Influence of the floor-based obstructions on contaminant removal efficiency and effectiveness

Dimensioning of dilution ventilation is often made using the perfect mixing approximation, assuming uniform contaminant concentration throughout the room space. However, the contaminant removal efficiency and effectiveness of air conditioning system should be accounted for during design. The effectiveness is in this context used as a measure of the contaminant distribution uniformity within the occupied zone. Influence of an occupied zone obstruction level, air distribution method, air change rate, cooling load and contaminant source non-uniformity on the contaminant removal efficiency and occupied zone contaminant concentration uniformity were studied in scale model. The room air distribution method results in contaminant concentration non-uniformity inside the occupied zone. A method was developed to take this into account during the design of air distribution system. Contaminant supply non-uniformity was found to have great influence on the concentration non-uniformity with two tested air distribution methods.     

Effects of inlet and exhaust locations and emitted gas density on indoor air contaminant concentrations

The steady-state distribution of contaminant concentrations in a workroom is a function of several factors, of which the types and relative position of air inlets and exhausts are some of the most important. Here several different inlet and exhaust locations and types (with or without diffuser) were investigated to determine the optimum inlet and exhaust positions. Room concentration patterns for a workroom were explored by computational fluid dynamics (CFD) simulations for various inlet locations, exhaust locations, contaminant gas densities, and dilution air flow rates. Average contaminant concentrations were calculated for the entire room, the breathing zone plane, and the near-source breathing zone (BZ).     

置换通风的实验研究

通过对单一热源情况的实验,得到了置换通风时垂直方向的温度梯度和三维温度场,并对不同墙壁的传热系数和不同的外环境温度作了４个对比实验,结果表明：①热源不影响房间温度水平方向上的均匀度,热源或污染源无横向扩散;②除热源上方有较大的上升气流外,整个速度场均匀平稳;③围护结构的热损失对温跃层高度无明显影响,外部环境温度则使室内温度垂直分布有所改变。     

Radon and Natural Ventilation in Newer Danish Single-Family Houses

Abstract To investigate the effect of ventilation on indoor radon (²²²Rn), simultaneous measurements of radon concentrations and air change rates were made in 117 Danish naturally ventilated slab-on-grade houses built during the period 1984–1989. Radon measurements (based on CR-39 alpha-track detectors) and air change rate measurements (based on the perfluorocarbon tracer technique; PFT) were in the ranges 12–620 Bq m^?3 and 0.16?0.96 h^?1, respectively. Estimates of radon entry rates on the basis of such time-averaged results are presented and the associated uncertainty is discussed. It was found that differences in radon concentrations from one house to another are primarily caused by differences in radon entry rates whereas differences in air change rates are much less important (accounting for only 80,0% of the house-to-house variation). In spite of the large house-to-house variability of radon entry rates it was demonstrated, however, that natural ventilation does have a significant effect on the indoor radon concentration. Most importantly, it was found that the group of houses with an air change rate above the required level of 0.5 h^?1 on average had an indoor radon concentration that was only 50% (0.5±0.1) of that of the group of houses with air change rates below 0.5 h^?1. The reducing effect of increased natural ventilation on the indoor radon concentration was found to be due mainly to dilution of indoor air. No effect could be seen regarding reduced radon entry rates.     

Indoor dispersion of airborne nano and fine particles: Main factors affecting spatial and temporal distribution in the frame of exposure modeling

A particle exposure experiment inside a large climate‐controlled chamber was conducted. Data on spatial and temporal distribution of nanoscale and fine aerosols in the range of mobility diameters 8‐600 nm were collected with high resolution, for sodium chloride, fluorescein sodium, and silica particles. Exposure scenarios studied included constant and intermittent source emissions, different aggregation conditions, high (10 h^?1) and low (3.5 h^?1) air exchange rates (AERs) corresponding to chamber Reynolds number, respectively, equal to 1 × 10⁵ and 3 × 10⁴. Results are presented and analyzed to highlight the main determinants of exposure and to determine whether the assumptions underlying two‐box models hold under various scenarios. The main determinants of exposure found were the source generation rate and the ventilation rate. The effect of particles nature was indiscernible, and the decrease of airborne total number concentrations attributable to surface deposition was estimated lower than 2% when the source was active. A near‐field/far‐field structure of aerosol concentration was always observed for the AER = 10 h^?1 but for AER = 3.5 h^?1, a single‐field structure was found. The particle size distribution was always homogeneous in space but a general shift of particle diameter (?8% to +16%) was observed between scenarios in correlation with the AER and with the source position, presumably largely attributable to aggregation.     

