置换通风焊接厂房空气品质的实验研究

对某置换通风焊接厂房进行了气流组织实验,在正常工况下测试了温湿度、臭氧浓度、室内压强、室内风速、粉尘浓度等数据,实验结果表明该厂房的温湿度、室内压强、室内风速,臭氧浓度达到设计要求,但其颗粒物PM2.5浓度超标,基于该厂房室内品质现状,从劳动保护的角度,提出了相应的改善措施。     

Numerical modeling of a complex diffuser in a room with displacement ventilation

A micro/macro-level approach (MMLA) has been proposed which makes it possible for HVAC engineers to easily study the effect of diffuser characteristics and diffuser placement on thermal comfort and indoor air quality. In this article the MMLA has been used to predict the flow and thermal behavior of the air in the near-zone of a complex low-velocity diffuser. A series of experiment has been carried out to validate the numerical predictions in order to ensure that simulations can be used with confidence to predict indoor airflow. The predictions have been performed by means of steady Reynolds Stress Model (RSM) and the results have good agreement both qualitatively and quantitatively with measurements. However, measurements indicated that the diffusion of the velocity and temperature was to some extent under-predicted by the RSM, which might be related to high instability of the airflow close to the diffuser. This effect might be captured by employing unsteady RSM. The present study also shows the importance of detailed inlet supply modeling in the accuracy of indoor air prediction.     

A study of perceived air quality and sick building syndrome in a field environment chamber served by displacement ventilation system in the tropics

This paper presents a study of Perceived Air Quality (PAQ) and Sick Building Syndrome (SBS) using tropically acclimatized subjects in a Field Environmental Chamber (FEC) served by Displacement Ventilation (DV) system. The FEC, 11.12 m (L)×7.53 m (W)×2.60 m (H), simulates a typical office layout. A total of 60 subjects, 30 males and 30 females, were engaged in sedentary office work for 3 h. Air velocity in the space near the subjects was kept at below 0.2 m/s. Relative Humidity (RH) at 0.6 m height and outdoor air provision were maintained at 50% and 10 l/s/p, respectively. Subjects were exposed to three vertical air temperature gradients, nominally 1, 3 and 5 K/m, between 0.1 and 1.1 m heights and three room air temperatures 20, 23 and 26 °C at 0.6 m height. The main objective of this study is to evaluate the influence of temperature gradient and room air temperature (at 0.6 m height) on PAQ and SBS in DV environment. It was found that temperature gradient had insignificant impact on PAQ and SBS. Dry air sensation, irritations and air freshness decreased with increase of room air temperature.     

Experimental study of airflow characteristics of stratum ventilation in a multi‐occupant room with comparison to mixing ventilation and displacement ventilation

The motivation of this study is stimulated by a lack of knowledge about the difference of airflow characteristics between a novel air distribution method [i.e., stratum ventilation (SV)] and conventional air distribution methods [i.e., mixing ventilation (MV) and displacement ventilation (DV)]. Detailed air velocity and temperature measurements were conducted in the occupied zone of a classroom with dimensions of 8.8 m (L) × 6.1 m (W) × 2.4 m (H). Turbulence intensity and power spectrum of velocity fluctuation were calculated using the measured data. Thermal comfort and cooling efficiency were also compared. The results show that in the occupied zone, the airflow characteristics among MV, DV, and SV are different. The turbulent airflow fluctuation is enhanced in this classroom with multiple thermal manikins due to thermal buoyancy and airflow mixing effect. Thermal comfort evaluations indicate that in comparison with MV and DV, a higher supply air temperature should be adopted for SV to achieve general thermal comfort with low draft risk. Comparison of the mean air temperatures in the occupied zone reveals that SV is of highest cooling efficiency, followed by DV and then MV.     

A review of ventilation and the quality of ventilation air

Ventilation is pivotal in terms of securing optimum indoor air quality. In addition, it also has a major impact on energy use in buildings. It is important, therefore, that the role and impact of ventilation is fully understood and that ventilation is employed efficiently. The purpose of this paper is to review these aspects with particular reference to recent research and developments. Key aspects are concerned with identifying the role of ventilation and reviewing this role in the context of the other measures that must be taken to secure a healthy indoor environment. References are particularly made to the development of standards and recent related research. Although good progress is being made, areas that still need to be addressed include maintaining good outdoor air quality and preventing contaminated outdoor air from entering buildings. The outcome of recent research must also be disseminated in practical ways to policy makers, building occupiers and practitioners. Good indoor climate can be achieved, not so much by introducing expensive concepts, but by developing a rationale approach to identifying needs and applying the necessary tools to deal with each need.     

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。     

Thermal comfort and indoor air quality in the lecture room with 4-way cassette air-conditioner and mixing ventilation system

We performed the experimental and the numerical studies on thermal comfort (TC) and indoor air quality (IAQ) in the lecture room with cooling loads when the operating conditions are changed. Predicted mean vote (PMV) value and CO₂ concentration of the lecture room were measured and compared to the numerical results. Both of them showed a reasonable agreement with each other and then we applied the numerical model to analyze TC and IAQ for a couple of different operating conditions. From the results we found that the increment of the discharge angle of 4-way cassette air-conditioner makes uniformity of TC worse, but rarely affects IAQ. It turned out that TC and IAQ are hardly affected by the variation of the discharge airflow. Finally TC was merely affected by the increment of the ventilation rate, but when the ventilation rate is more than 800 m³/h, the average CO₂ concentration can be satisfied with the standard limits of Japanese in our case studies.     

