The basic idea is to apply a time-independent velocity distribution with realistic spatial statistics, and to add temporal fluctuations by rotation. The method is simple to use, requires only one extra parameter, and does not necessitate large storage files. It needs a momentary velocity distribution on the inflow surface with the desired volume flow rate obtained from a time-accurate internal simulation of the diffuser alone. In a room-scale simulation, this velocity distribution is put in rotating movement in order to mimic a turbulent inlet boundary. The method is verified by comparing the outcome with published measurements and with a simulation containing the interior of the diffuser.     

第四层:光怪陆离的几何空间

Plasm a工作室设计的第四层完全是一个光怪陆离的世界,找不到一点传统酒店的影子,一扫酒店在人们心目中只是安静的休息场所的形象,尝试充分利用表面面积来营造不同的空间效果。伊娃和霍格喜欢大胆的轮廓,整个四层像是一个巨大的时尚聚会,到处是用不锈钢三角碎片制作凹凸不平的表面,闪闪放光,设计师用简洁的直线条和一些冷酷的材料追求一种不真实的感受。在这个前卫的建筑中,不锈钢材料从大厅延续到每个客房内,甚至延续到了书桌窗台,三维构成向人们展示了它好斗冷静的一面。卫生间的隔断全是玻璃的,用鲜亮的色彩和不锈钢形成对比。Plasma工…     

After After Geometry

Michael Meredith of MOS Architects examines his own practice's preoccupation with physics and the particle-oriented world, and the persistent problem of meaning and meaninglessness against the backdrop of the architecture of a previous era: a period that spanned the Deconstruction movement of the late 1980s and closed with Greg Lynn's seminal 1997 Architecture After Geometry edition of AD.     

办公建筑中旋流风口地板送风系统的设计及实验研究

基于地板送风与置换通风原理的相似性,参考办公室中置换通风的设计方法,结合旋流风口地板送风系统的特性,提出旋流风口地板送风系统的设计方法。通过实验对设计方法进行了验证,并对室内热舒适性进行了评价。     

高诱导比低温风口在工程中的应用

简要介绍了用于低温空调工程中的高诱导比低温风口的工作原理，对实际工程中应用的这种低温风口的送风性能作了实测，分析了测试数据，认为这种风口可获得满意的气流组织和均匀的温度场，而且在低温工况下送风口未出现结露现象。     

Membrane properties change in fine-pore aeration diffusers: full-scale variations of transfer efficiency and headloss

Fine-pore diffusers are the most common aeration system in municipal wastewater treatment. Punched polymeric membranes are often used in fine-pore aeration due to their advantageous initial performance. These membranes are subject to fouling and scaling, resulting in increased headloss and reduced oxygen transfer efficiency, both contributing to increased plant energy costs. This paper describes and discusses the change in material properties for polymeric fine-pore diffusers, comparing new and used membranes. Three different diffuser technologies were tested and sample diffusers from two wastewater treatment facilities were analysed. The polymeric membranes analysed in this paper were composed of ethylene-propylene-diene monomer (EPDM), polyurethane, and silicon. Transfer efficiency is usually lower with longer times in operation, as older, dilated orifices produce larger bubbles, which are unfavourable to mass transfer. At the same time, headloss increases with time in operation, since membranes increase in rigidity and hardness, and fouling and scaling phenomena occur at the orifice opening. Change in polymer properties and laboratory test results correlate with the decrease in oxygen transfer efficiency.     

Energy saving in activated sludge plants by the use of more efficient fine bubble diffusers

Many activated sludge plants (ASP) use fine bubble diffused air as their source of oxygen. Blowers are attached to air pipework, which distributes air to a network of diffusers installed on the floor of the ASP tank. Modern diffusers are made from a rubber membrane which flexes to allow fine bubbles of air to pass through holes in the diffusers which then pass into the mixed liquors in the tank. The diffusers come as circular discs, tubes and more recently mats or panels. Yorkshire Water is in the process of building new ASP at some of their biggest sewage treatment works to meet new final effluent consent standards associated with the freshwater fisheries directive (FFD). These new works will treat sewage from a combined population of over two million people in the Yorkshire area. Black & Veatch is involved in some of the first works to have a new type of fine bubble diffuser installed in the ASP basins. These diffusers resemble a mat or panel and are fixed to the floor of the tank as opposed to circular and tubular diffusers which as fixed above the floor. Oxygen transfer testing has been carried out to show the efficiency of these aeration systems, which may offer significant savings in operating costs to water operators. This paper examines the results from the tests and compares them with other tests carried out in the United States and tests that have been carried out on other types of diffusers. The paper will discuss the results of the oxygen transfer tests and present capital and net present costs (NPC) for various diffuser installations.