Study on contamination control in a minienvironment inside clean room for yield enhancement based on particle concentration measurement and airflow CFD simulation

A study was carried out to look for the source of contamination and examine the route of contaminant transfer in the minienvironment applied in LCD process clean room of Korea. As the minienvironment model, one of the clean room with much large space and low particle concentration was selected to investigate. Firstly, the particle concentrations were measured without any information on the source and the route of contaminants transfer. Through considering the results of particle measurements and CFD simulations simultaneously, however, it was revealed that the critical contamination source was the stocker and the contaminants were transferred by the airflow pattern in this study. As an improvement action, reducing the airflow rate of exhaust fans and installing additional fan filter units (FFUs) were carried out. As a result, the velocity distribution was improved and the particle concentration was reduced in the target minievironment. Also, the defect rate related to this minienvironment decreased. With the help of the experimental and the numerical tools, the effective method for contamination control was developed. Furthermore, this article provides recommendation for future work to improve the yield and save the energy consumption simultaneously.     

Comparison of gaseous contaminant diffusion under stratum ventilation and under displacement ventilation

The gaseous contaminant diffusion under stratum ventilation is investigated by numerical method which is validated by experiments carried out. The concentration of gaseous contaminants along the supply air jet is found to be lower than the other parts of the room. Compared with displacement ventilation, the formaldehyde concentration in breathing zone is lower when a contaminant source locates close to the occupant. The concentration is at the same level when the contaminant source locates up-steam to the occupant. The concentration in the occupied zone (<1.9 m from the floor) is also lower when the contaminant source locates on the floor. At supply air temperature optimized for displacement ventilation, the toluene concentration in breathing zone for stratum ventilation is higher than that for displacement ventilation when the area source locates on the four surrounding walls of the room.     

Experimental validation of a computational fluid dynamics model for IAQ applications in ice rink arenas

Many ice rink arenas have ice resurfacing equipment that uses fossil fuel as power. The combustion byproducts are a major source of contamination. Ventilation along with other pollution source control measures is the most widely applied strategy to lower the contaminant level below the threshold limit and maintain acceptable indoor air quality (IAQ). A computational fluid dynamics (CFD) model has been developed and used to predict the contaminant concentrations, air velocity, and air temperature distributions in ice rinks. The numerical results agree reasonably with the corresponding experimental data for both steady-state and transient conditions. The CFD model is a useful and inexpensive tool to investigate ventilation parameters, such as air distribution methods, ventilation effectiveness, air exchange rates, and various ventilation control strategies.     

Ein neues integrales Verfahren zur Quantifizierung der Grundwasserimmission, Teil I: Beschreibung der Grundlagen

A new investigation method was developed for a highly reliable assessment of groundwater contamination at waste sites or industrial locations. The method is based on an integral estimation of contaminant mass fluxes downstream of a pollutant source zone, employing an inversion of contaminant concentration time series measured within the discharge of pumping wells. Depending on the setup, the application of the method yields the total mass flux, as well as the contaminant concentration distribution over a control plane within a contaminant plume (see Ptak et al. 2000). Since there is no need to interpolate point scale concentration measurements, site assessment at a high level of certainty is obtained. The method was tested within a demonstration project and applied under conditions of practice for site assessment within a large (urban) industrialized area in the city of Stuttgart.     

A study of the effect of heat source location in a ventilated room using multiple regression analysis

Multiple regression analysis is a statistical technique which allows to predict a dependent variable from more than one independent variable and also to determine influential independent variables. Using experimental data, in this study the multiple regression analysis is applied to predict the room mean velocity and determine the most influencing parameters on the velocity. More than 120 experiments for four different heat source locations were carried out in a test chamber with a high level wall mounted air supply terminal at air change rates 3–6 ach. The influence of the environmental parameters such as supply air momentum, room heat load, Archimedes number and local temperature ratio, were examined by two methods: a simple regression analysis incorporated into scatter matrix plots and multiple stepwise regression analysis. It is concluded that, when a heat source is located along the jet centre line, the supply momentum mainly influences the room mean velocity regardless of the plume strength. However, when the heat source is located outside the jet region, the local temperature ratio (the inverse of the local heat removal effectiveness) is a major influencing parameter.     

