Performance evaluation of air distribution systems in three different China railway high-speed train cabins using numerical simulation

Air distribution system is very important to indoor air quality (IAQ) in China railway high-speed (CRH) train cabin. Air distribution systems in three different CRH train cabins are simulated and evaluated in this paper by using the computational fluid dynamic (CFD) method. CFD models of CRH1, CRH2 and CRH5 train cabins are developed and validated basing on the field experiments in three train cabins. Flow field, temperature field, and airflow pattern in the three train cabins are investigated respectively by using the CFD models developed. Four improved performance indexes which can eliminate influences of geometric dimension are utilized to evaluate the air distribution systems in the cabins. The cough droplets dispersion processes inside the CRH train cabins are simulated to investigate the cough droplets removal ability. Simulation results show that good airflow pattern is very critical to guarantee the uniform distribution of flow field, temperature field and thermal comfort in the train cabin. The air distribution system employed in CRH5 train cabin is the most efficient among the three train cabins. Moreover, CRH5 train cabin has stronger cough droplets removal ability than CRH1 and CRH2 train cabins. Air distribution system in CRH5 train cabin should be adopted in the next generation CRH train cabin in the future.     

Comparison of underfloor and overhead air distribution systems in an office environment

This study compares thermal environment of two air distribution systems in an office setting. Airflow, heat and mass (water vapor and contaminant gas) transfer in steady-state condition are modeled for an underfloor air distribution system and an overhead air distribution system. The models include a typical cubicle in a large office floor with a chair, a desk with a personal computer on top, and heat sources such as seated person, desktop computer, and lights. For underfloor air distribution system, cool air enters the occupied zone through an inlet located at the floor level supplying a vertical upward inflow. Three different locations of the inlet diffuser are considered. For overhead air distribution, the inlet is located on the ceiling with slower and cooler inflow. Three inlet angles are considered. For both systems, the air return location is on the ceiling at the same place. Distributions of velocity, temperature, relative humidity, and contaminant concentration in various cases for both systems are computed. Thermal comfort factors are assessed for the two systems. The results are compared among cases of each system, as well as between two typical cases of the two systems and to experimental data for an actual office building given in literature. The results provide a detailed understanding of air transport and its consequence on thermal comfort and indoor air quality that are useful for office building air conditioner design. It is found that underfloor system gives better performance than overhead system in contaminant removal and significantly in energy saving while maintaining the same thermal comfort condition.     

影响室内空气品质的VOC特性及其定量评估

介绍了用于挥发性有机化合物评估的空气耗氧量（COD）指标，阐述了COD与室内空气品质其他指挥的显著相关性，指出空气耗氧量是综合性很强的空气污染指标。指出了改善室内空气品质的技术和措施。     

水系统中三例气塞故障的分析

对工程中遇到的三例水系统气塞故障加以总结，分析其原因，认为气塞是建筑水系统常见故障，应从设计、施工、运行管理三方面加以重视。     

低温送风系统的研究进展

总结了近年来与冰蓄冷相结合的低温送风空调系统的研究成果及进展,认为低温送风系统的研究主要集中在经济性评价和室内气流组织及热舒适性评价两个大的方面.低温送风系统的经济性评价主要取决于室内参数和送风温度的设定及末端送风方式的选择,分析了省能器循环的减少对低温送风系统全年经济性的影响.低温送风的通风及舒适性主要取决于射流结构是否合理及描述室内空气品质和热舒适性的各项指标是否达到标准,总结了在低温送风系统通风及舒适性方面的主要研究方法及研究成果.最后提出了该技术未来的研究方向.     

地板送风系统性能分析

地板送风通常被认为是适用于置换通风的一种通风方式,然而当送风射流的初始动量足够大时,却能导致室内气流形成混合流动.所以定量地界定混合流与分层流产生的条件以及建立其性能分析方法对于地板送风系统的工程实践是十分必要的.     

多联机空调系统的性能域

给出了建筑物室内负荷分布特征的描述方法.以制冷工况下室内机容量连续调节的多联机为对象,模拟研究了室内负荷分布不均匀性对多联机系统部分负荷特性的影响规律.指出在室内外环境参数不变的条件下,多联机空调系统在部分负荷下的COP存在一个由负荷率和负荷不均匀性指数决定的"性能域",并分析了影响性能域形状的因素.     