示踪气体浓度衰减法在民用建筑自然通风研究中的应用

用示踪气体浓度衰减法对某会议室的自然通风作了实测研究，分析了影响换气次数的各种因素、示踪气体浓度衰法的有效性及其正确应用。揭示出不同的房间布置及不同的门窗开启民政部对换气次数有很大影响，而示踪气体浓度衰减法是对此进行实验研究的有效手段。     

The outdoor air ventilation rate in high-rise residences employing room air conditioners

Ventilation is important because it affects indoor environmental conditions, including air pollutant concentrations that may modify the health of the occupants of a building, or their perceptions and comfort. This paper reports, first of all, on field studies monitoring indoor overnight CO₂ levels and outdoor ventilation rates in bedrooms employing room air conditioners (RACs), so the current situation of ventilation in actual high-rise residential buildings in Hong Kong can be appreciated. This is followed by a report of the results of laboratory experiments where two typical RACs were used in an examination of outdoor air ventilation characteristics in rooms employing RACs. The results of field studies showed that the outdoor ventilation rates in the measured bedrooms equipped with RACs in high-rise residential buildings in Hong Kong could not meet the ventilation requirement specified in the ASHRAE standard 62-2001 even if there was only one occupant in a bedroom. Although the use of a window-type air conditioner (WRAC) may provide a higher outdoor ventilation rate than the use of a split-type air conditioner (SARC), this may be ascribed to the fact there is more natural infiltration when a WRAC is used. The ventilation damper currently available in a WRAC does not significantly affect the outdoor ventilation rate. Therefore, such a damper cannot be expected to provide the ventilation rate as required by a ventilation code and its intended function of controlling ventilation is limited. In addition, the air exhausted from indoors to outdoors through the ventilation outlet in a WRAC is air that has just been cooled by the cooling coil (evaporator). This is unreasonable, because exhausting just-cooled and dehumidified air is a waste of energy. Therefore, an improved design for a WRAC has been suggested. Finally, the outdoor ventilation requirement for bedrooms at nighttime, when occupants are asleep, is discussed. A new ventilation rate of 3.0 l/s per person for the sleeping environment in high-rise residential buildings is proposed.     

送风高度对碰撞射流热风供暖房间热环境影响的实测研究

在人工气候室内,对碰撞射流通风两种送风高度下的室内温度与气流速度进行了实测。结果表明:碰撞射流送风高度对室内温度竖直分布影响不大,但对紧贴地面的空气温度的衰减过程有明显影响;送风高度对室内气流分布有较大影响,增大送风高度可以减小地面附近气流的速度,但增大了离地面较远处的风速;由于送风高度较低时近风口处的空气温度较高,导致碰撞射流热风供暖时送风口越低,人体吹风感越小。     

CFD study on effect of the air supply location on the performance of the displacement ventilation system

The purpose of this paper is to investigate using a numerical simulation (computational fluid dynamics or CFD) the effect of the air supply location on the design and performance of the displacement ventilation (DV) system. The results are reported in terms of thermal comfort and indoor air quality. The study focuses on the typical Hong Kong office under local thermal and boundary conditions. This includes the high cooling load used in Hong Kong. Several pollutants typically found in the office such as carbon dioxide and volatile organic compounds (VOCs) were investigated. The results indicate that the supply should be located near the center of the room rather than to one side of the room. This will provide a more uniform thermal condition in the office. The DV system was found to be effective in dispersing VOCs within an office environment for all cases studied. The exhaust was found to have minimal effect on the thermal comfort. For a DV system in Hong Kong, it is possible to use 100% fresh air without extra energy consumption.     

Indoor air quality in California homes with code-required mechanical ventilation

Data were collected in 70 detached houses built in 2011-2017 in compliance with the mechanical ventilation requirements of California's building energy efficiency standards. Each home was monitored for a 1-week period with windows closed and the central mechanical ventilation system operating. Pollutant measurements included time-resolved fine particulate matter (PM_2.5) indoors and outdoors and formaldehyde and carbon dioxide (CO₂) indoors. Time-integrated measurements were made for formaldehyde, NO₂, and nitrogen oxides (NO_X) indoors and outdoors. Operation of the cooktop, range hood, and other exhaust fans was continuously recorded during the monitoring period. Onetime diagnostic measurements included mechanical airflows and envelope and duct system air leakage. All homes met or were very close to meeting the ventilation requirements. On average, the dwelling unit ventilation fan moved 50% more airflow than the minimum requirement. Pollutant concentrations were similar to or lower than those reported in a 2006-2007 study of California new homes built in 2002-2005. Mean and median indoor concentrations were lower by 44% and 38% for formaldehyde and 44% and 54% for PM_2.5. Ventilation fans were operating in only 26% of homes when first visited, and the control switches in many homes did not have informative labels as required by building standards.     