Determining ventilation strategy to defend indoor environment against contamination by integrated accessibility of contaminant source (IACS)

With the recent occurrence of global terrorism, people are paying more and more attentions to ventilation strategy decision-making to avoid or reduce the influence of suddenly released contaminant when emergency occurs. This paper proposes a new uniform parameter, integrated accessibility of contaminant source (IACS), which combines the newly presented concept, accessibility of contaminant source (ACS) and occupied density (OD), to direct ventilation strategy to defend indoor environment against contamination. A 3-D full-scale room with displacement and mixing ventilation system is numerically studied by assuming contaminant released at certain positions in the room. By adopting IACS as the index in which the occupant distribution indoors is considered to evaluate the total influence of contaminant in a finite period of time, how to determine the ventilation strategy is discussed. It is shown that the new index can be applied to determine ventilation strategy for the purpose of defending indoor environment against contamination.     

Evaluation of RANS turbulence models for simulating wind-induced mean pressures and dispersions around a complex-shaped high-rise building

Re-ingestion of the contaminated exhaust air from the same building is a concern in high-rise residential buildings, and can be serious depending on wind conditions and contaminant source locations. In this paper, we aim to assess the prediction accuracy of three k-? turbulence models, in numerically simulating the wind-induced pressure and indoor-originated air pollutant dispersion around a complex-shaped high-rise building, by comparing with our earlier wind tunnel test results. The building modeled is a typical, 33-story tower-like building consisting of 8-household units on each floor, and 4 semi-open, vertical re-entrant spaces are formed, with opposite household units facing each other in very close proximity. It was found that the predicted surface pressure distributions by the two revised k-? models, namely the renormalized and realizable k-? models agree reasonably with experimental data. However, with regard to the vertical pollutant concentration distribution in the windward re-entrance space, obvious differences were found between the three turbulence models, and the simulation result using the realizable k-? model agreed the best with the experiment. On the other hand, with regard to the vertical pollutant concentration distribution in the re-entrant space oblique to the wind, all the three models gave acceptable predictions at the concentration level above the source location, but severely underestimated the downward dispersion. The effects of modifying the value of the turbulent Schmidt number in the realizable k-? model were also examined for oblique-wind case. It was confirmed that the numerical results, especially the downward dispersion, are quite sensitive to the value of turbulent Schmidt number.     

操作窗口对排风柜污染物控制效果影响的实验研究

为提升排风柜的控污能力,在排风柜性能测试实验台上,采用示踪气体测试法和正交试验法,研究了操作窗口竖直开度、水平开度、面风速和操作窗口位置对排风柜前呼吸区污染物控制效果的影响。极差分析和方差分析结果表明:各因素对呼吸区污染物控制效果影响的强弱顺序依次为竖直开度、水平开度、面风速、操作窗口位置;操作窗口水平开度、竖直开度增大,排风柜对呼吸区的污染物控制效果减弱;面风速增大,控制效果增强;水平开度与竖直开度对控制浓度的影响存在较大的相关性,这2个因素对控制浓度的影响仅在另一因素达到一定水平后才能体现。     

Influence of air stability and metabolic rate on exhaled flow

The characteristics of contaminant transport and dispersion of exhaled flow from a manikin are thoroughly studied in this article with respect to the influence of two important factors: air stability conditions and metabolic rates. Four cases with the combinations of stable and neutral conditions as well as lower (1.2 met) and higher (2 met) metabolic rates for a breathing thermal manikin are employed. The exhaled contaminant is simulated by smoke and N₂O to visualize and measure the contaminant distribution both around and in front of the manikin. The results show that the microenvironment around the manikin body can be affected by different air distribution patterns and metabolic heating. Under stable conditions, the exhaled contaminant from mouth or nose is locked and stratified at certain heights, causing potentially high contaminant exposure to others. In addition, velocity profiles of the pulsating exhaled flow, which are normalized by mean peak velocities, present similar shapes to a steady jet. The outlet velocity close to the mouth shows decrement with both exhalation temperature and body plume. The velocity decay and concentration decay also show significant dependence on air stability and metabolic level.     

Using air curtain to control pollutant spreading for emergency management in a cleanroom

The present investigation aims to examine the pollutant dispersion flowfield in an IQC cleanroom. Experimentally, the airflow velocities were measured using a TSI 8495 hot-wire anemometer to inspect the flow characteristics. Three ppbRAE PGM-7240 photoionization detectors were employed to concurrently measure the spatial and temporal distributions of ethanol concentration from a gas-pollutant leaking source. The computational analysis was based on the time-dependent three-dimensional conservation equations of mass, momentum and species concentration for the incompressible isothermal turbulent flow with a k-? two-equation turbulent model adopted for turbulence closure. Considering a massive amount of gaseous ethanol released from a malfunction machine, we presented a novel application of using an air curtain to resolve the personnel safety concern for emergency management in a contaminated cleanroom. For the cases without and with activation of an air curtain device, the airflow and contaminant characteristics were explored to better understand the pollutant spreading process for contamination control purpose. Numerical simulations were extended to verify if the air curtain device can establish a satisfactory shield for constraint of pollutant dispersal and optimize the sealing performance by systematically varying the parameters of ejection velocity, ejection angle and installation height.     