空调冷热源系统的选择

根据１９９５年９月１６日至１９日在成都市举行的“全国空调冷热源技术交流会”上所交流的内容和有关资料，将制冷剂替代，热泵机组的设计和应用，溴化锂吸收式机组，蓄冷空调等几个主要问题综合整理成此文，供参考。     

空气源热泵系统最低工作温度的研究

空气源热泵机组供热存在一个最低工作温度,在分析热泵的核心部件压缩机的热力学性能基础上,得出了压缩机适合的最低工作温度,并利用COP随蒸发温度变化的规律和北京地区的Bin参数,建立了以经济性为目标函数的最低工作温度数学模型,同时进行了求解分析。     

下送风空调气流组织设计方法

介绍了下送风气流组织中影响人体热舒适的四个主要因素：送风口型式，送风口到人体的距离，送风速度，送风温度。按因素重要性和最佳舒适性要求，提出了两种气流组织设计方法。     

多区域变风量空调系统及其分配控制研究

在多区域变风量空调及其控制系统的分析研究基础上,根据ASHRAE通风标准对新风量的要求,针对混合送风系统仿真分析了4种新风及其分配的控制方案,综合考虑了各方案的新同分配以及系统能耗。结果表明,通过VAV末端再热控制并结合AHU送风温度优化的控制方案,可以较好地解决多区域VAV空调系统新风分配问题,同时能有效地降低系统的能耗。     

The effect of nitrate on VOC removal in trickle-bed biofilters

In response to the growing concern over volatile organic compounds (VOCs), biofiltration is becoming an established economical air pollution control technology for removing VOCs from waste air streams. Current research efforts are concentrating on improving control over key parameters that affect the performance of gas phase biofilters. This study utilized diethyl ether as a substrate, nitrate as the sole nutrient nitrogen source within two co-currently operated trickle-bed biofilters, for over 200 days. The two pelletized medium biofilters were operated at a low empty bed contact time of 25 s, inlet gas flow rates of 8.64 m³/day, nutrient liquid flow rates of 1 liter/day, and COD loading rates of 1.8 and 3.6 kg/m³ per day, respectively. Operational parameters including contaminant concentration in the gas phase, nutrient nitrate concentration in the aqueous phase, and the frequency of biomass removal were considered. Special attention was given to the effect and the role of nitrate on VOC removal. Throughout the experiment, nitrate persisted in the liquid effluent and the ether removal efficiencies improved with increasing influent nitrate concentration, which suggest that the nitrate diffusion into the biofilms is rate determining. By increasing the concentration of oxygen in the feed to this biofilter from 21% (ambient air) to 50 and 100%, while maintaining an influent ether concentration of 133 ppmv and a feed nitrate concentration of 67 mg-N/liter, the performance of the biofilter was not significantly affected. These results suggest that nitrogen was rate limiting as a growth nutrient rather than as an electron acceptor for the respiration of ether. The results also indicated that removal of excess biomass is necessary to maintain long-term performance. However, the required frequency of biomass removal depends on operating parameters such as loading.     

Novel air distribution systems for commercial aircraft cabins

Air distribution systems in commercial aircraft cabins are important for providing a healthy and comfortable environment for passengers and crew. The mixing air distribution systems used in existing aircraft cabins create a uniform air temperature distribution and dilute contaminants in the cabins. The mixing air distribution systems could spread infectious airborne diseases. To improve the air distribution system design for aircraft cabins, this investigation proposed an under-floor displacement air distribution system and a personalized air distribution system. This study first validated a computational fluid dynamics (CFD) program with the experimental data of airflow, air temperature, and tracer-gas concentration from an environmental chamber. Then the validated CFD program was used to calculate the distributions of the air velocity, air temperature, and CO₂ concentration in a section of Boeing 767 aircraft cabin with the mixing, under-floor displacement, and personalized air distribution systems, respectively. By comparing the air and contaminant distributions in the cabin, this study concluded that the personalized air distribution system provided the best air quality without draft risk.     