置换通风式空调房间内速度场和温度场数值模拟

应用计算流体力学的理论和方法模拟了三维空调房间的空气的湍流流动,研究强迫对流作用下的置换通风式空调室内气流的速度和温度分布及换热规律,并利用CFD软件FLUENT对模型进行具体的计算,得出了一些有益的结论。     

双热源置换通风系统的实验研究

通过实验手段细致分析研究了置换通风系统中双热源的情况，结果表明：在相同的总热气流送入量下，单热源和双热源形成的温度场有很大的不同，辅热源的存在降低了温跃层的高度和上部区域的温度，分散的热源对置换通风系统不利。讨论了辅热源气流温度、辅热源气流流量、辅热源焓值等影响因素。     

Measurement and prediction of indoor air quality using a breathing thermal manikin

The analyses performed in this paper reveal that a breathing thermal manikin with realistic simulation of respiration including breathing cycle, pulmonary ventilation rate, frequency and breathing mode, gas concentration, humidity and temperature of exhaled air and human body shape and surface temperature is sensitive enough to perform reliable measurement of characteristics of air as inhaled by occupants. The temperature, humidity, and pollution concentration in the inhaled air can be measured accurately with a thermal manikin without breathing simulation if they are measured at the upper lip at a distance of <0.01 m from the face. Body surface temperature, shape and posture as well as clothing insulation have impact on the measured inhaled air parameters. Proper simulation of breathing, especially of exhalation, is needed for studying the transport of exhaled air between occupants. A method for predicting air acceptability based on inhaled air parameters and known exposure-response relationships established in experiments with human subjects is suggested. PRACTICAL IMPLICATIONS: Recommendations for optimal simulation of human breathing by means of a breathing thermal manikin when studying pollution concentration, temperature and humidity of the inhaled air as well as the transport of exhaled air (which may carry infectious agents) between occupants are outlined. In order to compare results obtained with breathing thermal manikins, their nose and mouth geometry should be standardized.     

Domestic ventilation with heat recovery to improve indoor air quality

Recently in the U.K., and particularly in Scotland, domestic ventilation systems have been considered as means of reducing condensation in existing housing stock. A simple ventilation model which is suitable for ventilation systems with a heat recovery unit is presented. Using field data of temperature and relative humidity, air supply and extract rates for individual rooms are estimated by applying this model. Unlike conventional systems, extract from bedrooms is considered necessary for the type of dwellings considered to reduce surface condensation.     

Numerical study on temperature stratification in a room with underfloor air distribution system

In this study, numerical prediction using computational fluid dynamics (CFD) was utilized to investigate air temperature stratification in a room with an underfloor air distribution (UFAD) system. The numerical modeling using CFD computation was validated with physical test in a full size experimental room with an UFAD system. The different supply air conditions and heat loads were discussed. The results show that the effect of three parameters, heat load, supply volume flux and supply air velocity, on room air temperature would be expressed by the length scale of the floor supply jet. When the length scale increased from 0.8 to 1.56 m, the ratio of vertical temperature difference between 2.5 and 0.1 m at the occupied zone to the difference between return and supply air temperature decreased from 0.62 to 0.25. When there was only one local heat source in the room, there was a thermal stratified interface at the occupied zone. The interface height was about 1.42 times the length scale. The results may suggest ways to optimize UFAD design and operation.     

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.     

Respiratory symptoms, perceived air quality and physiological signs in elementary school pupils in relation to displacement and mixing ventilation system: an intervention study

Schools may be poorly ventilated and may contain furry pet allergens, particles and microorganisms. We studied health effects when changing from mixing ceiling ventilation to two types of displacement ventilation, front ventilation system (FVS) and floor master system (FMS). The study included pupils in three elementary school classes (N = 61), all with floor heating. One class received blinded interventions; the two others were unchanged (controls). Ventilation flow and supply air temperature was kept constant. The medical investigation included tear film stability (BUT), nasal patency and a questionnaire containing rating scales. When changing from mixing ventilation to FVS, the pupils (N = 26) perceived better air quality (P = 0.006) and less dyspnoea (P = 0.007) as compared to controls (N = 35), and BUT was improved (P = 0.03). At desk level, mean CO(2) was reduced from 867 to 655 ppm. Formaldehyde and viable bacteria were numerically lower, while total bacteria and molds were higher with displacement ventilation. There was no difference in symptoms or signs when changing from FVS to FMS. Cat (Der p1), dog (Can f1) and horse allergen (Equ cx) were common in air at all conditions. In conclusion, displacement ventilation may have certain positive health effects among pupils, as compared to conventional mixing ceiling systems. PRACTICAL IMPLICATIONS: Displacement ventilation may be a suitable ventilation principle for achieving good indoor environment in classrooms. The type of supply air diffuser does not seem to be of major importance. The combination of floor heating and displacement ventilation can be a useful way of avoiding the previously described problem of thermal discomfort.