Outdoor Air Contaminants and Indoor Air Quality under Transient Conditions

The indoor concentrations of contaminants originating from outdoor sources have been measured and calculated under transient conditions. The results show that contaminants that are supplied to an office building via the ventilation system can reach considerably high concentration levels. The indoor/outdoor concentration ratio and time lag are dependent on the air change rate. In buildings with low air change rates the indoor concentration variations are smoothed out compared to buildings with high air change rates. The results from the theoretical model are compared to the results from both laboratory and field measurements and the model is verified for well mixed conditions in a 20 m³ test chamber. The model can be used to simulate different control strategies for reduction of indoor contaminant concentrations related to outdoor sources. One such control strategy is based on reduction of the outdoor air change rate during periods with peak outdoor contaminant concentrations.     

An experimental study on ventilation efficiency of isolation room

This paper presents an experimental modeling of contaminant dispersion in a mock-up isolation room with different negative pressure differentials and ventilation rates. A hypothetical contaminant (sulfur hexafluoride, SF₆) is emitted from a patient lying on a bed in the mock-up isolation room. The impacts of ventilation rates 12 and 24 h⁻¹ and pressure differentials −2.5, −5.0, −8.0, and −15.0 Pa on the ventilation effectiveness in the room are evaluated quantitatively. A local air quality index and an exposure index for healthcare workers are introduced in the research to evaluate the ventilation efficiency of the isolation room. Based on the results of our experiment, the ventilation efficiency of the isolation room ranks the highest at −15.0 Pa/24 h⁻¹, followed, respectively, by −15.0 Pa/12 h⁻¹, −8.0 Pa/24 h⁻¹, −5.0 Pa/24 h⁻¹, −2.5 Pa/24 h⁻¹, −8.0 Pa/12 h⁻¹, −5.0 Pa/12 h⁻¹, and −2.5 Pa/12 h⁻¹.     

地板送风对流热转移

针对下部有集中热源的地板送风空调小室,利用PHOENICS软件,对多种工况下室内气流流动的速度场和温度场进行了模拟,利用模拟结果计算对流热转移量,得出对流热转移量的变化规律。分析了影响对流热转移量的相关因素,主要是由于送风冷射流与热源的热射流在不同的影响因素下对室内气流流动及温度分布产生影响,从而造成对流热转移量的变化。结果表明:地板送风空调小室的对流热转移量与热源数目、送风口密度、热源强度、送风量4个因素有关;回风口数目对对流热转移量的影响很小,可以忽略不计。     

Effects of Climatic Parameters on Formaldehyde Concentrations in Indoor Air

The results of measurements of indoor air formaldehyde concentrations in occupational and private residences are presented for the period 1986 to 1993, based on requests of persons who complained about irritations. In many cases, climatic parameters such as the air exchange rate, temperature and relative humidity were also monitored. Calculated mean values for temperature and humidity were 22°C and 45% respectively. The average air exchange rate was 0.36 h^?1, which is well below a recommended guideline value of 0.8 h?' and it was evident that the ventilation is clearly insufficient in many rooms. The average formaldehyde concentration was 119 μg/m ^?3 (252 data), which is only slightly below the German guideline value of 125 μg/m ^?3. In 31% of the cases this guideline was exceeded. As expected, a clear relation between formaldehyde concentrations and the air exchange rate was found. The highest levels result at AE≤0.8 h^?1, but only a single value exceeds 125 μg/m ^?3 at AE≥0.8 h^?1. The association of law ventilation rates with high formaldehyde levels is also evident from a comparison with theoretical data after normalization to AE=0.8 h^?1, using the Hoetjer-equation. It was also observed that the calculated annual mean concentrations decreased from 1986 to 1993.     

Dynamic airflow simulation within an isolation room

In many hospitals, isolation rooms are used to contain patients who are highly infectious, and the spread of air and bacteria within the isolation room is closely relates to room air distribution. This article uses the computational fluid dynamics (CFD) method to investigate the effects of a moving person and the opening and closing of a sliding door on room air distribution, including velocity, pressure and contaminant fields. Dynamic meshes are employed to simulate the movement of the walking person and sliding door. According to numerical results, the impact of those moving objects on room air distribution is addressed in this study.