西安地区应用空气源热泵的经济性分析

以西安市某宾馆为例,结合具体工程概况,对该建筑采用空气源热泵、燃油热水锅炉加冷水机组两种冷热源方案时的初投资和运行费用进行了比较,通过分析评价,得出了在西安地区应用空气源热泵的优势。     

Performance of thermal distribution systems in large commercial buildings

This paper presents major findings of a field study on the performance of five thermal distribution systems in four large commercial buildings. The five systems studied are typical single-duct or dual-duct constant air volume (CAV) systems and variable air volume (VAV) systems, each of which serves an office building or a retail building with floor area over 2000 m². The air leakage from ducts is reported in terms of effective leakage area (ELA) at 25 Pa reference pressure, the ASHRAE-defined duct leakage class C_L, and air leakage ratios. The specific ELAs ranged from 0.7 to 12.9 cm²/m² of duct surface area, and from 0.1 to 7.7 cm²/m² of floor area served. The ASHRAE-defined duct leakage classes ranged from 34 to 606 for the five systems and systems sections tested. The air leakage ratios were estimated to be up to approximately one-third of the fan-supplied airflow in the constant air volume systems. The specific ELAs and leakage classes indicated that air leakage in large commercial duct systems varied significantly from system to system, and from system section to system section even within the same thermal distribution system. Overall, the duct systems measured were much leakier than the ductwork specified as “unsealed ducts” by ASHRAE. On the other hand, thermal losses from supply ducts induced by conduction (including convection and radiation) were significant, on the scale that was comparable to the losses induced by air leakage in the duct systems. The energy losses induced by leakage and conduction suggested that there exist significant energy savings potentials from duct sealing and duct insulation practice in large commercial buildings.     

空气源热泵供热最佳经济平衡点的探讨

提出了最佳经济平衡点的概念,建立了适合计算机求争的通用的最佳经济平衡点的数学模型,以算例形式给出了我国几个适用空气源热泵地区的最佳经济平衡点温度。     

高大空间恒温空调气流组织设计方法研究

提出了一套通用的高大空间恒温空调气流组织设计方法：在气流组织初步计算的基础上，用数值分析的方法得到最优的设计方案，并用模型实验进行验证或修正。该方法用于某高大空间实验室证明是可行的。研究同时发现，室内的温度场和速度场同时受到冷射流和热源的影响，因此以往单纯用射流理论进行的气流组织实际计算结果不能直接应用于精度要求较高的恒温空调系统中。     

北京地区空调新风系统保温问题的探讨

讨论了北京地 机盘管吊顶回风和非吊顶回风上的新风管保温设计，指出通过吊顶回风时，只有室内温度大于新风温度的情况下才需要保温，而在非吊顶回风方式下，需视不同新风终状态加以区别对待。     

空气源热泵在游泳池恒温系统中的应用

结合实际工程,分析了空气源热泵在游泳池恒温系统中应用的经济效益、设备选型要点和设备安装要求.     

Spatial and temporal evolution of trihalomethanes in three water distribution systems

Spatial and seasonal changes in trihalomethane (THM) concentrations were investigated in three distribution systems of Quebec (Canada) which are supplied by different surface waters and which use a variety of physicochemical treatment strategies. The investigation was based on an intensive 25-week sampling programme, undertaken at a time of year when the temperature of southern Quebec surface waters exceeds 4 degrees C (April-November). THMs and other water quality and operational parameters were monitored at points along the distribution system--between the treatment plant and the system extremities--which represented variable residence times of water. Results showed that THM concentrations vary significantly (from 1.5 to 2 times, depending on the utility) between finished waters as they leave the plant and water at the system extremities. When water temperature exceeds 15 degrees C, spatial THM variations are particularly high (from 2 to 4 times, depending on the utility). The development of multivariate regression models showed that water temperature was a better predictor of THM seasonal variability than chlorine dose, surrogates of natural organic matter and pH. Also, initial THM formation (in finished waters leaving the plant) was a good predictor of THM levels at distribution system extremities.